Journal of Applied Biomechanics, 2015, 31, 19-27 http://dx.doi.org/10.1123/JAB.2014-0105 © 2015 Human Kinetics, Inc.
An Official Journal of ISB www.JAB-Journal.com ORIGINAL RESEARCH
Lower Limb Joint Angular Position and Muscle Activity During Elliptical Exercise in Healthy Young Men Max R. Paquette,1 Audrey Zucker-Levin,2 Paul DeVita,3 Joseph Hoekstra,1 and David Pearsall4 1University
of Memphis; 2University of Tennessee Health Science Center; 3East Carolina University; 4McGill University
The purpose of this study was to compare lower extremity joint angular position and muscle activity during elliptical exercise using different foot positions and also during exercise on a lateral elliptical trainer. Sixteen men exercised on a lateral elliptical and on a standard elliptical trainer using straight foot position, increased toe-out angle, and a wide step. Motion capture and electromyography systems were used to obtain 3D lower extremity joint kinematics and muscle activity, respectively. The lateral trainer produced greater sagittal and frontal plane knee range of motion (ROM), greater peak knee flexion and extension, and higher vastus medialis activation compared with other conditions (P < .05). Toe-out and wide step produced the greatest and smallest peak knee adduction angles, respectively (P < .05). The lateral trainer produced greater sagittal and frontal plane hip ROM and greater peak hip extension and flexion compared with all other conditions (P < .05). Toe-out angle produced the largest peak hip external rotation angle and lowest gluteus muscle activation (P < .05). Findings from this study indicate that standard elliptical exercise with wide step may place the knee joint in a desirable frontal plane angular position to reduce medial knee loads, and that lateral elliptical exercise could help improve quadriceps strength but could also lead to larger knee contact forces. Keywords: kinematics, exercise, electromyography, low-impact, biomechanics Regular aerobic exercise along with a healthy diet can significantly improve body composition, promote weight loss, and reduce the risks for or consequences of cardiovascular and musculoskeletal diseases (eg, sarcopenia, osteoarthritis).1–3 Some aerobic exercises however may be too demanding for both healthy and clinical populations, including people with osteoarthritis (OA), obesity, or ageinduced frailty. For example, lower extremity joint OA patients may not be able to adhere to high-impact aerobic exercise programs such as jogging due to joint pain and discomfort. In recent years, lowimpact aerobic exercise modalities such as elliptical cross trainers have become increasingly popular and widely available in fitness facilities. These trainers have been shown to reduce peak knee and hip internal abductor moments,4 increase sagittal and frontal plane knee and hip joint range of motion (ROM),4–7 increase internal knee and hip extensor moments,4,6 and reduce peak vertical reaction force (ie, pedal versus ground) and its loading rate8 compared with level walking. Further, elliptical trainers yield greater activations of the rectus femoris,9 vastus lateralis, and gluteus maximus,5 but lower activations of the biceps femoris and gastrocnemius5 compared with level walking. Finally, elliptical trainers yield similar physiological improvements (ie, maximal oxygen uptake, maximal expiratory volume) compared with stair climbing and treadmill running,10 but require greater energy expenditure compared with treadmill and cycling exercise with similar rated perceived exertion.11 Due to the high prevalence of knee OA in older adults, interventions that lower knee loads and pain and improve knee function Max R. Paquette and Joseph Hoekstra are with the University of Memphis, Health & Sport Sciences, Memphis, TN. Audrey Zucker-Levin is with the University of Tennessee Health Science Center, Physical Therapy, Memphis, TN. Paul DeVita is with East Carolina University, Kinesiology, Greenville, NC. David Pearsall is with McGill University, Kinesiology & Physical Education, Montréal, QC, Canada. Address author correspondence to Max R. Paquette at [email protected].
during level walking and other activities of daily living need to be identified. Peak knee internal abduction moment has commonly been used as a surrogate for medial knee load.12 In addition, knee adduction angular position (ie, genu varus) is another important variable to assess medial knee loads, as increased varus alignment creates greater medial bone contact in the knee.13 Strength training, including knee extensor (ie, quadriceps) strengthening, is effective for improving knee joint function and reducing knee pain during level walking in knee OA patients.1,14,15 Based on the consistent finding that knee extensor moment and muscle activation are greater in elliptical training compared with level walking, it is possible that elliptical training exercise could improve knee function and reduce knee pain due to knee extensor strengthening in patients with knee OA. D’Lima et al16 showed that in vivo knee forces of three patients during elliptical training exercise measured with force sensor instrumented knee implants were no different than during treadmill walking. Therefore, elliptical training exercise may strengthen knee extensors due to larger knee moments and muscle activations and also improve function and reduce pain during level walking, and it may do so without higher joint loads compared with level walking. In addition to exercise training interventions, simple gait modifications also change knee function, pain, and load.17–22 Such gait adaptations, including increased toe-out angle, reduce the peak knee internal abduction moment in the later stages of stance phase.17–19,22,23 Further, increased step width during level and stair walking reduce knee adduction angular positions24–26 and peak knee internal abduction moment24,26,27 in healthy adults and patients with knee OA. Newly-modified elliptical trainers are available that incorporate lateral motion. Such elliptical trainers add lateral motion to the backward directed pedal stroke, producing a modified skating motion. This motion would be expected to increase step width and place the knee in a more abducted position (ie, knee valgus) due to the anticipated large hip abduction caused 19
20 Paquette et al.
by the side-to-side motion. These varied data are the basis of the hypothesis that lateral elliptical trainers and standard elliptical trainers with modified foot positions will create kinematic adaptations favorable for individuals with knee pathology and will also activate hip and knee extensor muscles to levels that induce beneficial neuromuscular adaptations. We plan to fully investigate this hypothesis through a series of integrated studies that will identify both acute and chronic elliptical training outcomes in both healthy and knee OA populations. We begin this line of work with the current study, the purpose of which was to compare knee and hip angular position and lower extremity muscle activity in healthy young men during exercise on an elliptical trainer using a straight foot position, toe-out angle, and wide step width, and also on a lateral trainer.
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Methods Participants Sixteen healthy, recreationally active young men (23.2 ± 1.9 y; 81.5 ± 9.2 kg; 1.8 ± 0.1 m; 25.7 ± 2.8 kg/m2) were recruited to participate in the study. Subjects were included in the study if they had no previous lower extremity joint surgeries and no current lower extremity joint injuries. Institutional review board approval was obtained and all subjects signed a written informed consent document before data collection.
(straight foot), (3) on a standard elliptical trainer with toe-out angle (toe-out), and (4) on a standard elliptical trainer with wide step (wide step). The elliptical conditions were randomized to avoid an order effect and all tests were performed on the same day. For the lateral trainer and straight foot conditions, participants were asked to place their feet in the middle of the pedals in a straight line (Figure 2A). For the toe-out angle condition, participants were instructed to have the distal end of the feet touch the lateral aspect of the pedal while the heel was touching the medial aspect of the pedal (Figure 2B). For the wide step condition, participants were asked to move their feet to the most lateral aspect of the pedal (Figure 2C). Subjects were required to maintain a stride rate of 50 strides per minute, which was cued using a metronome (Beats Metronome; Positive Grid, LLC). Based on the set stride rate, the resistance level on both trainers was adjusted to yield similar power measures (ie, 65 and 70 W). Participants were instructed to lightly touch the stationary handle bars for stability but to support their weight during exercise bouts. They were also instructed to move the pedals through their full ROM. For all conditions data were collected for 15 seconds at the fourth minute of exercise and thus, participants were able to familiarize themselves with each condition for four minutes before data were collected. In addition, a researcher visually monitored foot position during testing to ensure that participants maintained the required foot position during each testing condition. The lateral trainer produced an anteroposterior
Instrumentation A 10-camera motion analysis system (100 Hz, Qualisys, Sweden) and a wireless electromyography (EMG) system (2000 Hz, Delsys, USA) were used to obtain 3D lower extremity joint kinematics and muscle activity, respectively. Bipolar EMG surface electrodes (Trigno, Delsys, USA) were placed over the right vastus medialis (VM), biceps femoris (BF), gluteus maximus (GMax), gluteus medius (GMed) and medial gastrocnemius (MG) according to existing guidelines.28 The skin below each electrode placement site was shaved, lightly abraded, and cleaned with an alcohol swab before application. Two maximal voluntary isometric contractions (MVIC) for each muscle separated by one minute rest periods were performed to obtain voluntary maximal muscle activity signals of each participant. The MVIC were performed using manual muscle testing by the researcher for all subjects.29 Following the EMG procedures, unilateral retro-reflective markers were placed over the right and left anterior superior iliac spines (ASIS) and posterior superior iliac spines (PSIS), the sacrum, medial and lateral femoral epicondyles and malleoli, and the first and fifth metatarsal heads of the right leg to define lower extremity segments and joint centers. Arrays of four noncollinear markers placed on semirigid thermoplastic shells were attached to the thigh and shank using elastic wrap to track the segments during movement trials. Noncollinear markers were secured directly on the skin over the superior, inferior, and lateral aspect of the calcaneus and on the foot dorsum to track foot motion. A static calibration trial was performed and nontracking markers were removed for the elliptical exercise bouts.
Figure 1 — Illustration of the (A) lateral elliptical trainer and (B) standard elliptical trainer.
Testing Procedures Participants performed five minute exercise bouts under each of the four elliptical device conditions: (1) on a lateral trainer (Crossover, Technogym, USA; Figure 1A), (2) on a standard elliptical trainer (EX-5, Matrix Fitness, USA; Figure 1B) with straight foot position
Figure 2 — Illustration of the straight (A), toe-out angle (B), and wide step (C) position used during standard elliptical exercise.
Joint Kinematics and Electromyography During Elliptical Exercise 21
(AP) pedal displacement of 0.23 m and a mediolateral (ML) displacement of 0.32 m with a resultant pedal displacement of 0.39 m. The standard elliptical produced a ML displacement of 0.008 m and an AP pedal displacement of 0.46 m (ie, resultant pedal displacement as ML displacement is negligible). These displacements were measured within the laboratory coordinate system using a reflective marker placed on the elliptical pedals.
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Data Analyses Visual3D (C-Motion, Germantown, MD, USA) was used to obtain the 3D lower extremity joint kinematic and EMG variables of the middle six strides (ie, one full pedal revolution) during the last 30 seconds of each elliptical exercise bout. For the middle six strides, kinematic data were analyzed during the six load phase (ie, the most anterior to most posterior pedal position). The ASIS, PSIS, and sacrum markers were used to track the pelvis and the CODA pelvis was used in the Visual3D model.30,31 Kinematic data were filtered using a fourth-order Butterworth low-pass filter with a cut-off frequency of 6 Hz. A right-hand rule with a Cardan rotational sequence (x-y-z) was used for the 3D angular computations where x represents the ML axis, y represents the AP axis, and z represents the longitudinal axis. The knee joint kinematic data were expressed in the thigh coordinate system while the hip joint kinematics were expressed in the pelvis coordinate system. Dependent kinematic variables included the peak knee and hip flexion, extension, abduction, and adduction angles, the knee and hip sagittal and frontal plane ranges of motion (ROM: angular excursion between flexion-extension and abduction-adduction), and the peak hip external rotation angle. Foot progression angle was measured as the transverse plane deviation of the foot in the laboratory coordinate system at the time of the most anterior pedal position (negative value indicates toe-out). The elliptical trainers were aligned with the AP axis of the laboratory coordinate system to ensure consistent foot progression angle calculations. The EMG signals during MVIC and elliptical exercise were band-pass filtered with cut-off frequencies of 20 Hz and 400 Hz. The signals were then full-wave rectified and smoothed using a root-mean-square (RMS) filter with a moving window of 150 milliseconds. The EMG signals during exercise were normalized to the larger of the two MVIC RMS peak values for each muscle for each participant. The normalized EMG signals were then integrated (iEMG; % · s) during all six load phases for each muscle.
Results The results on knee kinematics indicate that toe-out angle during standard elliptical exercise alters peak knee frontal plane angular positions, while lateral trainer exercise significantly alters both frontal and sagittal plane knee ROM and peak knee sagittal plane angular positions compared with other elliptical conditions (Table 1) (Figure 3). Peak knee abduction angular position was smaller in toe-out angle compared with lateral trainer (ES = 1.36), straight foot (ES = 1.12), and wide step (ES = 1.33); and smaller in straight foot compared with lateral trainer (ES = 0.46) (Table 1). Peak knee adduction angular position was smaller in lateral trainer compared with toe-out angle (ES = –0.99) but greater compared with wide step (ES = 0.48); smaller in straight foot compared with toe-out angle (ES = –1.02) but greater in straight foot compared with wide step (ES = 0.36); and greater in toe-out angle compared with wide step (ES = 1.37) (Table 1). Frontal plane knee ROM was greater in lateral trainer compared with straight foot (ES = 0.91), toe-out angle (ES = 1.16), and wide step (ES = 0.97) (Table 1). Peak knee extension angular position was greater in lateral trainer compared with straight foot (ES = 0.67), toe-out angle (ES = 0.98), and wide step (ES = 0.86); and greater in straight foot compared with toe-out angle (ES = 0.40) (Table 1). Peak knee flexion angular position was larger in the lateral trainer condition compared with straight foot (ES = 4.95), toe-out angle (ES = 5.90), and wide step (ES = 6.12) (Table 1). Sagittal plane knee ROM was greater in lateral trainer compared with straight foot (ES = 4.09), toe-out angle (ES = 3.82), and wide step (ES = 4.10) (Table 1).
Statistical Analyses A repeated-measures ANOVA was performed on the average values of all dependent variables from all six load phases with elliptical condition as the within-subject factor (SPSS 20.0; IBM, Chicago, IL). Mauchly’s test of sphericity was used to test the assumption that the variances of the difference between repeated measures were all equal. When the assumption of sphericity was not met (ie, P < .05), the Greenhouse-Geisser adjustment was used to assess within-subject differences. When an ANOVA revealed a main effect of elliptical condition, post hoc comparisons with least significant difference (LSD) were used to compare means between conditions. Only statistically significant mean differences from post hoc comparisons are reported in the results section. The alpha level was set at .05 for all tests. Cohen’s d effect sizes were reported for mean differences with ≤ 0.20 representing a small effect, > 0.20 and < 0.80 representing a moderate effect, and ≥ 0.80 representing a large effect.32
Figure 3 — Sagittal (A) and frontal (B) plane knee angular position ensemble mean curves during load phase from all participants during lateral trainer (solid line) and standard elliptical with straight (dashed line), increased toe-out angle (dotted line), and wide step (dash-dotted line) positions. Note: Standard deviations of critical variables are presented in Table 1.
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22 Paquette et al.
The results on hip kinematics indicate that lateral trainer exercise significantly alters hip angular position in all three planes and that toe-out angle during standard elliptical also alters transverse plane hip angular position (Table 2) (Figure 4). Peak hip abduction angular position was smaller in straight foot compared with lateral trainer (ES = 1.49), toe-out angle (ES = 1.37), and wide step (ES = 0.75); and smaller in wide step compared with lateral trainer (ES = 0.81) (Table 2). Peak hip adduction angular position was smaller in wide step compared with lateral trainer (ES = 0.80) and straight foot (ES = 0.99); and smaller in toe-out angle compared with lateral trainer (ES = 0.73) and straight foot (ES = 0.87) (Table 2). Frontal plane hip ROM was larger in lateral trainer compared with straight foot (ES = 1.21), toe-out angle (ES = 0.97), and wide step (ES = 1.35); and larger in toe-out angle compared with wide step (ES = 1.27) (Table 2). Peak hip extension angular position was larger in lateral trainer compared with straight foot (ES = 1.94), toe-out angle (ES = 1.59), and wide step (ES = 1.93) conditions (Table 2). Peak hip flexion angular position was larger in lateral trainer compared with straight foot (ES = 2.67), toe-out angle (ES = 2.39), and wide step (ES = 2.76) conditions (Table 2).
Sagittal plane hip ROM was greater in lateral trainer compared with straight foot (ES = 1.37), toe-out angle (ES = 1.13), and wide step (ES = 1.17) (Table 2). Peak hip external rotation angular position was greater in toe-out angle compared with lateral trainer (ES = 0.74), straight foot (ES = 1.42), and wide step (ES = 1.38); and greater in lateral trainer compared with straight foot (ES = 0.74) and wide step (ES = 0.74) (Table 2). Integrated normalized EMG results indicate that lateral elliptical exercise produces greater vastus medialis activation compared with other conditions and that the toe-out position on a standard elliptical reduces the gluteus medius activation compared with other conditions (Table 3) (Figure 5). Vastus medialis iEMG was larger in lateral trainer compared with straight foot (ES = 1.11), toe-out angle (ES = 0.97), and wide step (ES = 1.04) conditions (Table 3). Gluteus medius iEMG was smaller in the toe-out angle condition compared with lateral trainer (ES = –0.89) and straight foot (ES = –0.48) (Table 3). There were no significant differences in iEMG between elliptical conditions for the biceps femoris, gluteus maximus, or medial gastrocnemius (P > .05) (Table 3).
Table 1 Load phase frontal and sagittal plane knee angular position variables between elliptical conditions (mean ± SD) and p values Angular Positions (deg) Knee abduction Knee adduction Knee ROMy Knee extension Knee flexion Knee ROMx
Lateral –6.8 ± 5.2 –0.3 ± 3.3 6.6 ± 3.2b,c,d –20.3 ± 7.7b,c,d –69.6 ± 5.3b,c,d 49.2 ± 8.3b,c,d
Elliptical Exercise Straight Toe-Out –1.2 ± 3.0a,b,d –4.8 ± 3.6a –0.5 ± 3.1 2.7 ± 3.1a,b,d 4.3 ± 1.8 3.8 ± 1.5 –15.6 ± 6.7c –12.7 ± 8.3 –38.5 ± 7.5c –35.1 ± 6.7 22.9 ± 4.4 22.4 ± 6.0
Wide Step –5.6 ± 3.8 –1.4 ± 3.0a,b 4.1 ± 2.0 –14.6 ± 5.8 –37.0 ± 5.7 22.4 ± 4.7
p < .001 < .001 .003 .002 < .001 < .001
Note. Add(+)/Abd(-); Ext(+)/Flex(-); ROM = range of motion. p values are bold when significant. a Significantly different than lateral elliptical trainer (P < .05). b Significantly different than straight foot position (P < .05). c Significantly different than toe-out position (P < .05). d Significantly different than wide step position (P < .05).
Table 2 Load phase frontal, sagittal, and transverse planes hip angular position variables between elliptical conditions (mean ± SD) and p values Angular Positions (deg) Hip abduction Hip adduction Hip ROMy Hip extension Hip flexion Hip ROMx Hip external rotation Toe-out angle
Lateral –7.9 ± 3.5d 3.0 ± 5.2 10.8 ± 5.9b,c,d 26.1 ± 7.8b,c,d 60.2 ± 7.7b,c,d 34.1 ± 5.4b,c,d –16.3 ± 6.2b,d –3.2 ± 4.3
Elliptical Exercise Straight Toe-Out –3.4 ± 2.7a,c,d –6.8 ± 2.4 2.2 ± 2.4 0.1 ± 2.6a,b 5.6 ± 2.1 6.8 ± 1.2d 12.5 ± 6.6 14.4 ± 7.4 40.4 ± 7.6c 43.4 ± 6.8 27.8 ± 4.0 29.1 ± 3.6 –11.7 ± 6.6 –21.1 ± 7.1a,b,d a –26.9 ± 4.2a,b,d –7.9 ± 4.3
Wide Step –5.4 ± 2.8 –0.2 ± 2.6a,b 5.2 ± 1.4 12.7 ± 6.5 41.4 ± 6.3 28.7 ± 4.0 –11.3 ± 7.6 –2.8 ± 4.5
Note. Add(+)/Abd(-); Ext(+)/Flex(-); ROM = range of motion. p values are bold when significant. a Significantly different than lateral elliptical trainer (P < .05). b Significantly different than straight foot position (P < .05). c Significantly different than toe-out position (P < .05). d Significantly different than wide step position (P < .05).
p < .001 .025 .003 < .001 < .001 < .001 < .001 < .001
Joint Kinematics and Electromyography During Elliptical Exercise 23
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Discussion
Figure 4 — Sagittal (A), frontal (B), and transverse (C) plane hip angular position ensemble mean curves during load phase from all participants during lateral trainer (solid line) and standard elliptical with straight (dashed line), increased toe-out angle (dotted line), and wide step (dashdotted line) positions. Note: Standard deviations of critical variables are presented in Table 2.
It was expected that lateral elliptical training and standard elliptical training with modified foot placement (ie, toe-out and wide step width) would reduce peak knee adduction angular position, increase frontal and sagittal plane knee ROM, and increase knee extensor muscle activity compared with the straight foot position on the standard elliptical. Secondly, it was also expected that lateral elliptical training and standard elliptical training with modified foot placement would increase peak hip abduction and extension angular positions and hip abductor and extensor muscle activity compared with the straight foot position during elliptical exercise. It is further expected that the findings of this study will provide a foundation to justify additional comprehensive investigations of elliptical training as a potential effective training modality for people with knee OA. The hypothesis that the lateral trainer and standard elliptical trainer with modified foot placement (ie, toe-out angle and wide step) would reduce peak knee adduction angular position, increase frontal and sagittal plane knee ROM, and increase knee extensor muscle activity compared with standard elliptical with straight foot position was partially supported. A greater knee adduction angular position (ie, genu varus) creates greater medial bone-on-bone contact in the knee13 and could indicate greater medial compartment knee contact forces, especially when the limb supports body weight (eg, stance in walking). In agreement with the first hypothesis, the peak knee adduction angular position was significantly smaller during wide step compared with all other conditions and, in fact, the findings indicate that peak frontal plane knee position is never in an adducted position during elliptical exercise using the wide step foot position. Previous research has shown reductions in peak internal knee abduction moments (ie, surrogate for medial knee loading) and, similar to the current findings in peak knee adduction, angular positions in healthy adults24,26 and medial compartment knee OA patients26 during stair walking with a wide step. A wide step is expected to shift the center of pressure (COP) under the feet laterally and in turn, move the frontal plane ground reaction force (GRF) vector closer to the knee joint center. The lever arm of the GRF to the joint center is then reduced and as a result, so is the peak knee abduction moment. Thus, the reduction in peak adduction angular position in the current study may suggest reductions in medial knee loads during elliptical exercise with a wide step.
Table 3 Integrated RMS EMG during load phase normalized to peak MVIC for all five muscles between elliptical conditions (mean ± SD) and p values Muscles (%·s) Vastus medialis Biceps femoris Gluteus medius Gluteus maximus Medial gastrocnemius
Lateral 23.5 ± 16.1b,c,d 4.6 ± 4.0 8.3 ± 3.2 4.9 ± 2.3 4.2 ± 3.7
Elliptical Exercise Straight Toe-Out Wide Step 10.0 ± 8.5 11.5 ± 8.9 10.8 ± 8.5 7.4 ± 9.6 7.4 ± 7.4 6.8 ± 8.5 7.1 ± 3.1 7.1 ± 2.5 6.1 ± 1.8a,b 4.2 ± 2.6 4.3 ± 2.2 4.2 ± 2.5 6.7 ± 4.0 4.3 ± 3.8 6.1 ± 4.8
p < .001 .075 .013 .089 .072
Note. RMS = root-mean-square; EMG = electromyography; MVIC = maximal voluntary isometric contractions. p values are bold when significant. a Significantly different than lateral elliptical trainer (P < .05). b Significantly different than straight foot position (P < .05). c Significantly different than toe-out position (P < .05). d Significantly different than wide step position (P < .05).
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24 Paquette et al.
Figure 5 — Normalized load phase integrated electromyography ensemble curves for vastus medialis (A), biceps femoris (B), gluteus medius (C), gluteus maximus (D), and medial gastrocnemius (E) during lateral trainer (solid line), and standard elliptical with straight (dashed line), increased toe-out angle (dotted line), and wide step (dash-dotted line) positions. Note: Standard deviations of critical variables for each muscle are presented in Table 3. RMS = root-mean-square.
Contrary to the first hypothesis, peak knee adduction angular position was greater in toe-out angle compared with all other conditions. A larger toe-out angle is effective in reducing peak knee internal abduction moment in the later stages of the stance phase during walking.17–19,22,23 Similar to using a wide step, a lateral shift of the COP has been suggested as the mechanism related to reduction in knee abduction moment with toe-out angle.22 The results confirmed that the toe-out condition was in fact performed with increased toe-out angle compared with all other conditions (Table 2). The increased toe-out angle appears to have been achieved with an increased hip external rotation. In the current study, the increased peak adduction angular position in the increased toe-out angle condition may suggest greater loads applied to the medial compartment of the knee joint. Joint kinetics data were not computed in the current study as the elliptical trainers were not instrumented with force sensors. Nevertheless, the peak knee adduction angular position
findings suggest that wide step may be the most effective elliptical exercise condition to potentially reduce medial knee loads. The frontal and sagittal plane knee ROMs were significantly greater in the lateral trainer condition compared with all other elliptical conditions. The EMG data support the finding of greater sagittal plane knee ROM and peak flexion in lateral trainer exercise, with a significantly larger integrated load phase vastus medialis activation (ie, knee extensor) compared with other conditions; these results may suggest greater knee extensor involvement (ie, internal torque). The EMG RMS signals were integrated within the absolute load phase time (ie, not expressed as a percentage) and thus, the iEMG data differences between elliptical devices could be caused by differences in load times. In fact, the lateral elliptical condition had a shorter load phase because stride rate was controlled (ie, 50 strides per min) during testing sessions, and resultant pedal displacement was smaller during the lateral
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Joint Kinematics and Electromyography During Elliptical Exercise 25
elliptical condition than the other conditions. The greater iEMG values of vastus medialis during a shorter load phase suggest that the lateral elliptical has a greater effect on knee extensor activation per stride compared with the standard elliptical. Due to the different pedal movement patterns between elliptical devices, it was important to avoid time-normalization of the load phase to observe functional and relevant differences in joint kinematics and muscle activity. Muscles, especially the quadriceps, play an important role in increasing knee joint contact forces,33–35 as they can add up to 3.5 BW to the net compressive knee contact forces during level walking.34 If knee extensor involvement is greater during the lateral trainer condition, it is possible that the net compressive knee contact force would also be increased in the lateral trainer condition compared with other elliptical conditions. However, the time spent exercising on an elliptical device is minimal relative to the time spent walking and standing while performing daily tasks. Further, knee extensor strengthening has proven to be effective in improving knee joint function and reducing knee pain during level walking in knee OA patients.14,15,36 Although potential higher muscle force contributions may increase the net compressive knee joint contact force during lateral trainer exercise, muscular adaptions from higher knee extensor activation may be beneficial to help improve knee function and reduce knee pain during gait and daily tasks in patients with knee pain (ie, knee OA). It was also expected that the lateral trainer and standard elliptical trainer with modified foot placement would increase peak hip abduction and extension angular positions and hip abductor and extensor muscle activity compared with the standard elliptical trainer in straight foot position. The lateral trainer showed greater peak hip abduction compared with the straight foot and wide step positions, but was not different compared with the toe-out angle condition. In addition, frontal plane hip ROM was largest in the lateral trainer condition compared with all other conditions. These results suggest that the lateral trainer may be effective for targeting training of the hip abductors. However, gluteus medius activation during load phase was higher in the lateral trainer condition compared with the toe-out angle, and although slightly higher, it was not significantly different than the other two conditions. The current data only provide acute differences between elliptical conditions, but the increased peak abduction angle, greater frontal plane hip ROM, and very small increase in gluteus medius activation (ES = 0.39–0.43) in the lateral trainer condition could potentially lead to training adaptations for hip abductor strengthening. Research shows that short-term (ie, four weeks) hip abductor strengthening leads to reduced peak knee internal abduction moments during gait in knee OA patients.37 Effective hip abductor strengthening from elliptical training could have positive benefits for knee joint load reduction during gait in people with knee OA. Finally, sagittal plane hip ROM and peak hip flexion and extension were significantly greater in the lateral trainer condition compared with all other conditions. The peak hip extension during load phase still occurs in hip flexion (Figure 3a) and thus, these hip sagittal plane results suggest that lateral trainer exercise places the hip in a more flexed position throughout the pedal cycle. Surprisingly, the findings did not indicate greater gluteus maximus muscle activation in the more flexed position. It is therefore suggested that this muscle was operating on a more favorable position of its force-length curve on the lateral trainer and produced sufficient force and torque with EMG magnitudes identical to other conditions. The data from this study provide information to suggest that elliptical exercise, especially lateral trainer and standard elliptical with a wide step foot position, could elicit kinematic (ie, greater knee abduction during lateral and
wide step) and neuromuscular adaptations (ie, greater knee extensor muscle activity during lateral) to help improve knee function and potentially reduce knee pain and knee loads in individuals with knee disorders such as knee OA. In addition, the greater knee and hip ROM found on the lateral trainer may have implications for rehabilitative mobility training in patients suffering from neuromuscular diseases or injuries that result in reduced ROM in activities of daily living (eg, Parkinson’s disease, incomplete spinal cord injuries). Finally, we now plan to identify both acute and chronic elliptical training outcomes in knee OA populations. This study has a few limitations. The workload during elliptical exercise was set between 65–70 W at a set pedal rate (ie, 50 strides/min) and was not standardized to each participant’s relative fitness and body height. However, the aim of this study was to obtain preliminary data on joint kinematics and muscle activation at low exercise intensity. The participants were all college-aged healthy men of similar height (1.8 ± 0.1 m) and none of them had difficulty performing the short exercise bouts during all four elliptical conditions. Women were excluded to avoid introducing a confounding factor of dynamic frontal and transverse plane knee and hip excursion found between sexes.38,39 The elliptical trainers used in the current study were not instrumented with pedal force sensors to calculate pedal reaction forces and joint kinetics. Although our interpretations of joint kinematics in relation to joint kinetics remain speculative, the joint kinematic and muscle activation data provide insightful evidence to support our interpretations. The current work only investigates acute differences between elliptical conditions in healthy men. For this reason, a direct generalization of the findings to knee OA populations is currently impossible. However, the study was intended to obtain preliminary results with a healthy population to first identify potential biomechanical benefits of these elliptical conditions before including an at-risk population (ie, knee OA). In summary, the results indicated lower peak knee adduction angular position during standard elliptical exercise with a wide step but greater peak adduction position with a toe-out foot position. Lateral trainer exercise increased vastus medialis activation and sagittal plane knee angular displacement, which could potentially help improve knee extensor strength but could also lead to larger net knee contact forces. The lateral trainer appears to have the greatest effect on hip motion, as it showed greater frontal and sagittal plane hip ROM. The need for future research investigating effective and safe aerobic exercise programs as interventions to improve quality of life and reduce knee pain and knee loads for individuals with knee diseases is highly important. Acknowledgments The authors would like to thank Technogym USA for providing the lateral elliptical device for testing.
References 1. Messier SP, Mihalko SL, Legault C, et al. Effects of intensive diet and exercise on knee joint loads, inflammation, and clinical outcomes among overweight and obese adults with knee osteoarthritis: the IDEA randomized clinical trial. JAMA. 2013;310(12):1263–1273. PubMed doi:10.1001/jama.2013.277669 2. Messier SP, Gutekunst DJ, Davis C, DeVita P. Weight loss reduces knee-joint loads in overweight and obese older adults with knee osteoarthritis. Arthritis Rheum. 2005;52(7):2026–2032. PubMed doi:10.1002/art.21139
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26 Paquette et al. 3. Messier SP, Legault C, Loeser RF, et al. Does high weight loss in older adults with knee osteoarthritis affect bone-on-bone joint loads and muscle forces during walking? Osteoarthritis and cartilage / OARS. Osteo Cart. 2011;19(3):272–280. doi:10.1016/j.joca.2010.11.010 4. Lu TW, Chien HL, Chen HL. Joint loading in the lower extremities during elliptical exercise. Med Sci Sports Exerc. 2007;39(9):1651– 1658. PubMed doi:10.1249/mss.0b013e3180dc9970 5. Burnfield JM, Shu Y, Buster T, Taylor A. Similarity of joint kinematics and muscle demands between elliptical training and walking: implications for practice. Phys Ther. 2010;90(2):289–305. PubMed doi:10.2522/ptj.20090033 6. Rogatzki MJ, Kernozek TW, Willson JD, Greany JF, Hong DA, Porcari JR. Peak muscle activation, joint kinematics, and kinetics during elliptical and stepping movement pattern on a Precor Adaptive Motion Trainer. Res Q Exerc Sport. 2012;83(2):152–159. PubMed doi:10.10 80/02701367.2012.10599845 7. Damiano DL, Norman T, Stanley CJ, Park HS. Comparison of elliptical training, stationary cycling, treadmill walking and overground walking. Gait Posture. 2011;34(2):260–264. PubMed doi:10.1016/j. gaitpost.2011.05.010 8. Chien HL, Tsai TY, Lu TW. The effects of pedal rates on pedal reaction forces during elliptical exercise. Biomed Eng: App Basis Comm. 2007;19:207–214. doi:10.4015/S1016237207000367 9. Prosser LA, Stanley CJ, Norman TL, Park HS, Damiano DL. Comparison of elliptical training, stationary cycling, treadmill walking and overground walking. Electromyographic patterns. Gait Posture. 2011;33(2):244–250. PubMed doi:10.1016/j.gaitpost.2010.11.013 10. Egana M, Donne B. Physiological changes following a 12 week gym based stair-climbing, elliptical trainer and treadmill running program in females. J Sports Med Phy Fitness. 2004;44(2):141–146. PubMed 11. Kim JK, Nho H. M HW. Inter-modal comparisons of acute energy expenditure during perceptually based exercise in obese adults. J Nutr Sci Vitaminol (Tokyo). 2008;54(1):39–45. PubMed doi:10.3177/ jnsv.54.39 12. Zhao D, Banks SA, Mitchell KH, D’Lima DD, Colwell CW, Jr., Fregly BJ. Correlation between the knee adduction torque and medial contact force for a variety of gait patterns. J Ortho Res. 2007;25(6):789-797. 13. Andriacchi TP, Mundermann A, Smith RL, Alexander EJ, Dyrby CO, Koo S. A framework for the in vivo pathomechanics of osteoarthritis at the knee. Ann Biomed Eng. 2004;32(3):447–457. PubMed doi:10.1023/B:ABME.0000017541.82498.37 14. O’Reilly SC, Muir KR, Doherty M. Effectiveness of home exercise on pain and disability from osteoarthritis of the knee: a randomised controlled trial. Ann Rheum Dis. 1999;58(1):15–19. PubMed doi:10.1136/ ard.58.1.15 15. Wortley M, Zhang S, Paquette MR, et al. Effects of resistance and Tai Ji training on mobility and symptoms in knee osteoarthritis patients. J Sport Health Sci. 2013;2(4):209–214. 16. D’Lima DD, Steklov N, Patil S, Colwell CW, Jr. The Mark Coventry Award: in vivo knee forces during recreation and exercise after knee arthroplasty. Clin Orthop Relat Res. 2008;466(11):2605–2611. PubMed doi:10.1007/s11999-008-0345-x 17. Andrews M, Noyes FR, Hewett TE, Andriacchi TP. Lower limb alignment and foot angle are related to stance phase knee adduction in normal subjects: a critical analysis of the reliability of gait analysis data. J Ortho Res. 1996;14(2):289-295. 18. Rutherford DJ, Hubley-Kozey CL, Deluzio KJ, Stanish WD, Dunbar M. Foot progression angle and the knee adduction moment: a crosssectional investigation in knee osteoarthritis. Osteoarthritis and cartilage / OARS. Osteo Cart. 2008;16(8):883–889. doi:10.1016/j. joca.2007.11.012
19. Guo M, Axe MJ, Manal K. The influence of foot progression angle on the knee adduction moment during walking and stair climbing in pain free individuals with knee osteoarthritis. Gait Posture. 2007;26(3):436–441. PubMed doi:10.1016/j.gaitpost.2006.10.008 20. Bechard DJ, Birmingham TB, Zecevic AA, Jones IC, Giffin JR, Jenkyn TR. Toe-out, lateral trunk lean, and pelvic obliquity during prolonged walking in patients with medial compartment knee osteoarthritis and healthy controls. Arthritis Care Res (Hoboken). 2012;64(4):525–532. PubMed doi:10.1002/acr.21584 21. Hunt MA, Birmingham TB, Bryant D, et al. Lateral trunk lean explains variation in dynamic knee joint load in patients with medial compartment knee osteoarthritis. Osteoarthritis and cartilage / OARS. Osteo Cart. 2008;16(5):591–599. doi:10.1016/j.joca.2007.10.017 22. Jenkyn TR, Hunt MA, Jones IC, Giffin JR, Birmingham TB. Toe-out gait in patients with knee osteoarthritis partially transforms external knee adduction moment into flexion moment during early stance phase of gait: a tri-planar kinetic mechanism. J Biomech. 2008;41(2):276– 283. PubMed doi:10.1016/j.jbiomech.2007.09.015 23. Hurwitz DE, Ryals AB, Case JP, Block JA, Andriacchi TP. The knee adduction moment during gait in subjects with knee osteoarthritis is more closely correlated with static alignment than radiographic disease severity, toe out angle and pain. J Ortho Res. 2002;20(1):101-107. 24. Paquette MR, Zhang S, Milner CE, Fairbrother JT, Reinbolt JA. Effects of increased step width on frontal plane knee biomechanics in healthy older adults during stair descent. Knee. 2014;21(4):821–826. PubMed doi:10.1016/j.knee.2014.03.006 25. Paquette MR, Zhang S, Milner CE, Klipple G. Does increasing step width alter knee biomechanics in medial compartment knee osteoarthritis patients during stair descent? Knee. 2014;21(3):676–682. PubMed doi:10.1016/j.knee.2014.02.020 26. Paquette MR, Zhang S, Klipple G. Greater step widths reduce knee abduction moments in knee osteoarthritis patients during stair ascent. Paper presented at: American College of Sport Medicine. 2013; Indianapolis, IN. 27. Fregly BJ, Reinbolt JA, Chmielewski TL. Evaluation of a patientspecific cost function to predict the influence of foot path on the knee adduction torque during gait. Comput Methods Biomech Biomed Engin. 2008;11(1):63–71. PubMed doi:10.1080/10255840701552036 28. Hermens HJ, Freriks B, Merletti R, et al. European Recommendations for Surface ElectromyoGraphy. Roessingh Research and Development; 1999. 29. Lin HT, Hsu AT, Chang JH, Chien CS, Chang GL. Comparison of EMG activity between maximal manual muscle testing and cybex maximal isometric testing of the quadriceps femoris. J Formosan Med Assoc. 2008;107(2):175-180. 30. Bell AL, Pedersen DR, Brand RA. A comparison of the accuracy of several hip center location prediction methods. J Biomech. 1990;23(6):617–621. PubMed doi:10.1016/0021-9290(90)90054-7 31. Bell AL, Pederson DR, Brand RA. Prediction of hip joint centre location from external landmarks. Hum Mov Sci. 1989;8:3–16. doi:10.1016/0167-9457(89)90020-1 32. Cohen J. Statistical power analysis for the behavioral sciences. Hillsdale, New Jersey: Lawrence Erlbaum Associates, Inc.; 1988. 33. Winby CR, Lloyd DG, Besier TF, Kirk TB. Muscle and external load contribution to knee joint contact loads during normal gait. J Biomech. 2009;42(14):2294–2300. PubMed doi:10.1016/j.jbiomech.2009.06.019 34. Richards C, Higginson JS. Knee contact force in subjects with symmetrical OA grades: differences between OA severities. J Biomech. 2010;43(13):2595–2600. PubMed doi:10.1016/j.jbiomech.2010.05.006
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35. Sasaki K, Neptune RR. Individual muscle contributions to the axial knee joint contact force during normal walking. J Biomech. 2010;43(14):2780–2784. PubMed doi:10.1016/j.jbiomech.2010.06.011 36. Foley A, Halbert J, Hewitt T, Crotty M. Does hydrotherapy improve strength and physical function in patients with osteoarthritis–a randomised controlled trial comparing a gym based and a hydrotherapy based strengthening programme. Ann Rheum Dis. 2003;62(12):1162– 1167. PubMed doi:10.1136/ard.2002.005272 37. Thorp LE, Wimmer MA, Foucher KC, Sumner DR, Shakoor N, Block JA. The biomechanical effects of focused muscle training on
medial knee loads in OA of the knee: a pilot, proof of concept study. J Musculoskelet Neuronal Interact. 2010;10(2):166–173. PubMed 38. Hurd WJ, Chmielewski TL, Axe MJ, Davis I, Snyder-Mackler L. Differences in normal and perturbed walking kinematics between male and female athletes. Clin Biomech (Bristol, Avon). 2004;19(5):465– 472. PubMed doi:10.1016/j.clinbiomech.2004.01.013 39. Kerrigan DC, Todd MK, Della Croce U. Gender differences in joint biomechanics during walking: normative study in young adults. Am J Phys Med Rehabil. 1998;77(1):2-7.
An Official Journal of ISB www.JAB-Journal.com ORIGINAL RESEARCH
Lower Limb Joint Angular Position and Muscle Activity During Elliptical Exercise in Healthy Young Men Max R. Paquette,1 Audrey Zucker-Levin,2 Paul DeVita,3 Joseph Hoekstra,1 and David Pearsall4 1University
of Memphis; 2University of Tennessee Health Science Center; 3East Carolina University; 4McGill University
The purpose of this study was to compare lower extremity joint angular position and muscle activity during elliptical exercise using different foot positions and also during exercise on a lateral elliptical trainer. Sixteen men exercised on a lateral elliptical and on a standard elliptical trainer using straight foot position, increased toe-out angle, and a wide step. Motion capture and electromyography systems were used to obtain 3D lower extremity joint kinematics and muscle activity, respectively. The lateral trainer produced greater sagittal and frontal plane knee range of motion (ROM), greater peak knee flexion and extension, and higher vastus medialis activation compared with other conditions (P < .05). Toe-out and wide step produced the greatest and smallest peak knee adduction angles, respectively (P < .05). The lateral trainer produced greater sagittal and frontal plane hip ROM and greater peak hip extension and flexion compared with all other conditions (P < .05). Toe-out angle produced the largest peak hip external rotation angle and lowest gluteus muscle activation (P < .05). Findings from this study indicate that standard elliptical exercise with wide step may place the knee joint in a desirable frontal plane angular position to reduce medial knee loads, and that lateral elliptical exercise could help improve quadriceps strength but could also lead to larger knee contact forces. Keywords: kinematics, exercise, electromyography, low-impact, biomechanics Regular aerobic exercise along with a healthy diet can significantly improve body composition, promote weight loss, and reduce the risks for or consequences of cardiovascular and musculoskeletal diseases (eg, sarcopenia, osteoarthritis).1–3 Some aerobic exercises however may be too demanding for both healthy and clinical populations, including people with osteoarthritis (OA), obesity, or ageinduced frailty. For example, lower extremity joint OA patients may not be able to adhere to high-impact aerobic exercise programs such as jogging due to joint pain and discomfort. In recent years, lowimpact aerobic exercise modalities such as elliptical cross trainers have become increasingly popular and widely available in fitness facilities. These trainers have been shown to reduce peak knee and hip internal abductor moments,4 increase sagittal and frontal plane knee and hip joint range of motion (ROM),4–7 increase internal knee and hip extensor moments,4,6 and reduce peak vertical reaction force (ie, pedal versus ground) and its loading rate8 compared with level walking. Further, elliptical trainers yield greater activations of the rectus femoris,9 vastus lateralis, and gluteus maximus,5 but lower activations of the biceps femoris and gastrocnemius5 compared with level walking. Finally, elliptical trainers yield similar physiological improvements (ie, maximal oxygen uptake, maximal expiratory volume) compared with stair climbing and treadmill running,10 but require greater energy expenditure compared with treadmill and cycling exercise with similar rated perceived exertion.11 Due to the high prevalence of knee OA in older adults, interventions that lower knee loads and pain and improve knee function Max R. Paquette and Joseph Hoekstra are with the University of Memphis, Health & Sport Sciences, Memphis, TN. Audrey Zucker-Levin is with the University of Tennessee Health Science Center, Physical Therapy, Memphis, TN. Paul DeVita is with East Carolina University, Kinesiology, Greenville, NC. David Pearsall is with McGill University, Kinesiology & Physical Education, Montréal, QC, Canada. Address author correspondence to Max R. Paquette at [email protected].
during level walking and other activities of daily living need to be identified. Peak knee internal abduction moment has commonly been used as a surrogate for medial knee load.12 In addition, knee adduction angular position (ie, genu varus) is another important variable to assess medial knee loads, as increased varus alignment creates greater medial bone contact in the knee.13 Strength training, including knee extensor (ie, quadriceps) strengthening, is effective for improving knee joint function and reducing knee pain during level walking in knee OA patients.1,14,15 Based on the consistent finding that knee extensor moment and muscle activation are greater in elliptical training compared with level walking, it is possible that elliptical training exercise could improve knee function and reduce knee pain due to knee extensor strengthening in patients with knee OA. D’Lima et al16 showed that in vivo knee forces of three patients during elliptical training exercise measured with force sensor instrumented knee implants were no different than during treadmill walking. Therefore, elliptical training exercise may strengthen knee extensors due to larger knee moments and muscle activations and also improve function and reduce pain during level walking, and it may do so without higher joint loads compared with level walking. In addition to exercise training interventions, simple gait modifications also change knee function, pain, and load.17–22 Such gait adaptations, including increased toe-out angle, reduce the peak knee internal abduction moment in the later stages of stance phase.17–19,22,23 Further, increased step width during level and stair walking reduce knee adduction angular positions24–26 and peak knee internal abduction moment24,26,27 in healthy adults and patients with knee OA. Newly-modified elliptical trainers are available that incorporate lateral motion. Such elliptical trainers add lateral motion to the backward directed pedal stroke, producing a modified skating motion. This motion would be expected to increase step width and place the knee in a more abducted position (ie, knee valgus) due to the anticipated large hip abduction caused 19
20 Paquette et al.
by the side-to-side motion. These varied data are the basis of the hypothesis that lateral elliptical trainers and standard elliptical trainers with modified foot positions will create kinematic adaptations favorable for individuals with knee pathology and will also activate hip and knee extensor muscles to levels that induce beneficial neuromuscular adaptations. We plan to fully investigate this hypothesis through a series of integrated studies that will identify both acute and chronic elliptical training outcomes in both healthy and knee OA populations. We begin this line of work with the current study, the purpose of which was to compare knee and hip angular position and lower extremity muscle activity in healthy young men during exercise on an elliptical trainer using a straight foot position, toe-out angle, and wide step width, and also on a lateral trainer.
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Methods Participants Sixteen healthy, recreationally active young men (23.2 ± 1.9 y; 81.5 ± 9.2 kg; 1.8 ± 0.1 m; 25.7 ± 2.8 kg/m2) were recruited to participate in the study. Subjects were included in the study if they had no previous lower extremity joint surgeries and no current lower extremity joint injuries. Institutional review board approval was obtained and all subjects signed a written informed consent document before data collection.
(straight foot), (3) on a standard elliptical trainer with toe-out angle (toe-out), and (4) on a standard elliptical trainer with wide step (wide step). The elliptical conditions were randomized to avoid an order effect and all tests were performed on the same day. For the lateral trainer and straight foot conditions, participants were asked to place their feet in the middle of the pedals in a straight line (Figure 2A). For the toe-out angle condition, participants were instructed to have the distal end of the feet touch the lateral aspect of the pedal while the heel was touching the medial aspect of the pedal (Figure 2B). For the wide step condition, participants were asked to move their feet to the most lateral aspect of the pedal (Figure 2C). Subjects were required to maintain a stride rate of 50 strides per minute, which was cued using a metronome (Beats Metronome; Positive Grid, LLC). Based on the set stride rate, the resistance level on both trainers was adjusted to yield similar power measures (ie, 65 and 70 W). Participants were instructed to lightly touch the stationary handle bars for stability but to support their weight during exercise bouts. They were also instructed to move the pedals through their full ROM. For all conditions data were collected for 15 seconds at the fourth minute of exercise and thus, participants were able to familiarize themselves with each condition for four minutes before data were collected. In addition, a researcher visually monitored foot position during testing to ensure that participants maintained the required foot position during each testing condition. The lateral trainer produced an anteroposterior
Instrumentation A 10-camera motion analysis system (100 Hz, Qualisys, Sweden) and a wireless electromyography (EMG) system (2000 Hz, Delsys, USA) were used to obtain 3D lower extremity joint kinematics and muscle activity, respectively. Bipolar EMG surface electrodes (Trigno, Delsys, USA) were placed over the right vastus medialis (VM), biceps femoris (BF), gluteus maximus (GMax), gluteus medius (GMed) and medial gastrocnemius (MG) according to existing guidelines.28 The skin below each electrode placement site was shaved, lightly abraded, and cleaned with an alcohol swab before application. Two maximal voluntary isometric contractions (MVIC) for each muscle separated by one minute rest periods were performed to obtain voluntary maximal muscle activity signals of each participant. The MVIC were performed using manual muscle testing by the researcher for all subjects.29 Following the EMG procedures, unilateral retro-reflective markers were placed over the right and left anterior superior iliac spines (ASIS) and posterior superior iliac spines (PSIS), the sacrum, medial and lateral femoral epicondyles and malleoli, and the first and fifth metatarsal heads of the right leg to define lower extremity segments and joint centers. Arrays of four noncollinear markers placed on semirigid thermoplastic shells were attached to the thigh and shank using elastic wrap to track the segments during movement trials. Noncollinear markers were secured directly on the skin over the superior, inferior, and lateral aspect of the calcaneus and on the foot dorsum to track foot motion. A static calibration trial was performed and nontracking markers were removed for the elliptical exercise bouts.
Figure 1 — Illustration of the (A) lateral elliptical trainer and (B) standard elliptical trainer.
Testing Procedures Participants performed five minute exercise bouts under each of the four elliptical device conditions: (1) on a lateral trainer (Crossover, Technogym, USA; Figure 1A), (2) on a standard elliptical trainer (EX-5, Matrix Fitness, USA; Figure 1B) with straight foot position
Figure 2 — Illustration of the straight (A), toe-out angle (B), and wide step (C) position used during standard elliptical exercise.
Joint Kinematics and Electromyography During Elliptical Exercise 21
(AP) pedal displacement of 0.23 m and a mediolateral (ML) displacement of 0.32 m with a resultant pedal displacement of 0.39 m. The standard elliptical produced a ML displacement of 0.008 m and an AP pedal displacement of 0.46 m (ie, resultant pedal displacement as ML displacement is negligible). These displacements were measured within the laboratory coordinate system using a reflective marker placed on the elliptical pedals.
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Data Analyses Visual3D (C-Motion, Germantown, MD, USA) was used to obtain the 3D lower extremity joint kinematic and EMG variables of the middle six strides (ie, one full pedal revolution) during the last 30 seconds of each elliptical exercise bout. For the middle six strides, kinematic data were analyzed during the six load phase (ie, the most anterior to most posterior pedal position). The ASIS, PSIS, and sacrum markers were used to track the pelvis and the CODA pelvis was used in the Visual3D model.30,31 Kinematic data were filtered using a fourth-order Butterworth low-pass filter with a cut-off frequency of 6 Hz. A right-hand rule with a Cardan rotational sequence (x-y-z) was used for the 3D angular computations where x represents the ML axis, y represents the AP axis, and z represents the longitudinal axis. The knee joint kinematic data were expressed in the thigh coordinate system while the hip joint kinematics were expressed in the pelvis coordinate system. Dependent kinematic variables included the peak knee and hip flexion, extension, abduction, and adduction angles, the knee and hip sagittal and frontal plane ranges of motion (ROM: angular excursion between flexion-extension and abduction-adduction), and the peak hip external rotation angle. Foot progression angle was measured as the transverse plane deviation of the foot in the laboratory coordinate system at the time of the most anterior pedal position (negative value indicates toe-out). The elliptical trainers were aligned with the AP axis of the laboratory coordinate system to ensure consistent foot progression angle calculations. The EMG signals during MVIC and elliptical exercise were band-pass filtered with cut-off frequencies of 20 Hz and 400 Hz. The signals were then full-wave rectified and smoothed using a root-mean-square (RMS) filter with a moving window of 150 milliseconds. The EMG signals during exercise were normalized to the larger of the two MVIC RMS peak values for each muscle for each participant. The normalized EMG signals were then integrated (iEMG; % · s) during all six load phases for each muscle.
Results The results on knee kinematics indicate that toe-out angle during standard elliptical exercise alters peak knee frontal plane angular positions, while lateral trainer exercise significantly alters both frontal and sagittal plane knee ROM and peak knee sagittal plane angular positions compared with other elliptical conditions (Table 1) (Figure 3). Peak knee abduction angular position was smaller in toe-out angle compared with lateral trainer (ES = 1.36), straight foot (ES = 1.12), and wide step (ES = 1.33); and smaller in straight foot compared with lateral trainer (ES = 0.46) (Table 1). Peak knee adduction angular position was smaller in lateral trainer compared with toe-out angle (ES = –0.99) but greater compared with wide step (ES = 0.48); smaller in straight foot compared with toe-out angle (ES = –1.02) but greater in straight foot compared with wide step (ES = 0.36); and greater in toe-out angle compared with wide step (ES = 1.37) (Table 1). Frontal plane knee ROM was greater in lateral trainer compared with straight foot (ES = 0.91), toe-out angle (ES = 1.16), and wide step (ES = 0.97) (Table 1). Peak knee extension angular position was greater in lateral trainer compared with straight foot (ES = 0.67), toe-out angle (ES = 0.98), and wide step (ES = 0.86); and greater in straight foot compared with toe-out angle (ES = 0.40) (Table 1). Peak knee flexion angular position was larger in the lateral trainer condition compared with straight foot (ES = 4.95), toe-out angle (ES = 5.90), and wide step (ES = 6.12) (Table 1). Sagittal plane knee ROM was greater in lateral trainer compared with straight foot (ES = 4.09), toe-out angle (ES = 3.82), and wide step (ES = 4.10) (Table 1).
Statistical Analyses A repeated-measures ANOVA was performed on the average values of all dependent variables from all six load phases with elliptical condition as the within-subject factor (SPSS 20.0; IBM, Chicago, IL). Mauchly’s test of sphericity was used to test the assumption that the variances of the difference between repeated measures were all equal. When the assumption of sphericity was not met (ie, P < .05), the Greenhouse-Geisser adjustment was used to assess within-subject differences. When an ANOVA revealed a main effect of elliptical condition, post hoc comparisons with least significant difference (LSD) were used to compare means between conditions. Only statistically significant mean differences from post hoc comparisons are reported in the results section. The alpha level was set at .05 for all tests. Cohen’s d effect sizes were reported for mean differences with ≤ 0.20 representing a small effect, > 0.20 and < 0.80 representing a moderate effect, and ≥ 0.80 representing a large effect.32
Figure 3 — Sagittal (A) and frontal (B) plane knee angular position ensemble mean curves during load phase from all participants during lateral trainer (solid line) and standard elliptical with straight (dashed line), increased toe-out angle (dotted line), and wide step (dash-dotted line) positions. Note: Standard deviations of critical variables are presented in Table 1.
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22 Paquette et al.
The results on hip kinematics indicate that lateral trainer exercise significantly alters hip angular position in all three planes and that toe-out angle during standard elliptical also alters transverse plane hip angular position (Table 2) (Figure 4). Peak hip abduction angular position was smaller in straight foot compared with lateral trainer (ES = 1.49), toe-out angle (ES = 1.37), and wide step (ES = 0.75); and smaller in wide step compared with lateral trainer (ES = 0.81) (Table 2). Peak hip adduction angular position was smaller in wide step compared with lateral trainer (ES = 0.80) and straight foot (ES = 0.99); and smaller in toe-out angle compared with lateral trainer (ES = 0.73) and straight foot (ES = 0.87) (Table 2). Frontal plane hip ROM was larger in lateral trainer compared with straight foot (ES = 1.21), toe-out angle (ES = 0.97), and wide step (ES = 1.35); and larger in toe-out angle compared with wide step (ES = 1.27) (Table 2). Peak hip extension angular position was larger in lateral trainer compared with straight foot (ES = 1.94), toe-out angle (ES = 1.59), and wide step (ES = 1.93) conditions (Table 2). Peak hip flexion angular position was larger in lateral trainer compared with straight foot (ES = 2.67), toe-out angle (ES = 2.39), and wide step (ES = 2.76) conditions (Table 2).
Sagittal plane hip ROM was greater in lateral trainer compared with straight foot (ES = 1.37), toe-out angle (ES = 1.13), and wide step (ES = 1.17) (Table 2). Peak hip external rotation angular position was greater in toe-out angle compared with lateral trainer (ES = 0.74), straight foot (ES = 1.42), and wide step (ES = 1.38); and greater in lateral trainer compared with straight foot (ES = 0.74) and wide step (ES = 0.74) (Table 2). Integrated normalized EMG results indicate that lateral elliptical exercise produces greater vastus medialis activation compared with other conditions and that the toe-out position on a standard elliptical reduces the gluteus medius activation compared with other conditions (Table 3) (Figure 5). Vastus medialis iEMG was larger in lateral trainer compared with straight foot (ES = 1.11), toe-out angle (ES = 0.97), and wide step (ES = 1.04) conditions (Table 3). Gluteus medius iEMG was smaller in the toe-out angle condition compared with lateral trainer (ES = –0.89) and straight foot (ES = –0.48) (Table 3). There were no significant differences in iEMG between elliptical conditions for the biceps femoris, gluteus maximus, or medial gastrocnemius (P > .05) (Table 3).
Table 1 Load phase frontal and sagittal plane knee angular position variables between elliptical conditions (mean ± SD) and p values Angular Positions (deg) Knee abduction Knee adduction Knee ROMy Knee extension Knee flexion Knee ROMx
Lateral –6.8 ± 5.2 –0.3 ± 3.3 6.6 ± 3.2b,c,d –20.3 ± 7.7b,c,d –69.6 ± 5.3b,c,d 49.2 ± 8.3b,c,d
Elliptical Exercise Straight Toe-Out –1.2 ± 3.0a,b,d –4.8 ± 3.6a –0.5 ± 3.1 2.7 ± 3.1a,b,d 4.3 ± 1.8 3.8 ± 1.5 –15.6 ± 6.7c –12.7 ± 8.3 –38.5 ± 7.5c –35.1 ± 6.7 22.9 ± 4.4 22.4 ± 6.0
Wide Step –5.6 ± 3.8 –1.4 ± 3.0a,b 4.1 ± 2.0 –14.6 ± 5.8 –37.0 ± 5.7 22.4 ± 4.7
p < .001 < .001 .003 .002 < .001 < .001
Note. Add(+)/Abd(-); Ext(+)/Flex(-); ROM = range of motion. p values are bold when significant. a Significantly different than lateral elliptical trainer (P < .05). b Significantly different than straight foot position (P < .05). c Significantly different than toe-out position (P < .05). d Significantly different than wide step position (P < .05).
Table 2 Load phase frontal, sagittal, and transverse planes hip angular position variables between elliptical conditions (mean ± SD) and p values Angular Positions (deg) Hip abduction Hip adduction Hip ROMy Hip extension Hip flexion Hip ROMx Hip external rotation Toe-out angle
Lateral –7.9 ± 3.5d 3.0 ± 5.2 10.8 ± 5.9b,c,d 26.1 ± 7.8b,c,d 60.2 ± 7.7b,c,d 34.1 ± 5.4b,c,d –16.3 ± 6.2b,d –3.2 ± 4.3
Elliptical Exercise Straight Toe-Out –3.4 ± 2.7a,c,d –6.8 ± 2.4 2.2 ± 2.4 0.1 ± 2.6a,b 5.6 ± 2.1 6.8 ± 1.2d 12.5 ± 6.6 14.4 ± 7.4 40.4 ± 7.6c 43.4 ± 6.8 27.8 ± 4.0 29.1 ± 3.6 –11.7 ± 6.6 –21.1 ± 7.1a,b,d a –26.9 ± 4.2a,b,d –7.9 ± 4.3
Wide Step –5.4 ± 2.8 –0.2 ± 2.6a,b 5.2 ± 1.4 12.7 ± 6.5 41.4 ± 6.3 28.7 ± 4.0 –11.3 ± 7.6 –2.8 ± 4.5
Note. Add(+)/Abd(-); Ext(+)/Flex(-); ROM = range of motion. p values are bold when significant. a Significantly different than lateral elliptical trainer (P < .05). b Significantly different than straight foot position (P < .05). c Significantly different than toe-out position (P < .05). d Significantly different than wide step position (P < .05).
p < .001 .025 .003 < .001 < .001 < .001 < .001 < .001
Joint Kinematics and Electromyography During Elliptical Exercise 23
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Discussion
Figure 4 — Sagittal (A), frontal (B), and transverse (C) plane hip angular position ensemble mean curves during load phase from all participants during lateral trainer (solid line) and standard elliptical with straight (dashed line), increased toe-out angle (dotted line), and wide step (dashdotted line) positions. Note: Standard deviations of critical variables are presented in Table 2.
It was expected that lateral elliptical training and standard elliptical training with modified foot placement (ie, toe-out and wide step width) would reduce peak knee adduction angular position, increase frontal and sagittal plane knee ROM, and increase knee extensor muscle activity compared with the straight foot position on the standard elliptical. Secondly, it was also expected that lateral elliptical training and standard elliptical training with modified foot placement would increase peak hip abduction and extension angular positions and hip abductor and extensor muscle activity compared with the straight foot position during elliptical exercise. It is further expected that the findings of this study will provide a foundation to justify additional comprehensive investigations of elliptical training as a potential effective training modality for people with knee OA. The hypothesis that the lateral trainer and standard elliptical trainer with modified foot placement (ie, toe-out angle and wide step) would reduce peak knee adduction angular position, increase frontal and sagittal plane knee ROM, and increase knee extensor muscle activity compared with standard elliptical with straight foot position was partially supported. A greater knee adduction angular position (ie, genu varus) creates greater medial bone-on-bone contact in the knee13 and could indicate greater medial compartment knee contact forces, especially when the limb supports body weight (eg, stance in walking). In agreement with the first hypothesis, the peak knee adduction angular position was significantly smaller during wide step compared with all other conditions and, in fact, the findings indicate that peak frontal plane knee position is never in an adducted position during elliptical exercise using the wide step foot position. Previous research has shown reductions in peak internal knee abduction moments (ie, surrogate for medial knee loading) and, similar to the current findings in peak knee adduction, angular positions in healthy adults24,26 and medial compartment knee OA patients26 during stair walking with a wide step. A wide step is expected to shift the center of pressure (COP) under the feet laterally and in turn, move the frontal plane ground reaction force (GRF) vector closer to the knee joint center. The lever arm of the GRF to the joint center is then reduced and as a result, so is the peak knee abduction moment. Thus, the reduction in peak adduction angular position in the current study may suggest reductions in medial knee loads during elliptical exercise with a wide step.
Table 3 Integrated RMS EMG during load phase normalized to peak MVIC for all five muscles between elliptical conditions (mean ± SD) and p values Muscles (%·s) Vastus medialis Biceps femoris Gluteus medius Gluteus maximus Medial gastrocnemius
Lateral 23.5 ± 16.1b,c,d 4.6 ± 4.0 8.3 ± 3.2 4.9 ± 2.3 4.2 ± 3.7
Elliptical Exercise Straight Toe-Out Wide Step 10.0 ± 8.5 11.5 ± 8.9 10.8 ± 8.5 7.4 ± 9.6 7.4 ± 7.4 6.8 ± 8.5 7.1 ± 3.1 7.1 ± 2.5 6.1 ± 1.8a,b 4.2 ± 2.6 4.3 ± 2.2 4.2 ± 2.5 6.7 ± 4.0 4.3 ± 3.8 6.1 ± 4.8
p < .001 .075 .013 .089 .072
Note. RMS = root-mean-square; EMG = electromyography; MVIC = maximal voluntary isometric contractions. p values are bold when significant. a Significantly different than lateral elliptical trainer (P < .05). b Significantly different than straight foot position (P < .05). c Significantly different than toe-out position (P < .05). d Significantly different than wide step position (P < .05).
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24 Paquette et al.
Figure 5 — Normalized load phase integrated electromyography ensemble curves for vastus medialis (A), biceps femoris (B), gluteus medius (C), gluteus maximus (D), and medial gastrocnemius (E) during lateral trainer (solid line), and standard elliptical with straight (dashed line), increased toe-out angle (dotted line), and wide step (dash-dotted line) positions. Note: Standard deviations of critical variables for each muscle are presented in Table 3. RMS = root-mean-square.
Contrary to the first hypothesis, peak knee adduction angular position was greater in toe-out angle compared with all other conditions. A larger toe-out angle is effective in reducing peak knee internal abduction moment in the later stages of the stance phase during walking.17–19,22,23 Similar to using a wide step, a lateral shift of the COP has been suggested as the mechanism related to reduction in knee abduction moment with toe-out angle.22 The results confirmed that the toe-out condition was in fact performed with increased toe-out angle compared with all other conditions (Table 2). The increased toe-out angle appears to have been achieved with an increased hip external rotation. In the current study, the increased peak adduction angular position in the increased toe-out angle condition may suggest greater loads applied to the medial compartment of the knee joint. Joint kinetics data were not computed in the current study as the elliptical trainers were not instrumented with force sensors. Nevertheless, the peak knee adduction angular position
findings suggest that wide step may be the most effective elliptical exercise condition to potentially reduce medial knee loads. The frontal and sagittal plane knee ROMs were significantly greater in the lateral trainer condition compared with all other elliptical conditions. The EMG data support the finding of greater sagittal plane knee ROM and peak flexion in lateral trainer exercise, with a significantly larger integrated load phase vastus medialis activation (ie, knee extensor) compared with other conditions; these results may suggest greater knee extensor involvement (ie, internal torque). The EMG RMS signals were integrated within the absolute load phase time (ie, not expressed as a percentage) and thus, the iEMG data differences between elliptical devices could be caused by differences in load times. In fact, the lateral elliptical condition had a shorter load phase because stride rate was controlled (ie, 50 strides per min) during testing sessions, and resultant pedal displacement was smaller during the lateral
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Joint Kinematics and Electromyography During Elliptical Exercise 25
elliptical condition than the other conditions. The greater iEMG values of vastus medialis during a shorter load phase suggest that the lateral elliptical has a greater effect on knee extensor activation per stride compared with the standard elliptical. Due to the different pedal movement patterns between elliptical devices, it was important to avoid time-normalization of the load phase to observe functional and relevant differences in joint kinematics and muscle activity. Muscles, especially the quadriceps, play an important role in increasing knee joint contact forces,33–35 as they can add up to 3.5 BW to the net compressive knee contact forces during level walking.34 If knee extensor involvement is greater during the lateral trainer condition, it is possible that the net compressive knee contact force would also be increased in the lateral trainer condition compared with other elliptical conditions. However, the time spent exercising on an elliptical device is minimal relative to the time spent walking and standing while performing daily tasks. Further, knee extensor strengthening has proven to be effective in improving knee joint function and reducing knee pain during level walking in knee OA patients.14,15,36 Although potential higher muscle force contributions may increase the net compressive knee joint contact force during lateral trainer exercise, muscular adaptions from higher knee extensor activation may be beneficial to help improve knee function and reduce knee pain during gait and daily tasks in patients with knee pain (ie, knee OA). It was also expected that the lateral trainer and standard elliptical trainer with modified foot placement would increase peak hip abduction and extension angular positions and hip abductor and extensor muscle activity compared with the standard elliptical trainer in straight foot position. The lateral trainer showed greater peak hip abduction compared with the straight foot and wide step positions, but was not different compared with the toe-out angle condition. In addition, frontal plane hip ROM was largest in the lateral trainer condition compared with all other conditions. These results suggest that the lateral trainer may be effective for targeting training of the hip abductors. However, gluteus medius activation during load phase was higher in the lateral trainer condition compared with the toe-out angle, and although slightly higher, it was not significantly different than the other two conditions. The current data only provide acute differences between elliptical conditions, but the increased peak abduction angle, greater frontal plane hip ROM, and very small increase in gluteus medius activation (ES = 0.39–0.43) in the lateral trainer condition could potentially lead to training adaptations for hip abductor strengthening. Research shows that short-term (ie, four weeks) hip abductor strengthening leads to reduced peak knee internal abduction moments during gait in knee OA patients.37 Effective hip abductor strengthening from elliptical training could have positive benefits for knee joint load reduction during gait in people with knee OA. Finally, sagittal plane hip ROM and peak hip flexion and extension were significantly greater in the lateral trainer condition compared with all other conditions. The peak hip extension during load phase still occurs in hip flexion (Figure 3a) and thus, these hip sagittal plane results suggest that lateral trainer exercise places the hip in a more flexed position throughout the pedal cycle. Surprisingly, the findings did not indicate greater gluteus maximus muscle activation in the more flexed position. It is therefore suggested that this muscle was operating on a more favorable position of its force-length curve on the lateral trainer and produced sufficient force and torque with EMG magnitudes identical to other conditions. The data from this study provide information to suggest that elliptical exercise, especially lateral trainer and standard elliptical with a wide step foot position, could elicit kinematic (ie, greater knee abduction during lateral and
wide step) and neuromuscular adaptations (ie, greater knee extensor muscle activity during lateral) to help improve knee function and potentially reduce knee pain and knee loads in individuals with knee disorders such as knee OA. In addition, the greater knee and hip ROM found on the lateral trainer may have implications for rehabilitative mobility training in patients suffering from neuromuscular diseases or injuries that result in reduced ROM in activities of daily living (eg, Parkinson’s disease, incomplete spinal cord injuries). Finally, we now plan to identify both acute and chronic elliptical training outcomes in knee OA populations. This study has a few limitations. The workload during elliptical exercise was set between 65–70 W at a set pedal rate (ie, 50 strides/min) and was not standardized to each participant’s relative fitness and body height. However, the aim of this study was to obtain preliminary data on joint kinematics and muscle activation at low exercise intensity. The participants were all college-aged healthy men of similar height (1.8 ± 0.1 m) and none of them had difficulty performing the short exercise bouts during all four elliptical conditions. Women were excluded to avoid introducing a confounding factor of dynamic frontal and transverse plane knee and hip excursion found between sexes.38,39 The elliptical trainers used in the current study were not instrumented with pedal force sensors to calculate pedal reaction forces and joint kinetics. Although our interpretations of joint kinematics in relation to joint kinetics remain speculative, the joint kinematic and muscle activation data provide insightful evidence to support our interpretations. The current work only investigates acute differences between elliptical conditions in healthy men. For this reason, a direct generalization of the findings to knee OA populations is currently impossible. However, the study was intended to obtain preliminary results with a healthy population to first identify potential biomechanical benefits of these elliptical conditions before including an at-risk population (ie, knee OA). In summary, the results indicated lower peak knee adduction angular position during standard elliptical exercise with a wide step but greater peak adduction position with a toe-out foot position. Lateral trainer exercise increased vastus medialis activation and sagittal plane knee angular displacement, which could potentially help improve knee extensor strength but could also lead to larger net knee contact forces. The lateral trainer appears to have the greatest effect on hip motion, as it showed greater frontal and sagittal plane hip ROM. The need for future research investigating effective and safe aerobic exercise programs as interventions to improve quality of life and reduce knee pain and knee loads for individuals with knee diseases is highly important. Acknowledgments The authors would like to thank Technogym USA for providing the lateral elliptical device for testing.
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