IJSPT
ORIGINAL RESEARCH
ELECTROMYOGRAPHY DURING PEDALING ON UPRIGHT AND RECUMBENT ERGOMETER Alexandre Dias Lopes, PT, PhD1 Sandra Regina Alouche, PT, PhD1 Nils Hakansson, PhD2 Moisés Cohen, MD, PhD3
ABSTRACT Background: Ergometers are used during rehabilitation and fitness to restore range of motion, muscular strength, and cardiovascular fitness. The primary difference between upright and recumbent ergometers is that the seat and crank spindle are aligned nearly vertically on upright bicycles and nearly horizontally on recumbent ergometers. In addition, recumbent ergometers are characterized by large seats with backrests to provide support for the upper body and are low to the ground, permitting easier access for wheelchair users and individuals with mobility impairments. Despite the great utility of the recumbent bike, it has not been studied with regard to energy costs or muscular output. This is the first study to investigate the differences between two commercial ergometers by analyzing of lower limb EMG in participants who are not habitual cyclers. Methods: Ten non-cyclist males with no history of musculoskeletal lower limb injury pedaled on standard recumbent and upright ergometers. EMG data were recorded from the volunteers’ lower limb muscles (rectus femoris, semitendinosus, tibialis anterior, and medial gastrocnemius muscles). EMG signals were normalized to the highest EMG signals recorded for the maximum voluntary isometric contractions (MVIC). The peak normalized EMG value of the studied muscles over the average of the 10 pedal cycles was analyzed. Results: The differences in average peak muscle activity were not statistically significant for any of the four muscles tested. Pedaling a recumbent ergometer resulted in greater activity in two (semitendinosus and tibialis anterior) of the four muscles studied. Only the rectus femoris muscle demonstrated greater activity during upright pedaling. Conclusion: There were no differences in the EMG activity of the muscles studied during pedaling on a standard recumbent and an upright stationary exercise ergometer at moderate workload. This increased understanding of muscle activity during pedaling may be useful in the development of new exercise protocols and therapeutic approaches. Level of Evidence: 2c Key words: Bicycling, electromyography, ergometry, lower extremity, pedaling
1
Universidade Cidade de Sao Paulo (UNICID), Sao Paulo, Brazil Wichita State University, Kansas, USA 3 Federal University of Sao Paulo, Sao Paulo, Brazil 2
This study was approved and received ethical approval by the Institutional Review Board – Federal University of Sao Paulo.
CORRESPONDING AUTHOR Alexandre Dias Lopes Master’s and Doctoral Programs in Physical Therapy Universidade Cidade de Sao Paulo (UNICID) Rua Cesário Galeno, 448 Sao Paulo – SP/Brasil, 03071-000 Phone/Fax: +55 11 2178.1479 E-mail: [email protected]
The International Journal of Sports Physical Therapy | Volume 9, Number 1 | February 2014 | Page 76
INTRODUCTION Ergometers are used during rehabilitation and fitness to restore range of motion, muscular strength, and cardiovascular fitness. Several authors have reported on muscle activity during pedaling exercises.1-6 Muscle activity during pedaling is influenced by many factors, including seat height, positioning of the feet on the pedals, cadence, workload, and rider experience.1,7-9 The primary difference between upright and recumbent ergometers is that the seat and crank spindle are aligned nearly vertically on upright bicycles and nearly horizontally on recumbent ergometers. In addition, recumbent ergometers are characterized by large seats with backrests to provide support for the upper body and are low to the ground, permitting easier access for wheelchair users and individuals with mobility impairments. Despite the great utility of the recumbent bike, few studies have focused on the use of recumbent ergometers during exercise/fitness or rehabilitation.10-14 In a study to determine the limb kinetics in low work rate recumbent pedaling, Reiser et al. reported that the general muscle moments profiles were similar to those reported for upright pedaling.11 No differences in leg kinematics and similar joint moment trajectories in knee joint kinetics between upright bicycles and the simulated recumbent pedaling position were identified in another study that compared muscle activity patterns for the two pedaling positions.14 To date, the majority of studies addressing muscle activity during pedaling have been conducted on the upright, or standard, pedaling position. Therefore, the objective of this study was to compare the muscle activity level while pedaling conventional upright and recumbent stationary ergometers with moderate intensity exercise. This is the first study to investigate the differences between two commercial ergometers by analyzing of lower limb EMG in participants who are not habitual cyclers. METHODS Ten non-cyclists (mean ± SD) 18 ± 2.5 years; mass 73.9 ± 10.2 kg; height 187 ± 6.5 cm, with no history of musculoskeletal lower limb injury, pedaled on standard recumbent and upright ergometers. All participants expressed written consent to participate in this study.
The study received ethical approval from the Institutional Review Board - Federal University of Sao Paulo. Kinematic and electromygographic (EMG) were collected from the dominant side of each participant as they pedaled both a Cybex 700C stationary upright ergometer and a Cybex 700R stationary recumbent ergometer. The upright and recumbent ergometers were selected from the same manufacturer (Cybex International, Inc., Medway, MA, USA) in order to minimize the potential differences that could arise from mechanical components (e.g., crankarm lengths, inertia, gear ratios) and electronics (e.g., electromechanical brakes and cadence calculations). A standard positioning protocol was developed to reduce differences in pedaling kinematics resulting from the use of two different exercise ergometers. First, the feet were positioned such that the second metatarsals were over the pedal spindle. Second, the feet were fixed in place on the pedal with a strap. Third, the seat was positioned so that the knee flexion angle was between 20 and 30 degrees (referencing full knee extension at 0 degrees) when the ankle was in the neutral position (i.e., the foot and tibia form a 90 degree angle) and the pedal was at the maximum leg extension position reached during the pedaling cycle. The 10-degree knee flexion angle range was due to pre-established incremental seat positions on the ergometers. A goniometer was used to measure the joint angle when establishing seat height. A sensor was attached to the arm of the crank and to the body of the ergometer to identify the beginning of the crank cycle. The beginning of the crank cycle was referred to as top-dead-center, that is, the moment when the crank arm was aligned vertically and in the upright position. To identify the activity of flexor and extensor muscles that cross the knee and ankle, surface EMG activity was recorded from the rectus femoris, semitendinosus, tibialis anterior, and medial gastrocnemius muscles as the participants pedaled. The surface electrodes were placed on the chosen muscles, according to the SENIAM recommendations.15 The electrode was attached to the shaved, abraded skin surface with adhesive tape. These muscles were included because they are very important to pedaling movement, principally for flexion/extension of the knee and plantar/dorsiflexion of the ankle.4,16,17
The International Journal of Sports Physical Therapy | Volume 9, Number 1 | February 2014 | Page 77
EMG signals were recorded using active, bipolar, and differential electrodes. Each electrode bar was 1 cm long and 1 mm thick. There was a 1-cm distance between the electrodes, which were coupled to a 20 mm wide, 33 mm long, 5 mm thick polyurethane mold (AqDados 4.0 version, Lynx Electronics Technology Inc., Sao Paulo, SP, Brazil). The differential electrode EMG signal was preamplified by a factor of 10 and the common-mode rejection ratio was 80 dB. Before passing through the analog/digital converter, the analog signal was filtered and amplified by a factor of 100, thus providing a gain 1000 times the original EMG signal. EMG signals were recorded with a sample frequency of 1000 Hz. EMG signals were normalized to the highest EMG signals recorded for the maximum voluntary isometric contraction (MVIC) for the respective muscle and participant as the EMG signal was smoothed. MVIC tests were performed in prescribed muscular test positions and with resistance applied by the evaluator.18 Each of the MVIC EMG signals was recorded for five seconds, three times. The mean of the three tests EMG maximum output was to define the MVIC for data analysis. The maximal contractions were performed with the volunteer positioned on the middle range of motion. The tests were executed 10 minutes before the cycling test. Before each participant was seated on the ergometer and the EMG electrodes were positioned over the muscles, the participant was instructed to pedal for 10 minutes to adapt to the equipment and to gradually achieve the test pedaling conditions of 80 rpm and a work rate of 100W (moderate intensity). The participants received feedback regarding the pedaling rate from the display on the ergometer controller. The work rate was set using the same controller. After the adaptation period, EMG data was recorded for 30 seconds. Data representing 10 pedal cycles occurring between the 10 to 20-second time period were analyzed in this study. These ten cycles were used to determine the peak mean EMG values for each muscle. The ergometer pedaling order was randomly allocated among the volunteers. Therefore, five athletes started the data collection procedure on the recumbent ergometer and the other five on the upright ergometer. Two minutes of rest was provided to
avoid muscle fatigue between the two data collection periods. All the procedures including electrode position, data gathering, recording, and EMG signal processing complied with International Society of Electrophysiology and Kinesiology recommendations concerning the use of EMG and did not expose the participants to any risks.19 Statistical Analysis The sample size was calculated based on the difference in the response of matched pairs, which is normally distributed with a standard deviation of 2. If the true difference in the mean response of matched pairs is 2, it was proposed to analyze 10 subjects to be able to reject the null hypothesis that the response difference is zero with probability (power) 0.8. The Type I error probability associated with the test of the null hypothesis was 0.05 (Power and Sample Size Calculation Software, Department of Biostatistics, Vanderbilt University, USA). The normal distribution of the residuals was investigated by visual inspection of the histograms. The results obtained through processing the EMG signal were submitted to Wilcoxon signed-rank test because the data was not normally distributed. The independent variable was the ergometer model (recumbent or upright) and the dependent variable was the peak mean values obtained during 10 pedal cycles of the studied muscles (rectus femoris, semitendinosus, tibialis anterior, and medial gastrocnemius muscles). Statistical significance was established at α = 0.05. RESULTS The peak medial tibialis anterior EMG value was greater for eight participants participants pedaling the upright ergometer. The peak rectus femoris, semitendinosus and medial gastrocnemius EMG value were greater for six participants pedaling the upright ergometer too (Table 1), however no statistically significant differences were observed between conditions for all muscles. The plots in Figure 1 show that during the initial portion of the crank cycle (0-50% of percent of the crank cycle), the rectus femoris and the tibialis anterior EMG activities decreased while semitendinosus and medial gastrocnemius increased. It was observed
The International Journal of Sports Physical Therapy | Volume 9, Number 1 | February 2014 | Page 78
Table 1. Participant peak EMG values for the recumbent (R) and upright (U) ergometer as a percent of maximum voluntary isometric contraction (MVIC)
Figure 1. Plots of the normalized EMG signals averaged for a participant as a function of percent of the crank cycle. Sub-figure A) shows the smoothed EMG curves for the rectus femoris, B) the semitendinosus, C) the tibialis anterior, and D) the medial gastrocnemius. The curves with the thick lines represent the recumbent bike and the fine lines represent the upright bike. Legend: (EMG) Electromyography; (%MVIC) Percent of maximum voluntary isometric contraction. The International Journal of Sports Physical Therapy | Volume 9, Number 1 | February 2014 | Page 79
Table 2. Peak Mean ± SD for EMG values for the upright and recumbent ergometers as a percent of MVIC and corresponding Wilcoxon signed-rank test p values.
that the peak EMGs of rectus femoris and the tibialis anterior were present during the last portion of the crank cycle (50-100% of percent of the crank cycle) as the peak EMGs of the semitendinosus and medial gastrocnemius were observed during the last crank cycles. The average peak muscle activity was not statistically different between conditions for any of the four muscles tested (Table 2). The analyses of the average peak muscle activity while using both ergometers indicated that when pedaling the recumbent ergometer subjects demonstrated greater activity in two (semitendinosus and tibialis anterior) of the four muscles studied, however these differences were not statistically significant. Only the rectus femoris muscle presented more activity in upright pedaling. DISCUSSION Recumbent leg cycle ergometers are gaining popularity in fitness centers and rehabilitation clinics as a mode of exercise and rehabilitation therapy. Traditionally, upright leg cycle ergometers have dominated this role. No statistically significant differences were observed in EMG activity for the rectus femoris, semitendinosus, tibialis anterior, and medial gastrocnemius muscles during two ergometers studied. According these results, the alternate use of both ergometers during rehabilitation and exercise/fitness is an option. Although, the theoretical differences in core stability demands during recumbent and upright position suggests variations in EMG activity, the results of this study were not able to identify them.
In an earlier study, Hakansson and Hull20 examined the effects of the recumbent and upright pedaling position on the activity and functional roles of the leg muscles. They observed similarities in muscle activation and timing between the two pedaling positions. Differences between that study and the current one include their use of an upright road bike on an electromagnetic trainer to minimize rider adaptation effects and the use of competitive cyclists. In that study, the authors used upright and recumbent ergometer models from the same manufacturer in order to more accurately reproduce activities carried out in fitness centers and rehabilitation clinics. The ergometers used in Hakansson and Hull study were standard stationary exercise models and were available in fitness and rehabilitation centers. By analyzing the average values of the peak muscle activity for the four studied muscles, both in recumbent and upright pedaling, the authors noticed that the medial gastrocnemius muscle presented a muscle activity level significantly higher (34%) than the other muscles (rectus femoris muscle: 22%, semitendinosus muscle: 26%, and tibialis anterior muscle: 24%). These values are similar to the ones described in Ericson et al. and show the importance of the medial gastrocnemius muscle during pedaling activity.16 The importance of the triceps surae and tibialis anterior muscles in transferring power from the limb segments to the crank was identified in another study in which forward dynamic simulations were used to examine the influence of pedaling rates on muscle mechanical energy in recumbent pedaling.21 Limitations and Suggestions for Future Research The individual variability of the EMG output, small sample size, and small number of muscles studied were limitations of this study. These results cannot be translated to road biking in either the upright or recumbent positions. Further studies assessing muscles of hip and trunk are necessary to continute to test the differences between these two types of cycle ergometers. CONCLUSION There were no statistically significant differences in the EMG activity of the muscles studied (rectus fem-
The International Journal of Sports Physical Therapy | Volume 9, Number 1 | February 2014 | Page 80
oris, semitendinosus, tibialis anterior, and medial gastrocnemius) during pedaling on a standard recumbent and an upright stationary lower extremity exercise ergometer at a moderate workload. The improved understanding of the muscle activity during pedaling may be useful in the development of new exercise protocols and therapeutic approaches. REFERENCES 1. Gregor RJ, Green D, Garhammer JJ. An electromyographic analysis of selected muscle activity in elite competitive cyclists. In: Biomechanics VII. Baltimore, MD: University Park; 1982. 2. Li L, Caldwell GE. Muscle coordination in cycling: effect of surface incline and posture. J Appl Physiol. Sep 1998;85(3):927-934. 3. McIlroy WE, Brooke JD. Response synergies over a single leg when it is perturbed during the complex rhythmic movement of pedalling. Brain Res. Mar 31 1987;407(2):317-326. 4. Suzuki S, Watanabe S, Homma S. EMG activity and kinematics of human cycling movements at different constant velocities. Brain Res. May 27 1982;240(2):245-258. 5. Takaishi T, Yasuda Y, Ono T, Moritani T. Optimal pedaling rate estimated from neuromuscular fatigue for cyclists. Med Sci Sports Exerc. Dec 1996;28(12):1492-1497. 6. Usabiaga J, Crespo R, Iza I, Aramendi J, Terrados N, Poza JJ. Adaptation of the lumbar spine to different positions in bicycle racing. Spine. Sep 1 1997;22(17):1965-1969. 7. Despires M. An electromyographic study of competitive road cycling conditions simulated on a treadmill. In: Biomechanics IV. Baltimore, MD: University Park; 1974. 8. Faria IE, Cavanagh PR. The physiology and biomechanics of cycling. New York: John Wiley & Sons; 1978. 9. Jorge M, Hull ML. Analysis of EMG measurements during bicycle pedalling. J Biomech. 1986;19(9):683694. 10. Diaz FJ, Hagan RD, Wright JE, Horvath SM. Maximal and submaximal exercise in different positions. Med Sci Sports. Fall 1978;10(3):214-217.
11. Gregor SM, Perell KL, Rushatakankovit S, Miyamoto E, Muffoletto R, Gregor RJ. Lower extremity general muscle moment patterns in healthy individuals during recumbent cycling. Clin Biomech (Bristol, Avon). Feb 2002;17(2):123-129. 12. Perell KL, Gregor RJ, Scremin AME. Lower limb cycling mechanics in subjects with unilateral cerebrovascular accidents. J. Appl. Biomech. May 1998;14(2):158-179. 13. Reiser RF, 2nd, Peterson ML, Broker JP. Understanding recumbent cycling: instrumentation design and biomechanical analysis. Biomed Sci Instrum. 2002;38:209-214. 14. Reiser RF, 2nd, Broker JP, Peterson ML. Knee loads in the standard and recumbent cycling positions. Biomed Sci Instrum. 2004;40:36-42. 15. Hermens HJ, Freriks B, Disselhorst-Klug C, Rau G. Development of recommendations for SEMG sensors and sensor placement procedures. J Electromyogr Kinesiol. 2000;10(5):361-374. 16. Ericson MO, Nisell R, Arborelius UP, Ekholm J. Muscular activity during ergometer cycling. Scand J Rehabil Med. 1985;17(2):53-61. 17. Hug F, Dorel S. Electromyographic analysis of pedaling: a review. J Electromyogr Kinesiol. Apr 2009;19(2):182-198. 18. Kendall FP, McCreary EK, Provance PG. Muscles testing and function. 4th ed. Philadelphia, PA: WB Saunders; 1980. 19. Merletti R. Standards for reporting EMG data. Journal of Electromyography and Kinesiology. 1996;6(1):3-4. 20. Hakansson NA, Hull ML. Functional roles of the leg muscles when pedaling in the recumbent versus the upright position. J Biomech Eng. Apr 2005;127(2):301310. 21. Hakansson NA, Hull ML. Influence of pedaling rate on muscle mechanical energy in low power recumbent pedaling using forward dynamic simulations. IEEE Trans Neural Syst Rehabil Eng. Dec 2007;15(4):509-516.
The International Journal of Sports Physical Therapy | Volume 9, Number 1 | February 2014 | Page 81
ORIGINAL RESEARCH
ELECTROMYOGRAPHY DURING PEDALING ON UPRIGHT AND RECUMBENT ERGOMETER Alexandre Dias Lopes, PT, PhD1 Sandra Regina Alouche, PT, PhD1 Nils Hakansson, PhD2 Moisés Cohen, MD, PhD3
ABSTRACT Background: Ergometers are used during rehabilitation and fitness to restore range of motion, muscular strength, and cardiovascular fitness. The primary difference between upright and recumbent ergometers is that the seat and crank spindle are aligned nearly vertically on upright bicycles and nearly horizontally on recumbent ergometers. In addition, recumbent ergometers are characterized by large seats with backrests to provide support for the upper body and are low to the ground, permitting easier access for wheelchair users and individuals with mobility impairments. Despite the great utility of the recumbent bike, it has not been studied with regard to energy costs or muscular output. This is the first study to investigate the differences between two commercial ergometers by analyzing of lower limb EMG in participants who are not habitual cyclers. Methods: Ten non-cyclist males with no history of musculoskeletal lower limb injury pedaled on standard recumbent and upright ergometers. EMG data were recorded from the volunteers’ lower limb muscles (rectus femoris, semitendinosus, tibialis anterior, and medial gastrocnemius muscles). EMG signals were normalized to the highest EMG signals recorded for the maximum voluntary isometric contractions (MVIC). The peak normalized EMG value of the studied muscles over the average of the 10 pedal cycles was analyzed. Results: The differences in average peak muscle activity were not statistically significant for any of the four muscles tested. Pedaling a recumbent ergometer resulted in greater activity in two (semitendinosus and tibialis anterior) of the four muscles studied. Only the rectus femoris muscle demonstrated greater activity during upright pedaling. Conclusion: There were no differences in the EMG activity of the muscles studied during pedaling on a standard recumbent and an upright stationary exercise ergometer at moderate workload. This increased understanding of muscle activity during pedaling may be useful in the development of new exercise protocols and therapeutic approaches. Level of Evidence: 2c Key words: Bicycling, electromyography, ergometry, lower extremity, pedaling
1
Universidade Cidade de Sao Paulo (UNICID), Sao Paulo, Brazil Wichita State University, Kansas, USA 3 Federal University of Sao Paulo, Sao Paulo, Brazil 2
This study was approved and received ethical approval by the Institutional Review Board – Federal University of Sao Paulo.
CORRESPONDING AUTHOR Alexandre Dias Lopes Master’s and Doctoral Programs in Physical Therapy Universidade Cidade de Sao Paulo (UNICID) Rua Cesário Galeno, 448 Sao Paulo – SP/Brasil, 03071-000 Phone/Fax: +55 11 2178.1479 E-mail: [email protected]
The International Journal of Sports Physical Therapy | Volume 9, Number 1 | February 2014 | Page 76
INTRODUCTION Ergometers are used during rehabilitation and fitness to restore range of motion, muscular strength, and cardiovascular fitness. Several authors have reported on muscle activity during pedaling exercises.1-6 Muscle activity during pedaling is influenced by many factors, including seat height, positioning of the feet on the pedals, cadence, workload, and rider experience.1,7-9 The primary difference between upright and recumbent ergometers is that the seat and crank spindle are aligned nearly vertically on upright bicycles and nearly horizontally on recumbent ergometers. In addition, recumbent ergometers are characterized by large seats with backrests to provide support for the upper body and are low to the ground, permitting easier access for wheelchair users and individuals with mobility impairments. Despite the great utility of the recumbent bike, few studies have focused on the use of recumbent ergometers during exercise/fitness or rehabilitation.10-14 In a study to determine the limb kinetics in low work rate recumbent pedaling, Reiser et al. reported that the general muscle moments profiles were similar to those reported for upright pedaling.11 No differences in leg kinematics and similar joint moment trajectories in knee joint kinetics between upright bicycles and the simulated recumbent pedaling position were identified in another study that compared muscle activity patterns for the two pedaling positions.14 To date, the majority of studies addressing muscle activity during pedaling have been conducted on the upright, or standard, pedaling position. Therefore, the objective of this study was to compare the muscle activity level while pedaling conventional upright and recumbent stationary ergometers with moderate intensity exercise. This is the first study to investigate the differences between two commercial ergometers by analyzing of lower limb EMG in participants who are not habitual cyclers. METHODS Ten non-cyclists (mean ± SD) 18 ± 2.5 years; mass 73.9 ± 10.2 kg; height 187 ± 6.5 cm, with no history of musculoskeletal lower limb injury, pedaled on standard recumbent and upright ergometers. All participants expressed written consent to participate in this study.
The study received ethical approval from the Institutional Review Board - Federal University of Sao Paulo. Kinematic and electromygographic (EMG) were collected from the dominant side of each participant as they pedaled both a Cybex 700C stationary upright ergometer and a Cybex 700R stationary recumbent ergometer. The upright and recumbent ergometers were selected from the same manufacturer (Cybex International, Inc., Medway, MA, USA) in order to minimize the potential differences that could arise from mechanical components (e.g., crankarm lengths, inertia, gear ratios) and electronics (e.g., electromechanical brakes and cadence calculations). A standard positioning protocol was developed to reduce differences in pedaling kinematics resulting from the use of two different exercise ergometers. First, the feet were positioned such that the second metatarsals were over the pedal spindle. Second, the feet were fixed in place on the pedal with a strap. Third, the seat was positioned so that the knee flexion angle was between 20 and 30 degrees (referencing full knee extension at 0 degrees) when the ankle was in the neutral position (i.e., the foot and tibia form a 90 degree angle) and the pedal was at the maximum leg extension position reached during the pedaling cycle. The 10-degree knee flexion angle range was due to pre-established incremental seat positions on the ergometers. A goniometer was used to measure the joint angle when establishing seat height. A sensor was attached to the arm of the crank and to the body of the ergometer to identify the beginning of the crank cycle. The beginning of the crank cycle was referred to as top-dead-center, that is, the moment when the crank arm was aligned vertically and in the upright position. To identify the activity of flexor and extensor muscles that cross the knee and ankle, surface EMG activity was recorded from the rectus femoris, semitendinosus, tibialis anterior, and medial gastrocnemius muscles as the participants pedaled. The surface electrodes were placed on the chosen muscles, according to the SENIAM recommendations.15 The electrode was attached to the shaved, abraded skin surface with adhesive tape. These muscles were included because they are very important to pedaling movement, principally for flexion/extension of the knee and plantar/dorsiflexion of the ankle.4,16,17
The International Journal of Sports Physical Therapy | Volume 9, Number 1 | February 2014 | Page 77
EMG signals were recorded using active, bipolar, and differential electrodes. Each electrode bar was 1 cm long and 1 mm thick. There was a 1-cm distance between the electrodes, which were coupled to a 20 mm wide, 33 mm long, 5 mm thick polyurethane mold (AqDados 4.0 version, Lynx Electronics Technology Inc., Sao Paulo, SP, Brazil). The differential electrode EMG signal was preamplified by a factor of 10 and the common-mode rejection ratio was 80 dB. Before passing through the analog/digital converter, the analog signal was filtered and amplified by a factor of 100, thus providing a gain 1000 times the original EMG signal. EMG signals were recorded with a sample frequency of 1000 Hz. EMG signals were normalized to the highest EMG signals recorded for the maximum voluntary isometric contraction (MVIC) for the respective muscle and participant as the EMG signal was smoothed. MVIC tests were performed in prescribed muscular test positions and with resistance applied by the evaluator.18 Each of the MVIC EMG signals was recorded for five seconds, three times. The mean of the three tests EMG maximum output was to define the MVIC for data analysis. The maximal contractions were performed with the volunteer positioned on the middle range of motion. The tests were executed 10 minutes before the cycling test. Before each participant was seated on the ergometer and the EMG electrodes were positioned over the muscles, the participant was instructed to pedal for 10 minutes to adapt to the equipment and to gradually achieve the test pedaling conditions of 80 rpm and a work rate of 100W (moderate intensity). The participants received feedback regarding the pedaling rate from the display on the ergometer controller. The work rate was set using the same controller. After the adaptation period, EMG data was recorded for 30 seconds. Data representing 10 pedal cycles occurring between the 10 to 20-second time period were analyzed in this study. These ten cycles were used to determine the peak mean EMG values for each muscle. The ergometer pedaling order was randomly allocated among the volunteers. Therefore, five athletes started the data collection procedure on the recumbent ergometer and the other five on the upright ergometer. Two minutes of rest was provided to
avoid muscle fatigue between the two data collection periods. All the procedures including electrode position, data gathering, recording, and EMG signal processing complied with International Society of Electrophysiology and Kinesiology recommendations concerning the use of EMG and did not expose the participants to any risks.19 Statistical Analysis The sample size was calculated based on the difference in the response of matched pairs, which is normally distributed with a standard deviation of 2. If the true difference in the mean response of matched pairs is 2, it was proposed to analyze 10 subjects to be able to reject the null hypothesis that the response difference is zero with probability (power) 0.8. The Type I error probability associated with the test of the null hypothesis was 0.05 (Power and Sample Size Calculation Software, Department of Biostatistics, Vanderbilt University, USA). The normal distribution of the residuals was investigated by visual inspection of the histograms. The results obtained through processing the EMG signal were submitted to Wilcoxon signed-rank test because the data was not normally distributed. The independent variable was the ergometer model (recumbent or upright) and the dependent variable was the peak mean values obtained during 10 pedal cycles of the studied muscles (rectus femoris, semitendinosus, tibialis anterior, and medial gastrocnemius muscles). Statistical significance was established at α = 0.05. RESULTS The peak medial tibialis anterior EMG value was greater for eight participants participants pedaling the upright ergometer. The peak rectus femoris, semitendinosus and medial gastrocnemius EMG value were greater for six participants pedaling the upright ergometer too (Table 1), however no statistically significant differences were observed between conditions for all muscles. The plots in Figure 1 show that during the initial portion of the crank cycle (0-50% of percent of the crank cycle), the rectus femoris and the tibialis anterior EMG activities decreased while semitendinosus and medial gastrocnemius increased. It was observed
The International Journal of Sports Physical Therapy | Volume 9, Number 1 | February 2014 | Page 78
Table 1. Participant peak EMG values for the recumbent (R) and upright (U) ergometer as a percent of maximum voluntary isometric contraction (MVIC)
Figure 1. Plots of the normalized EMG signals averaged for a participant as a function of percent of the crank cycle. Sub-figure A) shows the smoothed EMG curves for the rectus femoris, B) the semitendinosus, C) the tibialis anterior, and D) the medial gastrocnemius. The curves with the thick lines represent the recumbent bike and the fine lines represent the upright bike. Legend: (EMG) Electromyography; (%MVIC) Percent of maximum voluntary isometric contraction. The International Journal of Sports Physical Therapy | Volume 9, Number 1 | February 2014 | Page 79
Table 2. Peak Mean ± SD for EMG values for the upright and recumbent ergometers as a percent of MVIC and corresponding Wilcoxon signed-rank test p values.
that the peak EMGs of rectus femoris and the tibialis anterior were present during the last portion of the crank cycle (50-100% of percent of the crank cycle) as the peak EMGs of the semitendinosus and medial gastrocnemius were observed during the last crank cycles. The average peak muscle activity was not statistically different between conditions for any of the four muscles tested (Table 2). The analyses of the average peak muscle activity while using both ergometers indicated that when pedaling the recumbent ergometer subjects demonstrated greater activity in two (semitendinosus and tibialis anterior) of the four muscles studied, however these differences were not statistically significant. Only the rectus femoris muscle presented more activity in upright pedaling. DISCUSSION Recumbent leg cycle ergometers are gaining popularity in fitness centers and rehabilitation clinics as a mode of exercise and rehabilitation therapy. Traditionally, upright leg cycle ergometers have dominated this role. No statistically significant differences were observed in EMG activity for the rectus femoris, semitendinosus, tibialis anterior, and medial gastrocnemius muscles during two ergometers studied. According these results, the alternate use of both ergometers during rehabilitation and exercise/fitness is an option. Although, the theoretical differences in core stability demands during recumbent and upright position suggests variations in EMG activity, the results of this study were not able to identify them.
In an earlier study, Hakansson and Hull20 examined the effects of the recumbent and upright pedaling position on the activity and functional roles of the leg muscles. They observed similarities in muscle activation and timing between the two pedaling positions. Differences between that study and the current one include their use of an upright road bike on an electromagnetic trainer to minimize rider adaptation effects and the use of competitive cyclists. In that study, the authors used upright and recumbent ergometer models from the same manufacturer in order to more accurately reproduce activities carried out in fitness centers and rehabilitation clinics. The ergometers used in Hakansson and Hull study were standard stationary exercise models and were available in fitness and rehabilitation centers. By analyzing the average values of the peak muscle activity for the four studied muscles, both in recumbent and upright pedaling, the authors noticed that the medial gastrocnemius muscle presented a muscle activity level significantly higher (34%) than the other muscles (rectus femoris muscle: 22%, semitendinosus muscle: 26%, and tibialis anterior muscle: 24%). These values are similar to the ones described in Ericson et al. and show the importance of the medial gastrocnemius muscle during pedaling activity.16 The importance of the triceps surae and tibialis anterior muscles in transferring power from the limb segments to the crank was identified in another study in which forward dynamic simulations were used to examine the influence of pedaling rates on muscle mechanical energy in recumbent pedaling.21 Limitations and Suggestions for Future Research The individual variability of the EMG output, small sample size, and small number of muscles studied were limitations of this study. These results cannot be translated to road biking in either the upright or recumbent positions. Further studies assessing muscles of hip and trunk are necessary to continute to test the differences between these two types of cycle ergometers. CONCLUSION There were no statistically significant differences in the EMG activity of the muscles studied (rectus fem-
The International Journal of Sports Physical Therapy | Volume 9, Number 1 | February 2014 | Page 80
oris, semitendinosus, tibialis anterior, and medial gastrocnemius) during pedaling on a standard recumbent and an upright stationary lower extremity exercise ergometer at a moderate workload. The improved understanding of the muscle activity during pedaling may be useful in the development of new exercise protocols and therapeutic approaches. REFERENCES 1. Gregor RJ, Green D, Garhammer JJ. An electromyographic analysis of selected muscle activity in elite competitive cyclists. In: Biomechanics VII. Baltimore, MD: University Park; 1982. 2. Li L, Caldwell GE. Muscle coordination in cycling: effect of surface incline and posture. J Appl Physiol. Sep 1998;85(3):927-934. 3. McIlroy WE, Brooke JD. Response synergies over a single leg when it is perturbed during the complex rhythmic movement of pedalling. Brain Res. Mar 31 1987;407(2):317-326. 4. Suzuki S, Watanabe S, Homma S. EMG activity and kinematics of human cycling movements at different constant velocities. Brain Res. May 27 1982;240(2):245-258. 5. Takaishi T, Yasuda Y, Ono T, Moritani T. Optimal pedaling rate estimated from neuromuscular fatigue for cyclists. Med Sci Sports Exerc. Dec 1996;28(12):1492-1497. 6. Usabiaga J, Crespo R, Iza I, Aramendi J, Terrados N, Poza JJ. Adaptation of the lumbar spine to different positions in bicycle racing. Spine. Sep 1 1997;22(17):1965-1969. 7. Despires M. An electromyographic study of competitive road cycling conditions simulated on a treadmill. In: Biomechanics IV. Baltimore, MD: University Park; 1974. 8. Faria IE, Cavanagh PR. The physiology and biomechanics of cycling. New York: John Wiley & Sons; 1978. 9. Jorge M, Hull ML. Analysis of EMG measurements during bicycle pedalling. J Biomech. 1986;19(9):683694. 10. Diaz FJ, Hagan RD, Wright JE, Horvath SM. Maximal and submaximal exercise in different positions. Med Sci Sports. Fall 1978;10(3):214-217.
11. Gregor SM, Perell KL, Rushatakankovit S, Miyamoto E, Muffoletto R, Gregor RJ. Lower extremity general muscle moment patterns in healthy individuals during recumbent cycling. Clin Biomech (Bristol, Avon). Feb 2002;17(2):123-129. 12. Perell KL, Gregor RJ, Scremin AME. Lower limb cycling mechanics in subjects with unilateral cerebrovascular accidents. J. Appl. Biomech. May 1998;14(2):158-179. 13. Reiser RF, 2nd, Peterson ML, Broker JP. Understanding recumbent cycling: instrumentation design and biomechanical analysis. Biomed Sci Instrum. 2002;38:209-214. 14. Reiser RF, 2nd, Broker JP, Peterson ML. Knee loads in the standard and recumbent cycling positions. Biomed Sci Instrum. 2004;40:36-42. 15. Hermens HJ, Freriks B, Disselhorst-Klug C, Rau G. Development of recommendations for SEMG sensors and sensor placement procedures. J Electromyogr Kinesiol. 2000;10(5):361-374. 16. Ericson MO, Nisell R, Arborelius UP, Ekholm J. Muscular activity during ergometer cycling. Scand J Rehabil Med. 1985;17(2):53-61. 17. Hug F, Dorel S. Electromyographic analysis of pedaling: a review. J Electromyogr Kinesiol. Apr 2009;19(2):182-198. 18. Kendall FP, McCreary EK, Provance PG. Muscles testing and function. 4th ed. Philadelphia, PA: WB Saunders; 1980. 19. Merletti R. Standards for reporting EMG data. Journal of Electromyography and Kinesiology. 1996;6(1):3-4. 20. Hakansson NA, Hull ML. Functional roles of the leg muscles when pedaling in the recumbent versus the upright position. J Biomech Eng. Apr 2005;127(2):301310. 21. Hakansson NA, Hull ML. Influence of pedaling rate on muscle mechanical energy in low power recumbent pedaling using forward dynamic simulations. IEEE Trans Neural Syst Rehabil Eng. Dec 2007;15(4):509-516.
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