Training & Testing
705
Authors
C. J. Stevens1, J. Hacene1, D. V. Sculley2, L. Taylor3, R. Callister4, B. Dascombe1
Affiliations
Affiliation addresses are listed at the end of the article
Key words ▶ reproducibility of results ● ▶ physical endurance ● ▶ sports performance ● ▶ pacing strategy ● ▶ electromyography ● ▶ near-infrared spectroscopy ●
Abstract
▼
The purpose of the study was to establish the reliability of performance and physiological responses during a self-paced 5 km running time trial on a non-motorized treadmill. 17 male runners (age: 32 ± 13 years, height: 177 ± 7 cm, body mass: 71 ± 9 kg, sum of 7 skinfolds: 55 ± 21 mm) performed familiarization then 2 separate maximal 5 km running time trials on a non-motorized treadmill. Physiological responses measured included heart rate, oxygen uptake, expired air volume, blood lactate concentration, tissue saturation index and integrated electromyography.
Introduction
▼ accepted after revision January 12, 2015 Bibliography DOI http://dx.doi.org/ 10.1055/s-0034-1398680 Published online: March 19, 2015 Int J Sports Med 2015; 36: 705–709 © Georg Thieme Verlag KG Stuttgart · New York ISSN 0172-4622 Correspondence Christopher John Stevens, B. Exercise and Sport Science (Hons) Exercise and Sport Sciences University of Newcastle Brush Rd Ourimbah 2258 Australia Tel.: + 61/411/797 245 Fax: + 61/243/484 145 christopher.j.stevens@uon. edu.au
Laboratory simulated exercise time trials are commonly used to assess endurance exercise performance in intervention studies [14]. Time trials require a set amount of work or time period of exercise to be completed with the highest average speed. To measure performance, time trials appear more favorable than time to exhaustion protocols, which require exercise to be performed until exhaustion at a fixed workload. Time trials simulate endurance competition, are self-paced and appear highly reliable [14, 15, 17], whereas time to exhaustion protocols have been criticized for lacking specificity to endurance competition and poor reliability [14, 15]. Reliability refers to the consistency of a variable measured during repeated tests under the same conditions. Scientific tests must be reliable to ensure changes are the result of an intervention, are not measurement error or inter-individual differences [2] and to detect the smallest worthwhile change [18]. The main measure of reliability used to compare between different protocols is the typical error of measurement expressed as a coefficient of variation (CV); the lower the CV the greater the reliability [12]. Low CVs of 1 %
Running time (1 522 ± 163 s vs. 1 519 ± 162 s for trials 1 and 2, respectively) demonstrated a low CV of 1.2 % and high ICC of 0.99. All physiological variables had CVs of less than 4 % and ICCs of > 0.92, with the exception of blood lactate concentration (7.0 ± 2 mmol · L − 1 vs. 6.5 ± 1.5 mmol · L − 1 for trials 1 and 2, respectively; CV: 12 %, ICC: 0.83) and the electromyography measures (CV: 8–27 %, ICC: 0.71–0.91). The data demonstrate that performance time in a 5 km running time trial on a non-motorized treadmill is a highly reliable test. Most physiological responses measured across the 5 km run also demonstrated good reliability.
[13] and 1.7 % [15] have been reported for 5 km running time trials performed over-ground and on a motorized treadmill, respectively. However, the reliability of endurance running on a nonmotorized treadmill (NMT) has not been established. The NMT requires the runner to manually produce the force to rotate the running belt with each step, rather than a motor dictating a constant belt speed. Such treadmills work either by the act of pushing backwards on an inclined treadmill belt (Curve NMT, Woodway, Waukesha, Wisconsin, USA) or by pushing backwards on a flat treadmill belt with the aid of a cable attached to the runner (Force NMT, Woodway, Waukesha, Wisconsin, USA). The NMT was originally created to offer a cheaper alternative to more expensive motorized treadmills, but these have since been used to simulate the demands of team sports, where sudden changes in running speed are required [1, 19]. Recently, the Curve 3TM NMT has been used as a laboratory measure of endurance running performance following a cognitive task [16]. However, no reliability data was presented and as such it is unclear if the measured change was greater than natural variation. If the Curve 3TM displays high reliability, it may be more
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The Reliability of Running Performance in a 5 km Time Trial on a Non-motorized Treadmill
favorable than a motorized treadmill, as the runner can change speed freely, without the need to actively adjust the speed on a computer. Therefore, changes in speed and pacing strategy are more likely to be instantaneous and better reflect subconscious fatigue. Despite the established reliability of self-paced time trial performance in both cycling [20, 22, 26] and motorized treadmill running [15, 17, 23], few investigations have reported on the reliability of physiological and perceptual responses within such protocols and no reliability data currently exists for tissue saturation index or integrated electromyography during self-paced exercise. Therefore, the aim of the present study was to determine the reliability of performance, as well as the physiological and perceptual responses between repeated self-paced 5 km running time trials on a NMT.
Materials and Methods
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17 moderately trained male runners (age: 32 ± 13 years, height: 177 ± 7 cm, body mass: 71 ± 9 kg, sum of 7 skinfolds: 55 ± 21 mm) volunteered to participate. Inclusion criteria stipulated participants have a current 5 km over-ground personal best of 17–23 min in the past 6 months. The present study doubled the sample size of the previous studies to assess the reliability of running performance in the laboratory more accurately [15, 17, 23]. The Human Ethics Research Committee at the University of Newcastle granted approval for the project (UoN H-2012-0311) and the investigators followed the ethical guidelines of the journal [10]. All running was performed on a NMT (Curve 3TM, Woodway, Waukesha, USA) and a pre-exercise screening determined all participants had not previously completed any exercise on such a treadmill. An anthropometric profile was performed on all subjects including height, body mass and sum of 7 skinfolds. The participants performed 2 separate familiarization sessions. The first was a 2 km run on the treadmill at a self-selected intensity and the second was a 5 km maximal running time trial. Since the effect of familiarization has already been well established and is common practice in exercise performance research [2, 23], only the data from the test-retest trials were reported. For 24 h prior to the first experimental trial, caffeine, alcohol and high intensity exercise were not permitted. The participants performed a self-selected 15-min warm-up for which intensity was recorded for repetition prior to the second trial. During the time trials, the participants were blinded to all measures except for elapsed distance. A 50 cm fan was placed 1 m in front of the NMT and provided a wind speed of 4 m · s − 1 to simulate the convective cooling of outdoor wind resistance. No music, fluids or food were permitted and footwear, clothing, instruction and time of day were standardized between trials. All trials were separated by 5–10 days. Power output was continuously measured by the treadmill and recorded by Pacer Performance software at 200 Hz (Innervations Software, Joondalup, Australia). Heart rate was continuously measured at 1 Hz by a Garmin 910XT monitor (Garmin Ltd., Schaffhausen, Switzerland). Measurements of relative VO2 and expired air volume were performed on a breath-by-breath basis using a portable gas analyzer (Cosmed K4 b2, Rome, Italy). Capillary blood samples were collected at 1, 3 and 5 km intervals from a hyperaemic fingertip for blood lactate analysis using a Lactate Scout (EKF-Diagnostic, Berlin, Germany). Stevens CJ et al. The Reliability of Running … Int J Sports Med 2015; 36: 705–709
Near infrared spectroscopy (NIRS) derived measurements of oxygenation in the calf were taken using a portable NIRS device (Portamon, Artinis Medical Systems, Zetten, the Netherlands). The system is a 2-wavelength continuous wave system that simultaneously uses the modified Beer-Lambert law and spatially resolved spectroscopy methods. This non-invasive technique measures the changes in muscle oxygenation by determining the reflection of light at near infrared wavelengths of 750 and 860 nm. Tissue saturation index (TSI) was measured as the difference between tissue oxyhaemoglobin and deoxyhaemoglobin, representing the mean saturation of the underlying muscle tissue. An arbitrary value of 3.83 was used for the differential path length factor [6]. The NIRS device was positioned on the left gastrocnemius lateralis as per previous research [3]. The probe and skin were covered with strapping tape and a dark bandage to prevent penetration of ambient light. Skinfold thickness at the measurement site was taken to ensure that fat tissue was not sufficient to interfere with light penetration. The mean skinfold was 7.4 ± 3.3 mm, which was less than half the distance between source and detector and therefore fat tissue was considered inconsequential. The NIRS device was connected to a personal computer via bluetooth, with data acquired continuously at a sampling rate of 10 Hz. The electromyography (EMG) signal of 4 muscles (gastrocnemius medianus, tibialis anterior, vastus lateralis and rectus femoris) were recorded from the right limb via TringoTM wireless surface electrodes (Delsys Inc., Boston, USA). Electrode placement and skin preparation was as per international standards [11]. The surface electrodes had a single differential configuration, interelectrode distance of 10 mm, 4-bar formation, bandwidth of 20–450 Hz and 99.9 % silver contact material. 12 s of raw data was collected midway through each kilometer. The EMG signal was sampled at 3 kHz and the raw data was multiplied by 1 000 to match those gain settings used previously [4]. A 4th order Butterworth filter of 12–500 Hz was applied to the data before the root mean square and integral were calculated with a 0.050 ms window length and 0.025 ms overlap. The muscles were analyzed separately but also added together to form the parameter of summated integrated-EMG (sum-iEMG; V · s − 1), which has been used previously to represent the general behavior of muscle electrical activity of the lower limb [4]. Rating of perceived exertion was measured using a Borg Scale of 0.5–10 where 10 = very, very heavy, for the heaviest running intensity perceived and 0.5 = very, very weak, equal to the weakest running intensity perceived [5]. Thermal sensation was measured using Young’s Thermal Sensation Scale [25]. Perceptual measurements were obtained in every kilometer. Stride rate was measured continuously using a foot pod taped to the participant’s right shoelaces, an accessory of the 910XT (Garmin Ltd., Schaffhausen, Switzerland). The mean ± SD was calculated for all data, with normality assessed using a Kolmogorov-Smirnov test. Differences in data between trials were examined with a paired samples t-test for global means and repeated measures ANOVA for 1-km intervals within SPSS software V22.0 (IBM Corporation, Somers, USA). Alpha (p) was set at 0.05. The p value remained unadjusted to conservatively identify differences between trials. Measures of reliability, including typical error as a CV ( %) and intraclass correlation coefficient (ICC) were calculated within a custom made spreadsheet [Hopkins, W.G. Precision of measurement (2011) in internet: newstats.org/precision.html; (22/06/12)]. The smallest
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Table 1 Descriptive and reliability statistics of variables calculated from 2 repeat 5 km running time trials on a non-motorized treadmill. Trial 1 Mean ± SD
Trial 2 Mean ± SD
1 522 ± 163 117.9 ± 12.1 177 ± 11 51.2 ± 5.7 119.9 ± 13.7 7.0 ± 2 52.77 ± 6.13 6.5 ± 1 5.4 ± 0.6 86.6 ± 4.8
1 519 ± 162 118.1 ± 11.8 176 ± 12 51.5 ± 5.1 118.5 ± 13.0 6.5 ± 1.5 53.40 ± 6.31 6.4 ± 0.8 5.4 ± 0.7 86.1 ± 5.3
5 km run time (s) mean power (W) mean heart rate (b · min − 1) mean VO2 (mL · kg − 1 · min − 1) mean VE (L) mean [BLa− ] (mmol · L − 1) mean TSI ( %) mean RPE (AU) mean TS (AU) mean stride rate (steps · min − 1)
CV ( %) (95 % CI) 1.2 (0.9–1.8) 1.2 (0.9–1.8) 1.2 (0.9–1.9) 3.3 (2.4–5.3) 2.7 (2–4.3) 12 (8.6–20.1) 3 (2.1–5.1) 5.0 (3.7–7.6) 5.7 (4.2–8.8) 0.7 (0.5–1.3)
ICC (95 % CI) 0.99 (0.97–1) 0.99 (0.97–1) 0.97 (0.92–0.97) 0.92 (0.77–0.97) 0.96 (0.88–0.98) 0.83 (0.54–0.94) 0.94 (0.82–0.98) 0.9 (0.75–0.96) 0.81 (0.55–0.93) 0.99 (0.96–1)
SWC 4 0.3 1 0.4 0.7 0.2 0.39 0.1 0.1 0.2
AU = arbitrary units, b · min − 1 = beats per minute, CI = confidence interval, CV = coefficient of variation, ICC = intraclass correlation coefficient, RPE = rating of perceived exertion,
Trial 1 Mean ± SD mean GM iEMG (V · s − 1) mean TA iEMG (V · s − 1) mean RF iEMG (V · s − 1) mean VL iEMG (V · s − 1) mean sum-iEMG (V · s − 1)
1.53 ± 0.52 1.36 ± 0.61 0.52 ± 0.21 0.92 ± 0.26 4.33 ± 1.17
Trial 2 Mean ± SD
CV ( %) (95 % CI)
ICC (95 % CI)
12.5 (8.8–21.5) 13.7 (9.6–23.6) 26.2 (18.2–46.8) 10.9 (7.7–18.6) 8.4 (6–14.3)
0.9 (0.70–0.97) 0.93 (0.80–0.98) 0.71 (0.29–0.90) 0.89 (0.67–0.96) 0.91 (0.73–0.97)
1.54 ± 0.54 1.20 ± 0.53 0.49 ± 0.20 0.85 ± 0.31 4.08 ± 1.33
Table 2 Descriptive and reliability statistics of electromyography variables calculated from 2 repeat 5 km running time trials on a nonmotorized treadmill.
CI = confidence interval, CV = coefficient of variation, GM = gastrocnemius medianus, ICC = intraclass correlation coefficient, RF = rectus femoris, Sum-iEMG = summated integrated electromyography, TA = tibiarlis anterior, VL = vastus lateralis
375
1800 1700
Trial 1 Trial 2
350
1500
Time (s)
Time (s)
1600
1400
325 300
1300 275
1200 1100 Trial 1
Fig. 1 Spaghetti plot of individual 5 km running performance times (empty circles) and mean 5 km running performance times (solid circles) for trial 1 and trial 2.
worthwhile change (0.3 × within subject SD) was also calculated to determine the minimum difference required to represent a real world change [18].
Results
▼
250
Trial 2
All data and residuals were normally distributed (p > 0.05). The test-retest descriptive and reliability statistics of all variables measured as a global mean over each 5 km run are presented in ● ▶ Table 1, 2. There was no significant difference between trials for any of these variables (p > 0.05). The variables of 5 km run time, mean power, heart rate and stride rate had the lowest CVs ( 0.05).
Discussion
▼
The novel finding of the present study was that a 5 km NMT running time trial is a highly reliable test of endurance performance in trained, male runners. The CV and ICC reliability statistics (1.2 %, 0.99) suggest that this test protocol is appropriate for use in intervention studies, with a smallest worthwhile change in performance of 4 s. The demonstrated variability is slightly lower than repeat 5 km running time trials on a motorized treadmill (1.7 %, 0.95) [15] and superior to most ‘pre-load’ running time trials on motorized Stevens CJ et al. The Reliability of Running … Int J Sports Med 2015; 36: 705–709
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SWC = smallest worthwhile change, TS = thermal sensation, TSI = tissue saturation index, VE = expired air volume, VO2 = oxygen uptake, [BLa− ] = blood lactate concentration
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Table 3 Reliability statistics of variables calculated from each 1-km interval of 2 repeat 5 km running time trials on a non-motorized treadmill. 0–1 km 1 km run time (s) mean power (W) mean heart rate (b · min − 1) mean VO2 (mL · kg − 1 · min − 1) mean VE (L) [BLa− ] (mmol · L − 1) Sum-iEMG (V · s − 1) mean TSI (%) RPE (AU) TS (AU) mean stride rate (steps · min − 1)
1–2 km
CV %
ICC
CV %
2.6 2.3 2.1 3.5 5.1 17.6 15.7 3.3 15.6 5.2 1.3
0.93 0.94 0.95 0.87 0.82 0.76 0.71 0.94 0.78 0.84 0.97
2.0 2.0 1.6 2.7 4.1 – 11.5 3.3 9.1 9.6 1.1
2–3 km ICC 0.99 0.97 0.96 0.92 0.91 – 0.84 0.94 0.79 0.53 0.98
3–4 km
4–5 km
CV %
ICC
CV %
ICC
CV %
ICC
2.4 2.4 1.3 4.2 3.1 17.5 10.9 3.2 7.1 8.8 1.0
0.99 0.97 0.97 0.88 0.95 0.80 0.86 0.94 0.83 0.58 0.98
2.3 2.2 1.1 4.3 3.1 – 11.7 3.3 7.6 7.1 0.8
0.97 0.97 0.98 0.90 0.95 – 0.88 0.93 0.76 0.77 0.99
2.4 2.1 1.2 4.3 3.6 14.1 10.2 3.8 5.7 8.4 1.1
0.97 0.97 0.97 0.92 0.95 0.82 0.92 0.92 0.88 0.75 0.98
AU = arbitrary units, bpm = beats per minute, CV = coefficient of variation, ICC = intraclass correlation coefficient, RPE = rating of perceived exertion, Sum-iEMG = summated inte-
treadmills (CV: 1–5 %), where a submaximal exercise bout precedes the performance test [9, 17, 23]. However, variation was higher than repeat competitive 5 km over-ground running time trials (1 %, 0.98) [13]. Lower variability is to be expected in an over-ground protocol that replicates an athlete’s usual running environment and incorporates competition that may increase motivation [8]. As a result, the NMT provides a reliable alternative to both over-ground and motorized treadmill running for the assessment of running performance in the laboratory. The reliability statistics of commonly measured physiological responses to endurance running were also assessed in the present study. Variation of mean heart rate (CV: 1.2 %, ICC: 0.97) was similar to those calculated from repeat endurance cycling time trials previously (CV: 1–3 %, ICC: 0.96) [22, 26]. The CV for mean expired air volume was almost half that reported previously (CV: 2.7 vs. 4.6 %), despite a higher variation in mean VO2 (CV: 3.3 vs. 2.9 %) between the studies [20]. However, the variability of mean VO2 in the present study was lower than that reported for absolute oxygen uptake (CV: 5 %) during time trial cycling [26], which may result from recording measurements continuously, rather than for short intervals. Overall, the variations between these cardiorespiratory variables assessed during repeat 5 km runs on the NMT are acceptable. The variability for mean NIRS-derived TSI of the gastrocnemius lateralis (CV = 3 %, ICC: 0.94) was lower than that previously reported for steady-state running on a motorized treadmill at lactate threshold (ICC: 0.87) and during a maximal effort (ICC: 0.88) [3]. Variability of TSI was also much lower than that previously reported for NIRS-derived muscle oxygen uptake during rhythmic handgrip exercise (CV: 16–25 %) [24] and re-uptake following over-ground running (CV: 6–37 %) [7]. Lower variability in the present study may be a result of the freedom to work at a self-selected, steady state intensity, most likely below the lactate threshold. Hence, oxygen utilization may have been more consistent across the exercise test. The present study is the first to quantify reliability statistics for the sum-iEMG method, which has been used previously [4]. The CV for mean sum-iEMG was 8.4 %, which was lower than when muscles were analyzed individually (CV: 10–27 %). Similar individual muscle iEMG reliability data during running (vastus lateralis: 19.7 %, rectus femoris: 29.3 %) has been reported previously [21]. Hence, it appears as though the summated method may be more reliable and useful in situations when the general behavior of muscle electrical activity is of interest.
Stevens CJ et al. The Reliability of Running … Int J Sports Med 2015; 36: 705–709
The present study also identified the reliability of 1-km intervals within the 5 km running time trial for all variables measured. The CVs for each 1-km interval for run time varied between 2–3 %, which was slightly higher than the reliability of overall 5 km run time. The majority of other responses also demonstrated greater variability across each 1-km interval when compared to the 5 km mean. This higher variability is likely due to slight alterations in the pacing strategy used between trials. Interestingly, there was a tendency for participants to begin the time trial at a slightly slower pace and finish faster in the second ▶ Fig. trial compared to the first, without affecting overall time ( ● 2). With reliability established for the physiological responses for both 1-km intervals and the 5 km time trial as a whole, changes in these measures in future research can be better identified as a result of an intervention or normal variation. The current research highlights that a 5 km running time trial on a non-motorized treadmill is a highly reliable test protocol for the assessment of endurance performance in trained runners. Therefore, this protocol is appropriate for the assessment of sports conditioning and as a laboratory endurance performance test for intervention-based research. Since reliability of the NMT was superior to previous reports of motorized treadmill running, it is the recommended ergometer, especially in situations when subconscious or immediate changes in running speed are of interest. The physiological and perceptual responses measured during the self-paced 5 km run also demonstrated good reliability, but these responses had greater variation when analyzed as 1-km intervals. Collectively, the current data supports the use of endurance running time trials on the NMT.
Acknowledgements
▼
The authors would like to thank the participants for their involvement in the study.
Conflict of interest: The authors have no conflict of interest to declare. Affiliations 1 ASSET Laboratory Exercise and Sport Sciences, University of Newcastle, Ourimbah, Australia 2 School of Biomedical Sciences and Pharmacy, University of Newcastle, Ourimbah, Australia
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grated electromyography, TS = thermal sensation, TSI = tissue saturation index, VE = expired air volume, VO2 = oxygen uptake, [BLa− ] = blood lactate concentration
3
Sport Science and Physical Activity, University of Bedfordshire, Bedford, United Kingdom 4 School of Biomedical Sciences and Pharmacy, University of Newcastle, Callaghan, Australia
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Training & Testing
705
Authors
C. J. Stevens1, J. Hacene1, D. V. Sculley2, L. Taylor3, R. Callister4, B. Dascombe1
Affiliations
Affiliation addresses are listed at the end of the article
Key words ▶ reproducibility of results ● ▶ physical endurance ● ▶ sports performance ● ▶ pacing strategy ● ▶ electromyography ● ▶ near-infrared spectroscopy ●
Abstract
▼
The purpose of the study was to establish the reliability of performance and physiological responses during a self-paced 5 km running time trial on a non-motorized treadmill. 17 male runners (age: 32 ± 13 years, height: 177 ± 7 cm, body mass: 71 ± 9 kg, sum of 7 skinfolds: 55 ± 21 mm) performed familiarization then 2 separate maximal 5 km running time trials on a non-motorized treadmill. Physiological responses measured included heart rate, oxygen uptake, expired air volume, blood lactate concentration, tissue saturation index and integrated electromyography.
Introduction
▼ accepted after revision January 12, 2015 Bibliography DOI http://dx.doi.org/ 10.1055/s-0034-1398680 Published online: March 19, 2015 Int J Sports Med 2015; 36: 705–709 © Georg Thieme Verlag KG Stuttgart · New York ISSN 0172-4622 Correspondence Christopher John Stevens, B. Exercise and Sport Science (Hons) Exercise and Sport Sciences University of Newcastle Brush Rd Ourimbah 2258 Australia Tel.: + 61/411/797 245 Fax: + 61/243/484 145 christopher.j.stevens@uon. edu.au
Laboratory simulated exercise time trials are commonly used to assess endurance exercise performance in intervention studies [14]. Time trials require a set amount of work or time period of exercise to be completed with the highest average speed. To measure performance, time trials appear more favorable than time to exhaustion protocols, which require exercise to be performed until exhaustion at a fixed workload. Time trials simulate endurance competition, are self-paced and appear highly reliable [14, 15, 17], whereas time to exhaustion protocols have been criticized for lacking specificity to endurance competition and poor reliability [14, 15]. Reliability refers to the consistency of a variable measured during repeated tests under the same conditions. Scientific tests must be reliable to ensure changes are the result of an intervention, are not measurement error or inter-individual differences [2] and to detect the smallest worthwhile change [18]. The main measure of reliability used to compare between different protocols is the typical error of measurement expressed as a coefficient of variation (CV); the lower the CV the greater the reliability [12]. Low CVs of 1 %
Running time (1 522 ± 163 s vs. 1 519 ± 162 s for trials 1 and 2, respectively) demonstrated a low CV of 1.2 % and high ICC of 0.99. All physiological variables had CVs of less than 4 % and ICCs of > 0.92, with the exception of blood lactate concentration (7.0 ± 2 mmol · L − 1 vs. 6.5 ± 1.5 mmol · L − 1 for trials 1 and 2, respectively; CV: 12 %, ICC: 0.83) and the electromyography measures (CV: 8–27 %, ICC: 0.71–0.91). The data demonstrate that performance time in a 5 km running time trial on a non-motorized treadmill is a highly reliable test. Most physiological responses measured across the 5 km run also demonstrated good reliability.
[13] and 1.7 % [15] have been reported for 5 km running time trials performed over-ground and on a motorized treadmill, respectively. However, the reliability of endurance running on a nonmotorized treadmill (NMT) has not been established. The NMT requires the runner to manually produce the force to rotate the running belt with each step, rather than a motor dictating a constant belt speed. Such treadmills work either by the act of pushing backwards on an inclined treadmill belt (Curve NMT, Woodway, Waukesha, Wisconsin, USA) or by pushing backwards on a flat treadmill belt with the aid of a cable attached to the runner (Force NMT, Woodway, Waukesha, Wisconsin, USA). The NMT was originally created to offer a cheaper alternative to more expensive motorized treadmills, but these have since been used to simulate the demands of team sports, where sudden changes in running speed are required [1, 19]. Recently, the Curve 3TM NMT has been used as a laboratory measure of endurance running performance following a cognitive task [16]. However, no reliability data was presented and as such it is unclear if the measured change was greater than natural variation. If the Curve 3TM displays high reliability, it may be more
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The Reliability of Running Performance in a 5 km Time Trial on a Non-motorized Treadmill
favorable than a motorized treadmill, as the runner can change speed freely, without the need to actively adjust the speed on a computer. Therefore, changes in speed and pacing strategy are more likely to be instantaneous and better reflect subconscious fatigue. Despite the established reliability of self-paced time trial performance in both cycling [20, 22, 26] and motorized treadmill running [15, 17, 23], few investigations have reported on the reliability of physiological and perceptual responses within such protocols and no reliability data currently exists for tissue saturation index or integrated electromyography during self-paced exercise. Therefore, the aim of the present study was to determine the reliability of performance, as well as the physiological and perceptual responses between repeated self-paced 5 km running time trials on a NMT.
Materials and Methods
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17 moderately trained male runners (age: 32 ± 13 years, height: 177 ± 7 cm, body mass: 71 ± 9 kg, sum of 7 skinfolds: 55 ± 21 mm) volunteered to participate. Inclusion criteria stipulated participants have a current 5 km over-ground personal best of 17–23 min in the past 6 months. The present study doubled the sample size of the previous studies to assess the reliability of running performance in the laboratory more accurately [15, 17, 23]. The Human Ethics Research Committee at the University of Newcastle granted approval for the project (UoN H-2012-0311) and the investigators followed the ethical guidelines of the journal [10]. All running was performed on a NMT (Curve 3TM, Woodway, Waukesha, USA) and a pre-exercise screening determined all participants had not previously completed any exercise on such a treadmill. An anthropometric profile was performed on all subjects including height, body mass and sum of 7 skinfolds. The participants performed 2 separate familiarization sessions. The first was a 2 km run on the treadmill at a self-selected intensity and the second was a 5 km maximal running time trial. Since the effect of familiarization has already been well established and is common practice in exercise performance research [2, 23], only the data from the test-retest trials were reported. For 24 h prior to the first experimental trial, caffeine, alcohol and high intensity exercise were not permitted. The participants performed a self-selected 15-min warm-up for which intensity was recorded for repetition prior to the second trial. During the time trials, the participants were blinded to all measures except for elapsed distance. A 50 cm fan was placed 1 m in front of the NMT and provided a wind speed of 4 m · s − 1 to simulate the convective cooling of outdoor wind resistance. No music, fluids or food were permitted and footwear, clothing, instruction and time of day were standardized between trials. All trials were separated by 5–10 days. Power output was continuously measured by the treadmill and recorded by Pacer Performance software at 200 Hz (Innervations Software, Joondalup, Australia). Heart rate was continuously measured at 1 Hz by a Garmin 910XT monitor (Garmin Ltd., Schaffhausen, Switzerland). Measurements of relative VO2 and expired air volume were performed on a breath-by-breath basis using a portable gas analyzer (Cosmed K4 b2, Rome, Italy). Capillary blood samples were collected at 1, 3 and 5 km intervals from a hyperaemic fingertip for blood lactate analysis using a Lactate Scout (EKF-Diagnostic, Berlin, Germany). Stevens CJ et al. The Reliability of Running … Int J Sports Med 2015; 36: 705–709
Near infrared spectroscopy (NIRS) derived measurements of oxygenation in the calf were taken using a portable NIRS device (Portamon, Artinis Medical Systems, Zetten, the Netherlands). The system is a 2-wavelength continuous wave system that simultaneously uses the modified Beer-Lambert law and spatially resolved spectroscopy methods. This non-invasive technique measures the changes in muscle oxygenation by determining the reflection of light at near infrared wavelengths of 750 and 860 nm. Tissue saturation index (TSI) was measured as the difference between tissue oxyhaemoglobin and deoxyhaemoglobin, representing the mean saturation of the underlying muscle tissue. An arbitrary value of 3.83 was used for the differential path length factor [6]. The NIRS device was positioned on the left gastrocnemius lateralis as per previous research [3]. The probe and skin were covered with strapping tape and a dark bandage to prevent penetration of ambient light. Skinfold thickness at the measurement site was taken to ensure that fat tissue was not sufficient to interfere with light penetration. The mean skinfold was 7.4 ± 3.3 mm, which was less than half the distance between source and detector and therefore fat tissue was considered inconsequential. The NIRS device was connected to a personal computer via bluetooth, with data acquired continuously at a sampling rate of 10 Hz. The electromyography (EMG) signal of 4 muscles (gastrocnemius medianus, tibialis anterior, vastus lateralis and rectus femoris) were recorded from the right limb via TringoTM wireless surface electrodes (Delsys Inc., Boston, USA). Electrode placement and skin preparation was as per international standards [11]. The surface electrodes had a single differential configuration, interelectrode distance of 10 mm, 4-bar formation, bandwidth of 20–450 Hz and 99.9 % silver contact material. 12 s of raw data was collected midway through each kilometer. The EMG signal was sampled at 3 kHz and the raw data was multiplied by 1 000 to match those gain settings used previously [4]. A 4th order Butterworth filter of 12–500 Hz was applied to the data before the root mean square and integral were calculated with a 0.050 ms window length and 0.025 ms overlap. The muscles were analyzed separately but also added together to form the parameter of summated integrated-EMG (sum-iEMG; V · s − 1), which has been used previously to represent the general behavior of muscle electrical activity of the lower limb [4]. Rating of perceived exertion was measured using a Borg Scale of 0.5–10 where 10 = very, very heavy, for the heaviest running intensity perceived and 0.5 = very, very weak, equal to the weakest running intensity perceived [5]. Thermal sensation was measured using Young’s Thermal Sensation Scale [25]. Perceptual measurements were obtained in every kilometer. Stride rate was measured continuously using a foot pod taped to the participant’s right shoelaces, an accessory of the 910XT (Garmin Ltd., Schaffhausen, Switzerland). The mean ± SD was calculated for all data, with normality assessed using a Kolmogorov-Smirnov test. Differences in data between trials were examined with a paired samples t-test for global means and repeated measures ANOVA for 1-km intervals within SPSS software V22.0 (IBM Corporation, Somers, USA). Alpha (p) was set at 0.05. The p value remained unadjusted to conservatively identify differences between trials. Measures of reliability, including typical error as a CV ( %) and intraclass correlation coefficient (ICC) were calculated within a custom made spreadsheet [Hopkins, W.G. Precision of measurement (2011) in internet: newstats.org/precision.html; (22/06/12)]. The smallest
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Table 1 Descriptive and reliability statistics of variables calculated from 2 repeat 5 km running time trials on a non-motorized treadmill. Trial 1 Mean ± SD
Trial 2 Mean ± SD
1 522 ± 163 117.9 ± 12.1 177 ± 11 51.2 ± 5.7 119.9 ± 13.7 7.0 ± 2 52.77 ± 6.13 6.5 ± 1 5.4 ± 0.6 86.6 ± 4.8
1 519 ± 162 118.1 ± 11.8 176 ± 12 51.5 ± 5.1 118.5 ± 13.0 6.5 ± 1.5 53.40 ± 6.31 6.4 ± 0.8 5.4 ± 0.7 86.1 ± 5.3
5 km run time (s) mean power (W) mean heart rate (b · min − 1) mean VO2 (mL · kg − 1 · min − 1) mean VE (L) mean [BLa− ] (mmol · L − 1) mean TSI ( %) mean RPE (AU) mean TS (AU) mean stride rate (steps · min − 1)
CV ( %) (95 % CI) 1.2 (0.9–1.8) 1.2 (0.9–1.8) 1.2 (0.9–1.9) 3.3 (2.4–5.3) 2.7 (2–4.3) 12 (8.6–20.1) 3 (2.1–5.1) 5.0 (3.7–7.6) 5.7 (4.2–8.8) 0.7 (0.5–1.3)
ICC (95 % CI) 0.99 (0.97–1) 0.99 (0.97–1) 0.97 (0.92–0.97) 0.92 (0.77–0.97) 0.96 (0.88–0.98) 0.83 (0.54–0.94) 0.94 (0.82–0.98) 0.9 (0.75–0.96) 0.81 (0.55–0.93) 0.99 (0.96–1)
SWC 4 0.3 1 0.4 0.7 0.2 0.39 0.1 0.1 0.2
AU = arbitrary units, b · min − 1 = beats per minute, CI = confidence interval, CV = coefficient of variation, ICC = intraclass correlation coefficient, RPE = rating of perceived exertion,
Trial 1 Mean ± SD mean GM iEMG (V · s − 1) mean TA iEMG (V · s − 1) mean RF iEMG (V · s − 1) mean VL iEMG (V · s − 1) mean sum-iEMG (V · s − 1)
1.53 ± 0.52 1.36 ± 0.61 0.52 ± 0.21 0.92 ± 0.26 4.33 ± 1.17
Trial 2 Mean ± SD
CV ( %) (95 % CI)
ICC (95 % CI)
12.5 (8.8–21.5) 13.7 (9.6–23.6) 26.2 (18.2–46.8) 10.9 (7.7–18.6) 8.4 (6–14.3)
0.9 (0.70–0.97) 0.93 (0.80–0.98) 0.71 (0.29–0.90) 0.89 (0.67–0.96) 0.91 (0.73–0.97)
1.54 ± 0.54 1.20 ± 0.53 0.49 ± 0.20 0.85 ± 0.31 4.08 ± 1.33
Table 2 Descriptive and reliability statistics of electromyography variables calculated from 2 repeat 5 km running time trials on a nonmotorized treadmill.
CI = confidence interval, CV = coefficient of variation, GM = gastrocnemius medianus, ICC = intraclass correlation coefficient, RF = rectus femoris, Sum-iEMG = summated integrated electromyography, TA = tibiarlis anterior, VL = vastus lateralis
375
1800 1700
Trial 1 Trial 2
350
1500
Time (s)
Time (s)
1600
1400
325 300
1300 275
1200 1100 Trial 1
Fig. 1 Spaghetti plot of individual 5 km running performance times (empty circles) and mean 5 km running performance times (solid circles) for trial 1 and trial 2.
worthwhile change (0.3 × within subject SD) was also calculated to determine the minimum difference required to represent a real world change [18].
Results
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250
Trial 2
All data and residuals were normally distributed (p > 0.05). The test-retest descriptive and reliability statistics of all variables measured as a global mean over each 5 km run are presented in ● ▶ Table 1, 2. There was no significant difference between trials for any of these variables (p > 0.05). The variables of 5 km run time, mean power, heart rate and stride rate had the lowest CVs ( 0.05).
Discussion
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The novel finding of the present study was that a 5 km NMT running time trial is a highly reliable test of endurance performance in trained, male runners. The CV and ICC reliability statistics (1.2 %, 0.99) suggest that this test protocol is appropriate for use in intervention studies, with a smallest worthwhile change in performance of 4 s. The demonstrated variability is slightly lower than repeat 5 km running time trials on a motorized treadmill (1.7 %, 0.95) [15] and superior to most ‘pre-load’ running time trials on motorized Stevens CJ et al. The Reliability of Running … Int J Sports Med 2015; 36: 705–709
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SWC = smallest worthwhile change, TS = thermal sensation, TSI = tissue saturation index, VE = expired air volume, VO2 = oxygen uptake, [BLa− ] = blood lactate concentration
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Table 3 Reliability statistics of variables calculated from each 1-km interval of 2 repeat 5 km running time trials on a non-motorized treadmill. 0–1 km 1 km run time (s) mean power (W) mean heart rate (b · min − 1) mean VO2 (mL · kg − 1 · min − 1) mean VE (L) [BLa− ] (mmol · L − 1) Sum-iEMG (V · s − 1) mean TSI (%) RPE (AU) TS (AU) mean stride rate (steps · min − 1)
1–2 km
CV %
ICC
CV %
2.6 2.3 2.1 3.5 5.1 17.6 15.7 3.3 15.6 5.2 1.3
0.93 0.94 0.95 0.87 0.82 0.76 0.71 0.94 0.78 0.84 0.97
2.0 2.0 1.6 2.7 4.1 – 11.5 3.3 9.1 9.6 1.1
2–3 km ICC 0.99 0.97 0.96 0.92 0.91 – 0.84 0.94 0.79 0.53 0.98
3–4 km
4–5 km
CV %
ICC
CV %
ICC
CV %
ICC
2.4 2.4 1.3 4.2 3.1 17.5 10.9 3.2 7.1 8.8 1.0
0.99 0.97 0.97 0.88 0.95 0.80 0.86 0.94 0.83 0.58 0.98
2.3 2.2 1.1 4.3 3.1 – 11.7 3.3 7.6 7.1 0.8
0.97 0.97 0.98 0.90 0.95 – 0.88 0.93 0.76 0.77 0.99
2.4 2.1 1.2 4.3 3.6 14.1 10.2 3.8 5.7 8.4 1.1
0.97 0.97 0.97 0.92 0.95 0.82 0.92 0.92 0.88 0.75 0.98
AU = arbitrary units, bpm = beats per minute, CV = coefficient of variation, ICC = intraclass correlation coefficient, RPE = rating of perceived exertion, Sum-iEMG = summated inte-
treadmills (CV: 1–5 %), where a submaximal exercise bout precedes the performance test [9, 17, 23]. However, variation was higher than repeat competitive 5 km over-ground running time trials (1 %, 0.98) [13]. Lower variability is to be expected in an over-ground protocol that replicates an athlete’s usual running environment and incorporates competition that may increase motivation [8]. As a result, the NMT provides a reliable alternative to both over-ground and motorized treadmill running for the assessment of running performance in the laboratory. The reliability statistics of commonly measured physiological responses to endurance running were also assessed in the present study. Variation of mean heart rate (CV: 1.2 %, ICC: 0.97) was similar to those calculated from repeat endurance cycling time trials previously (CV: 1–3 %, ICC: 0.96) [22, 26]. The CV for mean expired air volume was almost half that reported previously (CV: 2.7 vs. 4.6 %), despite a higher variation in mean VO2 (CV: 3.3 vs. 2.9 %) between the studies [20]. However, the variability of mean VO2 in the present study was lower than that reported for absolute oxygen uptake (CV: 5 %) during time trial cycling [26], which may result from recording measurements continuously, rather than for short intervals. Overall, the variations between these cardiorespiratory variables assessed during repeat 5 km runs on the NMT are acceptable. The variability for mean NIRS-derived TSI of the gastrocnemius lateralis (CV = 3 %, ICC: 0.94) was lower than that previously reported for steady-state running on a motorized treadmill at lactate threshold (ICC: 0.87) and during a maximal effort (ICC: 0.88) [3]. Variability of TSI was also much lower than that previously reported for NIRS-derived muscle oxygen uptake during rhythmic handgrip exercise (CV: 16–25 %) [24] and re-uptake following over-ground running (CV: 6–37 %) [7]. Lower variability in the present study may be a result of the freedom to work at a self-selected, steady state intensity, most likely below the lactate threshold. Hence, oxygen utilization may have been more consistent across the exercise test. The present study is the first to quantify reliability statistics for the sum-iEMG method, which has been used previously [4]. The CV for mean sum-iEMG was 8.4 %, which was lower than when muscles were analyzed individually (CV: 10–27 %). Similar individual muscle iEMG reliability data during running (vastus lateralis: 19.7 %, rectus femoris: 29.3 %) has been reported previously [21]. Hence, it appears as though the summated method may be more reliable and useful in situations when the general behavior of muscle electrical activity is of interest.
Stevens CJ et al. The Reliability of Running … Int J Sports Med 2015; 36: 705–709
The present study also identified the reliability of 1-km intervals within the 5 km running time trial for all variables measured. The CVs for each 1-km interval for run time varied between 2–3 %, which was slightly higher than the reliability of overall 5 km run time. The majority of other responses also demonstrated greater variability across each 1-km interval when compared to the 5 km mean. This higher variability is likely due to slight alterations in the pacing strategy used between trials. Interestingly, there was a tendency for participants to begin the time trial at a slightly slower pace and finish faster in the second ▶ Fig. trial compared to the first, without affecting overall time ( ● 2). With reliability established for the physiological responses for both 1-km intervals and the 5 km time trial as a whole, changes in these measures in future research can be better identified as a result of an intervention or normal variation. The current research highlights that a 5 km running time trial on a non-motorized treadmill is a highly reliable test protocol for the assessment of endurance performance in trained runners. Therefore, this protocol is appropriate for the assessment of sports conditioning and as a laboratory endurance performance test for intervention-based research. Since reliability of the NMT was superior to previous reports of motorized treadmill running, it is the recommended ergometer, especially in situations when subconscious or immediate changes in running speed are of interest. The physiological and perceptual responses measured during the self-paced 5 km run also demonstrated good reliability, but these responses had greater variation when analyzed as 1-km intervals. Collectively, the current data supports the use of endurance running time trials on the NMT.
Acknowledgements
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The authors would like to thank the participants for their involvement in the study.
Conflict of interest: The authors have no conflict of interest to declare. Affiliations 1 ASSET Laboratory Exercise and Sport Sciences, University of Newcastle, Ourimbah, Australia 2 School of Biomedical Sciences and Pharmacy, University of Newcastle, Ourimbah, Australia
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grated electromyography, TS = thermal sensation, TSI = tissue saturation index, VE = expired air volume, VO2 = oxygen uptake, [BLa− ] = blood lactate concentration
3
Sport Science and Physical Activity, University of Bedfordshire, Bedford, United Kingdom 4 School of Biomedical Sciences and Pharmacy, University of Newcastle, Callaghan, Australia
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