A maximal exercise test on a treadmill is commonly used to assess maximal aerobic capacity (V[Combining Dot Above]O2max), peak treadmill velocity (PTV), and various thresholds (ventilatory, lactate, and anaerobic). By virtue of the term “maximal,” it is presumed that results of any given testing procedure would show the same results for any given participant and the end of the test would display a peak or plateau of aerobic capacity as measured by V[Combining Dot Above]O2 (7). As the speed and grade of the treadmill increase during the test, there is an increased risk of falling, which may lead to early termination of the test. Amateur runners can exceed speeds of 19 km·h−1 during maximal treadmill testing (23). Therefore, the termination of a maximal treadmill exercise test may be because of the subject’s concern for comfort and safety while running at high velocities. Consequently, the potential premature termination may result in an inaccurate assessment of maximal aerobic capacity. A proper support or spotting system may provide the subject with the confidence to give a maximal effort along with accurate data collection, leading to more specific training programs. To assure the subject’s comfort and safety, a harness may provide protection from injury.
Maximal exercise testing is clearly important for athletes because PTV and maximal oxygen consumption have been shown to predict performance (11,13,17). Accurate testing data among elite athletes is an important consideration, as measurements made during maximal testing are used to develop training programs. Research among elite runners has determined several key indicators of performance that include maximal oxygen consumption or V[Combining Dot Above]O2max, lactate and ventilatory threshold (VT), running economy, running velocity at V[Combining Dot Above]O2max, and maximal treadmill running speed (4,17,19,20). Noakes et al. (17) showed a strong correlation between maximal treadmill running speed and performance at distances from 10 to 90 km (r = −0.88 to −0.94). Additional performance prediction measurements made by Noakes et al. (17) were running economy at 16 km·h−1 (r = −0.76 to 0.90) and V[Combining Dot Above]O2max (r = 0.55 to −0.86). Other research has shown that treadmill velocity at V[Combining Dot Above]O2max, V[Combining Dot Above]O2max itself, and running economy may be the best indicators of performance among well-trained athletes (2,5,6,11,13,22,23). These studies show that PTV is an important indicator of performance and that elite runners can run for extended time at speeds of up to 26.91 km·h−1 or 16.72 mph.
At such speeds, it is reasonable to assume that an athlete’s results may be compromised by both fatigue and fear of falling off the treadmill. We were interested in whether a safety harness (SH) might improve the ability of a high level athlete to give a potentially greater maximal effort during the laboratory test and if performance indicators such as V[Combining Dot Above]O2max, maximal velocity, VT, and rating of perceived exertion (RPE) would be affected. The goal of this study was to determine if an SH system is effective in allowing athletes to reach V[Combining Dot Above]O2max by increasing their perception of comfort and safety.
Experimental Approach to the Problem
The purpose of the study was to compare the physiological results of maximal treadmill testing and perceived comfort and safety with and without an SH system in collegiate middle- and long-distance runners. The SH was used as a device to catch the athlete at the termination of the test to determine whether there is a difference in maximal effort between conditions (harness and no harness).
Subjects included 13 (8 men and 5 women) collegiate middle- and long-distance runners ranging between the ages of 18 and 31 years. All participants competed on a division I collegiate cross-country or track team. Each participant completed a health history questionnaire and signed an informed consent in accordance with the university’s Human Research Review Committee. Subject characteristics and physiological profiles are presented in Table 1.
Subjects reported to the exercise physiology laboratory on 2 occasions; visits were separated by at least 48 hours (Figure 1). Laboratory was on 2 separate occasions; visits were separated by at least 48 hours. Participants were required to arrive at least 3 hours after their last meal, and the time of day was consistent for both visits. In each session, a maximal treadmill running test until volitional fatigue was completed, with one test performed while the subject was equipped with a SH and the other performed without the harness (NSH). The order of the testing was randomized. A familiarization session was carried out before the harness test. This familiarization included a demonstration of the catch mechanism shown through video. Each trial required approximately 1.5 hours to complete.
Graded Exercise Testing
All maximal exercise tests were performed on a belt driven treadmill (model C966; Precor, Woodinville, WA, USA). Participants were allowed to warm-up to their comfort level. Male subjects began at a velocity of 14.5 km·h−1 (9.0 mph) and a grade of 1%. Speed increased 0.8 km·h−1 (0.5 mph) every minute until subjects reached volitional fatigue. Female subjects followed same protocol but started at a velocity of 12.0 km·h−1 (7.5 mph). The goal of the test was for subjects to reach maximal effort within 8–10 minutes as reported by Yoon et al. (24). Subjects were blinded to speed and grade during the test by placing a towel over the digital readings of the treadmill.
The SH test involved having the subject run while wearing a SH (model Pandion; Petzl, Crolles, France). A rope was connected to the posterior side of the harness with a knot and a belay device (model Grigri; Petzl) was connected to the floor. A technician held the line securely during the maximal test without unweighting the subject while running. Before the start of the test, subjects viewed a safety video of the harness system. Before any testing, all subjects practiced falling using the SH system. The subjects were instructed to run until they could not keep pace with the treadmill upon which they would fall, and the SH would catch them, preventing injury. The same protocol was followed during each SH trial. In the NSH treadmill test, the subjects ran until they could not keep pace with the treadmill at volitional fatigue. They either signaled their desire to stop the test by placing their hands on the handrails of the treadmill or straddled the treadmill at which time the test was ended.
Height and weight were measured before the first exercise test. Three-site skinfold measurements were taken for percent body fat calculations (Lange; Beta Technology Inc, Cambridge, MD, USA) using the appropriate Jackson equation for men and women (9,10). Each site was measured 3 times with the mean of the 2 closest values used. The same technician measured all subjects.
Oxygen consumption (V[Combining Dot Above]O2) and carbon dioxide production (V[Combining Dot Above]CO2) were recorded during each exercise test using a metabolic cart (True One; Parvomedics, Sandy, UT, USA). Calibration was performed before each test with gases of known concentration. Volume was calibrated using a 3-L syringe. The respiratory exchange ratio of carbon dioxide production to oxygen consumption (V[Combining Dot Above]CO2/V[Combining Dot Above]O2) was recorded during each trial. Heart rate was also recorded at rest and continuously during each trial (model Wearlink; Polar, Kempele, Finland).
Maximal oxygen consumption (V[Combining Dot Above]O2max) was defined as the highest value achieved using an 11 breath running average. Velocity at V[Combining Dot Above]O2max was defined as the maximal measured treadmill running speed (milliseconds per second) achieved. The 6–20 Borg’s RPE scale was measured at the end of each stage during the maximal tests (3). Ventilatory threshold was determined by graphing the ventilatory equivalents for oxygen (V[Combining Dot Above]E/V[Combining Dot Above]O2) and carbon dioxide (V[Combining Dot Above]E/V[Combining Dot Above]CO2) along the y-axis and V[Combining Dot Above]O2 along the x-axis. The VT was identified as the point where a nonlinear increase in V[Combining Dot Above]E/V[Combining Dot Above]CO2 occurred, while V[Combining Dot Above]E/V[Combining Dot Above]O2 continued to increase. Two technicians made the decisions on the points in the graph with a third observation if needed.
At the end of each exercise test, subjects answered a series of 7 questions (Table 3). This questionnaire asked subjects to rate their comfort and safety level during each trial and asked if they felt they were able to give a maximal effort.
Data were analyzed using a dependent t-test with trial type (SH or NSH) as the independent variable. Responses to the safety questionnaire were analyzed using nonparametric Wilcoxon Signed Ranks Test. Significant differences were determined at p ≤ 0.05. A statistical power of 0.80 was used to determine sample size of 13.
The results for V[Combining Dot Above]O2max, PTV, and trial time are shown in Table 2. The trial time for the NSH was significantly longer than the SH (611.06 vs. 537.38 seconds, respectively, p < 0.05). V[Combining Dot Above]O2max criteria were met during all trials with no differences between groups. The percent of V[Combining Dot Above]O2max at VT were not significantly different between trials. Questionnaire results revealed a significant difference between the 2 trials for perceived level of safety (question 6, Table 3) only.
The major finding of this study is that there was no difference between the harness trial (SH) and the no harness trial (NSH) with regard to maximal aerobic capacity and maximal running speed. This indicates that a safety system used during maximal run testing in collegiate middle- and long-distance runners will neither prevent nor assist the athletes in performing to exhaustion. Spotting during a bench press or squat 1-repetition maximum test is critical for the safety of the subject to prevent catastrophic injury. Many laboratories currently use a spotting system for treadmill testing.
Surprisingly, the SH test time was significantly shorter than the NSH test time, but both tests terminated within the same stage, and again, maximal running velocity and maximal oxygen consumption were not different between trials. One explanation may be that subjects exhibited a “survival instinct” during the NSH trial, which is similar to the central governor theory of exercise fatigue (16,18). Under this model, the central nervous system regulates muscle contraction to prevent injury to the muscle and cardiovascular system (8,15,16). Subjects were able to maintain a high level of muscle contraction beyond the point of maximal oxygen consumption to prevent falling and the possibility of injury. In the harness trials, once the maximal level of oxygen consumption was achieved, perhaps the brain regulated muscle contraction sooner to prevent damage, thus leading to earlier termination of the test. However, it should be noted that the protocol for this investigation involved 2-minute stages rather than shorter stages, and it was possible for a statistical difference to be uncovered for time without having an impact on maximal treadmill speed or V[Combining Dot Above]O2.
To date, there has been limited research conducted to explore the use of an SH system as a safeguard in the final moments of a maximal exercise test. In separate studies, McKay-Lyons et al. (12) and Millslagle et al. (14) used healthy subjects to perform maximal exercise tests on treadmills using a suspension harness system. The Lyons group had subjects run under 3 separate conditions: with no harness, in a harness with 0% body weight suspension, and in a harness with 15% body weight suspension. Results showed no significant difference in maximal oxygen consumption or maximum heart rate even though the length of maximal test was significantly longer for the 15% suspension trial. Furthermore, 6 of the 15 subjects reported feeling safer while wearing the supportive harness. The study of Millslagle et al. (14) tested healthy men under conditions of 0, 20, and 40% body weight suspension while recording gait characteristics. The authors identified that increasing body weight suspension resulted in longer steps with the foot in less contact with the treadmill belt, but V[Combining Dot Above]O2max was not measured. Suspension harness systems have been used to safely measure gait analysis and walking speed among clinical populations (1,21).
Maximal oxygen consumption results were similar to those reported in previous research, where no difference was demonstrated between suspension and no suspension groups (12). Our data show that the harness system does not affect V[Combining Dot Above]O2max in a population of collegiate middle- and long-distance runners, who are familiar with the physical stress of maximal exercise.
This is the first study to demonstrate the effect of using an SH system during maximal treadmill testing. Previous studies have measured maximal oxygen consumption and gait analysis using body weight suspension systems. In our system, body weight was not altered and thus gait did not change. Full body weight bearing testing is more accurate and useful in athletic populations. Although this study was initiated under the hypothesis that a harness system would allow the runner to feel greater comfort and safety, which would manifest in increased measures of aerobic capacity, PTV, and various thresholds, results did not support the hypothesis. An SH can provide comfort for runners using high-speed protocols while not impacting metabolic measurements.
It is recommended that testing for maximal aerobic capacity of athletes occur with the use of an SH if possible. We found no difference in the measured aerobic capacity between the trials, but the athletes did indicate a greater feeling of comfort and safety when using the SH. Therefore, this recommendation is not for the purpose of an increased V[Combining Dot Above]O2 but for the perceived comfort and safety of the athlete. It should also be noted that the harness system did not negatively affect V[Combining Dot Above]O2max results.
1. Barbeau H, Visintin M. Optimal outcomes obtained with body-weight support combined with treadmill training in stroke subjects. Arch Phys Med Rehabil 84: 1458–1465, 2003.
2. Bassett DR Jr, Howley ET. Limiting factors for maximum oxygen uptake and determinants of endurance performance. Med Sci Sports Exerc 32: 70–84, 2000.
3. Borg GA. Psychophysical bases of perceived exertion. Med Sci Sports Exerc 14: 377–381, 1982.
4. Costill DL, Sparks KE. Rapid fluid replacement following thermal dehydration. J Appl Physiol 34: 299–303, 1973.
5. Coyle EF. Integration of the physiological factors determining endurance performance ability. Exerc Sport Sci Rev 23: 25–63, 1995.
6. Coyle EF. Physiological regulation of marathon performance. Sports Med 37: 306–311, 2007.
7. Day JR, Rossiter HB, Coats EM, Skasick A, Whipp BJ. The maximally attainable VO2 during exercise in humans: The peak vs. maximum issue. J Appl Physiol 95: 1901–1907, 2003.
8. Gandevia SC. Spinal and supraspinal factors in human muscle fatigue. Physiol Rev 81: 1725–1789, 2001.
9. Jackson AS, Pollock ML. Generalized equations for predicting body density of men. Br J Nutr 40: 497–504, 1978.
10. Jackson AS, Pollock ML, Ward A. Generalized equations for predicting body density of women. Med Sci Sports Exerc 12: 175–181, 1980.
11. Joyner MJ. Modeling: Optimal marathon performance on the basis of physiological factors. J Appl Physiol 70: 683–687, 1991.
12. MacKay-Lyons M, Makrides L, Speth S. Effect of 15% body weight support on exercise capacity of adults without impairments. Phys Ther 81: 1790–1800, 2001.
13. McLaughlin JE, Howley ET, Bassett DR Jr, Thompson DL, Fitzhugh EC. Test of the classic model for predicting endurance running performance. Med Sci Sports Exerc 42: 991–997, 2010.
14. Millslagle D, Levy M, Matack N. Kinematic assessment of treadmill running using different body-weight support harnesses. Percept Mot Skills 103: 607–618, 2006.
15. Noakes TD. From catastrophe to complexity: A novel model of integrative central neural regulation of effort and fatigue during exercise in humans: Summary and conclusions. Br J Sports Med 39: 120–124, 2005.
16. Noakes TD. The central governor model of exercise regulation applied to the marathon. Sports Med 37: 374–377, 2007.
17. Noakes TD, Myburgh KH, Schall R. Peak treadmill running velocity during the VO2 max test predicts running performance. J Sports Sci 8: 35–45, 1990.
18. Noakes TD, Peltonen JE, Rusko HK. Evidence that a central governor regulates exercise performance during acute hypoxia and hyperoxia. J Exp Biol 204: 3225–3234, 2001.
19. Pate RR, Sparling PB, Wilson GE, Cureton KJ, Miller BJ. Cardiorespiratory and metabolic responses to submaximal and maximal exercise in elite women distance runners. Int J Sports Med 8(Suppl. 2): 91–95, 1987.
20. Pollock M. Characteristics of elite runners. Ann N Y Acad Sci 301: 278–282, 1975.
21. Protas EJ, Holmes SA, Qureshy H, Johnson A, Lee D, Sherwood AM. Supported treadmill ambulation training after spinal cord injury: A pilot study. Arch Phys Med Rehabil 82: 825–831, 2001.
22. Støa EM, Støren Ø, Enoksen E, Ingjer F. Percent utilization of VO2 max at 5-km competition velocity does not determine time performance at 5 km among elite distance runners. J Strength Cond Res 24: 1340–1345, 2010.
23. Stratton E, O'Brien B, Harvey J, Blitvich J, McNicol A, Janissen D, Paton C, Knez W. Treadmill velocity best predicts 5000-m run performance. Int J Sports Med 30: 40–45, 2008.
24. Yoon BK, Kravitz L, Robergs R. VO2max, protocol duration, and the VO2 plateau. Med Sci Sports Exerc 39: 1186–1192, 2007.