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The Effects of a Harness Safety System During Maximal Treadmill Run Testing in Collegiate Middle- and Long-Distance Runners

Mermier, Christine M.1; Zuhl, Micah N.2; Wilmerding, M. Virginia1; Beam, Jason R.1; White, Ailish C.1; Salgado, Roy M.1; Beverly, J. Marc1

Journal of Strength and Conditioning Research: November 2013 - Volume 27 - Issue 11 - p 2934–2938
doi: 10.1519/JSC.0b013e318289e463
Original Research

Mermier, CM, Zuhl, MN, Wilmerding, MV, Beam, JR, White, AC, Salgado, RM, and Beverly, JM. The effects of a harness safety system during maximal treadmill run testing in collegiate middle- and long-distance runners. J Strength Cond Res 27(11): 2934–2938, 2013—This study compared the results of graded maximal treadmill testing with and without a safety harness (SH) spotting system among collegiate middle- and long-distance runners. Thirteen (n = 8 men, n = 5 women) collegiate runners completed 2 randomly selected maximal treadmill tests. One trial used an SH, and one trial used no harness. All tests were separated by at least 48 hours. The subjects began the test at a velocity of 14.5 or 12 km·h−1 with 1% grade for men and women, respectively, and increased 0.80 kilometers/hr per stage. During each trial, metabolic data and running speed values were recorded along with the completion of a safety questionnaire. No significant difference was found for maximal oxygen consumption (60.84 ± 8.89 vs. 60.733 ± 9.38 ml·kg−1·min−1) and velocity at maximal oxygen consumption (5.33 ± 0.62 vs. 5.24 ± 0.57 m·s−1) between the no harness and harness trials, respectively. Test time was found to be significantly longer in the no harness trial (611.06 ± 119.34 vs. 537.38 ± 91.83 seconds, p < 0.05). The results of the safety questionnaire demonstrated that the runners felt significantly more comfortable during the SH trial (p < 0.05).

1Exercise Physiology Laboratory, Department of Health, Exercise, and Sport Science, University of New Mexico, Albuquerque, New Mexico; and

2Health Sciences, School of Health Professions, Central Michigan University, Mount Pleasant, Michigan

Address correspondence to Christine M. Mermier, cmermier@unm.edu.

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Introduction

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.

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Methods

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).

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Subjects

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.

Table 1

Table 1

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Experimental Protocol

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.

Figure 1

Figure 1

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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.

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Data Collection

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.

Table 2

Table 2

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Statistical Analyses

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.

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Results

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.

Table 3

Table 3

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Discussion

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.

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Practical Applications

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.

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Keywords:

V[Combining Dot Above]O2max; 2max">2max">vVO2max; trial time; spotting

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