John K. DeWitt

Exercise Countermeasures and a New Ground-Based Partial-g Analog for Exploration

The enhanced Zero-gravity Locomotion Simulator (eZLS) at NASA Glenn Research Center is described and summary data from a pilot research study comparing comfort and pressure data from two different International Space Station crew exercise harness designs are presented. This new ground-based simulation capability was developed to help address the detrimental physiological effects of spaceflight on the musculoskeletal system through improved exercise countermeasures systems, and to evaluate exercise countermeasures devices and prescriptions for space exploration. Aside from space applications, experiments conducted using the eZLS may help medical researchers develop insights into the role of exercise in the prevention of osteoporosis in the terrestrial population since the mechanism of bone and muscle loss is very similar, though greatly accelerated during space travel. The eZLS will be used as a ground-based testbed to support future missions for Space Exploration, and will eventually be used to simulate planetary locomotion in partial gravity environments including the Moon and Mars.

Lower limb position during treadmill jogging and fast running in microgravity.

INTRODUCTION The second-generation ISS treadmill has a faster maximum operating speed than the current ISS treadmill. In normal gravity (1 G), bone loading benefits and cardiorespiratory stress are directly related to locomotion speed. A kinematic comparison of locomotion between 1 G and microgravity will provide information to evaluate the potential efficacy of fast running as an in-flight exercise countermeasure. METHODS Subjects exercised on a treadmill at 3.13 m x s(-1) (8.5 min x mi(-1)) (JOG; N = 6) and 5.36 m x s(-1) (5 min x mi(-1)) (RUN; N = 5) in microgravity during parabolic flight and in 1 G. During microgravity trials, subjects performed locomotion using a subject loading system (in a configuration identical to ISS) with approximately 80% bodyweight loading. Kinematic analyses of joint position at heel strike were performed using video software. RESULTS During the JOG trials, differences were found in thigh angle (microgravity = 54.09 degrees +/- 4.87; 1 G = 64.04 degrees +/- 3.12, mean +/- SD) and knee angle (microgravity = 33.17 degrees +/- 8.68; 1 G = 21.28 degrees +/- 5.22), indicating a more squatted position at heel strike in microgravity. No kinematic differences were found during the RUN condition. DISCUSSION The subject loading system and decreased external load throughout the stride in microgravity may account for the observed kinematic differences during JOG. The kinematic compensations for microgravity during JOG may result in in-flight adaptations that are different from expected based on 1-G studies. However, similar kinematics between gravity conditions during RUN suggest in-flight training may provide benefits similar to 1 G.

Individual Variability in Aerobic Fitness Adaptations to 70 Days of Bed Rest and Exercise Training: 2448 June 3, 10

Change in maximal aerobic capacity (VO2pk) in response to exercise training and disuse is highly variable among individuals. Factors that could contribute to the observed variability (lean mass, daily activity, diet, sleep, stress) are not routinely controlled in studies. The NASA bed rest (BR) studies use a highly controlled hospital based model as an analog of spaceflight. In this study, diet, hydration, physical activity and light/dark cycles were precisely controlled and provided the opportunity to investigate individual variability. PURPOSE. Evaluate the contribution of exercise intensity and lean mass on change in VO2pk during 70-d of BR or BR + exercise. METHODS. Subjects completed 70-d of BR alone (CON, N=9) or BR + exercise (EX, N=17). The exercise prescription included 6 d/wk of aerobic exercise at 70 - 100% of max and 3 d/wk of lower body resistance exercise. Subjects were monitored 24 hr/d. VO2pk and lean mass (iDXA) were measured pre and post BR. ANOVA was used to evaluate changes in VO2pk pre to post BR. Subjects were retrospectively divided into high and low responders based on change in VO2pk (CON > 20% loss, n=5; EX >10% loss, n=4, or 5% gain, n=4) to further understand individual variability. RESULTS. VO2pk decreased from pre to post BR in CON (P<0.05) and was maintained in EX; however, significant individual variability was observed (CON: -22%, range: -39% to -.5%; EX: -1.8%, range: -16% to 12.6%). The overlap in ranges between groups included 3 CON who experienced smaller reduction in VO2pk (<16%) than the worst responding EX subjects. Individual variability was maintained when VO2pk was normalized to lean mass (range, CON: -33.7% to -5.7%; EX: -15.8% to 11%), and the overlap included 5 CON with smaller reductions in VO2pk than the worst responding EX subjects. High responders to disuse also lost the most lean mass; however, this relationship was not maintained in EX (i.e. the largest gains/losses in lean mass were observed in both high and low responders). Change in VO2pk was not related to exercise intensity. CONCLUSION. Change in VO2pk in response to disuse and exercise was highly variable among individuals, even in this tightly controlled study. Loss in lean mass accounts for a significant degree of variability in the CON; however, training induced gains in VO2pk appear unrelated to lean mass or exercise intensity.

External loading is dependent upon game state and varies by position in professional women’s soccer

ABSTRACT Objectives: This investigation examined relationships between game state and external loading in professional women’s soccer. Methods: Match motion and accelerometer data were collected and used to determine running distance, high-speed distance, number of high-speed runs, number of sprints, and total player load (AU). These data were compared by game state (draw 0–0, leading, trailing, or drawing where the score was not 0–0) and playing position: Full back (FB), center back (CB), center midfield (CM), and forward (FW). Results: External loading was not dependent upon game state for FW. Total distance (d = 0.51–0.54), meterage (d = 0.051–0.55), and total player load (d = 0.32–0.76) were less when leading or trailing than when drawn 0–0 for CM. Total distance (d = 0.45–0.80) and meterage (d = 0.31–0.80) were less when leading or trailing than drawing 0–0 for CB. High-speed distance was greater for CB when trailing than when leading (d = 0.62). Total player load for FB was greater (d = 0.49–1.12) when drawn 0–0 than when leading or trailing. Conclusions: Some external loads in women’s professional soccer players are different by position and game state; fatigue or tactical adjustments may influence loading.

Ground Reaction Forces and Gait Parameters during Motorized and Non-Motorized Treadmill Walking and Runing on the International Space Station Treadmill

Both motorized (T-M) and non-motorized (T-NM) treadmill locomotion are used on the International Space Station (ISS) as countermeasures to the deleterious effects of prolonged weightlessness. However, the ground reaction forces (GRF) and gait parameters of these exercise modes have not been examined.

Physiologic Responses to Motorized and Non-Motorized Locomotion Utilizing the International Space Station Treadmill

: Treadmill locomotion is used onboard the International Space Station (ISS) as a countermeasure to the effects of prolonged weightlessness. The treadmill operates in two modes: motorized (T-M) and non-motorized (T-NM). Little is known about the potential physiologic differences between modes which may affect countermeasure exercise prescription.