Thursday Morning Poster Presentations: Posters displayed from 7:30 a.m.–12:30 p.m.: One-hour author presentation times are staggered from 8:30–9:30 a.m. and 9:30–10:30 a.m.: D-29 Free Communication/Poster – Space Physiology and Microgravity: THURSDAY, JUNE 1, 2006 2:00 PM – 5:00 PM ROOM: Hall B
Astronauts onboard the International Space Station use treadmill locomotion as an exercise countermeasure to musculoskeletal deconditioning. A subject loading device (SLD) provides an external load (EL) that tethers the astronaut to the treadmill surface and applies axial skeletal loading via the ground reaction force (GRF). GRF parameters while running in microgravity should be equivalent to those obtained in normal gravity (1g) if musculoskeletal benefits are to be received.
PURPOSE: To determine the relationship between mean dynamic EL and vertical GRF parameters during running in weightlessness (0g).
METHODS: Four subjects (28.0 ± 5.6 yrs, 170.2 ± 8.6 cm, 74.5 ± 14.0 kg) ran on an instrumented treadmill at 3.13 m/s during 0g (parabolic aircraft flight) and 1g (laboratory). During 0g, EL was provided by an SLD that attached to a waist and shoulder harness worn by the subjects. EL was measured via load cells (120 Hz) and the instrumented treadmill measured the vertical GRF (250 Hz). GRF parameters included peak impact force (PIF), peak active force (PAF), max loading rate (LR), and impulse (Imp). Simple linear regression examined the relationship between mean dynamic EL and each vertical GRF parameter (p <0.05). Mean 1g GRF values were placed back into significant regression equations for calculations of the predicted mean dynamic EL to replicate values found in 1g.
RESULTS: The mean dynamic EL ranged between 57% and 94% of body weight (BW). Significant relationships were observed between mean dynamic EL and both PAF (r2=0.58) and Imp (r2=0.78). No significant relationships were found between EL and PIF or LR. The predicted mean dynamic EL for 1 g replication was 126% BW for PAF and 109% BW for Imp.
CONCLUSION: These results suggest that not all GRF parameters are dependent on EL provided by an SLD while running in weightlessness. The observed r2values for PAF and Imp suggest that EL accounts for only a portion of the variance in vertical GRF. Future regression analysis should try to determine what variables correlate to PIF and LR in weightlessness, as these GRF parameters may be the most beneficial for musculoskeletal integrity.