Biomechanics Of Running In Weightlessness On A Gravity Simulator

Willems, Patrick [UCL] Heglund, Norman [UCL] Gosseye, Thierry [UCL]

Muscle and bone loss, plus cardiovascular and neuro-vestibular de-conditioning, are serious impediments to long-term human spaceflight. Evidence indicates that impact loading, bone stress, muscular work and physical exercise are important countermeasures for maintaining crew health in space. An instrumented treadmill/force-plate/ergometer was constructed to duplicate in weightlessness the biomechanics of running on Earth (Gosseye et al., 2005). Gravity was simulated by two pneumatic pistons pulling the subject downwards with a force equal to their body weight on Earth. The pistons were mounted on chariots which tracked the subject’s horizontal movements on the treadmill, resulting in nearly constant vertical force, as in gravity. This study compares the biomechanics of running on the gravity simulator to running on Earth. Four transducers, mounted under the treadmill, measured the three components of the force exerted by the foot on the treadbelt. A high-speed video camera recorded the movements of limb segments delimited by reflective markers. Bipolar surface electrodes recorded electromyographic activity (EMG) of the vastus lateralis, biceps femoris, tibialis anterior and lateral gastrocnemius muscles. Experiments in weightlessness where conducted during four ESA parabolic flight campaigns between 2004 and 2006: 322 samples of 20 s running were recorded on 6 subjects at 2.2 to 4.4 m s-1. Control experiments were performed on the same subjects on Earth. The peak vertical force, contact and aerial time, vertical stiffness of the body (i.e. slope of the vertical force vs vertical displacement curve during contact), muscular work (divided into external work to move of the centre of mass of the body relative to the surroundings and internal work to move the limb segments relative to the centre of mass), bone stress and muscular power generated at the lower limb joints (computed by inverse dynamics) differed by less than 5In addition, the EMG patterns of the lower limb muscles were comparable, except for the biceps femoris which was silent during the second part of the contact phase when running on the simulator (Gosseye et al., 2007). This is probably due to the traction system that retains the subject so that the belt drags the foot backwards and extends the hip passively. In conclusion, the biomechanics of running at 3.3 m s-1 on Earth can be accurately duplicated in weightlessness using the gravity simulator. Ongoing analysis will determine if this conclusion can be extended to other running speeds. Gosseye T.P., Willems P.A. and Heglund N.C. (2005) Design of an active gravity simulator Computer Methods in Biomechanics and Biomedical engineering 8 (S1): 121-122 Gosseye T.P., Schepens B., Heglund N.C. and Willems P.A. (2007) Electromyographic pattern (EMG) of the lower limb muscles during running in weightlessness on a gravity simulator Computer Methods in Biomechanics and Biomedical engineering