Biomechanical analyses of flywheel resistance exercise: From a space- and ground-based perspective

Astronauts suffer degradation of postural muscles and weight-bearing bones during long-duration spaceflight. Resistance exercise is used as a primary countermeasure against these degradations. However, it has proven difficult to predict appropriate exercise loads, and the countermeasure regimens in current use are not fully preventing bone and muscle loss. It is likely that gravity-independent exercise devices, based on flywheel inertial resistance, will be implemented in future musculoskeletal countermeasure regimens. In this thesis, biomechanical analyses of external and internal exercise loads during flywheel leg resistance exercises, were performed through experimental data collection and musculoskeletal modelling. The thesis is based on four separate studies with the collective aim to provide knowledge that can be implemented when designing flywheel-based strength-training regimens to be used both in terrestrial settings and as countermeasures against musculoskeletal deconditioning in weightlessness. The first study analyzed computed joint kinematics and kinetics, and relative muscle forces in the lower limb during maximal effort flywheel leg press (FWLP) and flywheel squat (FWS) exercises. Results showed that total exercise load was slightly higher during FWS than FWLP, whereas relative muscle force did not differ between the two exercises, suggesting that they may have similar strength training effects. The second study investigated the effect of gravity on internal joint load distribution during leg resistance exercise. This was done in two steps: 1) by comparing joint kinetics during FWLP and FWS at a given submaximal exercise load (80% of the isometric maximum load in FWLP), and 2) by simulating both FWLP and FWS in zero gravity and studying changes in joint loads. The first step revealed greater hip extension moment and lumbar joint-contact forces in FWLP than in FWS, indicating a notable effect of the direction of motion relative to the gravity vector, on body load distribution. Step two showed similar, or lower, joint loads in FWLP when gravity was removed, whereas in FWS, removal of gravity resulted in increased hip extension moment and lumbar force. Collectively, the results suggest that FWLP is a better ground-based analogue than FWS for leg-resistance exercise in space. The third study examined the accuracy of a pressure insole system regarding measurements of centre of pressure and ground reaction force during resistance exercises. The re