Abstract
Humans are accustomed to Earth’s constant gravitational acceleration of 1g. Here we assessed if complex movements such as jumps can be adapted to different acceleration levels in a non-constant force field elicited through centrifugation. Kinematics, kinetics and muscle activity of 14 male subjects (age 27±5years, body mass 77±6kg, height 181±7cm) were recorded during repetitive hopping in a short-arm human centrifuge for five different acceleration levels (0.5g, 0.75g, 1g, 1.25g, 1.5g). These data were compared to those recorded during normal hops on the ground, and hops in a previously validated sledge jump system. Increasing acceleration from 0.5g to 1.5g resulted in increased peak ground reaction forces (+80%, p<0.001), rate of force development (+100%, p<0.001) and muscle activity (+30 to +140%, depending on phase, side and muscle). However, most of the recorded parameters did not attain the level observed for jumps on the ground or in the jump system. For instance, peak forces during centrifugation with 1g amounted to 60% of the peak forces during jumps on the ground, ground contact time was prolonged by 90%, and knee joint excursions were reduced by 50%. We conclude that in principle, a quick adaptation to acceleration levels other than the normal constant gravitational acceleration of 1g is possible, even in the presence of a non-constant force field and Coriolis forces. However, centrifugation introduced additional constraints compared to a constant force field without rotation, resulting in lower peak forces and changes in kinematics. These changes can be interpreted as a movement strategy aimed at reducing lower limb deflections caused by Coriolis forces.
Highlights
On earth, everything is subjected to Earth’s constant gravitational acceleration
The main result of the study was that the neuromuscular system is able to adapt rather complex full-body movements such as repetitive jumps to a non-constant force field and Coriolis forces
Peak ground reaction forces during centrifugation were 30–50% lower compared to vertical jumps, ground contact times were 60–90% longer, and rate of force development (RFD) 50–80% lower, see Fig 4
Summary
On earth, everything is subjected to Earth’s constant gravitational acceleration Whether this leads to a strong adaptation of human movement to a constant acceleration of 1g, or whether humans can quickly adapt to unaccustomed accelerations levels and non-constant force fields, is an open question. Adaptability to a non-constant force field space missions, as they do not experience this gravitational acceleration, leading to substantial undesirable adaptations to this microgravity environment, such as loss of bone mass, muscle mass and function, aerobic capacity and orthostatic tolerance [1]. Artificial gravity elicited in a human centrifuge might have the potential to preserve orthostatic tolerance and counteract other systemic effects [7], even though it is unlikely that it will have a substantial effect on muscle and bone mass due to its lack of impact loading [8] Combining these two countermeasures—plyometrics and artificial gravity elicited via centrifugation—might have the potential to offset all of the negative effects of unloading in space
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