The human body is perfectly adapted to move in the 1 g gravitational environment on Earth. How can it cope with different gravity conditions, for instance when performing jumps? To answer this question, Prof Daniel Theisen from the Sports Medicine Research Laboratory at LIH’s Department of Population Health, working in close collaboration with the Catholic University of Louvain (UCL) in Belgium, left his usual work place repeatedly to take off in an aircraft and monitor jumps in hypo- and hypergravity conditions.

Landing from a jump is a complex action which requires the body to anticipate the moment of contact with the ground. Since humans have developed motor actions on Earth, the central nervous system and the sensory input processing are optimised to the Earth’s gravity. The project termed “Effect of gravity on the muscular control of landing” served to understand the body’s neuro-muscular control mechanisms during vertical jump tasks in different gravity levels.

To simulate hypo- and hypergravity conditions ranging from 0.2 to 1.6 g, experiments were carried out in the world’s largest aircraft for weightless research, the ‘Zero-G’ Airbus A300 made available by the European Space Agency (ESA). Hypogravity can be simulated by parabolic flights whereas hypergravity is obtained by circular turns creating centrifugal forces. As a comparison, the same experiments were also performed on Earth using a system which generates a pull-down force applied to the trunk.

For each study, eight subjects had to perform counter-movement jumps to assess motor control of landing. External forces applied to the body, movements of the lower limb segments and muscular activity of six lower limb muscles were recorded. In all the gravitational conditions the subjects were able to cope with altered sensory signals, adapt their limb position to the gravitational conditions, anticipate the contact with the ground and thus stabilise their landing.

The researchers could conclude that even if in daily living activities, gravity can be perceived as a constant factor, the central nervous system is able to adequately modify the motor control of landing. The slight changes in the landing strategy that the research team observed are most probably based on altered sensory (proprioceptive and otolithic) signals.

Prof Theisen participated himself for the jumps. He tells about this unusual gravity experience: ”This is certainly one of the most exciting research projects I have been involved in. The experimental paradigm is very unusual, the research team was fantastic and the results really exciting. Plus, the experience of weightlessness is truly overwhelming. I feel extremely privileged to have been part of this scientific and human adventure.”

This project may be relevant both for developing injury prevention methods in sports for athletes and in space flights for astronauts who are more susceptible to injury as their bones and muscles are weakened by long periods in weightlessness. Further investigations are however necessary to determine the potential use of landing tasks as countermeasure for preventing injury.

The project was supported by ESA-Prodex (Belgium) and co-funded by the Luxembourg Government through an ESA Contract in the Luxembourg Third Party Programme. Prof Bénédicte Schepens from the Laboratory of Physiology and Biomechanics of Locomotion (UCL) was the principal investigator together with Prof Patrick Willems (UCL) and Prof Daniel Theisen working as co-investigators. The project also led to a successful PhD thesis by Dr Clément Gambelli (UCL) who first-authored three publications and obtained his PhD degree in April 2016.