Table 1.
Population characteristics, number of trials per experimental condition and number of trials per experimental condition where kinematics data were available (in parenthesis) for each subject.
Fig 1.
Experimental set-up (left) and typical trace in 1 g (right).
Left: scheme of the experimental set-up in the laboratory to simulate hypergravity. The additional pull-down force simulating hypergravity was generated by two pneumatic pistons placed horizontally on each side of the subject under the ground level. The force generated by each piston was transmitted to the harness by a rope, which passed through two pulleys. A first pulley, moving horizontally, doubled the movement of the harness as compared to the piston. A second pulley changed the direction of the force from horizontal to vertical. A force transducer placed at the level of this last pulley measured the tension in the rope and a force-plate measured the ground reaction forces under the feet (for more details see Methods). Right: typical trace of one subject (60 kg, 1.69 m, 46 yo) in 1 g in the laboratory: the vertical component of the ground reaction force (Fz normalized in BW), the vertical acceleration (az), velocity (Vz) and displacement (Sz) of the COM are expressed as a function of time, from 500 ms before take-off (TO) until 500 ms after touchdown (TD). The jump is divided into sub-periods: the instant of TO and the instant of TD delimit the aerial phase (taer). The land1 is the period between TD and the moment at which the vertical force reaches its peak (Fz-peak); land2 is the period between the time of Fz-peak and the moment at which the COM reaches its lowest vertical position (Sz-min). The dotted line on the az-time curve during land1 represents the function computed from a spring-mass model. The black interrupted line after land1 represents the function computed from a damped harmonic oscillator model (see Methods).
Fig 2.
Counter-movement jump in 1 g and 1.6 g.
Typical traces of the kinetics and kinematics as a function of time, during a counter-movement jump (CMJ) of a female subject (54 kg, 1.65 m, 23 yo). Left: 1 g, middle: 1.6 g-A300, right: 1.6 g-SLS. Traces start when the subject initiates the CMJ, and end when the subject returns to the standing position. Three top panels: (from top to bottom): vertical component of the ground reaction force (Fz normalized in BW on Earth), vertical velocity (Vz) and vertical displacement (Sz) of the COM. On the Fz/BW trace, the horizontal dotted line indicates: BW at 1 g (left), 1.6 BW in the A300-condition (middle) and Ft in the SLS-condition (right). Three bottom panels: (from top to bottom): angle of the left hip, knee and ankle joints. The vertical dotted lines indicate the instant of touchdown (TD).
Fig 3.
Effect of the experimental conditions on kinetic variables.
The aerial time (taer), the maximal height of the jump (Sz-max), the vertical velocity of the COM at TD (Vz-TD) and the maximal vertical ground reaction force normalized by body weight on Earth. (Fz-peak/BW) are plotted as a function of the gravity level. Points represent the grand mean of all subjects ± one standard deviation. Grey symbol are for the 1 g-condition in the laboratory; black symbol are for the SLS-condition and white symbol for the A300-condition. In each panel, G indicates a significant effect of gravity, E the effect of the experimental condition (A300 or SLS) and GxE the interaction between gravity and experimental condition (p<0.05).
Fig 4.
Effect of the experimental conditions on the EMG–pattern.
EMG-patterns of soleus (Sol), tibialis anterior (TA), gastrocnemius lateralis (GL), peroneus brevis (PB), vastus lateralis (VL) and biceps femoris (BF) muscles are presented from 450 ms before TD to 250 ms after TD. Positive traces are for the 1 g and the SLS-conditions and negative traces for the A300-condition. Black line is for 1 g; blue lines are for 1.2 g, green for 1.4 g and red for 1.6 g. Traces are the grand mean of the eight subjects averaged over periods of 5 ms and are synchronized to TD (vertical interrupted line). Dotted vertical colored lines correspond to the TO (same color than the curves) in each condition.
Fig 5.
Effect of the experimental conditions on the kinematics of the lower limb joints.
Top panels: Angle of the hip, knee and ankle joint at TD, Middle panels: range of motion of the lower limb joints during land1 (RoM1), Bottom panels, from left to right: range of motion of the lower limb joints during land2 (RoM2). Other indications as in Fig 3.
Table 2.
Effect of the experimental conditions on landing periods and on the vertical displacement of the COM during land1 (ΔSz1), during land2 (ΔSz2) and during landing (ΔSz)
Table 3.
Statistical analysis: effect of the gravity G (1 g, 1.2 g, 1.4 g and 1.6 g), of the experimental condition E (SLS or A300), and of the interaction between G and E.
Fig 6.
Effect of experimental conditions on the parameters of the biomechanical model of landing.
Left: overall mass-specific stiffness k1 generated by the lower limb muscles during land1. Middle and right: overall mass-specific stiffness k2 and damping coefficient c2 generated by the lower limb muscles during the second part of landing (i.e. during and after land2, until the subjects returns to his standing position—see Fig 1). Other indications as in Fig 3.