Introduction: Most studies on simulated gravity showed reduced vertical ground reaction forces (Minetti et al. 2012) and longer contact time (Donelan and Kram 1997). The aim of this study was to identify the temporal and dynamical features of the running pattern when controlled external forces are continuously providing body unweighing and reloading. Methods: Seven healthy male adults volunteered for this study on AlterG treadmill®. The test included 2 randomized running series of 9 min performed at preferred speed and separated by a 5 min walk. Each series included 3 successive steps of 3 min (at 100% BW, 60 or 80% BW, and 100% BW). Reduced gravity was provided by positive lower body pressure technology. The air pressure variation inside the harness was measured to assess the partial body support provided by AlterG technology. Vertical reaction force and centre of mass accelerations were simultaneously recorded at 1 kHz. Initial impact peak force, tolerance to impact, loading rate and active peak force were analysed. Braking and push-off phase durations, and impulses were calculated as well vertical stiffness. The temporal analysis included flight, contact, braking and push-off phase durations as well as step frequency. The two running series were analysed separately using repeated-measures ANOVA for Body weight, Limb and Time (first vs. last 30 sec of each step) effects, with p=0.05 and Bonferroni`s post-hoc. Results: For both running series, there was no interaction, but a main Body weight effect on most parameters. Independently of the limb and time period, unweighing led to increased flight time (p<0.001) and decreased contact time (p<0.001) that resulted in decreased step frequency (p<0.001). Only the braking phase duration was reduced (p<0.001). Despite the decreases of impact peak force (p<0.05) and loading rate (p<0.05), tolerance to impact was not improved. Active peak force (p<0.001) and the push-off impulse were also reduced (p<0.001) whereas harness pressure and vertical stiffness increased (p<0.05). All parameters came back to their initial values after reloading, except for the braking duration. Discussion: Temporal and dynamical changes of the running pattern of the healthy runners operated within 3 min when body weight was modified. Unweighing allowed runners to face lower impact peak force, produce lesser force during push-off and reduce minimally contact time. The associated increases in vertical stiffness and flight time give support to the energy recoil provided by the harness. In conclusion such technology appears as useful for rehabilitation purpose as it reduces external forces and lowers internal forces on lower limb joints.
© Copyright 2014 19th Annual Congress of the European College of Sport Science (ECSS), Amsterdam, 2. - 5. July 2014. Veröffentlicht von VU University Amsterdam. Alle Rechte vorbehalten.