Influence of short-term unweighing and reloading on running kinetics and muscle activity
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In running, body weight reduction is reported to result in decreased lower limb muscle activity with no change in the global activation pattern (Liebenberg et al. in J Sports Sci 29:207–214). Our study examined the acute effects on running mechanics and lower limb muscle activity of short-term unweighing and reloading conditions while running on a treadmill with a lower body positive pressure (LBPP) device.
Eleven healthy males performed two randomized running series of 9 min at preferred speed. Each series included three successive running conditions of 3 min [at 100 % body weight (BW), 60 or 80 % BW, and 100 % BW]. Vertical ground reaction force and center of mass accelerations were analyzed together with surface EMG activity recorded from six major muscles of the left lower limb for the first and last 30 s of each running condition. Effort sensation and mean heart rate were also recorded.
In both running series, the unloaded running pattern was characterized by a lower step frequency (due to increased flight time with no change in contact time), lower impact and active force peaks, and also by reduced loading rate and push-off impulse. Amplitude of muscle activity overall decreased, but pre-contact and braking phase extensor muscle activity did not change, whereas it was reduced during the subsequent push-off phase.
The combined neuro-mechanical changes suggest that LBPP technology provides runners with an efficient support during the stride. The after-effects recorded after reloading highlight the fact that 3 min of unweighing may be sufficient for updating the running pattern.
KeywordsRunning Unweighing Reloading SSC EMG GRF
Active peak force
First 30 s sample of each running condition
Center of mass
Vertical displacement of CoM during the braking phase
Last 30 s sample of each running condition
Vertical ground reaction force
Ground reaction force
Impact peak force
Lower body positive pressure
Minimal force after IPF
Rating of perceived exertion
We are particularly grateful for the assistance given by Dr. Antoine Morice and Dr. Cedric Morio for data analyses.
Conflict of interest
None of the authors had any financial or personal conflict of interest with regard to this study.
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