Résumé
We tested the hypothesis that backward downhill walking (eccentric component) impairs both voluntary activation and muscle contractile properties in the plantar flexors and delays recovery as compared to a gradient and distance-matched uphill walk. Fourteen males performed two 30-min walking exercises (velocity: 1m/s; grade: 25%; load: 12% of body weight), one downhill (DW) and one uphill (UP), in a counterbalanced order, separated by 6weeks. Neuromuscular test sessions were performed before, after, 24-, 48- and 72-h post-exercise, including motor nerve stimulations during brief (5s) and sustained (1min) maximal isometric voluntary contractions of the plantar flexors. DW (-18.1 +/- 11.1%, P<.001), but not UP (-6.0 +/- 7.7%, P=.15), decreased torque production during brief contractions for at least three days post-exercise (P<.05). Voluntary activation during brief contractions decreased after DW (P<.05), but not UP, and recovered by 24h. Both UP (-9.3 +/- 9.0%, P=.024) and DW (-25.6 +/- 10.3%, P<.001) decreased torque production during sustained contractions but voluntary activation (P=.001) was lower in DW than UP. Peak twitch torque and maximum rates of torque development and relaxation were equally reduced after UP and DW (P<.05), and recovered by 24h. DW induced an increase in muscle soreness with peak values observed 48h post-walking (P<.001), whereas post-UP exercise changes were non-significant (all P>.05). Using a direct comparison, the capacity to drive the plantar flexors during sustained contractions remains sub-optimal during the three-day recovery period in response to non-exhaustive, downhill backward walking in reference to an uphill exercise matched for distance covered.