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Article dans une revue

High Altitude Increases Alteration in Maximal Torque but Not in Rapid Torque Development in Knee Extensors after Repeated Treadmill Sprinting

Abstract : We assessed knee extensor neuromuscular adjustments following repeated treadmill sprints in different normobaric hypoxia conditions, with special reference to rapid muscle torque production capacity. Thirteen team-and racquet-sport athletes undertook 8×5-s " all-out " sprints (passive recovery = 25 s) on a non-motorized treadmill in normoxia (NM; FiO 2 = 20.9%), at low (LA; FiO 2 = 16.8%) and high (HA; FiO 2 = 13.3%) normobaric hypoxia (simulated altitudes of ∼1800 m and ∼3600 m, respectively). Explosive (∼1 s; " fast " instruction) and maximal (∼5 s; " hard " instruction) voluntary isometric contractions (MVC) of the knee extensors (KE), with concurrent electromyographic (EMG) activity recordings of the vastus lateralis (VL) and rectus femoris (RF) muscles, were performed before and 1-min post-exercise. Rate of torque development (RTD) and EMG (i.e., Root Mean Square or RMS) rise from 0 to 30, −50, −100, and −200 ms were recorded, and were also normalized to maximal torque and EMG values, respectively. Distance covered during the first 5-s sprint was similar (P > 0.05) in all conditions. A larger (P < 0.05) sprint decrement score and a shorter (P < 0.05) cumulated distance covered over the eight sprints occurred in HA (−8 ± 4% and 178 ± 11 m) but not in LA (−7 ± 3% and 181 ± 10 m) compared to NM (−5 ± 2% and 183 ± 9 m). Compared to NM (−9 ± 7%), a larger (P < 0.05) reduction in MVC torque occurred post-exercise in HA (−14 ± 9%) but not in LA (-12 ± 7%), with no difference between NM and LA (P > 0.05). Irrespectively of condition (P > 0.05), peak RTD (−6 ± 11%; P < 0.05), and normalized peak RMS activity for VL (−8 ± 11%; P = 0.07) and RF (−14 ± 11%; P < 0.01) muscles were reduced post-exercise, whereas reductions (P < 0.05) in absolute RTD occurred within the 0–100 (−8 ± 9%) and 0–200 ms (−10 ± 8%) epochs after contraction onset. After normalization to MVC torque, there was no difference in RTD values. Additionally, the EMG rise for VL muscle was similar (P > 0.05), whereas it increased (P < 0.05) for RF muscle during all epochs post-exercise, independently of the conditions. In summary, alteration in repeated-sprint ability and post-exercise MVC decrease were greater at high altitude than in normoxia or at low altitude. However, the post-exercise alterations in RTD were similar between normoxia and low-to-high hypoxia.
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Dernière modification le : mercredi 28 septembre 2022 - 14:20:09
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Olivier Girard, Franck Brocherie, Grégoire P Millet. High Altitude Increases Alteration in Maximal Torque but Not in Rapid Torque Development in Knee Extensors after Repeated Treadmill Sprinting. Frontiers in Physiology, Frontiers, 2016, 7, pp.97. ⟨10.3389/fphys.2016.00097⟩. ⟨hal-01627090⟩

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