Impact of systemic hypoxia and blood flow restriction on mechanical, cardiorespiratory, and neuromuscular responses to a multiple-set repeated sprint exercise

Figures

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  FIGURE 1. Schematic representation of the exercise protocol. The training session consisted of a 10-min warm-up at 100 W, followed by short recovery periods (i.e., 54 s) preceding two sprints of 6 seconds. After 4 min of passive recovery, participants performed three sets of five 10-s sprints with 20 s of passive recovery. The three conditions are represented at the moment they were applied. The black rectangles represent the sprints. BFR, bilaterally-cuffed blood flow restriction; FiO2, fraction of inspired oxygen; MVC, maximal voluntary contraction; NMES, neuromuscular electrical stimulation; SL, sea level.

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  FIGURE 2. Schematic representation of the electrical nerve stimulation. MVC, maximal voluntary contraction; Tmax, twitch torque during the MVC; Tb, torque before the superimposed doublet; D, difference between the torque level just before the double twitch and the maximum torque during the double twitch; TDTW, torque reached with the isolated doublet; Tt, twitch torque. The arrows represent the electrical stimuli of the femoral nerve (1 ms).

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  FIGURE 3. Power output under the different conditions. (A) Average peak power output, (B) Mean power output, (C) Time to reach power output, (D) Fatigue index, (E) Percentage decrement. BFR: bilaterally cuffed blood flow restriction of the lower limbs at 45% of resting arterial occlusion, HYP: simulated hypoxia (fraction of inspired oxygen = 13%), NOR: normoxia. *: significantly different from NOR (p < 0.05), $: significantly different from HYP (p < 0.05). Of note, whisker plots represent the quartiles the horizontal line corresponds to the median and the cross is the mean. Circles, squares and triangles represent the sprints of the first, second, and third sets, respectively.

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  FIGURE 4. Neuromuscular fatigue under the different conditions. (A) Percentage difference in maximal voluntary contraction (ΔMVC). (B) Percentage difference in activation level (ΔAL), (C) Percentage difference in twitch torque (ΔTt), (D) Percentage difference in M-wavemax (ΔM-wavemax). BFR: bilaterally cuffed blood flow restriction of the lower limbs at 45% of resting arterial occlusion, HYP: simulated hypoxia (fraction of inspired oxygen = 13%), NOR: normoxia. *: significantly different from NOR (p < 0.05), $: significantly different from HYP (p < 0.05). Of note, whisker plots represent the quartiles the horizontal line corresponds to the median and the cross is the mean.