HYPOXIA REDUCES THE POTENTIAL OF MUSCULAR ENDURANCE WORK
Matsura, C., Gomes, P. S., Hayknowsky, M., & Bhambhani, Y. (2007). Cardiorespiratory responses to resistance exercise under hypoxia in healthy subjects. ACSM Annual Meeting New Orleans, Presentation Number, 921.
This study examined the effects of acute exposure to hypoxia on muscle endurance and cardiorespiratory responses to unilateral knee extensions at 50, 75, and 100% of 1 RM in healthy Ss (M = 14; F = 10) who participated in three test sessions, 48 hours apart. Sets of knee extensions were completed at 50, 75, or 100% 1 RM until volitional fatigue under normoxia and hypoxia. The protocol consisted of two minutes of baseline, five minutes of rest (in normoxic or hypoxic conditions), the knee-extension exercises, four minutes of recovery, five minutes of rest (normoxic or hypoxic conditions), the knee-extension exercises again, and four minutes of recovery. At 50% and 75% 1 RM, the knee extensions were performed dynamically at a controlled cadence of two seconds each at 100% of isometric contraction.
The duration of knee extensions was significantly longer under normoxia that hypoxia. Endurance time was significantly higher in females when compared to males. There was a lower relative increase in VO2, heart rate, and cardiac output, and a higher increase in ventilation during normoxia than hypoxia. Stroke volume decreased during the exercises similarly in both conditions but was different between genders (males decreased more than females).
Implication. Hypoxia significantly decreased endurance time during knee-extension exercises and increased the metabolic and cardiovascular responses in healthy males and females. This reduction occurred despite the fact that the aerobic contribution during the contractions increased significantly.
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