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1 The John Rankin Laboratory of Pulmonary Medicine, University of Wisconsin Medical School, Madison, WI, USA; School of Sport and Education, Brunel University, Middlesex, United Kingdom
* To whom correspondence should be addressed. E-mail: amann{at}wisc.edu.
The effect of arterial oxygen content (CaO2) on quadriceps fatigue was assessed in healthy, trained, male athletes. On separate days, eight participants completed three constant workload trials on a bicycle ergometer at fixed workloads (314±13 W). The first trial was performed while breathing a hypoxic gas mixture [inspired O2 fraction / hemoglobin saturation (%) / CaO2 (ml O2.dl blood-1) 0.15/81.6/18.2; HYPO] until exhaustion (4.5 ± 0.4 min). The remaining two trials were randomized and time-matched with HYPO. The second and third trials were performed while breathing a normoxic (0.21/95.0/21.3; NORM) or hyperoxic (1.0/100/23.8; HYPER) gas mixture, respectively. Quadriceps muscle fatigue was assessed via magnetic femoral nerve stimulation (1- 100 Hz) before and 2.5-min post exercise. Myoelectrical activity of the vastus lateralis was obtained from surface electrodes throughout exercise. Immediately following exercise, the mean force response across 1 to 100 Hz decreased from pre-exercise values (p<0.01) by -26 ± 2%, -17 ± 2%, -13 ± 2% for HYPO, NORM, HYPER, respectively, each of the decrements differed significantly (p<0.05). Integrated electromyogram increased significantly throughout exercise (p<0.01) by 23 ± 3%, 10 ± 1%, 6 ± 1% for HYPO, NORM, HYPER, respectively, each of the increments differed significantly (p<0.05). Mean power frequency fell more (p<0.05) during HYPO (-15 ± 2%), the difference between NORM (-7 ± 1%) and HYPER (-6 ± 1%) was not significant (p=0.32). We conclude that delta CaO2 during strenuous systemic exercise at equal workloads and durations affects the rate of locomotor muscle fatigue development.
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