Hemodynamics and O₂ uptake during maximal knee extensor exercise in untrained and trained human quadriceps muscle: effects of hyperoxia

Abstract

To elucidate the potential limitations on maximal human quadriceps O2 capacity, six subjects trained (T) one quadriceps on the single-legged knee extensor ergometer (1 h/day at 70% maximum workload for 5 days/wk), while their contralateral quadriceps remained untrained (UT). Following 5 wk of training, subjects underwent incremental knee extensor tests under normoxic (inspired O2 fraction = 21%) and hyperoxic (inspired O2 fraction = 60%) conditions with the T and UT quadriceps. Training increased quadriceps muscle mass (2.9 +/- 0.2 to 3.1 +/- 0.2 kg), but did not change fiber-type composition or capillary density. The T quadriceps performed at a greater peak power output than UT, under both normoxia (101 +/- 10 vs. 80 +/- 7 W; P < 0.05) and hyperoxia (97 +/- 11 vs. 81 +/- 7 W; P < 0.05) without further increases with hyperoxia. Similarly, thigh peak O2 consumption, blood flow, vascular conductance, and O2 delivery were greater in the T vs. the UT thigh (1.4 +/- 0.2 vs. 1.1 +/- 0.1 l/min, 8.4 +/- 0.8 vs. 7.2 +/- 0.8 l/min, 42 +/- 6 vs. 35 +/- 4 ml x min(-1) x mmHg(-1), 1.71 +/- 0.18 vs. 1.51 +/- 0.15 l/min, respectively) but were not enhanced with hyperoxia. Oxygen extraction was elevated in the T vs. the UT thigh, whereas arteriovenous O2 difference tended to be higher (78 +/- 2 vs. 72 +/- 4%, P < 0.05; 160 +/- 8 vs. 154 +/- 11 ml/l, respectively; P = 0.098) but again were unaltered with hyperoxia. In conclusion, the present results demonstrate that the increase in quadriceps muscle O2 uptake with training is largely associated with increases in blood flow and O2 delivery, with smaller contribution from increases in O2 extraction. Furthermore, the elevation in peak muscle blood flow and vascular conductance with endurance training seems to be related to an enhanced vasodilatory capacity of the vasculature perfusing the quadriceps muscle that is unaltered by moderate hyperoxia.

Is the balance between skeletal muscular metabolic capacity and oxygen supply capacity the same in endurance trained and untrained subjects?

“…Previous studies have found the 1-KE mass-specific O 2 uptake, measured by invasive methods, to range from 350 to 602 ml·kg -1 ·min -1 (Andersen & Saltin, 1985i;Rowell et al, 1986;Richardson et al, 1993a;Radegran et al, 1999a;Richardson et al, 1999a;Mourtzakis et al, 2004). The mass specific O 2 uptake found in the present study of 386 and 570 ml·kg -1 ·min -1 for controls and ET, closely agree with this range.…”

Increase in calf post-occlusive blood flow and strength following short-term resistance exercise training with blood flow restriction in young women

“…In the ''restricted blood flow'' condition all training was performed with an occlusion cuff, whereas the contralateral limb training was performed without restriction. It has been recently demonstrated that changes in vascular capacity are limited to the trained region following resistance training (Alomari and Welsch 2007) and there are no cardiovascular effects on the contra-lateral limb (Mourtzakis et al 2004;Saltin et al 1976). All pretraining tests were performed 3-5 days prior (baseline) to the commencement of the resistance training programme and post-training measurements performed 3-5 days after the final training session.…”

Regular endurance training reduces the exercise induced HIF-1α and HIF-2α mRNA expression in human skeletal muscle in normoxic conditions

“…The quadriceps training induced increases in peak work rate of 24% (Mourtzakis et al 2004), and the relative load on the trained versus the untrained leg was therefore also different during the 3 h two-legged exercise. The subjects performed two-legged knee extensor exercise for 3 h at 87±5 W, and as the two legs performed similar amount of work (Pilegaard et al 2003), i.e.…”