Exercise training induces similar elevations in the activity of oxoglutarate dehydrogenase and peak oxygen uptake in the human quadriceps muscle

Abstract

During exercise involving a small muscle mass, peak oxygen uptake is thought to be limited by peripheral factors, such as the degree of oxygen extraction from the blood and/or mitochondrial oxidative capacity. Previously, the maximal activity of the Krebs cycle enzyme oxoglutarate dehydrogenase has been shown to provide a quantitative measure of maximal oxidative metabolism, but it is not known whether the increase in this activity after a period of training reflects the elevation in peak oxygen consumption. Fourteen subjects performed one-legged knee extension exercise for 5-7 weeks, while the other leg remained untrained. Thereafter, the peak oxygen uptake by the quadriceps muscle was determined for both legs, and muscle biopsies were taken for assays of maximal enzyme activities (at 25°C). The peak oxygen uptake was 26% higher in the trained than in the untrained muscle (395 vs. 315 ml min(-1) kg(-1), respectively; P<0.01). The maximal activities of the Krebs cycle enzymes in the trained and untrained muscle were as follows: citrate synthase, 22.4 vs. 18.2 μmol min(-1) g(-1) (23%, P<0.05); oxoglutarate dehydrogenase, 1.88 vs. 1.54 μmol min(-1) g(-1) (22%, P<0.05); and succinate dehydrogenase, 3.88 vs. 3.28 μmol min(-1) g(-1) (18%, P<0.05). The difference between the trained and untrained muscles with respect to peak oxygen uptake (80 ml min(-1) kg(-1)) corresponded to a flux through the Krebs cycle of 1.05 μmol min(-1) g(-1), and the corresponding difference in oxoglutarate dehydrogenase activity (at 38°C) was 0.83 μmol min(-1) g(-1). These parallel increases suggest that there is no excess mitochondrial capacity during maximal exercise with a small muscle mass.

One‐legged endurance training: leg blood flow and oxygen extraction during cycling exercise

“…Further, Klausen et al (1982) reported an increased a-v O 2 diff of 4% paralleled by a 20-30% increase in oxidative enzyme capacity. However, even if excess activity of citrate synthase compared with in vivo maximal oxygen uptake has been demonstrated in isolated mitochondria from quadriceps muscles (Rasmussen et al 2001), Blomstrand et al (1997Blomstrand et al ( , 2011 found a significant correlation (r = 0.79 and 0.56) also between leg VO 2 and citrate synthase. Taken together, these data indicate that the higher oxidative capacity of the mitochondria is as important as an increased mean transit time for oxygen extraction.…”

“…Capillary density was not evaluated in the present study, but blood flow was increased by 16%, which is identical to the increase found by Klausen et al (1982) after 8 weeks of one-legged training. Interpretation of classical enzyme markers for mitochondrial oxidative capacity remains debated (Tweedie et al 2011), andBlomstrand et al (2011) found only oxoglutarate dehydrogenase to provide a quantitative measure of the oxidative capacity of the muscles. However, Klausen et al (1981Klausen et al ( , 1982 reported a 20% increase in muscle capillarization following one-legged training indicating an almost unchanged mean transit time.…”

Skeletal muscle vasodilatation during maximal exercise in health and disease

“…Cross‐sectional studies in humans indicate that endurance trained muscles may have a 30–60% higher peak hyperaemic responses to exercise than untrained muscles (Andersen & Saltin, 1985; Snell et al 1987; Richardson et al 1993). There are few longitudinal studies in humans where the effect of training on peak exercise muscle hyperaemia has been examined (Juel et al 2004; Mourtzakis et al 2004; Blomstrand et al 2011). Blomstrand et al (2011) studied 14 recreationally active subjects who performed one‐legged knee extension exercise for 5–7 weeks, 3–5 days per week (∼1 h per session), while the other leg remained untrained (Fig.…”

“…There are few longitudinal studies in humans where the effect of training on peak exercise muscle hyperaemia has been examined (Juel et al 2004; Mourtzakis et al 2004; Blomstrand et al 2011). Blomstrand et al (2011) studied 14 recreationally active subjects who performed one‐legged knee extension exercise for 5–7 weeks, 3–5 days per week (∼1 h per session), while the other leg remained untrained (Fig. 3).…”

“…oxygen delivery. Since the muscle mass was increased by 5.8%, the normalized peak quadriceps muscle hyperaemia was increased by 22%, from 216 to 265 ml (100 g) −1 min −1 (Blomstrand et al 2011). In six subjects, Juel et al (2004) reported an increase of peak quadriceps muscle blood flow of 25% after 7–8 week of one‐legged knee extension high‐intensity interval training with (15 × 1 min bouts at 150% of , with 3 min rest periods).…”