Skiing across the Greenland icecap: divergent effects on limb muscle adaptations and substrate oxidation

This study investigates the adaptive response of the lower limb muscles and substrate oxidation during submaximal arm or leg exercise after a crossing of the Greenland icecap on cross-country skies. Before and after the 42-day expedition, four male subjects performed cycle ergometer and arm-cranking exercise on two separate days. On each occasion, the subjects exercised at two submaximal loads (arm exercise, 45 W and 100 W; leg exercise, 100 W and 200 W). In addition, peak oxygen uptake ((VO(2max))) was determined for both leg and arm exercise. Before and after the crossing, a muscle biopsy was obtained from the vastus lateralis and the triceps brachii muscles prior to exercise (N=3). After the crossing, body mass decreased by 5.7+/-0.5 kg (in four of four subjects), whereas (VO(2max)) was unchanged in the arm (3.1+/-0.2 l min(-1)) and leg (4.0+/-0.1 l min(-1)). Before the crossing, respiratory exchange ratio (RER) values were 0.84+/-0.02 and 0.96+/-0.02 during submaximal arm exercise and 0.82+/-0.02 and 0.91+/-0.01 during submaximal leg exercise at the low and high workloads, respectively. After the crossing, RER was lower (in three of four subjects) during arm exercise (0.74+/-0.02 and 0.81+/-0.01) but was higher (in three of four subjects) during leg exercise (0.92+/-0.02 and 0.96+/-0.01) at the low and high workloads, respectively. Citrate synthase and beta-hydroxy-acyl-CoA-dehydrogenase activity was decreased by approximately 29% in vastus lateralis muscle and was unchanged in triceps brachii muscle. Fat oxidation during submaximal arm exercise was enhanced without a concomitant increase in the oxidative capacity of the triceps brachii muscle after the crossing. This contrasted with decreased fat oxidation during leg exercise, which occurred parallel to a decreased oxidative capacity in vastus lateralis muscle. Although the number of subjects is limited, these results imply that the adaptation pattern after long-term, prolonged, low-intensity, whole body exercise may vary dramatically among muscles.