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

Abstract

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, 45W and 100W; leg exercise, 100W and 200W). In addition, peak oxygen uptake (V̇o2max) 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±0.5kg (in four of four subjects), whereas V̇o2max was unchanged in the arm (3.1±0.21min-1) and leg (4.0±0.11 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 (0.9±0.02 and 0.96±0.01) at the low and high workloads, respectively. Citrate synthase and β-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.