Transfer effects in endurance exercise

Summary

The effects of 8 weeks of bicycle endurance training (5 x /week for 30 min) on maximal oxygen uptake capacity ($\dot V_{O_{2max} }$) during arm and leg ergometry, and on the ultrastructure of an untrained arm muscle (m. deltoideus), and a trained leg muscle (m. vastus lateralis) were studied. With the training, leg-$\dot V_{O_{2max} }$ for bicycling increased by +13%, while the capillary per fiber ratio and the volume density of mitochondria in m. vastus lateralis increased by +15% and +40%, respectively. In contrast, the untrained m. deltoideus showed an unchanged capillary per fiber ratio and a decreased mitochondrial volume density (−17%). Despite this decrease of mitochondrial volume arm-$\dot V_{O_{2max} }$ increased by +9%. It seems unlikely that the observed discrepancy can be explained by cardiovascular adaptations, since arm cranking did not fully tax the cardiovascular system (arm-$\dot V_{O_{2max} }$/leg-$\dot V_{O_{2max} }$: 0.74 and 0.71 before and after training, respectively). Thus neither cardiovascular adaptations nor local structural changes in the untrained muscles could explain the increased arm-$\dot V_{O_{2max} }$. However, the enhanced capacity for lactate clearance after endurance training could be sufficient to account for the larger$\dot V_{O_{2max} }$ during arm cranking. We propose that an increased net oxidation of lactate might be responsible for the increased arm-$\dot V_{O_{2max} }$ found after bicycle endurance training.