Transfer effects in endurance exercise

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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.

This work was supported by grant 3.128.81 from the Swiss National Science Foundation, and by Cilo S.A., Bicycles, Romanel/Switzerland