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Endurance training in humans: aerobic capacity and structure of skeletal muscle
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1985
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Physical ActivityMuscle FunctionEndurance TrainingStrength TrainingMuscle StructureMetabolic SyndromeMuscle PhysiologyKinesiologyBody CompositionSkeletal MuscleExerciseApplied PhysiologySport PhysiologyMetabolic StateHealth SciencesPower OutputPhysical FitnessExercise ScienceEnergy MetabolismExercise PhysiologyPhysiologyAerobic CapacityMetabolismLocal Level
The study proposes that preferential proliferation of subsarcolemmal mitochondria and increased intracellular lipid stores enable muscle cells to adapt to greater fat utilization during endurance training. Six weeks of high‑intensity bicycle ergometer training (30 min/day, heart rate >85 % max for two‑thirds of the session) was performed on ten subjects, with vastus lateralis biopsies and VO₂max measured before and after. Training raised maximal maintained power by 33 % and total mitochondrial volume by 40 %, while VO₂max/Mb increased only 14 %; the local rise in aerobic capacity explains the modest overall VO₂max improvement.
The adaptation of muscle structure, power output, and mass-specific rate of maximal O2 consumption (VO2max/Mb) with endurance training on bicycle ergometers was studied for five male and five female subjects. Biopsies of vastus lateralis muscle and VO2max determinations were made at the start and end of 6 wk of training. The power output maintained on the ergometer daily for 30 min was adjusted to achieve a heart rate exceeding 85% of the maximum for two-thirds of the training session. It is proposed that the observed preferential proliferation of subsarcolemmal vs. interfibrillar mitochondria and the increase in intracellular lipid deposits are two possible mechanisms by which muscle cells adapt to an increased use of fat as a fuel. The relative increase of VO2max/Mb (14%) with training was found to be smaller by more than twofold than the relative increase in maximal maintained power (33%) and the relative change in the volume density of total mitochondria (+40%). However, the calculated VO2 required at an efficiency of 0.25 to produce the observed mass-specific increase in maximal maintained power matched the actual increase in VO2max/Mb (8.0 and 6.5 ml O2 X min-1 X kg-1, respectively). These results indicate that despite disparate relative changes the absolute change in aerobic capacity at the local level (maintained power) can account for the increase in aerobic capacity observed at the general level (VO2max).