METABOLIC CAPACITY, FIBER-TYPE AREA AND CAPILLARIZATION OF RAT PLANTARIS MUSCLE - EFFECTS OF AGE, OVERLOAD AND TRAINING AND RELATIONSHIP WITH FATIGUE RESISTANCE

1. The influences of age (5, 13 and 25-month-old rats), overload as ob tained by denervation of synergists, and training on the metabolic cap acity, relative muscle cross-sectional area occupied by each fibre typ e, capillarization and fatigue resistance of the rat m. plantaris were investigated. 2. Creatine kinase, phosphorylase and citrate synthase activities were lower in muscles of 25 than in those of 13-month-old r ats (P < 0.001). 3. Overload resulted in an increased relative area of type I and IIa fibres at all ages (P = 0.001). 4. Capillary density d ecreased with overload and increasing age (P < 0.001). 5. Fatigue resi stance was higher in muscles of 13 than in those of 5-month-old rats ( P < 0.05), and increased with overload (P < 0.05) at all ages. 6. Fati gue resistance of the whole muscle was not closely related to its oxid ative capacity in contrast to what is generally found for single fibre s or motor units.