PHOSPHATE-METABOLISM OF PRIOR ECCENTRICALLY LOADED VASTUS MEDIALIS MUSCLE DURING EXERCISE IN HUMANS

The possible alteration of metabolism of the m. vastus medialis was in vestigated during exercise after eccentric loading. Twelve male subjec ts performed stepping exercise for 25-60 min. One week before and 24 h after stepping they performed concentric leg exercise at stepwise inc reasing intensity, while power output was measured. During this concen tric exercise and recovery therefrom, phosphorous metabolites were als o measured in the m. vastus medialis with magnetic resonance spectrosc opy. Creatine kinase and myoglobin in blood were measured before and 7 2 h after stepping. T1 and T2 H-1-relaxation times for water were calc ulated from magnetic resonance images collected 72 h after stepping, a nd used as measures for oedema. The subjects perceived substantial sor eness from 24 to 72 h after stepping. The ratio of inorganic phosphate over phosphocreatine at rest increased from 0.12+/-0.02 (before) to 0 .19+/-0.04 (24 h after stepping) (P < 0.05). Creatine kinase activity was slightly elevated 72 h after stepping (71 [49-812] U L(-1) [median , range]; P < 0.05) compared with baseline values (58 [26-409] U L(-1) ), whereas myoglobin concentration was not significantly elevated (15 [8-120] mu g L(-1) compared with 8 [8-41] mu g L(-1)). In the eccentri cally exercised muscles, T1 and T2 values were not or only slightly hi gher than in the concentrically exercised contralateral muscles. The r elation between power and the ratio of inorganic phosphate over phosph ocreatine during concentric exercise, and the recovery data for inorga nic phosphate, phosphocreatine and pH did not alter after stepping. Th ese data suggest that quadriceps metabolism during concentric exercise and recovery therefrom is not affected by prior eccentric overload, b ut it cannot be excluded that metabolism will alter during exercise af ter more strenuous prior eccentric overload.