ATP and phosphocreatine changes in single human muscle fibers after intense electrical stimulation

The recovery pattern of adenine nucleotides and glucolytic intermediates after short-lasting anaerobic exercise was studied. Biopsies were obtained from the vastus lateralis muscle at rest, immediately after intermittent electrical stimulation with occluded circulation (total time 166 s), and after 20 s, 60 s, 5 min, and 15 min of recovery. ATP in single fibers decreased from 23.9 +/- 1.41 to 14.2 +/- 3.20 in type I fibers and from 25.01 +/- 1.20 to 13.1 +/- 2.65 mmol/kg dry muscle in type II fibers postexercise. After 15 min of recovery, ATP was resynthesized to 95 and 76% in type I and type II fibers, respectively. The phosphocreatine (PCr) content in type I fibers at rest was 72.3 +/- 4.50 and 83.3 +/- 9.76 mmol/kg dry muscle in type II fibers. After exercise, PCr was depleted in both fiber types. After the 60 s of recovery the PCr content in type I fibers was significantly higher (P less than 0.05) compared with type II fibers, but, after 5 min of oxidative recovery, the PCr levels were equal in the two fiber types. Fifteen minutes postexercise, type II fibers demonstrated a significantly higher content (97.8 mmol/kg dry muscle) compared with its resting value (P less than 0.05).