An Initial Phase of Phosphocreatine Recovery after Exercise with Flow Occlusion can be Explained by Glycogenolysis

Abstract

PURPOSE: Classic studies (e.g., Sahlin, et al, Scand. J. Clin. Lab Invest. 39:551, 1979) suggested that phosphocreatine (PCr) resynthesis in human muscle after exercise is entirely dependent on oxidative metabolism. These results reinforce the view that glycogenolytic flux is strongly dependent on feedforward activation by calcium or other signals associated with contractile activity. In contrast, recent modeling studies (e.g., Lambeth and Kushmerick, Ann. Biomed. Eng. 30:808, 2002) suggest that the observed dependence of glycogenolysis on contractile activity is explained by strong coupling of the pathway to ATPase rate via classic feedback mechanisms. According to this modeling, glycogenolytically-driven PCr recovery ought to be observed under some conditions. METHODS: In this study, PCr resynthesis after 1 min of repetitive isometric ankle dorsiflexion exercise was measured in anterior tibial muscle of human subjects (n=4) by 31P-NMR spectroscopy (51.7 MHz, TR 3s) via a small surface coil under 3 conditions: no occlusion, partial flow occlusion (120 Torr cuff placed above knee), and near complete occlusion (160-180 Torr cuff). RESULTS: As expected, PCr recovery after exercise with no occlusion followed an exponential time course (see Figure top panel). In contrast, recovery during partial occlusion was biphasic, with a brief fast phase, followed by linear PCr recovery. During near-complete occlusion, only the brief, fast-phase of PCr recovery was observed. These three patterns of PCr recovery could be mimicked by a metabolic model in which glycogenolytic rate depends solely on changes in cytoplasmic AMP and inorganic phosphate (see Figure bottom panel).FigureFigureCONCLUSION: The results suggest that PCr recovery in human muscle is not entirely dependent on oxidative metabolism, and that feedforward mechanisms are not required to explain control of muscle glycogenolysis.