MUSCLE GLYCOGEN RESYNTHESIS AFTER SHORT-TERM, HIGH-INTENSITY EXERCISEAND RESISTANCE EXERCISE

Typical rates of muscle glycogen resynthesis after short term, high in tensity exercise (15.1 to 33.6 mmol/kg/h) are much higher than glycoge n resynthesis rates following prolonged exercise (approximate to 2 mmo l/kg/h), even when optimal amounts of oral carbohydrate are supplied ( approximate to 8 mmol/kg/h). Several factors differ during post-exerci se recovery from short term, high intensity exercise compared with pro longed exercise. The extremely fast rate of muscle glycogen resynthesi s following short term, high intensity exercise may originate from the se differences. First, peak blood glucose levels range from 6.6 to 8.9 mmol/L during recovery from short term, high intensity exercise. This is markedly higher than the blood glucose values of 2 to 3.4 mmol/L a fter prolonged exercise. In response to this elevation in plasma gluco se levels, insulin levels increase to approximate to 60 mu U/ml, a 2-f old increase over resting values. Both glucose and insulin regulate gl ycogen synthase activity, and higher levels of them improve muscle gly cogen synthesis. Secondly, high intensity exercise produces high level s of glycolytic intermediates in muscle, as well as high lactate level s ([La]) in muscle and blood. Finally, fast-twitch glycolytic muscle f ibres are more heavily used in short term, high intensity exercise. Th is promotes greater glycogen depletion in the fast-twitch fibres, whic h have a higher level of glycogen synthase activity than slow-twitch f ibres. While the exact contribution of each of these factors is unknow n, they may act in combination to stimulate rapid muscle glycogen resy nthesis rates. Muscle glycogen resynthesis rates following resistance exercise (1.3 to 11.1 mmol/kg/h) are slower than the rates observed af ter short term, high intensity exercise. This may be caused by slightl y lower muscle and blood [La] after resistance exercise. In addition, a greater eccentric component in the resistance exercise may cause som e interference with glycogen resynthesis.