INFLUENCE OF MUSCLE BLOOD-FLOW ON FATIGUE DURING INTERMITTENT HUMAN HANDGRIP EXERCISE AND RECOVERY

1. The influence of muscle blood Bow on fatigue and recovery was studi ed in the forearm muscles of eight male subjects performing a powerful isometric hand-grip exercise. The exercise was performed with the exe rcising forearm normally perfused and, on a separate occasion, with it s blood flow occluded with a sphygmomanometer cuff. 2. In the no cuff condition, peak force declined to an initial plateau at 40-50% of the maximal voluntary grip force (MVC), When perfusion was occluded, the f orce decline was similar during the first minute of exercise, then for ce fell rapidly to exhaustion. 3. In a separate experiment to investig ate the mechanisms underlying the plateau in force loss, occlusion of blood flow during the force plateau phase resulted in a rapid decline in force to exhaustion. 4. Recovery of peak force after the cuff exerc ise was significantly greater during the initial 3.5 min of recovery t han after no-cuff exercise, After this time, recovery was similar for both conditions. 5. Muscle blood flow occlusion during intermittent ex ercise profoundly reduces endurance without prolonging recovery, Recov ery time may depend on the duration and energy cost of the exercise ra ther than on the degree of force loss. 6. The present study suggests t hat the fall in muscle force induced by a continuous MVC is a combinat ion of profound short-term fatigue in anaerobic muscle fibres due to t he consumption of their short-term energy supplies, plus a decline in force production by aerobic muscle fibres that is the consequence of h ypoxia, Thus, MVC may not be a good model of fatigue occurring under s ubmaximal conditions, as hypoxia of type I fibres is unlikely to occur under physiological conditions in which muscle contractions are usual ly intermittent.