Muscle Fatigue
The inability of a muscle to maintain force of contraction after prolonged activity is called muscle fatigue. The exact mechanism of muscle fatigue is not fully understood however, several factors logically are thought to contribute. Inadequate release of Ca++ from the SR, depletion of creatine phosphate, insufficient oxygen, depletion of glycogen and other nutrients, buildup of lactic acid and ADP and the failure of action potentials to release enough ACh. It is interesting that the ATP levels in fatigued muscle are often not much lower than those in resting muscle.
Oxygen Consumption After Exercise
Prolonged periods of muscle contraction result in increased breathing rate and blood flow to the muscle tissue. This results in enhanced O2 delivery. After contraction, heavy breathing continues and O2 consumption remains above resting level. Depending on the nature of the activity, recovery may take a fewminutes to several hours. Oxygen debt (Recovery Oxygen Uptake) refers to added oxygen that is taken into the body after exercise. This oxygen is used to “pay back” or restore metabolic conditions to resting levels. This is achieved in 3 ways:
i) Conversion of lactic acid back to glycogen stores in the liver. ii) Resynthesis of creatine phosphate and ATP in muscle fibres iii) Replacement of oxygen removed from myoglobin
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