On muscle strength and the threshold of anaerobic work

Summary 1.When subjects are exercised on a bicycle ergometer at 80% of aerobic power, there is a progressive increase of arterial lactate for 5–15 min, and in subjects of poor cardio-respiratory fitness the terminal level may approach that found in maximal exercise. 2. 5 min of sub-maximal exercise at 70 or 80% of aerobic power leads to a substantial accumulation of arterial lactate (38.3±8.9, 47.6±8.9 mg/100 ml) respectively. 3. The arterial lactate levels following 5 min of sub-maximal exercise are negatively correlated with the strength of hand-grip and knee extension. 4. Evidence is presented that lactate accumulation represents an effect of muscle contraction on oxygen supply rather than an overloading of intracellular biochemical mechanisms. 5. Perceived exertion in sub-maximal exercise is related to pulse rate as previously described byBorg. However, it is not related to arterial lactate or sensitivity to thermal stress.