Jacobs, I. (1983). Blood lactate and the evaluation of endurance fitness. SPORTS, W-2, 6 pp.

A German study (Hollman, Rost, Liesen, Dufaux, Heck, & Mader, 1981) showed that endurance training at a running speed which elicited a blood lactic acid concentration of 4 mM caused a greater improvement in endurance performance than did training at a higher intensity which elicited 7-9 mM. This finding does not support the old axiom that the "harder" one trains, the greater will be the improvement. There are numerous studies which suggest that exercise corresponding to a 4 mM level of lactic acid accumulation, or close to it, is optimal in terms of the stimulus for aerobic adaptation in the muscle cell, and that this intensity reflects the highest exercise intensity at which most of the energy for muscular contraction is still derived from aerobic metabolism.

The measurement of heart rate during submaximal exercise is a popular means of estimating VO2max. However, such estimates have been reported to result in erroneous evaluations, sometimes over- or underestimating VO2max by as much as 15 to 20 percent, a value that is greater than can usually be expected to result from training. Thus, because of this inaccuracy heart-rate-based estimates of VO2max are of little value to a coach.

Reference: Hollman, W., Rost, R., Liesen, H., Dufaux, B., Heck, H., & Mader, A. (1981). Assessment of different forms of physical activity with respect to preventive and rehabilitative cardiology. International Sports Medicine, 2, 67-80.

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