The blood lactate threshold refers to:
a. the work rate or oxygen uptake where there is a systematic rise in aerobic metabolism
b. the work rate or oxygen uptake where there is a systematic rise in blood levels of lactic acid
c. the work rate or oxygen uptake where there is a systematic decrease in blood levels of lactic acid
d. all of the above are correct

b. the work rate or oxygen uptake where there is a systematic rise in blood levels of lactic acid

Explanation:

Currently, the anaerobic threshold is one of the most commonly used parameters, both as an indicator of physical performance capacity and training prescription, and there is evidence that performance in continuous and prolonged exercises correlates better with the anaerobic threshold than with maximum aerobic power. The anaerobic threshold can be understood as the point of imbalance between lactate production and removal (blood lactate threshold).