The effect of active recovery at a decreasing % of MVC following intense muscular exercise on intramuscular pH was investigated in vivo using 31P-MRS. Seven healthy men participated, and their right wrist flexor muscle group was examined. The subjects were asked to flex their right wrist at 60 % of the maximum voluntary contraction (MVC) every 2 s until the intracellular pH in the wrist flexor muscle decreased to 6.4. After the exercise period, the subjects underwent active or passive recovery for 10 min. For the active recovery (AR), the subject was asked to continue exercising at a decreasing % of MVC, decreasing from 25 to 5 % MVC every two min during AR. 31P-MR-spectra were obtained throughout the experiments, and from the spectra the intracellular pH (pHi) was calculated as an indicator of intracellular events. AR data were compared to data collected during passive recovery (PR). During AR, the pHi increased immediately after the exercise period; whereas in that of PR, it did not recover within 5 minutes after exercise. The results suggested that mild exercise was an effective manoeuver to promote recovery from intramuscular metabolic acidosis.