This study examined the effect of glycogen supercompensation on glycogen breakdown, muscle and blood lactate accumulation, blood-pH, and performance during short-term high-intensity exercise. Young healthy volunteers performed two supramaximal (125% of VO2max) exercise tests on a bicycle ergometer, either for 1 min 45 s (protocol 1; N = 18) or to exhaustion (protocol 2; N = 14). The exercise tests were preceded by either 5 d on a controlled normal (N) diet, or by 2 d of glycogen-depleting exercise accompanied by the normal diet followed by 3 d on a carbohydrate-rich (CHR) diet. In protocol 1, preexercise muscle glycogen concentrations were 364 +/- 23 and 568 +/- 35 mumol.g-1 d.w. in the N and CHR condition, respectively (P < 0.05). During the exertion, glycogen concentration in the M. quadriceps decreased to the same extent in both groups. Accordingly, the exercise-induced increases in muscle and blood-lactate, and the fall in blood-pH were similar during N and CHR. In protocol 2, time to exhaustion was identical for N and CHR. It is concluded that during short-term intense exercise during which muscle glycogen availability exceeds glycogen demand, rate of glycogen breakdown, lactate accumulation, and performance are regulated irrespective of the preexercise muscle glycogen level.