SKELETAL-MUSCLE BUFFER VALUE, FIBER-TYPE DISTRIBUTION AND HIGH-INTENSITY EXERCISE PERFORMANCE IN MAN

Interrelationships between quadriceps femoris muscle buffer value (bet a), fibre type distribution, and lactate concentration and pH followin g short-term high intensity exercise were examined in eighteen young h ealthy human volunteers. Muscle biopsy samples were taken from the lat eral portion of the quadriceps femoris muscle at rest and after fatigu ing dynamic or isometric exercise. Isometric exercise required the mai ntenance of 60 % quadriceps maximum voluntary contraction, and dynamic exercise, the performance of a modified Wingate Test. The muscle buff er value displayed a positive, but non-significant correlation with th e relative area of the muscle occupied by type II fibres (r = 0.42, P = 0.09). An elevated beta was associated with a lesser decrement in mu scle pH during intensive exercise but did not permit the accumulation of a higher muscle lactate concentration or allow for an enhanced dyna mic or isometric exercise performance. A superior performance during d ynamic exercise was associated with a high concentration of muscle lac tate and a low muscle pH post-exercise; in turn, each of these factors was positively dependent on the relative area of the muscle occupied by type II fibres. The converse was found for isometric exercise, wher e there was a tendency for an enhanced performance to be associated wi th a low muscle lactate and high muscle PH post-exercise. No significa nt relationship between the relative type II fibre area and isometric performance capacity could be established. It was concluded that the m uscle buffer value is not a major limiting factor to the performance o f high intensity exercise, suggesting that the involvement of intramus cular acidosis in the development of fatigue may be indirect, The most important determinant of high intensity exercise capacity appears to be the proportional area of the muscle occupied by type II fibres, whe re a high value provides for a superior dynamic but inferior isometric exercise performance.