Skeletal muscle buffer value, fibre type distribution and high intensity exercise performance in man.

ABSTRACT

Interrelationships between quadriceps femoris muscle buffer value (beta), fibre type distribution, and lactate concentration and pH following short-term high intensity exercise were examined in eighteen young healthy human volunteers. Muscle biopsy samples were taken from the lateral portion of the quadriceps femoris muscle at rest and after fatiguing dynamic or isometric exercise. Isometric exercise required the maintenance of 60% quadriceps maximum voluntary contraction, and dynamic exercise, the performance of a modified Wingate Test. The muscle buffer value displayed a positive, but non-significant correlation with the 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 muscle pH during intensive exercise but did not permit the accumulation of a higher muscle lactate concentration or allow for an enhanced dynamic or isometric exercise performance. A superior performance during dynamic exercise was associated with a high concentration of muscle lactate 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, where there was a tendency for an enhanced performance to be associated with a low muscle lactate and high muscle pH post-exercise. No significant relationship between the relative type II fibre area and isometric performance capacity could be established. It was concluded that the muscle buffer value is not a major limiting factor to the performance of high intensity exercise, suggesting that the involvement of intramuscular 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, where a high value provides for a superior dynamic but inferior isometric exercise performance.