Determination of human muscle pH in needle-biopsy specimens.

The homogenate technique for the determination of muscle pH (pHm) has been studied to assess the influence of delayed freezing and the composition and volume of the homogenizing medium on human muscle pH at rest and after exhaustive exercise. It was concluded that resting muscle samples must be frozen within 2 s to prevent falsely high pHm values. Muscle specimens used for lactate determinations (HLam), on the other hand, can be delayed in freezing for up to 30 s without altering the HLam content. A 30- to 40-s delay in biopsying the muscle after the cessation of exhaustive exercise does not appear to alter pHm or HLam values. Although the homogenate method does not provide information relative to the status of selected muscle fibers, it does offer a reliable sensitive measure of mean changes in the acidification of muscle with intense exercise.