Determination of human skeletal muscle buffer value by homogenate technique: methods of measurement.

The human muscle buffer value (beta) is most frequently determined by either fixed acid titration of a homogenate ["in vitro" beta (beta vit)] or measurement of the change in lactate concentration (delta [La]) relative to the change in muscle homogenate pH after high-intensity exercise ["in vitro" beta = - delta [La]/delta pH (beta viv)]. We sought to compare beta viv, determined after isometric and dynamic exercise to exhaustion (approximately 60 s), with beta vit. Resting (R) and postexercise (E) biopsy samples were taken from vastus lateralis muscles of 43 human volunteers. Freeze-dried muscle was homogenized (30 mg/ml) in NaF (0.01 M) for the measurement of muscle pH (R and E). beta vit was determined by HCl (0.01 M) titration of the homogenate over the pH range 7.1-6.5. Muscle lactate was measured by enzymatic assay. There was no significant difference between beta viv determined after isometric (n = 35) or dynamic (n = 8) exercise to fatigue (170 vs. 168 mmol H+.kg dry muscle mass-1.pH-1, respectively; P > 0.05). Values for beta vit in the corresponding muscle samples (R) were approximately 7-8% lower (156 +/- 25 vs. 157 +/- 18 mmol H+.kg dry muscle mass-1.pH-1, respectively). There was no significant difference (P = 0.278) between the measured decline in muscle homogenate pH after exercise and the reduction in pH predicted from beta vit and delta [La], indirectly confirming the lack of any significant difference between beta viv and beta vit.(ABSTRACT TRUNCATED AT 250 WORDS)