The content of anserine and carnosine in the lateral portion of the quadriceps femoris muscle of 50 healthy, human subjects has been studied. Anserine was undetectable in all muscle samples examined. Muscle carnosine values for the group conformed to a normal distribution with a mean (SD) value of 20.0 (4.7) mmol.kg-1 of dry muscle mass. The concentration of carnosine was significantly higher in the muscle of male subjects (21.3, 4.2 mmol.kg-1 dry mass) than in females of a similar age and training status (17.5, 4.8 mmol.kg-1 dry mass) (P less than 0.005). The test-retest reliability of measures was determined on a subgroup of 17 subjects. No significant difference in mean carnosine concentration was found between the two trials [21.5 (4.0) and 22.0 (5.2) mmol.kg-1 dry muscle mass; P greater than 0.05]. The importance of carnosine as a physicochemical buffer within human muscle was examined by calculating its buffering ability over the physiological pH range. From the range of carnosine concentrations observed (7.2-30.7 mmol.kg-1 dry muscle mass), it was estimated that the dipeptide could buffer between 2.4 and 10.1 mmol H+.kg-1 dry mass over the physiological pH range 7.1-6.5, contributing, on average, approximately 7% to the total muscle buffering. This suggests that in humans, in contrast to many other species, carnosine is of only limited importance in preventing the reduction in pH observed during high intensity exercise.

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)

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Knowledge of variations in normal human thigh musculature is important for the interpretation of various clinical and biomedical investigations. In this study, cross-sections from whole thighs of 34 cadavers were analyzed qualitatively and morphometrically. Sections were cut from right and left limbs at three levels in the region often used for muscle biopsy. Measurements were made of limb circumferences and cross-sectional areas of the three vasti and of the femur, and of the extent of overlap and fusion between the vasti on the lateral aspect of the thigh. Limb circumference proved to be a good predictor of total cross-sectional area of the quadriceps muscle. Large individual variations were found for most measurements but especially for the amount of fusion between the muscle bellies of vastus lateralis and vastus intermedius. Significant differences were found for most variables between the three levels, but there were few differences between sides except for the cross-sectional area of vastus lateralis which was greater on the right at the most distal level. These variations in size and form of thigh musculature should be considered when interpreting data obtained from muscle biopsy, imaging, biomechanical, electromyographic, and functional studies of the human thigh. Review of the literature on variability of quadriceps muscle and its clinical relevance showed a diversity of approaches but insufficient definitive data suitable for interpreting functional outcomes in response to exercise or following surgery. Further work is suggested combining current anatomical datasets with advanced imaging techniques capable of determining muscle fiber orientation and fiber type composition, and including 3D reconstruction.

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