Onset of blood lactate accumulation and enzyme activities in m. vastus lateralis in man.

In an earlier study, we reported close relationships between marathon running performance and the running velocity (V) at which the "onset of blood lactate accumulation" (VOBLA) occurs in a group of marathon runners. Using biopsy material from the m. vastus lateralis of the same subjects (n = 19), we have evaluated the relationship of VOBLA to different muscle enzyme activities together with muscle fiber composition and capillary density in the present study. The activities of lactate dehydrogenase (LDH EC 1.1.1.27), phosphofructokinase (PFK EC 2.7.1.11), and citrate synthase (CS EC 4.1.3.7) were determined. VOBLA was negatively correlated to LDH (r = -0.54) and PFK/CS (r = -0.68). Using multiple regression analysis, the PFK/CS ratio together with the capillary density accounted for 61% of the variation in VOBLA. Absolute training kilometrage was the most significant variable measured and accounted for 77% of the variation in VOBLA. Subjects were divided into elite runners (n = 6) and nonelite runners (n = 13) for an additional analysis of the relationship between VOBLA and the ratios of PFK/CS or LDH/CS. Significant relationships between VOBLA and the ratios were observed only in the nonelite runners (r = -0.77 and -0.66, respectively). The vertical distances between the regression lines for these two subject groups could not be explained only on the basis of the enzyme activity ratios. A greater adaptation to fat combustion in the elite runners might explain the disproportionally high VOBLA in relation to the PFK/CS or LDH/CS activity ratios.