Lactate in blood, mixed skeletal muscle, and FT or ST fibres during cycle exercise in man

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Abstract
The relationship between muscle and blood lactate levels during progressively step-wise incrementing cycle exercise was investigated in 10 male subjects. Steps between power outputs during exercise was investigated in 10 male subjects. Steps between power outputs during exercise were 50 W and each stage, from loadless pedaling until voluntary exhaustion, lasted 4 min. Blood samples and biopsies (m [musculus] vatus lateralis) were taken for lactate determination at each power output beginning with the exercise intensity perceived by the subject as being rather moderate. The ratio muscle:blood lactate was greater than 1 at all power outputs and increased most markedly at the power output closest to that eliciting 4 mmol .times. 1-1 blood lactate (WOBLA). At WOBLA, blood lactate was positively correlated to muscle lactate concentrations which covaried widely among subjects (mean 8.3, range 4.5-14.4 mmol .times. kg-1 wet wt). Muscle fibers from the WOBLA biopsy in 6 subjects were dissected out and identified as fast twitch (FT) or slow twitch (ST). No significant difference in lactate concentration was observed between pools of FT or ST fibers.