The release of interleukin (IL)-6 from contracting skeletal muscle is thought to contribute to some of the health benefits bestowed by exercise. This IL-6 response appears proportional to exercise volume and to lactate production. Unfortunately, high volumes of exercise are not feasible for all people. Caffeine augments the magnitude of increase in circulating IL-6 in response to high-intensity and long-duration exercise. Caffeine also increases circulating concentrations of lactate during exercise. We hypothesized that caffeine, ingested prior to short-duration, moderate-intensity exercise, would lead to greater circulating concentrations of lactate and IL-6 in a study population comprising both males and females.
20 healthy adults (10 males and 10 females, aged 25 ± 7 years, (mean ± SD)) completed 30-minutes of moderate-intensity cycle ergometer exercise, at an intensity corresponding to 60% peak oxygen uptake, after ingesting either caffeine (6 mg/kg) or placebo. Arterialized-venous blood was collected throughout each of the exercise sessions.
Compared with placebo, caffeine increased circulating concentrations of lactate at the end of exercise (5.12 ± 3.67 vs. 6.45 ± 4.40 mmol/L, P < 0.001) and following 30-minutes of inactive recovery (1.83 ± 1.59 vs. 2.32 ± 2.09 mmol/L, P = 0.006). Circulating IL-6 concentrations were greatest following 30-minutes of inactive recovery (P < 0.001) and higher with caffeine (2.88 ± 2.05 vs. 4.18 ± 2.97, pg/mL, P < 0.001). Secondary analysis indicated sex differences; caffeine increased the IL-6 response to exercise in males (P = 0.035) but not females (P = 0.358).
In response to moderate-intensity exercise, caffeine evoked greater circulating lactate concentrations in males and females but only increased the IL-6 response to exercise in males. These novel findings suggest that for males unwilling or unable to perform high-intensity and/or long-duration exercise, caffeine may augment the health benefits of relatively short, moderate-intensity exercise.