The Effects of Caffeine Supplementation on Physiological Responses to Submaximal Exercise in Endurance-Trained Men

Abstract

ObjectivesThe aim of this study was to evaluate the effects of caffeine on physiological responses to submaximal exercise, with a focus on blood lactate concentration ([BLa]).MethodsUsing a randomised, single-blind, crossover design; 16 endurance-trained, male cyclists (age: 38 ± 8 years; height: 1.80 ± 0.05 m; body mass: 76.6 ± 7.8 kg; : 4.3 ± 0.6 L∙min-1) completed four trials on an electromagnetically-braked cycle ergometer. Each trial consisted of a six-stage incremental test (3 minute stages) followed by 30 minutes of passive recovery. One hour before trials 2–4, participants ingested a capsule containing 5 mg∙kg-1 of either caffeine or placebo (maltodextrin). Trials 2 and 3 were designed to evaluate the effects of caffeine on various physiological responses during exercise and recovery. In contrast, Trial 4 was designed to evaluate the effects of caffeine on [BLa] during passive recovery from an end-exercise concentration of 4 mmol∙L-1.ResultsRelative to placebo, caffeine increased [BLa] during exercise, independent of exercise intensity (mean difference: 0.33 ± 0.41 mmol∙L-1; 95% likely range: 0.11 to 0.55 mmol∙L-1), but did not affect the time-course of [BLa] during recovery (p = 0.604). Caffeine reduced ratings of perceived exertion (mean difference: 0.5 ± 0.7; 95% likely range: 0.1 to 0.9) and heart rate (mean difference: 3.6 ± 4.2 b∙min-1; 95% likely range: 1.3 to 5.8 b∙min-1) during exercise, with the effect on the latter dissipating as exercise intensity increased. Supplement × exercise intensity interactions were observed for respiratory exchange ratio (p = 0.004) and minute ventilation (p = 0.034).ConclusionsThe results of the present study illustrate the clear, though often subtle, effects of caffeine on physiological responses to submaximal exercise. Researchers should be aware of these responses, particularly when evaluating the physiological effects of various experimental interventions.

Caffeine, exercise physiology, and time-trial performance: no effect ofADORA2AorCYP1A2genotypes

“…Nevertheless, the mechanisms responsible, and the short-and long-term associated health risks are, at present, unclear (De Giuseppe et al 2019). Similarly, the effects of caffeine on heart rate agree with those previously reported (Fredholm et al 1999;Glaister et al 2016), in that caffeine typically reduces resting heart rate by ~ 3 b•min -1 , with the effect dissipating as exercise intensity increases (Glaister et al 2016). Moreover, caffeine typically increases heart rate during time-trials due to the corresponding caffeine-induced increase in time-trial intensity (Glaister and Moir 2019).…”

“…Although most of the physiological responses to caffeine measured in the present study were the same as reported previously, there were some anomalous findings. The effect of caffeine on RER is particularly confusing in that while the increase at rest fits with previous reports (Glaister et al 2016), the submaximal and time-trial responses do not. In a recent meta-analysis, Glaister and Gissane (2018) found no effect of caffeine on RER during submaximal exercise at 60 -85% V O 2max; indeed, the tendency was for RER to be reduced with caffeine, though there was considerable between-study heterogeneity.…”

“…Although differences in mean V O 2 between caffeine and placebo in the present study were reflective of the typical response in time trials (Glaister and Moir 2019), it is difficult to explain why no significant difference was observed (possibly a Type II error). In contrast, the absence of any significant effect of caffeine on V O2 at rest and during submaximal exercise is in line with previous findings (Glaister et al 2016;Glaister and Gissane 2018), but conflicts with the suggestion that caffeine can increase metabolic rate. Then again, as suggested by Fredholm et al (1999), as a way to explain a caffeine-induced increase in cerebral energy metabolism in the absence of any change in V O2, it is possible that caffeine increases metabolic rate in the absence of a change in V O2 via an increase in anaerobic glycolysis, as supported by the aforementioned increase in [BLa] (during exercise at least).…”

“…In a recent meta-analysis, Glaister and Gissane (2018) found no effect of caffeine on RER during submaximal exercise at 60 -85% V O 2max; indeed, the tendency was for RER to be reduced with caffeine, though there was considerable between-study heterogeneity. Similarly, research investigating the effects of caffeine on RER during incremental exercise shows a supplement × intensity interaction, with RER either reducing significantly (Stadheim et al 2013) or tending to be reduced (Glaister et al 2016) as exercise intensity increases. While the pattern of the submaximal RER response in the present study was suggestive of a convergence between caffeine and placebo trials as exercise intensity increased, particularly in the CYP1A2 AC/CC genotypes, there was no suggestion of any reduction in RER with increasing intensity.…”

Effects of Caffeine on Time Trial Performance and Associated Physiological Responses: A Meta-Analysis

“…effect between caffeine and exercise intensity on RER, with values reducing, relative to placebo, as exercise intensity increases. 48,73 Although the mechanisms to explain that response are unclear, 6 it is possible that the absence of an effect of caffeine on RER during the time trials is due to caffeine counteracting the increase in RER that would be expected after an increase in exercise intensity.…”