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Meta-Analysis
. 2020 Aug 12;10(1):13636.
doi: 10.1038/s41598-020-70499-9.

Menthol can be safely applied to improve thermal perception during physical exercise: a meta-analysis of randomized controlled trials

Patrik Keringer  1 , Nelli Farkas  2   3 , Noemi Gede  2 , Peter Hegyi  2   4 , Zoltan Rumbus  1 , Zsolt Lohinai  5 , Margit Solymar  1 , Kasidid Ruksakiet  5   6 , Gabor Varga  6 , Andras Garami  7
Affiliations
Meta-Analysis

Menthol can be safely applied to improve thermal perception during physical exercise: a meta-analysis of randomized controlled trials

Patrik Keringer et al. Sci Rep. .

Abstract

Menthol is often used as a cold-mimicking substance to allegedly enhance performance during physical activity, however menthol-induced activation of cold-defence responses during exercise can intensify heat accumulation in the body. This meta-analysis aimed at studying the effects of menthol on thermal perception and thermophysiological homeostasis during exercise. PubMed, EMBASE, Cochrane Library, and Google Scholar databases were searched until May 2020. Menthol caused cooler thermal sensation by weighted mean difference (WMD) of - 1.65 (95% CI, - 2.96 to - 0.33) and tended to improve thermal comfort (WMD = 1.42; 95% CI, - 0.13 to 2.96) during physical exercise. However, there was no meaningful difference in sweat production (WMD = - 24.10 ml; 95% CI, - 139.59 to 91.39 ml), deep body temperature (WMD = 0.02 °C; 95% CI, - 0.11 to 0.15 °C), and heart rate (WMD = 2.67 bpm; 95% CI - 0.74 to 6.09 bpm) between the treatment groups. Menthol improved the performance time in certain subgroups, which are discussed. Our findings suggest that different factors, viz., external application, warmer environment, and higher body mass index can improve menthol's effects on endurance performance, however menthol does not compromise warmth-defence responses during exercise, thus it can be safely applied by athletes from the thermoregulation point of view.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Flowchart of study selection and inclusion.
Figure 2
Figure 2
Forest plot of the weighted mean differences (WMDs) showing the effect of menthol on thermal sensation during exercise. Here, and in Figs. 3, 4, 5, 6, 7, and 8, black circles represent the WMD for each study, while the left and right horizontal arms of the circles indicate the corresponding 95% confidence intervals (CI) for the WMD. The size of the grey box is proportional to the sample size; bigger box represents larger sample size, thus bigger relative weight of the study. The diamond represents the average WMD calculated from the WMDs of the individual studies. The left and right vertices of the diamond represent the 95% CI of the average WMD. The vertical dashed line is determined by the low and top vertices of the bottom diamond and indicates the value of the average WMD of all studies in the forest plot. A WMD lesser than 0 indicates that the thermal sensation value (intensity of cold sensation) is higher in menthol-treated group, whereas a WMD higher than 0 indicates that thermal sensation is higher in control group.
Figure 3
Figure 3
Forest plot of the weighted mean of differences (WMDs) for thermal comfort showing the effect of menthol during exercise.
Figure 4
Figure 4
Forest plot of the weighted mean of differences (WMDs) for power output showing the effect of menthol during exercise.
Figure 5
Figure 5
Forest plot of the weighted mean of differences (WMDs) for sweat production showing the effect of menthol during exercise.
Figure 6
Figure 6
Forest plot of the weighted mean of differences (WMDs) for deep body temperature showing the effect of menthol during exercise.
Figure 7
Figure 7
Forest plot of the weighted mean of differences (WMDs) for heart rate showing the effect of menthol during exercise.
Figure 8
Figure 8
Forest plot of the weighted mean of differences (WMDs) for performance time showing the effect of menthol in (a) time-trial (TT) and (b) time-to-exhaustion (TTE) tests of athletes with lower (< 23.5) and higher (> 23.5) body mass index (BMI). The diamonds in the panels represent the average WMD calculated from the WMDs of the individual studies in each subgroup (top and middle) or in all studies (bottom).
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