How Cool is That? The Effects of Menthol Mouth Rinsing on Exercise Capacity and Performance: A Systematic Review and Meta-analysis

Abstract

Background Menthol (MEN) mouth rinsing (MR) has gained considerable interest in the athletic population for exercise performance; however, the overall magnitude of effect is unknown. Objective The aim of this systematic review and meta-analysis was to determine the efficacy of menthol MEN MR and the impact it has on exercise capacity and performance. Methods Three databases were searched with articles screened according to the inclusion/exclusion criteria. Three-level meta-analyses were used to investigate the overall efficacy of MEN MR and the impact it has on exercise capacity and performance. Meta-regressions were then performed with 1) mean VO2peak, 2) MEN swilling duration; 3) the MEN concentration of MR solution, 4) the number of executed swills throughout a single experiment, 5) the use of flavoured sweetened, non-caloric, or non-flavoured neutral solutions as controls, 6) mean environmental temperature at the time of exercise tests, and 7) exercise type as fixed factors to evaluate their influence on the effects of MEN MR. Results Ten MEN MR studies included sufficient information pertaining to MEN MR and exercise performance and capacity. MR with MEN resulted in no significant change in capacity and performance (SMD = 0.12; 95% CI − 0.08, 0.31; p = 0.23, n = 1, tau21 < 0.0001, tau22 = < 0.0001, I2 = 0%). No significant influence was detected in meta-regressions for VO2peak, (estimate: 0.03; df = 8; 95% CI − 0.03, 0.09; p = 0.27), swilling duration (5 vs. 10 s: 0.00; df = 16; 95% CI − 0.41, 0.41; p = 1.0), MEN concentration (low [0.01%] vs. high [0.1%]: − 0.08; df = 15; 95% CI − 0.49, 0.32; p = 0.67), number of swills (estimate: 0.02; df = 13; 95% CI − 0.05, 0.09; p = 0.56), the use of flavoured sweetener or non-caloric as control (non-flavoured vs. flavoured: 0.12; df = 16; 95% CI − 0.30, 0.55; p = 0.55) or mean room temperature during exercise tests (estimate: 0.01; df = 16; 95% CI − 0.02, 0.04; p = 0.62). Conclusion MEN MR did not significantly improve overall exercise capacity and performance, though those involved in endurance exercise may see benefits.

The Effect of Menthol Mouth Rinsing and Fluid Temperature on Male Cycling Performance in Thermoneutral Conditions

“…This study demonstrated that there was not a significant difference in the cycling TT performance with a repeated MEN MR in thermoneutral conditions when MEN was combined with either CW or TNW. Although the results of this study are in contrast to research demonstrating the significant effect of MEN MR on cycling performance in hot conditions [6,11], the results are aligned with the one available paper investigating the effects of MEN MR in thermoneutral conditions [15] and a recent meta-analysis by Gavel et al [8] reported that there was no significant improvement in the vertical jump, isometric mid-thigh pull, or six-second sprint performance with the use of repeated MEN MR. In both the study by [15] and the current one, it is plausible that the overall stress of the thermoneutral environment and the MR stimulus (despite repeated MEN MR) may not have been strong enough to elicit a central effect leading to increased motor output and an acute increase in exercise performance [3].…”

“…This study demonstrated no performance improvement with the use of a MEN MR on strength and power exercises [15]. The effect of a MEN MR on endurance performance in a thermoneutral environment remains unknown [8]. Moreover, the synergistic effect of MEN MR and fluid temperature is also unknown.…”

“…Previous research has demonstrated that during moderate to high intensity endurance exercise (>20 min) in a hot environment, a MEN MR can elicit a cooling sensation atten-uating the perception of fatigue, leading to increases in ventilatory drive, enabling an individual to work harder to complete an exercise task [2,[4][5][6][7]. While it has been documented that MEN has an effect on performance when applied topically and consumed [6], an area gaining great interest is MEN mouth rinsing (MR) [6,8]. Some published research has demonstrated the efficacy of MEN MR at different concentrations, frequencies, and temperatures when used during endurance tasks in hot environments (≥30 • C) [4,[6][7][8][9][10].…”

“…While it has been documented that MEN has an effect on performance when applied topically and consumed [6], an area gaining great interest is MEN mouth rinsing (MR) [6,8]. Some published research has demonstrated the efficacy of MEN MR at different concentrations, frequencies, and temperatures when used during endurance tasks in hot environments (≥30 • C) [4,[6][7][8][9][10]. With oral swilling, MEN appears to lower the thermal sensation and decrease the ratings of perceived exertion (RPE) for a given workload [6,11,12], providing a perceptual "cooling" benefit, which has been shown to improve performance during prolonged exercise in the heat [6,[9][10][11].…”

“…While MEN MR has been studied during exercise in hot conditions, less is known about the effect MEN MR may have during endurance exercise in a thermoneutral (19)(20)(21)(22) • C) environment [8,13,14]. To date, there is only one known study that has investigated the effects of repeated MEN MR on exercise performance in thermoneutral conditions [8,15].…”