A 0.1% L-Menthol Mouth Swill in Elite Male Rugby Players Has Different Effects in Forwards and Backs

Abstract

Purpose: Menthol mouth swills can improve endurance performance in the heat, which is attributed to attenuations in nonthermally derived thermal sensation (TS) and perception of effort. However, research in elite team-sport athletes is absent. Therefore, this study investigated the performance and TS responses to a 0.1% menthol mouth rinse (MR) or placebo (PLA) among elite male rugby union players. Method: Twenty-seven (15 Forwards and 12 Backs) elite male Super Rugby players completed two 3-minute 15-a-side rugby-specific conditioning blocks, with MR or PLA provided at the start of training (baseline), at the start of each 3-minute block (swill 1 [S1] and swill 2 [S2]), and at the end of training (swill 3 [S3]). TS was assessed using the American Society of Heating, Refrigerating and Air-Conditioning Engineers 9-point Analog Sensation Scale after each swill and at baseline (preconditioning block). Acceptability was measured after baseline swill and S3 using a 5-question Likert scale. Physical performance was measured throughout training using global positioning system metrics. Results: MR attenuated TS from baseline to S1 (P = .003, SD = 1.01) and S2 (P = .002, SD = 1.09) in Forwards only, compared with PLA. Acceptability was higher only for Forwards in MR versus PLA at baseline (P = .003, SD = 1.3) and S3 (P = .004, SD = 0.75). MR had no effect on physical performance metrics (P > .05). Conclusion: MR attenuated the rise in TS with higher acceptability at S1 and S3 (in Forwards only) with no effect on selected physical performance metrics. Longer-duration exercise (eg, a match) in hot–humid conditions eliciting markedly increased body temperatures could theoretically allow favorable changes in TS to enhance performance—these postulations warrant experimental investigation.

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

“…Although not statistically significant, our results demonstrate a moderate effect and trend in higher mean power output in the MEN + CW trial from 45% of work completed to the end of the TT (Figure 2); however, with the large variability between participants in power output, the difference is statistically insignificant. This effect and trend align with published work on MEN MR demonstrating improved endurance performance in the latter stages of exercise in hot conditions [6,[9][10][11]15,28,29]. Limitations in study methodology, specifically, a lack of tight control in the training status (large SD in mean power output) may have blunted the statistical differences in the mean power output between MR conditions.…”

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

“…Whenever more than one datapoint was available for the same exercise test (i.e. repeated measure or time splits) [ 16 , 24 ], SMDs and variances were combined as described by [ 25 ]. Since a correlation between timepoints could not be obtained, an r value of 0.7 was always assumed.…”