Abstract
Background: Heat strain is a large limiting factor that athletes experience when carrying out exercise in hot environments. As many sporting events are carried out in these environments this can be problematic as it could mean the difference between winning and losing. Due to this, there has been growing interest into research on the effects of L-menthol on exercise in the heat as its natural cooling properties have the potential to impact performance. To date, it has been seen that menthol can have positive effects on endurance exercise performance however there is no conclusive insight into its use in short term high-intensity exercise.
Objective: To evaluate the use of a 25 mL 0.1% L-menthol mouth swill as an ergogenic aid (total distance covered, distance per minute, sprint distance and high metabolic load distance) for elite rugby union players carrying out high-intensity exercise in the heat.
Design: A total of 30 elite male rugby union players were recruited for participation in this randomised crossover study. Players were fitted with Global Positioning Systems (GPS) for the duration of the testing which consisted of a ‘warm up’ prior to a training session containing three blocks of three-minute high-intensity rugby specific conditioning. Between these blocks, players were provided with either 25mL of 0.1% L-menthol or water control to swill for 10 seconds before spitting out. Participants then reported their thermal sensation before beginning the next block.
Results: Due to injuries in two participants, and GPS faults in a further two, this study analysed data from 26 remaining participants (age: 24.7 ± 3.0 years, body mass: 107.2 ± 12.9 kg). Distance per minute was unchanged by the menthol intervention when compared to the control with standardised differences of -0.099 (p=0.36) and -0.073 (p=0.38) being observed in test 1 and 2 respectively. There were also no significant differences observed during any of ii the training blocks in High Metabolic Load Distance (p=0.08, p=0.32, p=0.50 and p=0.34) or sprint distance (p=0.38, p=0.36, p=0.42 and p=0.47). There were no significant thermal sensation differences between menthol and control interventions during the pre-test (p=0.73), test 1 (p=0.31) and test 2 (p=0.72) stages; however, thermal sensation was significantly lower following the menthol intervention during the posttest block when compared to the control group (p=0.04).
Conclusion: The results from this study suggest that a 0.1% L-menthol mouth swill does not impart performance benefits during high-intensity exercise in the heat. As previous literature has reported benefits in endurance exercise it is probable that exercise intensity plays a role in the effectiveness of menthol. Despite this, more research should be carried out investigating menthol use in these environments as this study failed to see thermal sensation changes which may have impacted the results. Therefore, future research should first focus on achieving thermal sensation changes to determine if this is essential in gaining performance benefits from menthol interventions in high-intensity exercise in the heat.