The Effect of Isolated and Combined Application of Menthol and Carbohydrate Mouth Rinses on 40 km Time Trial Performance, Physiological and Perceptual Measures in the Heat

Abstract

The current study compared mouth swills containing carbohydrate (CHO), menthol (MEN) or a combination (BOTH) on 40 km cycling time trial (TT) performance in the heat (32 °C, 40% humidity, 1000 W radiant load) and investigates associated physiological (rectal temperature (Trec), heart rate (HR)) and subjective measures (thermal comfort (TC), thermal sensation (TS), thirst, oral cooling (OC) and RPE (legs and lungs)). Eight recreationally trained male cyclists (32 ± 9 y; height: 180.9 ± 7.0 cm; weight: 76.3 ± 10.4 kg) completed familiarisation and three experimental trials, swilling either MEN, CHO or BOTH at 10 km intervals (5, 15, 25, 35 km). The 40 km TT performance did not differ significantly between conditions (F2,14 = 0.343; p = 0.715; η2 = 0.047), yet post-hoc testing indicated small differences between MEN and CHO (d = 0.225) and MEN and BOTH (d = 0.275). Subjective measures (TC, TS, RPE) were significantly affected by distance but showed no significant differences between solutions. Within-subject analysis found significant interactions between solution and location upon OC intensity (F28,196 = 2.577; p < 0.001; η2 = 0.269). While solutions containing MEN resulted in a greater sensation of OC, solutions containing CHO experienced small improvements in TT performance. Stimulation of central CHO pathways during self-paced cycling TT in the heat may be of more importance to performance than perceptual cooling interventions. However, no detrimental effects are seen when interventions are combined.

Menthol Mouth Rinsing Maintains Relative Power Production during Three-Minute Maximal Cycling Performance in the Heat Compared to Cold Water and Placebo Rinsing

“…Results showed no significant differences between beverages with all perceptual measures increasing over time. In a longer duration time trial over 40 km when MEN rinsing was compared to carbohydrate (CHO) or a MEN+ CHO rinse, similar findings were observed [ 35 ]. Menthol solutions did induce elevated localised sensations of oral cooling, but given extended exercise duration it was thought that glycogen reduction was a more deleterious signal than alterations in thermal perception as a result of exercise associated heat storage [ 35 ].…”

“…In a longer duration time trial over 40 km when MEN rinsing was compared to carbohydrate (CHO) or a MEN+ CHO rinse, similar findings were observed [ 35 ]. Menthol solutions did induce elevated localised sensations of oral cooling, but given extended exercise duration it was thought that glycogen reduction was a more deleterious signal than alterations in thermal perception as a result of exercise associated heat storage [ 35 ]. Gavel et al [ 16 ], state that several previous studies have seen lower thermal perceptual measures however, there have been an equal number of studies reviewed that have observed no change at all, especially with increased exercise intensity.…”

“…MEN did not significantly modify participants’ ventilation throughout the maximal test compared to WAT or PLA, but menthol has been postulated to reduce the effort of breathing [ 5 ], suggesting that if exercise were performed in domains of lesser intensity or was paced differently, alternate ventilatory responses may have been observed independent of other physiological factors. For instance, core temperature has been seen to increase at a steady rate throughout endurance trials, in proportion to either the work performed or the heat load experienced by the athlete (e.g., [ 35 ]). The outcome of aerobic exercise in the heat is individuals becoming fatigued more quickly, they have a decrease in cardiac output, higher glycogen use, higher core temperature, increased heart rate and increased rate of ventilation [ 36 , 37 , 64 ].…”

“…A further pertinent extension of the present work, which would incorporate elements of pacing and other applied and mechanistic factors would be to administer menthol to athletes who experience significant drafting effects e.g., as part of a team pursuit. Airflow appears critical in one’s experience of oropharyngeal sensations of cool and therefore menthol [ 35 , 62 ], thus if one were experiencing a significant drafting effect i.e., a reduction in wind resistance [ 77 , 78 ], the efficacy of menthol administration may be blunted but will still likely depend on other factors such as athlete preference and habituation to menthol and mentholated products, and TRPM8 receptor density [ 79 , 80 , 81 ].…”

“…Considering current evidence, a recent consensus statement found insufficient research regarding the effect of menthol on either intermittent or explosive exercise, with literature exploring the effect of menthol on short duration high-intensity bouts of exercise also scarce [ 1 , 34 ]. Previously, longer durations have been examined, with participants completing trials to exhaustion or extended time trials that rely on aerobic energy provision [ 5 , 14 , 35 ]. When exercising in the heat, these durations permit a sufficient ‘hyperthermic dose’, with T core significantly elevated as a correlate of exercise duration.…”