Mid Sweden University

INTRODUCTION: Winter endurance athletes such as cross-country skiers have an increased prevalence of asthma (Eriksson et al., 2018, Scand J Med Sci Sport). Heat-and-moisture exchangers (HMEs) such as masks and mouthpieces with a filter to facilitate warming and humidification of inspired air may protect the airways from injury during exercise in cold, dry climates. However, if there is evidence of impaired exercise capacity, athletes will likely avoid using such devices. The aim of this study was to investigate the influence of an HME mask (AirTrim Sport, Vapro AB, Västerås, Sweden) on heart rate (HR), breathing rate (BR), muscle oxygenation (SmO2) and perceived exertion at fixed submaximal workloads. METHODS: 23 active, healthy participants without asthma aged 31 ± 8 years (15 men, 8 women) performed a familiarisation test followed by two experimental trials with and without HME in a randomised, crossover design. All tests were performed at a 4% gradient on a motorised treadmill and consisted of a submaximal incremental warm-up followed by a maximal, self-paced 4-min running time trial (TT). During the familiarisation test, participants wore a portable oxygen uptake system (Metamax 3B, Cortex Biophysik, Leipzig, Germany) with the TT used to derive VO2peak. Submaximal VO2 was interpolated to derive speeds estimated to elicit 65, 70, 75 and 90% of VO2peak. In two subsequent trials performed in a climate chamber at -15 degrees Celsius, participants ran for 5 min at speeds equivalent to 65, 70 and 75% VO2peak, 3 min at 90% and 12 min at 65% VO2peak. HR and BR were monitored via a chest harness (LifeMonitor, Equivital, Cambridge, UK); mean SmO2 from the right and left quadriceps was derived using near infra-red sensors (MOXY, Fortiori Design, Hutchinson MN, USA). Data were summarised as 1 min epochs, taken from 90 to 30 s before the end of each stage. Borg 6-20 rating of perceived exertion (RPE) was reported 1 min before the end of each stage. Data were analysed using repeated-measures ANOVA and linear mixed models. The study was approved by the regional ethical review board and conducted according to the Declaration of Helsinki. RESULTS: HR was 2.5 beats/min higher during the HME trial (95% CI: 0.3 - 4.6, p=.03). In the male participants only, SmO2 was lower during the HME trial than control (-2.3%, 95% CI: -0.1 - -4.5, p=.04). The female participants reported higher RPE (0.65 AU) during the HME trial (p=.009). There was no difference in BR between the HME and control trials. CONCLUSION: Despite potentially small increases in dead space and resistance to breathing, an HME did not affect BR during submaximal exercise in -15 degrees C. However, higher HR during exercise with an HME, as well as lower SmO2 in the male participants and higher RPE in the female participants, indicates slightly higher physiological stress during steady-state exercise with an HME. It would therefore be relevant to investigate whether an HME affects maximal exercise capacity in sub-zero temperatures.