Optimising strategies to enhance endurance running performance under hot and humid conditions

The purpose of this project was to optimise preparation for endurance runners competing in a hot environment. A multidisciplinary approach was adopted, investigating acute and chronic interventions to identify the most effective preparation. Considerable, recent, evidence documents the ergogenic benefits of both chronic strategies such as heat acclimation and acute strategies, such as precooling for endurance performance in the heat.

However, many strategies are not practical for routine use during competition and there is a dearth of direct comparisons between different strategies. Moreover, competition strategies that seek to alleviate the deleterious effects of hyperthermia on endurance performance, habitually adopt a uni-dimensional approach with athletes advised to either precool, or undertake heat acclimation. This dichotomous practice pervades despite a relative dearth of direct comparisons between acute and chronic strategies to assess the more effective approach.

Therefore, through a series of studies, this project sought to understand the physiological responses to prominent thermal and non-thermal interventions during endurance exercise in the heat and inform athlete preparation. The novel use of the determinants of endurance performance model facilitated simultaneous investigation of the efficacy of interventions as well as the physiological mechanisms through which interventions influence performance. Finally, a retrospective analysis was conducted to identify the relationship between physiological markers and endurance running in the heat.

The objectives of this project were to:
> investigate how acute and chronic strategies, both individually and collectively, mediate the decline in endurance performance in the heat, in order to optimise competition preparation for an endurance runner competing in the heat
> develop a better understanding of the determinants of endurance performance in the heat
> determine whether traditional physiological markers still strongly predict performance in the heat.

External precooling techniques afford a greater alleviation of physiological and perceived thermal strain than internal precooling, as shown in Figures 1 and 2, respectively.

The benefits of another acute intervention, ischaemic preconditioning, do not transfer to exercise in the heat. Five days of heat acclimation training results in large increases in VO2max, blood lactate thresholds and perceived thermal strain, ultimately improving endurance performance to a greater degree than precooling. Combining heat acclimation and precooling does not appear to elicit an additive benefit, possibly because of nativity concerning optimal pacing following combined interventions.

Coaches and athletes are therefore encouraged to prioritise heat acclimation strategies wherever possible, but precooling remains beneficial when heat acclimation is not logistically or financially possible. Finally, the traditional markers of endurance physiology, VO2max, running economy and blood lactate thresholds, do not appear to predict performance in the heat as strongly as has previously been reported in cool conditions.

James, C.A., Hayes, M., Willmott, A.G.B., Gibson, O.R., Flouris, A.D., Schlader, Z.J. and Maxwell, N.S. Defining the determinants of endurance performance in the heat (in preparation)

James, C, Richardson, A., Watt, P., Gibson, O., Willmott, A. & Maxwell, N. (2016) Short-term heat acclimation improves the determinants of endurance performance and 5,000m running performance in the heat. Applied Physiology, Nutrition, and Metabolism, DOI: 10.1139/apnm-2016-0349.

James, C, Richardson, A., Watt, P., Gibson, O., Willmott, A. & Maxwell, N. Short term heat acclimation and precooling, independently and in combination, improve 5km time trial performance in the heat. Journal of Strength and Conditioning Research, (Under Review)

James, C.A., Willmott, A.G., Richardson, A.J., Watt, P.W. and Maxwell, N.S. (2016). Ischaemic preconditioning does not alter the determinants of endurance running performance in the heat. European Journal of Applied Physiology, 116(9):1735-1745.

James, C, Richardson, A., Watt, P., Gibson, O., & Maxwell, N. (2015) Physiological responses to incremental exercise following internal and external precooling. Scandinavian Journal of Medicine & Science in Sports, 25 (Suppl. 1): 190-199.

James, C., Richardson, A., Watt, P., & Maxwell, N. (2014) Reliability and validity of skin temperature measurement by telemetry thermistors and a thermal camera during exercise in the heat. Journal of Thermal Biology, 45, 141–149.

Slushies vs frozen underwear for hot weather workouts, New York Times, 27 May 2015