Independent or simultaneous lowering of core and skin temperature has no impact on self-paced intermittent running performance\xa0in hot conditions

G Thomas,T Cullen,B Duncan,M Davies,C Hetherton,N Gerrett

doi:10.1007/s00421-019-04173-y

Abstract

PurposeTo investigate the effects of lowering core (Tgi) and mean skin temperature (Tsk) concomitantly and independently on self-paced intermittent running in the heat.Methods10 males (30.5 ± 5.8 years, 73.2 ± 14.5 kg, 176.9 ± 8.0 cm, 56.2 ± 6.6 ml/kg/min) completed four randomised 46-min self-paced intermittent protocols on a non-motorised treadmill in 34.4 ± 1.4 °C, 36.3 ± 4.6% relative humidity. 30-min prior to exercise, participants were cooled via either ice slurry ingestion (INT); a cooling garment (EXT); mixed-cooling (ice slurry and cooling garment concurrently) (MIX); or no-cooling (CON).ResultsAt the end of pre-cooling and the start of exercise Tgi were lower during MIX (36.11 ± 1.3 °C) compared to CON (37.6 ± 0.5 °C) and EXT (36.9 ± 0.5 °C, p < 0.05). Throughout pre-cooling Tsk and thermal sensation were lower in MIX compared to CON and INT, but not EXT (p < 0.05). The reductions in thermophysiological responses diminished within 10–20 min of exercise. Despite lowering Tgi, Tsk, body temperature (Tb), and thermal sensation prior to exercise, the distances covered were similar (CON: 6.69 ± 1.08 km, INT: 6.96 ± 0.81 km, EXT: 6.76 ± 0.65 km, MIX 6.87 ± 0.70 km) (p > 0.05). Peak sprint speeds were also similar between conditions (CON: 25.6 ± 4.48 km/h, INT: 25.4 ± 3.6 km/h, EXT: 26.0 ± 4.94 km/h, MIX: 25.6 ± 3.58 km/h) (p > 0.05). Blood lactate, heart rate and RPE were similar between conditions (p > 0.05).ConclusionLowering Tgi and Tsk prior to self-paced intermittent exercise did not improve sprint, or submaximal running performance.

Highlights

Training and competition for many intermittent team sports take place in environmental conditions exceeding 30 °C, as seen during the 2014 Fédération Internationale de Football Association (FIFA) World Cup in Brazil (Nassis et al 2015)
There was a significant decline in all performance variables from period 1 to period 3 (p < 0.05); there was no interaction with condition or activity
This study demonstrated a practical mixed-method pre-cooling technique does not improve self-paced intermittent exercise in hot dry conditions

Summary

Introduction

Training and competition for many intermittent team sports take place in environmental conditions exceeding 30 °C, as seen during the 2014 Fédération Internationale de Football Association (FIFA) World Cup in Brazil (Nassis et al 2015). Cooling administered before intermittent exercise in the heat may have a potential benefit to mitigate the reduction in performance (d = 0.47) (Tyler et al 2015), but the effectiveness of pre-cooling appears to be dependent on the magnitude of thermal strain experienced and the volume of the cooling applied. We demonstrated that pre-cooling via ice slurry ingestion (7.5 g/kg) successfully lowered core temperature and thermal sensation with no change in mean skin temperature (Tsk), in comparison to a control beverage (Gerrett et al 2017). Lowering core temperature alone did not result in favourable changes to intermittent exercise performed in 30 °C, 40% RH. Studies demonstrating some evidence of enhanced intermittent exercise following precooling report a decrease in both core temperature and Tsk (Duffield and Marino 2007; Minett et al 2011). Supporting the notion of a dose-dependent response to precooling; the larger the surface exposed to cooling the greater the distance achieved during submaximal running

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