Differences in team sport players’ repeated sprint performance, physiology and biomechanics between temperate and hot environments

Abstract

Repeated sprinting is defined as a minimum of three sprints with a mean recovery duration interspersed by less than or equal to 60 s of recovery time (Taylor et al., 2015; Sirotic and Coutts, 2007). These occur frequently in team sports, which are played around the world, often in hot environments (Girard, Brocherie and Bishop, 2015). At present, there is an abundance of research exploring the physiological strain of repeated sprinting in the heat (e.g. Almudehki et al., 2012; Drust et al., 2005; Kilduff et al., 2013), but data on the biomechanical alterations is limited (Girard et al., 2017). Therefore, the aim of the present study was to investigate the effect of heat on team sports players’ physical performance, physiological strain and biomechanical variables during repeated sprint performance when compared to a temperate environment. Six male recreational team sports players completed four trials; one V̇O2MAX test, one familiarisation and two randomised, counterbalanced experimental trials of the repeated sprint protocol (CON: 20C 50% rH and HOT: 35C 50% rH). For the experimental trials, participants completed a warm-up, followed by the repeated sprint protocol on a non-motorised force plate instrumented treadmill, which consisted of four blocks of six 6 s sprints, with 30 s recovery between each sprint and five-minute recovery between each block. Rectal temperature, heart rate, RPE, thermal comfort and thermal sensation were all taken and the beginning and end of each block and spatiotemporal characteristics (Optojump) and angular kinematics (Quintic 2D motion analysis) were recorded for every sprint. All physical performance variables were significantly lower (P < 0.05) in HOT compared with CON. Rectal temperature, skin temperature, sweat loss, TC and TS were all significantly higher (P < 0.05) in HOT compared with CON. Average step length and peak propulsive horizontal force were significantly lower (P < 0.05) in HOT, whilst peak plantar flexion and hip and ankle range of motion were significantly larger (P < 0.05) in HOT compared with CON. Peak hip flexion, peak plantar flexion angular velocity, peak hip flexion angular velocity, peak knee flexion angular velocity and peak dorsi flexion angular velocity were all significantly higher (P < 0.05) in CON compared with HOT. Considering the performance decrements found in the hot condition, practitioners should be aware of the biomechanical causes of these, particularly as a decreased step length reduces the propulsive horizontal forces. The shorter steps lengths observed in the heat can be explained by the lower force production of the muscles, with heat decreasing the number of muscle fibre units recruited, creating less propulsive force. Therefore, strategies need to be developed to maintain step length in the heat or be able to increase step frequency to compensate for the decrements in step length to maintain running velocity. Further research is required to support the understanding of the underpinning cause for the change in step length in the heat.