Team-sports (requiring multiple short sprints) played for 60+ min in heat can increase core temperature (Tc) by 2+[degrees]C (Duffield et al., 2009). Importantly, when hyperthermia (Tc >38.0[degrees]C; Faulds and Meekings, 2013) occurs, heat strain may begin to manifest, with a Tc >39.4[degrees]C during exercise linked to an increased risk of heat illness (Casa, 1999), impaired central nervous system motor drive, reduced force output (Kay et al., 2001; Morrison et al., 2004) and premature fatigue during exercise (Gonzalez-Alonso, 1999). Consequently, team-sport players often utilise cooling modalities prior to and during breaks in play to reduce Tc (Marino, 2002) and hence limit the effects of heat on subsequent exercise performance (Bongers et al., 2014; Ranalli et al., 2010). However, a limitation of many cooling modalities (e.g. cold water immersion/fans) is their impracticality, particularly for field-sports, where water and/or power sources may be restricted.
As such, the use of cooling jackets (CJ) are popular in many field team-sports (i.e., Australian football, hockey) due to their practicality and ease of use. Notably, Brade et al. (2010) reported higher Tc cooling rates (d=0.60) associated with a gel CJ compared to no-cooling (0.040 [+ or -] 0.009[degrees]C/min versus 0.034 [+ or -] 0.010[degrees]C/min after 30-min) following exercise in heat. Wearing a CJ prior to exercise in the heat has also been reported to improve subsequent exercise performance compared to no-cooling (5 km time-trial running, Arngrimsson et al., 2004; 40-min of repeat-sprint cycling, Castle et al., 2006; incremental run to exhaustion time, Uckert and Joch, 2007). Further, wearing a CJ during a 10-min half-time break was found to improve subsequent exercise performance (power/work; d>0.50) in hyperthermic athletes compared to ingestion of an ice slushy (Brade et al., 2014). However, while practical, the CJ need to be soaked in icy water before use and kept cold (ice chest) throughout the match in order to maintain effectiveness.
Another cooling modality that could be used in team-sports is a cooling glove (CG), which uses cold circulating water (~16[degrees]C, as set by the manufacturer to avoid vasoconstriction) in combination with negative subatmospheric pressure (-40 mmHg) to increase blood flow to the arteriovenous anastomoses underlying the glabrous (non-hairy) palm of the hand, and in turn, cool blood returning to the core (Grahn et al., 2005). Notably, glabrous skin surfaces contain packed vascular structures that facilitate heat loss faster than non-glabrous body surfaces (Grahn et al., 2009). To date, significantly faster Tc cooling rates have been reported for the CG compared to no-cooling in hyperthermic individuals by Adams et al. (2016; 0.020[degrees]C/min versus 0.013[degrees]C/min for 10-min), Grahn et al. (2009; 0.017[degrees]C/min versus 0.007[degrees]C/min for 60-min), and Kuennen et al. (2010; 0.0076[degrees]C/min versus 0.0006[degrees]C/min for 50-min) when cooling was performed in the heat. Recently, Maroni et al. (2018) reported faster Tc cooling rates (d=0.50-0.54) over 10-min for the CG (one hand; 0.084[degrees]C/min) compared to CG (two hands; 0.081[degrees]C/min) and no-cooling (0.068[degrees]C/min), with cooling performed in an air-conditioned lab (22.3[degrees]C). Notably, Maroni et al., (2018) also reported comparable cooling rates between the CG (1 hand) and the CJ (0.044 versus 0.047[degrees]C/min respectively after 30 min of cooling) with similar effects possibly being due to the CG targeting a small but glabrous skin surface area (~1% per hand; Adams et al., 2016), while the CJ targeted a larger but non-glabrous skin surface area (~17%; Young et al., 1987). As the CG is easily transported and applied, and does not require power (i.e., battery operated), immersion in icy water or cold storage, it may represent a better alternative to CJ for use in field-sport events played in heat.
Importantly, the effect of using the CG on subsequent exercise performance is unknown; similarly, the combined effect of using CJ and CG together has not been studied. This is of relevance, as using multiple cooling methods can result in greater cooling rates than when undertaken in isolation (i.e; CJ and ice slushy: Brade et al., 2014; hand/head/torso and thigh cooling using ice packs and cold towels; Minett et al., 2011). Furthermore, as many team-sports represent multi-million dollar businesses where winning is paramount, the assessment of the effects of different cooling modalities on subsequent exercise performance would be of interest to coaches and players, particularly if the aid can also reduce the risk of heat illness.
A potential issue relating to the use of the CG, and of importance to team-sport athletes, is that manual dexterity has been found to be significantly impaired after 5 min of hand immersion in 10[degrees]C water compared to no-cooling (Cheung et al., 2003). As the CG leaves the hand cold after use, it is important to determine whether this impairs subsequent dexterity, as ball throwing, catching and holding a bat/ball are integral to success in many sports.
Therefore, the aims of this study were to assess the effects of cooling (CG, CJ and CG+CJ) and no-cooling on manual dexterity performance and on subsequent repeat-sprint performance (work and power) in the heat. It was hypothesised that Tc cooling rates would be significantly higher in CG and CJ combined, compared to these conditions alone and to NC, and that cooling rates for the CG and CJ alone would be higher than NC yet similar. Consequently, it was further hypothesised that manual dexterity would be impaired following use of the CG and that the trial with the highest cooling rates would result in greater power and work output during subsequent exercise performance compared to a no-cooling control.
Male, team-sport players [n = 12, mean [+ or -] SD: training status: 7.7 [+ or -] 4.4 h/wk of moderate-high intensity exercise; age: 20.5 [+ or -] 1.9 y; height: 1.83 [+ or -] 0.07 m; body-mass (BM): 76.7[+ or -]7.8 kg; sum of six skinfolds: 49.0 [+ or -] 8.3 mm] participated in this study. Testing was performed during the winter months; therefore participants were not heat acclimatised. All provided informed consent and the Human Research Ethics Committee of the University granted ethical approval.
After familiarisation, four experimental trials were performed in a randomised, counterbalanced manner, at the same time of day (a week apart) to control for circadian variability. The exercise component of each trial comprised 2 x 30 min halves of repeat-sprint cycling, separated by a 20 min half-time break, all performed in heat (35.0 [+ or -] 1.2[degrees]C, 52.5 [+ or -] 7.4% RH). Players cooled in the heat in order to simulate situations where access to air-conditioned rooms and powered cooling methods are not available. The repeat-sprint cycling protocol has been previously used to simulate the intermittent and variable intensity efforts typical of team sports (Brade et al., 2014; Duffield et al., 2003). During half-time, participants cooled for 15 min using either: (1) the CG, (2) the CJ, (3) the CG and CJ (CG+J) and (4) a NC control. This half-time duration is similar to that used in Australian football, rugby union, soccer and hockey. Prior to exercise, immediately pre- and post-cooling, and on completion of exercise the Purdue Pegboard test (Model 32020, J.A. Preston Corporation, New York) (3 min) was performed. Participants abstained from alcohol and vigorous activity for 24 h and caffeine 3 h prior to testing, and replicated food and fluid intake in the 24 h prior to testing.
Anthropometric measurements (as above) were first obtained. Participants then performed 10 min of the repeated-sprint cycling protocol in heat in the climate chamber and were familiarised to all other tests and equipment to be used in the experimental trials.
On entering the climate chamber, a 5-min cycling warm-up was performed comprising 3 min at 75 W and 2 min at 100 W, with 2 x 5 s maximal sprints also undertaken at 3.5 and 4.5 min. The repeated-sprint cycling test followed, with a 20 min break separating the two 30 min halves. Each half comprised 30 x 5 s cycle sprints interspersed by 55 s of cycling performed at prescribed...