The effect of intermittent head cooling on aerobic performance in the heat.

Author:Walters, Peter
Position:Research article - Report
 
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Introduction

The physiological demands of thermoregulation during intense physical activity are substantial, particularly for athletes performing in hyperthermic conditions. Several studies have reported diminished physical performance in environmental conditions greater than 32[degrees]C (Howley et al., 1995; Midgley et al., 2007; Tyler et al., 2015). Humans seem to be especially susceptible to heat in that they can generally tolerate twice the decline in core temperature (10[degrees]C) as they can in its increase (5[degrees]C) (McArdle et al., 2010). In an effort to ameliorate the effects of thermal stress, various cooling methods have been employed. To date, approximately 100 original investigations and 13 reviews have examined the effectiveness of cooling on motor performance (Stevens et al., 2016). The results of these studies indicate that external cooling methods, in general, have a positive effect on performance (Ruddock et al., 2016; Stevens et al., 2016; Tyler et al., 2015).

As cooling research emerged a more nuanced understanding of when cooling can be applied has developed. Most early investigations administered cooling prior to physical activity, commonly referred to as pre-cooling. A strong majority of these studies demonstrated that pre-cooling had a positive effect on subsequent motor performance (Stevens et al. 2016; Tyler et al. 2015). More recently, investigators have examined the effect of cooling during performance, referred to as mid-cooling. As with pre-cooling, positive results were largely reported with some investigators suggesting that the benefits gained from mid-cooling outweigh that of pre-cooling (Tyler et al. 2015; Stevens et al. 2016).

Mid-cooling can further be subdivided into continuous and intermittent cooling. Continuous mid-cooling is when cooling is applied throughout activity. This is often accomplished by having participants don cooling equipment such as a vest, collar, hand pads or the administration of spray/fanning (Tyler and Sunderland 2011; Minniti et al. 2011; Amorim et al. 2010; Kenny et al. 2011). Intermittent mid-cooling is when cooling is applied during a motor task periodically rather than continuously. Such as ingesting a cold drink or ice slurry every 15 minutes while cycling (Mundel et al. 2006; Siegel et al. 2010). Both continuous and intermittent mid-cooling have resulted in positive effects to heat stressed participants ( (Gonzalez-Alonso et al. 1999; Ruddock et al. 2016; Stevens et al. 2016).

The purpose of this study is to investigate whether seven minutes of head cooling applied in between a bout of aerobic exercise in hot (35 [+ or -] 1.0 degree[degrees]C) and dry (15 [+ or -] 3% rh) conditions could benefit participant's aerobic performance. The scope of this study was selected for four reasons. First, intermittent cooling is the least examined form of cooling research. In a recent review, approximately 80% of cooling studies examined pre-cooling will 20% investigated mid-cooling (Stevens et al. 2016). In addition, the majority of mid-cooling studies have utilized continuous cooling strategies as compared to intermittent (Ruddock et al. 2016; Stevens et al. 2016). Second, the application of intermittent cooling to many popular sports such as cricket, field hockey, tennis, volleyball, baseball, golf, basketball, and football is compelling. Each of these events have naturally occurring phases of inactivity in which cooling could be applied. Third, intermittent cooling allows for the application of cooling at strategic times when the outcome of competitive events is decided. Finally, investigators in the most review of mid-cooling strategies recommended that head cooling be examined (Stevens et al., 2016). Some of the rational for head-cooling includes: ease of access, high degree of blood flow to this region, and the ability to cool without reducing working muscle temperature (Palmer et al., 2001). Currently, no studies exist examining this method of head cooling on performance.

Methods

Experimental approach to the problem

A randomized cross-over study design was selected to determine whether seven minutes of head cooling between bouts of activity could attenuate the decline in performance that is often associated with heat stressed performances. This design was selected in order to minimize the effects of between participants physiological variability.

Each subject was required to complete three sessions. Session one consisted of acclimatizing participants to testing procedures and obtaining baseline measures. The second and third sessions were counterbalanced and consisted of treatment and placebo (See Table 1).

The independent variable in this investigation was head cooling via the Welkins Sideline Cooling System (Downers Grove, IL). This device consists of three major components: a cooling cartridge, heat exchange, and tethered neoprene cap (see Figure 1). The heat exchange circulates 9oz of cooling fluid through the tubing and neoprene cap which snuggly fits on the subject's head. During maximal cooling, the circulating fluid maintains a temperature between 5-10[degrees]C. During treatment conditions, maximal cooling from this device was applied. Power to this device is supplied via internal batteries.

In order to create a placebo condition, participants were informed that the focus of this investigation was to compare the effects of two modes of cooling on aerobic performance: traditional and innovative. The traditional method of cooling was explained as cooling the head via circulating fluid, in which participants would recognize the sensation of cooling via the head gear. The innovative method of cooling (placebo) was explained as using MRI technology to target thermoreceptors within the brain for deep brain cooling. Participants were told that although inner cooling of the brain was occurring, no noticeable cooling via sensation could be recognized. These explanations were given to minimize the effect of the sensory reinforcement.

The dependent variable was peak power output. A graded exercise test (GXT) was used to measure performance indicators.

Participants

Twenty-two recreationally active men between the ages of 18 and 23 years participated in the study (19.8 [+ or -] 1.6 yrs.). The average mass and height of the participants were 1.82 [+ or -] 0.08 m. and 78.4 [+ or -] 15.6 kg. All participants reported participating in at least 90 minutes of moderate to vigorous physical activity per week within the previous six months. Each participant agreed not to alter their typical activity and dietary habits throughout the duration of this study. Participants reported no cardiovascular, neural, or musculoskeletal disease or injuries that would prevent them from completing the exercise bouts. After reviewing research procedures, protocol, and potential risks, participants were given an opportunity to ask questions before reading and signing an informed consent form, which received approval from the Institutional Review Board (IRB). Each participant that complied with all established procedures and guidelines...

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