Our findings provide new insight into the relationship between neck cooling, physiological and perceived fatigue, skin temperature, and actual performance during repeated, high-intensity exercise intervals. These data show that holding an ice bag on the back of the neck for one minute between rounds of HEX attenuates the rise in skin temperature and, as a result, makes participants feel cooler and, at times, less exerted, but does not alter cardiovascular or metabolic function. Thus, intermittent neck cooling may function as an effective, practical, and legal cooling option for combat sport athletes (or others who participate in repeated HEX for sport or recreation) to utilize during competition and training.

Temperature, Perception, and Performance

PEAK , VE AVE , HR AVE , and HR PEAK ) indicated HEX2 was more physiologically challenging than HEX1. They also felt cooler after a matched workload (TTE) and 2 min into recovery. Additionally, lower pre-exercise TS corresponded with lower post-exercise RPE (when compared to a standardized work bout—HEX2). Unfortunately, our study design eliminated the ability to determine if the reduced post-RI2 RPE was a function of ICE (1) aiding recovery from HEX1; (2) pre-cooling the neck in preparation for HEX2; (3) or both. Research from others suggests intermittent cooling of other body parts reduces RPE [ Temperature, perception, and actual exercise performance significantly influence each other [ 20 ]. In fact, Mündel [ 4 ] suggested the temperature of a skin surface area ≤10% of the body may significantly effect hormonal and perceptual responses to exercise [ 9 ]. The attenuated rise in neck, chest, and arm skin temperature seen here with ICE did not correspond with a reduced rise in heart rate (or altered metabolic function) as proposed by others [ 20 ]. However, the ability of ICE to cool the skin is similar to previous research [ 21 ] and likely explains our improvements in TS [ 13 ]. This reduction in TS allowed participants to enter subsequent exercise bouts feeling cooler. Interestingly, while the effect of the first application of ICE on TS was eliminated by the next round of exercise (i.e., post HEX2 TS was not different between treatments), its effects on RPE persisted (i.e., post HEX2 RPE was significantly lower in ICE). This continued through RI2, suggesting that participants both (1) completed the standardized exercise bout (HEX2) and (2) went into the third bout of exercise (TTE) feeling less exerted and cooler, even though several cardiovascular and metabolic markers (RER, VE, HR, and HR) indicated HEX2 was more physiologically challenging than HEX1. They also felt cooler after a matched workload (TTE) and 2 min into recovery. Additionally, lower pre-exercise TS corresponded with lower post-exercise RPE (when compared to a standardized work bout—HEX2). Unfortunately, our study design eliminated the ability to determine if the reduced post-RI2 RPE was a function of ICE (1) aiding recovery from HEX1; (2) pre-cooling the neck in preparation for HEX2; (3) or both. Research from others suggests intermittent cooling of other body parts reduces RPE [ 22 ], but we are the first to show such changes with intermittent neck cooling.

The ability of ICE to attenuate the rise in skin temperature diminished as the exercise session extended. This means changes in skin temperature either (1) did not fully explain the continual decrease in TS or RPE; or, more likely, (2) caused a continued perception of cooling, even when actual cooling was not occurring. Actual temperature changes are not required to alter thermoregulatory responses or to improve performance [ 7 ]. We chose to globally account for both actual and perceived cooling by including a treatment group that received an over-the-counter spray (SPRAY) containing menthol, a substance that interacts with cold receptors in sensory neurons [ 6 ] and alters exercise performance [ 5 23 ]. Recent evidence suggests an L-menthol spray with a concentration of 0.2% lowers TS [ 23 ]. Our data show a limited effectiveness of SPRAY, which is probably a result of differences in exercise protocols (i.e., our repeated HEX vs. 40 min of steady-state) [ 5 23 ], or our use of an 8% commercially available product. None of our participants reported skin irritation or discomfort from SPRAY, as has been reported in some previous studies. Thus, it was unlikely to explain our findings.

25, Changes in physical and perceptual markers during intermittent [ 13 14 ] or pre-cooling [ 20 ] of the actual exercising muscle, face and palm, and/or neck usually correspond with improvements in endurance and time trial performance [ 24 ]. The inability of ICE to influence leg temperature and subsequently improve TTE in our study is most likely explained by a combination of (a) the location and (b) a short duration (1 min) of cooling, and the (c) high-intensity and (d) short duration (~1 min) of TTE. Cooling the legs directly would obviously maximize the influence on skin temperature and likely improve TTE performance [ 14 ]. However, this strategy is unrealistic for combat sport athletes or during any exercise bout that uses multiple muscle groups. As opposed to previous research, which typically use >5 min [ 24 26 ] or even leaves the cooling device on the neck during the actual exercise [ 17 ], our cooling period was limited to 1 min. This distinction is important as the amount of cooling time significantly alters its effectiveness [ 27 ]. Our time was chosen as it reflects the timeframe of combat sports, and excessive cooling may actually harm repeated sprint performance [ 26 ].

2 max that last ~20–60 min [ Cooling is typically effective for exercise tasks performed at 40–70% VOmax that last ~20–60 min [ 14 17 ], but not always [ 15 ]. We are the first to examine intermittent neck cooling at normal room temperature at this high of exercise intensity. Drust et al. (2005) showed that performance during a 40-min high-intensity, intermittent cycling protocol (15 s on, 15 s off) was worse when performed in a hot room compared to a normal temperature room [ 28 ]. Moreover, the effects of intermittent cooling during high-intensity exercise may be enhanced when in hot environments. Individual perception of recovery, independent of physiological measures [ 27 ], relates to subsequent sprint performance [ 29 ]. Therefore, the fact that our reduced TS persisted through HEX2 suggests that RPE and performance might have actually improved if a standardized HEX was performed instead of the short TTE (TTE required maximal effort, eliminating our ability to compare the effects of ICE during RI2 on post-TTE RPE), or had additional rounds of HEX been performed. The combination of short duration, high RPE, and reduced cardiovascular or metabolic demand (which was significantly greater in HEX2, but not TTE, compared to HEX1) suggest that failure during TTE was a muscle, not cardiovascular issue. The apparent delayed improvements in perception caused by reduced skin temperature means intermittent cooling might enhance performance in exercise tasks lasting longer than were tested here.

In concert with previous literature, our data suggest ICE might be effective for combat sports or other activities that require repeated, high-intensity exercise intervals that last more than two rounds and result in high physiological and perceived fatigue ratings [ 2 ]. ICE could also help long-term training motivation as how one (athlete or non-athlete) feels during exercise predicts future exercise intentions and behavior [ 30 ], which is probably why RPE is regarded as a highly effective tool for monitoring combat sport training [ 31 ]. The specific mechanisms explaining our findings are unknown. Several postulates exist (e.g., altered sensory perception, pain reduction, Gate Control Theory, and Central Fatigue Theory) and have been reviewed elsewhere [ 14 ].