Athletes training for endurance competitions, especially multi-sport athletes, often participate in multiple training bouts within 24 hrs leaving little time for recovery between exercise sessions. Quick and efficient recovery methods are necessary for athletes to return to physiological readiness before the next exercise bout begins (Barnett, 2006). Cold water immersion (CWI) is commonly used by endurance athletes to speed recovery and attenuate the deleterious effects of muscle damaging or fatiguing exercise (Wilcock et al., 2006b). The analgesic and vasoconstrictive effects of cold temperature combined with the hydrostatic effects of water pressure remove heat from the body, reduce edema and pain by limiting fluid movement, reduce inflammation, and decrease transport time of substrates and metabolic waste (Merrick et al., 1999; Wilcock et al., 2006a).
Despite wide use of CWI, evidence of CWI as an effective recovery technique is contradictory (Leeder et al., 2012). Conflicting findings are a result of differences in methodology. The initial degree and type of exercise insult, duration of treatment, temperature of treatment, frequency of treatment, and time between treatment and performance measure all vary in the literature (Wilcock et al., 2006a; 2006b). CWI as a recovery method is typically used to address reduced performance due to structural damage to muscles that occurs during unaccustomed, eccentric, or prolonged, fatiguing exercise. Research on the use of CWI following primarily eccentric, muscle-damaging exercise is abundant (Eston and Peters, 1999; Goodall and Howatson, 2008; Paddon-Jones and Quigley, 1997; Paschalis et al., 2005; Vaile et al., 2008a; Yanagisawa et al., 2003). Damage to muscle fibers is associated with the movement of intramuscular proteins and enzymes into extracellular spaces (Armstrong et al., 1991; Cheung et al., 2003). Damage impairs muscle structure and function, which may cause pain, swelling, inflammation, and performance limitations, all of which are theoretically improved with CWI (Armstrong et al., 1991; Cheung et al., 2003). While eccentric contractions are particularly damaging, most forms of exercise are not entirely eccentric, but contain both eccentric and concentric muscle actions. Previously, researchers have examined the effects of CWI on muscle injury from eccentric heavy exercises, specifically strength training and plyometric exercises (Jakeman et al., 2009; Paddon-Jones and Quigley, 1997). Additionally, some researchers have used CWI as a recovery method immediately prior to exercise in an attempt to reduce rating of perceived exertion, increase central blood volume, and reduce thermal strain (Dunne et al., 2013; Yeargin et al, 2006). Fewer researchers have examined the effects of CWI on fatigue from intense endurance exercise when the performance measure was 24 hrs or longer after immersion (Brophy-Williams et al., 2011; Lane and Wenger, 2004; Rowsell et al., 2014). Fast twitch, glycolytic fibers are more susceptible to muscle damage and thus, easier to quantify the effects of recovery treatments such as CWI; however, some researchers have documented muscle damage in slow-oxidative muscle fibers following marathon and half-marathon races (Linjen et al., 1988; Lippi et al., 2008; Warhol et al., 1985). While intense endurance exercise may not produce the same degree of muscle damage as eccentric or strength training exercises, muscle soreness and fatigue also necessitate recovery methods to ensure that subsequent performance is maintained.
Previously, researchers reported improved performance on a sprint cycling task after intense exercise and CWI performed 24 hrs prior to the performance measure (Lane and Wenger, 2004). Further, researchers found improved running performance 24 hrs after CWI was used as a recovery treatment from high-intensity running in a thermoneutral environment (Brophy-Williams et al., 2011). Running and cycling performance improvements have also been documented when CWI was performed immediately or shorty prior to the performance measure (Rowsell et al., 2014; Vaile et al., 2008b; Yeargin et al., 2006). Positive effects of CWI were often found when the initial exercise and subsequent performance tests required the same or similar muscular and bioenergetics demands. The use of primarily slow oxidative muscle fibers for both the initial exercise protocol and performance measure are rarely used because of the greater susceptibility of fast, glycolytic fibers to incur damage during exercise, and the use of performance measures that consist of both slow oxidative and fast glycolytic fibers (Friden and Lieber, 1992; Paschalis et al., 2005; Warren et al., 1999). For the best indication of performance impairment or recovery efficacy, performance measurements following the initial exercise protocol and treatment should possess muscle and fiber type specificity relative to the initial exercise protocol (Warren et al., 1999).
The purpose of this study was to examine the effects of CWI on performance and recovery 24 hrs after an acute bout of intense, prolonged interval training. CWI is a popular recovery tool among endurance runners and triathletes who often complete hard training sessions separated by 24 hrs or less. With this study, we attempted to replicate a typical training schedule, which would require fast and effective recovery techniques. A randomized crossover design was used in which participants were tested under each treatment. The interval training was designed to be a prolonged, intense exercise bout, similar to an interval training session for a long-distance runner. Prolonged or intense endurance exercise can cause significant muscle fatigue and possible muscle damage, but are not as well researched as resistance or plyometric exercises which can easily produce a great deal of muscle damage (Linjen et al., 1988; Lippi et al., 2008; Warhol et al., 1985). Because there is some fiber-type specificity to muscle damage and muscular fatigue, it was important that the interval training session and the performance measure used in the present study required similar muscular and bioenergetics demands. The 5000 m run was used because it mimicked the muscular and bioenergetic demands of the interval session and because it is a common race distance. Two major hypotheses were tested. Specifically, that 5000 m run time would improve 24 hrs after an intense interval session and CWI treatment compared to a control (CON) treatment. Further, thigh circumference (TC), joint range of motion (ROM), perceived muscle soreness (PMS), and rating of perceived exertion (RPE) would improve 24 hrs post interval training when participants received the CWI treatment. TC, ROM, PMS, and RPE were measured to easily identify any potential muscle damage or muscular fatigue caused by the interval training.
Nine male participants completed the study (mean [[+ or -].sub._] SD; age: 35.89 [+ or -] 7.80 years; height: 1.81 [+ or -] 0.06 m; weight: 76.53 [+ or -] 10.30 kg; percent body fat: 11.35 [+ or -] 2.41%; peak V[O.sub.2]: 67.16 [+ or -] 6.49 [ml.sup.-1] x [kg.sup.-1] x [min.sup.-1]). The Institutional Review Board of Springfield College approved all procedures. All participants were briefed on the risks of the study and were given the opportunity to ask questions prior to providing written informed consent. The participants were endurance trained long distance runners and triathletes and had been training at their current level for at least 6 months. Participants reported an average of 7 [+ or -] 2 endurance training sessions per week for an average of 96 [+ or -] 19 min per session. Participants had no history of cardiovascular disease, pulmonary disease, musculoskeletal disorders, cold exposure disorders, diabetes, or other metabolic disorders. All participants were asked to report to testing normally hydrated, but were not required to report food or fluid intake prior to each testing session. Participants were asked to record and replicate dietary intake only between the interval sessions and the 5000 m time trials to control for the potential recovery benefits of dietary macronutrient compositions. Participants were asked to refrain from strenuous exercise and to abstain from caffeine, alcohol, and therapeutic treatments including cryotherapy, massage, and anti-inflammatory medications for 24 hrs prior to...