Despite the widespread integration of hydrotherapy into an athlete’s postexercise recovery regime, information regarding these interventions is largely anecdotal. Although a number of physiological responses to water immersion are well researched, the underlying mechanisms related to postexercise recovery are poorly understood. The human body responds to water immersion with changes in cardiac response, peripheral resistance, and blood flow (Wilcock et al. 2006). In addition, both hydrostatic pressure and temperature of the immersion medium may influence the success of different hydrotherapy interventions (Wilcock et al. 2006).
Immersion of the body in water can result in an inward and upward displacement of fluid from the extremities to the central cavity due to hydrostatic pressure. As identified by Wilcock and colleagues (2006), the resulting displacement of fluid may increase the translocation of substrates from the muscle. Therefore, postexercise edema may be lessened and muscle function maintained. Another physiological response to water immersion is an increase in stroke volume, which has been shown to increase cardiac output.
Although the effects of hydrostatic pressure exerted on the body during water immersion may be beneficial, the temperature of water that the body is exposed to is also thought to influence the success of such recovery interventions. The main physiological effect of immersion in cold water is a reduction in blood flow due to peripheral vasoconstriction (Meeusen and Lievens 1986). In contrast, immersion in hot water increases blood flow via peripheral vasodilation (Bonde-Petersen et al. 1992; Knight and Londeree 1980).
Cold Water Immersion
Cryotherapy (meaning “cold treatment,” often in the form of an ice pack) is the most commonly used treatment for acute soft tissue injuries, given its ability to reduce the inflammatory response and alleviate spasm and pain (Eston and Peters 1999; Meeusen and Lievens 1986; Merrick et al. 1999). Multiple physiological responses to various cooling methods have been observed, including a reduction in heart rate and cardiac output and an increase in arterial blood pressure and peripheral resistance (Sramek et al. 2000; Wilcock et al. 2006). Additional responses include a decrease in core and tissue temperature (Enwemeka et al. 2002; Lee et al. 1997; Merrick et al. 2003; Yanagisawa et al. 2007), acute inflammation (Yanagisawa et al. 2004), and pain (Bailey et al. 2007; Washington et al. 2000) and an improved maintenance of performance (Burke et al. 2000; Yeargin et al. 2006). Merrick and colleagues (1999) suggested that cryotherapy is an effective method for decreasing inflammation, blood flow, muscle spasm, and pain as well as skin, muscular, and intra-articular temperatures.
The use of cryotherapy for the treatment of muscle damage and exercise-induced fatigue has been investigated with varying findings. Eston and Peters (1999) investigated the effects of cold water immersion (of the exercised limb in 15 °C for 15 min) on the symptoms of exercise-induced muscle damage following strenuous eccentric exercise. The muscle-damaging exercise consisted of eight sets of five maximal isokinetic contractions (eccentric and concentric) of the elbow flexors of the dominant arm (0.58 rad · s–1and 60 s rest between sets). The measures used to assess the presence of exercise-induced muscle damage included plasma CK concentration, isometric strength of the elbow flexors, relaxed arm angle, local muscle tenderness, and upper arm circumference. Eston and Peters (1999) found CK activity to be lower and relaxed elbow angle to be greater for the cold water immersion group on days 2 and 3 following the eccentric exercise, concluding that the use of cold water immersion may reduce the degree to which the muscle and connective tissue unit becomes shortened after strenuous eccentric exercise (Eston and Peters 1999).
Bailey and colleagues (2007) investigated the influence of cold water immersion on indices of muscle damage. Cold water immersion (or passive recovery) was administered immediately following a 90 min intermittent shuttle run protocol; rating of perceived exertion (RPE), muscular performance (maximal voluntary contraction of the knee extensors and flexors), and blood variables were monitored prior to exercise, during recovery, and following recovery for 7 days. The authors concluded that cold water immersion was a highly beneficial recovery intervention, finding a reduction in muscle soreness, a reduced decrement of performance, and a reduction in serum myoglobin concentration 1 h following exercise (Bailey et al. 2007). However, further values across the 7-day collection period were not cited, and CK response was unchanged regardless of intervention. Lane and Wenger (2004) investigated the effects of active recovery, massage, and cold water immersion on repeated bouts of intermittent cycling separated by 24 h. Cold water immersion had a greater effect compared with passive recovery, active recovery, and massage on recovery between exercise bouts, resulting in enhanced subsequent performance (Lane and Wenger 2004). This is an important investigation, as most studies in the area of cold water immersion have been conducted using muscle damage models or recovery from injury. Despite these promising results, some studies have found negligible changes when investigating the recovery effects of cold water immersion (Paddon-Jones and Quigley 1997; Sellwood et al. 2007; Yamane et al. 2006).
In a randomized controlled trial, Sellwood and colleagues (2007) investigated the effect of ice-water immersion on delayed-onset muscle soreness (DOMS). Following a leg extension exercise task (5 ×10 sets at 120% concentric 1RM), participants performed either 3 × 1 min water exposure separated by 1 min in either 5 °C or 24 °C (control) water. Pain, swelling, muscle function (one-leg hop for distance), maximal isometric strength, and serum CK were recorded at baseline, 24, 48, and 72 h after damage. The only significant difference observed between the groups was lower pain in the sit-to-stand test at 24 h postexercise in the ice-water immersion group (Sellwood et al. 2007). In accordance with Yamane and colleagues (2006), only the exercised limb was immersed at a temperature of 5 °C. In this study, ice-water immersion was no more beneficial than tepid water immersion in the recovery from DOMS (Yamane et al. 2006). Paddon-Jones and Quigley (1997) induced damage in both arms (64 eccentric elbow flexion), and then one arm was immersed in 5 °C water for 5 × 20 min, with 60 min between immersions, while the other served as a control. No differences were observed between arms during the next 6 days for isometric and isokinetic torque, soreness, and limb volume (Paddon-Jones and Quigley 1997). In the aforementioned studies, cold water immersion appeared to be an ineffective treatment, specifically when immersing an isolated limb in 5 °C water.
Only one study has investigated the effect of cold water immersion on training adaptation. Yamane and colleagues (2006) investigated the influence of regular postexercise cold water immersion following cycling or handgrip exercise. Exercise tasks were completed 3 to 4 times per week for 4 to 6 weeks, with cooling protocols consisting of limb immersion in 5 °C (leg) or 10 °C (arm) water. The control group showed a significant training effect in comparison to the treatment group, and the authors concluded that cooling was ineffective in inducing molecular and humoral adjustments associated with specified training effects (e.g., muscle hypertrophy, increased blood supply, and myofibril regeneration).
Despite these findings, the majority of research supports the notion that cold water immersion is effective in reducing symptoms associated with DOMS (Eston and Peters 1999), repetitive high-intensity exercise (Bailey et al. 2007; Lane and Wenger 2004), and muscle injury (Brukner and Khan 1993). A more refined investigation into the individual components of a specific recovery protocol is needed to reveal the effect of varying the duration of exposure, the temperature, and the medium used, whether it is ice, air, or water. In addition, training studies are required to investigate the effectiveness of such interventions on training adaptations.
Hot Water Immersion
The use of heat as a recovery tool has been recommended to increase the working capacity of athletes (Viitasalo et al. 1995) and assist in the rehabilitation of soft tissue injuries and athletic recovery (Brukner and Khan 1993; Cornelius et al. 1992). The majority of hot water immersion protocols are performed in water warmer than 37 °C, resulting in an increase in muscle and core body temperature (Bonde-Petersen et al. 1992; Weston et al. 1987). The physiological effects of immersion in hot water remain to be elucidated. One of the main physiological responses associated with exposure to heat is increased peripheral vasodilation, resulting in increased blood flow (Bonde-Petersen et al. 1992; Wilcock et al. 2006).
The effect of hot water immersion on subsequent performance is also poorly understood. Only one study has investigated the effect of hot water immersion on postexercise recovery. Viitasalo and colleagues (1995) incorporated three 20 min warm (~37 °C) underwater water-jet massages into the training week of 14 junior track-and-field athletes. The results indicated an enhanced maintenance of performance (assessed via plyometric drop jumps and repeated bounding) following the water treatment, indicating a possible reduction in DOMS. However, significantly higher CK and myoglobin concentrations were observed following the water treatment, suggesting either greater damage to the muscle cells or an increased leakage of proteins from the muscle into the blood. Viitasalo and colleagues (1995) concluded that combining underwater water-jet massage with intense strength training increases the release of proteins from the muscle into the blood, while enhancing the maintenance of neuromuscular performance (Viitasalo et al. 1995).
Evidence to support these findings is lacking, and the use of hot water immersion for recovery has received minimal research attention. Despite the hypothesized benefits of this intervention, anecdotal evidence suggests that hot water immersion is not widely prescribed on its own or as a substitute for other recovery interventions. Speculation surrounds the possible effects, timing of recovery, and optimal intervention category (e.g., following which type or intensity of exercise) for the use of hot water immersion.
Contrast Water Therapy
During contrast water therapy, athletes alternate between heat exposure and cold exposure by immersion in warm and cold water, respectively. This therapy has frequently been used as a recovery intervention in sports medicine (Higgins and Kaminski 1998) and is commonly used within the sporting community. Although research investigating contrast water therapy as a recovery intervention for muscle soreness and exercise-induced fatigue is limited in comparison to that for cold water immersion, several researchers have proposed possible mechanisms that may support the use of contrast water therapy. Higgins and Kaminski (1998) suggested that contrast water therapy can reduce edema through a pumping action created by alternating peripheral vasoconstriction and vasodilation. Contrast water therapy may bring about other changes such as increased or decreased tissue temperature, increased or decreased blood flow, changes in blood flow distribution, reduced muscle spasm, hyperemia of superficial blood vessels, reduced inflammation, and improved range of motion (Myrer et al. 1994). Active recovery has traditionally been considered superior to passive recovery. Contrast water therapy may elicit many of the same benefits of active recovery and may prove to be more beneficial, given that contrast water therapy imposes fewer energy demands on the athlete (Wilcock et al. 2006).
Contrast water therapy has been found to effectively decrease postexercise lactate levels (Coffey et al. 2004; Hamlin 2007; Morton 2006; Sanders 1996). After conducting a series of Wingate tests, investigators found that blood lactate concentrations recovered at similar rates when using either contrast water therapy or active recovery protocols and that after passive rest blood lactate removal was significantly slower (Sanders 1996). Coffey and colleagues (2004) investigated the effects of three different recovery interventions (active, passive, and contrast water therapy) on 4 h repeated treadmill running performance. Contrast water therapy and active recovery reduced blood lactate concentration by similar amounts after high-intensity running. In addition, contrast water therapy was associated with a perception of increased recovery. However, performance during the high-intensity treadmill running task returned to baseline levels 4 h after the initial exercise task regardless of the recovery intervention performed.
In a more recent study investigating the effect of contrast water therapy on the symptoms of DOMS and the recovery of explosive athletic performance, recreational athletes completed a muscle-damaging protocol on two separate occasions in a randomized crossover design (Vaile et al. 2008a). The two exercise sessions differed only in recovery intervention (contrast water therapy or passive recovery/control). Following contrast water therapy, isometric force production was not significantly reduced below baseline levels throughout the 72 h data collection period; however, following passive recovery, peak strength was significantly reduced from baseline by 14.8% ± 11.4% (Vaile et al. 2008a). Strength was also restored more rapidly within the contrast water therapy group. Thigh volume measured immediately following contrast water therapy was significantly less than that following passive recovery, indicating lower levels of tissue edema. These results indicate that symptoms of DOMS and restoration of strength are improved following contrast water therapy compared with passive recovery (Vaile et al. 2007; Vaile et al. 2008a). However, Hamlin (2007) found contrast water therapy to have no beneficial effect on performance during repeated sprinting. Twenty rugby players performed two repeated sprint tests separated by 1 h; between trials subjects completed either contrast water therapy or active recovery. Although substantial decreases in blood lactate concentration and heart rate were observed following contrast water therapy, compared with the first exercise bout, performance in the second exercise bout was decreased regardless of intervention (Hamlin 2007). Therefore, although contrast water therapy appears to be beneficial in the treatment of DOMS, it may not hasten the recovery of performance following high-intensity repeated sprint exercise.
The physiological mechanisms underlying the reputed benefits remain unclear. Temperatures for contrast water therapy generally range from 10 to 15 °C for cold water and 35 to 38 °C for warm water. It is evident that contrast water therapy is being widely used; however, additional research needs to be conducted to clarify its optimal role and relative efficacy.
Pool or beach recovery sessions are commonly used by team sport athletes in an attempt to enhance recovery from competition. Almost all Australian Rules, Australian Rugby League, and Australian Rugby Union teams use pool recovery sessions to perform active recovery in a non–weight-bearing environment. These sessions are typically used to reduce muscle soreness and stiffness and therefore are thought to be effective in sports that involve eccentric muscle damage or contact. Sessions often include walking and stretching in the pool and occasionally some swimming.
Dawson and colleagues (2005) investigated the effect of pool walking as a recovery intervention immediately following a game of Australian Rules Football. Pool walking was compared with contrast water therapy, stretching, and passive recovery (control) to determine the effect on subjective ratings of muscle soreness, flexibility (sit and reach test), and power (6 s cycling sprint and vertical jumps) assessed 15 h after the game. For all four recovery interventions, muscle soreness was increased 15 h after the game; however, only pool walking resulted in a significant reduction in subjective soreness. There was a trend for lower flexibility and power scores; however, this was only significant in the control trial. Although there were no differences between the three recovery interventions with respect to flexibility and power, players subjectively rated pool walking as the most effective and preferable strategy. The authors speculated that the active, light-intensity exercise with minimal impact stress or load bearing, combined with the hydrostatic pressure, may have enhanced recovery (Dawson et al. 2005).