The water-immersion recovery technique consists of covering part of the body, or the whole body, in water. The scientific literature describes four main means of immersion, which differ depending on the water temperature used:
- Thermoneutral-water immersion, between 15 °C and 36 °C (TWI)
- Hot-water immersion >36 °C (HWI)
- Cold-water immersion
- Contrasting water temperature (CWT), which consists of alternating immersion in cold and hot water.
Several aspects of the results of these recovery procedures, including metabolic, neurological, cardiovascular, and muscular aspects, were studied as a function of various indicators of fatigue. Different immersion methods were also studied (Barnett 2006). Athletes generally use either hot- or cold-water immersion rather than a combination of the two (Howatson and van Someren 2003).
Based on the assumption that immersion in varying depths of warm water may be more beneficial than simple immersion, recent work has studied the effects of both water immersion and hydrostatic pressure on early recovery (Wilcock, Cronin, and Hing 2006).
Physiological Responses to Water Immersion
The hypotheses advanced to explain the improved quality of recovery, or the reduced time necessary for recovery, when using immersion are mainly linked to three factors: hydrostatic pressure (Vaile et al. 2008b, c), analgesic phenomena and an anti-inflammatory process (linked to local vasoconstriction in the case of immersion in cold water), and vasomotricity (when contrasting water temperature immersion is used) (Cochrane 2004).
In the first case, hydrostatic pressure under water is higher than in air (at sea level) over the entire surface of the body. This causes gases, substances, and fluids to move toward the thorax; enables improved recovery; and reduces the swelling induced by exercise (Wilcock, Cronin, and Hing 2006). In addition, the nervous influx should be limited by compression of muscles and nerves due to the hydrostatic pressure.
Immersion in thermoneutral water was used to determine how hydrostatic pressure affects recovery. In the literature, this type of immersion consists of submerging all or part of the body in water at a temperature between 16 °C and 35 °C. However, water is considered thermoneutral when body temperature can be maintained when immersed for 1 h (35 °C). Thus, depending on the amount of subcutaneous fat, body temperature can be maintained for 1 h in water between 30 °C and 34 °C. Indeed, no alteration in body temperature is noted for subjects immersed in water at temperatures between 33 °C and 35 °C.
In the second case, the decrease in body temperature, due to immersion in cold water, also has benefits for nerve transmission and inflammatory phenomena. Exposure to cold water may alter nerve transmission by reducing temperature. Nevertheless, other phenomena may be involved, such as local vasoconstriction, which limits both metabolic by-products and the extent of inflammation, thus reducing the pain and discomfort experienced during movement. In addition, exposure to cold reduces the heart rate and increases peripheral resistance as the body seeks to counterbalance the drop in body temperature. To survive, the body favors irrigation of the core rather than the extremities (limbs) (Bonde-Petersen, Schultz-Pedersen, and Dragsted 1992). Historically, cold-water immersion was first used for therapeutic purposes for its analgesic potential, since it plays a major role in the treatment of acute muscle injury. It consists of submerging the part of the body to be treated in water between 4 °C and 16 °C for 5 to 20 min (depending on the study).
In the third case, cold temperatures cause blood vessels in the skin to constrict, while warm temperatures induce vasodilatation (Wilcock, Cronin, and Hing 2006; Bleakley and Davison 2009). The combination of vasodilatation and vasoconstriction stimulates blood flow, and thus reduces both the extent and duration of inflammation. This blood pumping (or vaso-pumping) might be one of the mechanisms allowing displacement of metabolic substances, repair of exercised muscles, and reduction of metabolic processes (Cochrane 2004; Hing et al. 2008). The increased blood flow is thought to promote an appropriate response to the gradient, favoring intra- and extracellular exchanges. The increase in blood flow also results in an increase in stroke volume (SV) by increasing cardiac preload. In addition to the increase in SV, a reduction in peripheral resistance during CWT immersion up to the neck has also been observed. By increasing cardiac preload, this can increase blood flow without affecting the heart rate. Conversely, edema can sometimes cause local vasocompression, which may alter the metabolite transport rate. This means that contrasting water temperature immersion and edema have opposing effects on blood flow and biochemical movements.
While immersion techniques theoretically favor the recovery process, studies in the field have shown very variable results depending on the techniques used (Wilcock, Cronin, and Hing 2006). To offer a clearer, and more practical, view of the situation with regard to the scientific data, we will address the effects of the various immersion techniques based on the type of exercise performed before their application. We will therefore distinguish studies relating to immersion-based recovery following exercises inducing muscle damage from those based on high-intensity exercises (all-out or time trial) and those directly integrated into sporting practice (match, tournament, and so on).
Exercise-Induced Muscle Damage and Immersion
The number of articles covering immersion-based recovery grew considerably between the years 2000 and 2010. However, the percentage of these that specifically investigate recovery following exercise that induces muscle damage remains low. This is in spite of the interest it would attract from trainers and athletes for use in specific muscle-building sessions, for example (Bailey et al. 2007; Burke et al. 2000; French et al. 2008; Eston and Peters 1999; Goodall and Howatson 2008; Howatson, Goodall, and van Someren 2009; Jakeman, Macrae, and Eston 2009; Robey et al. 2009; Sellwood et al. 2007; Skurvydas et al. 2008; Vaille, Gill, and Blazevich 2007; Vaile et al. 2008a, b; Pournot et al. 2010). A common method emerges from these few studies that mirrors the method used in many studies investigating exercise-induced muscle damage (EIMD). It consists of inducing muscle damage based on repeated, mainly eccentric, contractions (jumps, repeated maximal contractions, and so on), followed by immediate application of the recovery method (figure 14.1). Several indicators are then measured and compared with initial values. The most commonly used indicators are pain perception; mechanical markers, such as maximal voluntary contraction (isometric or isokinetic MVC); and biological markers, particularly blood or plasma concentration of creatine kinase (CK) or myoglobin. In contrast, very few in situ performance markers are used.
In addition to the similarity of the methods applied in these studies, the hydrotherapy method is also shared. Indeed, all of the studies use cold-water immersion (or CWT for three of them) as the technique with the potential for the greatest effect on reducing exercise-induced muscle damage. This is not very surprising given the number of studies indicating a positive effect of cold (ice pack, pulsed cold, and so on) on muscle damage. However, the results reported are surprising. Indeed, of the 12 studies cited previously, 8 conclude that recovery based on immersion in cold water is ineffective, while the other 4 observe only a partial effect. Thus, for mechanical indicators, the majority of these studies found that immersion in cold water did not reduce strength loss after tiring exercise. This result has recently been confirmed by a meta-analysis review dedicated to this topic (Leeder et al. 2012). For example, Howatson and colleagues (2009) showed that 96 h after exercise (100 drop jumps), the control group and the group using immersion were able to reproduce only 96% and 93%, respectively, of their initial isometric strength production for knee extensions. Immediately after exercise, both groups could produce 75% of their initial strength. Similarly, Bailey and associates (2007) observed that recovery of maximal voluntary isometric force for knee extensions was not affected by the type of recovery used after intermittent shuttle exercises for 90 min followed by 10 min of immersion at 10 °C. Like the mechanical indicators, the biological markers of muscle damage are only marginally affected by cold-water immersion. By measuring CK enzymatic activity after eccentric leg exercises, Sellwood and colleagues (2007) showed no difference in effect between recovery based on cold-water immersion (3 × 1 min at 5 °C) and immersion in warm water (24 °C). Similarly, Jakeman and associates (2009) observed no effect on creatine kinase activity following 100 countermovement jumps followed by immersion at 10 °C for 10 min compared to a control group.
The hypotheses explaining this lack of results would be, on one hand, the uncontrollable nature of the inflammatory response and, on the other, the cold-related reduction in nerve conduction. This may, for a time, prevent the athlete from producing maximal power (Rutkove 2001) and voluntary or stimulated maximal strength (Peiffer, Abbiss, Watson, et al. 2009). Indeed, some studies have shown a correlation between reduced muscle temperature and muscle activity (i.e., electromyography signal) (Kinugasa and Kilding 2009). In addition, postimmersion comparison of the two voluntary contractile modes (maximal or stimulated) suggests that the loss of neuromuscular function is likely to be peripheral rather than central (Peiffer, Abbiss, Watson, et al. 2009). Finally, a study on reflexes also concluded that cold reduces muscular performance because of the increased excitability of the motoneuron pool (Oksa et al. 2000).
On reviewing these data, it would be easy to conclude that no form of recovery using immersion-based hydrotherapy has any effect on muscle damage. However, four studies indicate significant positive results (Eston and Peters 1999; Vaile, Gill, and Blazevich 2007; Vaile et al. 2008b; Pournot et al. 2010). This suggests that it would be an error to conclude too rapidly on the question, especially with regard to the CWT technique. Vaile and colleagues (2008b) showed that, 24 h after muscle-damaging exercise, a 14 min full-body immersion in water at 15 °C limits the increase in CK to 3.6%, compared to more than 300% with passive recovery (figure 14.2). In addition, these studies were generally performed out of the context of real athletic conditions, where the levels of muscle damage involved are generally much milder. The following section shows that during repeated matches or training sessions, the effect of immersion-based recovery on muscle damage can be very different.