Cold water immersion (CWI) and the importance of sleep

The role of sleep in recovery

James Marshall says that complicated and rigorous training and recovery schedules are worthless unless athletes also get enough rest – and that means proper sleep.

Training and competing in sport requires a balance between work, rest and play. Athletes are getting better at planning their work alongside their coaches, but they are still not so good at planning their rest and play. Too much work without enough rest could lead to illnesses, injury and burnout. The harder you train, the harder you need to work at your recovery.

A coach is good at planning out sessions, and good coaches try to quantify the work involved. They know how far, how fast, how heavy an athlete has worked.

What is not often quantified are the nontraining stressors such as exams, relationships, travel and financial worries.

In two previous articles I have looked at the background behind training and non-training stress and how it affects the athlete. I also showed how to implement a recovery strategy to help reduce emotional, mental and physical fatigue. We looked at physical tools such as active versus passive recovery, compression pants and a sound nutrition strategy. Since then, the more I have worked with athletes, the more I have come to realise that they are neglecting the most important recovery tool of all. It is now my firm belief that all recovery strategies are worth naught if the athlete does not sleep.

In this article I will look at the problem of sleep deficit and how we can tailor the recovery strategy to enhance sleep quality and quantity. First, I will expand further on the latest research studying cold water immersion, and how that might affect the athlete’s sleep.

The value of cold water immersion

Success in sports depends on an athlete’s ability to perform functional movements, such as running, jumping or changing direction, to a high level on a daily basis. However, the fatiguing effect of high intensity competition and training experienced by elite athletes can reduce the quality of performance.

In recent years, ice baths or cold water immersion (CWI) have been used widely in an attempt to help athletes recover following training and competition. But are they really effective? And what is the correct protocol? Quite often they are done for home matches because the facilities are readily available, but not at away matches. This doesn’t lead to a consistent approach.

Reducing muscle soreness with CWI

One of the potential benefits of CWI is the reduction in muscle soreness associated with intense exercise, otherwise known as delayed onset muscle soreness (DOMS). There is now a vast body of research which supports the use of CWI following intense exercise to reduce DOMS (1, 3, 6, 10, 11, 17, 18, 19, 20,), with benefits including reduced pain at rest, reduced pain on stretch and increased active range of motion.

Several mechanisms have been suggested to be responsible for this reduced soreness including:

1. reduced swelling due to hydrostatic pressure of water; (20)

2. reduced swelling due to constriction of blood vessels at low temperature; (6)

3. reduced nerve conduction velocity due to cold temperature, resulting in increased pain tolerance.(1)

It is not known for certain which of the mechanisms play the biggest role in relieving soreness. However, a recent study(9) comparing different CWI strategies has found that water immersion at 6°C was more effective than both water immersion at 10°C and contrast water immersion alternating between 10°C and 38°C. This would suggest that the cold temperature plays a more important role than the water immersion itself.

However, it has been suggested that this benefit only exists with trained athletes, and that those new to exercise or performing a new training regime will not see a reduction in muscle soreness.

Recovery of performance with CWI

Despite the benefits of CWI for reducing muscle soreness, the effects on recovery of physical performance are less clear. Numerous studies have examined the effects of CWI on a variety of performance-related parameters; however the mixed results make it difficult to draw solid conclusions about its effectiveness.

The table below indicates the discrepancies between studies


Although the results are varied, some patterns do exist across the studies. For instance, the studies which retested performance on the same day seemed to find either no effect or a negative effect. This has been attributed to decreased nerve velocity and also restricted blood flow to the muscle (1, 8).

Studies which tested between 24 and 48 hours later were more likely to find a positive result, suggesting that CWI could help recovery for next day performance. This could be due to a reduced perception of fatigue and/or a reduction in localised swelling which has been shown to reduce force generation (5).

These could be important implications for the use of CWI in sport. Sportsmen and women in sports involving several bouts of competition within one day such as multi-event athletics or rugby sevens would be advised to abstain from CWI in between bouts.

On the other hand, CWI may be beneficial for athletes competing on consecutive days such as tennis, cycling or tournament football.

Due to the varied nature of the results, however, there is no ‘best practice’ which can be advised regarding the use of CWI and so athletes should use with caution on an individualised basis.

Reducing adaptation and sleep disruption

Despite some research supporting the use of CWI for recovery of short-term performance in sport, there are suggestions that long-term use could actually have a negative impact on physical adaptation.

Immersion in cold water has been shown to elicit an increase in the stress hormones cortisol and norepinephrine for up to 60 minutes postimmersion (4). These hormones are catabolic in nature, meaning that they act to break down muscle tissue, which would reduce the body’s ability to adapt to training. If we are looking to get a good night’s sleep, then an increase in stress hormones in the evening will not be conducive to rest.

In addition, the reduction in swelling associated with CWI and relieving muscle soreness may also be detrimental to adaptation: “the inflammatory response may be responsible for initiating, amplifying, and/or resolving skeletal muscle injury” (MacIntyre, 1995) (13).

The researchers in that study also presented evidence of the role of white blood cells in the inflammatory response, which would be significantly reduced during cold water immersion due to the vasoconstriction of localised blood vessels.

Timing CWI carefully

The role of cold water immersion in recovery from intense exercise is still unclear. There is strong evidence which suggests muscle soreness resulting from exercise can be reduced in trained athletes, and that this may have a positive effect on performance in the following days. However, the long-term effects of CWI on the physical adaptation to exercise remain uncertain. The timing of the bout of CWI should be considered carefully, as an immediate stress response will not be beneficial at the end of the day, nor immediately post-competition.

Shakespeare had it right when he described sleep as “tired Nature’s sweet restorer”. Establishing a great recovery strategy and implementing it without having adequate sleep will lead to sub-par performances. Conversely, getting a good recovery strategy in place should enhance your sleep quality and improve performance.

Sleep deprivation has been shown to
– increase cortisol levels
– decrease activity of human growth hormone
– reduce the efficiency for glucose metabolism

All of these things can affect sporting performance (22).

Sleep deprivation


In addition, when tired, concentrating is hard, and reaction times are slower – not great for competition. On top of these physiological changes, sleep deprivation is also shown to reduce cognitive function and therefore reduce the ability to learn a new skill (23). In a study of high school students in Rhode Island, Students who described themselves as struggling or failing school (achieving grades of C, D or F) reported that on school nights they obtain about 25 minutes less sleep and go to bed an average of 40 minutes later than A and B students (24).

A series of studies on the sleep patterns of Stanford University athletes over the last few years has found increasing sleep has led to improved sports performance for all types of athletes (25). One specific study on university swimmers found increasing the athletes sleep to 10 hours a night improved their 15m sprint time, start reaction time and increased their kick strokes. Participants in this ongoing study were five healthy students on the Stanford University men’s and women’s swimming teams. For the first two weeks of the study, the students maintained their usual sleepwake pattern. The athletes then extended their sleep to 10 hours per day for six to seven weeks.

Athletic performance was assessed after each regularly scheduled swim practice. After obtaining extra sleep, athletes swam a 15-metre sprint 0.51 seconds faster, reacted 0.15 seconds quicker off the blocks, improved turn time by 0.10 seconds and increased kick strokes by 5.0 kicks.

These findings were replicated in American Football athletes with increased sleep improving their 20-yard shuttle time and 40-yard dash time. After seven to eight weeks of sleep extension average sprint time in the 20-yard shuttle improved from 4.71 seconds to 4.61 seconds, and the average 40-yard dash time decreased from 4.99 seconds to 4.89 seconds. Daytime sleepiness and fatigue also decreased significantly, while vigour scores significantly improved.

Am I getting enough sleep?

With evidence that sleep deprivation can physiologically and psychologically affect individuals and evidence of increased sleep improving sporting performance, are you getting enough?

If you fall asleep within 20 minutes of going to bed and wake without an alarm you are probably getting enough sleep. However, if you fall asleep as soon as your head hits the pillow and wake to an alarm you are probably sleep deprived. If you feel yourself being more clumsy than usual, that could be another sign(29).

When I ask teenagers about their sleep patterns, I am no longer surprised to hear that they are not getting enough. This is especially true in holiday times with sleepovers and late- night DVD watching or video game playing with friends. Playing video games and watching television have been shown to disrupt sleep patterns and reduce sleep efficiency(30). Combine this with the excitement of having friends over to stay, or updating Facebook statuses on a smartphone and you have an ever bigger disruption to establishing a sleep routine. This then carries over into schoolwork and a diminished cognitive function the next day.

Bedtimes might be the first period of autonomy that teenagers have negotiated with their parents, but maybe it should not be up for discussion. A recent study of 15,569 US adolescents looked at the links between parental-set bed times versus teenager-set bed times and the link between sleep deprivation and depression. Children whose bedtime was later than midnight were 24% more likely to be depressed and had a 20% higher suicidal ideation than those who went to bed before 10pm.

Sleep routine


Sleep is the most important recovery tool of all. As a coach, it is an area that you may trust to your athlete and their parents. All other recovery tools that are at your disposal such as CWI, massage, fuel, hydration, compression garments and active recovery can be utilised to enhance the athlete’s sense of well-being. If an athlete feels better and can unwind from the rigours and mental exertions of sport, then they are more likely to sleep well.

Ensuring that CWI is not over-used in the long term and not used late in the day will limit any negative effects such as an increase in cortisol. Enforcing a strict bedtime and adopting a sound bedtime routine will help your athlete deal not only with the demands of their sport, but also their young life.

James Marshall MSc, CSCS, ACSM/HFI, runs Excelsior, a sports training company


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