The science behind cooling for exercise recovery.
C O L D W A T E R T H E R A PY \ W E L L B E I N G
Heather Massey of the Extreme Environments Laboratory, School of Sport, Health and Exercise Science at the University of Portsmouth, takes the heat out of recovery and talks us through the latest science behind recovery cooling.
Recovery is an important component of any training programme, enabling the repair of muscle fibres and replenishment of muscle glycogen. But, recovery takes time. Athletes training and competing frequently can compromise their sporting performance or reduce their capacity to train as a result of the stress caused by each individual training bout. Inadequate time for recovery between bouts of exercise can lead to injury or a downward spiral into overreaching or overtraining. Some look for ways to promote the right conditions for recovery, or speed up or short cut the recovery required. Recovery cooling is a strategy that has been used by many, without much understanding of the processes involved – namely, providing improved functional recovery by reducing muscle blood flow and tissue temperature, reducing inflammation as well as perceived muscle soreness. But there is a running debate about the long-term use of cooling for recovery, safe use of cooling interventions and whether it is advantageous for training adaptations. Here, I unpick the latest scientific evidence and expert guidance.
Types of cooling
There are several commonly used methods of cooling for post-exercise recovery. These include cold-water immersion, placing the whole body (except your head) or part of the body in cold water (between 8-15°C water temperature) for 8-12 minutes. Or there’s cryotherapy, which can be partial or whole body and involves entering a specialist chamber as cold as -140°C for 2-4 minutes wearing only shorts, a t-shirt, a headband covering the ears, gloves, shoes and socks. Or, finally, placing ice packs or phase change materials (long chain alkenes that melt at higher temperatures than ice) on the skin to cool the skin and underlying muscle. These are more portable than either of the other two methods and can be used for longer.
Cold-water immersion requires a supply of cold water and a vessel to contain it. As both can be easily come by in the UK, this is in common usage, whereas cryotherapy chambers are highly specialised chambers with few available, so are less frequently used.
Research: Blowing hot and cold
With over 60 studies investigating the use of cooling as a recovery modality, there are some patterns emerging that demonstrate when post-exercise cooling for recovery hinders or helps. One recent questionnaire survey of practitioners1 points out that many practitioners are aware of when cooling for recovery is and isn’t advantageous, but don’t have the understanding behind this.
Understanding the mechanisms at play will aid practitioners to optimise the use of cooling in recovery from exercise, ultimately benefiting the athlete.
What does cooling do in the post-exercise recovery phase?
Cooling in the short term reduces elevated body temperature, central nervous system fatigue and reductions in cardiovascular strain. Post-exercise cooling for recovery doesn’t seem to enhance metabolite or lactate clearance as is often purported2, with mixed findings for the effect on inflammatory and immune responses. Cooling in recovery reduced nerve impulse speed in sensory and motor nerves. Sensory nerves are affected to a greater extent, with only modest changes in temperature. In addition, cold receptor activation resulting from exposure to cold can support analgesia by inhibiting pain receptors3.
Both these pathways suggest that an analgesic effect may occur before cooling can impact on contractile function of the muscle, reducing the perception of muscle soreness resulting from exercise-induced muscle damage. The key is to optimise cooling to reduce the sensation of pain without impacting on muscle function.
Reducing the sensation of pain from damaged muscles still leaves the microdamage resulting from the exercise. Pain can act as a protective mechanism to prevent or reduce the likelihood of further damaging exercise while recovery and repair processes occur. There is a balancing act needed to allow adequate recovery. Layering too many sessions of muscle damaging exercise on top of each other without adequate recovery may set people up for injuries as a consequence. Carefully planned recovery and training programmes may help reduce this risk.
When to use post-recovery cooling – and when not to
Cold exposure is detrimental to shortduration, high-intensity sprint performance, especially when activity is performed in repeated bouts. This is possibly due to lowered muscle temperature and subsequent impairments in muscle contractile function. When cooling the working muscles precedes the exercise, the use of cooling in recovery may hinder subsequent performance.
In contrast, cold exposure can accelerate some components of the recovery process. Cold exposure provided strong perceptions of immediate relief from fatigue, with frequent reports of ‘feeling fresher’, ‘a feel-good factor’, ‘more alert’ or ‘reduced mental and/or physical fatigue’.
Long-term effects of cold exposure in the post-exercise recovery phase can impact on the adaptive responses to exercise. This is believed to be dependent on the mode of exercise. Malta and colleagues4 combined a number of studies (in a systematic review and meta-analysis) that investigated the impact on endurance-based performance (time trials) and resistance/strength-based performance (1RM and ballistic exercises) following cold-water immersion. They found that adaptation to aerobic exercise performance was not affected by exposure to cold-water immersion; however, subsequent adaptation to resistance exercise was diminished. No effects on adaptive responses to resistance training were found when using whole-body cryotherapy chambers.
Long-term effects of cold exposure in the post-exercise recovery phase can impact on the adaptive responses to exercise.
Aerobic exercise adaptations aren’t impacted by cold-water immersion, maybe because endurance performance is mainly determined by cardiovascular and haematological adaptations and changes in muscle aerobic function make a smaller contribution to performance.
For resistance exercise, regular cold-water exposure has been shown to cool the muscle and reduce anabolic signalling and protein synthesis necessary for muscle hypertrophy, which can lead to smaller gains in muscle mass and strength following a resistance training programme which includes post-exercise cooling. Using a cryotherapy chamber for post-exercise recovery cooling is a much shorter exposure, cooling the skin and superficial muscles, but quickly returns the tissues to normal temperatures, so may not have the same impact of prolonged muscle cooling and subsequent detrimental effect on adaptation to resistance exercise.
However, more study is needed. The information included so far has focused on laboratory-based studies. Few athletes and practitioners focus solely on endurance-based or strength-based programmes in isolation. Training for most people, including professional athletes, will incorporate a variety of activities, some endurance based, some resistance based, others more technical or tactical. Yet cold exposure in the post-exercise recovery phase is regularly used by many competitors.
Lab-based studies tend to have a much smaller number of sessions, possibly two to three per week, rather than the 10 plus sessions some professionals will have. The small number of sessions incorporated in lab-based studies may allow full recovery, without the need for cold exposure. For more frequent training, where recovery between sessions is not possible, cold exposure in recovery may improve subsequent training performances and stimulate adaptation.
It should also be noted that many practitioners using cold-water exposure tend to avoid its use following resistance training sessions and plan when it is used. Similar to designing a training programme in a periodised fashion, recovery may also need to be periodised to optimise athletic recovery and maximise training adaptations.
Is more cooling better?
While the dose of cold donated to the skin and muscles for different methods of cooling may differ, one thing most research is united upon is that more cold is not better. Humans thermoregulate at a deep body temperature of between 36.5°C and 37.5°C. Longer exposures resulting in significant cooling of the core towards hypothermia (a deep body temperature of 35°C or less) are unlikely to support recovery from exercise. As core temperature declines, shivering to defend deep body temperature and rewarm the body occurs. Shivering is an involuntary asynchronous muscular contraction which increases internal heat production. But it will also result in muscular fatigue and contribute to exercise-induced muscle damage rather than enhance recovery.
There are also risks associated with the use of cold exposure for recovery. These range from the effects of cold shock, an inspiratory gasp and subsequent hyperventilation upon initial immersion in water. Cold shock also increases blood pressure and the work of the heart. In those with underlying cardiac conditions, this can develop into arrythmias or heart attack, or possibly lead to transient ischaemia, amnesia or cerebrovascular accidents.
Cold air exposures could result in freezing (frostbite and frostnip) and non-freezing cold injuries to the skin or deep tissue. Freezing injuries occur when the tissue freezes; human tissue freezes at about -0.55°C. Frostbite or nip can easily occur if participants touch any of the structures in the cryochamber or peripheral tissues such as the ear, fingers and toes are exposed to such extreme cold.
Non-freezing cold injuries are more challenging to diagnose but can result in acute pain, swelling and result in damage to peripheral blood vessels and nerves. Long-term damage and pain may occur. The dose of cold needed to develop a nonfreezing cold injury has not been established, but individual susceptibility may play a part. Cases of non-freezing cold injury are present in people in air temperatures of 15°C for prolonged periods. Extended stays in cryochambers could put people at risk of non-freezing cold injuries.
Care in the administration of cold exposure in the post-exercise recovery phase is needed to mitigate the risks and act upon any problems if they occur. It is advisable that practitioners are present during the use of cooling in recovery to ensure correct procedures are followed and to support athletes in entering and exiting the water or cryochamber, or help to remove ice packs.
There are also a number of conditions for which consultation with the doctor is required prior to using cold exposure for exercise recovery. It is particularly important in those with a history of cardiovascular disorders, including blood disorders, high blood pressure and arrythmias, seizures, urticaria (hives) or kidney disorders.
Recent guidance
Several recent guides have been produced to support the optimisation of cooling in recovery from exercise. These highlight the paucity of evidence for the dose of cold used and also address some of the safety concerns of cooling5,6.
The British Association of Sport and Exercise Scientists recently published an expert statement6. This provides links to the most recent evidence and guidance for the use of cold as part of a recovery strategy. It suggests that if there is sufficient time for recovery between training bouts, and fatigue is not excessive, athletes are encouraged to recover naturally without the need for cooling interventions. Attention is needed to optimise all aspects of training and recovery, including hydration, nutrition, sleep, active recovery and massage, to enhance recovery before considering cooling in recovery.
As with most scientific studies in sport and exercise, there is little evidence of the impact post-exercise recovery cooling has on women and also adolescents. As such, guidance for use in these groups cannot be given with any degree of assurance. We need to make sure that any intervention such as cooling is safe, effective and does not harm the long-term potential for adaptation in women and young athletes.
Take-home message
✔ Optimise all parts of the recovery strategy, including hydration, diet, sleep and other forms of active recovery including massage, before considering cooling.
✔ Check medical history for contraindications.
✔ Work out the utility as a post-exercise recovery tool for you or your athletes and the intended location of use, as well as the cost, accessibility and safety requirements.
✔ Plan when cooling in recovery will be undertaken, preferably not following resistance-training exercise.
✔ Stick to the temperature and time limits (more is not better): cold-water immersions at water temperatures of 10-15°C for 8-10 minutes; cryochamber as low as -140°C for 2-4mins; and ice packs or phase change material packs that are covered and placed on the skin overlying the working muscles for up to three to six hours.
✔ Discontinue use of cooling and seek medical support if there is an adverse reaction, injury or illness resulting from cold exposure.
Reference
HEATHER MASSEY - MAR/APR - fitpro.com