We've all heard of athletes across all sports who swear by ice baths to get them into peak performance - but what is cold exposure, and what evidence is out there that it may help your recovery from exercise?
Cryotherapy is a popular tool used in sport with many top level football teams spending vast sums in the hope of reducing recovery times from strenuous exercise and increasing subsequent athletic performance. Various methods are advocated, most commonly Cold Water Immersion (CWI) and Whole Body Cryotherapy (WBC) (where participants are subject to air chambers cooled to as low as -150 C). A fair amount of research has been done over the years, although there is as yet no standard protocol for administering cyrotherapy. So, what is it meant to do? Generally researchers investigate two types of variables: 1) physiological markers of inflammation (muscle injury) and 2) sports performance (either exhaustive exercise performance or max strength production), both before and after cold exposure to look for potential benefits.
Most hypotheses concerning CWI/WBC’s potential benefits in recovery focus on the physiological recovery from muscular effort. Physiologically, both WBC and CWI are thought to reduce muscular injury from training by producing peripheral vasoconstriction (squeezing the blood out of the skin) and reduced blood vessel permeability (resulting in less oedema and better cellular transit and respiration)(Pournot et al., 2011), although exact mechanisms are still debated (Bouzid et al., 2018; Krueger et al., 2019). To assess whether this has any impact on muscle injury and recovery (the process that leads to our desired training effects), inflammatory markers such as Interleukin (especially Interleukin-6 (IL-6)), Creatine Kinase (CK) and C Reactive Protein (CRP) as they are known to be associated with muscle damage. It is thought that by limiting the inflammatory response post exercise, recovery and subsequent performance will be improved, although there is still some debate as to whether other mechanisms may be at play in any observed recovery enhancement (Bouzid et al., 2018).
A recent systematic review by Rose et al. (2017) suggests that, on balance, cold exposure seems to have small but significant positive effect on physiological recovery through the attenuation of circulating CK and IL-6. While many studies have shown a significant effect on the circulating CK post CWI, there are generally significant methodological problems in these studies. Namely, there is a lack of consistent CWI testing criteria and dosing of CWI/WBC (or even consensus in the use of CWI or WBC as an individual treatment), inconsistent selection of physiological markers to test (and, indeed, a lack of consensus in markers to evaluate), very small sample sizes (some as low as 8 participants), sample biasing (especially in gender (Polidori et al., (2018) found that women proved more physiologically sensitive to the environment and had increased internal thermal resistance, meaning that female athletes may respond differently to the same CWI treatment) and bias in sport selection leading to generalised conclusions about the benefit on recovery as a whole for all athletes (Rose et al., 2017; White and Wells, 2013).
All of this makes comparing studies challenging, especially with many authors suggesting that effects may be highly dependent upon length and number of cold exposures as well as timing post exercise. Most studies, though seem to agree on short term effects of single dose WBC/CWI on measured recovery markers (hours post effort) these markers reach parity with passive recovery controls by the 24 hour mark generally (and some studies show parity in as little as 120 min (De Pauw et al., 2011)). This may point to potential benefits for pitch sports such as football where short-term recovery from maximal efforts may provide additional performance gains in later portions of the game. Frequency of exposure seems to have an impact, for instance all the studies examined in Rose et. al’s 2017 review using multiple cooling sessions showed significantly more consistent results both in performance and physiological markers (namely CK).
While conferring unique acute recovery benefits for pitch sports, CWI/WBC may be problematic in other sports, such as multi-day endurance events. As some authors point out, inflammation is necessary as a normal driving force behind recovery and tissue regeneration, so the desire is to inhibit undue inflammation (the point where neutrophil and macrophage activity increases risk of secondary muscle damage) (White and Wells, 2013) but avoid undue suppression of inflammation which may actually result in poorer recovery (there is little consensus as to where this exact point may lie). Another important factor, the muscle cell’s ability to absorb glucose and replenish its glycogen stores (an obvious requirement for improved muscle performance) is temperature dependant. The rate of glycogen synthesis appears to decrease with cryotherapy intervention, thus impairing recovery and when paired with repeated exhaustive exercise may actually lead to increased fatigue, reduced recovery and performance and even potential overtraining injuries, especially in multi-day events (Naradajah et al., 2018).
So, what about performance? While tests for performance vary widely, most generally include sprint and jump performance, although a wide variety of types and protocols have been used, from single limb exhaustive eccentric training to simulated real-sport scenarios, with no agreed standard (Rose et al., 2017; White and Wells, 2011). Elucidating the mechanism of performance recovery is difficult as it is reliant on many inter-dependent factors such as: glycogen resynthesis, cardiovascular strain and muscle metabolite removal (Bouzid et al., 2018). Commonly investigated variables are pain scores (to judge the severity of delayed onset muscle soreness (DOMS)) and physical performance testing such as aerobic endurance or maximal power/exertion.
The most significant effects observed post CWI/WBC is on DOMS (Hohenauer et al., 2015; Leeder et al., 2011). However, as there is no way to introduce a control group (participants will obviously know if they are being exposed to cold) and, given the large amount of press coverage promoting the benefits of cryotherapy, such a subjective measure is to be treated with suspicion. In many studies, an increase in performance was found with no corresponding change in physiological markers measured (Bouzid et al., 2018).
On the whole, the lack of ability to introduce a true control for cold exposure, paired with the many varied doses of both exercise exertion and cold exposure means that drawing firm conclusions on the efficacy of CWI/WBC is challenging at the moment, with further studies of a uniform design needed to clarify its potential benefits. More importantly, numerous high quality systematic reviews of WBC/CWI have found no significant impact of either regime on performance after 24 hours and studies have as yet failed to delineate if observed improvements in performance are genuine physiological phenomena or merely a change in perceived levels of exertion/soreness by the athlete (Hohenauer et al., 2015; Leeder et al., 2011; Rose et al., 2017; White and Wells, 2013).
Does this mean that you should forgo your cold shower or ice bath? In sort no, the jury's still out - there are some interesting effects observed so far - and athletes do generally perceive they are performing better after cold exposure, which can make a huge impact on your training or race performance. So, in short give it a try and if you dig it - you might just improve your performance and training.
References
Bouzid, M., Ghattassi, K., Daab, W., Zarzissi, S., Bourchiba, M., Masmoudi, L. and Chtourou, H. (2018) ‘Faster physical performance recovery with cold water immersion is not related to lower muscle damage level in professional soccer players.’ Journal of Thermal Biology, 78, pp. 184–191.
De Pauw, K., De Geus, B., Roelands, B., Lauwens, F., Verscheuern, J., Heyman, E. and Meeusen, R. (2011) ‘Effect of Five Different Recovery Methods on Repeated Cycle Performance.’ Medicine And Science In Sports And Exercise, 43(5), pp. 890–897.
Dupuy, O., Douzi, W., Theurot, D., Bosquet, L. and Dogue, B. (2018) ‘An Evidence-Based Approach for Choosing Post-exercise Recovery Techniques to Reduce Markers of Muscle Damage, Soreness, Fatigue, and Inflammation: A Systematic Review With Meta-Analysis.’ Frontiers in physiology, 9, p. 403.
Hohenauer, E., Costello, J., Stoop, R., Kung, U., Clarys, P., Deliens, P. and Clijsen, R. (2015) ‘The Effect of Post-Exercise Cryotherapy on Recovery Characteristics: A Systematic Review and Meta-Analysis.’ PLoS ONE, 10(9), pp. e0139028.
Leeder, J., Gissane, C., Van Someren, K., Gregson, W. and Howatson, G. (2012) ‘Cold water immersion and recovery from strenuous exercise: a meta-analysis.’ British Journal of Sports Medicine, 46(4), pp. 233–40.
Nadarajah, S., Ariyagunarajah, R. and Jong, E.D. (2018) ‘Cryotherapy: not as cool as it seems.’ Journal of Physiology, 596(4), pp. 561–562.
Polidori, G., Cuttell, S., Hammond, L., Langdon, D., Legrand, F., Taiar, R., Boyer, F. C. and Costello, J. T. (2018) ‘Should whole body cryotherapy sessions be differentiated between women and men? A preliminary study on the role of the body thermal resistance.’ Medical Hypotheses, 120, pp. 60–64.
Pournot, H., Bieuzen, F., Louis, J., Fliiard, J., Barbiche, E. and Hausswirth, C. (2011) ‘Time-Course of Changes in Inflammatory Response after Whole-Body Cryotherapy Multi Exposures following Severe Exercise (Inflammatory Response after Whole-Body Cryotherapy).’ PLoS ONE, 6(7), pp. e22748.
Rose, C., Edwards, K., Siegler, J., Graham, K. and Caillaud, C. (2017) ‘Whole-body Cryotherapy as a Recovery Technique after Exercise: A Review of the Literature.’ International Journal of Sports Medicine, 38(14), pp. 1049–1060.
White, G.E. and Wells, G.D. (2013) ‘Cold-water immersion and other forms of cryotherapy: physiological changes potentially affecting recovery from high-intensity exercise.’ Extreme Physiology & Medicine, 2(1), pp. 26.