What is the rationale behind cold-water immersion to enhance endurance adaptations?
I have written previously about the science surrounding the use of cold-water immersion (CWI) and other forms of cold therapies on recovery in athletes. However, another recently popularized use of CWI is to help enhance the long-term adaptation response to and performance of endurance exercise. In other words, CWI done after an endurance training session is reportedly being used to help improve the adaptive response to endurance training and long-term performance. But, does this really work? What is the evidence to support it?
Before I dive into the evidence, let’s discuss briefly the rationale behind this theory. A single endurance training session elicits a massive molecular and biochemical response from your body, known as a hormetic response. The short-term stress, and the associated molecular and biochemical responses of a single endurance session results in a temporary reduction in performance, but the adaptive response to repeated short-term stresses ultimately yields a positive net improvement in function and performance. Figure 1 below represents how long-term adaptation to endurance training takes place:
It is thought that CWI after endurance exercise helps to augment this process above, specifically at the molecular and biochemical level during the short-term stress response to a single exercise session. For example, research has shown that CWI following a single bout of endurance exercise increases the protein content of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (or PGC-1aplha for short) to a greater extent than just endurance exercise alone (1,3,4). This is one of the molecular responses to endurance training, an increased PGC-1aplha concentration in the muscle, that leads to increased mitochondrial biogenesis (the formation of new mitochondria).
This research has gotten some thinking that maybe CWI after endurance exercise can actually enhance the adaptation response to chronic endurance training. However, it is important to know that there is a big difference between what happens initially after a single exercise session and what happens long-term after repeated exercise sessions. In other words, just because CWI after a single exercise session increases PGC-1alpha content of skeletal muscle, one cannot then assume that this will certainly lead to greater mitochondrial content, and therefore greater endurance adaptations, in the long-term.
Why? Because the adaptive responses to endurance exercise are insanely complex, and there are literally thousands of molecular and biochemical responses that ensue from a single exercise session. The long-term adaptation process is even more complex as it takes into account these thousands of molecular and biochemical responses to a single session and multiplies it over days, weeks, and months. To truly know whether or not CWI after endurance exercise helps augment long-term adaptation, we need to look at research that has studied the long-term effects of CWI on endurance adaptation and performance. Let’s take a look at this research next.
What Does the Research Say Regarding Cold-Water Immersion on Endurance Adaptation and Performance?
Broatch and colleagues (2) published a systematic review of the literature in 2018 in which they aimed to examine the influence that CWI had on adaptive responses to exercise across both endurance exercise and strength exercise. For the purposes of this write-up, I’m only focusing on their findings as they relate to endurance exercise, but I would recommend you check this review paper out if you want more detail as it pertains to strength exercise.
Essentially, the authors found that while some studies do show short-term increases in markers of mitochondrial biogenesis (e.g., increased PGC-1alpha among other markers), there was no long-term changes from regular CWI post-exercise over time. In other words, although CWI immediately after endurance training might elicit or augment increases in certain molecular pathways important for long-term training adaptations, this doesn’t appear to actually play out with increased endurance training adaptation in the long-run, including a lack of increase in mitochondrial proteins, which one would expect to see if CWI helped augment greater changes in endurance adaptation compared to exercise alone.
Malta and colleagues (5) published a slightly more recent systematic review and meta-analysis in 2021 that aimed to examine the influence of CWI on actual performance outcomes across both strength training and endurance exercise; however, I will again only focus on the endurance findings herein. I do recommend you read this paper as well though if you want to deepen your understanding of CWI on exercise performance. Interestingly, and in line with the prior 2018 systematic review that found no beneficial effects of CWI on adaptive responses to chronic endurance exercise, this 2021 review found that CWI had no significant negative or positive effect on markers of endurance performance (cycling time-trial mean power, maximal aerobic power, and cycling time trial performance).
The findings from these two papers taken together demonstrate no real effect of chronic CWI post-endurance exercise on adaptive responses nor endurance performance. The research that has been done so far is not without its limitations, however, namely the length of cold exposure time possibly being insufficient to elicit long-term adaptive effects or performance improvements. The typical CWI protocols across all studies included within these papers typically consists of immersing oneself in water at 40-50 degrees F for 10-20 minutes after exercise for 3-7 weeks in length. Broatch and colleagues (2) noted that extremely long cold air exposure in the order of multiple months at a time in animals has elicited long-term increases in mitochondrial proteins, which would mark improvements in endurance adaptations. However, the exposure time each day is likely far longer than what any normal athlete would expose themselves to, which has been upwards of 24 hours/day of cold exposure in the animals studied. Malta and colleagues (5) also mentioned that it is largely unknown if longer CWI exposure per session would result in more favorable findings on long-term performance outcomes.
There might be an optimal window of time that is longer than current protocols (e.g., >20 minutes at a time) or colder than current protocols (e.g., <40 degrees F) that does indeed work. It is also possible that longer-term studies (i.e., longer than 7 weeks) are needed to see endurance adaptations or performance benefits take place from CWI. Finally, it could also be possible that extremely cold air exposure has the potential to augment endurance adaptations and performance as one can expose themself to far colder temperatures than they otherwise could with cold water. However, these types of studies have not been done yet. Further research is needed to answer these questions.
Broadly, the use of CWI is not recommended as a means of enhancing long-term endurance training adaptations and performance outcomes. Despite promising research showing short-term increases in markers of endurance adaptation, these short-term increases do not seem to materialize into long-term adaptations indicative of enhanced endurance adaptation nor actual performance improvements. The use of CWI to enhance recovery after training is another popular use of this modality. The evidence is very mixed on whether CWI works to enhance the recovery process between hard training sessions as well (2). However, there does not seem to be any harm to doing CWI post-endurance exercise, both in terms of its short-term effects and its long-term effects, so if you already use CWI after exercise and you enjoy it, there would be no reason to discontinue. Go on with it at your pleasure, or discomfort, depending on how you view CWI.
Personally, I enjoy short bouts of cold showers each day for reasons other than recovery or the possibility of enhanced endurance adaptation. I also like to pair up infrared sauna sessions with cold showers immediately afterwards for contrast therapy. I enjoy the invigorating sensation I get after a few minutes of cold exposure, so I’ll continue doing this with the knowledge that it is likely not helping my performance nor hindering it.
Allan, R., Sharples, A. P., Close, G. L., Drust, B., Shepherd, S. O., Dutton, J., ... & Gregson, W. (2017). Postexercise cold water immersion modulates skeletal muscle PGC-1α mRNA expression in immersed and nonimmersed limbs: evidence of systemic regulation. Journal of Applied Physiology, 123(2), 451-459.
Broatch, J. R., Petersen, A., & Bishop, D. J. (2018). The influence of post-exercise cold-water immersion on adaptive responses to exercise: a review of the literature. Sports Medicine, 48(6), 1369-1387.
Ihsan, M., Watson, G., Choo, H. C., Lewandowski, P., Papazzo, A., Cameron-Smith, D., & Abbiss, C. R. (2014). Postexercise muscle cooling enhances gene expression of PGC-1. Med Sci Sports Exerc, 46(10), 1900-1907.
Joo, C. H., Allan, R., Drust, B., Close, G. L., Jeong, T. S., Bartlett, J. D., ... & Gregson, W. (2016). Passive and post-exercise cold-water immersion augments PGC-1α and VEGF expression in human skeletal muscle. European journal of applied physiology, 116(11), 2315-2326.
Malta, E. S., Dutra, Y. M., Broatch, J. R., Bishop, D. J., & Zagatto, A. M. (2021). The effects of regular cold-water immersion use on training-induced changes in strength and endurance performance: a systematic review with meta-analysis. Sports Medicine, 51(1), 161-174.
Happy training and racing!
-Ryan Eckert, MS, CSCS
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