Welcome back to the Science Series! If you missed last week, check it out here.
The Science Series is designed to help you navigate the obscure and confusing world of health research; a world in which almost anything appears to be provable and nothing is written in stone; a world in which one week eggs cause heart disease and the next they cure diabetes. I’ll be looking at topics in the field, paper by paper, to help you understand the data and the evidence so that you can figure out for yourself what to believe.
As ever, bear in mind that I’m not a medical or scientific professional. Nothing I say should be taken as advice and feel free to add a pinch of salt too.
Today I’m looking at a paper that examines the effects of post-workout cold water therapy on strength training results. Cold water and ice baths have been used for decades as post-workout recovery strategies to reduce inflammation and allow athletes to perform at their best in the next workout or game. But is it possible that cold water actually reduces strength and muscle adaptations? This paper claims that it does.
The headlines: researchers found that post-workout (PWO) cold water immersion (CWI) reduced muscle gain by 67% and strength gains by 34% over the course of a 12-week lower body strength programme. In a separate study, they found that CWI reduced the acute expression of anabolic genes by 30%.
The first study was a randomised controlled trial in which participants were initially paired up to match for strength and lean body mass. Then, one of each pair was randomly assigned to 10 minutes of CWI and the other to low intensity active recovery (ACT), post-workout. Participants then went through an identical 12-week strength programme, after which muscle mass in the quadriceps and leg press strength was re-measured.
The differences between the two groups were pretty significant. While the ACT group on average added 309g of new muscle mass to their dominant-leg quad, the CWI group only managed 103g. You definitely care if a strategy denies you 206g of muscle over 12 weeks, in just one of your quads. Assuming that both legs accrue muscle similarly, we’re talking about close to half a kilo of lean mass left on the table. And how detrimental could this potentially be over longer periods of time?
The effects were equally visible for strength. The average ACT group participant increased their leg-press 1RM by 201kg over the 12 weeks, while the CWI group saw an increase of 133kg. If you’re a CrossFitter, you don’t like the sound of this at all. Imagine if someone tried to take ⅓ of your squat gains in the next strength cycle! You should have increased your squat from 100kg to 130kg, but because of your ice baths you only got to 110kg…
A natural objection is that there’s likely high variability in how individuals respond to recovery strategies and high variability in the rate at which individuals increase strength and gain muscle mass. And this is correct. The standard deviation of strength gains in the ACT group was 65kg, or 32%, and was similarly high across all measurements. But, when researchers corrected for this, the effects were still large. They used a metric called Cohen’s effect size, which expresses effects as a multiple of ‘pooled’ standard deviation (standard deviation for the pooled data set including both ACT and CWI groups – check out the footnotes for nerdiness). Muscle mass gain was 4.1 pooled standard deviations greater for the ACT group than the CWI group, on average. The ACT group’s strength gains were 1.5 pooled standard deviations greater than they were for the CWI group. Anything with a Cohen’s effect size above 0.8 is considered a large effect and if you remember your stats 101 from school, you know that 4.1 standard deviations is enormous. In other words, you can’t explain away the average effects of cold water therapy with the variation between individuals.
In order to figure out how post-workout cold water therapy might be blunting gains, researchers conducted another clever experiment to look at anabolic signalling in muscles. In this set-up, rather than splitting subjects into two groups, each participant applied CWI to one leg and ACT to the other leg, post-training. This unilateral approach is a standard trick in the sport scientist’s tool-box and allows them to eliminate all inter-individual variations. All the differences in signalling observed between legs is due to the recovery interventions.
The authors studied an enzyme called p70S6 kinase as a marker of anabolic activity. This protein is activated by the mTOR and IGF-1 pathways, classic anabolic pathways important for muscle hypertrophy. p70S6K’s function is to stimulate cells to increase protein synthesis. Phosphorylation of p70S6K (a measure of its activity) was 90% higher 2 hours post-exercise and 60% higher 24 hours after in the ACT trial as compared with CWI. Total p70SK protein did not change significantly 48 hours after exercise in the CWI trial, but increased by an average of 30% in the ACT trial. The paper also looked at satellite cells in the muscle tissue. Satellite cells are precursors to full-blown muscle cells. They proliferate in response to trauma and exercise in order to help repair damaged muscle and are therefore an important marker of anabolism. In the study, satellite cell counts increased by 48% post-exercise in the ACT trial but remained at baseline for CWI.
So it looks like cold water therapy blunts acute anabolic responses to strength training and consequently reduce gains over time. The authors offer a few hypotheses as to why this might be the case. Cold exposure limits blood flow which has been associated with muscle protein synthesis. The reduction in blood flow might limit the delivery to muscle cells of amino acids and other compounds that serve as fuel and signalling molecules for repair processes. The researchers also suggest that low temperatures may interfere with the expression of genes important for muscle synthesis.
Are there any problems or limitations with this study? As always: yes. First of all, it’s worth noting that the subjects were young men with an average age of 21. As we all know, anabolic responses are typically highly up-regulated in young individuals. A 30 or 40 year old will naturally have decreased anabolic responses to exercise. What difference does the general anabolic context of an individual have on their responses to cold water therapy? Is it possible that those with a lower natural anabolic state are affected less? Secondly, although the study was supposedly conducted on ‘trained’ individuals, the subjects were clearly starting from a fairly low baseline. If you can add 200kg to your leg press over 12 weeks, my guess is you haven’t done much leg-pressing before that! That naturally leads me to wonder what the effects would be for truly trained individuals. The study was also conducted on men, so there is no telling whether these results necessarily translate to women.
It’s also important to keep in mind the exact context of CWI being studied. I don’t think this study implies that cold water immersion is without any benefits. if you avoid CWI immediately after training, you can likely avoid all the potentially deleterious effects. If the authors are right, then all we need to do is make sure that blood flow and temperature are normal post-exercise in order to initiate the recovery processes. In fact, the very problems with CWI outlined here also give a picture of how cold water might have other positive effects. In the context of muscle hypertrophy and strength, mTOR and IGF-1 up-regulation is critical. But there is evidence that chronic down-regulation (as opposed to acute up-regulation) of these pathways is an effective means of increasing longevity. High IGF-1 levels are associated with increased risk of all-cause mortality and inhibition of mTOR is the mechanism of one of the most researched longevity drugs, rapamycin. So if cold water therapy can globally decrease these signalling pathways, perhaps it has a role to play in long-term health. That’s pure speculation, of course. But it goes to show that what might be a benefit in one context can quickly look like a problem in another.
The takeaway for me is that I should avoid ice baths and cold-exposure post-training. This study also points to a more general rule of thumb. Given damage to muscle caused by training or injury, I think you should avoid excessive anti-inflammatory approaches. This paper found that taking ibuprofen post-workout had a similar effect to CWI in terms of reductions in training results. And another paper found that applying ice to crush injuries actually lengthened the recovery process and led to lower quality muscle tissue (in rats). Acute inflammation is a critical part of the recovery process (see this review). It has nothing to do with the dreaded chronic low-level inflammation of modern diseases. So interfere with these mechanism at your peril! What do you think? Leave comments below and feel free to disagree with me over email at firstname.lastname@example.org