I live very close to Lake Ontario and I’ve noticed over the past two years that the number of people that are doing morning cold plunges in the lake – throughout the winter – has grown dramatically. It’s no longer an oddity – I see people every single day doing cold plunges, and some are regulars. I’m typically walking the dog bundled up with a coat, hat and gloves, and right beside me, people are stripping down and taking cold plunges, usually in groups.
Cold therapy, which advocates believe can boost the immune system, enhance cardiovascular health, and is just a tough thing to do, has been growing in popularity. Back in 2021, the late Harriet Hall wrote about Wim Hof, the Dutch athlete famous for his ability to tolerate extreme cold temperatures, and one of the most well known proponents of this activity. His Wim Hof Method® says you’ll be “happier, healthier, and stronger” with his method of hyperventilation, cold plunges and “commitment”. Harriet’s conclusion at the time was that while this practice could conceivably reduce inflammation, it would be limiting a “normal protective response that promotes healing.” She concluded that most of Hof’s claims were speculation, and not supported by evidence.
Since Harriet’s post, cold plunges seem to have increased in popularity, and more evidence has emerged on the merits of this therapy. With respect to exercise, its benefits are not so clear cut.
First of all, it should be obvious that you can’t do a double-blind randomized controlled trial with cold therapy. While researchers have tried to examine objective measures, the subjective is harder to assess. If you simply like to do cold plunges because it makes you feel good/tough/alive/strong – then have at it. There’s no evidence that I can present that’s going to confirm or refute how cold bathing makes you feel by doing it.
I should also point out that the trials I found focused primarily on cold baths and did not appear to include the hyperventilation that Hof advocates as part of his method. So this is less a review of Hof’s specific recommendations, but of the act of cold plunges/cold water immersion.
It’s worth summarizing what actually happens physiologically when you immerse your body in cold water. A sudden plunge can lead to the cold shock response: a rapid increase in breathing, heart rate and blood pressure which can place stress on the heart, even causing heart attacks. Within minutes, the loss of heat from the body can start to cause other problems. Blood will move from the extremities to the core to protect vital organs. Hypothermia can result. These effects can be mitigated or delayed in part through training over time – but the heat loss from the body is inevitable – it’s physics. (It should be noted that deaths have been attributed to Hof’s approach and cold plunge therapy.)
Effects on exercise recovery
Russian and Chinese researchers completed a meta-analysis looking specifically at fatigue recovery. Twenty studies were analyzed, including some randomized controlled trials (RCTs). Cold water immersion was defined as immersion in water at ≤15°C (59℉). Control groups would typically rest, with no cold immersion. They looked at measures of recovery from high-intensity exercise (e.g., rugby, football) after 0, 24 and 48 hours. Ratings of perceived exertion, delayed-onset muscle soreness (DOMS), and countermovement jump test results, as well as blood markers of exercise recovery were also examined.
The analysis found that cold water immersion reduced DOMS at 0 hours and 24 hours, but not at 48 hours. Ratings of perceived exertion and countermovement jump were improved at 0 hours, but not subsequently. Some lab measures improved (that is, they were reduced) but others were not affected. A subgroup analysis showed that colder water (<10°C (<59℉)) was more effective than ≥10°C, in improving countermovement jump, but had no effect on other measures, like fatigue recovery. There was also no difference noted between partial plunges (waist) to full plunges (shoulders). The authors concluded that immersion in cold water immediately after exercise improved subjective symptoms such as muscle soreness and could accelerate recovery. However, because the quality of the trials was poor (which was acknowledged by the authors), it’s reasonable and prudent to consider these findings as interesting but not conclusive.
Effects on muscle growth
Another meta-analysis examined effects of cold water immersion on muscle growth in subjects that were doing resistance (strength) training. Eight studies were included, with studies ranging 4-12 weeks and adults (almost all males) aged 20-26. Some trials uses untrained volunteers, others used those accustomed to resistance training. Studies looked at different measures of strength, including handgrip strength, wrist flexors, but also lower body and whole body workouts.
All studies used post-exercise cold water immersion – with some exposing upper or lower limbs, and some using whole-body immersion. Water temperatures were 10–15℃ (50–59℉), and the duration of immersion was 10-20 minutes.
Muscle size was assessed using different imaging techniques but also biopsy and also limb circumference.
The study found that cold water therapy combined with resistance training had less muscle gain (hypertrophy), compared to resistance training alone. The supports the hypothesis that cold water immersion may be blunting or attenuating the inflammatory response, which reduces muscular adaptation – and ultimately, fewer gains.
Inflammation isn’t all bad
Cold water plunges may seem trendy and may even feel subjectively good, but that doesn’t mean that health benefits are a certainty. For those that exercise, it’s important to remember that the benefits of your workout are realized during the recovery period. Hard workouts can be painful, through damage to tissues that prompt the body to remodel and strengthen itself for the next workout. Inflammation is an expected (and desirable) result, even if it is painful. Blocking the inflammation process, which cold plunges appear to do, may delay that recovery and adaptation process. When rapid recovery is the priority, cold baths may be worthwhile and subjectively beneficial. When growth in muscle size is sought, cold therapy’s benefits are less clear.
Photo from flickr user Andrey Papko used under a CC license.