Immersion in cold water is not always beneficial

I live very close to Lake Ontario and over the past couple of years I have noticed that the number of people taking dips in the lake on cold mornings during the winter has grown dramatically. It’s not an oddity anymore: I see people cold-dipping every day, and some are regulars. I usually walk the dog in a coat, hat and gloves, and right next to me, people are stripping and warming up, usually in groups.

Cold therapy, which proponents believe can boost the immune system, improve cardiovascular health and is just a difficult thing to do, has been growing in popularity. 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 best-known advocates 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 might reduce inflammation, it would limit a “normal protective response that promotes healing.” He concluded that most of Hof’s claims were speculation, and not supported by evidence.

Since Harriet’s publication, cold immersions seem to have increased in popularity and more evidence has emerged about the merits of this therapy. As for exercise, its benefits are not so clear.

First, it should be obvious that you cannot do a double-blind randomized controlled trial with cold therapy. Although researchers have attempted to examine objective measures, subjective measures are more difficult to assess. If simply I like take cold plunges because it makes you feel good/tough/alive/strong; then you have it. There is no evidence I can present to confirm or disprove how a cold bath does you feel doing it

I should also note that the trials I found focused mostly on cold baths and did not seem to include the hyperventilation that Hof advocates as part of his method. So this is less a review of Hof’s specific recommendations, and more of the act of cold immersion/cold water immersion.

It’s worth summarizing what actually happens physiologically when you submerge your body in cold water. A sudden fall can trigger a cold shock response—a rapid increase in breathing, heart rate, and blood pressure that can stress the heart, even leading to heart attacks. Within minutes, the loss of body heat can start to cause other problems. Blood will move from the extremities to the core to protect the vital organs. Hypothermia may occur. These effects can be partially mitigated or delayed by training over time, but loss of body heat is inevitable; it’s physics (Note that the deaths have been attributed to Hof’s approach and cold immersion therapy.)

Effects on exercise recovery

Russian and Chinese researchers completed a meta-analysis that looked specifically at recovery from fatigue. Twenty studies were analyzed, including some randomized controlled trials (RCTs). Cold water immersion was defined as immersion in water at 15ºC (59). Control groups usually rest, without cold immersion. They analyzed measures of recovery from high-intensity exercise (eg rugby, football) after 0, 24 and 48 hours. Ratings of perceived exertion, delayed onset muscle soreness (DOMS), and countermovement jump test results were also examined, as well as blood markers of exercise recovery.

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 later. Some laboratory measures improved (ie, decreased) but others were unaffected. A subgroup analysis showed that colder water (<10C (<59)) was more effective than 10C, in improving the countermovement jump, but had no effect on other measures, such as recovery from fatigue. There was also no difference observed between partial (waist) and full (shoulder) submersions. The authors concluded that immersion in cold water immediately after exercise improved subjective symptoms such as muscle soreness and could speed recovery. However, as the quality of the trials was poor (which was acknowledged by the authors), it is reasonable and prudent to regard these findings as interesting but not conclusive.

Effects on muscle growth

Another meta-analysis examined the effects of cold water immersion on muscle growth in resistance (strength) training subjects. Eight studies were included, with studies between 4 and 12 weeks and adults (almost all male) aged 20 to 26 years. Some trials used untrained volunteers, others used those accustomed to resistance training. The studies looked at different measures of strength, including hand strength, wrist flexors, but also lower and full body workouts.

All studies used cold water immersion after exercise: some exposed the upper or lower extremities and some used whole body immersion. The water temperature was 1015 (5059) and the duration of the dive was 10-20 minutes.

Muscle size was assessed using different imaging techniques, but also biopsy and also limb circumference.

The study estimated that cold water therapy combined with resistance training had less muscle gain (hypertrophy), compared to resistance training alone. This supports the hypothesis that cold water immersion may be blunting or blunting the inflammatory response, which reduces muscle adaptation and ultimately less gain.

Inflammation isn’t all bad

Cold water plunges may seem trendy and may even feel subjectively good, but that doesn’t mean the health benefits are a certainty. For those who exercise, it’s important to remember that the benefits of your workout come true during the recovery period. Hard workouts can be painful, due to tissue damage that causes the body to remodel and strengthen itself for the next workout. Inflammation is an expected (and desirable) outcome, even if it is painful. Blocking the inflammation process, which cold dives seem to do, can delay this recovery and adaptation process. When speedy recovery is the priority, cold baths can be helpful and subjectively beneficial. When looking to increase muscle size, the benefits of cold therapy are less clear.

Photo by flickr user Andrey Papko used under a CC license.