'Cold water immersion', more commonly known as 'ice baths' are routinely used by professional athletes after sports events.
Dipping into 'icy' water (usually around 10 °C) for 5 to 10 minutes is claimed to improve muscle recovery and enhance future sports performances, but what is the science behind these claims?
We asked 5 experts in exercise physiology: Do post-exercise ice baths improve performance? Here is what they said.
What happens to muscles when they get cold?
Many people use ice packs or a bag of frozen peas at home to reduce pain and swelling if they have pulled a muscle.
Johanna Lanner, an expert in muscle physiology from the Karolinska Institute in Sweden, explains how this works:
"Cooling i) reduces nerve impulse transmission and thus reduces the level of pain perception and ii) induces constriction of blood vessels in peripheral tissues (e.g., muscle) which results in reduced fluid diffusion that may assist in reducing exercise-induced acute inflammation."
Llion Roberts, an expert in exercise physiology from Griffith University in Australia, says: "Cold water immersion is also known to help restore heart rate variability, the variation in the millisecond time periods between successive heart beats."
Interestingly, ice baths can influence our minds as well as our muscles. James Broatch, an expert in exercise physiology from Victoria University in Australia, undertook a research study which compared "the effects of an ice bath with a placebo condition that participants were tricked into thinking was as effective as an ice bath".
In the placebo condition participants had a warm bath with what they thought was a special 'recovery oil' but was actually just a skin cleanser.
Broatch says "participants in both the ice bath and placebo conditions rated their belief in the benefits of their assigned recovery condition similarly, which in turn translated into a similar recovery of leg extension strength over a 48-hour post-exercise period."
What effect do ice baths have on muscle recovery after exercise?
Lanner says that ice baths are effective at "reducing the symptoms of exercise-induced delayed onset muscle soreness i.e., pain and stiffness experienced in muscles several hours to days (usually 24-72 hours) after unaccustomed or strenuous exercise".
For this reason, ice baths are commonly used for muscle recovery after sports competitions.
What effect do ice baths have on exercise performance?
As ice baths help muscles recover, it may follow that they can improve sports performance. Unfortunately it is not that simple – Hakan Westerblad, an expert in cellular muscle physiology from the Karolinska Institute in Sweden, says "scientific studies show varying outcomes regarding the effect of post-exercise ice baths on subsequent performance, with results ranging from minor positive effects, via no effects, to negative effects."
One of the issues with measuring the effect of ice baths on exercise performance is that there are many different types of exercise, such as endurance or strength training.
Roberts says "somewhat surprisingly, after strength exercise, cold water immersion may in fact hinder the benefits of exercise".
He and his colleagues "found large reductions and/or blunting of the desired results from strength training such as increasing strength and muscle mass, and cellular improvements within the muscle. This was most likely a result of the cold water negatively interfering with the natural protein and cellular responses that happen in the muscle after each strength session."
Effects on endurance training may be quite different. Christopher Mawhinney, an expert in sports science from Mahidol University in Thailand, says: "Interestingly, there is evidence which suggests that cooling the exercised muscle increases the cellular signal which turns on mitochondrial biogenesis".
Mitochondrial biogenesis is when cells increase their numbers of mitochondria, which are structures that release energy. Mitochondrial biogenesis is one of the positive effects that comes from endurance training, so ice baths could help to amplify this benefit.
The effects of ice baths on exercise performance differ depends on what kind of exercise is involved.
Rogers summarizes: "Cold water immersion following strength exercise should be undertaken with caution or avoided. Its use following one-off circumstances like big sports events or endurance exercise is recommended, and may even provide additional benefits for subsequent endurance exercise performance."
The takeaway: Don't use ice baths to improve your strength training, but they could be useful for endurance exercises.
Article based on 5 expert answers to this question: Do post-exercise ice baths improve performance?