Researcher and PhD candidate Milan Betz says he was not entirely surprised by the results, as he shows a picture of himself with his leg in an enormous bucket. He was not exempt from his own research, which was a continuation of a study done at Maastricht University in 2019. At the time, there was already cause to question the healing properties of ice baths much lauded by athletes.
“It has been shown numerous times over the last ten or fifteen years, that the cold may not be that great for muscle adaptation,” says Betz. That is the process by which muscles are stimulated to grow through stressors, such as exercise. But why would it be worse when they are cooled? That was the question Betz was eager to answer in his own research. “Do certain enzymes in the muscles work less well in the cold? Are signal molecules [which transmit information between cells] not triggered? Or is it related to circulation? And many more questions. That was the starting point for my PhD track.”
Smallest veins
In the Human Biology department of the Faculty of Health Medicine and Life Sciences (FHML), Betz managed to map out the circulation of even the smallest veins. He used an advanced ultrasound device to scan the legs of twelve male subjects. Because there are two such machines available – “thank you, Internal Medicine” – the circulation in both legs could be measured at the exact same time.
That happened in the morning, when the test subjects were still in bed and the circulation was relatively low. “Then everyone would do strength training exercises, at maximum intensity. Very tough,” says Betz, who added the leg press to the list, in which you have to push away a weight while seated. “You could see the circulation shoot up, in both legs.”
So far, so good, but then came the ice bath. In order to take correct measurements, on both legs simultaneously, the test subject was made to sit on an exercise bike. In place of the pedals, Betz and his team had added large, round buckets. One was filled to the brim with body-temperature water, the other with ice. After the subjects had sat on the bikes, legs in the buckets up to their groins, they would be measured again.
Barely any blood
“That’s when we saw that the circulation in the cold leg was 60 to 70 per cent lower than the control leg, the volume was way less.” In other words, “There was literally less blood flowing to the muscles.” The cold had constricted or blocked off the veins. “The most remarkable thing was how long it lasted,” Betz continues. “Even three hours after the ice bath, when the muscle had long since warmed up again, the circulation was up to 25 per cent lower.”
He also gave the test subjects a protein shake “with special amino acids, a building block for proteins, as it were, which we were able to track”. That way, Betz was able to see exactly how many nutrients reached the muscles – an important indicator of recovery. “We noticed that a lot less of the shake reached the cold leg than the control leg. The people whose circulation had been most affected, also absorbed the fewest amino acids.”
Building muscle
In the long term, this can have a negative effect on muscle growth and strength, something athletes work so hard to achieve. “This has also been shown in yet more research, where the subjects were monitored for three months as they completed strength training three times a week, followed by a dive into cold water. Betz: “It is odd that you would first stimulate your muscles to grow and then slow that process down with the cold.”
But what about all those professional athletes who deliberately seek out the cold once they leave the track or their bikes? “That is slightly different,” emphasises Betz. “Our research is focused on muscle growth and adaptation, specifically after strength training. In addition, we made people sit in the ice bath for twenty minutes, that doesn’t always happen. There are also lots of other situations with different results, such as runners or people who do endurance training. And a tournament or match is different again, with different levels of effort. The mental factor also plays a role. Cold muffles the pain, which is helpful if you need to be ready to go again the next day.” That doesn’t take away the other negative effects, though, “such as fewer nutrients reaching the muscles”.
Betz still has questions. For example, what is the effect on women, who are not currently included in this research. “Their body composition is different, as is the underlying layer of fat. That is definitely worth investigating,” says Betz. “But I do think we can conclude that someone who wants to get stronger and build muscle, should just not take an ice bath.”