Warm those muscles for a real chill-out

Relaxing in a warm spa or using other warming methods might be one way to help tired muscles recover.
Relaxing in a warm spa or using other warming methods might be one way to help tired muscles recover.LIANHE WANBAO FILE PHOTO

Swedish study suggests that warmth bolsters the recovery process after strenuous exercise

NEW YORK • Muscles recover better after exhausting exercise if they are warmed than if they are chilled, a new study finds.

The results should bring succour to participants in next Sunday's Standard Chartered Singapore Marathon and other upcoming strenuous events if they would rather ease afterwards into a sybaritic hot tub than an ice bath.

Athletes and others involved in sports training have long debated how best to help tired muscles recover after draining workouts and competitions. Some experts tout icing. Others prefer ibuprofen tablets. Still others swear by Tens machines, which use a mild electrical current to stimulate nerves and supposedly reduce soreness.

Little, if any, scientific evidence supports these methods, however. In fact, a number of recent studies have indicated that many of these techniques, especially the use of anti-inflammatory painkillers, can slow muscle recovery after harsh exercise and do not reduce soreness.

Other research has shown that icing, which remains the most popular way to treat overworked muscles, does not reduce inflammation in the tired tissues, although it remains a popular choice for many athletes.

Faced with these largely disappointing experimental results, researchers at the Karolinska Institute in Sweden and other universities began to wonder recently about heat. Might warming muscles after hard exercise help them to regain strength and power?

To find out, they invited five fit young men and women to a human performance laboratory and sat them in front of arm-pedalling machines. Then they asked each volunteer to spin the pedals through a series of brief but gruelling intervals, followed by 20 minutes of easier but almost non-stop exercise, while the researchers tracked their heart rates and power output.

This routine was designed to exhaust the volunteers' arm muscles. Many processes are involved in muscular exhaustion, but the one that is best understood is the depletion of the muscles' glycogen, which is the name for their stored carbohydrates. Once the muscles burn through most of this fuel source, they become weak.

The Swedish scientists suspected that finding ways to rapidly replenish these stores might help the muscles to recover relatively rapidly from their fatigue.

So they asked their volunteers to consume large amounts of carbohydrates in the two hours after their session of hard pedalling but not to otherwise coddle their muscles.

Then, on subsequent visits to the lab, they had the young people repeat the pedalling workout twice more, and immediately afterwards, slip long cuffs over their arms that could be heated or chilled with water coils. The cuffs were warmed during one session to about 100 deg F (37.7 deg C) and chilled during another to about 5 deg F (-15 deg C). The volunteers wore the cuffs for two hours while also downing carbohydrates.

Finally, at the end of each session, the men and women repeated the interval portion of their original pedalling, since it was the most tiring.

And each of them could pedal hardest at that point if their arm muscles had been warmed beforehand. Their power output then was "markedly better" than after the other two sessions, the scientists wrote in their paper, suggesting that their muscles had better regained strength. Their power was worst after their muscles had been cooled.

But these results, while interesting, could not explain why heat might be boosting recovery, so the inquisitive scientists next turned to individual leg-muscle fibres obtained from mice. They attached the fibres to a mechanism that could record the strength of contractions and then zapped the fibres with electricity so that they contracted, over and over. The researchers noted when these contractions slowed, indicating the fibres had grown tired.

They then tired other fibres before dousing some of them with glycogen and subsequently warming or cooling all of the fibres and re-stimulating them a final time.

They also examined whether warming or cooling had affected how much glycogen the muscle tissue absorbed.

As with the young men and women's arms, the muscle fibres turned out to have recovered best after being heated - but only if they also had been exposed to glycogen. When the fibres had not received any refuelling after their exercise, they did not regain their original power, even after warming.

The lesson of these findings, published in the Journal of Physiology, seems to be that "warming muscles probably aids in recovery by augmenting the muscles' uptake of carbohydrates," said Arthur Cheng, a researcher at the Karolinska Institute, who led the study.

This study looked only at one aspect of recovery after exercise, however, concentrating on how tired muscles might best regain their ability to generate power. It cannot tell us whether warm baths might lessen muscle pain after long, hard exercise. (Unfortunately, most recent studies suggest that nothing substantially reduces this soreness, except time.)

But the study does provide a rationale for filling your bathtub with warm water after a marathon or other hard exertion, grabbing a sports bar or chocolate milk to replace lost carbohydrates, and settling in for a long soak.


A version of this article appeared in the print edition of The Sunday Times on November 26, 2017, with the headline 'Warm those muscles for a real chill-out'. Print Edition | Subscribe