Wonder if you should use heat or cold for your sore muscles? Well, the answer is…it depends
When you get two different answers to a question, sometimes even diametrically opposed, you can assume that there is no convincing evidence for either. One example is the seemingly age-old question: Shall I use heat or cold to treat muscle soreness? My answer is: It depends.
What does cold treatment do? First, it numbs the local pain neurons, so the sense of relief is immediate. It also reduces the local tissue temperature, which in turn reduces inflammation and swelling. The mechanism for that is by vasoconstriction, which reduces the blood flow and the release of inflammatory mediators into the site of injury. In the case of serious tissue injury, you want to reduce swelling and inflammation. This is not only reasonable—it works for muscle strains. If you get a shooting pain during or immediately after an exercise—you have a muscle strain.
But what if we are not dealing with injuries like muscle or tendon tears or strains? What about the run of the mill post-exercise muscle soreness?
Muscle soreness after exercise, otherwise known as delayed onset muscle soreness or DOMS, can hinder both your exercise routine and daily activities. If you feel a dull soreness starting about 8 hours and lasting for a few days after an intense bout of physical activity, it is likely that you are suffering from this common condition. What’s the treatment for it? Some “experts” say a cold bath or a cold compress. Others advocate a hot bath or warm compresses. Some cover all bases: do cold first, and follow with heat. Confused?
If you check the internet, you’d find so much nonsense that I can’t blame you for being confused. Here is an example of advice given in Fitness Magazine [Update: We noticed they removed the article]:
Question: “Will a hot bath help prevent muscle soreness after a workout?”
Answer: “Cold water is a better bet,” says Marty Jaramillo, CEO of the I.C.E. Sports Health Group. “Immersing yourself in chilled water is like an ice pack for your entire body,” he says.
“When you exercise, your blood vessels open wider and stay that way for at least an hour afterward. Soreness occurs when waste products like lactic acid settle in your muscles through these dilated vessels. Colder temps constrict vessels, limiting the amount of waste product that accumulates,” explains Jaramillo.
You got it backward, Mr. Jaramillo. Lactic acid is not dumped by the circulation into the muscle—it is generated by the muscle and is removed from it by the blood vessels. So constricting the vessels would actually accomplish the exact opposite of what is desired—it would reduce the rate of lactic acid removal. Besides, the theory that lactic acid causes the soreness has been proven wrong.
The soreness we experience after vigorous exercise is the result of micro-injuries to muscle fibers, and the repair process results in stronger muscles; precisely the reason why we exercise. So, a certain degree of soreness is actually good for you.
Like any healing, a certain amount of inflammation is required to repair the exercised muscle. White cells rushing to the site of the injury remove injured and dead tissue and release peptides, called cytokines and growth factors (fibroblast growth factor, epithelial growth factor, platelet-derived growth factor, to name a few) that, in a marvelously orchestrated fashion, go about repairing the damage. So why would you impede their access to the injury site with cold? It makes more sense to dilate the vessels, to better allow the cells to reach the site and do their job.
Another reason why a cold bath or compress doesn’t make sense: after exercise, a muscle is contracted, and only gradually does it return to its pre-exercise state. Cold will impede the relaxation. Heat relaxes the muscle and thus contributes to faster relief of the soreness.
Where is the evidence?
Amazingly, with all the hot/cold controversy, you’d expect somebody would do the study. I couldn’t find one (please send references, if you know of one). Such a study should be quite easy to do, you don’t even need human volunteers.
Run rats on a treadmill for a pre-determined period to induce micro-injuries in the quadriceps muscles, then treat one group with heat, the other with cold, and a third untreated. Then take periodic blood samples to measure lactic acid and inflammatory mediators, as well as muscle biopsies at different times after the exercise to document the histology of the injured muscle, and its rate of repair. Any sports scientist reading this?
So what’s to be done?
Until such an experiment is done, we need to just use common sense. So here is my routine:
I usually warm up before exercise by doing some stretching and light exercise, lasting about 10-15 minutes. After exercise, I stretch again and then take a hot bath for about 20 minutes. I used to regularly incur running and weight-lifting injuries. But through trial and error, and some common sense, I now manage to avoid injuries and heal faster using this simple recipe.
Bear in mind, though, this is a sample with N of 1. But at least for this experimental subject, it is 100% effective.