Detecting muscle soreness with infrared

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One of the big challenges for researchers trying to figure out how to reduce post-workout muscle soreness is that it’s really hard to quantify that soreness. Asking someone “How sore are you?” is important, but highly susceptible to placebo effects; more objective measures like the enzyme creatine kinase (which is supposed to indicate muscle damage) now tend to be viewed as pretty unreliable proxies for muscle soreness. So how about this:

That’s an image from a new study that used an infrared camera to measure skin temperature before and after a series of biceps curls (press release here; freely available article and video in the Journal of Visualized Experiments here). They suggest that skin temperature that remains elevated 24 hours after exercise indicate muscle damage:

This damage in the muscle causes additional heat transfer from the muscle to the overlying skin, which causes a detectable hot spot under the skin.

And sure enough, their study did find elevated skin temperature in the biceps (33.96 C instead of 32.80 C) 24 hours after exercise. The problem is that the temperature returned to normal (32.82 C) after 48 hours. The subjects’ subjective assessment of soreness, on the other hand, was equally elevated after 24 and 48 hours — so clearly skin temperature isn’t a perfect proxy for what we experience as soreness. Still, it could be an interesting way for researchers to look at the early stages of delayed-onset muscle soreness in a quantifiable way. And it makes pretty pictures.