For decades, sports scientists have been searching for ways to banish the "delayed-onset muscle soreness," or DOMS, that plagues athletes the day after a hard workout. The latest candidate: curcumin, the potent antioxidant and anti-inflammatory found in the curry spice turmeric.
But there's a problem, according to new data from scientists at the University of Guelph and the University of Prince Edward Island: It may work too well. Post-workout inflammation and the associated soreness, it turns out, may be a crucial part of getting fitter. Lose the DOMS, and you may also lose some of the workout's benefits.
The study, which was presented at the American College of Sports Medicine's annual meeting in Boston earlier this summer, involved 21 volunteers who ran for 40 minutes on a treadmill at a steep downhill grade of 12 per cent – a task well-known to induce painful DOMS in subsequent days. Over the following seven days, half the volunteers took 200 milligrams of curcumin daily while the other half were given a placebo; then they completed another downhill treadmill run.
The initial results were encouraging. Those who took curcumin had lower levels of creatine kinase, a marker of muscle damage, in their blood seven days after the first run, and lower peak levels after the second run. As hoped, the supplement seemed to be reducing muscle damage.
In contrast, the actual soreness experienced by the runners after the second run was much higher in the curcumin group than the placebo group. Normally, you get less soreness the second time you do a hard workout, a phenomenon known as the "repeated bout effect – but the curcumin interfered with this protective adaptation.
It's hard to know whether these effects are a result of curcumin's antioxidant status, anti-inflammatory powers or other properties, since the precise causes of DOMS remain poorly understood.
"For something that has been so broadly studied, it is actually pretty remarkable that we haven't been able to explain it more thoroughly," says lead researcher Dr. Jamie Burr, who heads the Human Performance Lab at the University of Guelph.
Still, the results join a growing body of evidence suggesting that anything that artificially accelerates recovery from exercise may also carry a hidden cost, since post-exercise inflammation and oxidative damage may be crucial signals that tells your body to adapt and get stronger.
For example, in a separate session at the ACSM conference, Dr. Jeff Coombes of the University of Queensland in Australia presented a decade's worth of evidence suggesting that antioxidant supplements such as vitamin C interfere with the growth of new mitochondria, one of the key adaptations triggered by endurance training.
Another recent study, published in the Journal of Applied Physiology last month[AUGUST], tested over-the-counter antihistamines, which reduce the inflammation-promoting flow of blood to your muscles after exercise. In this case, unlike with curcumin, volunteers experienced less soreness after downhill running when they took antihistamines, but higher levels of creatine kinase, indicating greater muscle damage.
Confused yet? You should be, because the picture that emerges from all these studies is far from clear. Still, the overall theme is that short-term gains in recovery tend to be balanced by longer-term costs.
"My personal opinion is that these types of supplements, or other interventions intended to alter inflammation such as ice baths, need to be used sparingly," Burr says.
That doesn't mean that curry or antioxidant-rich fruits are bad for you. But what's healthy in the small amounts found in food isn't necessarily better as a megadose. Burr and Coombes both cite the concept of "hormesis," in which something that's toxic at high doses provokes a beneficial adaptation at low doses.
For athletes, one message from this research is that timing matters. If you're playing in a tournament where you need to perform at your best on consecutive days, you might choose to emphasize short-term recovery with antioxidants and ice baths. But during routine training, where long-term adaptation is the goal, you would abstain from these recovery aids.
More generally, these findings reinforce the idea that feeling sore and tired after a workout isn't necessarily a bad thing. Of course, overdoing it so that you can barely walk the day after a killer workout is counterproductive.
But if, once or twice a week, you find yourself shuffling around with lead-filled legs the morning after a hard workout, consider it a sign that fitness-building adaptations in your muscles are operating at full power. Then take an easy day or two to allow your body to recover on its own – you've earned it.
Alex Hutchinson's latest book is Which Comes First, Cardio or Weights? Follow him on Twitter @sweatscience