In the Instagram photo, LeBron James gave a look that’s a cross between a grimace and a snarl. The superstar forward was submerged waist deep in a bathtub filled with ice cubes, and his powerful shoulders bulged as he held his arms and hands up out of the frigid water.

“Training camp ain’t nothing nice! #MyFaceTellItAll #ThisTubColdAsYouKnowWhat #StriveForGreatness,” reads the caption on the image, which James shared with his nearly 30 million Instagram followers. The message was clear: James wasn’t just training hard; he was recovering hard too.

Training camps like the one ­LeBron was attending that year can push athletes to utter exhaustion. This is by design — blocks of intense, multiple daily training sessions are intended to force athletes into a state of “supercompensation,” where the body adapts to stress by fortifying its resources to become faster, fitter, stronger.

But the road to supercompensation is paved in pain, and icing is a popular way of coping with the hurt. Although it’s painful at first, icing eventually numbs the affected areas and people swear it reduces soreness.

Today, ice packs have become as ubiquitous as aspirin — they’re a fixture in every athletic training facility and sold in drugstores throughout the country. Cold baths and ice tubs have also become one of sport’s most popular recovery aids. Nearly every high school, college and pro trainer’s room has at least one ice tub, and over the last 10 or 15 years they’ve become an essential post-workout or injury ritual for athletes in every sport.

Yet science now shows that icing is often the wrong thing to do.

The rationale behind recovery ice packs, baths and cold tubs goes something like this: the cold stimulates your sympathetic nerve fibers, which react by signaling blood vessels in the area to constrict and send blood back to your core to protect your vital organs. This rush of blood away from the extremities reduces blood flow to the areas you’re icing and slows the metabolic processes in these regions, including the inflammatory response, and thus reduces any swelling that might otherwise happen. The pressure of the water may also provide some compression against your muscles and blood vessels, which could also slow swelling and inflammation. Finally, icing relieves pain by numbing sore areas, at least temporarily.

That icing might suppress inflammation has been its big selling point. But physician Gabe Mirkin, who helped popularize its use as part of the RICE (rest, ice, compression, elevation) method by co-writing in 1978 “The Sports Medicine Book,” now denounces the icing methods he once championed. There’s no question that icing can reduce pain, at least temporarily, he told me, but it comes at a cost. “Anything that reduces your immune response will also delay muscle healing,” Mirkin says. “The message is that the cytokines of inflammation are blocked by icing — that’s been shown in several studies.”

Instead of promoting the process of healing and recovery, icing might actually impair it, he says.

The agony of DOMS

Here’s an example of why: One of the most common (and painful) aftereffects of a hard training session is muscle soreness, particularly the phenomenon called delayed-onset muscle soreness, or DOMS, that can leave runners hobbled after a marathon.

The agony of DOMS normally maxes out about 24 to 72 hours after the exercise, and it’s most acute when you exercise your muscles in a way that they are under strain while they’re lengthening. These opposing forces tug at the muscles, producing microscopic tears in the muscle fibers.

Your body responds to this injury by mobilizing a cleanup crew to remove damaged tissues and rebuild the muscles. This process fortifies the muscles, making them stronger. The repair response is also why a repeat bout of muscle-damaging exercise produces less DOMS than the first — because your muscle has become stronger and more resilient in response to the initial bout.

The cleanup and repair process is essentially the inflammation process, say Mirkin and other icing skeptics. inflammation is your body’s way of healing, and the only thing that icing does is delay this healing response. And that’s true whether you’re icing an injury or the micro-damage from a hard workout.

Gary Reinl, a personal trainer and prominent icing skeptic who over the years has worked with professional athletic teams, elite military squads and coaches and trainers around the world, says the problem is that icing merely slows blood flow to the area, it doesn’t halt it indefinitely. Once the icing stops and the blood flow returns to normal, whatever process you were trying to hinder will proceed again. The swelling will continue and the inflammation will start. The only thing you did was delay things, he says.

Indeed, recent studies confirm Reinl’s hunch that, rather than speeding recovery, icing or cooling could actually hinder it. A 2006 study compared the training effects of a cycling ergometer or handgrip exercise with or without a cold bath afterward. Participants did the same exercise on all limbs, but only one arm or leg was subjected to the ice bath. Over the course of four to six weeks of training, the cooled limbs made fewer performance improvements than their counterparts that were spared the cold plunge. Yes, ice can reduce the pain of swelling, but it doesn’t seem to expedite the healing.

A 2013 study looked at what happened when cold packs were applied to the exercised muscles for 15 minutes after a bout of arm extensions. It turned out that subjects who iced had more fatigue than those who didn’t, and the cold packs actually delayed recovery.

Similarly, a 2015 study reported on two experiments looking at how cold water immersion influenced how muscles responded to a strength training program, and found that cold treatment reduced gains in muscle mass and strength and blunted the activation of key proteins in the skeletal muscle.

The studies “challenge the notion that cold water immersion improves recovery after exercise,” the authors wrote.

Yet . . .

Despite the evidence that icing and cold therapy could have downsides, not everyone is ready to leave icing behind, at least not entirely.

Shona Halson, a physiologist who spent years studying fatigue and is former head of recovery at the Australian Institute of Sport, knows the recovery literature inside and out, having been a leading contributor to the body of research. And she also has more than 15 years of experience applying the science to athletes.

There are basically two competing theories regarding icing and cold therapy, she says. The first is that by decreasing inflammation, ice baths might stunt the body’s ability to adapt to whatever training has just occurred. The other is that if an ice bath can reduce pain and soreness, then the athlete could potentially train harder, sooner

Which theory is correct, she says, is still up in the air, and it might be that they’re both right, depending on the circumstance. The research on this issue is still rapidly evolving, and more studies are needed to make the answers more definitive.

Given the current evidence, she has some recommendations that do encompass ice:

Ice baths are probably not a great idea after strength training if your goal is to get stronger, she says. They’re also not the best approach if the athlete is in a building phase of training where the goal is supercompensation. But, in light of what’s currently known, athletes likely can benefit from icing or cold water immersion when they are seeking short-term recovery in between events and are not worried about long-term adaptations.

In other words, she says, if it makes you feel better, go ahead and ice between prelims and finals of your track meet or between events at the CrossFit Games. She also sees a role for cold therapy when an athlete is feeling excessively tired. But if you want to maximize your results from training camp or a hard workout, she believes it may be best to skip the ice.

In practice, Halson has found that athletes generally report small, but meaningful improvements in how they feel after cold water immersion.

A 2011 meta-analysis published online in the British Journal of Sports Medicine which looked at many previous studies also estimated that cold tubs reduced perceived soreness by an average of 16 percent. But the study also identified a major flaw in the studies that weakened their conclusion.

The problem is that there’s no easy way to blind participants to whether they’re getting the treatment — if you get an ice bath, you’ll know it. And if volunteers know they’re getting something that’s supposed to help their recovery, they’re susceptible to the placebo effect. The expectation that they will benefit may nudge them to perceive an improvement.

Is a 16 percent reduction in soreness a meaningful difference? Maybe. Previous studies have calculated that for a decrease in pain to make a real difference in everyday life, it needs to be on the order of 14 to 25 percent. That implies that reductions in muscle soreness seen in these studies were just on the border of making a noticeable difference in anyone’s life.

It may turn out that an ice bath’s greatest benefits are psychological. A 2014 study employed a clever placebo group to test the effects of a cold water tub. Researchers had the placebo group apply a fake pain-relieving cream and then soak in a room-temperature tub, while a control group just took a dip in the pleasant water. It turned out the placebo was just as effective as the cold soak.

What cold soaks do best is give people a recovery ritual and a sense of agency — the feeling that they’ve done something good for themselves. Surely that’s worth something, even if it’s just a way to pass the time while recovery happens as it will.

Reprinted from “Good to Go: What the Athlete in all of Us can Learn From the Strange Science of Recovery” by Christie Aschwanden. Copyright © 2019 by Christie Aschwanden. With permission of the publisher, W.W. Norton & Co. All rights reserved