“It looks like it’s not a great idea” to soak in freezing water after lifting weights, said Milan Betz, a doctoral student at Maastricht University in the Netherlands, who led the study.

The findings add to mounting evidence that ice baths may undermine the effects of lifting and also raise the provocative issue of when, if ever, ice baths are a great idea.

Fans of cold plunging typically say the practice is beneficial for both body and mind, lifting moods, building grit, soothing aches and stiffness, and, perhaps above all, speeding up and intensifying recovery from exercise, so you get more from each workout.

But little science has supported the purported benefits of ice baths, and in recent years, studies have frequently undercut them. In a 2015 experiment, for instance, scientists in Australia asked 21 men to lift weights twice a week. Half of the men cold plunged after every session; the others didn’t. After three months, the cold plungers’ muscles were nearly 20 percent smaller and weaker than the other men’s, although everyone followed the same exercise routine.

Similarly, a 2024 review of prior research, cheekily titled “Throwing Cold Water on Muscle Growth,” concluded that the best available research indicated cold plunges after resistance training can “attenuate hypertrophic changes.” In other words, your muscles won’t grow as much.

How would cold water undo resistance exercise? The review’s authors speculated that frigid temperatures shrink blood vessels, impeding blood flow to muscles. Blood carries nutrients, including protein, that muscles rely on to rebuild and bulk up after draining exercise. Less blood flow means less protein and a feebler recovery.

But no study had yet shown that process in action.

Enter Betz and his colleagues. They wanted to see what happens to blood flow after ice baths, so they recruited 12 healthy young men and used portable ultrasound machines to track baseline blood flow in their legs as they rested at the lab.

The volunteers then sweated though a tough session of leg press and leg extension exercises, before immediately clambering onto a bicycle-like contraption with large buckets where the pedals should be. One contained tepid 80-degree water, the other icy 30-degree water. The men slid a leg into each bucket, so one limb cold plunged, the other didn’t, and stayed there for 20 minutes.

Afterward, the volunteers drank a recovery shake containing protein molecules marked with a biochemical tracer. Researchers could track the tracer to see whether the proteins wound up in muscles or not. The scientists also checked blood flow with an ultrasound several more times over the next few hours.

What they found was that blood flow dropped substantially in the volunteers’ cold-plunged leg, compared to their other limb, and stayed low for hours. The muscles in that chilled leg consequently received and absorbed far less protein from the shake. Over time, this reduced protein intake would likely mean blunted gains in strength and muscle mass from the lifting.

The results “provide confirmatory evidence” that cold plunges can alter the desired effects of weight training by reducing blood flow and protein uptake, said Brad Schoenfeld, an exercise scientist at Lehman College in New York, who studies resistance training and co-wrote the 2024 review.

But this was a single, small study, and many questions remain unanswered. Would ice bathing likewise affect recovery from other exercise? “I would think you’d see similar effects with other sports” such as running, cycling and team sports, Betz said.

What about the effects on women and older people, who weren’t studied here? Betz said he believes, again, the impacts would be much the same in almost everyone, but those studies need to be done.

It’s also unclear whether and to what extent timing and other details matter, said Denis Blondin, a professor of health sciences who studies metabolism and cold exposure at the University of Sherbrooke in Canada. He wasn’t involved with the new study. Maybe ice baths several hours after a workout would have different effects on muscles, he said, as might tweaking how long you soak, how much of your body is submerged and the water’s exact temperature. More large-scale research is needed to understand the nuances of cold soaks and exercise response, Blondin said.

Some people also ice bathe for reasons unrelated to exercise recovery, including to make themselves feel mentally stronger and more resilient. The new study did not consider psychological outcomes from chilling out, Betz said, and, if you find comfort in cold plunges, “there’s no reason to change your mind.”

But, to get the most gains from weight training, he said, the bulk of the available evidence, including the new study, suggest you should probably skip an ice bath soon afterward.

Do you have a fitness question? Email YourMove@washpost.com, and we may answer your question in a future column.