The Hidden Cost of Cold Plunges

This Week’s Research Highlight

No pain, no gain.

It’s one of those expressions that’s hard to escape.

Plastered on gym walls. Repeated ad nauseum in fitness classes. Baked indelibly into our cultural understanding of what effort should feel like.

Yet in practice, we spend much of our time trying to escape that discomfort. We ice sore muscles. We pop anti-inflammatories. We chase recovery tools that promise to make hard training feel easier, faster. And we assume that by reducing the pain, we are accelerating the payoff.

But what if that’s not always the case?

Some of the pain — or more precisely, the physiological pathways behind it — isn’t just a side effect. It’s a signal. A necessary message telling the body to adapt. And by quieting those signals, we may also be dampening the response.

Take oxidative stress, for example. During exercise, skeletal muscle produces reactive oxygen species (ROS). For years, these exercise-induced ROS were perceived as harmful byproducts that impaired performance and caused tissue damage. That view fueled widespread use of antioxidant supplements like vitamin C and E, intended to neutralize ROS and speed recovery.

But that model missed something crucial: elevations in ROS after training are required for the adaptive cascade that makes us stronger, faster, and healthier. These molecules serve as signaling messengers that trigger key adaptations: greater insulin sensitivity, new mitochondria, stronger contractile proteins. In other words, the very benefits of training.

In one 10-week study, participants who took vitamin C and E saw just half the strength gains in their biceps, compared to the placebo group, despite following identical workouts. Molecular analysis revealed why: the supplements blunted the activation of key signaling proteins involved in muscle adaptation. The stress signal was muted. And so was the response.

Now, new research suggests that post-exercise cold exposure may follow a similar pattern.

Cold exposure didn’t start as a wellness trend. It began as a recovery tactic in elite sports, especially in high-impact, high-frequency settings like college and professional football. The goal here was never to boost long-term adaptation, it was to keep athletes moving. Reduce soreness, tame inflammation and get players back on the field the next day.

From there, the practice spread. First to other sports, then to gyms and training centers. And finally to wellness culture more broadly, where ice baths and cryo chambers are now marketed as catch-all recovery tools for anyone chasing performance.

But here’s the thing: if cold exposure works by dampening stress, could it also be dampening the signal to adapt, much like antioxidants?

One group of scientists decided to test it in the most controlled way they could think of: by sending both legs through the same workout —then plunging just one of them into icy water.

Let's take a closer look.

Inside the Experiment

To test whether cold plunges interfere with muscle recovery, researchers at Maastricht University devised a randomized controlled trial with a clever twist: instead of comparing different people, they compared one leg to the other in the same individual.

Twelve healthy young men reported to the lab for a tightly controlled test day. First came a heavy lower-body workout — leg presses and knee extensions, four sets each, all at 80% of their max. A serious strength stimulus, designed to kickstart the process of muscle repair.

Then came the split.

One leg was submerged in icy water — just 8°C (46°F), cold enough to sting. The other leg went into thermoneutral water at 30°C (86°F). Warm enough to avoid triggering a cold response, but too mild to actively influence recovery.

Both legs had done the same work. Only the temperature changed.

And everything was carefully tracked.

All participants were given a recovery shake that contained a molecular tracer: the amino acid phenylalanine, tagged with carbon-13. This small tweak doesn’t change how the amino acid behaves, but it gives researchers a molecular fingerprint to follow. By taking muscle biopsies four hours later, they could see exactly how much of it was used to build new muscle protein.

So what happened?

The Price of Cold

The cold leg fell behind. And not just by a little.

Immediately after immersion, blood flow to the cooled leg declined sharply — more than 50% lower microvascular perfusion, compared to the control.

And that effect was sustained. Even hours later, the cold leg still showed impaired blood delivery at the capillary level, where nutrients actually reach the muscle.

This is where the tracer came in.

When researchers analyzed the muscle biopsies, they found that the cold leg had absorbed and incorporated about 31% less of the labeled amino acid into muscle protein. That’s a sizable drop in synthesis, and it wasn’t random. The legs with the lowest blood flow also had the weakest amino acid uptake. Those two variables — perfusion and protein incorporation — were strongly correlated.

Post-exercise cold exposure reduced muscle protein synthesis. Each line represents one participant. The cold leg incorporated significantly less of the labeled amino acid into muscle protein.

Think of it this way: the bloodstream is a delivery network. Capillaries are the on-ramps. After cold exposure, many of them were effectively closed. The nutrients were there, circulating. But the muscle couldn’t access them.

This finding complicates a common assumption: that easing post-workout discomfort means faster recovery. But here, we see that the cold plunge reduced blood flow and protein synthesis — two key drivers of repair. What looked like recovery on the surface may have stalled the deeper process that leads to long term gains in health and performance.

Why Blood Flow Matters

When we think about recovery, we often focus on soreness and inflammation, and for good reason. These are part of the signaling cascade that tells muscle to repair and adapt. But signaling alone isn’t enough. Once the message is sent, the muscle still needs raw materials: amino acids, oxygen, growth factors. That’s where blood flow comes in, as the delivery system.

More specifically, it’s microvascular perfusion — the capacity of tiny capillaries inside the muscle to open up, allow nutrient exchange, and feed the tissue what it needs to adapt. It’s not just about how much blood is circulating, but where it’s going and how easily it gets in.

In this study, cold exposure dramatically restricted that access. The perfusion bottleneck lasted for hours, even with a protein-rich recovery drink on board. And because amino acid uptake is a rate-limited process, that delay matters. The muscle only stays receptive for so long.

Now, a single missed opportunity probably isn't a big deal. But repeated often enough, it will start to reshape the outcome.

The Long-Term Cost

What exactly does a 31% reduction in amino acid incorporation after a single session mean?

Well, in practical terms, it’s kind of like losing a third of your post-workout protein shake. If you typically absorb 25 grams’ worth of amino acids after training, cold exposure could drop that to around 17.

And remember that hypertrophy is cumulative. It’s the slow layering of tiny, repeated gains. If cold exposure consistently blunts that process, the toll adds up.

That’s exactly what researchers saw in a 12-week training study: participants who used cold water immersion after every strength session gained two-thirds less muscle mass than those who did active recovery instead — just 103 grams versus 309 grams. Strength improvements also lagged behind. Leg press gains in the cold group were 57% smaller, and increases in knee extension strength were nearly halved.

Strength gains were significantly smaller in the cold water group. Over 12 weeks, participants who used cold plunges after training (CWI) showed reduced improvements across multiple metrics — including leg press strength, knee extension strength, and isometric torque — compared to those who used active recovery (ACT). From Roberts et al, 2015.

When the scientists examined muscle biopsies to figure out what was going on, they observed that cold water immersion blunted satellite cell activity, the process by which muscle builds new nuclei to support growth. It also suppressed key signaling proteins like p70S6K, which help transform resistance training into actual gains.

So does that mean you should skip the plunge entirely?

Not necessarily.

Should You Still Use Cold Plunges?

The short answer is that it depends on what you're recovering for.

If the goal is long-term adaptation — building muscle, increasing strength, or optimizing training gains over time — this study adds to a growing body of evidence that cold plunges may do more harm than good. The very thing that makes them feel effective also appears to interfere with the recovery processes that lead to growth.

But not all recovery is about building for the future. Sometimes, it’s about bouncing back for tomorrow.

Recall that is the context cold plunges were originally built for. For athletes competing multiple times a week, or in tournaments with short turnarounds, there's definitely value in accelerating recovery, even if it blunts some longer-term gains. The goal in those moments isn’t really to build muscle, it’s to bounce back faster. In that setting, dulling soreness and restoring performance is the whole point.

So no, cold exposure isn’t inherently bad. But the timing matters. Used strategically — on off days, or far from heavy lifting — it might offer benefits without interfering with adaptation. As a regular post-lift ritual, though? The costs are becoming harder to ignore.

And here’s another wrinkle: while cold seems to close the door on recovery signaling, heat may do the opposite.

Small studies suggest that heat exposure, via sauna or hot water immersion, can improve microvascular blood flow, increase capillary density, and boost eNOS expression. In this way, heat can potentially enhance nutrient delivery without blunting training response.

So if your goal is to build muscle, not just manage fatigue, maybe skip the cold plunge. And keep your muscles warm.

Summary: In a randomized controlled crossover study, twelve healthy young men performed a lower-body resistance workout, after which one leg was immersed in cold water (8°C) and the other in thermoneutral water (30°C). Both limbs received identical exercise and post-workout nutrition, including a protein shake containing a carbon-13–labeled amino acid tracer to assess muscle protein synthesis. Four hours later, muscle biopsies showed that the cold leg exhibited over 50% lower microvascular perfusion and 31% less incorporation of amino acids into muscle protein. The reduction in synthesis strongly correlated with reduced blood flow, suggesting that post-exercise cold exposure may impair nutrient delivery and blunt the muscle’s adaptive response.

Random Trivia & Weird News

💪 Why are they called muscles?

Believe it or not, the word muscle derives from the Latin musculus, which literally means... “little mouse.”

Apparently, ancient anatomists thought contracting muscles — especially the flexed biceps — resembled the back of a mouse.

(Not sure we see it either, but I guess the name stuck.)

Behold: musculus, the “little mouse.” As seen in Gray’s Anatomy.

Podcasts We Loved This Week

• Tommy Wood & Josh Turknett: Can the brain heal itself after years of poor sleep? Via Better Brain Fitness.

• Emily Ho: How zinc insufficiency impacts inflammation, immunity, and aging. Via Sigma Nutrition Radio.

Products We Like

Bulk Supplements Creatine Monohydrate

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Creatine monohydrate has been shown in hundreds of studies to enhance strength, support lean mass gains, and improve high-intensity performance. It works by increasing intramuscular phosphocreatine stores, allowing for greater ATP regeneration during training. That means more energy for hard reps, and faster recovery between sets.

But its benefits go beyond energy: creatine may also lead to greater satellite cell activation and an increase in myonuclei, making it a true adaptation enhancer — not just a performance boost.

If you’d like to dig deeper into how creatine works, and explore its many lesser-known benefits, I’d suggest checking out this pod from our good friend Dr. Tommy Wood.

humanOS Catalog Feature of the Week

The How-to Guide to Ergogenic Aids

Like cold plunges and antioxidant supplements, not all recovery tools are harmless. They may reduce discomfort in the short term — but also blunt the very signals your body needs to adapt.

Our How-To Guide to Ergogenic Aids helps you spot the difference.

Learn which supplements enhance performance and recovery, and which ones may silently undermine your long-term progress.

To Access:

1. Log in to humanOS.
2. See How-to Guides in navigation on the left-hand side
3. Click Ergogenic Aids.

Wishing you the best,