Hot Water Immersion Beats Cold for Muscle Regeneration Post-Injury
Key findings: 60-second read
- Hot water immersion helped muscles recover better - Soaking for 60 minutes daily at 107.6°F (42°C) for 10 days lowered signs of muscle damage in the blood, reduced how sore people felt, and showed better results than cold water immersion.
- Cold water immersion showed no benefit - Contrary to popular belief, soaking for 15 minutes daily at 53.6°F (12°C) did not improve pain, lower muscle damage markers, or help the body's repair processes.
- Hot water boosted protective proteins (HSP27 and HSP70) - These "helper" proteins, which repair damaged cells, went up only in the hot water group.
- Hot water calmed harmful inflammation - A key driver of inflammation and muscle wasting stayed flat in the hot water group but rose in cold and neutral groups. At the same time, an anti-inflammatory signal increased only with hot water.
- Muscle strength recovery was similar across all groups - Despite the positive molecular changes, how quickly people regained their full muscle strength did not differ between hot water, cold water, or neutral treatments over the 10 days.
If you've ever pulled a muscle, you've probably been told to put ice on it. Ice packs, cold baths, cryotherapy - these are the usual go-to treatments for muscle injuries. But what if the evidence for cold therapy is much weaker than people think? And what if heat therapy might actually work better?
A major new study published in The Journal of Physiology (Dablainville et al., 2025) directly compared cold water immersion, hot water immersion, and a neutral-temperature control using a lab model of muscle injury. Thirty-four healthy men went through a procedure that used electrical stimulation to cause a significant muscle injury - similar to a real muscle tear or strain.
The findings challenge decades of common practice. Cold water immersion did not reduce pain, did not lower blood markers of muscle damage, and did not help repair pathways. In contrast, hot water immersion reduced perceived pain, lowered blood markers of muscle damage, increased protective heat shock proteins, and improved inflammation signals.
"Our results support the use of hot water immersion but not cold, to improve muscle regeneration following an injury. This is the first study to examine the effects of cold and hot water immersion on muscle repair after an electrically stimulated exercise that caused damage."
On this page
Study design: 34 people, 10-day treatment
Thirty-four healthy men (average age 33) took part in this carefully controlled trial. All of them went through a standard muscle damage procedure on their right thigh muscle using electrical stimulation. This method has been proven to cause significant muscle fiber damage, closely mimicking a real muscle tear.
Temperature treatments (done daily for 10 days)
- Cold water immersion (CWI): 15 minutes at 53.6°F (12°C)
- Neutral water immersion (sham control): 30 minutes at 89.6°F (32°C) — this feels neither hot nor cold
- Hot water immersion (HWI): 60 minutes at 107.6°F (42°C)
Researchers took small muscle samples (biopsies) before the injury started, at day 5, and at day 11. Blood samples were taken at the start, day 4, and day 8. They also measured muscle strength, pain levels, and body temperatures throughout.
How they caused muscle damage
The electrical stimulation procedure successfully damaged muscles in all participants. Looking at the muscle tissue under a microscope confirmed that muscle fibers had died and that immune cells had moved in to clean up the damage. The amount of damage was the same across all three groups, so any differences later were due to the treatments.
"Muscle fibers with dark spots (cell nuclei moving in) and lacking a key structural protein (dystrophin) appeared after the injury, confirming that muscle fibers were going through cell death."
Muscle strength and pain: Hot water helped pain, but strength recovered the same
The muscle damage procedure caused a big drop in muscle strength - strength went down by 59% two days after injury, and even by day 10 it was still 32% below normal. There was no real difference in how fast muscle strength returned between any of the treatments. This matches what other studies have found: both cold and heat therapy have mixed results when it comes to actual function.
However, people in the hot water group reported less pain when the sore muscle was pressed compared to the neutral group (a statistically meaningful difference). The cold water group showed no pain benefit compared to either other group. Pain during squatting was similar across all groups.
While not a sure thing statistically, the hot water group did show a trend toward better strength at day 4 (31% below normal) compared to the cold and neutral groups (47% below normal). This suggests there might be a real benefit that a larger study could confirm.
Key finding on pain
"Heat led to lower perceived muscle pain compared to the neutral treatment. The main reason people use cold therapy is to reduce muscle pain and soreness after injury. But our results show that cold water immersion didn't help with pain perception."
Blood markers: Hot water lowered damage signs
Creatine kinase (CK) and myoglobin are substances that leak from damaged muscles into the blood. Higher levels mean more muscle damage or slower cleanup.
Key findings:
- At day 8, CK levels were much lower in the hot water group than in both the neutral group and the cold water group, with a large effect size. There was no difference between cold water and neutral groups.
- At day 4, myoglobin levels were much lower in the hot water group than in both the neutral group and the cold water group, also with a large effect size. Again, cold water made no difference.
These results suggest that hot water immersion helped the body clear out muscle damage markers faster, most likely because heat increases blood flow. Cold water immersion did nothing to lower these markers.
"Our results show no meaningful effect of cold water immersion on blood markers of muscle damage. This suggests no benefit of cold in limiting further damage or improving muscle recovery after significant muscle injury. On the other hand, our results showed lower levels of CK and myoglobin following hot water immersion."
Heat shock proteins: Only hot water raised these helpers
Heat shock proteins (HSPs) are like little helpers inside your cells that protect them from stress, stabilize damaged proteins, and aid in repair. They are crucial for muscle recovery after injury.
HSP27 levels went up over time only with hot water, not with cold or neutral treatments. By day 11, HSP27 was significantly higher in the hot water group than in the cold water group.
HSP70 increased in both the neutral and hot water groups but not in the cold water group. By day 11, the hot water group had significantly higher levels than the cold water group.
The researchers note that muscle temperature probably needs to reach a certain level to trigger these helpful proteins. The cold water group never reached that threshold, which may explain why they saw no benefit.
The heat shock protein connection
"Heat shock proteins may have played a key role in protecting and helping skeletal muscle repair. The observed increase in HSP27 and HSP70 with hot water could explain the lower CK and myoglobin levels, possibly by reducing the extent of muscle damage."
Inflammation: Hot water calmed harmful signals, boosted helpful ones
Getting inflammation just right is essential for muscle repair. Too much or too long-lasting inflammation actually gets in the way of healing.
A key pro-inflammatory signal (p-NF-κB) went up in both the neutral and cold water groups but stayed flat in the hot water group. By day 11, this harmful signal was much higher in both the cold and neutral groups than in the hot water group.
An anti-inflammatory signal (IL-10) increased only in the hot water group. By day 11, IL-10 was significantly higher in the hot water group than in the cold water group.
These findings suggest that hot water promoted a healthier inflammatory environment - dampening harmful signals while boosting helpful ones. Cold water showed no beneficial effect on these inflammation pathways.
"In contrast, hot water blunted the harmful p-NF-κB signal, suggesting a possible reduction in inflammation and muscle-wasting pathways between day 5 and day 11. The increase in HSP70 we saw earlier likely played a role in reducing p-NF-κB."
Practical takeaways: Should you stop icing muscle injuries?
This study adds to a growing pile of evidence that questions the routine use of ice for muscle injuries. While ice may still help for joint injuries (like a twisted ankle) where reducing swelling is the main goal, its role in muscle healing is looking shakier.
Based on this research and other studies, consider the following:
- For muscle strains and tears, hot water immersion (60 minutes at 107.6°F / 42°C daily) may work better than ice - better molecular signs of repair, less pain, and increased helpful heat shock proteins.
- Cold water immersion (15 minutes at 53.6°F / 12°C) gave no repair benefit - no pain reduction, no lowering of muscle damage markers, no helpful protein boost, and no positive effect on inflammation.
- Muscle temperature matters - the hot water protocol raised muscle temperature significantly (up to 12°C at 1 cm depth), while cold lowered it. This heat seems to be the trigger for heat shock proteins.
- Short-term vs. long-term use - this study applied treatments daily for 10 days. It doesn't fully answer whether ice might still be useful in the very first few hours after injury to limit bleeding.
- One size doesn't fit all - not everyone can tolerate 60 minutes of hot water. The study allowed people in the hot group to cool their upper bodies with cold water or ice towels to stay comfortable. You may need to do the same.
What about other markers of blood vessel growth and protein building?
VEGF (helps form new blood vessels) stayed steady with cold but went down with hot. Protein-building signals increased with both neutral and hot water, but not differently between groups. A fibrosis (scarring) marker stayed low across all groups. The researchers note that the timing of the muscle samples (days 5 and 11) might have missed early changes in these markers.
Study limitations
Several limitations should be kept in mind:
- Only men were studied - the study was open to women, but only one volunteered and couldn't be included. Sex differences in muscle repair are well known, so the findings may not fully apply to women.
- Lab model of injury - electrical stimulation causes muscle damage but may not perfectly match every type of real muscle injury (like bruises or tears with bleeding).
- No blinding of treatments - people knew whether they were getting hot, cold, or neutral water, which could have influenced their pain ratings (the placebo effect). However, the researchers note that people generally believed strongly in cold therapy, so that would have worked against finding hot water superior.
- Different soak times - the study couldn't separate the effects of temperature from how long people soaked or from water pressure. Cold was 15 minutes, neutral 30 minutes, hot 60 minutes.
- Muscle temperature measured only in the uninjured leg - to avoid messing with the injured leg, they measured temperature in the opposite leg. So we don't know the exact temperature reached in the damaged muscle.
- No check on diet compliance - people got dietary advice, but researchers didn't formally track whether they followed it.
- Missing early time points - muscle samples were taken at days 5 and 11, missing the very early inflammation phase (hours to first few days).
- No detailed look at cell types - researchers didn't count specific immune cells, satellite cells, or regenerating fibers.
Conclusions: Heat, not cold, for muscle repair
This is the first human study to directly compare cold and hot water immersion on muscle repair after a simulated injury that causes muscle fiber death. The findings are clear:
Cold water immersion (15 minutes at 53.6°F / 12°C daily for 10 days) provided no benefit - no pain improvement, no reduction in blood markers of muscle damage, no heat shock protein increase, and no helpful effect on inflammation.
Hot water immersion (60 minutes at 107.6°F / 42°C daily for 10 days) showed multiple benefits - less perceived pain, lower CK and myoglobin levels, increased HSP27 and HSP70, dampened harmful inflammation signals, and boosted anti-inflammatory signals.
The authors conclude: "Our results support the use of hot water immersion but not cold, to improve muscle regeneration following an injury."
This research challenges the widespread practice of icing muscle injuries and suggests that heat therapy may be a more effective strategy for promoting muscle healing. However, larger studies, especially including women, are needed to confirm these findings and fine-tune the best approach.
One key insight from this research
"Cold water immersion (15 minutes at 53.6°F / 12°C daily) did not reduce perceived muscle pain, lower blood markers of muscle damage, or increase heat shock proteins. In contrast, hot water immersion (60 minutes at 107.6°F / 42°C daily) reduced pain, lowered CK and myoglobin, increased HSP27 and HSP70, dampened harmful NF-κB, and increased helpful IL-10. These results support using heat therapy, not cold, to improve muscle repair after injury."
Frequently asked questions
Does this mean I should never ice a muscle injury?
Not necessarily. This study looked at daily hot or cold treatments for 10 days after a simulated injury. It doesn't directly address the first few hours after injury, where ice might still help limit acute swelling and bruising. But for ongoing muscle recovery beyond the first day or two, this study suggests heat is better than cold.
Can I use a hot bath instead of a hot tub or special tank?
Yes, the study used a water bath, not a special hot tub. A regular bathtub filled with 107.6°F (42°C) water is a reasonable substitute. However, keeping the water at exactly 107.6°F for 60 minutes may require adding more hot water from time to time. Always check the water temperature with a thermometer before getting in.
Is 60 minutes of hot water immersion safe?
The people in this study were healthy men with no heart or other health problems. The hot water group was allowed to use cooling methods (cold water, ice towels on the upper body) to keep their core temperature from rising too much and to stay comfortable. If you have any medical conditions (heart disease, high blood pressure, diabetes, pregnancy, or others), talk to your doctor before trying prolonged hot water immersion.
What about joint injuries like ankle sprains - does this apply?
No. This study specifically looked at muscle tissue repair. Joint injuries (like ligament sprains) involve different tissue types and healing processes. The evidence for ice in acute joint injuries is stronger, especially for reducing swelling. Don't apply these findings to ligament or joint injuries without more research.
Why didn't cold water immersion work?
The researchers suggest a few possibilities. First, the muscle temperature drop from cold water may not have been enough to reduce pain in this type of injury. Second, while animal studies show ice can help with very small muscle injuries (less than 10% muscle fiber death), this study caused larger damage where ice might actually be harmful. Third, the specific timing and frequency of cold water (15 minutes daily for 10 days) might not have been ideal. But these are educated guesses after the fact — the clear result is that this particular cold water protocol provided no repair benefit.
As a physiotherapist, I have long been uneasy about routinely prescribing ice for muscle injuries. The evidence has always been shaky, but the practice is so deeply embedded in sports medicine culture that questioning it can feel like heresy. This study adds to a growing chorus of research suggesting that cold therapy may be ineffective, and possibly even harmful, for muscle healing.
Does this mean I will never recommend ice again? No. Ice may still have a role. But for ongoing muscle recovery, I will be recommending heat therapy more often.
If you have a muscle strain or tear, talk to your physiotherapist about whether hot water immersion might be right for your situation. And if you've been religiously icing your muscle injuries with little benefit, it may be time to reconsider.
If you would like to discuss your specific injury and the best approach to recovery, I am available for telehealth consultations.
- Grant
Living With Persistent Pain?
If your pain has lasted longer than expected, feels out of proportion to the injury, or hasn't responded to standard treatment, you may benefit from a more nervous-system-focused approach. Learn more about our physiotherapy services in Port Macquarie.
Want personalised guidance?
If you would like help making sense of your aches, pains, or ongoing symptoms, you can book with Grant either in Port Macquarie or via telehealth.
Disclaimer: This information is for educational purposes and does not replace individualised medical advice. If you have an acute muscle injury or any medical conditions, consult a qualified healthcare professional before attempting heat or cold therapy. This blog post summarises a published research study (Dablainville V, Mornas A, Normand-Gravier T, et al. Muscle regeneration is improved by hot water immersion but unchanged by cold following a simulated musculoskeletal injury in humans. J Physiol. 2025); the original source should be consulted for full methodological details.
