Warm Water Therapy for Muscle Pain: How It Works and What the Research Shows

Key Takeaways

• Warm water immersion at 36–40°C reduces muscle pain through three mechanisms: increased blood flow to damaged tissue, activation of nerve receptors that block pain signals, and relaxation of muscle spasm.
• A 2021 systematic review of 32 randomised controlled trials found heat therapy reduces delayed-onset muscle soreness (DOMS) pain both within 24 hours and beyond 24 hours after exercise.
• Warm water immersion after exercise helps maintain muscle power. A recent study found hot water immersion prevented the decline in rate of force development that normally follows exercise-induced muscle damage.
• For acute muscle pain after exercise, the ideal protocol is 15–20 minutes of immersion at 38–40°C within the first few hours — and repeated at 24 and 48 hours.
• Warm water works differently from cold water. Cold reduces inflammation and numbs pain. Warm increases blood flow and relaxes tight muscles. Both help, but for different reasons and at different times.

Why Warm Water Helps Muscle Pain

Muscle pain comes in two forms: the acute ache during or right after exercise, and the deeper soreness that peaks 24–72 hours later (called delayed-onset muscle soreness, or DOMS). Warm water helps both, but through different pathways.

What happens when you soak sore muscles in warm water

1. Your blood vessels widen. Warm water at 36–40°C causes blood vessels near the surface to dilate. This increases blood flow to your muscles, delivering more oxygen and nutrients while flushing out metabolic waste products (like lactate and hydrogen ions) that contribute to that burning, heavy feeling after hard exercise.

2. Your pain receptors get overridden. Warm water activates thermal receptors in your skin. These receptors send signals to your spinal cord that compete with pain signals from your muscles — a process called gate control. The result is that your brain receives less pain input. This is the same reason a hot water bottle on a sore back provides relief.

3. Tight muscles relax. Heat reduces the firing rate of muscle spindles — the sensors that control muscle tension. When these sensors calm down, the muscle physically relaxes. If your pain is partly caused by spasm or guarding (muscles clenching protectively around a sore area), warm water directly addresses that.

4. Hydrostatic pressure reduces swelling. When you are submerged, water pushes on your body from all directions. This gentle compression helps move excess fluid out of swollen muscle tissue and back into your bloodstream, reducing the puffiness and tightness that accompanies muscle damage.

Warm Water for DOMS (Delayed-Onset Muscle Soreness)

DOMS is the soreness that appears 24–72 hours after intense or unfamiliar exercise. It is caused by microscopic damage to muscle fibres, local inflammation, swelling around the muscle, and activation of pain receptors. It is a normal part of the adaptation process — your muscles are rebuilding stronger.

A 2021 systematic review and meta-analysis of 32 randomised controlled trials examined heat and cold therapy for DOMS. The findings showed that heat therapy — including warm water immersion — reduced pain both within 24 hours and beyond 24 hours after exercise. Hot pack therapy showed the most obvious pain-reducing effect at both timepoints.

A separate study found that warm water immersion at 40°C for 15 minutes, applied at 1, 24, and 48 hours post-exercise, helped manage DOMS symptoms. Another recent study found that hot water immersion preserved rate of force development (a measure of how quickly your muscles can produce power) after exercise-induced damage — meaning your muscles may function better the next day despite the soreness.

Warm vs. Cold Water: When to Use Which

This is the question most people get confused about. Both warm and cold water help muscle pain, but they work differently and are better suited to different situations.

Factor	Warm water (36–40°C)	Cold water (10–15°C)
Primary effect	Increases blood flow, relaxes muscles	Reduces inflammation, numbs pain
Best for	Chronic muscle tension, stiffness, general soreness, stress-related muscle pain	Acute post-exercise soreness, reducing inflammation after intense training
Timing	Any time, but especially 1–48 hours post-exercise	Within 0–2 hours after exercise for best effect
Duration	15–20 minutes	10–15 minutes
How it feels	Comforting, relaxing	Uncomfortable, then numbing
Evidence strength	Good for pain relief and muscle relaxation	Strong for reducing DOMS severity

Contrast therapy — switching between warm and cold — combines both effects. The alternating vasodilation and vasoconstriction creates a pumping action that may enhance fluid removal from damaged tissue. A 2013 meta-analysis found contrast water therapy significantly reduced muscle soreness at every follow-up point up to 96 hours.

Practical Protocols

After a hard gym session or run

• Fill your bathtub with warm water at 38–40°C
• Soak for 15–20 minutes, ensuring sore muscle groups are submerged
• Gently stretch or move the sore muscles while in the water — the warmth makes stretching easier and less painful
• Repeat at 24 and 48 hours if soreness persists

For chronic muscle tension (neck, shoulders, back)

Chronic tension responds particularly well to warm water because the pain is largely driven by sustained muscle contraction rather than tissue damage.

• Warm bath or hot tub at 37–39°C for 15–20 minutes
• Focus on relaxing the tense muscles — consciously let your shoulders drop, unclench your jaw, slow your breathing
• If you have a whirlpool or hot tub with jets, direct them at the tense area. The Im and Han (2013) whirlpool trial showed a 53% pain reduction for myofascial pain in the upper trapezius
• Regular use (3–5 times per week) produces the best results for chronic tension

Warm pool exercise for ongoing muscle pain

Passive soaking helps, but active movement in warm water helps more. If you have persistent muscle pain, exercising in a warm pool (30–34°C) — including options like underwater treadmill walking — combines pain relief with muscle strengthening. A 2023 systematic review of 32 trials confirmed that aquatic exercise reduced musculoskeletal pain more effectively than no exercise — and even more than land-based exercise for some conditions (Shi et al., 2023).

Common Mistakes

• Water too hot. Above 42°C, you risk burns, dizziness, and excessive cardiovascular strain. The therapeutic range is 36–40°C. Hotter is not better.
• Staying in too long. Beyond 20 minutes at high temperatures, you dehydrate and your body struggles to regulate temperature. Keep sessions to 15–20 minutes.
• Using warm water for acute inflammation. If a muscle is hot, swollen, and recently injured (first 24–48 hours after a tear or strain), cold is usually better. Warm water increases blood flow, which can increase swelling in the acute phase.
• Expecting a cure. Warm water manages muscle pain. It does not fix the underlying cause. If you have persistent muscle pain that does not improve with regular warm water treatment, see a physiotherapist to identify what is causing it.

Who Should Be Careful

• People with heart conditions — warm water lowers blood pressure and increases heart rate. Get medical clearance.
• Pregnant women — avoid water above 38°C, especially in the first trimester.
• People with multiple sclerosis — some MS patients are heat-sensitive (Uhthoff’s phenomenon). Warm water may temporarily worsen symptoms.
• Anyone on blood pressure medication — the combined blood pressure drop from medication and warm water can cause dizziness or fainting.

The Bottom Line

Warm water is one of the simplest and most effective tools for muscle pain. It increases blood flow, relaxes tight muscles, reduces swelling, and blocks pain signals — all at once, with no side effects for most people, and at no cost beyond running a bath.

For post-exercise soreness, soak at 38–40°C for 15–20 minutes within a few hours of training, and repeat at 24 and 48 hours. For chronic muscle tension, regular warm water immersion 3–5 times per week produces the best results. For persistent or severe muscle pain, combine warm water treatment with professional guidance from a physiotherapist. Our equipment guide can help you find the right setup for regular use at home.

Related Reading

• How Hydrotherapy Machines Actually Work: The Physics
• Extreme Hydrotherapy Techniques for Fast Recovery
• Home Hydrotherapy Equipment: What Works
• Choosing the Right Hydrotherapy Equipment

References

• Wang, Y. et al. (2021). Heat and cold therapy reduce pain in patients with delayed onset muscle soreness: a systematic review and meta-analysis of 32 randomized controlled trials. Physical Therapy in Sport. PubMed
• Li, J. et al. (2024). The effects of hydrotherapy and cryotherapy on recovery from acute post-exercise induced muscle damage — a network meta-analysis. BMC Musculoskeletal Disorders, 25, 724. PMC11409518
• Shi, Z. et al. (2023). Efficacy of aquatic exercise in chronic musculoskeletal disorders: a systematic review and meta-analysis. Journal of Orthopaedic Surgery and Research, 18, 906. DOI link
• Im, S.H. & Han, E.Y. (2013). Improvement in anxiety and pain after whole body whirlpool hydrotherapy among patients with myofascial pain syndrome. Annals of Rehabilitation Medicine, 37(4), 534–540. PMC3764348
• Mooventhan, A. & Nivethitha, L. (2014). Scientific evidence-based effects of hydrotherapy on various systems of the body. North American Journal of Medical Sciences, 6(5), 199–209. PMC4049052

Last reviewed: February 2026. This article is for informational purposes and does not replace medical advice.