SEE RESEARCH
The Science of Heat, Light & Circulation Therapy
A plain-English summary of peer-reviewed and NASA-funded research on how therapeutic heat, red/near-infrared light, and massage affect circulation, healing, and pain — why it matters more with age — with the scientists behind each finding and their measured results.
Part 1 · Therapeutic Heat
How warmth changes what happens inside the tissue.
Heat opens blood vessels and feeds the tissue — even a one-degree rise matters.
“[Heat causes] increased metabolism and vasodilation, thus accelerating the healing processes by enhanced supply of nutrients and oxygen.”
“An elevation in tissue temperature of just 1°C is associated with a 10%–15% increase in the local metabolism.”
Rossi R. Heat therapy for different knee diseases: expert opinion. Front. Rehabil. Sci. 2024;5:1390416. · Read the paper
A 1°C rise in tissue temperature raises local metabolism by 10–15%
Increase in local metabolic rate per +1°C of tissue warming.
Source: Rossi R., Front. Rehabil. Sci. 2024.
Heat increases tissue flexibility and blood flow.
“Heat applied just after exercise seems very effective in reducing soreness. Unlike cold, it increases flexibility of tissue and tissue blood flow.”
Petrofsky JS, Berk L, Bains G, et al. The Efficacy of Sustained Heat Treatment on Delayed-Onset Muscle Soreness. Clin J Sport Med. 2017;27(4):329–337. · PubMed
Heat therapy “produces the physiological effects of vasodilation, increases soft tissue extensibility, reduces joint stiffness, improves metabolism and local circulation, and provides analgesia.”
When heat is applied, blood flow is driven deep — into muscle, fat and the bone — not just the skin.
Heating induces “selective increases in skin, muscle, fat and bone blood perfusion in the extremities.”
In a controlled human study, local thigh heating “induced a two-fold increase in common femoral artery blood flow” — the main artery supplying the leg, knee and bone.
The Physiological Society, Thermal Physiology in Health and Disease. · Regional thigh-heating study, Experimental Physiology, 2024 (PMC10988708). · Read the study
Local heat doubles blood flow through the artery feeding the leg, knee & bone
Common femoral artery blood flow, at rest vs. with local heat applied (measured in people by Doppler ultrasound).
Source: Regional thigh-heating study, Experimental Physiology 2024 (PMC10988708); bone-perfusion finding from The Physiological Society.
Part 2 · Red & Near-Infrared Light NASA-funded
Research that began as a way to heal astronauts — now used for muscle and joint pain on Earth.
NASA-funded research found red and near-infrared LED light speeds healing and stimulates cell growth — by powering the cell’s energy engine, the mitochondria.
“High-intensity red and near-infrared LEDs significantly accelerated the healing of oxygen-deprived wounds… and also sped the growth and proliferation of skin, bone, and muscle cell cultures.”
“More than a 40 percent greater improvement in musculoskeletal injuries and a 50 percent faster healing time for lacerations, compared to control groups.”
The LED light-therapy device line was later FDA-cleared for “temporary relief of minor muscle and joint pain, arthritis, and muscle spasms.”
NASA Spinoff: NASA Research Illuminates Medical Uses of Light. · spinoff.nasa.gov
Primary study: Whelan HT, et al. Effect of NASA light-emitting diode irradiation on wound healing. J Clin Laser Med Surg. 2001;19(6):305–314. · PubMed
Measured effects of red / near-infrared light vs. control groups
Improvement over untreated control groups in NASA-funded research (Whelan et al.).
Source: NASA Spinoff & Whelan HT et al., J Clin Laser Med Surg 2001. Cell-growth figure from cultured skin/muscle cells under LED near-infrared light.
Part 3 · Massage & Mechanical Stimulation
The third mechanism: physical stimulation of the tissue and circulation.
Massage doesn’t just feel good — it measurably restores blood-vessel function and circulation.
“Massage therapy improves general blood flow and alleviates muscle soreness after exercise.” The study found massage restored healthy vascular (blood-vessel) function after exertion.
Franklin NC, Ali MM, Robinson AT, et al. Massage Therapy Restores Peripheral Vascular Function After Exertion. Arch Phys Med Rehabil. 2014;95(6):1127–1134. · PMC4037335
Part 4 · Why It Matters: Blood Flow Declines With Age
The core problem these therapies target — measured directly in people.
When researchers measured leg blood flow in healthy young vs. older men, the older group had dramatically less — in the very artery that feeds the knee.
“Basal whole-leg arterial blood flow and vascular conductance are reduced with age in healthy adult men.”
Femoral artery blood flow (measured by Doppler ultrasound) was 26% lower in the older men; a follow-up study found it 29% lower, with 53% higher vascular resistance.
Dinenno FA, Jones PP, Seals DR, Tanaka H. Limb blood flow and vascular conductance are reduced with age in healthy humans. Circulation. 1999;100(2):164–170. · PubMed · follow-up: Exp Physiol (PMID 11691889)
Leg blood flow is ~26–29% lower in older adults
Resting femoral artery blood flow — the main artery feeding the leg & knee — measured in healthy young vs. older men.
Source: Dinenno FA, Seals DR, et al., Circulation 1999 (26% lower) & Exp Physiol follow-up (29% lower).
What the science supports
- Blood flow declines with age — leg (femoral artery) blood flow is measured at 26–29% lower in older adults. This is the problem the therapies target.
- Heat drives blood flow deep — into muscle, fat and bone, doubling flow through the artery that feeds the knee; even a 1°C rise lifts local metabolism 10–15%.
- Heat reduces stiffness, relaxes muscle, and increases soft-tissue flexibility, with analgesic (pain-relieving) effects.
- Massage measurably improves circulation and restores blood-vessel function after exertion.
- Red / near-infrared light, in NASA-funded research, accelerated healing 40–50% and sped cell growth 150–200% by stimulating the mitochondria.
- The red-light modality is FDA-cleared for temporary relief of minor muscle and joint pain, arthritis, and muscle spasms.
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References
- 1. Rossi R. Heat therapy for different knee diseases: expert opinion. Front Rehabil Sci. 2024;5:1390416.
- 2. Petrofsky JS, Berk L, Bains G, Khowailed IA, Lee H, Laymon MS. The Efficacy of Sustained Heat Treatment on Delayed-Onset Muscle Soreness. Clin J Sport Med. 2017;27(4):329–337.
- 3. Pain Tolerance: The Influence of Cold or Heat Therapy. NLM/PMC7486461.
- 4. Whelan HT, Smits RL Jr, Buchman EV, et al. Effect of NASA light-emitting diode irradiation on wound healing. J Clin Laser Med Surg. 2001;19(6):305–314. (PMID 11776448)
- 6. The Physiological Society. Thermal Physiology in Health and Disease. · Regional thigh-heating study, Experimental Physiology 2024 (PMC10988708).
- 7. Franklin NC, Ali MM, Robinson AT, et al. Massage Therapy Restores Peripheral Vascular Function After Exertion. Arch Phys Med Rehabil. 2014;95(6):1127–1134. (Univ. of Illinois at Chicago)
- 8. Dinenno FA, Jones PP, Seals DR, Tanaka H. Limb blood flow and vascular conductance are reduced with age in healthy humans. Circulation. 1999;100(2):164–170. (Univ. of Colorado; American Heart Association)
- 5. NASA Spinoff. NASA Research Illuminates Medical Uses of Light. NASA Marshall Space Flight Center.