Tend to your tendons.
Achilles, kneecap, elbow, shoulder: a sore tendon can sideline you for months. The good news is that tendons respond to the right kind of work. Here's how far-infrared warmth can make that work more comfortable, and an honest look at what the research does and doesn't show.
Warming a tendon makes it stretch more easily, especially with gentle stretching1
shoulder tendon pain after 4 weeks of deep heat therapy in athletes2
of progressive strength exercise improved Achilles pain and function in a landmark trial3
A far-infrared patch increased circulation in the skin above it4
Photo source: University of Colorado Anschutz · Daniel Moon, MD
"-itis" or "-osis"?
Tendinitis
The "-itis" means inflammation. That's accurate for a fresh flare after a sudden jump in activity, when a tendon can be swollen and irritable.
Tendinopathy
Long-lasting tendon pain usually involves wear and disorganized repair in the tendon's fibers, with little inflammation.5That's why anti-inflammatories and rest often fall short, and why strengthening works.
Warm. Load. Recover.
Tendons get stronger when they're asked to work, gradually and consistently. Warmth fits around that work.
The closest evidence
Deep heat for shoulder tendinopathy in athletes
Giombini et al. · 37 athletes · randomized, 4 weeks
Italian researchers compared three treatments for athletes with shoulder tendon pain: deep heat therapy, therapeutic ultrasound, and a basic stretching routine.
pain with deep heat therapy
pain with ultrasound
pain with stretching
Only the heat group improved significantly.2 This study used microwave energy that heats deeper than far infrared, so it supports the idea that warmth can help tendons without proving the same result for a sauna.
Photo source: Hippocrates Wellness
Three ways to warm a stiff tendon
Relax Sauna
Warms the whole chain of muscles and tendons before your strengthening routine, with your head outside the cabin.
Evidence: based on how warmth affects tendons; no sauna trial for tendons yet.
Raylieve
Apply over an Achilles, kneecap, or elbow tendon for hours of interactive far infrared from your own body heat.
Evidence: a far-infrared patch increased local circulation;4 Raylieve not yet tested.
HexTex
Passive far infrared in the 7–14 µm band through the night, so tendons feel less stiff on that first morning step.
Evidence: based on far-infrared circulation research; not yet tested for tendons.
What warmth may do
Flexibility
Warm tendons stretch more easily, especially with gentle stretching. That can make the first steps of the day and warm-ups less painful.
Evidence: classic tendon research.1
Circulation
Far infrared increases blood flow in the skin and tissue near the surface by helping vessels relax through nitric oxide.
Cell protection
Far infrared switches on HSP70 and the body's NRF2 protective program, effects shown beyond heat alone.
Evidence: controlled human trial; not yet studied in tendons.6
Sticking with it
Recovery depends on doing the exercises for months. Anything that makes them more comfortable helps people keep going.
Evidence: program enjoyment linked to adherence in the Achilles trial.3
How strong is the evidence?
Progressive strengthening is the most effective treatment for tendinopathy.
Warmth makes tendons more flexible, and deep heat eased shoulder tendon pain.
Far infrared improves circulation and cell protection, measured outside tendons.
No clinical trial has tested far infrared for tendon problems.
What we do not claim
Tendons heal slowly, and anyone promising a shortcut deserves skepticism. Here's where we stand.
- Far infrared does not heal tendons or reverse tendon damage. It hasn't been tested in a tendon trial.
- It does not replace a strengthening program or your physical therapist's plan.
- It does not repair tears. A torn tendon needs medical care.
- "Bringing blood to the tendon" isn't proven to help. Painful tendons often already have extra blood vessels growing into them.
- Deep heat results may not match what far infrared does.
What would settle it?
A trial in people with Achilles or kneecap tendinopathy, all doing the same strengthening program, with half using far infrared before their sessions and half using a sham. Researchers would measure pain, function, morning stiffness, how well people stick with the exercises, and tendon structure on ultrasound over a year. That's the kind of question our research initiative is designed to pursue.
How to use it
A 15–20 minute sauna session, or far-infrared wear over the tendon, before your strengthening exercises can ease stiffness and start-up pain.
Slow, heavy exercises guided by a physical therapist do the real work. Warmth makes them easier to do.
Use Raylieve over the tendon or sleep on HexTex so your first steps or movements of the day feel smoother.
If a tendon is suddenly swollen and hot after a big jump in activity, ease off, use cold for a few days, then return to warmth and gradual loading.
Tendons remodel over months. Track pain, stiffness, and how much activity you can handle over 8–12 weeks.
See a clinician if you have
- A sudden pop, a gap you can feel in the tendon, or you can't push up onto your toes or lift your arm (possible tear)
- Tendon pain that started while taking a fluoroquinolone antibiotic, such as ciprofloxacin or levofloxacin
- Pain in several tendons or joints at once, or with fever
- Pain that keeps getting worse despite rest and a sensible program
- Heart disease, uncontrolled blood pressure, or pregnancy before using a sauna
Warm up for the work that heals
The Relax Sauna delivers 9.4 µm far infrared with your head outside the cabin, so you can loosen up at home before every strengthening session.
Explore the Relax SaunaReferences
- Lehmann JF, et al. Effect of therapeutic temperatures on tendon extensibility. Arch Phys Med Rehabil. 1970;51(8):481-487.
- Giombini A, et al. Short-term effectiveness of hyperthermia for supraspinatus tendinopathy in athletes. Am J Sports Med. 2006;34(8):1247-1253.
- Beyer R, et al. Heavy slow resistance versus eccentric training as treatment for Achilles tendinopathy. Am J Sports Med. 2015;43(7):1704-1711.
- Kraaij et al. A phase 1 randomized trial of a far-infrared emitting patch on local skin perfusion, microcirculation and oxygenation. Exp Dermatol. 2024.
- Khan KM, et al. Time to abandon the "tendinitis" myth. BMJ. 2002;324(7338):626-627.
- Bagabir H, et al. Far infrared therapy improves vascular function via cytoprotective pathways. Free Radic Biol Med. 2025;241:438-446.
- Coombes BK, et al. Efficacy and safety of corticosteroid injections and other injections for management of tendinopathy. Lancet.2010;376(9754):1751-1767.
- Park JH, et al. Far-infrared radiation acutely increases nitric oxide production. Biochem Biophys Res Commun. 2013;436(4):601-606.