The most undisputed finding regarding the use of heat and cold on the body is that they both reduce pain1Nadler SF, Weingand K, Kruse RJ (2004)The physiologic basis and clinical applications of cryotherapy and thermotherapy for the pain practitionerPain Physician · reviewView source →. This is important post-injury beyond just “feeling good.” For one, researchers have found that patients in pain who are given cryotherapy use fewer opioids2(2023)The Effect of Cryotherapy Application on Postoperative Pain: A Systematic Review and Meta-analysisAnnals of Surgery · studyView source →. As far as the healing process, pain relief can interrupt what’s called the pain-spasm-pain cycle. Without pain treatment, specialized pain nerves (nociceptors) send signals to your brain saying “Ow!” while neurotransmitters send signals to the spine saying “Emergency! Flex this muscle!” This continual flexion can result in spasms, which generate more tissue damage and pain.
Applying hot or cold temperatures instead activates specialized temperature nerves (thermoreceptors), which take over the same communication pathways to send the message “Warm!” or “Cold!”, blocking the pain signal and interrupting the vicious cycle1Nadler SF, Weingand K, Kruse RJ (2004)The physiologic basis and clinical applications of cryotherapy and thermotherapy for the pain practitionerPain Physician · reviewView source →.
The surprising part is that heat and cold both pull this off despite having opposite effects under the surface of the skin.
What Cold Does
A fresh injury or trauma to the body can be thought of like an earthquake hitting a town: there’s damage from the initial shock, but more harm unfolds in the hours and days afterward when the injured can’t get the resources they need. After a soft-tissue injury, surrounding cells inside your joint or limb keep dying for hours after the original trauma. This is partly because the damaged blood vessels can’t deliver oxygen (ischemia), partly because mitochondria are succumbing to damage, and partly because your inflammatory response (while necessary for healing) can overshoot and cause collateral damage3Merrick MA (2002)Secondary Injury After Musculoskeletal Trauma: A Review and UpdateJournal of Athletic Training · reviewView source →. Scientists call this secondary injury. Limiting secondary injury is the actual basis behind the advice to ice in the immediate days following trauma, especially the first 12 hours4Kwiecien SY, McHugh MP (2021)The cold truth: the role of cryotherapy in the treatment of injury and recovery from exerciseEuropean Journal of Applied Physiology · reviewView source →. Cooling down cells reduces the amount of activity they perform and oxygen they demand, so more of them survive the temporary shortage3Merrick MA (2002)Secondary Injury After Musculoskeletal Trauma: A Review and UpdateJournal of Athletic Training · reviewView source →5Merrick MA, Rankin JM, Andres FA, Hinman CL (1999)A preliminary examination of cryotherapy and secondary injury in skeletal muscleMedicine and Science in Sports and Exercise · RCTView source →.
In recent years, people have begun asking “But isn’t inflammation the body’s natural healing process? And wouldn’t cooling and reducing inflammation slow down healing?” There’s partial truth to this idea — after 72 hours, more icing mostly just numbs pain. One review even calls it “pointless”4Kwiecien SY, McHugh MP (2021)The cold truth: the role of cryotherapy in the treatment of injury and recovery from exerciseEuropean Journal of Applied Physiology · reviewView source →. Routine cooling after resistance training does reduce gains you’d otherwise get from the training6Petersen AC, Fyfe JJ (2021)Post-exercise Cold Water Immersion Effects on Physiological Adaptations to Resistance Training: A Narrative ReviewFrontiers in Sports and Active Living · reviewView source → (more on that later). And too much cold for too long after an injury may actually slow healing… at least in mice7Takagi R, Fujita N, Arakawa T, et al (2011)Influence of icing on muscle regeneration after crush injury to skeletal muscles in ratsJournal of Applied Physiology · animal studyView source →.
What Heat Does
Once you’re far enough out from an injury (practitioners usually draw the line around two weeks, the “chronic” stage) inflammation and secondary damage aren’t a concern anymore. This is when it makes sense to involve heat8Zanoli G, Albarova-Corral I, Ancona M, Grattagliano I, Hotfiel T, Iolascon G, Kruger K, Rodriguez Maruri G (2024)Current Indications and Future Direction in Heat Therapy for Musculoskeletal Pain: A Narrative Review Muscles · reviewView source →. Heat relieves pain while increasing blood flow, loosening stiffness, and improving range of motion and function9Clijsen R, Stoop R, Hohenauer E, et al (2022)Local Heat Applications as a Treatment of Physical and Functional Parameters in Acute and Chronic Musculoskeletal Disorders or PainArchives of Physical Medicine and Rehabilitation · meta-analysisView source →. Blood flow is especially important post-injury10Demidova-Rice TN, Hamblin MR, Herman IM (2012)Acute and impaired wound healing: pathophysiology and current methods for drug delivery, part 1Advances in Skin & Wound Care · reviewView source →, because blood is about the closest thing there is to “magical healing juice.” In one study, diabetic patients with leg wounds that hadn’t improved in months were treated with heat and electrical stimulation for four weeks to drive circulation. Their wounds healed significantly, while an untreated comparison group’s wounds got worse11Petrofsky J, Lawson D, Berk L, Suh H (2007)The influence of local versus global heat on the healing of chronic wounds in patients with diabetesDiabetes Technology & Therapeutics · studyView source →.
The American Academy of Orthopaedic Surgeons recommends having both ice and heat at your disposal12ReferenceHeat or Ice For Your Pain?web resourceView source →. But it leaves an obvious question: what do you do in between? Past 72 hours it’s “pointless” to ice… but using heat that early could re-provoke inflammation.
The Role of Contrast Therapy
Contrast therapy is the practice of alternating back and forth between the application of heat and cold for several minutes at a time13Greenhalgh O, Alexander J, Richards J, Selfe J, McCarthy C (2021)The use of contrast therapy in soft tissue injury management and post-exercise recovery: a scoping reviewPhysical Therapy Reviews · scoping reviewView source →. This is usually studied by placing separate tubs of hot (100–104°F) and cold (45–59°F) water side-by-side and instructing patients to move the target body part from one to the other at regular intervals14Bieuzen F, Bleakley CM, Costello JT (2013)Contrast Water Therapy and Exercise Induced Muscle Damage: A Systematic Review and Meta-AnalysisPLOS ONE · meta-analysisView source →. Exact protocols vary — the most rapid approach is to alternate 1 minute hot : 1 minute cold for 10 minutes total, while other practitioners subscribe to a 3 minutes hot : 1 minute cold ratio13Greenhalgh O, Alexander J, Richards J, Selfe J, McCarthy C (2021)The use of contrast therapy in soft tissue injury management and post-exercise recovery: a scoping reviewPhysical Therapy Reviews · scoping reviewView source →. The idea initially gained popularity as an athletic recovery practice15Hing W, White S, Bouaaphone A, Lee P (2008)Contrast therapy - A systematic reviewPhysical Therapy in Sport · reviewView source →, but researchers have noted that its observed benefits line up with the needs of the subacute window: you keep the pain relief, drive blood flow, and mix in cold so as not to provoke inflammation the way pure heat can.
Contrast therapy is less studied than cold or heat alone (after all, it’s the newest). But the evidence we do have is encouraging. One study measured blood flow in people’s feet across cold, heat, and contrast — cold did the worst, and contrast actually beat heat alone16Petrofsky J, Lohman E, Suh HJ, et al (2007)Contrast baths increase foot blood flow more than warm or cold alone (3:1; per your Science guide)Physiotherapy Theory and Practice · studyView source →. A larger study of 115 patients found contrast outperformed heat for sprained ankle recovery, especially in keeping swelling down17Weerasekara I, Tennakoon S, Suraweera H (2016)Contrast Therapy and Heat Therapy in Subacute Stage of Grade I and II Lateral Ankle SprainsFoot & Ankle Specialist · RCTView source →. A third found contrast eased osteoarthritis pain more effectively than either cold or heat by itself18Shehata AE, Fareed ME (2013)Effect of Cold, Warm or Contrast Therapy on Controlling Knee Osteoarthritis Associated ProblemsInternational Journal of Medical and Health Sciences · RCTView source →. In fairness, other studies give heat a slight edge for overall blood flow19Fiscus KA, Kaminski TW, Powers ME (2005)Changes in Lower-Leg Blood Flow During Warm-, Cold-, and Contrast-Water TherapyArchives of Physical Medicine and Rehabilitation · studyView source →, which is why it’s appropriate once you’re fully in the chronic stage of injury recovery.
Scientists are still working to understand how contrast can provide the best of both worlds. The leading theory points out that heat opens up blood vessels (vasodilation) while cold narrows them (vasoconstriction), suggesting that alternating the two pumps blood through the targeted site20Shadgan B, Pakravan AH, Hoens A, et al (2018)Contrast Baths, Intramuscular Hemodynamics, and Oxygenation as Monitored by Near-Infrared SpectroscopyJournal of Athletic Training · studyView source →. Skeptics have argued that contrast therapy applied at the surface of the skin couldn’t possibly penetrate deep enough into the body to change muscle temperature every few minutes the way sustained heat or sustained cold can21Higgins D, Kaminski TW (1998)Contrast therapy does not cause fluctuations in human gastrocnemius intramuscular temperature J Athl Train · RCTView source →22Myrer J, Measom G, Durrant E, Fellingham G (1997)Cold- and Hot-Pack Contrast Therapy: Subcutaneous and Intramuscular Temperature ChangeJ Athl Train · RCTView source →. This is true! But it overlooks the fact that you can drive changes in blood flow deep inside a muscle without changing the temperature inside the muscle itself, which contrast clearly does20Shadgan B, Pakravan AH, Hoens A, et al (2018)Contrast Baths, Intramuscular Hemodynamics, and Oxygenation as Monitored by Near-Infrared SpectroscopyJournal of Athletic Training · studyView source →.
Soreness, Fatigue & Athletic Recovery
Contrast is already a favorite among athletes for bouncing back from soreness, and is a better general-purpose tool than heat or cold alone. In one study, subjects were put through a brutal leg workout (50 overloaded, eccentric leg presses — a clinical dose of DOMS) and then randomly assigned to either rest passively or use contrast therapy; the contrast group recovered their jump performance significantly faster at 24, 48, and 72 hours23Vaile JM, Gill ND, Blazevich AJ (2007)The effect of contrast water therapy on symptoms of delayed onset muscle sorenessJournal of Strength and Conditioning Research · RCTView source →. A similar study stacked contrast therapy up directly against heat and cold alone and found that it “appears to be more beneficial than when the interventions are prescribed as an isolated exposure”24Vaile J, Halson S, Gill ND, Dawson B (2008)Effect of hydrotherapy on the signs and symptoms of delayed onset muscle sorenessEuropean Journal of Applied Physiology · RCTView source →. Even away from the controlled conditions of a science lab, beneficial results for contrast therapy have been demonstrated after real matches of rugby25Webb NP, Harris NK, Cronin JB, Walker C (2013)The relative efficacy of three recovery modalities after professional rugby league matchesJournal of Strength and Conditioning Research · studyView source →26Higgins TR, Cameron ML, Climstein M (2011)A random control trial of contrast baths and ice baths for recovery during competition in U/20 rugby unionJournal of Strength and Conditioning Research · RCTView source →.
For advanced athletes it’s worth pointing out that cold alone has a niche27Thorpe R (2021)Post-exercise Recover: Cooling and Heating, a Periodized ApproachFront. Sports Act. Living · reviewView source → — if you’re competing on back-to-back days and want to prioritize feeling your best ASAP, cooling may be your best choice28Ingram J, Dawson B, Goodman C, Wallman K, Beilby J (2009)Effect of water immersion methods on post-exercise recovery from simulated team sport exerciseJournal of Science and Medicine in Sport · studyView source →29Elias GP, Wyckelsma VL, Varley MC, et al (2013)Effectiveness of water immersion on postmatch recovery in elite professional footballersInternational Journal of Sports Physiology and Performance · studyView source →. But cold also has been shown to risk detrimental long-term effects, in particular reducing muscle growth benefits after resistance training6Petersen AC, Fyfe JJ (2021)Post-exercise Cold Water Immersion Effects on Physiological Adaptations to Resistance Training: A Narrative ReviewFrontiers in Sports and Active Living · reviewView source →30Jinnah AH, Luo TD, Mendias C, Freehill M (2019)Cryotherapy duration is critical in short-term recovery of athletes: a systematic reviewJISAKOS · systematic reviewView source →. Heat alone may be applicable for chasing endurance and heat tolerance31Zurawlew MJ, Mee JA, Walsh NP (2018)Post-exercise Hot Water Immersion Elicits Heat Acclimation Adaptations in Endurance Trained and Recreationally Active IndividualsFrontiers in Physiology · studyView source →, but for an everyday routine that will help you feel better tomorrow while carrying the least downside, contrast is the daily driver. There’s even some (very early) evidence that contrast may ease central-nervous-system fatigue, combatting the brain fog that can follow from exhaustive exercise32Cassar S, Kidgell D, Pearce A (2010)The effect of hydrotherapy recovery on central fatigue: a preliminary examination using TMS (conference abstract)Journal of Science and Medicine in Sport · conference abstractView source →.
When In Doubt, Do Something.
Contrast therapy is still in the early days of research. Large-scale meta-analyses frame the current state of evidence as positive but insufficient, calling for further research to be done14Bieuzen F, Bleakley CM, Costello JT (2013)Contrast Water Therapy and Exercise Induced Muscle Damage: A Systematic Review and Meta-AnalysisPLOS ONE · meta-analysisView source →33Wang Y, Lu H, Li S, et al (2022)Effect of cold and heat therapies on pain relief in patients with delayed onset muscle soreness: a network meta-analysisJournal of Rehabilitation Medicine · network meta-analysisView source →. It would be naive to think recommendations won’t need to update when new findings roll in down the road. But even for the most skeptical practitioner, it’s worth acknowledging that across every context studied, the intervention that consistently comes in last is… doing nothing. Researchers call it “passive recovery,” and it loses just about everywhere29Elias GP, Wyckelsma VL, Varley MC, et al (2013)Effectiveness of water immersion on postmatch recovery in elite professional footballersInternational Journal of Sports Physiology and Performance · studyView source →33Wang Y, Lu H, Li S, et al (2022)Effect of cold and heat therapies on pain relief in patients with delayed onset muscle soreness: a network meta-analysisJournal of Rehabilitation Medicine · network meta-analysisView source →34Dupuy O, Douzi W, Theurot D, Bosquet L, Dugué B (2018)An Evidence-Based Approach for Choosing Post-exercise Recovery Techniques (meta-analysis)Frontiers in Physiology · meta-analysisView source →35Block J (2010)Cold and compression in the management of musculoskeletal injuries and othropedic operative procedures: a narrative reviewOpen Access Journal of Sports Medicine · reviewView source →.
Part of this is due to the true positive influence of the various interventions studied, but part is likely due to the general benefit of doing something to address one’s own recovery. The mind-body connection is a real, studied phenomenon, and it underscores the finding that having any routine that keeps you engaged in your own recovery (even something as simple as positive self-talk!36Ievleva L, Orlick T (1991)Mental Links to Enhanced Healing: An Exploratory StudyThe Sport Psychologist · studyView source →) is associated with healing faster37Brooks T, Bradstreet T, Partridge J (2022)Current concepts and practical applications for recovery, growth, and peak performance following significant athletic injuryFrontiers in Psychology · reviewView source →. If stressing over the perfect modality, timing, or temperature of a recovery routine is keeping you from having one, dive into whatever feels best and is most convenient to you. Pick something you’ll look forward to. The best recovery is the one you’ll actually do.