Muscle regeneration is improved by hot water immersion but unchanged by cold following a simulated musculoskeletal injury in humans.
Level 2 - randomized trial
Individual controlled comparative trial in humans.
PubMed 40437768 · doi:10.1113/JP287777
What was done
Thirty-four participants underwent an electrically stimulated eccentric contraction protocol to simulate acute muscle damage. Participants were assigned to 10 consecutive days of daily lower body water immersion across three conditions: cold water immersion (CWI, 15 min at 12°C), thermoneutral water immersion (TWI, 30 min at 32°C), or hot water immersion (HWI, 60 min at 42°C). Muscle biopsies were taken at baseline, day 5 (D5), and day 11 (D11) post-injury to assess force recovery, perceived pain, circulating damage markers (creatine kinase, myoglobin), heat shock proteins (HSP27, HSP70), and inflammatory markers (NF-κB, IL-10).
What was found
Recovery of force-generating capacity did not differ significantly between water immersion conditions (P = 0.108). HWI resulted in significantly lower perceived muscle pain compared to TWI (P = 0.035), along with lower circulating creatine kinase (P ≤ 0.012) and myoglobin (P < 0.001) relative to both TWI and CWI. CWI showed no effect on muscle pain or circulating damage markers (P ≥ 0.207). HSP27 and HSP70 expression increased significantly in HWI at D11 (P < 0.038) but appeared blunted in CWI. NF-κB expression increased across all conditions except HWI, while IL-10 was upregulated exclusively in HWI at D11 (P = 0.014).
Why it matters
This study challenges the common practice of using cryotherapy for muscle injury recovery, suggesting that post-injury heat therapy more effectively limits pain, reduces circulating damage markers, and activates molecular regenerative pathways.
Limits
The sample size was small (34 participants divided across three intervention arms). Muscle injury was simulated via electrical stimulation rather than actual athletic trauma, and immersion durations differed between groups (15 min for cold vs. 60 min for heat), confounding temperature with exposure duration.
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