Comparative efficacy of portable active cooling vs. passive cooling for reducing core temperature in exertional heat stroke: a systematic review and meta-analysis

Background: Exertional heat stroke (EHS) and exercise-induced hyperthermia require rapid reduction of core temperature (Tc). Portable active cooling devices are uesed in field settings where cold-water immersion (the gold standard) is not feasible, but their efficacy compared to passive cooling remains unclear. Objective: This review and analysis compared cooling rates between portable active cooling and passive cooling. Methods: We performed a systematic review and meta-analysis (PRISMA 2020, PROSPERO: CRD420261292698) of randomized and crossover trials. Eligible studies compared portable active cooling (type A: external refrigerant-based cooling systems; type B: wearable pre-cooling systems) with passive cooling in adults with exercise-induced hyperthermia. The primary outcome was mean Tc cooling rate (°C/min), analyzed using a random-effects model. Subgroup analysis revealed that type A devices had superior cooling efficacy (MD = 0.04 °C/min, 95% CI: 0.02-0.04), particularly when ambient temperature exceeded 30 °C. In contrast, type B devices showed no significant advantage (MD = 0.00 °C/min). Conclusions: For field management of exertional heat stroke or severe exercise-induced hyperthermia, portable active cooling systems that use external refrigerant-based cooling (type A) are more effective than passive cooling. Wearable pre-cooling systems (type B) do not demonstrate superior efficacy. Selection of cooling devices should prioritize cooling mechanism over mere portability. Systematic review registration: https://www.crd.york.ac.uk/PROSPERO/view/CRD420261292698, identifier: CRD420261292698.