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Keywords

Clinical Practice in Athletic Training

Abstract

Focused Clinical Question: Does implementing a month-long passive heat protocol in a sauna affect a person’s active heat acclimatization by decreasing average heart rate (HR), decreasing internal body temperature, and increasing skin temperature (Tsk)? Data Sources: A comprehensive search was conducted in September 2023 through PubMed. The search terms used were passive heat therapy, heat acclimatization, and hypoxia. Manuscripts were limited to those published within the last 5 years. Study Selection: Inclusion criteria consisted of physically active participants, measures of HR and body temperature, and randomized-controlled trials and crossover studies using saunas as a passive heat intervention. Exclusion criteria consisted of systematic reviews, meta-analyses, case studies, individuals with cardiovascular disease or any other underlying health conditions, animal studies, and the use of water-profused suits. Data Extraction: Studies measured HR, internal body temperature, and Tsk as outcomes of heat acclimatization. Body temperature was measured via an infrared thermometer (skin) and an oral mucosa test (internal). HR was measured by HR monitors and electrocardiograph (ECG). Summary Measures: Intra-group data was determined with the Wilcoxon test for paired samples in both groups. Evidence Appraisal: All 3 studies were analyzed using the PEDro scale to identify threats to internal validity. Search Results: The computerized search returned 21 studies. Eighteen studies were excluded because they did not use saunas, did not match study design, and did not include physically active participants. Data Synthesis: One study found a decrease in average HR (123.68 vs. 106.89, p<0.05), no increase in internal body temperature (37.43°C vs. 37.42°C, p=0.002), and an increase in Tsk (36.92°C vs. 37.74°C, p=0.005) at higher sauna temperatures (42°C) from session 1 to session 9. However, another study found varying results with internal and Tsk at both higher and lower temperatures. The third study did not find any significant difference in HR, body temperature, and Tsk between the control and sauna groups (p>0.05). Evidence Quality: Each study was assessed using the PEDro scale, losing points for not blinding participants and experimenters (7/11, 6.5/11, and 7/11). Conclusions: The strength of recommendation taxonomy yields B evidence due to inconsistency in study findings, suggesting moderate evidence that passive heat interventions can improve someone's active heat acclimatization over a month-long period. Having a healthy HR contributes to adequate blood flow to the extremities. In addition, having an increase in Tsk while exercising in a hot environment can increase sweat rate which enhances the thermoregulatory response. An efficient thermoregulatory system can help inhibit inflammation markers in the cells, thus limiting the chance of developing hypoxia. A decrease in a person’s HR and internal body temperature attributes to effective heat acclimatization. Additional research can focus on at-risk populations, using Tsk patches, and hydration levels which play a vital role in thermoregulation.

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