Author(s): AHOKAS, E., HANSTOCK, H.G.2, KYRÖLÄINEN, H.1, IHALAINEN, J.K.1, Institution: UNIVERSITY OF JYVÄSKYLÄ, Country: FINLAND, Abstract-ID: 1015

INTRODUCTION:
Long-term exposure to heat has been observed to enhance muscle hypertrophy both in animals (1) and humans (2). Meanwhile, sauna bathing has gained popularity as a post-exercise recovery method among athletes. The aim of this study was to investigate the effects of regular use of an infrared sauna (IRS) after exercise on neuromuscular performance and hypertrophy.
METHODS:
A total of 36 female team sport athletes completed the study. The athletes were pair matched into two groups: IRS and control (CON). Physical performance tests and body composition measurements (dual-energy X-ray absorptiometry and ultrasound of m. vastus lateralis) were performed before (PRE) and after (POST) 6-weeks of strength and power training. Performance tests included a 20-m sprint, countermovement jump without extra weight (CMJ) and with extra weight, which were 15%, 25%, and 50% of body weight (CMJ15, CMJ25, and CMJ50), and a maximal isometric leg press (MVC). Participants in the IRS-group used IRS immediately after training three times per week (10 min, 50 °C). A generalized estimating equation (GEE) approach was used to analyze main (group and time) and interaction (time*group) effects. Following the GEE-models, paired and independent t-tests were used to assess main and interaction effects.
RESULTS:
There were no time, group, or interaction effects on 20-m sprint time, MVC, or CMJ, CMJ25 and CMJ50. There were group (p=0.002) and time*group interaction effects (p=0.002) for CMJ15 whereby jump height was higher POST-IRS (p=0.006) and PRE-CON (p=0.023) compared to PRE-IRS. There was a time effect (p=0.003) for lean mass which increased in CON (p=0.050). Furthermore, a time effect (p<0.001) was found for lower body lean mass and m. vastus lateralis cross-sectional area (CSA) which increased in both groups (IRS: p=0.002-0.041, CON: p=0.011-0.03).
CONCLUSION:
While six weeks of IRS following strength and power training improved performance in CMJ15, no significant improvements were observed in other measures of physical performance following regular IRS use. Consequently, regular IRS bathing after exercise does not appear to have a marked effect on training adaptations in strength and power. Training also improved lower body hypertrophy in female team sport athletes but the regular use of IRS after exercise did not potentiate further hypertrophy.

References:
1. Rodrigues, P, Trajano, GS, Wharton, L, and Minett, GM. 2020. Effects of passive heating intervention on muscle hypertrophy and neuromuscular function: A preliminary systematic review with meta-analysis. Journal of Thermal Biology 93: 102684.
2. Goto, K, et al. 2011. Responses of muscle mass, strength and gene transcripts to long-term heat stress in healthy human subjects. European Journal of Applied Physiology 111: 17–27.