Fuchs Cas J, Betz Milan W, Petrick Heather L, Weber Jil, Senden Joan M, Hendriks Floris K, Bels Julia L M, van Loon Luc J C, Snijders Tim
Department of Human Biology, Research Institute of Nutrition and Translational Research in Metabolism, Maastricht University Medical Centre+, Maastricht, the Netherlands.
Department of Intensive Care, Research Institute of Nutrition and Translational Research in Metabolism, Maastricht University Medical Centre+, Maastricht, the Netherlands.
J Physiol. 2025 Jan;603(1):167-186. doi: 10.1113/JP286986. Epub 2024 Oct 7.
Prolonged passive heat treatment (PHT) has been suggested to trigger skeletal muscle adaptations that may improve muscle maintenance in older individuals. To assess the effects of PHT on skeletal muscle tissue capillarization, perfusion capacity, protein synthesis rates, hypertrophy and leg strength, 14 older adults (9 males, 5 females; 73 ± 6 years) underwent 8 weeks of PHT (infrared sauna: 3× per week, 45 min at ∼60°C). Before and after PHT we collected muscle biopsies to assess skeletal muscle capillarization and fibre cross-sectional area (CSA). Basal and postprandial muscle tissue perfusion kinetics and protein synthesis rates were assessed using contrast-enhanced ultrasound and primed continuous l-[ring-C]phenylalanine infusions, respectively. One-repetition maximum (1RM) leg strength and vastus lateralis muscle CSA were assessed. Type I and type II muscle fibre capillarization strongly increased following PHT (capillary-to-fibre perimeter exchange index: +31 ± 18 and +33 ± 30%, respectively; P < 0.001). No changes were observed in basal (0.24 ± 0.27 vs. 0.18 ± 0.11 AU; P = 0.266) or postprandial (0.20 ± 0.12 vs. 0.18 ± 0.14 AU; P = 0.717) microvascular blood flow following PHT. Basal (0.048 ± 0.014 vs. 0.051 ± 0.019%/h; P = 0.630) and postprandial (0.041 ± 0.012 vs. 0.051 ± 0.024%/h; P = 0.199) muscle protein synthesis rates did not change in response to prolonged PHT. Furthermore, no changes in vastus lateralis muscle CSA (15.3 ± 4.6 vs. 15.2 ± 4.6 cm; P = 0.768) or 1RM leg strength (46 ± 12 vs. 47 ± 12 kg; P = 0.087) were observed over time. In conclusion, prolonged PHT increases muscle tissue capillarization but this does not improve muscle microvascular blood flow or increase muscle protein synthesis rates in healthy, older adults. Prolonged PHT does not induce skeletal muscle hypertrophy or increase leg strength in healthy, older adults. KEY POINTS: Repeated exposure to heat has been suggested to trigger skeletal muscle adaptive responses. We investigated the effect of 8 weeks of whole-body passive heat treatment (PHT; infrared sauna: 3× per week for 45 min at ∼60°C) on skeletal muscle tissue capillarization, perfusion capacity, basal, and postprandial muscle protein synthesis rates, muscle (fibre) hypertrophy, and leg strength in healthy, older adults. Prolonged PHT increases muscle tissue capillarization, but this does not improve muscle microvascular blood flow or increase muscle protein synthesis rates. Despite increases in muscle tissue capillarization, prolonged PHT does not suffice to induce skeletal muscle hypertrophy or increase leg strength in healthy, older adults.
长期被动热疗（PHT）被认为可以引发骨骼肌适应性变化，这可能有助于改善老年人的肌肉维持能力。为了评估PHT对骨骼肌组织毛细血管化、灌注能力、蛋白质合成速率、肥大及腿部力量的影响，14名老年人（9名男性，5名女性；73±6岁）接受了为期8周的PHT（红外桑拿：每周3次，在约60°C下进行45分钟）。在PHT前后，我们采集了肌肉活检样本以评估骨骼肌毛细血管化和纤维横截面积（CSA）。分别使用对比增强超声和灌注连续l-[环-C]苯丙氨酸输注评估基础状态和餐后肌肉组织灌注动力学及蛋白质合成速率。评估了一次重复最大负荷（1RM）腿部力量和股外侧肌CSA。PHT后，I型和II型肌纤维的毛细血管化显著增加（毛细血管与纤维周长交换指数分别增加31±18%和33±30%；P<0.001）。PHT后，基础状态（0.24±0.27对0.18±0.11 AU；P=0.266）或餐后（0.20±0.12对0.18±0.14 AU；P=0.717）的微血管血流量未观察到变化。基础状态（0.048±0.014对0.051±0.019%/小时；P=0.630）和餐后（0.041±0.012对0.051±0.024%/小时；P=0.199）的肌肉蛋白质合成速率在长期PHT后没有变化。此外，随着时间推移，股外侧肌CSA（15.3±4.6对15.2±4.6 cm；P=0.768）或1RM腿部力量（46±12对47±12 kg；P=0.087）未观察到变化。总之，长期PHT可增加肌肉组织毛细血管化，但这并未改善健康老年人的肌肉微血管血流量或提高肌肉蛋白质合成速率。长期PHT不会在健康老年人中诱导骨骼肌肥大或增加腿部力量。要点：反复暴露于热环境被认为可引发骨骼肌适应性反应。我们研究了为期8周的全身被动热疗（PHT；红外桑拿：每周3次，每次45分钟，约60°C）对健康老年人骨骼肌组织毛细血管化、灌注能力、基础和餐后肌肉蛋白质合成速率、肌肉（纤维）肥大及腿部力量的影响。长期PHT可增加肌肉组织毛细血管化，但这并未改善肌肉微血管血流量或提高肌肉蛋白质合成速率。尽管肌肉组织毛细血管化增加，但长期PHT不足以在健康老年人中诱导骨骼肌肥大或增加腿部力量。
