Purpose: The aim of this study was to investigate the effectiveness of thermal strategies on recovery rate of strength after exercise induced delayed onset of muscle soreness.
Methods: LSBU Ethics: ETH2223-0239.The study used a randomized, parallel group design (N=40 with 10 in each group) over four consecutive test days. Participants performed a single bout of eccentric knee extensions, with baseline and post maximal voluntary contraction (MVC) measurements on a isokinetic dynamometer (HUMAC NORM), followed by a thermal recovery strategy: hot water immersion (HWI;30 min at 42 °C), cold water immersion (CWI;15 min at 9 °C), hot air immersion (HAI; 30 min at 30°C, 30% RH) or control (CON: 30 min at 18 °C, 30% RH). Recovery rate of strength (via MVC), and pain and muscle soreness (via visual analogue scales) was monitored over 72hr (pre exercise, post exercise, post therapy, 24hrs, 48hrs, and 72hrs post therapy). Venous blood samples were collected each session to analyse Interleukin 6 (IL-6), heat shock proteins (HSP72), and Creatine Kinase Muscle-Muscle isoenzyme (CK-MM).
Results: HWI returned 85 and 89% of strength back to baseline MVC values at 48hr (284.30 ± 22.04N vs 243.70 ± 25.33N; p= 0.356) and 72hrs (284.30 ± 22.04N vs 256.00 ± 26.12N; p= 0.801) respectively. CON and HAI returned 88% and 89% of strength back to baseline MVC values at 72hrs (303.70±22.04N vs 268.50 ±26.12N; p= 0.314, and 299.70±22.04N vs 268.70±26.12N; p= 0.563 respectively). Whereas, CWI MVC values were still 25% higher than baseline at 72hrs (279.10 ± 22.04N vs 218.80 ± 26.12N; p=0.005). There was no significant difference in the recovery of pain or muscle soreness between groups over time (P >0.05). CK-MM increased from baseline to post-exercise in all groups (p < 0.05). However, HWI caused a significant decrease in CK-MM in comparison to other groups over time (p < 0.05). HSP72 increased significantly after HWI and HAI (1.36±0.11 vs 1.81±0.14 mg/ml and 1.36±0.11 to 1.6±0.14 mg/ml; p = 0.001), while CWI caused a significant decrease (1.36±0.11 vs 0.87±0.10 mg/ml; p = 0.001), with no change in CON (1.21±0.01; p = 0.671). Quadriceps muscle temperature increased with HWI (36.57±1.2 °C vs 38.83±1.3 °C; p= 0.005) and decreased with HAI (37.05±0.5 °C vs 34±1.7 °C; p= 0.05) and CON (36.61±0.9 °C vs 34.78±2.2 °C; p= 0.012). There was no significant difference in HAI (36.05±0.9 °C vs 36.27±0.5 °C; p = 0.444). HWI reduced IL6 after 48 hours (0.54±0.02 vs 0.56±0.02 pg/ml; p = 0.096), whereas CWI reduced after 72 hours (0.61±0.04 vs 0.61±0.03 pg/ml;mp = 0.953).
Conclusion: Hot water immersion was the most effective thermal therapy for returning strength via MVC back to baseline values. This was related to the physiological stimulus that hot water immersion caused on the body (elevation in muscle temperature and heat shock protein 70) and associated upregulation of inflammation (IL6) and low circulating markers of muscle damage (CK-MM) compared to other therapies. Therefore, hot water immersion should be favored for recovery rate of strength. However, all thermal therapies were not effective for reducing pain and muscle soreness.