Effects of exercise intensity on skin temperature and muscle oxygen saturation in the thigh during and after strength resistance training

Abstract

This study aimed to describe and correlate the skin temperature (Tsk) and muscle oxygen saturation (SmO₂) during leg extension exercises with higher load (HL) and lower-load (LL) demands. Seventeen active men (age: 25.6 ± 3.4 years) participated by performed 3 x 15 repetitions of leg extension at 70 % of 1RM (HL) and 35 % of 1RM (LL). The Tsk of the thigh, knees, and legs were recorded with a thermal camera. SmO₂ was assessed using non-invasive near-infrared spectroscopy (NIRS) technology. The percentage of muscle oxygen extraction (∇%SmO₂) and the hyperaemic response (Δ%SmO2) in the vastus lateralis (VL) was calculated. Also, the rating of perceived exertion (RPE) scale data was obtained. Data were collected after warm-up (Baseline), after the first set (Set 1), second set (Set 2), third set (Set 3), and twice during recovery (7 min and 15 min). The results indicate an increase in Tsk thigh from baseline to recovery, which was more differenced in the HL group (Tsk = 30.44 ± 1.24 °C to 31.38 ± 1.32 °C) than in the LL group (Tsk = 30.86 ± 0.96 °C to 31.32 ± 1.06 °C). Similarly, SmO₂ decreased during exercise, more in the HL group than in the LL group (SmO₂ = 18 ± 15 % vs. 23 ± 15 %), and ∇%SmO₂ increased more in the HL group than in the LL group (SmO₂ = 75 ± 20 % vs. 65 ± 20 %). Additionally, during recovery, the hyperaemic response was higher in HL group than in LL group (SmO₂ = 12 ± 14 % vs. 3.1 ± 9.1 %). The RPE was also higher in HL group (9.5 ± 0.6) than in LL group (4.8 ± 1.3). Moreover, the increase in Tsk thigh was associated with ∇%SmO₂ during exercise (r² = 0.43 to 0.55) and recovery (r² = 0.31 to 0.52). Tsk and SmO₂ metrics reflect metabolic changes occurring during and after resistance training, which can be useful for monitoring the internal response to the workout.