The influence of body composition on exercise-associated skin temperature changes after resistance training

Resistance exercise leads to an increase in skin temperature (T_skin) in the area of the exercised muscle. Infrared thermography seems to be applicable to identify these primary used functional muscles with measuring T_skin changes. The aim of the current study was to investigate the influence of body composition on T_skin patterns after resistance exercise. 38 male subjects (19-32 years, BMI 20.4-55.2 kg/m²) participated. Body fat percentage and biceps skinfold thickness were calculated. The subjects were divided into two groups: lean group (LG) with body fat percentage < 25%, obese group (OG) with body fat percentage ≥ 25%. All participants completed three sets with ten repetitions of unilateral biceps curl at 50% of the one repetition maximum. To represent exercise-induced changes of T_skin to rest (T_rest), the algebraic difference of each time point to T_rest was calculated. The resulting delta values (∆) are as follows: immediately after the first, second, and third set (∆T_set1,∆T_set2,∆T_set3), and at 1,2,3,4,5,6,7,8,9,10,15,20,25,30 min after the third set (∆T₁-∆T₃₀). The maximum positive difference to T_rest was defined as ∆T_max, and the time to reach ∆T_max was defined as Time to ∆T_max. LG and OG differed significantly at T_rest (32.8 ± 0.9 vs. 31.1 ± 1.4 °C), ∆T_max (1.9 ± 0.4 vs. 0.9 ± 0.8 °C), Time to ∆T_max (4.5 ± 2.0 vs. 17.6 ± 10.2 min) and at ∆T_set2 to ∆T₁₅ (p < 0.005). Correlations between body composition (BMI, body fat percentage, biceps skinfold thickness) and T_rest, ∆T_set2, ∆T_set3, ∆T_max (-0.47 max (0.52 skin pattern was found in all subjects, whereas heterogeneous T_skin progressions were shown in the OG. In conclusion, a greater body fat percentage and a greater skinfold thickness are associated with delayed and lower increases in T_skin after resistance exercise. In contrast to lean subjects, identifying the primary used functional muscles using infrared thermography in obese subjects is challenging.