The Influence of Body Composition and Skinfold Thickness on Skin Temperature Changes after Resistance Exercise

Abstract

Resistance exercise leads to an increase in skin temperature (T) in the area of the exercised muscle. Non-contact infrared thermography seems to be applicable to identify these primary used functional muscles with measuring T changes. In previous studies, lean men showed homogenous T patterns after standardized exercise protocols. Purpose: To examine the influence of body fat percentage (BF%) and skinfold thickness on T patterns after resistance exercise. Methods: 38 male subjects (19-32 years, BMI 20.4-55.2 kg/m2) participated. Means (min-max) of BF% and skinfold thickness of biceps brachii were 19.2 % (6.2-51.5) and 9 mm (2-36) respectively. After 15 min of acclimatization, the participants completed three sets with ten repetitions of unilateral biceps curl with 50 % of the individual one-repetition- maximum (two min rest between the sets). T of the exercised biceps was measured at rest (Trest), immediately following set 1, 2 and 3 (TS1, TS2, TS3) and up to 30 min post exercise (T1-T30) with an infrared camera. For statistical analysis, [INCREMENT]-values to Trest for every measuring time point, as well as Tmax, [INCREMENT]Tmax (=Tmax-Trest) and time to Tmax (min after the final set) were calculated. Results: One-way ANOVA detected a time effect on the T-values Trest to T30 (Eta2=0.64, p<0.001). Means (min-max) of Trest, Tmax , [INCREMENT]Tmax and time to Tmax were 32.3 °C (28.0-34.6), 34.0 °C (29.7-36.8), 1.7 °C (-0.3-2.8) and 8 min (2-30) respectively. BF% and skinfold thickness showed a negative correlation with Trest, Tmax, [INCREMENT]Tmax and time to Tmax (r>-0.52, p<0.001). A negative correlation between BF% and skinfold thickness with the [INCREMENT]-values to Trest was found from TS2 to T10 (for BF%: r>-0.49, p<0.001; for skinfold thickness: r>-0.66, p<0.001). All subjects up to a skinfold thickness of 10 mm showed a homogeneous T pattern in reaction to the exercise with a minimum [INCREMENT]Tmax of 1.3 °C and a time to Tmax between 2 and 9 min. The T patterns in subjects with a higher skinfold thickness were heterogeneous and some of these subjects did not respond to the resistance exercise with an increase of T. Conclusion: A higher BF% and a higher skinfold thickness is associated with delayed and lower increases in T after resistance exercise. In contrast to lean subjects, identifying the primary used functional muscles by infrared thermography in obese subjects seems to be challenging.