Thermal Infrared Imaging Can Differentiate Skin Temperature Changes Associated With Intense Single Leg Exercise, But Not With Delayed Onset of Muscle Soreness

Abstract

Muscle damage and soreness associated with increased exercise training loads or unaccustomed activity can be debilitating and impact the quality of subsequent activity/performance. Current techniques to assess muscle soreness are either time consuming, invasive or subjective. Infrared thermography has been identified as a quick, non-invasive, portable and athlete friendly method of assessing skin temperature. This study assessed the capability of thermal infrared imaging to detect skin temperature changes that may accompany the inflammatory response associated with delayed onset muscular soreness (DOMS). Eight recreationally trained participants (age 25 ± 3 years, mass 74.9 ± 13.6 kg, training minutes 296 ± 175 min·wk^-1) completed 6 sets of 25 maximal concentric/eccentric contractions of the right knee flexors/extensors on a dynamometer to induce muscle damage and DOMS. The left knee extensors acted as a non-exercise control. Neuromuscular performance, subjective pain assessment and infrared thermography were undertaken at baseline, 24 and 48 hr post the DOMS-inducing exercise protocol. Data were analysed using Bayesian hierarchical regression and Cohen's d was also calculated. Maximal voluntary contraction torque was statistically lower at 24 hr (d = -0.70) and 48 hr (d = -0.52) compared to baseline, after the DOMS-inducing exercise protocol. These neuromuscular impairments coincided with statistically higher ratings of muscle soreness at 24 hr (d = 0.96) and 48 hr (d = 0.48). After adjusting for ambient temperature, anterior thigh skin temperature was statistically elevated at 24 hr, but not 48 hr, compared with baseline, in both the exercised and non-exercised leg. Thigh temperature was not different statistically between legs at these time points. Infrared imaging was able to detect elevations in skin temperature, at 24 hrs after the DOMS inducing exercise protocol, in both the exercised and non-exercised thigh. Elevations in the skin temperature of both thighs, potentially identifies a systemic inflammatory response occurring at 24 hr after the DOMS-inducing exercise protocol.

Keywords: Infrared thermal imaging; muscle damage; muscle soreness; skin temperature.

Figure 1.

Experimental design. Panel A addresses the aim to examine the capability of thermal infrared imaging to detect skin temperature changes that accompany delayed onset muscular soreness. Panel B addresses the aim to determine if thermal infrared imaging of the skin could detect acute changes in muscle activity associated with a DOMS-inducing exercise protocol.

Figure 2.

Posterior mean (95% credible interval) of the RIGHT and LEFT anterior thigh skin temperature at baseline, 24 hr and 48 hr. Individual data are shown with numbers, ^a RIGHT and LEFT skin temperature statistically different to baseline, ^b RIGHT and LEFT skin temperature statistically different to 48 hr.

Figure 3.

Posterior mean (95% credible interval, CI) anterior RIGHT and LEFT thigh skin temperature during the warm-up, and pre- and post-exercise MVC assessments on the first testing day (A); the posterior mean difference (95% CI) of within-leg temperature change from pre-warm up temperature (B); and the posterior mean difference (95% CI) of between-leg comparisons (C). Individual data are shown in cross marks, ^c statistically different to pre warm-up in the same leg, ^d statistically different between legs at the same time point.