Assessment of alternative metrics in the application of infrared thermography to detect muscle damage in sports

<i>Objective.</i>The association between muscle damage and skin temperature is controversial. We hypothesize that including metrics that are more sensitive to individual responses by considering variability and regions representative of higher temperature could influence skin temperature outcomes. Here, the objective of the study was to determine whether using alternative metrics (TMAX, entropy, and pixelgraphy) leads to different results than mean, maximum, minimum, and standard deviation (SD) skin temperature when addressing muscle damage using infrared thermography.<i>Approach.</i>Thermal images from four previous investigations measuring skin temperature before and after muscle damage in the anterior thigh and the posterior lower leg were used. The TMAX, entropy, and pixelgraphy (percentage of pixels above 33 °C) metrics were applied.<i>Main results.</i>On 48 h after running a marathon or half-marathon, no differences were found in skin temperature when applying any metric. Mean, minimum, maximum, TMAX, and pixelgraphy were lower 48 h after than at basal condition following quadriceps muscle damage (<i>p</i>< 0.05). Maximum skin temperature and pixelgraphy were lower 48 h after than the basal condition following muscle damage to the triceps sural (<i>p</i>< 0.05). Overall, TMAX strongly correlated with mean (<i>r</i>= 0.85) and maximum temperatures (<i>r</i>= 0.99) and moderately with minimum (<i>r</i>= 0.66) and pixelgraphy parameter (<i>r</i>= 0.64). Entropy strongly correlates with SD (<i>r</i>= 0.94) and inversely moderately with minimum temperature (<i>r</i>= -0.53). The pixelgraphy moderately correlated with mean (<i>r</i>= 0.68), maximum (<i>r</i>= 0.62), minimum (<i>r</i>= 0.58), and TMAX (<i>r</i>= 0.64).<i>Significance.</i>Using alternative metrics does not change skin temperature outcomes following muscle damage of lower extremity muscle groups.