High intensity resistance exercise elicits accumulations of the damage-marker XIRP1A in a sex-specific manner in healthy human subjects

Resistance exercise (RE), particularly in high intensity programs, applies a considerable amount of mechanical stress on muscle tissue. Especially when unaccustomed to this strain, e.g. when initiating a training phase, damage occurs in the myofibrils as protein structures unfold. The formation of lesions indicates regions with disrupted myofibrils and is associated with proteostasis factors, as disrupted structures need to be repaired or cleared from the cell. In this explorative approach, we aimed to quantify the emergence of such lesions in general and in distinct myofiber types of healthy human males and females. › 18 participants (14 male, 4 female; 24 ± 3.4 yrs.; 179 ± 10 cm; 75,9 ± 12,3 kg) performed one training session of two sets at the respective 4, 8 & 16 repetition maximum (RM) on the leg extension machine as well as at the 4 and 8 RM on the leg press. Vastus lateralis biopsies were taken before and 1h after the intervention. Accumulations of the damage-marker XIRP1A were analysed immunohistochemically in muscle cross-sections. The number of lesions, their area and staining intensity were assessed with ImageJ. Preliminary statistics were performed in Microsoft excel. › At resting conditions, males exhibit a significantly higher percentage of XIRP-positive type 1 fibers than type 2 fibers in the examined cross-sections, and females show a lower percentage of XIRP-positive type 1 fibers than males (both p<0.05). The number of lesions (+190%) as well as their size (+51%) and staining intensity (+29%) increase significantly after one bout of RE across sexes, with females exhibiting even more pronounced increases in size and staining intensity than males. › High intensity RE-interventions induce myofibrillar lesions in skeletal muscle fibers, appearing as accumulations of the muscle damage-marker XIRP1A. The formation of these lesions occurs in a sex- and fiber-type-specific manner.