Skeletal muscle is prone to damage from a range of stimuli. The muscle repair process that ensues is complex, involving several phases and requiring the participation of many different cell types. Among the cells involved are various immune cells including neutrophils, macrophages, monocytes, and eosinophils. More recently, T cells were added to this list of immune cells known to participate in effective muscle repair from traumatic injuries in mice. We recently published data showing that T cells also accumulate in human muscle following contraction-induced damage. These data suggested that T cells might be involved an adaptation known as the repeated bout effect that renders muscle protected from future damage after an initial exposure. This document contains research on the role of the immune system, particularly T cells, in the "repeated bout effect."