Skeletal muscle is the most abundant tissue in the human body and can play various roles in the context of accidental injuries. First, muscles make up 38 ± 5 % of male total body mass and 31 ± 6 % of female total body mass (Janssen et al., J Appl Physiol 89(1):​81–88, 2000), and thus represent a considerable proportion of the body’s inertia. Second, muscles provide padding to many bones and other tissues, and thus can attenuate impacts to the body. Third, muscles generate forces within the body that alter the load state of other tissues during an impact. And finally, muscles themselves can be injured by impacts to the body. Despite these varied roles, muscles are often ignored in the study of accidental injury. For some types of accidental injury, muscles indeed contribute little or nothing to the injury mechanism. For other types of injury, however, muscle forces can exacerbate, mitigate and sometimes even cause specific injuries.

The goal of this chapter is to review our current understanding of how skeletal muscles affect accidental injury. Our focus is on traumatic injuries, but we address chronic or overuse injuries where they contribute to the understanding of traumatic injuries. We begin with a brief overview of muscle mechanics and then examine the role of muscles on injuries to various anatomic regions, including the head, spine, upper extremity and lower extremity. We close with a consideration of how muscle activation affects whole body motion and traumatic injury patterns in general.