Consequences of Skeletal Muscle Injury Induced by Unaccustomed Exercise

Unaccustomed exercise is exercise that has never been performed before or has not been performed previously at a certain intensity. Unaccustomed exercise commonly leads to an acute skeletal muscle injury. Several negative consequences develop as a result of this injury and can interfere with daily and recreational physical activities. This article describes what the consequences are, when they occur and recover, and what might cause them to occur. Also, the article discusses the nursing implications of these consequences for healthy young and older individuals and for those individuals who have disuse muscle atrophy. Unaccustomed exercise, especially involving eccentric contractions, commonly induces skeletal muscle injury (McHugh, 2000) (see Table 1). At least two orthopaedic populations are known to be at high risk for muscle injury from unaccustomed exercise. The competitive athlete is susceptible upon return to dynamic sports activities after recovering from an injury or at the start of a new season (McHugh, 2000). A different training regimen also may induce muscle injury. The nonathletic individual is susceptible upon starting a new dynamic sports or exercise activity, especially if the activity has an eccentric contraction component. Such activities include running, soccer, and bench stepping.Table 1According to Armstrong (1990), the “practical consequences” of unaccustomed exercise include muscle soreness and reduced muscle function, and the “clinical symptoms” include myofiber damage (p. 429). However, a distinction between consequences and symptoms will not be made for this discussion. All the effects that are listed in Table 2 are described as consequences of muscle injury induced by unaccustomed exercise.Table 2Much of our knowledge about the consequences is based on findings from studies involving healthy college-age subjects (Cleak & Eston, 1992a). Consequences in healthy children (∼10–13 years old) and older adults (˜>=60 years old) have been investigated in a few studies, and the findings suggest that some results from the young adult studies may not apply to children (Duarte et al., 1999) or older adults (Manfredi et al., 1991). Nevertheless, it is important for the nurse to be cognizant of the findings from the young adult studies. Therefore, the main objective of this article is to enhance the nurse's general understanding about the consequences of muscle injury induced by unaccustomed exercise.