Injury to skeletal muscle during altitude training: induction and prevention

A contracting skeletal muscle will shorten, remain isometric, or lengthen depending on the interaction between external load and the force developed by the muscle. Most physical activities involve shortening, isometric and lengthening contractions. The fluctuations in terrain encountered at altitude, increase both the likelihood that lengthening contractions will occur and the severity of the stretches. When performing a given amount of work, muscles lengthened during contractions expend less energy and fatigue less rapidly than muscles that shorten. Conversely, with equal activation, displacement, and velocity, the work done on a muscle during lengthening contractions is greater than the work performed by a muscle during shortening contractions, but force decreases more rapidly during lengthening. Furthermore, muscles are more likely to be injured during lengthening contractions than during shortening or isometric contractions. The occurrence of contraction-induced injury can be eliminated, or minimized, by prior training specific for the performance of lengthening contractions.