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Running has been the exercise of choice for thousands of individuals for many years, whereas many others integrate a component of running into their total fitness strategy. The popularity of running can be linked to a desire to achieve an aerobic and cardiovascular benefit, while other runners use running as a means to effectively control body weight and lean body mass. Running also can produce psychological benefits and can be a useful form of stress management. Finally, there are individuals who run to compete. A select few in top form aspire to “win the race,” but many simply work to better their own previous best effort and “personal record” (PR).

Recognizing the benefits derived from running aids the sports physical therapy practitioner in understanding why the injured runner may appear quite anxious and frustrated in seeking medical attention for his or her injury. The runner may be unable to derive the cardiovascular benefits to which he or she has become accustomed. Unless such runners modify their dietary caloric intake, a reduction in their running due to injury may be accompanied by weight gain, which may actually increase the forces that must be attenuated by the lower extremities while running. Injured runners often feel an increase in their psychological stress levels that may be related to the absence of the endorphins released by the body during sustained exercise such as running. When injured, both recreational and competitive runners may notice that instead of improving their race performance and setting new PRs, their race times are slowing. Adding to the frustration of the injured runner is a poor level of understanding by some medical practitioners, whose advice to any injured runner is simply, “If it hurts when you run, then just stop running.” An appreciation for the biomechanics of running provides new insights into the mechanical basis underlying the etiology of many running injuries.

General Differences Between Running and Walking

To describe running as “fast walking” ignores critical differences in the biomechanics of walking versus running. The peak vertical forces in walking are approximately 110% of body weight, but these forces increase to 275% of body weight during running.1 In walking gait, the stance phase lasts for 0.6 s and represents 62% of the gait cycle.2 In running gait, the stance phase shortens to 0.2 s and represents only 31% of the gait cycle.3 In walking, there is a transitional period termed double-limb support where both lower extremities are in contact with the ground at the same time. This overlap of the stance phase lasts for 12% of the early stance interval and again during the final 12% prior to toe-off, and in the period between, one limb remains in contact with the ground. Double-limb support does not occur in running; rather, the runner is in either single-limb support or a new phase termed float or nonsupport in which ...

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