PURPOSE: To better understand the mechanical factors differentiating forefoot and rearfoot strike (RFS) running, as well as the mechanical consequences of switching techniques, we assessed lower limb joint kinetics in habitual and imposed techniques in both groups. METHODS: All participants performed both RFS and forefoot strike (FFS) techniques on an instrumented treadmill at 4.5 m·s while force and kinematic data were collected. RESULTS: Total (sum of ankle, knee, and hip) lower limb work and average power did not differ between habitual RFS and FFS runners. However, moments, negative work and negative instantaneous and average power during stance were greater at the knee in RFS and at the ankle in FFS techniques. When habitual RFS runners switched to an imposed FFS, they were able to replicate the sagittal plane mechanics of a habitual FFS; however, the ankle internal rotation moment was increased by 33%, whereas the knee abduction moments were not reduced, remaining 48.5% higher than a habitual FFS. In addition, total positive and negative lower limb average power was increased by 17% and 9%, respectively. When habitual FFS runners switched to an imposed RFS, they were able to match the mechanics of habitual RFS runners with the exception of knee abduction moments, which remained 38% lower than a habitual RFS and, surprisingly, a reduction of total lower limb positive average power of 10.5%. CONCLUSIONS: There appears to be no clear overall mechanical advantage of a habitual FFS or RFS. Switching techniques may have different injury implications given the altered distribution in loading between joints but should be weighed against the overall effects on limb mechanics; adopting an imposed RFS may prove the most beneficial given the absence of any clear mechanical performance decrements. Copyright © 2014 by the American College of Sports Medicine.