The annual injury incidence rate among the 36 million runners in the United States is approximately 50%. The majority of those injuries occur at the knee joint. The purpose of this study was to measure lower extremity eccentric work and average vertical loading rates among four groups of runners. Seventy-four healthy runners volunteered for this study. The four groups of runners consisted of traditional shoe wearing rearfoot strikers (TSR), minimalist shoe wearing anterior footstrikers (MSA), certified Chi runners (Chi), and minimalist shoe wearing rearfoot strikers (MSR). Study variables were ankle dorsiflexion eccentric work (ADEW), ankle plantarflexion eccentric work (APEW), knee extension eccentric work (KEEW), and average vertical ground reaction force loading rates (VALR). Volunteers ran for five minutes at a self-selected speed on a Bertec instrumented treadmill with Vicon Nexus 3D motion capture. Eccentric joint work was obtained by integrating the negative portion of the joint power curves. VALR was defined as the slope of the vertical ground reaction force curve. TSR runners demonstrated greater ADEW, greater KEEW, and greater VALR than anterior footstriking runners. MSA runners demonstrated the greatest APEW with reduced ADEW, reduced VALR, and reduced KEEW compared to TSR runners. Chi runners demonstrated the least VALR, no ADEW, no significant additional APEW, and reduced KEEW compared to TSR runners. MSR runners demonstrated the greatest and potentially injurious VALR. The mere existence of the group of 17 MSR runners was an unexpected development. The prevailing thinking has been that runners who wore minimalist running shoes would automatically transition to using an anterior footstrike pattern. To our knowledge, this is the first biomechanical evaluation of Chi runners. These findings suggest Chi running may be a desirable alternative running style for a runner with a history of lower extremity overuse injuries or someone who desires to reduce potentially injurious forces on the lower extremity. Running with a rearfoot strike pattern in minimalist shoes may produce vertical ground reaction force loading rates that have been associated with injury. Clinicians should not assume that a runner who wears minimalist shoes uses an anterior footstrike pattern. Clinical evaluation and runner education are imperative.