Running is a popular physical activity with approximately 40 million Americans participating annually. Unfortunately, there is a high overuse risk with as many as 79% of runners experiencing an injury per year. Recommendations to reduce injury have included four simple, yet contradictory, solutions:​ 1) run on a softer surface, 2) run in maximal cushioned shoes 3) run in minimal cushioned shoes and 4) run uphill. The purpose of this thesis was to determine the effects of running on two different outdoor surfaces and two different shod conditions over a variety of slopes on components of the ground reaction force. First, we hypothesized that an outdoor grass (soft) surface would reduce loading rates and increase heel-strike index values compared to a compact gravel (hard) surface. Second, we hypothesized that running in minimally cushioned running shoes would reduce both loading rate and heel-strike index compared to maximally cushioned shoes. Third, we predicted that no condition would have a significantly higher active peak. Finally, we hypothesized that loading rate and heel-strike index would be lower during uphill running compared to downhill running regardless of surface stiffness or shoe cushion. Our data suggest that surface stiffness has no effect on running forces and may not be a valid method to reduce injury risk. However, loading rate was less during uphill running in minimally cushioned shoes compared to running downhill in maximally cushioned shoes and thus, may be one strategy to reduce forces to the lower extremity.