Running is the most popular recreational activity in Canada, and it is associated with a myriad of physical and mental health benefits. However, running is also associated with the development of musculoskeletal injuries, which lead to lower physical activity levels and interfere with reaping the health benefits of running. Chronic running injuries are thought to result from a fatigue-failure phenomenon, where injuries develop as damage accumulates at the tissue-level over the course of many bouts of running. Damage accumulation is governed by the mechanical loading environment experienced by musculoskeletal tissues;​ therefore, developing running and rehabilitation programs that can reduce the risk of running injury requires knowledge of the mechanical loading environment. The stress-strain response of a tissue during running is difficult to measure in vivo;​ however, computational approaches have been developed to infer tissue-level loading. In vivo tissue-level loading has been well characterized during level ground running, but running outdoors often involves traversing graded terrain, which is characterized by a different gait pattern. To develop a comprehensive understanding of musculoskeletal loading during running, it is necessary to capture the mechanical loading environment of the musculoskeletal system during graded and level running. The objective of this thesis was to characterize musculoskeletal loading during running as a function of running grade. To this end, four studies were performed analyzing how individuals adapt to graded terrain as a function of running grade, speed, and step length. It was observed that graded running alters musculoskeletal tissue loading;​ although the pattern is dependent on many parameters such as the tissue of interest, and the speed, grade, and step length of running. For soft-tissue injuries, it is likely that downhill running may be deleterious and the effect is concomitant with the grade of running. In contrast, the risk of developing a stress fracture may not be altered by running grade, as strains were relatively constant across all grades of running. The findings of this thesis demonstrate the difficulty in capturing in vivo loading and highlight the importance of using tissue geometry to truly capture the effect of different running conditions.