From recreational to elite athletes, greater than 50% of runners sustain overuse injuries each year, prompting substantial research efforts to identify causes of—and solutions to—the high injury rate. Different shoe types and material property degradation have been related to injury. Two popular footwear types are traditional shoes with thick graded soles and minimalist running footwear with thinner foam and/or non-graded soles. Notwithstanding 45 years of significant modifications to shoe design features, gained knowledge in kinesiology, and advanced technologies in polymer science, runner injury rates have not decreased and EVA foam has remained the primary running shoe midsole material since the 1970s. The purpose of this dissertation is to improve comprehensive understanding of energy management during multi-scale degradation of EVA foam and biomechanical responses of human runners.

The grand challenge of this research was to navigate, adapt, and weave together polymer and kinesiology techniques to:​ (i) quantify midsole foam macroscopic, microscopic, and molecular-level degradation, and (ii) characterize human responses to the dynamic material properties of contemporary footwear. In the pursuit of humanmaterial interactions, we first investigated fundamental energy management mechanisms. In Chapter II, we determined that humans innately reduced their impact preparatory mechanisms when foam thickness was increased from 0 – 50 mm. In Chapter III, we compared and defined molecular-level EVA foam degradation by thermal, UV, and mechanical exposures. The latter three chapters substantiated (Chapter IV) and utilized (Chapter IV-VI) a biofidelic footwear midsole mechanical ageing protocol informed by human running input variables. We determined that:​ (i) the foam midsole managed 90% of the shoe’s energy and inaccurate sample geometries overestimated energy absorption by 20% (Chapter IV), (ii) traditional and minimalist shoe energy management differences were due to thickness, wherein 66% thicker foams absorbed 83% more energy but degraded at a 49% faster rate (Chapter V), and (iii) subject-specific biomechanics were altered by unique degradation patterns induced from wearing and mechanically ageing traditional and minimalist shoes (Chapter VI). Overall, this dissertation improved multidisciplinary protocols, contributed data informed by end-use conditions, and incorporated body and shoe variables simultaneously, which is critical to future studies correlating energy management to running injuries.