Eccentric stepping exercise: Acute and chronic physiological responses in young and older adults

In comparison to concentric exercise, eccentric exercise allows an individual to achieve high mechanical loads for a lower cardiovascular and metabolic requirement. This highlights it as a possible efficacious rehabilitation intervention for exercise intolerant clinical populations, likely stimulating increases in strength and mobility without the development of exercise limiting symptoms that commonly present during traditional exercise. However, the majority of research utilises unnatural forms of eccentric exercise (i.e. reverse cycling), potentially restricting the compliance and translational benefits. Therefore, we have adapted an eccentric stepping ergometer, that may more closely replicate natural activity, and investigated the acute physiological responses and training adaptations within a young and older adult population. The ergometer adaptations enabled tight control of exercise parameters, and crucially allowed comparison of concentric and eccentric physiological responses on the same device. Consistent with previous literature, we demonstrated a lower eccentric oxygen uptake (V̇O2), heart rate (HR) and blood pressure (BP) at the same power, and a greater eccentric power required to match for concentric metabolic requirement. Interestingly, eccentric V̇O2 and HR progressively increased above a predicted steady state, suggesting a higher exercise intensity at this metabolic rate. Subsequently, we compared concentric and eccentric training within young adults at similar mechanical and metabolic requirements, showing that higher eccentric powers were required to match for concentric V̇O2 and resulted in substantial increases in concentric, eccentric, and isometric strength, not seen with concentric training. Finally, we assessed the feasibility of a short eccentric recumbent stepping programme within an older adult population, showing considerable increases in concentric, eccentric and isometric strength that were maintained at 30-days follow up. Importantly, within both populations, the exercise remained tolerable and resulted in minimal muscle soreness. These results provide further evidence to support the beneficial neuromuscular adaptions of eccentric exercise, and suggest that eccentric recumbent stepping may provide a safer, more tolerable and effective training modality. Pilot studies with additional measures of physiological function (specifically muscle oxidative capacity and fatigue) suggest that eccentric exercise may promote additional benefits beyond those reported in this thesis. It is hoped that the findings from this thesis will eventually contribute to the implementation of eccentric exercise within exercise intolerant populations that stand to benefit most.