Falling and getting up again

Summary How we walk or run is an inherent part of how we present ourselves. Gender, job, style, age, different aspects of who we are, are reflected in our walking or running patterns. For example, models adjust their walking pattern to look cool, sexy, and fashionable. Yet, no matter what we want our walking or running to express, for all of us it remains crucial to consider the energy cost and stability of the way we walk or run. Even though we might not actively consider it, energy and stability demands determine how we walk or run. Therefore, as the main aim of this thesis, we investigated the energy and stability demands of walking and running. In Chapter 2, we compared the degree of foot placement control between walking and running. Moreover, to verify the role of foot placement as a means to control medio-lateral stability in both modes of locomotion, we investigated the effect of external lateral stabilization on the degree of foot placement control. We found that medio-lateral foot placement is coordinated to medio-lateral trunk center of mass state to stabilize both walking and running and this coordination is stronger in walking than in running. External lateral stabilization reduced the degree of foot placement control in both walking and running, and this reduction was stronger in walking than in running. These results may imply that humans need a more accurately coordinated foot placement to maintain medio-lateral stability in walking than in running. In Chapter 3, the effect of general fatigue induced by an incremental exercise test on variability, stability, and energy cost of walking in male soccer players was investigated. To identify an optimal recovery mode, the effect of walking at Preferred Walking Speed (PWS), running at Individual Ventilation Threshold (IVT) (two active recovery modes), and Rest (a passive recovery mode) on aforementioned walking features were studied. Gait stability was not affected by an incremental exercise test, despite increases in variability and energy cost. Different from running at IVT, walking at PWS and Rest recovery modes reduced energy cost of walking after incremental exercise testing. Variability and energy cost of walking returned to their baselines after 8-12 and 16-20 minutes recovery intervals, respectively. No preference for active recovery modes (PWS and IVT) over passive recovery mode (Rest) was found in terms of variability and energy cost of walking. In Chapter 4, we explored the effects of external lateral stabilization with and without constrained transverse and frontal pelvis rotations on mechanical and metabolic walking features. We found that existing lateral stabilization devices not only constrain medio-lateral motions (i.e. medio-lateral pelvis displacement), but also constrain other movements such as transverse and frontal pelvis rotations, which leads to several other walking changes, such as reduced transverse thorax rotation, and arm swing. Our new devices allowed for normal frontal pelvis rotation and more transverse pelvis rotation (yet less than normal). However, this did not result in more normal thorax rotation and arm swing. Hence, more elaborate devices are needed to provide medio-lateral gait stability without constraining walking in other ways. In Chapter 5, we conducted a systematic review with meta-analysis of studies which directly assessed effects of lateral stabilization on energy cost in healthy young adult participants. We found that a small proportion of total energy cost is required to control medio-lateral stability; this proportion is larger when walking with zero step width.