Vision provides relevant information for safe locomotion in a variety of environments. During stair locomotion visual information may be important to detect step boundaries, transitions between ground level and stairs, handrail location, and potential hazards. Although there is a large body of literature on the role of vision during locomotion there is relatively little focused on how visual information is used during stair walking. Stairs are related to a significant number of accidents in daily living, and many of these accidents are attributed to visual factors. Therefore, understanding the role of vision during stair walking could provide insight into the mechanisms involved in stair accidents. The purpose of this thesis was to investigate the properties of the visual input used to guide locomotion on stairs. Study 1 was design to describe the gaze patterns during stair locomotion with a specific focus on transitions and handrails. Study 2 investigated the effects of performing concurrent visual and non-visual tasks on walking performance and associated gaze behaviour during stair ascent. Study 3 explored the role of peripheral visual information during visual and non-visual dual tasking. Finally, Study 4 investigated the effects of restricting the lower peripheral visual field to walk on stairs. Studies relied on the measurement in health young adults of: gaze behaviour using an eye tracker, temporal characteristics of walking using foot switches, and reaction time and errors of dual task performance. Overall, the findings of these studies highlight the importance of the lower visual field in guiding stair locomotion and the specific importance for stair transitions. Moreover, foveal vision is not specifically critical to detecting handrails or steps. Results are interpreted in the light of the specialization of the dorsal ventral stream in processing peripheral visual field information. Findings of this thesis provide basic understanding on the role of vision for stair navigation with potential applications in stair-related accident prevention programs and stair design.

Vision provides relevant information for safe locomotion in a variety of environments. During stair locomotion visual information may be important to detect step boundaries, transitions between ground level and stairs, handrail location, and potential hazards. Although there is a large body of literature on the role of vision during locomotion there is relatively little focused on how visual information is used during stair walking. Stairs are related to a significant number of accidents in daily living, and many of these accidents are attributed to visual factors. Therefore, understanding the role of vision during stair walking could provide insight into the mechanisms involved in stair accidents. The purpose of this thesis was to investigate the properties of the visual input used to guide locomotion on stairs. Study 1 was design to describe the gaze patterns during stair locomotion with a specific focus on transitions and handrails. Study 2 investigated the effects of performing concurrent visual and non-visual tasks on walking performance and associated gaze behaviour during stair ascent. Study 3 explored the role of peripheral visual information during visual and non-visual dual tasking. Finally, Study 4 investigated the effects of restricting the lower peripheral visual field to walk on stairs. Studies relied on the measurement in health young adults of: gaze behaviour using an eye tracker, temporal characteristics of walking using foot switches, and reaction time and errors of dual task performance. Overall, the findings of these studies highlight the importance of the lower visual field in guiding stair locomotion and the specific importance for stair transitions. Moreover, foveal vision is not specifically critical to detecting handrails or steps. Results are interpreted in the light of the specialization of the dorsal ventral stream in processing peripheral visual field information. Findings of this thesis provide basic understanding on the role of vision for stair navigation with potential applications in stair-related accident prevention programs and stair design.

Stair locomotion is one of the most difficult and challenging type of locomotion for older adults, with a high risk of fall and injuries. A major reason is that the neuromuscular system undergoes various changes through the aging process. The aim of this doctoral thesis is to study the age-related neuro-mechanical adjustments associated with stair locomotion and more specifically to investigate the interaction between neural and muscular changes in the plantarflexor muscles. To that aim, three main projects have been performed. The first two projects investigated the influence of age on spinal and supraspinal excitability when individuals stood at the bottom and the top of a 3-steps staircase and spinal excitability during stair locomotion. The third one focused on the age-related influence on the muscle-tendon behavior during stair locomotion. The result of the first project indicate a lower dependence on spinal pathway to control soleus motoneurons with a similar change observed in both age groups suggesting that healthy older adults preserved their ability to adjust postural control to environmental demands. The second project is the first to report the modulation of H-reflex amplitude in the plantarflexor muscles during stair ascent and descent in healthy young and older adults. This modulation likely reflects an increased role of descending inputs in controlling plantarflexor muscle activation during the stair gait cycle. However, similarly to the first project the modulation of the net excitatory inputs from group I afferents during the stair gait cycle does not seem to be influenced by healthy aging. The third project suggest that length changes of the Achilles tendon and lateral gastrocnemius (LG) fascicles favour the storage and recovery the tendon elastic strain energy over the muscle work, improving thereby the mechanical efficiency of stair ascent in young adults. In older adults, it seems that a different behavior is used to maintain a mechanical efficiency during stair ascent. In contrast, during stair descent, no difference was observed between age groups regarding the LG muscle-complex behavior despite some kinematics changes. In conclusion, this doctoral thesis indicates that despite some age-related structural and functional changes of the neuromuscular system, similar neural modulations occur during stair locomotion in young and healthy older adults. During stair ascent, a similar global pattern of change in length for the fascicle’s length and the modulation of the H reflex can be observed. However, during stair descent, H reflex modulation cannot be simply explained by the pattern of muscle length change. / Doctorat en Sciences de la motricité / info:eu-repo/semantics/nonPublished