Abstract
Walking on different grades becomes challenging on energetic and muscular levels compared to level walking. While it is not possible to eliminate the cost of raising or lowering the centre of mass (COM), it could be possible to minimize the cost of distal joints with shoes that offset downhill or uphill grades. We investigated the effects of shoe outsole geometry in 10 participants walking at 1 m s−1 on downhill, level and uphill grades. Level shoes minimized metabolic rate during level walking (Psecond-order effect < 0.001). However, shoes that entirely offset the (overall) treadmill grade did not minimize the metabolic rate of walking on grades: shoes with a +3° (upward) inclination minimized metabolic rate during downhill walking on a −6° grade, and shoes with a −3° (downward) inclination minimized metabolic rate during uphill walking on a +6° grade (Pinteraction effect = 0.023). Shoe inclination influenced (distal) ankle joint parameters, including soleus muscle activity, ankle moment and work rate, whereas treadmill grade influenced (whole-body) ground reaction force and COM work rate as well as (distal) ankle joint parameters including tibialis anterior and plantarflexor muscle activity, ankle moment and work rate. Similar modular footwear could be used to minimize joint loads or assist with walking on rolling terrain.
Highlights
The optimal way to locomote depends on the situation, for example, when walking up a grade, walking on uneven terrain royalsocietypublishing.org/journal/rsos R
We found significant effects of c2 on metabolic rate indicating that the effect of the foot segment angle on metabolic rate at each treadmill grade followed a parabolic trend
This shows that the effect of the treadmill grade on metabolic rate followed a U-shaped trend that was not centred at a 0° treadmill grade
Summary
The optimal way to locomote depends on the situation, for example, when walking up a grade, walking on uneven terrain royalsocietypublishing.org/journal/rsos R. Walking on level ground demands little effort, but walking on slopes quickly becomes challenging on a metabolic [2,3,4,5,6] and muscular level [7,8,9,10]. While it might not be possible to entirely eliminate the cost of raising or lowering the centre of mass (COM) against or with gravity during downhill or uphill walking, investigating the effects of whole-body and distal-limb mechanics on metabolic energy cost could inform new ways of minimizing metabolic rate. Stairs are one possible way to reduce metabolic cost compared to climbing an equivalent slope on a ramp surface [11]. Walking on stairs differs from walking on a ramp since stairs allow horizontal foot placement and require placing the feet in specific positions
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