It is important to maintain walking abilities in all individuals, especially those who are aging or have disabilities, as walking is a vital activity of daily living required for functional independence. Older adults and people with disabilities adjust their walking patterns to reduce the demands on their lower extremity muscles and joints. They tend to take shorter steps and walk at a slower speed in comparison to healthy young individuals (Kerrigan et al., 1998, Mckeon et al., 2008, Shih et al., 2014, Watelain et al., 2000, Winter et al., 1990). These spatiotemporal gait adjustments remain evident, even when walking at the same speed in older individuals and those with disabilities compared to healthy controls (Buddhadev and Martin, 2016, Cofré et al., 2011, DeVita and Hortobagyi, 2000, Silder et al., 2008). Data from several studies indicate that manipulating walking speed affects foot kinematics (Dubbeldam et al., 2010, Grant and Chester, 2015, Sun et al., 2018, Teixeira-Salmela et al., 2008, Tulchin et al., 2009, Van Hoeve et al., 2017). However, no research has examined the effect of step length on foot kinematics when walking speed is controlled.

Understanding the foot kinematics associated with the rocker mechanisms could provide insights into how people adapt foot motion when walking at different step lengths at the same speed. The heel, ankle, and forefoot rockers help propel the body forward and maintain forward progression during walking. From initial contact through the full foot contact on the ground, the foot pivots forward with the heel acting as a fulcrum (i.e., heel rocker). Once the foot is flat on the ground, the tibia pivots forward about the ankle (i.e., ankle rocker). As the tibia progresses forward the body weight vector is shifted over the forefoot. The foot then pivots forward about the forefoot or the metatarsophalangeal joint as the heel rises (i.e., forefoot rocker). During the forefoot rocker the foot continues pivoting forward from heel rise until toe-off. Among these three rockers, the forefoot rocker associated with the push-off effort of the foot on the ground, makes the largest contribution to forward propulsion (Adams and Cerny, 2018, Perry and Burnfield, 2010, Winter, 1987). Several studies examining multi-segmented foot kinetics have shown that the power at the push off is generated at the midfoot (Bruening et al., 2012, Eerdekens et al., 2019, Takahashi et al., 2017). Recently Buddhadev et al., 2020, Buddhadev and Barbee, 2020, demonstrated that increasing step length at fixed speeds increased ankle moments associated with the push-off effort in young and older adults. These findings suggest that kinematics associated with foot rockers, especially the forefoot rocker, could also be affected when walking at different step lengths at a controlled speed.

Hindfoot, midfoot, and forefoot motion during the stance phase of walking provide insights into the forward progression of the body over the feet via the rocker mechanisms. These segmental motions increase with increase in walking speed (Dubbeldam et al., 2010, Sun et al., 2018, Tulchin et al., 2009, Van Hoeve et al., 2017). As increases in walking speed are accomplished by increasing step length and cadence, we hypothesized peak hindfoot, midfoot, and forefoot joint angles associated with the heel, ankle, and forefoot rockers are larger when walking at longer compared to shorter step lengths, similar to the effect of increasing walking speed.

In summary, it is unknown how different step lengths at identical speed affects motions associated with the foot rocker, specifically the forefoot rocker. This study examined foot kinematics using the multisegmented Oxford foot model to determine these motions. The purpose of this study is to investigate effects of different step lengths at the same walking speed on peak forefoot, midfoot, and hindfoot motions related to the foot rockers.