Factors contributing to the equal forelimb and hindlimb stride lengths during quadrupedal walking

The forward motion of terrestrial vertebrates can be divided into stride lengths (distance traveled by the body from touchdown to the next touchdown of a limb) which is the sum of the lengths of stance and swing phases for each limb. Those lengths are influenced by the anatomy of the limbs; longer limbs, for example, produce longer steps and strides. During typical quadrupedal walking, at least one forelimb and hindlimb are in contact with the ground at any given time. This means the fore‐ and hindlimbs (regardless of limb proportions) should have the same stride length, though the length of the phases (stance, swing) may differ, as long as they sum to equal stride lengths. In addition to the anatomical limb length (ALL), joint excursion patterns, which often differs between the forelimb and hindlimb can influence stance and step. Animals can behaviorally adjust their limb postures to change their effective limb lengths (ELL, the minimum distance between the shoulder/hip and wrist/ankle) in order to achieve the necessary stride length. Thus, we hypothesize that forelimb and hindlimb stride lengths should be equal, but this may be achieved in different ways and therefore all other parameters may vary possibly in relation to limb proportions.To study this, we examined 69 quadrupedal walking bouts of four New World monkeys with differing ALL. Preliminary analyses indicate a close correlation of forelimb and hindlimb stride length (0.93, p<0.01), regardless of differences in ALL proportions. Factors that contribute to an equal stride length are more variable. Forelimb and hindlimb stance phase length were highly correlated (0.700, p<0.01), and forelimb and hindlimb swing phase length were highly correlated (0.834, p<0.01). Although significant, a low correlation of the length of swing and stance phase was found for both the forelimb (0.412, p<0.01) and the hindlimb (0.430, p<0.01). When modeling step length in stance by angular excursion and ELL, the model accounts for an average of 85% of the distance traveled. Taken as a whole, these data, especially the intralimb and interlimb patterns, suggest that the step and swing lengths are not easily predicted by limb anatomy or effective limb lengths alone. Thus, other factors must also contribute to step length and thus equal stride lengths, such as bending of the back and contributions made by hand and foot posture. Overall, these data indicate that although stride lengths do need to be equal between the forelimb and hindlimb, contributing parameters vary between strides and may vary by species anatomy and ecology.Support or Funding InformationNSF BCS‐9222526