Relationships between stride length, stride frequency, velocity, and morphometries of foals
Authors: Leach Doug , Cymbaluk Nadia F. 
Published: February 2025

Velocity-dependent changes in stride length and frequency were studied in 19 male foals, 6 to 8 months of age, and were related to body morphometries. Eighteen distance and 8 angle measurements were digitized from 16-mm films of standing foals. The total mass and the percentage of total mass acting through the forelimbs were also recorded. Stride length and frequency data were extracted from 16-mm films of 239 strides of the walk, trot, and canter-gallop. Polynomial-regression analysis was used to determine the equation that best described the relationship between data of stride length or frequency vs velocity and stride length vs stride frequency for each foal, for the total population, and for the walk, trot, and canter-gallop data from the total population. Stepwise-regression analysis was done of stride length, or slope of the stride length-velocity line (frequency−1) vs distance, angle, and mass measurements. The stride length for each foal was calculated for a stride frequency of 2 strides/s.

The maximum recorded velocity was 11.45 m/s. There was overlap in the velocity ranges at which gaits were used: the walk or trot were used at velocities between 1.7 to 2.0 m/s and a trot or canter were used over a wider velocity range of 3.2 to 5.8 m/s.

Stride length did not exceed 4.72 m. The mean stride length at a frequency of 2 strides/s was 2.57 m and was significantly (P < 0.05) correlated to total mass (r = 0.6335) and length of the metacarpus (r = - 0.5115), but not to wither height. The relationship between stride length and velocity for the total population of foals and for individual foals was explained by a Ist-degree polynomial equation. The R2 value for the total population was 0.9635. A lst-degree polynomial equation was required for the walk, trot, and canter and gave R2 values of 0.5427, 0.7986, and 0.9442, respectively.

The maximum observed stride frequency was 2.7 strides/s. A 3rd-degree polynomial equation described the relationship between stride frequency and velocity of data from the total population (R2 = 0.9353). Of 19 foals, a lst-degree polynomial was required in 7, a 2nd-degree polynomial in 8, and a 3rd-degree polynomial equation in 4 to describe this relationship. When individual gaits were analyzed, using data from the total population of foals, only a lst-degree polynomial equation (R2 = 0.5228) was required for the canter-gallop. The walk and trot were each described by 2nd-degree polynomial equations. All height measurements (except height of hip) and length measurements (except length of the metacarpus segment, length of the neck, and length of the forelimb and hindlimb digits) were negative and significantly (P < 0.05) correlated to frequency−1. Seemingly, foals that relied more on increases in stride frequency, rather than stride length, to increase velocity had higher values of these distance measurements, and foals with small dimensions relied preferentially on stride length, rather than frequency, to increase velocity.

A 3rd-degree polynomial equation explained the relationship between stride length and frequency data (R2 = 0.7865). A lst-degree polynomial was required in 12 foals and a 2nd-degree polynomial equation was required in 7. A lst-degree polynomial was selected for the walk, trot, and canter-gallop, but these gave low R2 values (0.1406, 0.1506, and 0.3000, respectively).

A stepwise-regression analysis of stride length vs distance, mass, and angle measurements selected 12 variables and gave an R2 value of 0.9877. Foals that were more upright in the distal portion of their limbs had a shorter stride length.