Duty Factor Is a Viable Measure to Classify Spontaneous Running Forms

Abstract

Runners were classified using two different methods based on their spontaneous running form: (1) subjectively using the V®score from the Volodalen® scale, leading to terrestrial and aerial groups; and (2) objectively using the duty factor (DF), leading to high (DFhigh) and low (DFlow) DF groups. This study aimed to compare these two classification schemes. Eighty-nine runners were divided in two groups using the V®score (VOL groups) and were also ranked according to their DF. They ran on a treadmill at 12 km·h−1 with simultaneous recording of running kinematics, using a three-dimensional motion capture system. DF was computed from data as the ratio of ground contact time to stride time. The agreement (95% confidence interval) between VOL and DF groups was 79.8% (69.9%, 87.6%), with relatively high sensitivity (81.6% (68.0%, 91.2%)) and specificity (77.5% (61.6%, 89.2%)). Our results suggest that the DF and V®score reflect similar constructs and lead to similar subgroupings of spontaneous running form (aerial runners if DF < 27.6% and terrestrial runners if DF > 28.8% at 12 km·h−1). These results suggest that DF could be a useful objective measure to monitor real-time changes in spontaneous running form using wearable technology. As a forward-looking statement, spontaneous changes in running form during racing or training could assist in identifying fatigue or changes in environmental conditions, allowing for a better understanding of runners.

Grizzlies and gazelles: Duty factor is an effective measure for categorizing running style in English Premier League soccer players

“…Overall, the results from the correlation analysis and the comparisons between high and low DF groups showed that the duty factor is a suitable measure to determine the running style. This supports the findings of Patoz et al ( 2019 ) who categorized recreational distance runners but provides more support through the inclusion of global stiffness and kinetic measures rather than a visual analysis method. Duty factor correlated with k leg at all three running speeds, as well as peak vGRF and CM vertical displacement (Lussiana et al, 2017 ).…”

“…The duty factor is calculated as the proportion of stride time (contact time plus swing time) when the foot is in contact with the ground (Hanley et al, 2022 ) and is thus a similar concept to the stance:swing ratio (Tao et al, 2019 ), where higher duty factors reflect a greater relative contribution of the contact phase (Lussiana et al, 2019 ). In recreational distance runners, Patoz et al ( 2019 ) found that the duty factor could be used to rank runners as a measure of running form, but whether this also applies to professional soccer players, who undertake multifactorial training and greater ranges of running pace within a game, from jogging to sprinting, has not yet been investigated.…”

“…The identification of running styles in soccer players could be useful for coaches in prescribing training that deals with either strengths or weaknesses, and using objective measures might be important in individualizing training programs (Patoz et al, 2019 ). It is difficult to measure stiffness values, for example, without advanced biomechanical equipment, and using simpler methods to prescribe running style would be beneficial.…”

Predicting Temporal Gait Kinematics: Anthropometric Characteristics and Global Running Pattern Matter

“…As pointed out by Gray et al (2019) , due to the fact that a of 64.9% was obtained for DF regression, DF seemed to rely on factors other than speed. Therefore, we took into account GRP in the DF estimation, which is in line with the fact that a shorter t c and larger t f were observed for AER than TER runners ( Gindre et al, 2016 ; Lussiana et al, 2017b ) and that classifying runners in two groups based on their DF led to kinematic differences of their running gait ( Lussiana et al, 2019 ) as well as similar subgroupings of runners between classifications based on GRP and DF ( Patoz et al, 2019b ). DF regression equations for AER and TER runners led to a reduction of SE by ≥147% and an improvement of of ≥133%.…”

PIMP Your Stride: Preferred Running Form to Guide Individualized Injury Rehabilitation

“…In addition, the method was shown to be a reliable tool to subjectively assess global running patterns, independently of the degree of expertise, whereas the subjective assessment of a single item of the V ® score was rater-dependent ( 10 ). Alternatively, our research team showed that the duty factor (DF), the proportion of time spent in contact with the ground during a running stride ( 11 ), can be used as a laboratory-based and objective alternative to the subjective V ® score ( 12 ). To summarize, a pronounced aerial running form is characterized by a spring-like running pattern with pronounced vertical oscillations and a more anterior (midfoot and forefoot) strike pattern than a terrestrial running form.…”