Author(s): CHAISSON, C., WEAVING, D., EMMONDS, S., BARRETT, S., HUDSON, A., HANLEY, B., Institution: LEEDS BECKETT UNIVERSITY, Country: UNITED KINGDOM, Abstract-ID: 2500

INTRODUCTION:
Duty factor (DF) is a simple marker of movement strategy, defined as the ratio of ground contact time to stride time during running.1 Athletes who adopt aerial-based running patterns (low DF) receive increased biomechanical loads on the foot, ankle, and calf muscles whereas terrestrial-based runners (high DF) place increased load on knees and hips. Given football players typically run 9-11 km in matches, including 111-255 m of sprinting,2 there is a need to better understand loading patterns regarding implications for optimal training regimens. The aim of this study was twofold: (1) to create a method that practitioners could implement easily into training routines and (2) to categorise running styles remotely during the maximum velocity phase of a controlled sprint.
METHODS:
53 football players across the Women’s Pro Game Academy League performed controlled sprints as part of their normal training routine across the 2024-25 season (161 observations total; 3.0 ± 1.5 per player). As minimal disruption to training was prioritised, a method was needed to automatically detect the maximum velocity phase while considering different routines in place at each club (e.g., 30 m or 40 m sprints, repeated sprints). An algorithm (RStudio, Posit Software, Boston, MA) was created to automatically detect the start and end times of the maximum velocity phase of the controlled sprints from 10-Hz acceleration, velocity, and distance data from a foot-mounted inertial measurement unit (Playermaker, London, UK), already in use in training by clubs. These times were manually entered into the Playermaker dashboard, which allowed the mean contact time and stride time to be calculated for the entered bout. Contact time and stride time were adjusted using a prior validation study comparing the F-IMU system with an instrumented treadmill and used to calculate DF. DF values were used to identify two separate groups (high and low DF) and to compare between playing positions.
RESULTS:
Results showed low DF (0.290 ± 0.016) and high DF (0.330 ± 0.015) groups achieved similar maximal sprint speeds (6.59 ± 0.41 m·s-1 and 6.61 ± 0.48 m·s-1, respectively), indicating that DF reflects movement strategy and leg stiffness rather than sprinting ability. Playing position itself did not meaningfully influence DF, with substantial variation in sprinting styles existing within positions (e.g., central [0.258-0.351] vs wide [0.268-0.330] defenders).
CONCLUSION:
This study provided a novel proof of concept for assessing running styles across several Women’s Pro Game Academies during the maximum velocity phase of a controlled sprint. DF can help contextualise sprint exposure beyond velocity metrics when individualising training. In team sports where there is limited time, this offers one method of monitoring running styles with minimal burden to practitioners.

1. Hanley et al. (2022). Frontiers in Sports and Active Living, 4:939676
2. Savolainen et al. (2023). Biology of Sport, 40(4):1187–1195