Author(s): SABIONI, M., LUCCHINI, L., WILLÉN, J., D'HULST, G., FIKOWSKI, B., JACOBSSON, M., Institution: KTH ROYAL INSTITUTE OF TECHNOLOGY, Country: SWEDEN, Abstract-ID: 2770

INTRODUCTION:
HYROX is a global fitness competition combining running with standardized functional tasks [1]. Although sled loads are fixed, athletes report differences in sled push and pull resistance within and between events, often attributed to turf conditions. This variability raises concerns about performance fairness. Existing friction assessment methods are not suited for field use due to limited portability [2], complex setup, or inability to quantify both static and dynamic friction. The aim of this study was to develop and test a field-deployable portable system for pre-race evaluation of turf friction in fitness competitions.
METHODS:
A motorized pulling device was built to move a loaded sled at a constant velocity, while recording pulling force at 50 Hz using an inline Bluetooth force sensor. The system performed automatic self-calibration at startup. For each trial, the user set the pulling speed and distance. The system recorded and analyzed force signal to identify the onset and steady-movement. Static coefficient of friction was calculated from the peak force before motion, and dynamic coefficient from the mean force during constant velocity, assuming equilibrium conditions.
Preliminary testing was conducted in a HYROX-affiliated gym in Stockholm. Two sled lanes were evaluated: synthetic grass-like turf (T1) and cloth-like turf (T2). Loads from 49 to 169 kg (15 kg increments) were tested with two repeated trials. An additional wet condition (T2-W) was tested to simulate moisture accumulation during events. The mean static and dynamic coefficients of friction of repeated trials were calculated and compared
RESULTS:
The system was transportable in a standard backpack. Setup time was under five minutes, with no reset required between trials. Repeated trials showed high repeatability and measured coefficients were within ranges reported in the literature [2].
Under dry conditions, T1 showed higher static and dynamic friction than T2 at all loads. Mean dynamic friction across loads was 0.34 for T1 and 0.28 for T2. Differences increased with load: static friction differed by 13–18% and dynamic friction by 12–15% from the lightest to the heaviest sled. In the wet condition, T2-W had higher static and dynamic friction compared with dry T2, where effect appears to decrease with load. T2-W showed greater variability, likely due to uneven water distribution.
CONCLUSION:
Preliminary data indicates that changes in material, differences between lanes or venues, as well as moisture changes during events affects sled resistance and can influence performance outcomes.
Pre-event friction assessment with a portable device is viable and can identify inconsistencies between surfaces and support improved competition standardization. Further testing will include a larger sample of repeated trials on official competition turf in collaboration with HYROX, and evaluation of additional conditions such as chalk, temperature, and floor attachment.
[1] Brandt et al. (2025)
[2] Andre et al. (2013)