The effect of stud design on ground reaction forces and subjective perception in football-specific movements

Anterior cruciate ligament (ACL) injuries are a common concern in football. They often require surgery, lead to lengthy recovery, can cause long-term knee instability, and prevent from returning to the same playing standard. Current research has suggested that football boot studs may play a role in determining lower limb loading and therefore affecting ACL injury factors (1), but evidence upon the effects of stud design on biomechanical factors related to injury is limited. We assessed the effect of stud mechanical features on lower limb loading and subjective perception during lab-based football-specific movements. 

METHODS: We measured the effects of three different stud types on 3D ground reaction forces (GRF) and subjective perception of comfort, stability, grip and overall appreciation. Seven male recreational football players (29.7±6.0 y.o.; height 1.81±7,4 m; weight 77.4±6.6 kg) performed 90° and 180° cutting manoeuvres (2), in 3 different stud conditions, presented in random order: STD, standard; FLX, flexible; and VFL, very flexible studs. SASpik (saspik.it) provided FLX and VFL. All participants wore standard 8-stud boots (Mizuno Morelia Neo IV β Elite), sprinted from ~5 m and landed with their dominant foot on a force plate (Kistler 9287CA, 2000 Hz), covered in artificial turf. Repeated measure non-parametric ANOVA (Friedman test) and statistical parametric mapping (www.spm1d.org) were used to compare scalar quantities (subjective feedback via Visual Analog Scales - VAS, GRF loading rates) and timeseries (the first 40 ms of the GRF curves) across conditions (α=0.05). 

RESULTS: Subjective evaluations of overall appreciation showed higher scores for FLX (+32.5%, P=0.028) than STD. Comfort (STD= 6.3±2.3; FLX= 8.4±1.1; VFL= 7.7±2.7), Stability (STD=5.8 ±2.3; FLX=7.9±1.2; VFL=6.7±2.4), and Grip (STD=6.7±1.9; FLX=7.2±2.2; VFL=7.2±2.7) did not show statistical differences from the sample tested. 

The vertical loading rate was higher in STD (226.03±134.36 BW/s) compared to FLX (127.88±81.45 BW/s; -43.4%) during the 90° cut (p=0.022). No significant differences were found in any of the three GRF components for any movement through SPM timeseries analysis. 

CONCLUSION: These preliminary findings suggest that football boots equipped with flexible studs are overall better perceived by users. Adding in-built flexibility to the 8 studs in the boot reduced the vertical force loading rate in 90° cutting, and did not appear to influence other features of the GRF during the initial contact phase of cutting and pivoting tasks. However, the small sample size analysed and variability of the outcomes observed warrant further research of the interplay between stud design and mechanical loading. 

References: 

1) Bennett HJ, et al. J Appl Biomech. 2015; 31(5):309-17. doi: 10.1123/jab.2014-0203. 

2) Cortes, N et al. Journal of Sports Sciences, 29(1), 83–92. doi: 10.1080/02640414.2010.523087.

ASTRACT ID: 2917. Available via https://sport-science.org/index.php/programme-25/search-engine.