Intensity gradients: a novel method for interpreting external loads in football

Purpose: Global navigation satellite system device-derived metrics are commonly represented by discrete zones with intensity often measured by standardising volume to per-minute of activity duration. This approach is sensitive to imprecision in duration measurement and can lead to highly variable outcomes – transforming data from zones to a gradient may overcome this problem. The purpose of this study was to critically evaluate this approach for measuring team sport activity demands.

Methods: Data were collected from 129 first team and 73 academy matches from a Scottish Premiership football club. Gradients were calculated for velocity, acceleration and deceleration zones, along with per-minute values for several commonly used metrics. Means and 95% confidence intervals were calculated for playing level as well as first team positional groups. Within-subjects coefficients of variation were also calculated for match level, position, and individual groups.

Results: The gradient approach showed consistency with per-minute metrics when measuring playing level and position groups. With coefficients of variation of 10.8% - 26.9%, the gradients demonstrated lower variability than most per-minute variables, which ranged from 10.7% - 84.5%.

Conclusions: Gradients are a potentially useful way of describing intensity in team sports and compare favourably to existing intensity variables in their ability to distinguish between match types and position groups, providing evidence that gradient variables can be used to monitor match and training intensity within team sports.