What is acceleration load?
Acceleration load was developed following research by Duthie and Delaney (2015) titled Acceleration-Based Running Intensities of Professional Rugby League Match-Play. The paper recognised potential limitations of traditional distance and velocity metrics for quantifying high intensity movements occurring at low velocities, such as acceleration and deceleration. This was especially important where positional requirements tended toward working in smaller, confined spaces more than open-style running. The study proposed the use of average acceleration as a way to measure what can be described as the amount of speed change activity.
How is acceleration load calculated?
Acceleration load is the accumulation of absolute acceleration values (derived from smoothed velocity and sampled at 10 Hz) over the specified period. By using absolute acceleration values, acceleration (positive) and deceleration (negative) are treated equally. Accumulating the acceleration values provides a volume measurement of total speed change activity.
How is acceleration density calculated?
Acceleration density is the average of absolute acceleration values over the specified period, i.e. acceleration load over time. As such, acceleration density can be described as quantifying the intensity of speed change activity. Relating this to more commonly used parameters, another way to conceptualise it is to say that meterage per minute is to total distance as acceleration density is to acceleration load.
How is acceleration density index calculated?
Whereas acceleration density is acceleration load over time, acceleration density index is acceleration load over distance - specifically, acceleration load per 10m distance covered. This quantifies the intensity of speed change activity exclusively during locomotive work, rather than the whole time period. This might be preferred to acceleration density as a way to analyse speed change demands excluding rest periods.
How do acceleration load parameters differ from threshold-based acceleration parameters?
Threshold-based acceleration parameters measure the number of discrete events (acceleration efforts) that occur within prescribed acceleration bands. This enables the user to focus on higher intensity movements by excluding efforts below a set threshold, assess accelerations and decelerations separately, and generally analyse acceleration and deceleration events in a greater level of detail and granularity. The rules around acceleration effort detection also exclude micro-movements with a duration less than 0.9 seconds.
Acceleration load parameters provide a more holistic measurement of speed change activity. By eschewing thresholds and a minimum effort duration, smaller and shorter accelerations and decelerations are not excluded. As such, acceleration load parameters are more comprehensive in measuring speed change activity but more concise in presenting that information.
Practical example of acceleration load parameters
The OpenField Cloud table below shows a training session broken down by drill. 'Criss-Cross Handball' is an example of a drill where the open running demands are relatively low (68.0 m/min) but the speed change demands are relatively high (Acc Density = 0.47; Acc Density Index = 4.12). The energy cost and intensity of this drill might be underestimated if relying exclusively on traditional distance and velocity metrics without acceleration load parameters.