A Novel Accelerometry-Based Metric to Improve Estimation of Whole-Body Mechanical Load

Abstract

While the Player Load is a widely-used parameter for physical demand quantification using wearable accelerometers, its calculation is subjected to potential errors related to rotational changes of the reference frame. The aims of this study were (i) to assess the concurrent validity of accelerometry-based Player Load against force plates; (ii) to validate a novel metric, the Accel'Rate overcoming this theoretical issue. Twenty-one recreational athlete males instrumented with two triaxial accelerometers positioned at the upper and lower back performed running-based locomotor movements at low and high intensity over six in-series force plates. We examined the validity of the Player Load and the Accel'Rate by using force plates. Standard error of the estimate was small to moderate for all tested conditions (Player Load: 0.45 to 0.87; Accel'Rate: 0.25 to 0.95). Accel'Rate displayed trivial to small mean biases (-1.0 to 6.1 a.u.) while the Player Load displayed systematic very large to extremely large mean biases (17.1 to 226.0 a.u.). These findings demonstrate a better concurrent validity of the Accel'Rate compared to the Player Load. This metric could be used to improve the estimation of whole-body mechanical load, easily accessible in sport training and competition settings.

Keywords: Accel’Rate; Player Load; external load; injury; team sport; training load monitoring.

Figure 1

Overview of the experimental design, instrumentation setup and measurements from the concurrent validity protocol. (A): Experimental procedure. (B): Representation of the force plates area (total length of 6.6 m) and the position of the accelerometers. (C): Typical examples of acceleration modulus (top layer), Player Load (middle layer) and Accel’Rate (bottom layer) metrics during the general locomotor movements (GLM) at low (left) and high (right) intensity. Data were obtained from the in-series force plates (light grey traces) and the accelerometer positioned at the upper back (black traces; classical position used in team-sports).

Figure 2

Bland-Altman plots of difference between criterion and practical measurements for general locomotor movements (GLM). For the sake of clarity, only data obtained for the upper back position are depicted. (A): Player Load measured by accelerometer (practical) versus by force plates (criterion) at low (LI) and high (HI) intensity; (B): Accel’Rate measured by accelerometer (practical) versus by force plates (criterion) at low (LI) and high (HI) intensity. Solid lines depict mean bias and dashed lines depict 95% limits of agreement (LoA).

Figure 3

Bland-Altman plots of difference between criterion and practical measurements for running start (RS). For the sake of clarity, only data obtained for the upper back position are depicted. (A): Player Load measured by accelerometer (practical) versus by force plates (criterion) at low (LI) and high (HI) intensity; (B): Accel’Rate measured by accelerometer (practical) versus by force plates (criterion) at low (LI) and high (HI) intensity. Solid lines depict mean bias and dashed lines depict 95% limits of agreement (LoA).

Figure 4

Bland-Altman plots of difference between criterion and practical measurements for run at constant velocity (RCV). For the sake of clarity, only data obtained for the upper back position are depicted. (A): Player Load measured by accelerometer (practical) versus by force plates (criterion) at low (LI) and high (HI) intensity; (B): Accel’Rate measured by accelerometer (practical) versus by force plates (criterion) at low (LI) and high (HI) intensity. Solid lines depict mean bias and dashed lines depict 95% limits of agreement (LoA).

Figure 5

Bland-Altman plots of difference between criterion and practical measurements for simulated one-on-one (1 vs. 1). For the sake of clarity, only data obtained for the upper back position are depicted. (A): Player Load measured by accelerometer (practical) versus by force plates (criterion) at low (LI) and high (HI) intensity; (B): Accel’Rate measured by accelerometer (practical) versus by force plates (criterion) at low (LI) and high (HI) intensity. Solid lines depict mean bias and dashed lines depict 95% limits of agreement (LoA).