Validity and reliability of a 10 and 20 m linear sprint protocol using a single-beam photocell system: an exploratory study with young male soccer players

Abstract

Single-beam photocell systems are the most cost-effective type of timing gates and are widely used to assess linear sprint performance. However, for short distances (<30 m), their validity may be compromised by early movement artifacts (e.g., arm swing, trunk lean, and foot motion), especially when the first timing gate is positioned very close to the athlete and at heights easily crossed by body segments. There is a need to develop low-cost standardized devices and protocols for timing short linear sprints. This exploratory study examined the validity and reliability of a single-beam photocell system applied to a short-distance linear sprint protocol with the initial timing gate positioned approximately below knee height (0.40 m) and a 0.5 m starting distance. Sixteen pre-professional young male soccer players [19.4 ± 1.4 years; 74.8 ± 6.8 kg; 1.79 ± 0.07 m] completed two 20 m linear sprints. Split (10 m) and total times were recorded simultaneously using a custom-built single-beam photocell system and a 240 fps (frames per second) panning camcorder (reference method). Results suggested good to excellent test-retest reliability [ICC ≥ 0.79; CV ≤ 1.26%], and good validity [ICC ≥ 0.84; CV ≤ 1.21%; Mean absolute error ≤ 0.040 s (1.40%)]. Systematic biases with small effect sizes between methods (p < 0.01; d < 0.5) indicated that photocell and video-based measurements are not fully interchangeable. This exploratory study suggests that the proposed photocell protocol is reliable for short-distance linear sprint assessment. The source code and hardware schematics are openly available, facilitating replication and adaptation.