Temporal Organisation and Projected Two-Dimensional Kinematics of the Barrier-Step Action in Elite Futsal Goalkeepers: An Observational Case Series

This study was designed as an exploratory descriptive observational case series aimed at characterising selected projected two-dimensional kinematic features of the barrier-step action in elite futsal goalkeepers. Given the limited biomechanical description of this goalkeeper-specific defensive movement, the purpose was to provide an initial field-based account of its temporal organisation and selected joint-angle configurations rather than to test inferential hypotheses.

Three male professional futsal goalkeepers with international representation were purposively recruited. Each participant completed three valid dominant-side trials in response to a standardised low ball stimulus delivered by the coach from the penalty mark at a distance of 5 m. To reduce between-trial variability in the initial condition, each repetition began with a standardised movement towards the opposite post. The analytical sequence began only after completion of this manoeuvre.

All trials were recorded using a GoPro Hero 10 camera operating at 240 frames per second. The camera was mounted on a tripod at a height of 0.9 m and positioned 6 m from the movement area, with the optical axis aligned as closely as possible to the primary plane of motion. Because the study relied on single-camera two-dimensional video analysis, all outputs were interpreted as projected image-plane measures rather than true three-dimensional joint kinematics.

For analytical purposes, the movement was segmented into three operational intervals: initiation-propulsion, lateral transfer, and terminal support-stabilisation. Angular variables were extracted at two analytical instants: the end of Interval 1 and the blocking configuration reached during Interval 2. The projected angular variables were shoulder, hip, knee, and ankle angles. Temporal variables included the duration of each operational interval. Video analysis was performed frame by frame in Kinovea by a single investigator, and intra-rater reliability was assessed by repeated analysis after a 7-day interval. Descriptive statistics were used throughout to characterise temporal organisation, angular configuration, and between-goalkeeper variation in the barrier-step action.