Reliability and Concordance of 15-metre (15-m) Sprint Performance on Sand and Firm Surfaces

Male athletes participating in beach soccer, beach volleyball, or beach handball completed three maximal 15-m linear sprint attempts on both sand and firm surfaces. Each attempt was performed from a standardised standing start, with at least two minutes of passive recovery between attempts. Testing comprised up to two sessions per participant on separate days. The order of the surface conditions was counterbalanced to reduce potential order and fatigue effects. Participants who attended two sessions completed the surfaces in the opposite order during the second session. The primary measured variable was 15-m sprint time in seconds. The arithmetic mean of the three attempts and the fastest individual attempt were calculated for each surface and session. Within-session and between-day reliability were evaluated using intraclass correlation coefficients, coefficients of variation, standard errors of measurement, typical errors, and minimal detectable changes. Agreement between sand and firm-surface measurements was assessed using Lin's concordance correlation coefficient and Bland-Altman analysis.