Background: Previous studies have shown that parameters derived from the 3-min all-out test (3MT) are related to anaerobic capacity and 50-200 m free-swimming performance. However, these parameters are typically obtained from the force-time (F-T) relationship, requiring a dynamometer (i.e. load cell) and limiting practical applicability. It is plausible that swimmer displacement from the pool edge may reflect force production, allowing estimation of 3MT parameters using a distance-time (D-T) approach. Aim: To examine the validity of 3MT parameters derived from the D-T relationship. Methods: Ten young swimmers (age: 15±1 years) performed two 3MT trials separated by 3-7 days. Tethered swimming was performed using a 6-m elastic cord (Auriflex nº204, Brazil) attached between a dynamometer fixed to the start block and the swimmer`s waist. Swimmers were instructed to keep the cord as stretched as possible. F-T data were collected using a dynamometer (0.5 Hz; HOMIS 2100), while D-T data were obtained using a 25-m tape aligned with the pool. Distance was manually recorded based on head position every 10s. Test-retest reliability was assessed using the coefficient of variation (CV=typical error/total average x 100), intraclass correlation coefficient (ICC), and minimal detectable change (MDC%). Pearson correlations were used to examine relationships between F-T and D-T parameters. Results: Reliability of most D-T parameters (CV<8%; ICC>0.80; MDC<15%) was comparable to F-T (CV<17%; ICC>0.60; MDC<15%). Strong correlations were observed between D-T (m or m.s) and F-T (N or N.s) parameters, including peak (r=0.97-0.98), mean (r=0.97-0.97), W* (r=0.93-0.97), and critical values (r=0.93-0.97). Conclusions: The D-T approach provides valid estimates of 3MT parameters. To enhance the generalizability of these findings, future studies should include larger samples encompassing a broader range of performance levels, including elite adult swimmers.
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