Background: The VASA ergometer is a staple dry-land training tool in competitive swimming, largely owing to its structural resemblance to the front crawl arm stroke. Whether the kinematic and propelling efficiency profiles it generates correspond to those observed during free swimming, however, has yet to be established. Aim: To compare and correlate stroke rate (SR), stroke length (SL), clean swimming velocity (v**), stroke index (SI), and arm-stroke propelling efficiency (*p) between the VASA ergometer and free swimming (FREE) at low and high intensity conditions. Methods: Ten competitive swimmers (age: 16 ± 2.1 years; height: 1.80 ± 0.12 m; body mass: 68.8 ± 6.7 kg) completed trials in two conditions: front crawl on the VASA ergometer and in a 25-m swimming pool. In each session, participants performed low-intensity (comfortable aerobic) and high-intensity (near-maximal race-pace) swimming. Clean swimming velocity (v**) was assessed over the central 10-m segment. SR, SL, SI, and *p were calculated using standard equations. Paired t-tests and Pearson's correlation coefficient were used to examine differences and associations between conditions (* = 0.05). The study was approved by the local Ethics Committee (CAAE: 27110314.6.0000.5347) and carried out in accordance with the Declaration of Helsinki. Results: SR at low intensity was the only variable showing no significant difference between conditions (p = 0.55), and the only one yielding a significant positive correlation (r = 0.68; p = 0.02). All remaining variables (SL, v**, SI, and *p) were significantly higher in FREE than in VASA across both intensities (p * 0.035). The *p gap was most pronounced at low intensity (VASA: 24.6 ± 2.5% vs. FREE: 32.1 ± 3.2%). At high intensity, a significant correlation was found only for v** (r = 0.68; p = 0.02). Conclusions: The VASA ergometer reliably replicates stroke cadence at submaximal workloads but falls short of reproducing the spatial kinematics and propelling efficiency of free swimming, most likely due to the absence of hydrodynamic drag — pointing to the continued need for in-water monitoring for accurate assessment of stroke efficiency and length
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