Swimming Tool
Stroke Efficiency Analysis
Use SWOLF, stroke rate, stroke length and stroke index to observe technical efficiency.
Set Data
m
strokes
50
SWOLF
90
avg per length
Stroke rate
48
strokes/min
Stroke length
1.25
m/stroke
Index
1.25
speed x length
Interpretation
Stroke rate is in a common endurance range; watch whether it stays stable.
Stroke length is acceptable; next watch whether it drops quickly under fatigue.
In the same pool and intensity, a lower SWOLF usually indicates better efficiency.
Theory
Speed = stroke rate x stroke length. Chasing only high stroke rate can become spinning, while chasing only long stroke length can break rhythm. Costill et al. (1985) studied 39 competitive swimmers and found Stroke Index (speed x stroke length) correlated with VO2max at r=0.97, and distance per stroke alone predicted 365.8m freestyle performance at r=0.88 — a long stroke length is not just "looking smooth", it directly tracks aerobic capacity and performance. SWOLF is best compared within the same pool length, stroke and intensity, not across strokes or distances.