SWOLF (“swim golf”) is a drill that measures swimming efficiency. A SWOLF score is your time (in seconds) on one lap of the pool, added to the number of strokes you took. Lower scores = Higher efficiency. SWOLF is a fuzzy, indirect measure of efficiency, because stroke count doesn’t necessarily reflect effort. In my view, the most precise definition of SWOLF is that it identifies the most efficient stroke count for a given level of effort.
I originally wrote about SWOLF in April 2012, and the post has become – by a wide margin – the most widely-read in the history of this blog. In a subsequent post a month later – “Stroke Count Games” – I described how SWOLF doesn’t quite capture the most efficient stroke count. At least for me, using stroke cycles (number of strokes divided by two) produces better results.
I wondered if this was true for other swimmers, so I asked any interested readers to send me their own data, using a test set of 8×100. Three readers sent me their results. In short, my suspicions were confirmed: Strokes cycles produces better results than stroke count. In essence, the original SWOLF formula seems to over-weight stroke length in its measure of efficiency (and thus under-weight speed).
Reader #1 is a 6-foot 2-inch (188 cm) male in his late-20′s with an ape index of 1.07 (arm-span greater than height). He did not swim competitively at the high school or college level. His recent best times include 25:21 for the 1650-yd Freestyle and 3 hours, 18 minutes for a 10km open-water swim. His typical open-water stroke rate at marathon pace is approximately 50 strokes per minute.
Here are his results for the test set of 8×100:
Reader #1 pegged his “natural” stroke count per 25 yards at 15-17. According to traditional SWOLF, he was most efficient at 14-15 SPL, followed by 13. According to SWOLF-improved, he was most efficient at 15 SPL, closely followed by 14 and 16 SPL. SWOLF-improved seems slightly more accurate in this case. In Reader #1′s own words:
15-17 feels natural. At 14 I could already notice some laboring. Anything at 13 or lower, inertia was a huge factor.
I think that’s why the curve is much steeper on the lower stroke side. It might have said 13 was more efficient than 17, but no way I’d want to swim more than a 100 at 13. 17 – no problem.
Reader #2 is a 5-foot 7-inch (170 cm) female in her late 20′s with an ape index of 1.0 (arm-span equal to height). She swam competitively in both high school and college, and is a Triple Crown marathon swimmer. Her recent best times in the pool include 19:15 for the 1650-yd Freestyle. Her typical open-water stroke rate at marathon pace is 70 strokes per minute.
Reader #2 insists her data include the caveat that she did a big training swim (21km) the previous day
Reader #2 puts her “natural” stroke count per 25 yards at 18-20, depending on pace. SWOLF-improved agrees. Traditional SWOLF, on the other hand, under-estimates her most efficient stroke count.
Reader #3 is a 5-foot 6-inch female in her early 20′s. She swam competitively in both high school and college, and is a national-caliber distance swimmer. Her recent best pool times include 17:09 for the 1650-yd Freestyle. Her typical open-water stroke rate is approximately 80 strokes per minute.
Reader #3 puts her “natural” stroke count per 25 yards at 16-17. SWOLF-improved agrees. Traditional SWOLF, once again, underestimates the most efficient stroke count.
For comparison, here are my results from the 8×100 set, as reported previously:
In sum, you may find that using stroke cycles instead of stroke count produces more useful SWOLF results. If you own a Swimsense, then you’re golden – it already uses stroke cycles for its SWOLF calculation. I don’t own a Garmin Swim watch, but from what I’ve read online it seems to use the traditional formula.