SWOLF and Swimming Efficiency
SWOLF, an elision of “swim golf,” is an imperfect but still useful metric of swimming efficiency. You only need a pace clock to measure SWOLF, although it is now included on many multi-sport watches.
In brief:
SWOLF is the sum of time (in seconds) and stroke count to complete a given distance.
Traditionally, that distance is 50 meters (or yards) - but there’s no reason you can’t get a SWOLF score for a longer distance. I once did a SWOLF face-off with David Barra for the buoy line at Lake Minnewaska, New York. I would not recommend measuring SWOLF for distances less than 50m (e.g., one length of a short-course pool) - the variability is too high.
Traditionally, “stroke count” means number strokes (one arm = one stroke) rather than number of stroke cycles (two arms = one cycle) - but as I will argue later in this article, stroke cycles may be preferable.
In the interest of terminological precision, SWOLF is defined as the measure itself (40 seconds for 20 stroke cycles = SWOLF score of 60); and swim golf is defined as the process or exercise of trying different combinations of stroke rate and stroke length to find an optimally efficient stroke.
SWOLF Drill
It’s important to understand how to use it correctly. Here’s the drill:
- Swim a set distance (50 or 100 yards/meters is best).
- Count the number of strokes you take
- Get your time (in seconds)
- Take the sum of (2) and (3). That is your SWOLF score.
- Repeat steps 1-4, trying different combinations of stroke rate, stroke length, and effort. Which combinations produce the lowest score?
Pro tips:
- Keep your streamline distance consistent. No cheating with long streamlines!
- No more than 3 kicks per pull - that’s also cheating!
- Don’t rely on a swim watch to count your strokes - counting in your head helps maintain mental focus.
Interpreting a SWOLF Score
The standard SWOLF distance, which most closely fits the golf analogy, is one length of a 50m (Olympic-size) pool. An excellent swimmer will score in the low-70s (e.g., 40 seconds in 32 strokes, or 35 seconds in 37 strokes) - just like a “scratch” or zero-handicap golfer. The (unofficial) world record for SWOLF is held by the Russian sprint legend Alexander Popov: 20 strokes + 25 seconds for a mind-boggling SWOLF score of 45!
SWOLF is an indirect measure of swim efficiency. Conceptually, swim efficiency can be thought of as [Speed / Effort]; however, measuring effort (% of max HR, V02, blood lactate, calorie burn, etc.) can be inconvenient in the pool. SWOLF uses stroke count as an indicator of effort - but it’s not a precise indicator.
An illustrative example:
Here is the famous final length of Sun Yang’s world-record setting 1500m last year (33 strokes in 26 seconds = SWOLF score of 59):
And here’s the final length of Janet Evans’ gold-medal winning 800m at the Seoul Olympics (49 strokes in 30 seconds = SWOLF score of 79).
Should we interpret Sun Yang’s much lower SWOLF score to indicate he is a much more efficient swimmer than Janet Evans? No. He is probably slightly more efficient, because he’s slightly faster - but we know nothing about their respective levels of effort. Sun’s stroke count is lower than Evans’ because he is 6'6" and she is 5'4". He has a naturally longer stroke.
I can pretty easily hit the low-70s for SWOLF; does that mean I’m more efficient than Janet Evans? Not likely!
The point being: SWOLF is usually not meaningful in comparing different swimmers. It’s meaningful in comparing different data-points for the same individual. If I can move from a SWOLF of 75 to 70, that probably means I’ve improved my efficiency. But my SWOLF of 70 doesn’t mean I’m more efficient than someone else with an 80.
(Though, this rule has a limit: What about a SWOLF of 110? Most likely, I’m more efficient than that swimmer.)
Finding the Optimal Combination of Stroke Rate and Stroke Length
Each swimmer has a certain combination of stroke rate and stroke length that is most efficient in producing speed. SWOLF is a useful drill to help swimmers zero in on that combination.
Through 30+ years of swimming - at club, high school, collegiate, and Masters levels - I’ve learned that my most efficient stroke count is in a range of 12-15 strokes per 25 yards, depending on my pace:
- 12-13 strokes at a leisurely pace
- 13-14 strokes for a typical workout pace
- 15 strokes for mid-distance race pace (200 yards up to a mile)
- And I might add 1 more stroke per length for an all-out sprint.
16 strokes or more and I’m “spinning my wheels” - arms pulling through so fast that I’m failing to gain full purchase on the water.
Below 12 strokes and I start to Overglide, as a “dead spot” begins to disrupt the momentum of my stroke. I can fairly easily swim 8-9 strokes per length if I want to - but it’s terribly inefficient, with a distinct dead spot as my momentum slows during each glide.
Controlled Stroke Count Exercise
Does SWOLF bear out my intutive sense of my most efficient stroke count?
To test this, I performed a set, which I call controlled stroke count 100s:
- 8×100 yards, as fast as possible
- About a minute rest between each.
- Within each 100, hold a constant SPL (strokes per length).
- #1 is your lowest sustainable SPL (for me, this is 9 SPL).
- On each subsequent 100, add one SPL (so for me, #8 is 16 SPL).
- Record all your times.
- The set is best done short-course, as it’s tougher to control SPL so tightly in a long-course pool.
Here are my results:
| SPL | Time |
|---|---|
| 9 | 1:20 |
| 10 | 1:14 |
| 11 | 1:10 |
| 12 | 1:07 |
| 13 | 1:05 |
| 14 | 1:02 |
| 15 | 1:00 |
| 16 | 1:01 |
What does this show?
- I maximize my speed by taking 15-16 strokes per 25.
- At 9 SPL, I’m 20 seconds slower per 100 than when I take 15 strokes.
- Subjectively, I can report that I felt most efficient (speed without much effort) at 13-14 SPL.
Does SWOLF confirm my subjective feeling?
| SPL | time | SWOLF (strokes) | SWOLF (cycles) |
|---|---|---|---|
| 9 | 1:20 | 116 | 98 |
| 10 | 1:14 | 114 | 94 |
| 11 | 1:10 | 114 | 92 |
| 12 | 1:07 | 115 | 91 |
| 13 | 1:05 | 117 | 91 |
| 14 | 1:02 | 118 | 90 |
| 15 | 1:00 | 120 | 90 |
| 16 | 1:01 | 121 | 93 |
Interestingly, I find that using stroke cycles (rather than strokes) as the input to SWOLF gets closer to my subjective feeling of optimal efficiency. So, according to my findings the best SWOLF formula is:
SWOLF = (Stroke Count / 2) + Time in seconds
In practice, it is more precise to count strokes (hand entries) and divide by two, rather than just counting left or right entries as a watch would do.
Further Testing of the SWOLF Formula
I wondered if my findings could be replicated by other swimmers, so I asked a few friends-of-the-blog to repeat the test set and send me their own data. In short, the findings were confirmed: SWOLF (using stroke cycles instead of strokes as the input) effectively identifies the most efficient SPL.
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:
| SPL | m:ss | SWOLF (strokes) | SWOLF (cycles) |
|---|---|---|---|
| 10 | 1:50 | 150 | 130 |
| 11 | 1:40 | 144 | 122 |
| 12 | 1:30 | 138 | 115 |
| 13 | 1:23 | 135 | 109 |
| 14 | 1:16 | 132 | 104 |
| 15 | 1:12 | 132 | 102 |
| 16 | 1:13 | 137 | 105 |
| 17 | 1:15 | 143 | 109 |
| 18 | 1:17 | 149 | 113 |
Reader #1 pegged his “natural” stroke count per 25 yards at 15-17. According to SWOLF, he was most efficient at 15 SPL, closely followed by 14 and 16 SPL. 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 😉
| SPL | m:ss | SWOLF (strokes) | SWOLF (cycles) |
|---|---|---|---|
| 15 | 1:20 | 140 | 110 |
| 16 | 1:18 | 142 | 110 |
| 17 | 1:15 | 143 | 109 |
| 18 | 1:12 | 144 | 108 |
| 19 | 1:10 | 146 | 108 |
| 20 | 1:08 | 148 | 108 |
| 21 | 1:08 | 152 | 110 |
| 22 | 1:10 | 158 | 114 |
Reader #2 puts her “natural” stroke count per 25 yards at 18-20, depending on pace. SWOLF agrees.
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.
| SPL | m:ss | SWOLF (strokes) | SWOLF (cycles) |
|---|---|---|---|
| 12 | 1:14 | 122 | 98 |
| 13 | 1:10 | 122 | 96 |
| 14 | 1:08 | 124 | 96 |
| 15 | 1:04.5 | 124.5 | 94.5 |
| 16 | 1:02 | 126 | 94 |
| 17 | 1:00 | 128 | 94 |
| 18 | 0:59.5 | 131.5 | 95.5 |
| 19 | 0:59 | 135 | 97 |
Reader #3 puts her “natural” stroke count per 25 yards at 16-17. SWOLF agrees.