Controlled Stroke Count Drill

In “Stroke Count Games” and “A Better SWOLF Formula” I suggested a test set of 8×100, as fast as possible, holding a specific number of strokes per length (SPL), to hone in on your most efficient combination of stroke length and tempo.

I frequently do a modified version of this set as a quick tune-up before a competition or a challenging distance workout: 12×100 short-course, aiming for the following SPL on each rep: 15, 14, 13, 12, 11, 10, 10, 11, 12, 13, 14, 15. Moderate, controlled pace on all – no more than 75%.

Obviously, the specific SPL goals will differ for each individual. For me, 15 SPL is my 400m/500yd race pace. 14 SPL is my 1-2 mile race pace. 13 SPL is my marathon pace.

The reason I like this set as a warm-up / tune-up is that the act of “depriving myself” of one stroke-per-length on each of the first 6 reps really focuses my attention on efficiency – maximizing the amount of water I’m pulling, and minimizing drag. Then, adding one SPL on the way up (11, 12, 13, 14, 15) feels increasingly luxurious and powerful.

The over-arching goal: the 13, 14, and 15 SPL reps on the way up should feel better, faster, and more efficient than the 15, 14, and 13 SPL reps on the way down.

I took some GoPro video of myself doing this set, so you can see the subtle differences in my stroke from one rep to the next. The video shows a bottom-of-the-pool view of me descending from 15 to 10 SPL; then a side-underwater view of 14 SPL; then an above-water view of 14 SPL.

(Direct link to video)

A better SWOLF formula

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:

SPL m:ss SWOLF SWOLF-improved
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 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 😉

SPL m:ss SWOLF SWOLF-improved
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-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.

SPL m:ss SWOLF SWOLF-improved
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-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:

SPL m:ss SWOLF SWOLF-improved
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

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.

Stroke count games

What’s the fewest number of strokes you can take for a single length of the pool? (No streamlining past the flags; no more than three kicks per stroke.)

I can get down to 8 strokes per 25 SCY, but it’s tough to sustain for more than one length. 9 strokes per length (SPL) I can do pretty much indefinitely – but it’s incredibly inefficient. The inefficiency is readily apparent: a huge dead spot in my momentum as I glide (glide, glide…) after each stroke. The Swim Smooth guys have a term for this: Overgliding.

I swim most efficiently between 13 and 15 SPL, depending on pace. 13 for channel/marathon pace; 14 for “threshold” pace (from the mile up to about 5K); 15 for 200/500 pace. For an all-out sprint, I’ll add one more stroke (16 SPL).

Experienced pool swimmers have an intuitive feel for this… but what if you don’t? Is there a formula to identify the most efficient stroke count for a given pace? This question led me to try the following set:

8×100, as fast as possible, with about a minute rest between each. But there’s a twist: Within each 100, hold a constant SPL. The first should be your lowest sustainable SPL. On each subsequent 100, add one SPL. So for me, #1 is 9 SPL, and #8 is 16 SPL. Record all your times. The set is best done short-course (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

Further evidence of the inefficiency of minimum stroke-count: At 9 SPL, the fastest I could go was 1:20! Merely by adding two strokes per length (8 total), I was able to go 10 seconds faster.

[Warning: Geeky content ahead.]

Does this remind you of anything? That’s right – it’s sort of like SWOLF! So, let’s sum the two columns above to produce SWOLF scores:

9    1:20  116  [(9*4) + 80]
10   1:14  114  [(10*4) + 74]
11   1:10  114  etc.
12   1:07  115
13   1:05  117
14   1:02  118
15   1:00  120
16   1:01  121

SWOLF doesn’t quite get it right. According to SWOLF, my efficiency peaks at 10/11 SPL (1:14 & 1:10 per 100y) – which I know to be false. Even at cool-down pace, 10 SPL is more taxing than 12-13 SPL, due to the constant stop/start motion of overgliding.

The key here is: I already know my most efficient SPL is 13-15, depending on pace. I have the result; so what’s the formula that produces it?

Given the above data, the problem with the original SWOLF formula (time in seconds + total number of strokes) seems to be that it overvalues stroke count (and by corollary, undervalues speed). So I just tried the simplest thing I could think of: dividing stroke-count by two (thus reducing its importance in the final equation).

(Stroke Count / 2) + Time = modified SWOLF

SPL time SWOLF(mod)
9    1:20   98  [(9*4/2) + 80]
10   1:14   94  [(10*4/2) + 74]
11   1:10   92
12   1:07   91
13   1:05   91
14   1:02   90
15   1:00   90
16   1:01   93


What’s funny about my “discovery” is that there’s another term for “stroke count divided by 2” — stroke cycles. Which incidentally is exactly how the Swimsense calculates SWOLF. So perhaps our friends at FINIS were on to something?

If any readers out there want to try this set and report back, I’d be grateful for additional data. Does modified SWOLF find your most efficient stroke count(s)?

SWOLF and swimming efficiency

Follow-up posts:

Swim golf – or SWOLF – is an interesting drill, intended to measure efficiency in swimming. It’s important to understand how to use it correctly. Here’s the drill:

  1. Swim one length of the pool
  2. Count the number of strokes you take
  3. Get your time (in seconds)
  4. Take the sum of (2) and (3). That is your SWOLF score.
  5. Repeat steps 1-4, trying different combinations of stroke rate, stroke length, and effort. Which combinations produce the lowest score?

Please note:

  • “Number of strokes” means total number of hand entries – left and right combined. It is not the number of stroke cycles – as the Swimsense uses in its SWOLF calculation. H2oustonSwims and TI get it right; gets it wrong. FINIS gets it right on its website but wrong on the Swimsense.
  • “One length of the pool” means one length of a 50-meter pool, starting from the wall. No long streamlines – that’s cheating. This doesn’t mean you can’t do SWOLF in a short-course pool. However, two lengths are necessary for a sufficient sample size (of strokes and seconds); and SWOLF scores are less meaningful if they include a turn.

The golf analogy works better in a 50m pool, too. 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 great Russian sprinter Alexander Popov: 20 strokes + 25 seconds for a mind-boggling SWOLF score of 45.

Interpreting a SWOLF Score

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 particularly good 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 Yang’s stroke count is lower than Janet 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.)

At any given level of effort, each swimmer has a certain combination of stroke rate and stroke length that is most efficient in producing speed. SWOLF is a great drill to help swimmers zero in on that combination.

To watch a video of me doing SWOLF drill, see this post.

Evan Morrison coaches at Fog City Masters in San Francisco, California. He is a USMS Level 1 and Level 2-certified coach.