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.

One year in the life of a marathon swimmers forum

One year (and one week) ago, Donal and I launched the Marathon Swimmers Forum with the following mission statement:

  • To celebrate and promote the sport of marathon swimming.
  • To foster connections and information sharing among the global community of marathon swimmers.
  • To provide an educational resource for aspiring marathon swimmers.

Donal and I are both pretty proud of what’s happened since then. Just by the numbers, 565 confirmed members have contributed 5,437 posts in 400 separate discussion threads. Even better, the quality of the contributions has been gratifyingly high.

To celebrate the Forum’s first birthday, here’s a quick peek at the site analytics:

A Global (yet, to be honest, mostly anglophone) Community

Geographical distribution of visits by city

Geographical distribution by country, full year

Geographical distribution by country, first month
Geographical distribution by country, first month

Everybody Loves a Controversy

Top Threads, as measured by pageviews:

Up and to the… Right!

Site Visits, weekly
Unique Visitors, weekly

Thank you to all who have helped make the Forum such a compelling, informative community this past year.


New Year, New Look

If you are an email or RSS subscriber, you may not have noticed the new banner image:

The WordPress theme has also been updated and the menus have re-arranged a bit. Come check it out sometime.

Anyway, the new banner image shows me stroking along in the middle of the Santa Barbara Channel. There’s Cathy in the kayak (this must have been about 7 hours into the swim), and behind her the Fuji III (containing Rob, Mark, Dave, Ben, Capt. Forrest), heading off at a strange angle. The photo is actually a GoPro still-frame from Ben, one of the filmmakers behind the documentary DRIVEN.

For old-times’ sake, here’s the previous banner image – that’s me warming up at the Noblesville 10K in July 2010.

freshwater swimmer
Freshwater Swimmer header image, 2012.

Incidentally, if you’re an RSS subscriber, you may have heard the sad news of Google Reader‘s impending demise. If you’re shopping around for a new feed reader, I recommend checking out Newsblur and Feedly. Feedly is slicker and prettier; Newsblur is closer to Google Reader’s layout and may be preferable for power users. Personally I’m going with Newsblur.

March Miscellany

A few items of interest:

  • The Siljan Diary” – a new and very worthwhile blog by Dave Van Mouwerik as he prepares to swim the length of Lake Siljan in Sweden. Dave is a fellow SBCSA director and was the official observer of my Santa Cruz Island swim. He’s a deep thinker, an excellent writer, and this blog is a must-read for anyone interested in how unique marathon swims happen – from the initial spark of an idea, to the planning, to the execution. 
lake siljan swim
Dave’s planned swim route across Lake Siljan, Sweden.
ted erikson
Ted Erikson at Promontory Point in Chicago. Photo by Michael Goss.
  • A re-edited version of my Catalina Channel video (using my newfound video editing skills and better software):

Catalina Channel solo swim from Evan Morrison on Vimeo.

That’s all for now!

The Alcatraz Swimming Society

Recently I had the pleasure of joining the Alcatraz Swimming Society (ASS) for one of their weekly swims. The ASSes are a few South Enders who really, really like to swim to (and from) Alcatraz. The day I swam, it was co-founder Gary Emich‘s 985th Alcatraz crossing (!). Gary and Stevie Ray Hurwitz (also in the water) are in a heated but friendly race to 1,000 crossings.

We jumped at 6:45am from Pier 33 into slack-ish 51.1-degree water. Air temp was around 50-flat, putting the combined “open water chill factor” right at the feared 100 barrier. Heightening the thermal challenge were 10-knot winds (gusting to 15) out of the SW.

Sync-swimming with Stevie Ray.
Sync-swimming with Stevie Ray.

I entered the water last, sprinted for a couple minutes to catch up to the others (and also to warm up), and then started filming. Swim, pause, film — rinse & repeat. At one point I was even doing single-armed backstroke while holding the wrist-mounted camera steady on the other arm.

The video’s a little bumpy (but so was the ocean):

Swimming to Alcatraz in March from Evan Morrison on Vimeo.

The crossing took a bit more than 35 minutes. According to Gary and Stevie Ray, it’s usually a ~25 minute swim, but we overestimated the ebb tide and started too far east.

Unidentified swimmer arm. Downtown SF skyline in the background.
Unidentified swimmer arm. Downtown SF skyline in the background.

I’m continuing to push the boundary of my cold-water swimming ability. Two years ago, the idea that I could swim year-round in San Francisco Bay would have been unfathomable to me. All it takes is a little practice. Seriously – anyone can do this! The toughest part of this swim was actually the ride back to SERC on the zodiac boat. The wind was brutal.

GPS tracks
GPS tracks from Gary’s watch

Thanks to Gary, Stevie Ray, Dianna, and Suzanne for having me along for the ride!

Postscript: I was interviewed about this swim by Tiffany at AlcatrazFavorites.com.

Same Water, Different Worlds: A tale of two swims in San Francisco Bay

Last weekend I had the pleasure of escorting Cathy on a big, cold swim in San Francisco Bay to celebrate her birthday. We’re calling it the “Three Bridges” swim: She swam from the Third Street Bridge in McCovey Cove (the original location of the South End Rowing Club in 1873), under the Bay Bridge, and under the Golden Gate Bridge, before finishing at Kirby Cove on the Marin Headlands.


8.7 miles in 2 hours, 10 minutes (with a push from the ebb tide) in 51-degree water, without a wetsuit. It was a damn impressive, inspiring swim, and I’ve never seen Cathy swim so well. She seems totally at home in cold, rough water – and indeed she seems to thrive, the worse conditions become.

With El Sharko‘s steady hand at the tiller, I managed the feedings and aimed my GoPro:

Cathy’s “Three Bridges” SF Bay Swim: 3rd St, Bay Bridge, Golden Gate from Evan Morrison on Vimeo.

Some interesting and sad context to Cathy’s swim: It was (coincidentally) the same morning as the Escape from Alcatraz triathlon, during which one of the athletes died in the swim leg. At 2:01 in the video above, you can see the San Francisco Belle that would soon ferry the Escapees to the Rock for the start. As shown at 3:04, we passed by Alcatraz only a few minutes before the race start.

In a subsequent discussion on SlowTwitch, there was lots of hand-wringing about the frigid water temperature and choppy conditions.

Yes, it was cold and choppy out there. This is San Francisco Bay we’re talking about. Yet it’s impossible not to draw the obvious comparisons: These people were wearing wetsuits! They were in the water for maybe 40-45 minutes on average. Cathy was out there three times as long, without a wetsuit.

And she loved it! Watch Cathy’s video again (2:56) — look at the joy and confidence in her stroke as she plows through the chop. This is how she chooses to celebrate her birthday!

Now watch this video, from the Escape:

These people are in way over their heads. The guy at 0:10 can hardly swim! What the hell is he even doing out there? These two swims took place in the same water, literally minutes apart in time. Yet they might as well be from different worlds.

Here’s a semi-rhetorical question: Which event do you think was safer? The nearly-9 mile, 2+ hour swim without a wetsuit, or the 1-mile wetsuit-assisted swim?

In my view, there’s absolutely no substitute for proper training and preparation. Cathy was prepared for this swim; many of these triathletes, evidently, were not. A wetsuit is not going to keep you safe. Swimming competence will keep you safe.

While wetsuits may decrease the chances of an individual person drowning, I believe they actually increase collective risk – by giving people a false perception of safety and encouraging them to put themselves in situations they are not prepared for.

Interview with Coach Mark

As I mentioned, Mark Warkentin (2008 10K Olympian, crew member on my Catalina swim, crew member on my Santa Cruz Island swim, and all-around good guy) was recently named head coach of the Santa Barbara Swim Club, the team we both grew up swimming with. Mark has been on the job a couple months now, and by all accounts things are going great. The future of swimming in Santa Barbara is bright indeed.

Here’s an interview he just did with SwimSwam:

Mike Lewis (author of other hard-hitting works of journalism) does a pretty good job keeping the conversation relevant to open water swimming, given the irony that Mark coaches mostly sprinters.