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.

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.

3bridges_gps

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.

Marathon Swimming Rules Survey: Results and Analysis

Marathon swimmers talk a lot about rules – what should and shouldn’t be allowed during a swim – but as far as I know, there has never been any systematic study of what marathon swimmers actually think, as a matter of public opinion.

Perhaps most would agree that goggles are OK, and fins are verboten… but what about swim streamers and stinger suits? Or drafting off the escort boat? If you only read blogs and forums, you might assume the most vocal opinions represent the majority. But do they really?

Earlier this month the SBCSA launched a survey to find out. Over 25 days, we received 175 responses from around the world.


First, a Summary of Findings (TL/DR). Click any of the following links to skip directly to the relevant section.

I. We received responses from a representative sample of marathon swimmers – current, former, and aspiring.

II(a). Marathon swimmers agree on basic channel-rules attire: traditional porous textile swimsuit (including jammers), goggles, one latex or silicone cap, ear plugs, and nose clips.

II(b). Marathon swimmers agree that substances or devices that protect the swimmer against dangerous marine life (e.g., sharks & jellyfish) – but unambiguously do not enhance performance – are acceptable.

II(c). Marathon swimmers agree that devices or substances that unambiguously enhance speed, buoyancy, or heat retention should NOT be allowed on marathon swims.

III. Controversial items include stinger suits, swim streamers, bubble caps, and shark divers.

IV. The more marathon swimming experience a person has, the more likely she/he is to embrace a minimalist approach to swim aids.


I. We received responses from a representative sample of marathon swimmers – current, former, and aspiring.

To argue that this survey accurately represents the opinion of the marathon swimming community, we must show that the 175 respondents are a representative sample of the community. We can do this in a few ways.

A. Geography

Of the 175 respondents, 71% live in North America, 19% live in the United Kingdom or Ireland, 5% live in Australia or New Zealand, and the remaining 5% live elsewhere.

As a baseline for comparison, here’s how those numbers compare to the unique visitors to the Marathon Swimmers Forum in February:

geog
Geographical distribution: Survey respondents vs. Marathon Swimmers Forum visitors

Another baseline for comparison? The Triple Crown list: as of 2012, 76% are from North America, 10% from the UK+Ireland, 4% from Australia+NZ, 4% from continental Europe, and the rest from elsewhere.

In sum, the survey sample has a lot of North Americans – but then, so does the global marathon swimming community generally.

B. Gender

gender
Gender distribution of survey respondents

What about the Triple Crown list? Exactly 60% men, 40% women. Pretty darned close.

C. Self-identification as a marathon swimmer

We asked respondents what they “identify most closely as.” Although we didn’t forbid non-marathon swimmers from taking the survey, we promoted and targeted it primarily at marathon swimmers, because that’s what our primary interest was: What do marathon swimmers think?

According to the data, 87% of respondents identified as either a current, former, or aspiring marathon swimmer.

Self-identification of survey respondents
Self-identification of survey respondents

D. Marathon swimming experience

We asked survey respondents about their specific experience in marathon swimming (and other endurance sports). We found that:

  1. 90% of survey respondents have swum at least 10km in open water.
  2. More than half have swum at least 25km in open water.
  3. Almost a third have swum the English Channel.
Accomplishments of survey respondents.
Marathon swimming experience of survey respondents.

Interesting sub-finding: Marathon swimmers are not as challenged on terra firma as the stereotypes might suggest. Almost half of respondents have done an Olympic-distance triathlon (or longer), and 30% have run a marathon. In comparison, Runners World estimates the percentage of the U.S. population who have run a marathon at 0.5% (ref).


II. Marathon swimmers largely agree on what should (and should not) be used in their sport.

Now to the meat of the study. What do marathon swimmers agree on?

Some critics and swim-aid proponents would have you believe the marathon swimming community can’t agree on what their own rules are. The implicit argument is typically: “Therefore, we might as well just let people use anything they want.”

Actually, the marathon swimming community agrees on quite a lot.

A. The marathon swimming community agrees on basic channel-rules attire: traditional porous textile swimsuit (including jammers), goggles, one latex or silicone cap, ear plugs, and nose clips.

B. The marathon swimming community agrees that substances or devices that protect the swimmer against dangerous marine life (e.g., sharks & jellyfish) – but unambiguously do not enhance performance – are acceptable.

More than 75% of survey respondents agreed that the following items are acceptable:

Percent of respondents who agree that item should be allowed on marathon swims
Percent of respondents who think item SHOULD be allowed on marathon swims

C. The marathon swimming community agrees that devices or substances that unambiguously enhance speed, buoyancy, or heat retention should NOT be allowed on marathon swims.

(Including drafting off the escort boat, which is allowed in the English Channel.)

More than 75% of survey respondents agreed that the following items are NOT acceptable:

Percent of respondents who agree that item SHOULD NOT be allowed on marathon swims
Percent of respondents who agree that item SHOULD NOT be allowed on marathon swims

D. More moderate consensus exists on the following:

agree3a
Percent of respondents who think item should be allowed

Some thoughts on why there is less consensus on these items:

  1. Using boat to shield from wind & waves – improves performance, but is already widely allowed, and it’s unclear how a prohibition could be enforced.
  2. Exiting water for safety reasons – allowed in MIMS and Cook Strait, but not elsewhere.
  3. Topical substance that retains body heat – does such a substance even exist? Perhaps a confusing question.
  4. Multiple caps – allowed by FINA, minimally performance enhancing.
  5. Shark sharpshooter – not performance enhancing, but harmful to sharks and thus morally problematic.
  6. Topical substance that warms the body – does such a substance exist? Confusing question.


III. Controversial items: stinger suits, swim streamers, bubble caps, and shark divers.

A. Shark divers. 59/41 (for/against).

B. Bubble caps. 43/57 (for/against).

C. Swim streamers. 46/54 (for/against).

D. Stinger suits. Tie – 50/50. 

(If you must know, the stinger suit vote was 84-yes, 83-no, with 8 no answers.)

My view: if an item is controversial, it cannot be considered “approved by the sport of ocean swimming.” At best, it might be considered a “local exception” to a more universal set of rules – for example, the use of streamers in Japan.

If an item is controversial, it is in some way approaching a line in the sand. In marathon swimming, if you’re flirting with this line – trying to find loopholes for some extra edge – quite simply, you’re doing it wrong.

Some stinger suit proponents claim that these enhanced-coverage suits are merely protective, not performance-enhancing – and that therefore they should be allowed on marathon swims.

Personally, I’m not sure about this claim. Couldn’t someone easily produce a stinger suit that is performance enhancing? Would we then have to define new rules about what is and is not a performance enhancing stinger suit? Could I put on my old full-body Blueseventy Nero tech suit and call it a “stinger suit”?


IV. The more marathon swimming experience a person has, the more likely she/he is to embrace a minimalist approach to swim aids.

The data presented so far represent the “collective” opinion of the marathon swimming community. However, within that collective, there is actually quite a diversity of opinions among individuals. For example, one person might think a streamer is OK but a stinger suit is not OK; while another person might think a streamer is not OK while a stinger suit is fine.

This diversity of opinions in the survey sample ranged from:

  • One extremely purist/minimalist individual who would only allow a standard cap, goggles, grease, sunblock, boat navigation, limited pace swimming, caffeine, anti-inflammatories, and touch starts. This person would prohibit everything else.
  • One extremely liberal-minded individual who would prohibit nothing – i.e., everything should be allowed (a troll, perhaps?).

For each survey respondent, I summed the total number of items the individual would allow – as an ideology index. So the minimalist respondent I mentioned above would get a 9 on the ideology index, while the everything-is-allowed respondent/troll would get a 48.

Here’s how the respondents were distributed according to ideology:

Histogram showing number of respondents grouped by how many items they would allow.
Histogram showing number of respondents grouped by how many items they would allow. Each number on the X-axis represents a “basket” of 5. So, the people in the ’25’ basket are those who would allow between 21 and 25 items, out of a possible 48.

One interesting question is: Why do some people prefer a minimalist approach, while others embrace technology and swim aids?

We would need a much longer survey to tease out the various reasons, but even in this brief survey there is a clear pattern:

The more marathon swimming experience a person has, the more likely she/he is to embrace a minimalist approach to swim aids.

The following chart shows the average “ideology index” score (out of 48) for four groups:

  1. People who have never done a marathon swim (27 of 175 total respondents)
  2. People who have done a 10km open-water swim but not a 25km (56 of 175)
  3. People who have done at least a 25km swim or one of the Triple Crown swims (57 of 175)
  4. People who have done two or three of the Triple Crown swims (35 of 175)
Average ideology score, depending on marathon swimming experience
Average ideology score, depending on marathon swimming experience

The same pattern emerges when we look at people’s opinions on just a single item, for example, the controversial stinger suit.

Percent of respondents who think stinger suits should be allowed, according to marathon swimming experience
Percent of respondents who think stinger suits should be allowed, according to marathon swimming experience

Obviously there’s much more we could get into with this data, but for now this report is quite long enough already. And I think I covered the big points. If readers are interested, I will do a follow-up post with additional summary data and analyses, as requested — an “appendix” of sorts. Let me know what you want to know.

For reference, here are screenshots of the original survey (click to enlarge):

Related External Posts

Maui Channel Relay: The Video

Last September I joined some San Francisco friends in Maui for a memorable few days of swimming and leisure (but mostly leisure). You may have seen the short video I posted a while back of my solo Maui Channel swim. Two days before the solo, I did the same swim with my friends in the annual Maui Channel Swim Relays.

So, this video has been a long time in the making. Maybe that’s not such a bad thing? Nothing beats the February doldrums like Hawaii (or at least, thinking about Hawaii).

The relay was loads of fun and mostly uneventful, with the unfortunate exception of our third swimmer getting tangled in a jellyfish (probably a box) only a few minutes into her 30-minute leg. She got on the boat and (as allowed by the rules) we turned off the engine and floated in place. At the next change-over, we put our next swimmer in the water and continued on our way.

We all got “zapped” a few times by jellies, but we made it to the finish at Kaanapali Beach without further incident. Our third swimmer was just unlucky, it seems. So it goes!

Anyway, here it is. It starts off with just photos, but there’s GoPro footage too! Click through to Vimeo for the HD version.

Maui Channel Relay 2012 from Evan Morrison on Vimeo.

We ended up 25th out of 47 teams in the overall standings, in 4 hours 34 minutes. Not bad considering the 23-odd minutes we spent sitting in place mid-channel! Even better, our divisional placing was good enough for a coveted plush Maui Channel Swim towel. It’s so nice, I still haven’t used it.

Eventually, I will put together a “director’s cut” of my solo swim – which incidentally would have placed fourth overall among the relays 🙂

Oh, one more thing. Our GPS tracks:

gpsUnfortunately, my GPS wasn’t able to get a fix until sometime near the beginning of Scott’s leg. Notice the “dogleg” that occurs in our path shortly thereafter – that’s when we turned the engine off to wait out Tara’s leg. In reality, we were drifting with the current, which was pushing due north.

The only three things that matter in channel swimming

I truly believe that a Channel Swim – performed under traditional rules – is among the greatest athletic feats that a human can achieve.

We are terrestrial animals, adapted to surviving on land with the assistance of clothing and shelter. We are capable of great efficiency of movement – on solid ground.

A Channel Swim turns all this on its head. Without shelter… naked but for a porous, skimpy textile garment… we step offshore into an environment we are terribly adapted to, and terribly inefficient at moving through. As the ocean floor drops beneath our ability to stand, and the cold begins its creeping march from the extremities to the core – there are really only two options: Swim to the other shore… or get on the boat.


I have another belief, which might seem to contradict or undermine my first belief (that a Channel Swim is one of the greatest athletic feats a human can achieve). And that is:

Almost any able-bodied human can accomplish a Channel Swim.

You don’t need to be athletic, or coordinated, or physically strong. You don’t even need to be a particularly skilled swimmer. By which I mean: the level of swimming skill necessary for a Channel Swim can be learned by almost anybody, even as an adult.

Some of the most famous and accomplished Channel Swimmers, you would not be able to pick out from the average noodler at your local lap pool. The distinguishing characteristic of the Channel Swimmer – the ability/motivation/inclination to keep swimming (and swimming, and swimming…) – is something that cannot be observed in a thin slice of behavior.


On the basis of these two beliefs, I propose that only three things truly matter in Channel Swimming:

1. Health

Sure, OK. If you are gravely ill or injured, perhaps a Channel Swim isn’t in the cards.

2. Will

a.k.a., persistence, stubbornness, tenacity.

Don’t know how to swim? You can learn, well enough (if you want it).

Not ready for the distance? You can build up to it (if you want it).

Not ready for the cold? You can acclimate. Find some cold water. Go swim in it. Do it again, and again, and again. That’s why it’s called “acclimation” – your body will adapt (if you want it to).

3. Money

gwbill

Channel Swimming is such a first world problem. Boats cost money. Sanction fees cost money. Travel costs money. The opportunity costs (training when you could have been working) cost money.

Whether the funds come from your rich uncle, from a sponsor (because you’re gifted – either athletically or self-promotionally), or out of your own pocket, there’s no way around it: Channel Swimming is a huge money drain.

If you don’t have it, or you’re too shy to solicit it, then, well — too bad. Life isn’t fair, and Channel Swimming ain’t a meritocracy. You may be a better swimmer than 90% of the English Channel soloists in a given year, but if you don’t have the money and time to get to Dover, then — too bad!

Does this undermine my belief that Channel Swimming is “one of the greatest athletic feats a human can achieve”? Maybe a little bit. Channel Swimmers may have to overcome a lot during their swimbut most of them probably don’t have much to “overcome” otherwise. When Channel Swimmers return to the harbor, most of them are going home to affluent situations.

Sometimes, when I read tales of seemingly-heroic Channel Swims in newspapers and blogs, it occurs to me that the real story is not how amazing the swim was, but rather, how fortunate the swimmer was to be able to attempt it in the first place.

I write these words as someone who has been very fortunate to have some incredible channel/marathon swimming experiences these past few years.

I am one of the lucky ones.


So you did a Channel Swim – congratulations. Any Channel Swim is, in my view, a heroic feat (for reasons described above).

But before you get too caught up in how awesome you are, remember how lucky you are – to even have the opportunity to put your toe in the water.

[This post benefited from (and was inspired by) conversations with Cathy – who, it should be emphasized, doesn’t necessarily agree with everything I wrote here.]