A Power Meter for Your Swim Sessions

I’ve become a curmudgeon of a swim coach late in my triathlon career, so bear with me as I air a grievance. For example, I give my swimmers something simple but hard, the classic 20×100 on 1:30, aiming to hold 1:25 per repeat. Wanting to ensure that they make the interval, they set off with abandon, swimming the first 50 in :40 (1:20 pace) and the second one in :45 (1:30). At the end of the set they are satisfied, reporting that they “nailed every interval exactly.” It takes a lot of restraint on my part to point out that, actually, they swam exactly zero yards at the goal pace of 1:25/100, starting too hard and then fading in the second half. This “fly and die” attitude is pervasive in endurance sports, born out of a well-meaning (but ill-fated) desire to “put some time in the bank.” Apply this approach to anything longer than, say, a 200, and you’ll quickly discover that you give back that time in the bank quickly, along with interest. The sad reality about athletes like this is that they are actually training to slow down in races, which is probably the opposite of what they’re trying to do in the first place.

So how to fix the problem? Any triathlete, faced with my criticism above, usually counters with a foreseeable argument, “But all triathlon swims start out fast, right? You’re supposed to race to that first buoy, so I’m just training specifically for my event.” Here’s the thing, those swimmers that race to the first buoy and then settle into a group once they’ve made a gap – they didn’t have to slow down. They chose to slow down. A group established with a gap behind them know that they’ve done the necessary work to whittle down the group to a more manageable size, and they can afford to back it off and save some energy. If you’re utilizing the fly and die method, you might make that group for a few meters before getting unceremoniously dumped out of the group, having exceeded your sustainable pace for that distance to the first buoy. As a triathlete or open-water swimmer, you have three main areas on which you need to focus on, ranked in order of importance:

  1. Aerobic endurance—basically your swim fitness. Your ability to hold long, steady intervals at a pace that is not easy, but isn’t gaspingly hard. This is a crucial area that I find too many athletes avoid, preferring the sexier, shorter and faster intervals that look good but do little for a triathlete / open-water specialist.
  2. Pace change—your ability to deal with weather accelerations and decelerations, once you’ve found the group you can finish the event with.
  3. Starts/lactate tolerance—yes, it is important to be able to deal with the red-line that occurs at the beginning of a triathlon or open water swim race. However, you will actually improve your lactate tolerance the most by focusing on aerobic endurance. So this third focus is actually a distant third.

So what do these subjective descriptions actually mean in a pool setting? It’s all well and good for me to tell you to focus on something, but I need to tell you how to get there, too. First of all, you need to establish your threshold pace, which is similar to your Functional Threshold Power on the bike or your threshold pace on the run. We could get into the weeds on what all those “thresholds” mean, but basically it’s your highest sustainable pace for a relatively extended period of time. For swimming, coaches have coalesced around your best 1500 pace as a good compromise for threshold. How to establish that number? Here are a few options.

  1. Go swim a 1500 time trial! Sounds like fun, right? Well, although you may think it’s fun, a lot of problems persist with this. Just like it’s hard to get an athlete to pace a 60-minute time trial on the bike, it’s hard to get someone new to swimming 1500s in the pool to pace correctly. That said, if you’re Bruce Lee where pacing is concerned, then this is a good option (of course, if that’s true, this article isn’t really for you…)
  2. Use the Critical Swimming Speed (CSS) formula. This formula has been around for a long time, and has been popularized by Swim Smooth. After a solid warmup, complete a 400 time trial followed by a 200 time trial. Take the difference between the two and divide in half. This will spit out a pace per 100 that you can probably hold for 1500. You’ve found your threshold pace.
  3. Perform the following “broken 1500” test, taking the exact rest specified: 2×250 with :25 rest; 2×200 with :20 rest; 2×150 with :15 rest; 2×100 with :10 rest; 2×50 with :05 rest. Take your time for THE WHOLE SET, rest included, and then subtract 2:25. This gives you an estimated 1500 time, which you can divide by 15 to get your pace per 100.

OK, you’ve got your threshold pace for swimming! Good work. Now how to use it? Well, let’s return to our types of workouts, above.

  1. Aerobic Endurance: complete longer intervals (300s to 1000s) at anywhere from threshold pace + 3 seconds per 100 to threshold pace + 6 seconds per 100 with short rest. A classic is the Swim Smooth “Red Mist” workout, which is 10×400 with :20 rest in between each interval, swum as follows: 4×400 @ TP + 6 seconds/100, 3×400 @ TP + 5 seconds/100, 2×400 @ TP + 4 seconds/100, 400 @ TP + 3 seconds/100. This workout looks easy at first, but I promise you it is not.
  2. Pace Change – get in a good warm up, then do the following:
    • 4×100 at threshold pace with :15 rest, 100 easy after the four 100s
    • 4×100 at threshold pace + 3 seconds per 100 with only :05 rest, 100 easy after the four 100s
    • 4×100 2 seconds faster than threshold pace with :20 rest, 100 easy after the four 100s
    • 4×100 at threshold pace + 2 seconds per 100 with only :05 rest, 100 easy after the four 100s
    • 4×100 4 seconds faster than threshold pace with :25 rest, 100 easy after the four 100s
  3. Lactate tolerance/starts – after you’ve gotten your aerobic endurance in place (a good test is that you can make it through the 10×400 workout above without slowing down or having to extend the rest), here’s a simple session for improving your body’s ability to deal with the start speed of triathlon. Get in a solid warmup, and then go through this following set twice:
    • 2×100 SPRINT with :20 rest (you may feel inclined to extend this rest—don’t. There’s a scientific reason not to – you can email me about it at chrisbagg@gmail.com).
    • 2×400 @ threshold pace + 2 seconds per 100 with :15 rest in between 400s
    • 100 easy and :30 rest before repeating the main set

OK, I’m over my word count, so I’ve gotta call it there, but I hope you found this useful/helpful. Remember, triathlon is a pacing game, not really a racing game.

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Chris Bagg
Chris Bagg has been an actor, cook, teacher, writer, professional triathlete, and coach. He's at his happiest surfing, riding a bike, backpacking, or playing board games. As a coach, his fondest wish is for athletes to achieve their dreams and to find value in those achievements.