Making Sense of Fatigue with the Swimsense™

My name is Bryan Allott and I’m the founder of, a site that looks at using technology and equipment to aide your training. In evaluating gadgets, I try to look for gadgets that embody simplicity and friendliness in ease of use while taking care of the really complex details. This usually requires a healthy mix of innovation and imagaintion on the manufacturer’s part. The Swimsense, in this regard, is the perfect model. Having used the Swimsense to understand pacing and evaluate swim efficiency, I next used the Swimsense on a negative split set to better understand the effects of fatigue and pacing.

The set: 3 x 10 x 100 (various) leaving every 2 minutes. Three 100s in each 10 were to be swum as a negative split; i.e. each length faster than the previous. This was the focus of the set while the surrounding 100s were designed to tax the swimmer (IMs, drills, kicks, fins). The objective: maintain a smooth negative split, working towards building a better finish in races especially when fatigued.

The first group of negative split 100s went swimmingly well.

Each lap was faster than the previous, and at this early point in the set, the objective of putting in a fast finish was being met. The SWOLF score sums up the effort quite nicely and showed me that the last length really was a great finish.

In the chart below, you can also see how clearly a negative split effort differs from my usual pacing effort. The negative split effort is in dark blue, while my usual pacing is underlaid in a light blue. Interestingly, wether I start out hard finish slow, or start out slow finish hard, I end up with more or less the same result; but this is only 100m. If we experimented over 200m, 400m or even 3km, reason (and research and history) tells me that the “go out slow, finish hard” is a much more sustainable strategy.

So what exactly happens after 2km with the negative splits?

Wait a minute? That’s not a negative split at all!

Exactly. In fact, when I underlay a regular effort with a negative split effort, you can’t really tell them apart. Hello, fatigue.

You might think you’re swimming fast (or on pace) while the reality is very different. The difference between perception and reality also tends to grow as fatigue sets in. The more tired you are, the harder you’re think you’re swimming, yet the slower you’re actually going. So, unless you have a dedicated coach giving you feedback on every effort in every swim, there’s no way for you to know just exactly how you are doing.

But with the Swimsense, I can give my swim the best effort possible and then once I’ve showered, warmed up and had a cup of coffee, I can sit down and look back on my swim with a clear mind and evaluate the goals of the set against the performances recorded. Knowing exactly how you’re progressing with your training, and how far you still need to go, will make a huge impact when lining up your next set. It allows you to build on measurable outcomes towards achieving your season’s goals.

But there’s still more. Where is the critical area that needs improvement?

If I take a closer look at the distance per stroke and stroke rate charts, I glean some important clues.

Starting out with a negative split, I can finish strong with just a little over 3m per stroke.

Interestingly, even on the last negative split (fatigued), I can still finish with just over 3m per stroke, whereas with a “normal” paced swim, I consistently get less than 3m per stroke.

The difference between the two comes in with work rate. For a “normal” swim, I’ll turn my arms quicker (but get less distance with each stroke) in order to move faster. However, when I’m focused on pacing, I turnover much slower but get much better mileage with each stroke (hence a lower SWOLF score) in order to move faster. Now if I can only turn over quicker with the same distance per stroke… :)

Knowing all this and monitoring the results, I can take to the pool more condfidently and purposefully armed with knowledge about myself based on fact, and not just on what I “feel” the set was like. Next time, I will look at how to use the Swimsense to monitor progress in the pool while swimming, and not just after the set.