Estimating Training Stress Scores for Swimming

I like data and I like analysing it. Hours of training recorded and logged. The results plotted into a Performance Management Chart (PMC) so I can watch my progress. Attempting to balance growth of fitness with growth of fatigue. I’ve written a lot about the process: using Training Peaks WKO, measuring performance, managing training and tapering. Despite my years of experience I’ve never analysed swimming.

Swimmers are focussed on performance, checking the pace clock at the end of each rep. A swimmer knows how they’re swimming. How much of that information makes it out of the water? I record every second of a ride or run. Heart rate, power, pace, altitude, a mountain of data. In the pool I struggle to count laps let alone remember the splits.

There’s no reason the principles of Training Stress Scores (TSS) and the PMC can’t be applied to swimming. We just need a threshold swim pace, a distance and a duration. Record the data and the maths is trivial.

1. Determine your Critical Swim Speed

Before you can begin scoring training stress you need to identify your threshold. Every lap you swim will be graded on intensity relative to this threshold pace. You can’t estimate TSS without it.

Performing a Critical Swim Speed (CSS) test is a simple way to find your threshold pace. It’s worth doing even if you have no intention of using TSS. The purpose of training is to improve the pace we can hold for a given effort. CSS provides a simple, standardised way to track this. Crudely, if your CSS isn’t falling your training isn’t working.

I first learnt of CSS from Swim Smooth’s Paul Newsome in Perth; his Swim Smooth site is an excellent resource on the topic (and swimming in general). His version of the test is a straightforward pair of time trials: 200m and 400m. For the masochistic a one hour time trial is a very precise way to find your threshold pace. I’ve used a test based on 100m reps on very short rest before. Whatever option is used testing should be consistent.

2. Record your Session

I leave my gadgets behind at the pool, not even a watch. The pace clock is all I need to track performance. Every set timed. I follow my splits throughout, but as reps and distance increase memory fails me. I’ll remember the highlights, my best 100m time, but rarely an accurate account of every split.

There are tools available: the Poolmate and Finis Swimsense. Every lap counted and timed with the added advantage of a stroke count too. I like the simplicity of the pool. How accurate do we need to be? TSS attempts to represent the feel and impact of a workout, we don’t need decimal precision. As long as a harder session had a higher TSS we’re taking the right approach.

Then there are the other strokes, drills, kick, rest intervals, changes of pace and the push off the wall. Each has a physiological impact, each stresses the body, but front crawl’s CSS has no relevance to them. A 200m and 400m butterfly time trial? I doubt many of us are willing to do that test. The pace of a well executed drill set relates more to the precision of your technique than threshold.

We will have to accept some limitations. We could define CSS for each stroke to increase precision. If you are a medley swimmer there might be some sense. We could give the numbers a tweak: scale down for drills and up for fly. Not perfect, but assuming we’re consistent, enough.

3. Calculate the TSS

TSS is the product of intensity and duration. For those interested in the maths I followed the process in this Training Peaks article on swim TSS. It’s worth noting they make one adjustment to the standard calculation. The Intensity Factor (IF) – the ratio of swim pace to CSS – is cubed rather than squared. They argue that water’s resistance means stress increases more significantly with speed. This seems reasonable and cubing lessens the impact of easy swimming.

Swim TSS Look Up Table: Critical Swim Speed and Swim Pace

I’ve taken the formulas and built a set of spreadsheets to simplify the calculations. Starting with the look-up table of swim pace and CSS above. A quick route to identifying the TSS impact of differing paces.

Useful at a top level, but not enough to easily produce TSS for a session. The document contains another sheet allowing you to split your workout into a series of sets. If you’ve recorded the distance and the total swim time (excluding rest) it will calculate pace and TSS. Enter a whole session and the sheet gives a total TSS.

It works. Take a copy and try it for yourself. I won’t claim it’s perfect. I’ve already hinted at the inadequacies of the model and the approach. It’s simplistic and lacks detail; it doesn’t distinguish between 1000m swum in 15 minutes or ten by 100m each swum in 90 seconds. Rest will influence the total TSS as more rest in a session probably means less swimming. Should swimmers see value in TSS there might be a future for the accurate tracking of those swim computers.

I’m open to feedback and thoughts on how I could improve the system.

4. Put it into Practice

The final step is field testing. My spreadsheet makes the process of scoring swim TSS easier, but does it get the numbers right? TSS is only useful if it appropriately reflects the physiological impact of swim training. To appreciate this it’s going to take a few months using the system and seeing how a Performance Management Chart forms. I’m willing to be a guinea pig.

It will be interesting to see if the changes in fitness and fatigue correlate with how I feel in the water. What will be the influence of technique? It’s vital to swim speed. Potentially I could build a high level of fitness, but lack the technique to see real gains in pace.

Whatever value tracking swim TSS has it will enforce a more precise approach to swimming. Keeping everything on record and publishing it ensures I follow through on my commitment to improve as a swimmer. Building fitness in the PMC has worked as a motivation before perhaps it can help me again. The experiment starts tonight at the pool.

Ironman Training Library

From nutrition to pacing - a collection of CoachCox blog posts focused specifically on Ironman training and racing.