For many years the analysis of performance in swimming has been tedious and manual. Cycling training has been transformed by power meters and power training, Running has been greatly impacted by GPS to provide pacing information. Accelerometers popular in consumer devices such as iPhone and Wii games are now being used to analyse swim strokes and provide performance metrics. Commercial versions of this technology are now about to hit the stores. As with many data collection tools, the secret is not in the collection of data, but the understanding of how to turn data into useful information to impact your training program.
Elite athletes make their sports look simple and elegant: Haile Gebrselassie running a marathon (at what looks like 4:30 pace, but is sub 3min/km), Lance Armstrong powering up Alpe d’Huez, or Ian Thorpe ripping up a 400m freestyle in the pool. At first it may seem that Thorpe’s stroke is long and slow, at least longer and slower than his rivals. The reality is that his rating (number of stroke cycles per minute, I.E the number of times his left arm (for example) enters the water) is about 36-38 cycles per minute. For many age group swimmers, they will struggle to hold a rating of 30.
Thorpe is a pool swimmer and the rating characteristics of pool swimming are very different to open water, and triathlon in particular. Open water is much rougher and your stroke can never be as smooth as in a controlled environment like a pool. As a result your rating will be much higher. Lets take a look at some real world rating data from a triathlon swim.
Figure 1 shows a typical rating graph during a triathlon swim. There are four key phases of the swim. The first is the initial 30 seconds of the race. This is complete chaos as people start, fight for position and try to get some clear water to swim in. Rating during this time is maximal, and above a sustainable level. The second phase, the period of time up until about the 300meter mark is where the race positions are decided. The rating will often be above what is sustainable, but will have a degree of variation. The ability to change rating is critical during this phase. The third phase, the middle part of the race is relatively easy. Stroke rating often drops as the swimmers are simply maintaining position. There will be some requirement for changing pace, particularly around turning marks and re-entering the water for a second lap of a two-lap swim. The final phase will often have an elevated rating as athletes fight for a better position out of the water and into transition for the bike leg.
Obviously this is a generic graph and just shows relative ratings for specific sections of the race, but it is derived from real race data. Specific race tactics will impact the rating. It is also different for swimmers at rear of the pack, rather than towards the front. Gender will also have an effect, with females normally rating slightly higher than males.
Specific conditions will also affect the exact rating. Freshwater, particularly “heavy” freshwater (think Lake Burley Griffin) will give relatively lower ratings. Salt water will result in higher ratings due to extra buoyancy. Similarly a wetsuit swim will rate higher than non-wetsuit.
How can I measure Rating?
Most decent swim stopwatches come with a function called base 3. This mode allows your coach to hit start, then stop after the third stroke (Two tips: remember the rating applies to one arm only. E.g. the time the left arm enters the water. In addition, remember that the first time the arm enters the water and your coach hits start, you count 0. This means I count 0 when the swimmers left arms enters the water, and hit start, I count 1,2 and on the 3rd stroke of the left arm I hit stop).
You can also use a table I have devised that takes into account stroke count and time for a 50 to calculate rating. This is not 100% accurate as it will not take into account the push and glide off the wall, but provides a relative measure.
As detailed in the table above, If you take 40 strokes/50meters and you do this in 37 seconds, this gives you a rating of 32 stroke cycles/minute. This is relatively low in triathlon terms. In order to increase your rating to 36 stroke cycles/min, you can either increase the number of strokes to 45 (holding the same time) or decrease the time to 34 seconds (holding the same number of strokes).
The point behind this table is to show the relationship between stroke count and rating. Many triathlon swimmers will be focusing on efficiency where they try to reduce the number of strokes per 50. This is great for developing good body position and streamline. If you look at some of the typically low stroke counts swimmers aim for (<40 strokes/50), you need to be holding a time of <30sec to achieve a rating of 40 stroke cycles/second.
If you are an elite triathlon swimmer, you can likely do this, but for the average age group athlete, this will be quite difficult. For all athletes, the skill of rating is critical, so it is important during rating development sessions to have a higher stroke count and hence higher rating.
You will also notice that rating is likely to drop off during the back half of an interval. As well as capturing rating information for the start of a swim interval, take it for the final 50 as well. A likely drop off in rating will also result in a drop off in speed. Similarly, if you do a strength session earlier in the set, you will find it harder to develop high rating later in the session. This is similar to the effect of doing big gear efforts on the bike, then trying to spin.
You need to be conscious of when you are measuring rating; time of the season, time through the set, time through an interval will all have variations.
So What Does This Mean to You?
If you are a swimmer who struggles to hold 1:30 for a 100m repeat, then you are better off to focus on efficiency and body position, before focusing on rating. Similarly, early in the season when you are in your base phase, it is better to focus on stoke mechanics and efficiency rather than rating. In the race preparation phase, rating is a powerful tool to improve speed and change the dynamics of your training program.
As new tools become available, getting access to rating data will be much simpler and allow similar sorts of analysis as we see with GPS and power data today. That is not to say there are not ways to use rating today. Your swim coach can give you an insight into rating with a cheap base 3 swimming stop watch.
A great first step would be getting your swim coach to give you some rating data from your next threshold set. This will give you a baseline and an understanding of how your rating changes with fatigue.
I will talk about specific techniques for developing rating in the next article.