1 HEART RATE WHILE TRAINING
Published data and diaries of age-group and elite endurance athletes reveal that at least 75-80% of your training volume must be below 80% of your maximum heart rate. This is more important than cadence measurement, stroke count and so on. So using a heart rate monitor on the bike and while running, to ensure that you execute the correct type of training session that your plan requires, is very important.
2 RAW RACE ABILITY
Your actual raw ability to swim, bike and run in a time trial is important so you can see if you’re getting faster. This could be a 500-750m swim time trial, a 16-19km bike and a 5-8km run, on separate occasions. Doing this year round, at 6-8 week intervals, gauges actual effectiveness of training or how your form may be dropping in the off-season.
3 SPORT-SPECIFIC METRICS
There are several key factors to measure in each sport to see if you’re training the muscles correctly and becoming as efficient as you can.
In swimming it would be measuring your ability in terms of strokes per length to see how much water you’re effectively pulling yourself through. This is cheap, simple to do and also allows you to see the point at which swimming speed starts to affect your stroke efficiency to the detriment of swim execution and the ability to exit into T1.
On the bike, power (measured in watts) is the key metric – but this may be too expensive a measure for many. Cadence in triathlon is optimally around 80-90rpm and this should be watched more than speed. Muscle tension at low revs (5min intervals at 55rpm uphill) focuses on the pushing down phase and will improve strength. Higher frequencies (20min blocks at 95-100rpm soft spinning) give the legs a higher ‘bandwidth’ to make race cadence easier.
Running is probably best assessed by how long it takes to do a 1-mile flat course at 80% of your maximum HR, and this may be improved by dropping excess weight. So get an HR monitor, count strokes on the swim, on the bike measure cadence and when running assess efficiency.
There are now also running power meters being developed, notably the Stryd run power meter, that will show you time, distance, pace, heart rate and running wattage, when paired with your phone. It also can be paired with a number of watches.