You need to tax your body when you train, right? By pushing yourself, and then allowing your body to recover, you get fitter. But, if you push yourself too hard, you’ll run yourself into the ground. So how do you know how hard is too hard?
There are quite a few ways to measure how hard your ride was. You could look at average heart rate or average power. The latter, however, doesn’t take into account the full physiological costs of a ride. A long easy ride might have the same average power as a short ride with a lot of climbing and descending. To show the “cost” of each workout, power-analysis software can calculate the “normalized power” of a ride. The easier ride will have a lower normalized power (NP), say 135 watts, while the ride with climbs will be higher, say 156 watts.
There are other metrics that you’ve seen if you ride with power. Functional threshold power (FTP) is
the average amount of watts you can hold at your lactate threshold for one hour. There’s also intensity factor (IF) which is normalized power divided by your FTP
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How do all these figures add up? Well, Andy Coggan and Hunter Allen invented a metric called the training
stress score (TSS). TSS takes into account NP, FTP, IF and the duration of a ride. Programs such as Training Peaks or Pioneer’s Cyclo-Sphere will calculate TSS after you upload a ride. You can then add up the TSS for the rides you do in a week to see how hard you taxed your body for those seven days. Once you understand how much TSS/week you can sustain, you can then use TSS to plan your workouts.
The TSS values across the two workouts are not significantly different. But look at the values for TSS/min. As you might expect, the workout with intervals is more taxing (1.52 TSS/min.) than the endurance workout (0.7 TSS/min.). The 137 TSS you gain in that interval workout is not something you could repeat more than two or three times per week. The 128 TSS from the endurance ride is something you could do three to five times a week. Of course, these numbers confirm the old training wisdom that you should be spending more time on endurance than intensity.
You can use the training stress score to monitor your training and to become a stronger cyclist. Just remember, TSS is one tool that you should use in conjunction with others to track your development. Stress yourself, but do it smartly