Am I getting stronger?

Sunshine and bird song are occasionally greeting me in the morning now that the days are getting longer. Longer days mean longer rides, which hopefully means more training, which should allow me to go on even longer rides. Ahh, the benefits of training.

A year ago, I started to keep track of my training not just in terms of the elevation gain, time and distance, but also in terms of how much effort it took, and hence how much benefit I received from this training. Now, as a physicist, I know that effort is not a well-defined concept, and so what I think I am trying to say is that I’d like to optimize the combination of maximum power, average power, and speed so as to minimize the amount of pain.

Not having a power meter on my mountain bike, I keep track of the training stress via my heart-rate. Results of becoming more trained would be that the same circuit could be completed in
a) less time at the same heart rate or,
b) in the same amount of time, but at a lower heart rate.

Thus, a convenient way to measure average heart rate and total duration is needed. The training stress score (TSS), is one way to quantify the training effect. It takes into account the intensity (based on your heart rate zones) and duration spent in that heart-rate zone to quantify the equivalent stress at aerobic threshold. I don’t fully understand it, to be honest, but the concept seems appealing – at least all that heart-rate data from my Garmin becomes 1 number at the end of a ride. I can understand 1 number, the TSS score. 100 TSS points correspond to 1 hour at aerobic threshold (more correctly, functional threshold power).

The downside to training is that it leaves you exhausted, you get tired. The beneficial effect of training arises when you train hard, and then allow enough time to fully recover. This is a bit like a pendulum. A hard ride pushes the pendulum away from equilibrium. With time, your body recovers, corresponding to the pendulum swinging back and over-shooting the equilibrium point: resulting in over-compensation. This is the purpose of training – letting your body overcompensate.

My own training can then be summarized by the Performance Management Chart from, below. Each red dot shows the training stress score. This creates an impulse in the acute and chronic training loads. The body’s response is fatigue, shown by the acute training load (red) which goes away quickly (~2 weeks to 30%). The cumulative training load (blue) has a longer time constant (~6 weeks), and measures the total gain from your training sessions.
Heart-rate based training stress ATL: acute training load CTL: cumulative training load TSB: training-stress balance TSS: training stress score

TSS (red dots): training stress score (from 1 ride)
ATL (pink): acute training load (from the last ~2 weeks of rides)
CTL (blue): cumulative training load (from the last ~6 weeks of rides)
TSB (yellow): training-stress balance (how much over-compensation has resulted from the training)

Usually, I only have time for 1 big ride per week, so you see one big training stress point per week. Doing these big rides requires me to wait about a week to be fully recovered. You can see that the Training-Stress Balance (TSB) hovers around 0. When the TSB stays negative for too long, I am hitting my body too quickly with too much training. If that is a long-term state, than this training is a waste of time as my body is not allowed to fully recovered and won’t over-compensate from the training load. Resting really is as important as training! No rest, no gain.

I can look back now and see that 1 year ago, last April, I was basically in the same shape that I am in now. This isn’t quite true, though, because the TSS is estimated from my heart rate, and not from my actual power output. So, what this only really means is that I am pushing myself as hard as I did last year this time. But hopefully, some lasting increase in power-output has resulted from all that riding I did last year.

The real answer to the question if all this training is helping would really have to come in the form of a race, where the identical course was ridden with the identical pre-ride training-stress balance. This seems really hard to achieve, as I had a couple colds last year. But, then what is all this training for anyhow? To win races? Nope, I am too slow to do that. I suppose the honest answer is that I just like big rides, and that playing with GPS and heart-rate data is just another hobby of mine.

Happy riding!

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