There is plenty of performance based evidence demonstrating that training frequency is paramount for optimal fitness long term.
It’s likely the single most important factor in endurance training.
Now as to the science, I’m not sure it’s been effectively studied, because it would be very complex, very long and very expensive to undertake.
The above posts summarize it well. Many small doses, many adaptations. One big dose, one slightly larger adaptation.
I think an important factor in this, is the rate of detraining. I’ve found that many people underestimate how quickly this takes place. Depending on the study etc, it’s been demonstrated to be VERY rapid. As in 3 days and things are going backwards.
One week off and you’ve lost a significant portion of your recent gains. From what I’ve read, it’s approx 4 times faster to lose fitness than it is to gain. Again, not ideal.
It is rather simple as an equation.
1000 TSS week. Applied in a single ride. Brutal. 6 days to recover. Sadly, the athlete would be close to losing most of the benefits of this ride by the time the next one came around.
1000 TSS week. Applied over 6 rides. Manageable. Athlete steadily improves. This method is demonstrated by virtually every professional endurance athlete on Earth.
Reducing your training frequency from 6 days a week to 3 days a week is absolutely a compromise. If it is dictated by life etc, fine. However, it is a compromise. One that year on year will produce sub optimal results.
Now, how far from optimal? 1% 5%? I have no idea.
For professionals this means the difference between winning and losing. For amateur’s it’s totally irrelevant. Or, it’s very relevant, because the amateur wants the best result.
In that case. Increase training frequency to the MAXIMUM you can recover from with an ideal distribution of intensity.
Basically, if you’re not training 6 days a week, you’re training sub optimally.
I’ll add a caveat. Reduce this to 5 days a week for older athletes and less experienced at high training loads. Some athletes simply need this extra recovery day.
Finally. Do what you enjoy. Train the way that keeps you excited and motivated. The difference is probably pretty small.
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