Intensity Distribution

What is Intensity Distribution?

Considering intensity distribution can be approached from various angles. Often, when this topic is mentioned in training articles or on social media, it typically refers to how frequently high, medium, or low intensity sessions occur within a mesocycle, like a 4-week period.

Within the meso cycle, there are microcycles (typically a week), and it's uncommon to engage in more than 2 or 3 intense sessions during that week. This depends on the total training volume (hours) in a standard week.

Many people overlook the intensity distribution during individual sessions and the variation in effort, especially during easier endurance rides.

The reason I emphasize this is that neglecting intensity distribution can lead to suboptimal training. Often, the easy days are too intense, and the hard days aren't challenging enough.

For instance, consider a 2 or 3-hour endurance ride, where the goal is a steady intensity around Z2. Ideally, there should be minimal variability in power and heart rate. If your effort fluctuates too much, you're likely spiking your power and increasing fatigue, which can be sustained over 3 hours. On the other hand, if you’re not maintaining consistent effort, you won't be maximizing your time effectively. It's about finding the right balance.

Below are two real world examples from two different athletes. The prescription was the same, go out and ride steady for 2.5 – 3 hours maintaining a consistent effort.

Things I’m looking for

• How much time was spent actually turning the cranks – was there a lot of coasting time

• How variable is the ride, what is the VI index telling me – is it steady or spikey

• Was there any HR/PwR drift, anything above 5% usually suggests it was probably too hard for this sort of ride.

• Heart rate and power profile and time in zone. Ideally most of the time in that endurance power zone.

Athlete 1

HR trace from the ride, mostly within the prescribed range

I have highlighted the key elements.

• The first thing is that the coasting time was minimal. That means the legs and aerobic system was working for pretty much all the ride.

• The VI index was only 1.06 – that also tells me it was pretty steady.

• There was also no HR / PwR drift. The HR trace looks good.

• Not much power above tempo and most of the time was spend at the endurance intensity.

This is great execution and this person will probably recover quickly from this ride and at the same time has accumulated 3 hours of endurance work.

Athlete 2

HR trace shows a lot more variation and is often way above or below the range

• Straight away you can see that over 20 mins (14%) of this ride was spent not turning the pedals.  That’s time that could have been working, albeit at a low intensity.

• The VI is 1.18. This is a very spikey ride. I’d expect this sort of variability in a crit or road race where you are consistently on and off the power

• This is further confirmed by the time accumulated across all the higher power zones.

• The HR profile tells me the same story.  

Although the average heart rate ended up in Z2 the demand on the legs could have been much higher than it needed to be. If too many of the endurance rides are like this it could  potentially lead to accumulated fatigue or conversely you might not be getting right stress response.

I want to point out that these rides are over similar terrain so we’re not talking about hilly versus flat.

Not all TSS is equal

You'll observe that both rides have a very similar TSS score, but this highlights where the concept of TSS can sometimes fall short and shouldn't be overly emphasized. From a metabolic and energy utilisation standpoint (fat and muscle glycogen), I'd argue that the ride with more variability was actually more demanding and will likely require a longer recovery period.

This is because more glycogen would have been depleted, necessitating time for the body to replenish it. Additionally, more muscle damage would have occurred, which also requires time to repair.

An important takeaway is that being able to manage your effort is a valuable skill to develop, especially if you are racing, particularly in time trials.

The key message is essentially to avoid doing intervals during your steady endurance ride; save that for interval day.

Hopefully you find this useful and if you have any questions with regards to your own training just reach out.