121 Conditioning 101 - Intensity

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Conditioning intensity can be divided into four domains: moderate, heavy, severe, and extreme. 

Moderate Intensity

Personal anecdote: walking to New York City

In athlete language: "easy", "Zone 2"

What it feels like: you can speak in complete sentences

Typical duration: 2+ hours

Moderate intensity is below the first Lactate Threshold (LT1), which is the pace at which lactate begins its sustained increase. 

Below LT1, the body is working in a physiologically steady state. 

If you hold this pace for long enough, the limitation will become either injury, overheating, or depletion of fuel substrates like blood glucose, muscle glycogen and intramuscular triglyceride (this is why ultra marathons are jokingly referred to as "eating competitions", one study found that IronMan finish was predicted by calories eaten during the race, the more they ate the faster they went).

If you do eat enough to keep your fuel substrates topped up, then eventually you encounter perceived limitations related to your neurophysiology, which feels like a loss of "drive" to keep going. 

Heavy Intensity

Personal anecdote: 10k row

In athlete language: "medium", "kind of hard"

What it feels like: you can speak, but only in one or a few words at a time

Typical duration: 40 minutes to 2 hours

Once you speed up to a pace above LT1, your blood lactate will steadily climb. 

If you continue working at your heavy intensity, lactate will continue to climb and then settle below the second lactate threshold (LT2).

These paces require more effort to maintain, but your body is still in a physiologically steady state. 

This is the intensity at which elite marathoners run 26.2 miles. Right below their critical power. 

Severe Intensity

Personal anecdote: 10 Minute Assault Bike

In athlete language: "hard", "tough"

What it feels like: breathing is heavy, you can't speak

Typical duration: 2-40 minutes

Once you speed up past LT2, your body is no longer in a physiologically steady state. 

Your VO2 and lactate will continue to climb until you reach task failure, when you can no longer hold the pace (this is also the point that defines your VO2max and your maximum metabolite tolerance). 

Depending on the pace, task failure can happen in 3 minutes (as in a 1k row) or 40 minutes (as in a world class 10k row).

Extreme Intensity

Personal anecdote: 30/30 Row

In athlete language: "full dummy", "blackout"

What it feels like: numb or extreme discomfort during the work, then a painful lactate bath seconds to minutes after completion

Typical duration: 2 minutes or less

For an example of extreme intensity, check out ​this video​ from the 2020 Games. 

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Every conditioning program is made up of some combination of exercise across these four intensity domains.

They provide a framework for coaches and athletes to better understand physiology and their training. 

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