Chronic Cardio = Aging Muscle Fibers

Other than genetics, your exercise habits have a direct impact on the composition of your muscle fibers. Since type-1 muscle fibers (slow-twitch) favor higher cortisol levels, and type-2 muscle fibers (fast-twitch) favor higher testosterone, this is an important consideration.

A poor testosterone-to-cortisol ratio produces a catabolic state (muscle wasting).

Sadly, endurance exercise not only produces far too much cortisol (and inhibits testosterone), but it produces a shift from type-2 to type-1 muscle fibers. Check out the unfortunate consequences in fiber shift from 3-4 sessions per week for 16 weeks of endurance exercise:

fiber change

Here’s the kicker – the inactive population has more type-2 fibers than endurance athletes:

muscle fibers

Which implies a more favorable testosterone (muscle building) to cortisol (muscle wasting) ratio, and suggests that:

For an improved testosterone-to-cortisol ratio, you’d be better off doing nothing, than doing CARDIO!

Even worse, is that as the body ages it naturally converts fast (type-2) fibers to slow (type-1) fibers. Meaning, chronic cardio not only accelerates the muscle loss and low testosterone that’s associated with aging, but it speeds up the fiber-shift. Add the oxidative stress from excess free radicals, and one could argue that:

“Chronic aerobic exercise accelerates the unfortunate consequences of aging.”

A shorter life in the long run?

Stay Lean!
Coach Mike


Chronic Cardio = Excess Free Radicals

Cardio...Ain't Nobody Got Time Fo Dat!

Working Too Hard For The Runners High