EUGENIZATION.

Dr. Larry McCleary describes (arguably) one of the best reasons for a person to engage in an exercise program.

It’s important to note that exercise, carried out for too long, can cause a stress reaction of its own accord.  After roughly 60 minutes or so serum levels of cortisol (which had been held in check by secreted testosterone) rise dramatically, which is pretty much the exact scenario you’d want to avoid, at least if muscle and strength gain (and brain health, apparently) is your primary concern.

Here’s the skinny: Hormonally speaking, what we want from strength training is a high testosterone (and a correspondingly high growth hormone) release, since these hormones have anabolic effects - they cause cell (specifically, muscle cell) growth.  Cortisol, the body’s main stress hormone, causes catabolic effects - it causes breakdown (catabolism) of muscle tissue for energy.  During exercise, this catabolic effect is kept in check by high serum levels of testosterone, until about 45 minutes into the activity (or thereabouts).  After 45 minutes or so, serum testosterone levels drop precipitously, allowing for increased muscle cell breakdown due to the actions of cortisol.

This makes sense from an evolutionary prespective.  If you’ve been engaged in “flight” mode for 45 minutes, your body figures, “Whoa, I guess I’m in it for the long haul” and settles into crisis mode.  It begins to tap into “emergency” stores of glucose (i.e., converting the amino acids in your muscles to glucose) since it figures, “Well, these muscles won’t be of much use anyway if that saber-tooth catches up to me.”

What does this imply for your exercise program?  You can condense this scientific gobbledygook into one simple guideline:

To maximize muscle and strength gain from a strength training workout, keep your workout length under 60 minutes. 

Besides, it’s good for your brain health, too.