The unexpected effects of a free weight workout

Recently, I switched my Monday strength training from machines to dumbbells: 

All single sets, done to failure. 

Free weight workouts develop stabilizer muscles:

Machines don’t recruit stabilizing muscles the way free weights do since they often require you to move a load in just one plane of motion. With free weights, the load is free to go anywhere. Stabilizer muscles therefore must work to make sure the load is being controlled and moved efficiently—a job that simply isn’t required when working on most machines.

But what is a stabilizer muscle? 

When performing an exercise, there are primary movers and stabilizer muscles. Stabilizer muscles are tasked with stabilizing the body and extremities during multiplanar movements, while primary movers are the muscles doing most of the work.

I’ve noticed this with my forearms, which are becoming more defined:

I’m still pro-machine-workouts. Some studies suggest you’re less likely to get injured using machines. And they’re convenient. I use machines for legs and my Friday upper body lifts.

Mostly, though, I’m pro-experiment. This one seems to be paying off.