Tremendously well written article from 2011.

Leads off describing the entire health industry (gyms, equipment makers, etc) and why the money incentives and health incentives don't align.

Here’s the problem: If you’re in the fitness-equipment business, free weights are a loser. The 2010 model looks too much like the 1950 model, and they both last forever. Far better to create gleaming $4,000 contraptions that can be reinvented every two years, and then hire a PR firm to promote some made-up training theory claiming that machines are the answer...

Meanwhile, the real reason your gym has so many strength machines is that anybody can figure out how to use them, and they make injury nearly impossible.

Also great high-level overview of the relationship between the exercise reps you do and the goals you are aiming for:

Strength means how much you can lift once, and it’s the backbone of every sport on Earth, from the crouch-holding power of a skier to the one-finger pull-up of a climber. Power is a more slippery term that means “speed strength,” or how much you can lift very, very quickly, and it gives you the explosive paddling speed to catch a big wave or the pedaling burst to fire your mountain bike up a grade. Muscle mass can be a liability in sports like climbing, where it’s all about strength-to-weight ratio, but mass helps enormously with games like rugby and football, and it can support strength and power — not to mention make you look better in a T-shirt. Muscular endurance means how many times you can lift a given weight in a row without stopping, and it’s the essence of running, swimming, and even a kayaker’s long-haul paddling.

As for your training sessions themselves, the number one thing to remember is that each of the Fundamental Four responds to a different number of repetitions per set. Lift a weight so heavy you can lift it only once, you’re building strength (and, oddly, not much mass); lift a weight you can move six to 12 times, you’re building mass (and, oddly, a little less pure strength); ease up to a weight you can lift 50 times, and you’re working muscular endurance (which is great for endurance sports but tends to undermine the first three, shrinking your strength, power, and muscle size).

Wow, I never realized that strength (lift once) conflicts with mass (lift 6-12 times) conflicts with endurance (lift 50 times).

It really is helpful knowing your goals going into it.

Thanks for stashing this, Matt!

See also: Exercise and the Ever-Smarter Human Brain