Arthur Jones (1926-2007) was the inventor of Nautilus machines in the 1970s, and MedX strength-training equipment in the 1990s. If you have read any of Jones's one-set-to-failure bodybuilding material, you will probably remember his unique way of painting pictures with words.
The following paragraphs were taken from his early writings – which detailed the proper way to perform a set of barbell curls. Note: When this material was written, Jones recommended two sets of most exercises. Even so, you will quickly get the feel of how Jones applied high-intensity training.
Barbell Curls by Arthur Jones
Select a weight on a barbell that you can curl in good form for 6 repetitions. Then, make yourself do 10 repetitions, or tear your arms off at the elbows trying.
Keep the lifting strict and emphasize the lowering. Do not just drop the barbell to the bottom. Resist it the entire way. At the bottom, immediately begin another repetition, smoothly.
Imagine from a side view, that during each repetition, your head, shoulders, and buttocks remain stable forming a vertical line. No leaning forward or backward, no arching of the lower back, no movement of the head and neck. Only your hands and forearms are tracking up and down.
This set should be so hard that the last repetition requires from 3 to 4 seconds on the lifting and another 3 to 4 seconds on the lowering. Afterwards, you should be breathing like a steam engine, dark blue in the face, and so weak that you have to sit down to keep from passing out.
The barbell curl is not an arm exercise. At least, it's not an arm-only exercise – although it will soon give you biceps like a gorilla. Rather, it is an every-damned-thing exercise, if it's performed properly. Done correctly, and heavily enough, the leverage is so great when the weight is in the halfway position, it works your back as much as a set of heavy deadlifts, and the pull downwards is so strong on your shoulders that it works the entire shoulder girdle intensely. The energy output is so great that it causes you to sound like a locomotive – thus building overall heart and lung efficiency and increasing the rib-cage size nearly as well as a set of breathing squats.
Rest, just long enough to get your breathing close to normal and repeat a second set of 8 repetitions with the same resistance. King Kong could not do more than two sets during the same workout. Thus, if you can, then you are not doing them correctly.
In fact, if you even consider doing a third set after finishing the second set, then you did not do those two sets properly. You should feel like puking after the second set – and a lot of serious guys do. If you do not, then give up. Get the hell out of the gym. You do not have what it takes to succeed in training.
I am not joking about this, not even slightly. Throughout your overall-body routine you must constantly walk a very fine line. The line between sickness and collapse... and simple, but complete exhaustion. You must stay just on the far side of that line, constantly on the bare edge of being nauseated. This is especially true in regard to barbell curls.
Outright hard work. That's my summation of barbell curls.