"Basically, what I am saying is that close-grip chins are going to be more productive for size and strength than concentration curls."
Overall, definitely. For the biceps, nope.
"Compare the stress(poundage)you impose on a muscle using each exercise.Compare a lifter performing 6 reps with a 45 ib dumbell doing concentration curls with a lifter(who weighs 180 ibs)doing 6 chins.The total workload for the set performed by the first lifter is 270 ibs(45 x 6=270).The total workload for the set performed by the second lifter is 1080 ibs(180 x 6=1080).Isn't that the way to build big strong muscles?"
Like i said the poundage doesn't matter.
In case you didn't see my post on a previous thread, I'll re-post it here:
Some of the so called shaping exercises are more effective than the so called mass building exercises at building muscle. For example, the cable cross-over. The cable cross-over removes the primary weak links of the bench press, which means the pecs have to do all of the work to complete the motion. Muscle fibers are stimulated by the nervous system by way of alpha motor neurons. Each neuron may control only several muscle fibers or as many as a thousand or more. Each muscle fiber, however, is innervated by only one neuron. A neuron and the fibers it innervates are referred to as a motor unit. All of the muscle fibers in a motor unit (stimulated by the same neuron) tend to be of the same fiber type. You may have heard of the 'all-or-none' theory in regards to this subject. It states that all of the fibers in a motor unit must fire or none of them, although this may not be 100% true in certain cases (such as fatigue).
How does the neuron "innervate" it's associated muscle fibers? Well, the neuron "connects" to the fibers at their center (their length-wise center). To innervate them they transmit an electric current to the fibers, which travels out from the center of the fibers to their ends, thus setting off a contraction. That is a nut-shell how contraction works. What i am getting at here is that the actual exercise does not matter, it's the force of the contraction. Doing a flye, at maximum intensity, to failure, will produce the highest possible force of muscle contraction to the pecs! This means - more muscle growth. There are also other reasons that isolation exercises induce more localized growth than compound exercises (localized hormone release, sarcomere multiplication is series, etc).
"Isn't that the way to build big strong muscles?By overloading them."
Yes it is, but what you are talking about is not overload. Overload is training at a level that exceed the normal level. Progression.
"Yes, the lats are involved in chins and the pecs/shoulders are involved in dips.The arm muscles are still being subjected to heavy stress.Alot more than by a single joint exercise like concentration curls or bar curls."
If we are talking strictly biceps and triceps, this statement is incorrect.
"Are you saying that the amount of weight used in exercise does not contribute to size and strength?"
Not exactly. I'm saying that the comparitive differences in weight between a multijoint and single joint exercise does not matter.
"If that is the case, shouldn't we be able to get the same benefits from single joint exercises(exercises performed with fairly light weights) that we do with multi joint exercises(exercises performed with heavy weights)?Please explain."
For the same muscle, yes. Potentially an even greater benefit.
Note - all of this is muscle growth specific.
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Complex problems have simple, easy to understand, wrong answers.