I can't really explain it better than I did.
Often the discussion has to do not so much with agreement but with clarity. That we are talking about the same thing. When I read the various replies and comments regarding the affect of resistance coming from free weights versus machines I keep a couple of things in mind. Muscle function is relatively simple and do just one thing, and one thing only, they contract. They contract to initiate movement, the concentric phase, like pushing open a door; they contract to hold or maintain a position, the static or isometric phase, like carrying a shoebox waiting in line at a cashier; and lastly, to act as a brake or control, the eccentric or negative phase so you don't go tumbling down a flight of stairs.
Now, if I recall correctly from my classes in human physiology muscle contraction is initiated by one thing: when a signal, and impulse, travels through a nerve cell, a motor unit, to be more precise. Not going into agonizing detail a chemical reaction takes place and the relationship between the chains of proteins within the muscle cells changes leading to the contraction.
So these two are just indisputable basic facts. All a muscle fiber does is contract and how it contracts is always the same. So from a muscles perspective it doesn't matter what causes it to contract; be it from pushing a barbell over head or pushing a bar from a Universal station or Nautilus overhead press, or simply doing a front double bi in front of a mirror. The process is the same, exactly the same, and therefore the stimulus is the same. A signal and an impulse is sent and the muscle contracts.
Though this basic process is fairly simple and unchanging, the coordination of the various cascade of these contractions that initiate and perform various movements postures, and positions is quite complex. Anyone involved in any type of physical activity be it in athletics, mechanics, medicine, engineering... know that even a slight deviaton from a specific movement, a muscle contraction, can make the difference between success, failure, or even complete disaster.
Now from a bbing perspective, how a targeted muscle responds does depend on the stimulous involved, i.e., the specific movement and resistance applied to that targeted muscle. For example, say we are talking about the pull-ups versus the lat pull-down. These are virtually identical movements with the resistance in both movements starting from the top and the muscle contracting drawing the elbows down and slightly back depending on form. From the muscle's perspective the main factor is simply the resistance, the weight involved, it makes no difference whether it is the bar that is being pulled down toward your chest or your chest being pulled up to the bar. The muscle contraction is the same and to claim that the traditional pull-up is inherently more productive to muscle, to lat, hypertrophy than the lat pull-down simply does not comport with common sense. This is proven in the real world as many professional bbers never do pull-ups but have great backs. Certainly I have never seen Dorian Yates or Ronnie Coleman do traditional pull-ups and these two have some of the greatest back development of all time. Ronnie in particular use the lat pull-down as a mainstay and never pull-ups.
So, from a muscle point of view it doesn't matter where the resistance is coming from be it free weights, machines, bands, body weight... just the amount of resistance and intensity, the force of effort, applied.
