triqui
Monstruo de las Galletas
leyendo articulos de Dave Tate (sobre otras cuestiones que no tienen nada que ver) encontre esta pequeña joya de texto que da otra buena razon por la que las maquinas son peores que los pesos libres. Esta en ingles, pero bueno. A ver si luego con mas tiempo me decido a traducirla 
Zatsiorsiky defines accommodating resistance as using special means to accommodate resistance throughout the entire range of motion rather than a specific point. Because of some joint angles and the velocity of movement, the force of the movement is less at certain joint angles. For example, in the barbell squat you may be able to quarter squat 500 pounds while you can only full squat 300. Another common example is the standard dumbbell curl. The force at the beginning is much greater than the force at the top. Max Herz addressed this problem around the year 1900 by inventing a cam. This cam was to be part of a machine that would accommodate the resistance to the strength curve.
Years later, Nautilus tried again to solve the problem with their cam. This odd shaped cam applied the resistance in a variable form so the load varies according to the average strength curve. This is to provide greater resistance where the athlete is strong and less where they're weak.
This cam poses several problems. First, it was designed on average strength curves that don't carry over well to most athletes. Louie uses the deadlift to demonstrate how individual strength curves can vary. One lifter may blast the weight off the floor and fight through the last three inches of the lift. Another may be slow off the floor and lock the weight out easy. The same machine may not benefit these lifters in the same way.
A second problem according to Zatsiornsky is that the number of degrees of freedom is limited from six in natural movements, to only one with machines. Paul Chek has also explained this in much greater detail in his pattern overload articles. Third, the acceleration and deceleration is also very different than natural movements. Fourth, the manufacturers of several machines have altered the cam (to avoided patent lawsuits) to the point that they don't even match average strength curves! Ever wonder why you can lift so much more with one machine when compared to another? Now you know.
Another way that's been used to accommodate resistance is isokinetic training. With isokinetic training the speed of the motion is constant no matter how much force is applied. The disadvantage with isokinetics is the same as machine training: it's applied on only one plane. Most isokinetic machines are also built for one joint movement and the velocity of movement can be too low.
Zatsiorsiky defines accommodating resistance as using special means to accommodate resistance throughout the entire range of motion rather than a specific point. Because of some joint angles and the velocity of movement, the force of the movement is less at certain joint angles. For example, in the barbell squat you may be able to quarter squat 500 pounds while you can only full squat 300. Another common example is the standard dumbbell curl. The force at the beginning is much greater than the force at the top. Max Herz addressed this problem around the year 1900 by inventing a cam. This cam was to be part of a machine that would accommodate the resistance to the strength curve.
Years later, Nautilus tried again to solve the problem with their cam. This odd shaped cam applied the resistance in a variable form so the load varies according to the average strength curve. This is to provide greater resistance where the athlete is strong and less where they're weak.
This cam poses several problems. First, it was designed on average strength curves that don't carry over well to most athletes. Louie uses the deadlift to demonstrate how individual strength curves can vary. One lifter may blast the weight off the floor and fight through the last three inches of the lift. Another may be slow off the floor and lock the weight out easy. The same machine may not benefit these lifters in the same way.
A second problem according to Zatsiornsky is that the number of degrees of freedom is limited from six in natural movements, to only one with machines. Paul Chek has also explained this in much greater detail in his pattern overload articles. Third, the acceleration and deceleration is also very different than natural movements. Fourth, the manufacturers of several machines have altered the cam (to avoided patent lawsuits) to the point that they don't even match average strength curves! Ever wonder why you can lift so much more with one machine when compared to another? Now you know.
Another way that's been used to accommodate resistance is isokinetic training. With isokinetic training the speed of the motion is constant no matter how much force is applied. The disadvantage with isokinetics is the same as machine training: it's applied on only one plane. Most isokinetic machines are also built for one joint movement and the velocity of movement can be too low.