is there any reason why when I use pulleys to do exercises such as rows on a pulley system that i never really feel a challange on the eccentric part of the movement? it can’t be due to lack of resistance, because the weight i use gives me a good challenge on the concentric part. I mean, with free weights i always get a good challenging eccentric, but with my rows on a pulley i don’t.Could anybody have any idea why this might be?
If a pulley system (or an exercise machine)
has too much friction you get an effect like this.
Let’s say that dynamic friction is 25% of the weight.
In this case, if you have selected a weight of 80 lb, it actually takes 100 lb to lift it – 80 lb against gravity, and 20 lb (25% of 80 lb) against friction.
But to lower it under control requires you to exert only 60 lb of force – friction provides the other 20 lb to counterbalance the force of 80 lb provided by gravity.
So only 60% as much force is needed for
eccentrics as needed for concentrics. This
would make them “no challenge.”
In contrast, with free weights the force
required for controlled eccentric movement
(steady speed) is 100% that required for
for concentric movement. Those exercise
machines that have extremely low friction
(e.g. Med-X, Hammer Strength, Avenger)
approach this very closely. Some machines
Friction can kiss my ass.
thanks bill for the detailed answer-but theres no way i can reduce the friction is there?
Reduce the friction by using free weights.