A proper exercise action definitely affects the outcome of your efforts. There are 3As you need to focus on when exercising. A natomy (muscles used), A lignment and A ction. These must be applied from the first to the last repetition of your exercise.
FORCE and MOVEMENT plays a crucial role in the 3As of your exercise. This determines the strength, size, balance, functionality and most importantly the safety of your exercise routine. FORCE stimulates body muscles. External force is considered to be the resistance coming from dumbbell, barbell, strength machines, etc., while internal force is the reaction of the muscle against the external resistance. MOVEMENT, execution or whatever you may want to call it, is an action coming from a joint to emphasize muscle function. All exercise requires a full range of movement.
Some other factors that is going to affect the force during your training are the weight, distance from the axis (joint) and the speed of action. Let's see how it works in the example below.
Most of the people would realize that if they could perform 40lbs of chest press, they could hardly perform the same weight in chest fly. If we consider the distance between the dumbbell and the body, the distance of chest fly is almost doubled (because you need to extend your arms a bit wider). According to the rotational inertia, double the distance equals to 4 times force at a joint, that is, if you could lift 40lbs in chest press, then you could probably lift 10lbs in chest fly.
The speed of motion is also important. Once you perform it faster, you will realize that it is easier and vice versa because the movement is highly coming from momentum. If you wish to add challenges to your workout and maximize muscle utility, try doing it slower than usual and you will have a new training experience.