There comes a point when you stop training muscles and start coaching movements. This doesn’t mean you become a “functional guru” and only do off-the-wall training methodologies to draw attention. Rather, this means that you stop thinking in terms of pectorals, biceps, and hamstrings, and start thinking in terms of push, pull, and hinge.
These fall under biomechanics, or as I like to call it, “the physics of the body”. It is quite the complex and mathematical subject involving centers of mass, ground reaction forces, and force vectors. Yet, for a personal trainer it really doesn’t have to be that complex.
Quite simply, a force vector is the direction that a force is “aiming”, or moving.
To understand what I mean, you must understand force vectors and how they relate to exercise:
Force is produced by the body to act upon force(s) that are imposed on the body by both the body and outside resistance. For example, muscles in the shoulder joint will begin to contract as a response to sticking your arm out straight to your side and leaving it there, where gravity will then act on it as well.
Force is best produced when the body’s joints are aligned properly to resist and overcome a resistance. This is why you will always bicep curl more weight than you front raise. Quite simply, the axis (range of motion) is shorter, and hence, makes the movement more efficient.
Force is best produced when the body is pressed against a stable, non-giving surface in an effort to create leverage. This is why you shouldn’t place your feet in the air during a barbell bench press if your goal is to press maximum weight.
One other thing to note: Just because movement may be upwards does not mean that there are no forces that exist downward. A vertical jump is an upward movement that overcomes gravity and is the result of applying downward force, into the ground. A machine chest press, on the other hand, is probably going to have opposing force vectors in a more horizontal plane. The weight functions as a force towards your body while your body creates force to press the load away from it.
There is no “one” ideal alignment. All vector positions will be related to the individual details of a client and an exercise. These details include limb length, pelvic alignment and shape, injury history, modality and specificity of exercise selection, and overall performance readiness. Always remember: forces are everywhere around the client. Those vectors are action and have action upon their body.
Excerpt from: Kevin Mullins’ Article off the ptdc.com website