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The Physics Of Weight Training
By Paul Becker
Part 3, Mechanical Advantage.
Here in the third part of this series we will examine mechanical advantage and how this effects weight training and how it can be used to our advantage to get better/faster results.
Mechanical Advantage - is the ratio of the force exerted by a machine to the force applied to a
Our muscles contract to exert force and our skeletal structures (made up of simple machines - hinges, ball and sockets, etc..) transfer that force into motion. But the force exerted by our muscles (input) is not equal to the force we can use to move our bodies or lift other objects (output). let's look at some of the factors that cause this increase in force output, first would be bone length and muscle attachment points. Generally shorter bone lengths are better for strength output then longer bones, also attachments further down the bone being moved would give better leverage and therefore the ability to lift more.
The above two factors explain why a smaller man may lift more then a bigger man, but there is nothing we can do about the length of our bones or the placement of our muscle attachments. There is another factor that we can use in our training and that is that even taking into consideration the information from Part 1 of this series (Gravity), due to the change in mechanical advantage during a full range of motion all exercises have a harder part and an easier part. Different movements have different strength curves, but usually the closer you get to full contraction the stronger you are.
All this just serves to show that when lifting fixed resistance over a full range of motion you are limited by the range of least mechanical advantage, in other words - The Sticking Point. If you are only lifting as much as you can handle in your weakest position you are not overloading your muscles to your fullest ability.
There are a few ways to overcome this - (1) Partial Movements and (2) Variable Resistance.
(1) Partial Movements, these are also called 1/4 reps or lockouts. With this method you need some adjustable squat stands or a power rack, set the barbell so you only do the top part of the movement. For example, the top 6 to 8 inches of the squat, this is when you're in your strongest position to lift some really heavy poundages. The benefits to this type of training are both physical and mental, on the physical side you will be forcing you muscles to lift heavier weights thus increasing their strength (most trainees find that they are much stronger, when they return to full movements after a cycle of partials), on the mental side you get over a fear of handling really heavy weights and feel like "I can lift this, I've lifted even more then this before".
You can do partials on overhead presses, bench press, deadlift, curls, etc., you will be able to handle a lot of weight with this technique, but to avoid the chance of injury work up to it gradually, so that your muscles, tendons and ligaments get used to the big poundages.
(2) Variable Resistance, this is done over a full range of motion and requires some method of increasing the resistance as your strength increases due to more mechanical advantage as you get closer to the fully contracted position. Nautilus was the first to put out machines that provided variable resistance and since then many manufacturers of exercise machines have also built this factor into their machines. But not everyone trains in a big commercial gym and even some that do prefer to train with free-weights, well there are some very simple ways to create an increasing resistance.
Before he released the first Nautilus machines, Arthur Jones experimented with chains to regulate resistance. It works this way, you attach some long sections of heavy chains to the bar or weight stack and as the chains are lifted off the floor they add more resistance. You can also use small plates tied every six inches to some long pieces of strong cord or rope, you can even tie some slightly larger plates near the end of the rope so that at the point just before full contraction/lock-out you are really pushing a lot of weight. Work with this a while to get the right amount of increasing weight, when you get it right the weight should feel consistent all the way through the movement, you will have to make some extra adjustments after using this method for a while because of the previously under worked areas of your strength curve will gain more then the area near the sticking point.
These methods force you to lift more weight and you will get bigger and stronger because of them.
About The Author: Paul Becker is a natural (steroid free for life) bodybuilder and fitness
consultant. He is the author of many ebooks and courses on training
and diet. For more information visit his website at