FRICTION

Friction is defined as the resistance to motion of moving surfaces that touch. Friction is everywhere. It's the driving force behind walking and the reason why rigid objects do not slide down incline planes. As you may have guessed, friction is present in just about every workout you do. From lifting free weights to the resistance you feel on cable machines, friction is behind the scenes. In the weight room, friction is ultimately narrowed down to two sources: the friction between your muscles and the friction from equipment.

Muscular Friction
There are three types of muscular friction: concentric, static and eccentric. Each of these terms refer to a specific type of muscle contraction. Concentric, also know as positive strength, is the contraction in which the muscle shortens against a resistance similar to when you lift a weight. Static contraction occur when the muscle exerts tension; however, there is no significant change in length. This is similar to when you hold weight in static equilibrium. As you lower the weight the muscle lengthens against a resistance. This contraction is known as eccentric or negative strength. Studies show that there is a relationship between these contractions and the amount of weight each contraction can handle.  It was determined by researchers that during static contraction your muscles can handle 20% more than concentric contractions. More astonishing, during eccentric contractions your muscles can handle 40% more weight than concentric contractions. In simpler terms, if you can lift 100 lbs concentrically then your muscles can hold 120 lbs statically and lower 140lbs eccentrically.
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You might be wondering what does friction have to do with all this technical talk. Well it is simple during concentric contraction while you are lifting weight, internal muscular friction is actually working against you. At the peak where you cannot raise the weight any further, you are no longer working against friction but force of gravity acting on the system is still working against you explaining why your muscles can handle 20% more weight statically. Finally during eccentric contraction, friction is working with you as the weights are lowered explaining why our muscles can handle 40% more weight. To learn more of how to adapt your workouts to increase your negative and positive strength feel free to refer to Body-Building.com

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 Mechanical Friction
Just about all the machines whether they are driven by cables, chains, or belts have some resistance due to the friction from the equipment. Its important to note that mechanical friction does not apply to free weights because there is no mechanical moving parts involved. Fitness companies attempt to minimize the mechanical friction of their equipment in order to reduce any additional resistance force. However, any time there are moving parts involved friction will always be present. The friction involved with exercise equipment follows the same behavior as muscular friction with the addition of the friction due to machine. For example during lat pull downs with stacked weights (as seen in the photo to the left) your muscles experience the combination of the stacked weight plus the internal muscular friction plus the mechanical friction from the machine. In simpler terms if you set the weight on the machine to 100 lbs, and internal muscular friction added an additional 10 lbs, with 5 lbs of mechanical friction then the total weight experience is 115 lbs. 


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