Muscle Contractions 101

by Grace Lin

Let’s learn about our muscles!  All of our movement is a derivative of our muscles (more specifically, muscle fibers) contracting.  Muscle fibers generate tension through the actin and myosin cross-bridge cycling – anatomy review, anyone?  Under tension, the muscle (specifically, the sarcomere) can lengthen, shorten, or remain the same.  Most of the time the term contraction implies shortening, but when referring to the muscular system, it means the generation of tension within a muscle fiber regardless of length change.

All movement requires muscle contractions.  These contractions are categorized into isotonic and isometric contractions.  Isotonic contractions generate force by changing the length of muscle fibers, while isometric contractions generate force without changing the length of muscle fibers.

Isotonic contractions can be categorized into concentric and eccentric contractions.  Concentric contractions occur when the muscles shorten while generating force.  An example of concentric contraction would be the upward pull during a pull up.

Eccentric contractions occur when the muscles lengthen while generating force.  An example of eccentric contraction would be lowering down from the top of a pull up (AKA the negative).  Many coaches implement eccentric loading to build strength because it allows athletes to push their muscles past their normal point of failure.  On average, you can lift 30-40% more weight eccentrically than you can concentrically.  For example, an athlete may not be able to perform a strict pull up (concentric contraction), but they can jump to the top of a pull up and slowly lower themselves down (eccentric contraction).  Additionally, eccentric movements cause the most damage to muscle fibers and is one of the main reasons we experience delayed onset muscle soreness (DOMS).

Isometric contractions also have an important place in training.  Some examples of these would be holding a hollow body, plank, the bottom of a pause squat, holding onto dumbbells, etc.  But the most important isometric contraction that we perform every day is our posture!  Engaging our core while sitting and standing is an isometric contraction.

All three types of muscle contractions are beneficial to strength training.  We use all three every day we are in the gym.  Understanding them better can help you fine tune your training to maximize your strength potential.  Stay tuned for the next post on how we implement these types of muscle contractions in tempo training!