Dynamic Concentric and Eccentric Muscle Movements

In my last blog post I discussed and demonstrated static concentric and eccentric muscle movements and I would now like to compare them to dynamic movements where the body is in a state of motion. 

Reducing risk of injury

In my recent posts I have discussed the risk of mainly lower back injury with improper performance of the push up secondary to increased acceleration of the movement. This risk actually holds true for any select exercise technique if proper stability isn't maintained around the joint. One of Newton's laws states F=ma (force=mass x acceleration) and this means that any change in either the resistance or the acceleration can cause an increase in the force. Since the joint is the movable segment in any exercise technique, there must be sufficient strength in the tissues surrounding the joint to offer the required stability. Although explosive motions offer good training results, the resistance offered by the bodies weight is usually more that adequate and there is less risk of over-stressing the joint.

Cobra Exercise vs Push-Up

The photo below is a picture of me doing a yoga exercise called the "Cobra". Notice that my back is arched during my performance of this exercise, and this may look like it goes against what I stated yesterday about keeping your back straight. The reason this exercise is good for you is due to the duration of time it is held to provide a slow relaxed stretch to the abdominal region and hip flexor muscles of the body. It also provides a gentle pressure on the joint and discs of the vertebrae which increases proper fluid transfer. The danger of doing a push up with the back in this position is the increased acceleration required to lift the body back off the floor. This explosive movement causes an enormous increase in the forces upon the lumbar spine and increased risk of injury.

Proper Push-Up Form

When performing a push up make sure that your abdominal muscles are strong enough to support your lower back and keep it from arching. This arching not only puts pressure on the facet joints of the posterior lumbar vertebrae, but also increased pressure in an anterior direction on the lumbar discs. Start out doing the push up on your knees or leaning in against the wall and progress as you get stronger.

Static Concentric and Eccentric Muscle Motions Explained

Below is a short video further illustrating concentric and eccentric muscle motions as I discussed in recent blog posts.

Concentric and Eccentric Exercises

In my last blog post, I described the differences in concentric and eccentric muscle contractions. I would now like to relate these actions to strength training exercises. When performing any strengthening exercise, I feel both the concentric and the eccentric contraction should be included to provide the most efficiency and practical application to daily physical activity.

The concentric motion occurs when the muscle shortens under load, such as the deltoid muscles of the shoulder shortening as you lift a  weight overhead. The same muscles are then called upon to perform the work in the eccentric phase when the weight is lowered from overhead back to its starting (or resting) position. Other surrounding muscle groups are again being brought into play throughout the full range of motion to stabilize and protect the joint, and allow the deltoids to perform the prime movement. I feel it is more efficient to increase the duration of the eccentric phase of a movement to avoid acceleration and thus decrease the risk of injury. Also, science has show that the longer time a muscle is under tension, the greater strength gain is achieved.

All the activities of our daily lives, such as, taking the dishes out of the cupboards, lifting boxes up onto shelves, getting the groceries into and out of the car, all require both concentric and eccentric muscle contractions. Working a muscle throughout both these phases strengthens it and makes these tasks easier and more efficient to perform.

Concentric vs. Eccentric Muscle Contractions

A muscle has two actions referred to as concentric and eccentric contractions. A concentric contraction occurs when the actin and myosin filaments slide over each other through a motion of their cross-linking connections to provide an increase in the overlap resulting in a shortening of the contractile unit. This shortening of every unit of the total length and width of the muscle results in a movement of the human joint through its full range of motion. A great example is the shortening of the biceps muscle when performing a biceps curl and another the shortening of the hamstring muscles in the back of the thigh to bend the knee.















An eccentric contraction is a lengthening of the muscle under load. Lengthening then occurs through the application of forces sufficient enough to pull the cross-links apart and return the contractile unit to its normal resting overlap. Applied forces come in the following three forms:

By the weight of the individual body part moving with the assistance of gravity.

The action of the muscle opposing the prime mover as the triceps straightening of the elbow.

Resistance as that provided by a free weight, strengthening equipment, or a resistance band.

It is during this motion that the actin and myosin filaments are strained leading to a condition referred to as delayed onset muscle soreness or DMOS. DMOS will usually subside within a day or two as the body adapts to the greater load and is a natural occurrence with any fitness program.

There is, however, an increased risk of injury to the joint and surrounding tissues during the eccentric phase if the motions performed at too great a speed with increased resistance. The muscles should have enough strength and flexibility to combat this increase in force if attempting this form of exercise. I always suggest my clients perform all plyometric exercises without additional resistance for this reason. I also feel that no one should walk or run while carrying weights in the hands or wearing them on their legs secondary to altering their normal gait pattern and increasing the risk of injury to the lower back.