Often, you may hear a therapist or technician ask you to perform a concentric or eccentric contraction. This vocabulary, while lesser-used for convenience, offers specificity in the type or direction of the exercise.
- An eccentric contraction involves lengthening the muscle, such as in a bicep curl, where you lower the weight down by your side.
- A concentric contraction moves in the opposite direction, shortening the muscle as performed in a bicep curl when you curl the weight towards your shoulder.
The muscles require these movements for balance in the musculoskeletal system and eloquently offer a metaphorical Yin and Yang about the body. Consider the bicep curl again; your biceps shorten to provide that concentric curl. During this, your triceps remain inactive until you extend your arm via the eccentric contraction back to the starting position. While the two muscles remain opposite to each other, they also work together to provide a fluid movement.
The video above provides a visual example of the bicep curl. Between the shoulder and the elbow is the biceps muscle, which contains two heads and forms one main muscle belly. On the other side of the arm is the triceps muscle, which you may notice activating when the patient lowers the weight back down towards the table. Note the good posture and controlled movement throughout the exercise so that the patient achieves optimum muscle contraction.
The therapists consider this information and how it relates to pain management and strengthening. They are aware of the force production and overall abilities for each muscle. They might encourage a certain contraction to better suit the injured patient or promote muscle gain in that region. They stay up to date on research and reviews regarding force-production, muscle-remodeling, and physiological responses to specific exercises. This allows the therapist to provide a strong foundation for their patients and tailor their program to be more focused.
Research and Other Uses
Not only do physical therapists use their knowledge of these types of muscle contractions, but strength and endurance athletes utilize this information as well. In athletes aiming for strength, their focus is on muscular gains and the potential to increase the contractile abilities of their muscles. They take a lot of the details into consideration, such as:
- Challenging the eccentric and concentric contractors for each limb encourages hypertrophy or size growth in muscles.
- Eccentric contractions provide the greatest force at the lowest metabolic cost.
- Eccentric contractions contribute highly to increases in muscle mass compared to concentric contractions.
A recent review on muscle contraction in the Frontiers in Physiology elaborates on the mechanisms, exercise economies, neural responses, muscle-gain reactions, and fiber assessments these audiences consider.