Concentric and Eccentric Contractions

A huge topic on the ACSM CPT exam is concentric and eccentric contractions. Muscle contractions are defined by the changes in the length of the muscle during contraction. It is necessary that you understand this topic. Let’s get started!

concentric-contraction

Concentric: Contracting the muscle while it is shortening.

eccentric-contraction

Eccentric: Contracting the muscle while it is lengthening.

The exam most commonly uses this topic in the form of an uphill/downhill running question. It may be written something like: “When running uphill, which muscle is concentrically contracting?” Let’s review the steps necessary to work through any question like this.

1. Identify what major muscles are used in uphill running. Picture yourself running up a hill. You’d lift one leg and bend that same knee. When you put your foot down and push off on the ground, you straighten your leg and knee.

2. Break down the actions and note what muscles are being used:
– Lift the leg: flexion of hip with hip flexors
– Bending the knee: flexion of hamstrings
– Straightening the knee: extension of knee with quads
– Straightening the leg: extension of hip with hamstrings and glutes

3. Identify which muscles are contracting the most. When you are pushing off the ground and straightening your leg, the muscles are contracting the most.

4. Is extension of the knee with the quads eccentric (lengthening) or concentric (shortening)? When you want to stretch your quad muscle, the knee is bent. So, if you lengthen your quad muscle when bending the knee, the muscle is shortening when you straighten it. You would be straightening your knee as you run uphill which means you are concentrically contracting this muscle.

To summarize:
Running uphill: concentrically contract quad and eccentrically contract hamstring
Running downhill: eccentrically contract quad and concentrically contract hamstring

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