Andy Haley
- Andy Haley is an Associate Content Director at STACK Media. A certified strength and conditioning specialist (CSCS), he received his bachelor’s degree in exercise science...

STACK Science: How Muscles Work and How To Make Them Work Better

April 1, 2011

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Every athlete knows muscles power sports performance—they're the source of strength, speed and overall movement. But although lots of buzz words are tossed around in training rooms—like "muscle contractions," "fast-twitch fibers," "agonist and antagonist," etc.—how muscles actually function remains a mystery to many. And the fact is that understanding how muscles really work can help athletes make improvements in the weight room.

Fibers and Fascia
Muscles are composed of individual muscle fibers, which are customized cells designed to contract. The fibers form bundles, which in turn form an entire muscle. Each fiber has the ability to shorten to produce a contraction. As more muscle fibers are signaled to contract, the contraction gets stronger.

The fibers, bundles and entire muscles are interwoven with fascia—i.e., connective tissue. The fascia forms tendons, which connect to bones. When a muscle shortens, it applies force on the tendon to move a bone.  Larger muscles produce more force due to increased contracting ability, while longer muscles shorten more quickly for powerful movements.

Making It Work For You
Strength and size gains occur when muscles are challenged with bodyweight or resistance training exercises. When a muscle is fatigued, its fibers break down and adapt to the stress of an exercise—whether from high reps or heavy weight. The muscle then uses amino acids [in protein] to rebuild with an improved contraction system in each cell and to increase in size, which builds strength over its pre-training status. Thus, athletes must continually challenge their muscles by performing a variety of exercises and adding reps or weight to ensure progress.

Muscles are signaled to contract by the nervous system and are activated when calcium enters their cells. When the nervous system stops signaling muscle cells to contract, calcium leaves the cells and they go into a resting state. Small muscle groups—such as those found in the hand—require precise control and have a high degree of connection to the nervous system. Large and powerful muscles, such as the quads, have larger groups of fibers connected to the nervous system and produce more strength than coordination.


The interaction between the muscles and nervous system can be improved with a training program. This is one of the primary reasons why athletes achieve strength gains when they first begin to train.

Making It Work For You
Athletes should focus their training on functional movements that incorporate multiple muscle groups to ensure that muscles contract in a coordinated fashion during a movement. Increasing strength within a sport-specific movement directly relates to improved on-field performance. Also, functional training activates small stabilizer muscles, which are highly integrated with the nervous system to balance and stabilize the body.

Stay tuned to learn the differences between different types of muscle fibers and how they relate to performance.


Andy Haley
- Andy Haley is an Associate Content Director at STACK Media. A certified strength and conditioning specialist (CSCS), he received his bachelor’s degree in exercise science...




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