E1 Force Generation Muscle

Topic

This skeletal muscle serves as the primary actuator for the organism's athletic movement. Consequently, the muscle generates force through the interaction of actin and myosin within each of its sarcomeres—a process regulated by a nerve signal that releases the calcium required for that interaction.

The muscle's ultimate maximum isometric force is proportional to its functional cross-sectional area—the same functional cross-sectional area addressed in another model in this series regarding muscle tears—with a notably high specific tension per unit of that cross-sectional area. A larger functional cross-sectional area results in a correspondingly higher ultimate maximum isometric force.

The muscle's Hill curve—the same Hill curve featured in another model in this series regarding muscle fatigue—describes the decline in the muscle's ultimate force as its shortening velocity increases during a concentric contraction: the higher the shortening velocity, the lower the available ultimate force. Conversely, if the muscle lengthens while generating force during an eccentric contraction, the resulting ultimate force can actually exceed its maximum isometric force.

The relationship between the muscle's ultimate force and its length demonstrates that maximum force is achieved at a specific optimal length for each sarcomere; outside this optimal length range, the overlap between actin and myosin within the sarcomere decreases, thereby reducing the muscle's available ultimate force. As the length of the muscle sarcomere deviates further from its specific optimal length, the overlap between actin and myosin within that sarcomere is consequently further reduced.

Thus, in this model—which began by considering the skeletal muscle as the primary actuator—the muscle's final mechanical power (the product of its force and shortening velocity) reaches its maximum at a specific fraction of the muscle's maximum shortening velocity; this corresponds exactly to the peak power output established by another model in this series regarding muscle fatigue. Furthermore, this Hill model—now incorporating a series elastic component—accounts for the energy the muscle stores and subsequently releases during the stretch-shortening cycle (a cycle described by yet another model in this series and critical for both running and jumping using the skeletal muscle in question).

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