RELATION BETWEEN MUSCLE LENGTH, TENSION AND VELOCITY OF CONTRACTION
MAXIMUM STRENGTH OF CONTRACTION → when muscle has the resting length before activation
VELOCITY OF MUSCLE CONTRACTION → maximal at the resting length.
- A muscle contracts extremely rapidly when no load is applied.
- When load is applied the velocity of contraction decreases and becomes zero if this load equals the maximum force that the muscle can exert.
SOURCES OF ENERGY FOR MUSCLE CONTRACTION
- PHOSPHOCREATINE → used to reconstitute the ATP
- Carries a high-energy phosphate bond similar to the bonds of ATP → has a slightly higher amount of free energy than that of each ATP bond.
- GLYCOLYSIS OF GLYCOGEN (previously stored in muscle cells) → used to reconstitute both ATP and phosphocreatine
- Rapid enzymatic breakdown of the glycogen to pyruvic acid and lactic acid liberates energy that is used to convert ADP to ATP; the ATP can then be used directly to energize additional muscle contraction and also to re-form the stores of phosphocreatine.
- OXIDATIVE METABOLISM → combining oxygen with the end products of glycolysis and with various other cellular foodstuffs to liberate ATP
- More than 95 % of all energy used by the muscles for sustained, long-term contraction is derived from oxidative metabolism.