Expansion
Force is greatest at optimal length and falls as shortening velocity rises
Expansion
Length-tension
- Active tension depends on cross-bridge overlap, peaking at a sarcomere length of about 2.0 to 2.2 micrometres
- Too short: filaments interfere and overlap is excessive
- Too long: insufficient overlap
- Passive tension rises steeply with stretch, from elastic elements such as titin
- Total tension is the sum, which is why the whole-muscle curve keeps rising at long lengths
This is the cellular basis of the Frank-Starling relationship in the heart, although cardiac muscle operates on the ascending limb only and adds length-dependent calcium sensitivity.
Force-velocity
- Maximum force occurs at zero velocity, that is an isometric contraction
- Force falls hyperbolically as shortening velocity increases
- Maximum velocity occurs at zero load
- Eccentric (lengthening) contractions generate more force than isometric ones, which is why they cause the most muscle damage and delayed soreness
Power, the product of force and velocity, is maximal at about one-third of maximum velocity.