Question

There is a trade-off between speed and force in muscle contraction.

a) Why does this trade-off exist (please explain in terms of force generation by myosin heads)?

b) How do glycolytic muscle fibers circumvent this trade-off?

Answer 1

a) Okay, force is given by the myosin heads' ability to attach to actin and form a bridge, the grater the number of heads attached the greater the force. But the fillaments' contraction speed might bring a problem for such attachment. Head take a just a few moments to achieve in attaching, if the fillaments' movement is faster than the heads' attachment then few heads will achieve and the force will decrease. Increased speed produces decreased force.

b) Well, the myosin heads' speed depends on the fast availability of ATP, the faster the ATP is available the faster the heads can work. So we need faster ATP availability, and that is achieved by the use of diversity in muscle fiber types. There are basically two ways for fibers to work, one is the oxdative pathway, which is the aerobic route and the other is the glycolitic pathway which is the anaerobic route.

Glycolytic fibers may circumvent this trade off because it can bring ATP faster, as it only requieres to undergo glycolysis to already produce energy for the myosin heads to work and overcome the speed needed. On the other hand, the oxydative fibers produce large amounts of energy but not as fast as the previous one. In other words the oxydative fibers produce great strength but low speed, and glycolytic fibers produce energy with low strength but at a greater speed.