Final answer:
The primary mechanisms for force production at intermediate and high forces are active cell mechanics and the number of myofibers.
Step-by-step explanation:
The primary mechanism for force production at intermediate and high forces is active cell mechanics due to the presence of acto-myosin force dipoles. The concept of force dipoles is useful at multiple scales, from the entire cell level to individual molecular force generators in the actin cytoskeleton. The force dipoles create a contractile force dipole pattern, resulting in force generation and deformation of the substrate.
In the context of muscle force production, the number of myofibers within the muscle that receive an action potential from the neuron is the primary variable determining force production. When a muscle is used for different tasks, such as picking up a pencil or lifting a piano, the motor cortex signals different numbers of neurons and myofibers, affecting the force produced.
Overall, both active cell mechanics and the number of myofibers play crucial roles in force production at intermediate and high forces.