This is a short description of how a muscle can develop force:
What is a motor unit
A motor unit is a functional unit that contains a single nerve and all the muscle fibers innervated by the nerve. All muscle fibers are grouped as motor units and have an average of 150 fibers pr motor neuron.
Larger muscle cells (larger square diameter) can generate more power. That is the most commonly known way to increase strength, though it is undesirable for cyclists. The problem is that a large muscle mass is heavy to carry, and there is a dilution of mitochondria. Thus, an increment of maximal strength made through hypertrophy will probably not improve overall cycling performance.
Nervous regulation of force
There are two ways to control a muscle’s force.
One way is to recruit more motor units, which will activate more motor units. You can think of this as the brain tells the muscle to use a larger percentile of the muscle’s fibers to generate power. Motor units are recruited in order of size. Small motor units are recruited before large motor units. This is called the size principle of recruitment.
The second way to regulate force production is through rate coding. It is an increment of the frequency of impulse signals to the motor unit. When a motor unit is stimulated more frequently, the twitches begin to overlap, generating a more significant force.
So now we know the basic physiology behind the mechanisms used to increase the force. It is either to build larger muscle mass, make better recruitment of motor units or fire a higher frequency of stimuli to the motor neurons.