  Myosin II plays a pivotal role in muscle contraction by generating force
through the cooperative action of multiple motors on actin filaments. In this
study, we integrate the nonlinear elasticity of the neck linker in individual
myosin II and comprehensively investigate the evolution of cooperativity and
dynamics at {\it microstate} and {\it mesostate} levels using a combined model
of single and multiple motors. We find that a substantial proportion of
actin-bound motors reside in the {\it mid-} and {\it post-power stroke} states,
and our nonlinear model reveals their increased capacity for load sharing.
Additionally, we systematically explore the impact of mechanical load and ATP
concentration on myosin II motors. Notably, we observe that the average net
distance of actin undergoes a transition from a weak load-sensitive regime at
low ATP concentrations to a load-sensitive regime at higher ATP concentrations.
Furthermore, increasing the load or raising the ATP concentration to saturation
can enhance the efficiency and output power of myosin filament. Moreover, the
efficiency of the myosin filament increases with the power stroke strength,
reaching a maximum at a specific range, and subsequently declining beyond that
threshold. Finally, we explore the mean run time/length and mean existence
probability of myosin filament, shedding light on its overall behavior.
