Some questions about a muscle physiology lab: Please Help!!

Any help with any of the following questions would be wildly appreciated!!!

Within a certain range, why doe the muscle response increase with increasing stimulus amplitude?

How do the thresholds of muscle fibers that respond to higher stimulus amplitudes compare to the thresholds of muscle fibers that respond to lower stimulus amplitude?

What is a reason for the latent period to be longer than the expected 4 milliseconds?  (This has to do with a finger muscle stimulation with "iworx"

Why did the amount of work initially increase with increased weight?

Why did the amount of work decrease when heavier weights were used?