In practical terms, doing a heavier single or double should make your reps feel lighter with your rep weight. Or at least thats what it looks like.
This was the most interesting part for me.
The first theory involves an increased phosphorylation (addition of a phosphate for the production of ATP) of myosin regulatory light chains (proteins of muscle contraction) during a maximum voluntary contraction (MVC). This allows the actin (the other protein of muscle contraction) and myosin binding (for muscle contraction) to be more responsive to the calcium ions released (from the sarcoplasmic reticulum), triggering a cascade of events leading to enhanced force muscle production at the structural level of muscle (Hamada, Sale, & MacDougall 2000). The greater the muscle activation, the greater the duration of calcium ions in the muscle cell environment (referred to as sarcoplasm) and the greater the phosphorylation of the myosin light chain protein (Rixon, Lamont, Bemden, 2007). As a result, faster contraction rates and faster rates of tension develop (Chiu, Fry, Weiss, et al. 2003).
Calcium and sodium ions trading places causes muscles to contract (at least on a level so simplistic to nearly be incorrect) Somewhere in the mix is potassium, but its 8 AM on a saturday and I'm not completely awake.
I spent a few minutes mangling how neurons fire and the gap between the neuron and muscle cells, but gave up as I really don't want to dig through physiology books right now. My interest is refraction periods for the muscle cell to fire again (which in my memory should be very low) vs neuron to fire (which seems like it was longer). It makes me wonder if there is any sort of refraction half life sort of response under maximum loads to explain why muscles are ready to go quickly after maximum contraction for the nervous system often rebels.