Our bodies do go through cycles much like the moon cycles each month. Most of us are unaware of these cycles, but it's the reason why one chest workout you my seem to have tons of strength and energy, and the next chest workout you may feel drained and run-down. Diet, mental stress, physical stress, and recuperation factor in to daily and weekly cycles of strength and energy, but the bigger picture is that there are monthly, or even yearly cycles that our bodies follow that are dictated by genetics. I don't think there is any way to counter-act this.