Cyclists who use single speeds spend more time at higher and lower cadences than those who use gears. When a cyclist uses gears, he or she concentrates the majority of his or her pedaling around a small, preferred cadence range. Riding a single speed requires cadences in a huge range, from 20 revolutions per minute (rpm) to over 130 rpm. Because of this, riding a single-speed bike will put you out of your cadence comfort zone and stimulate new abilities.
The force distribution differs significantly between both riding styles. Single-speed cyclists spend more time pedaling at higher force levels and lower cadences (i.e., they do a lot of mashing and a lot of standing).
It's a matter of physics—to maintain a given power output, if cadence decreases pedal force must increase, and as cadence gets really low pedal force must increase even more. To single speed successfully, you have to push a lot harder while pedaling slower. The cadence and force characteristics of a single speed are similar to other structured training drills such as spin-ups or force repeats. This makes a single-speed mountain bike a valuable training tool.