You keep using that word, I do not think it means what you think it means
– Inigo Montoya
I use the term range of motion a lot because it’s the transition point from exercise to injury. Every joint in your body has a working range of motion. That simply means you can move that joint to a certain point without reflexes limiting that movement. Once you get to that point the body’s defense mechanisms take over to reduce the damage. The real problem with limits of range of motion come from the fact that your body doesn’t cope well with being attached to a machine that controls movement.
Reflexes are weird things. They are there to defend the body agains injury, but they often supply the force needed to create injury. Your body sets limits on how much force you can generate in an amazingly intelligent way. As you use a muscle it both gains tensile strength (the amount of force needed to create damage) and changes how the muscle fibers are recruited. Muscles that are used infrequently are slow to respond and limited in the force they generate, thus lowering the chance of damage. There are no such limits put on your reflexes. In defending against injury your body will gladly injure itself…
What causes injury on a bike is when the bike is controlling movement and reflexes are fighting that control. A good example of that is when the saddle is too high or too far back and the distance from hip to foot when the pedals is at 5:00 (furthest point from the hip) is too great. The leg runs out of range of motion, the pedal is still moving away, so it pulls down on the foot. The foot now acts as a lever arm, pulling on the anterior tibialis (the muscle on the outside of the shin which lifts the foot). That muscle responds in what’s called a pull reflex – it contracts to counter the force of the pedal pulling the foot down. You now have two opposing forces pulling in different directions, the bike trying to increase the distance from hip to foot while the body is trying to shorten that distance, The end result is a tension spike, which is where injury starts.
Think of that point of reflex as a cliff. It doesn’t matter if you step off the cliff or take a running leap, what’s gonna kill you is the sudden stop at the bottom. 1mm beyond range of motion may be a tiny percentage of the whole distance, but it still causes the same damage.