Switch it Up
You find something you enjoy and decide you’re exclusive. This sounds great in theory, but in reality, different modalities of movement are important and here are a couple reasons why.
According to Wolff’s Law, bones become stronger in response to increased stress (exercise in this case). For that exercise to continue being as effective, the stress placed on the bone by weight bearing activity or impact must exceed the level to which it has adapted. So basically, your body gets used to that type of exercise and it is effective up to a point. Adding variety will keep challenging your muscles and bones, ultimately making you stronger.
Different patterns of movement work different muscle groups. I love to spin (good thing too since I’m a spin instructor), but you’re working in one plane of movement. Think strong quads, but weaker glute med (outer glute) and hamstrings. Adding in lateral (side to side) movements to work muscles like your glute med are just as important and it’ll not only make you stronger on the bike, it’ll ensure your body is aligned and prevent injury.
Ultimately, variety in types of movement means you’ll become stronger, faster and be able to move your body optimally in day-to-day life.