I may be looking to far into this! But I know by being a stronger person you can obviously generate more power, its not all about legs, its about core stability too. Practise something called the plank. Look it up on the internet. Also press ups and sit ups, there is much more you can do but im just saying basics. However as much as it is about power its about technique. Watch some videos of TOP riders who gap miles for fun, I would say TRA is a good example, watch how he pre loads and how he shifts his weight as he takes off, also what he does whilst in the air and landing? After doing all this, hopefully you will be able to gap as far as before using less power meaning you will be able to go further using more power! How old are you??