Red or slow twitch muscle is developed by riding long steady mileage. White or fast twitch muscle is developed by doing interval training or weight training. Up each steep, short hill (freeway crossing are good for this) click into a higher gear, stand and charge up the hill, rest coming down. On flats, go into a higher gear then is comfortable and push, maintaining the same cadence as the lower gear. Push then rest. Do this between every other telephone pole, or mailbox, or block, whatever you have. Devote one to two days a week with this type of interval training and your sprinting will improve. If you have access to a gym, do squats or leg extensions using heavy weights, low repetition. Think powerlifting. Running sprints are also helpful.