What is top end? There are several terms in use that describe pretty much the same thing. The key is rapid movement at high intensity. Think kicking a soccer ball on goal, or a volleyball player spiking the ball. Now extend that effort for thirty seconds to three minutes. For cyclists the best model is a sprint finish. I follow Joe Friel’s terminology and call this aerobic capacity work, since the goal of this exercise is to maximize the body's ability to process oxygen.
Senior athletes should keep aerobic capacity workouts in their weekly schedule year round, as the greatest contributor to the loss of performance due to aging is the lowering of aerobic capacity. What changes is the dose; how much time is spent at this high intensity. The early season is the time for high dose aerobic capacity intervals.
Lower intensity workouts tend to be sport specific. That is, the work done in the pool will not have as much impact on the bike, and vice versa. However, the benefits of aerobic capacity intervals benefit all sports disciplines, and doing them on the bike on a stationary trainer involves the lowest risk of injury.