You reach a plateau.
You push harder with more intensity and increased frequency yet still no improvement.
It is an irrefutable but too often overlooked fact that workouts help you achieve athletic conditioning only when followed by rest and recovery-promoting activities. Periods of outright rest are, of course, essential, but the person that performs active-recovery workouts between most pairs of key workouts will become fitter than the person that does not, provided he or she has gradually worked toward being able to handle the frequency of training involved. While the person that does not perform active-recovery workouts gets more rest than the person that does, it's actually the latter that gets more recovery. It may be counter-intuitive, but it's true nevertheless that in the context of a rigorous training program, light workouts accelerate recovery beyond what happens during outright rest by just slightly increasing the body's need for recovery.
A general "rule of thumb" regarding your active recovery workout is that you should finish the workout feeling better than you started.
Many professional football players do pool resistance exercises to actively recover from their on-field practices and traditional weight room training. It is a scientific fact that exercise in the water actually speeds up recovery by increasing circulation. Improved circulation means moreblood flow and delivery of nutrients to stressed or damaged muscle tissue.
BETTER RECOVERY = A BETTER ATHLETE