The key to getting in shape isn't so much the workouts you do as it is how fast you recover. The more rapidly you bounce back from a strenuous session, the sooner you can do it again. And the more hard workouts you can fit into your training in a given period of time, the more race-ready you will be. There are several factors that influence the rate at which you recover. The most significant is age.
Young athletes tend to respond more quickly than do aging athletes.
Experience is also important. Novices take longer to recover than do veterans. The more fit you are the faster you will recover, also. Psychological stress even plays a role. Financial concerns, negative thoughts, relationship issues, and business or school problems all slow recovery.