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In order to perform well, you have to leave enough time between training sessions to refill your glycogen stores. You must also eat a high carbohydrate diet, vary the intensity of training sessions, and allow yourself enough rest days.
If you have severely depleted your glycogen stores after a hard training session, you cannot expect to train hard again using the same muscles the following day. You need to allow more time to put the glycogen back. On the other hand, you may be able to do some light training as this will not tax the remaining glycogen stores. Better still, you may be able to do another form of training that exercises different muscle groups.
For example, if you work your legs muscles very hard on a Monday during a long cycle ride, multiple sprints or some heavy gym training, they will be very depleted. They will need several days (two to six, depending on how hard you have worked and how fit you are) to refuel completely. On Tuesday you could go on a short, gentle cycle ride, play tennis, or train a different muscle group (e.g. chest or arms) in the gym, or take a rest altogether.
If you attempt Monday's hard leg workout again on Tuesday, you will soon regret it! The exercises will feel extremely difficult to perform; you will not be able to work at the same intensity, or keep going for as long. You will also not be able to cycle as fast or as far; to sprint as fast or as many times; or to lift as many heavy weights in the gym for as many repetitions or sets.
In other words, you have to allow sufficient time for your muscles to recover and refuel between training sessions. Alternate heavy and light workouts, exercise different muscle groups, or take a complete rest between hard workouts.
If you have ever begun a training session with your legs feeling like hollow tubes, or had no power or strength during a workout, you now know why! These symptoms are a result of failure to refill your glycogen stores sufficiently.