Walking on empty could just mean you run out of energy to complete your workout. It's best to eat a light pre-workout meal 1-2 hours before you exercise.
Refuel your body with the right kind of food. A post-workout meal or small snack helps to replenish glycogen stores and rebuild muscles broken down or damaged during your workout.
Eating carbohydrates tops up the glycogen levels in your liver and muscles, giving you energy for your daily activities and your next exercise session.