These are adaptation, intensity, duration, frequency, periodization, progression, and proper periods of rest. Everyone's body will adapt to progressive overload if it is carefully challenged. Intensity is a critical factor in your summer workouts. Intensity is affected by both the degree of difficulty and by the length in time of your workouts. You need to have a combination of both aerobic and anaerobic exercises to enable the body to build a tolerance to lactate levels and facilitate rapid recovery as you compete.
Duration is the length of a training session.
If you are using drills of high intensity your training period should be short. The best results from training are achieved when you apply stress at a proper level of intensity, for a set duration, several times per week adjusted through the summer. If you follow proper training guidelines training improvement will occur. Periodization is how the training of an athlete or team is organized through-out a year long cycle. Proper training results in both peak conditioning and performance at the time of year it is required.