The use of five reps per set can be used for building both strength and muscle size.
Strength Training
If your primary goal is to build strength, I suggest doing three sets of five reps while using about 80% of your single rep max for each exercise. Rest at least three minutes between sets of the same exercise.
Building Both Strength and Size
If you want to build both strength and muscle size, I suggest doing two sets of five reps using 80% of your single rep max for each exercise. Rest at least three minutes between sets of the same exercise. Follow this with three sets of five reps using 65% of your single rep max while resting only 30 seconds between sets of the same exercise.
Building Strength and Speed
If you want to build both strength and speed, I suggest doing two sets of five reps using 80% of your single rep max for each exercise. Rest at least three minutes between sets of the same exercise. Follow this with three speed sets of five reps using 55% to 60% of your single rep max while resting 45 seconds between sets. The speed sets should be performed with maximum force and rep speed. In other words, lift using explosive reps.
Building Muscle Size
If your main emphasis is to build muscle size, a good option is to perform tri-sets consisting of three different exercises for the same muscle group, with each exercise being performed for one set of five reps. For example, when training the chest muscles, do one set of bench presses for five reps, followed by one set of decline benches or dips for five reps, and one set of incline dumbbell presses for five reps. If you choose to use this method, you can experiment with different combinations of three exercises from workout to workout to see which combination gives you the best pump.
When performing the tri-sets, move immediately from one exercise to the next without stopping to rest between the three sets that are performed for the same muscle group. I suggest switching to a tri-set for a different muscle group before returning to the first muscle group you were working. Do two to three tri-sets for each muscle group when switching back and forth between muscle groups.
The amount of effort that you use for each set of a tri-set is important. I do not recommend going all out on each set. I believe it works better to increase the intensity slightly for each set of 5 reps as follows:
Set 1: Use a weight that forces you to stop four to five reps short of failure.
Set 2: Use a weight that forces you to stop three to four reps short of failure.
Set 3: Use a weight that forces you to stop two reps short of failure.
Adjust According to your Goals
When used correctly, sets of five reps can be used for a variety of purposes to build strength and muscle size. The key to whether you emphasize strength versus size is based on how much weight you use, how many sets you perform, and how long, or how little you rest between sets. The heavier the weights and the more rest between sets, the more you will be emphasizing strength. Resting less between sets will force you to use lighter weights and will allow you to do more sets without overtraining. This will also facilitate the pump which is something that many bodybuilders value for building muscle size. That being said, I believe that the best gains in both size and strength will come from using a combination of heavy sets for five reps and lighter sets for five reps.
If you prefer simple training strategies, you can stick with sets of five reps and adjust the weight, the number of sets, and the amount of rest time between sets according to your goals. May you experience the best of training and the blessings of God.