As you may have heard often, many bodybuilders improve their size and shape by implementing higher reps sets and also a higher number of sets, believing that that specific number of reps or sets is the key to their progress. Often, people say: “Since I increased the number of reps from 8 to 15 everything changed and my arms almost doubled!” Also: “Since I started doing more sets, from 12 to 20 per muscle group I have experienced sudden growth in all muscle groups.”

This might be true, but the real reason for that improvement in muscle mass and therefore in fat loss is not in the specific number of reps or sets, but rather in the time under stress (tension under resistance) during a single set and overall training for particular muscle groups.

Take, for example, an average set that people do in the gym. On average, a set of 8-10 reps lasts between 10 and 15 seconds. Now multiply that with the average overall number of sets per muscle group which is around 10 and you will end up with astonishingly short total work duration of 100 to 150 seconds per muscle group! Yes, that is around 2 effective minutes per training session! People usually spend 45 minutes training a single muscle group, believing that that much is needed in order to optimize growth. In fact, they only spend 2 minutes per session, while resting 43! When people increase their number of reps and number of sets they simply increase the time of active stimulation of the muscle under resistance causing better response.

From my own experience, and also from the experience of thousands of my clients during the last 25 years, I can say that the critical time under stress (duration of tension under resistance) should be minimum 20 seconds and maximum 60. If your sets fall short of 20 seconds, there will be not enough stimulation to cause the wanted growth. Anything longer than 60 seconds and you will be getting into different energy sources within the muscle that will drastically reduce intensity of the set. If you perform 10 sets per muscle group with 60 seconds each that will amount to 600 seconds over the whole session for a single muscle group. That will result in 3 times more stimulation than the average training session.

Although time under stress can be increased simply by performing more reps and/or sets (as many people have done) I would advise the slower movement. Ideally would be to lift the weights smoothly in 2 seconds and then lower it in 2 seconds without stopping at any point during the set. Lowering it in 4 seconds is also great, but that will require much more experience. This way, you can perform 10 reps and your whole set will last 40 seconds, which will be enough time to stimulate growth of every single muscle group. Some people will experience better gains with 60 seconds sets, or just over 20, but that can only be established by experimenting.

So, remember, it is not the number of reps or number of sets that will sky rocket your progress, it is the critical time under tension!