After working out for many years, I’ve established what I believe is the optimal amount of repetitions you should do to build strength, muscle mass, and endurance. If your goal is to get as big and strong as possible in the shortest amount of time (it will still take time and effort, of course. There is no avoiding that) then you aim for the 5-7 rep range.
Now, when I say you should aim for the 5-7 rep range, I mean your muscles should be failing around this range. The best way to grow your muscles, regardless of how many repetitions you do, is to train your muscles until failure every time. Failure to me is when you are unable to complete your repetition with perfect form. If your form is not perfect with each work out, you will be doing more harm than good to your body. If you are unaware on how to complete a repetition for a specific workout, you should look up how to do the workout correctly.
The 5-7 rep range for me has shown the most benefit. I started out working out with my rep ranges being anywhere from 15-25, and I was really pushing the limit and pushing myself to failure. Even though I thought I was working really hard, I was exhausting my body with little results in strength. Working out doesn’t always have to be extremely hard, if you feel like you’re just working yourself out into an exhausted state, you are more likely working out wrong, and you are most likely not seeing the results you want. What high-rep workouts do though is stimulate something called sarcoplasmic hypertrophy. Sarcoplasmic hypertrophy is an increase of the sarcoplasm and other non-contractile proteins in your muscle cells and is mainly induced by lifting lighter weight for higher amounts of reps. This type of muscle growth, although not usually coupled with much strength gains, is the main reason why bodybuilders tend to look more muscular than power and strength lifters.. High reps also lead to higher protein synthesis.
Another method is to go for the 2-4 repetition range. This rep range is mostly used by heavy lifters, and it primarily activates fast-twitch muscle fibers. Low repetitions are effective for stimulating myofibrillar hypertrophy also. Myofibrillar hypertrophy is an increase in the size and number of the actin and myosin filaments within your muscle tissue. Hypertrophy of this kind will gain you strength since it includes an increase in your contractile tissue. This is important because it will activate progressive overload, which is necessary for growth. This rep range will likely give you massive strength, but less mobility and endurance.
The 5-7 rep range was a perfect balance between endurance and strength. When I first started working out like this, along with a good diet, I had put on 20 pounds of muscle in 3 months, and also the aesthetically pleasing muscle. I work with many different experience levels and have seen that this rep range will show the most benefit for any goal – gaining muscle and size OR losing weight. This is because it will stimulate both fast-twitch and slow-twitch muscles, and you will reap all the benefits that you could reap with doing either exclusively high rep or low rep workouts. This rep range will also give you a great muscle pump, which research shows has led to higher muscle growth.
As a final word, my recommendation is that you should be primarily sticking with the moderate range of reps such as the 5-7 repetition range. This will show you the most amount of progress in the smallest amount of time. That being said the other rep ranges have their time and place, and you should occasionally have a workout where you workout with high reps and a workout when you work with low reps.