How many reps should I do?
Choose Your Reps and Sets
The American College of Sports Medicine recommends 4 to 6 repetitions with heavier weight for hypertrophy (increased muscle size), 8 to 12 repetitions for muscular strength and 10 to 15 reps for muscular endurance.
But how long should you hold a stretch? Matt Dobler, Physician Assistant with OrthoCarolina and former competitive cross country runner, says that research has shown 30 seconds to be the optimal time to hold a static stretch. This amount of time allows the muscles to relax and be prepped to work.
According to a new study titled, Interset Stretching vs. Traditional Strength Training: Effects on Muscle Strength and Size in Untrained Individuals, stretching could actually help you gain muscle mass when performed between sets.
#3) Overstretching your muscles
Stretching should never be painful. Exerting too much energy or going too deep into a stretch can result in a torn muscle. Slowly ease into your stretches. You may feel slightly uncomfortable during a stretch, but it should never hurt.
Let's say you're doing triceps kickbacks. Two sets of 15 reps means you'll perform 15 kickbacks two times total, resting between each round. In total, you'll be doing 30 kickbacks. As with the number of reps you do, you can also tailor your sets to your fitness goals.
Training with weights where you can do about 1–5 reps per set (>85% of 1RM) seems to be the most effective for strength, but training with weights up to about 10–20 reps per set (~60% of 1RM) is still moderately effective. Lighter than that, and the strength gains diminish.
For optimal results, you should spend a total of 60 seconds on each stretching exercise. So, if you can hold a particular stretch for 15 seconds, repeating it three more times would be ideal. If you can hold the stretch for 20 seconds, two more repetitions would do the trick.
However it's also possible to over-stretch, with the resulting risk of muscle, tendon or ligament damage. Also, too much flexibility – hypermobility – can be detrimental in itself.
From a strictly scientific viewpoint, stretching can't make you any taller. Stretching elongates and relaxes your muscles, but height has nothing to do with muscles. The structure of your bones determines how tall you are.
Each stretch should be held 15-30 seconds and repeated 2 to 4 times. Many exercise studies on older adults include stretching exercises as part of a well-rounded exercise program.
How many sets of a stretch should you do?
A rule of thumb we find effective is to perform two sets of all stretching exercises and to hold each stretch for 30 seconds at a time. If you have specific flexibility goals, you may hold each stretch for a little longer or perform more sets.
Stretching can be time-consuming. But you can achieve the most benefits by stretching regularly, at least two to three times a week. Even 5 to 10 minutes of stretching at a time can be helpful. Skipping regular stretching means that you risk losing the potential benefits.

Stretch gently
Gradually and carefully move your body or the limb being stretched into the stretch position. Once you feel slight tension in the muscle, hold the position. Avoid bouncing or any other movements, which could overstretch the muscle and result in injury. Wait 15 seconds and then stretch further.
A sharp or stabbing pain means that you're stretching your muscles beyond their capacity for flexibility. You are overstretching and potentially injuring yourself. Another indication of overstretching, according to the Massachusetts Institute of Technology (MIT), is feeling sore the day after you stretched.
Herbert Haupt, of Orthopedic Associates in Des Peres, say static stretching inhibits performance and might even cause micro-tears in tendons, ligaments and muscle tissue.
Anything greater than 20 reps in a set is probably far too many. Performing this many reps in a set will have diminishing returns. If you can easily do more than 20 reps, then the weight you are using is probably too light or too easy to elicit any significant growth. The only exception to this rule is 20 rep squats!
Let's break that down: Traditionally, you might perform enough reps of an exercise so that you work for 40 seconds or so without stopping. That's about the time it takes to complete 10 to 12 reps, says Schoenfeld.
Sets of anywhere from 4–40 reps will stimulate muscle growth quite well, but most research shows that doing 6–20 reps per set is the most efficient way to build muscle. Bodybuilders often use the middle of that range, favouring 8–12 reps per set.
It means you do the exercise 10 times and then rest (for allotted time) and repeat 3 times.
A set is a group of repetitions (an example would be 3 sets of 12 repetitions). A repetition is a single time you perform the exercise.
How many reps and sets are enough?
Allowing your body at least 1 day to recover between each full-body workout is key, so three sessions per week is a good baseline to start with. Within these workouts, you'll choose one exercise for each muscle group — back, chest, shoulders, legs, core — and, as a beginner, aim for 3 sets of 10 to 12 reps.
Between 10 seconds to 3 minutes
It's fine to ease your way into it. According to Joely Franklin, a Level 3 personal trainer and sports therapist, “If you can bear it, even though it may be a bit uncomfortable, go ahead and hold the stretch for 45 seconds to a minute.”
The American Heart Association recommends sticking with your stretch for between 10 and 30 seconds, while Corinne Croce, physical therapist and founder of Bodyevolved, says that she prefers to hold them for up to two minutes. However you go about stretching, know you're doing your entire body a favor.
Hold each stretch for 20-30 seconds and repeat each stretch two to three times. Perform stretches on both sides to maintain a balanced flexibility. Focus on good mechanics.
A daily regimen will deliver the greatest gains, but typically, you can expect lasting improvement in flexibility if you stretch at least two or three times a week. In the videos below, you'll find examples of static stretches that can be worked into any exercise or stretching routines.