Generally, exercises with higher reps are used to improve muscular endurance, while higher weights with fewer reps are used to increase muscle size and strength.
If you're looking to build muscle quickly, whether you've been training for years or are just starting out, then doing slower reps is the way to go. Workouts with slower reps cause your muscles to experience more time under tension, much more than with faster reps.
So, which is more important? Confusingly, the answer is both. When you lift heavier, lower repetitions are advised for the obvious reason: it is harder to lift heavier weights and your muscles fatigue faster. But what this also means is that your muscle size will increase more and faster the heavier you lift.
If you're looking to gain muscle, and increase your strength in the most efficient way possible, then lifting heavy weights is a good option for you. Gaining strength all comes down to fatiguing your muscles, and heavy weights will get you there faster.
A loaded barbell isn't the only path to building muscle. According to a new study published in the Journal of Strength & Conditioning Research, you don't have to lift super heavy in order to boost strength and gain muscle. As long as you go to failure, it doesn't matter how much weight you lift.
You Don't Have Enough Training Volume
The more volume in your training (more sets and reps) the greater the hypertrophy response you will get (up to a point of course). If you like to stick to powerlifting specific programming this may very well be the reason you aren't seeing much progress in terms of muscle growth.
More repetitions with lighter weights can build muscle as well as heavier weights -- assuming they are done to the point of exercise-induced fatigue. And fatigue is the important point. That means even with light weight, the last two to three reps should be hard.
High reps build muscle and connective tissue strength, and give your body respite from the grind of low-rep sets, too. Similarly, low-rep sets build neuromuscular and CNS efficiency.
Lifting weights requires more supervision and instruction for maximum benefit and avoidance of injuries than cardio exercise. Using weights alone without cardio, you will most likely develop bulk instead of a toned and streamlined body.
The faster the speed, the lower the muscle tension. Reduce your rep speed to a more controlled tempo and you increase the muscle tension. Boiled down to its pure essence, developing muscle size is a matter of high muscle tension (coupled with progressive overload, of course). The higher the tension, the more you grow.
Reps for muscle growth
In order to get bigger and stronger, you must ensure your muscles work harder than they are used to. Generally, between 6-12 reps for 3-6 sets will help to build overall muscle size.
They found that based on all of the studies currently published on lifting tempo (which to be honest is quite limited) a lifting tempo between 2 to 6 seconds per rep seems to maximize growth.
Calves. Calf muscles are also considered as one of the most difficult to grow in the gym, to the point where many people give up trying. It turns out that the lower leg muscles are not that significantly different from other skeletal muscles.
Calves and forearms. To the point that if they aren't naturally gifted in these areas, you can count on them not growing much.
If you workout your biceps at least twice a week with high intensity and have a good healthy diet plan. You can increase an inch on your biceps within 2–3 months.
Lifting for pure strength is best partnered with heavy weights. "If you're trying for strength, or your max force output, the heavier the weight, the more strength gains you'll have, along with size gains," Tuminello says. It's also super time efficient.
Generally speaking, you want to train both low and high reps to get ripped. Not just high reps. Training with low to moderate rep ranges can help you get ripped as low rep training at hard intensities will help you maintain strength to ensure you are able to do more work with lighter weights.
Biceps are best suited for intermediate reps. High reps tend to make them look flatter once the pump subsides, but very low reps aren't effective at stimulating maximum growth.
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.
Muscle growth does not depend on the amount of weight you lift. It is a myth that one must lift more weight to bulk up. If you're regular and patient with lighter weights, you can achieve similar results.
Repetition-based sets can build both muscular strength and endurance. Generally, low reps (two to six) will build muscle strength. If you want more muscle growth, 6 to 12 repetitions build muscle mass. More than 12 reps build muscular endurance.
Downtime between workouts (whether you're lifting, doing cardio or training for a sport) is when our bodies have a chance to actually build muscle. Strenuous workouts cause muscle breakdown, while rest allows our bodies to build it back up.
You're not eating enough – one of the main causes of not being able to build muscle is not eating enough and more importantly, not eating enough of the right food. Everyone bangs on about the importance of protein, but carbs and fats are just as important when it comes to growing muscle.
That's why research shows that when you're new to resistance training, getting stronger does produce muscle growth, but you don't have to gain much strength to gain size.