Building Muscle Mass: More Weight or More Reps?

What’s better for getting bigger muscles? Heavy weight and few reps, or light weight and more reps? Here’s how it all breaks down.


Low Reps with Heavier Weight

The traditional method for building muscle mass, for both men and women alike, is to lift heavier weights and increase the amount of weight over time. On the intense end of the spectrum, powerlifters and many competitive bodybuilders pair very low reps (1 to 5) with extremely heavy weights (90-95% of their one-rep max).

Why does this work? Lifting heavier weight (approximately 70-75% of your one-rep max) activates Type 2 or “fast twitch” muscle fibers, which are important in developing strength and promoting hypertrophy (muscle growth along with an increase in the size of muscle cells).

The potential pitfall? Type 2 muscle fibers have greater power, but they also fatigue quickly—and muscle fiber stimulation correlates with how long they are under resistance. If they aren’t under tension long enough, they won’t be able to promote hypertrophy (muscle growth) as effectively.

For this reason, many people have found success with a more moderate approach (8-12 reps at 70-75% of your one-rep max). This allows you to lift enough weight to build strength and power, while also being able to extend the length of your set.


High Reps with Lighter Weight

So what happens when you extend your reps into the high range (15+ per set?) The amount of weight you can handle at this range is about 50-60% of your one-rep max. This isn’t enough weight to promote a response from the Type 2 muscle fibers, where the potential for big growth resides.

A high-rep/lighter-weight workout activates a different type of muscle fiber: Type 1. Also called “slow twitch” muscle fibers, they have less power than Type 2 but are endurance-based and much slower to fatigue.

That means that when you lift lighter weights for more reps, you’re still gaining strength, just a different kind—muscular endurance. The longer, high-intensity workouts also burn more calories, help melt fat for a more toned appearance, and give you a greater after burn effect.


Or, Mix Things Up?

So, in general, low reps with heavy weight tends to increase muscle mass, while high reps with light weight increases muscle endurance.

This doesn’t mean that you have to rely on one method exclusively. Alternating between the two may be the best approach for long-term success. Here’s why.

  1. Lifting heavy weights builds muscle, but constantly upping the weight exhausts the body. The nervous system must also adjust to the new fiber activation in the muscles. Lifting lighter weights with more reps gives the muscle tissue and nervous system a chance to recover while also building endurance.
  2. If you follow the same fitness program over a period of time, you will eventually hit the dreaded “plateau.” When your mind and body have adapted to the routine, it is no longer challenging and you stop making progress. Changing things up gives your body and nervous system the kick in the pants they need to start progressing again.
  3. Eventually, you’ll hit a point where you can’t lift any more weight, or can’t lift the weight long enough to be effective. This can cause your form to break down, putting you at greater risk for injury. Switching to high rep/low weight for a time will allow you to continue making progress, concentrate on your form, and build up endurance so you can hit those heavy weights again.

These workout change-ups should be planned and strategic, such as every other workout, every other week, or on a 6-8 week rotation. An unstructured, uneven approach will lead to uneven results.


A Final Thought…

It’s important to remember that there are many factors that go into building muscle mass, apart from the workouts you perform. Diet, genetics, metabolic rate, hormone levels, body type, and even your individual muscle fiber composition all contribute. No one workout plan is effective or appropriate for everyone.

A personal trainer can help you design a plan to build muscle safely and effectively. They are trained professionals and can tailor the workouts to fit your goals and lifestyle.

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