When you strength train, you want to see results. Right? If you train diligently, results come in the form of stronger, more defined muscles. Just as importantly, you train to PRESERVE strength and muscle mass – for good reason. After the age of 30, you lose muscle strength and size. In fact, by the time you reach age 90, you will have lost almost half of the lean body mass you had at age 20. That’s a pretty frightening amount of muscle tissue to lose, isn’t it? It’s this loss of mass and strength that causes older people to become frail and feeble. Along with frailty comes falls and injuries that can ultimately shorten lifespan. If we can hang on to more muscle, we’re more likely to stay functional as the years pass.
The best way to preserve muscle strength and mass is by training your muscles using a challenging resistance. When you stress a muscle, it has to adapt and become stronger. You might wonder how hard you have to work your muscles to get your muscles to grow? Is there a threshold at which you have to train at or beyond to get results?Strength Training: Is There a Threshold Intensity Needed for Hypertrophy?
You already know that you won’t build muscle size with very light dumbbells, especially if you only do a few reps. Muscles grow in response to overload and that overload has to be progressive. Even if you use a challenging weight, you’ll gradually “outgrow” that weight as your muscles adapt. Unless you increase the resistance or the number of reps, you won’t continue to experience muscle growth or gains in strength.
To develop muscle strength and muscle size, you need to lift with enough intensity to active fast-twitch muscle fibers, the fibers designed for strength and power. These are fibers that are large in diameter and that fatigue quickly because they have a low number of mitochondria, unlike slow-twitch muscle fibers that are mitochondria-rich and can contract for long periods of time without tiring. It’s fast-twitch muscle fibers that have the most potential for growth. That’s why fast-twitch fibers should be the focus of your training if you’re trying to build strength and size.
So, what is the intensity threshold for muscle growth? According to a study published in Sports Medicine, training at an intensity of 60% of your one-rep max or greater is the minimum needed for gains in muscle size if you’re not a training newbie. When you’re just starting out, you can see gains by lifting lighter loads because any resistance your muscles aren’t accustomed to will trigger adaptations. But is this the full story? Some research suggests you can hypertrophy muscles using a lighter resistance.
Can You Build Muscle Using Lighter Loads and Higher Volumes?
When you lift a heavy load, you recruit fast-twitch muscle fibers to handle that load. However, if you use lighter weights and train until your muscles fail, you’ll also call fast-twitch muscle fibers into play, once the slow-twitch fibers fatigue. Plus, some studies show you can build muscle size below the 60% one-rep max threshold intensity if you lift until volitional muscle failure.
In one study, researchers compared the effects of low-resistance, high-volume training at 30% of one-rep max to high-resistance, low-volume training using a resistance that’s 90% of one-rep max using leg extensions. Surprisingly, the low-resistance, high-volume group actually showed greater increases in muscle protein synthesis relative to the high-resistance group.
Another study found that three sets at 80% of one-rep max and three sets at 30% of one-rep max yielded similar gains in muscle hypertrophy when both groups of participants lifted to muscle failure. So, the key may be to thoroughly exhaust the muscle to optimize muscle growth. However, it takes more reps, and more time, when you use a lighter weight.
Blood Flow Restricted Training
Is there another approach? Studies show that lifting lighter weights using a technique called blood flow restriction elicits similar hypertrophy gains to lifting heavier weights. Blood flow restricted training is where you constrain blood flow to the veins, but not the arteries, when you lift. With this technique, blood enters the muscle but can’t escape as easily. When the blood can’t leave the muscle, lactate builds up and creates metabolic stress. This metabolic stress, in turn, stimulates muscle growth.
People who use restricted training (not something we recommend) wrap their limbs with cuffs, wraps, or tourniquets to reduce venous blood flow when they train. Some studies show you can build muscle using weights as light as 20% of one-rep max if you restrict venous blood flow. Of course, blood flow restriction training isn’t for everyone. That’s why if you’re not a newbie, you’ll likely make the most hypertrophy gains by lifting at 60% to 80% of your one-rep max or more. Generally, this is a resistance that will allow you to do 6 to 12 reps.
If your main goal is to build strength as opposed to muscle size, lifting heavier, 80 to 90% of your one-rep max, a resistance that allows you to do 2 to 5 reps, will optimize strength gains. Regardless of your goals, it’s a good idea to vary the resistance that you use so that your muscles are stimulated in different ways. This approach will help you avoid plateaus and reduce the risk of overtraining. If your goal is to build strength and you only do reps at 80 to 90% of your one-rep max, you’ll exhaust your muscles and your nervous system quickly.
The Bottom Line
For maximum gains without spending too much time lifting, choose a weight that’s at least 60% of your one-rep max for hypertrophy gains. Below that, you can still make gains, especially if you lift to failure or use blood flow restriction – but you’ll maximize your gains and reduce the time you spend lifting by selecting a weight at least 60% of your one-rep max. However, don’t be afraid to vary the intensity at which you lift to avoid plateaus and overtraining.
Sports Med (2013) 43:1279–1288. DOI 10.1007/s40279-013-0088-z.
STACK. “3 Ways to Develop Fast-Twitch Muscles”
PLOS One. “Low-Load High Volume Resistance Exercise Stimulates Muscle Protein Synthesis More Than High-Load Low Volume Resistance Exercise in Young Men”
J. Appl. Physiol. 113, 71-77 (2012)