When you lift weights, your muscles will grow. However, if you want to focus more on muscle strength vs. mass, you can lift heavier weights for fewer reps. You'll get stronger in less time than you would if you built muscle using lower weights and higher reps.
Rep Ranges for Different Goals
Some fitness organizations use rep ranges to focus on different goals, such as strength and mass. A general recommendation for growing muscle is to do six to 12 reps per set. For strength, you'd do fewer than six reps, and for endurance — more than 12.
These rather black and white general recommendations create the impression that one rep range makes you strong, while another makes you grow muscle. On the contrary, a 2018 study published in Frontiers in Physiology shows that you can build the same amount of muscle using lighter weights and more reps as you can with heavy weights and fewer reps.
Heavy Weights Make You Stronger
The big difference is that heavy weights are more efficient. If you train with light weights, you have to do a lot of repetitions to reach the point of muscle failure, but not so with heavy weights.
The other benefit of training with heavy weights is that you can get stronger than you would if you used only lighter weights, according to a 2018 study published in the European Journal of Sport Science. While both make your muscles bigger, heavy weights seem to give a slight edge to your strength gains.
Muscle Makes You Stronger
There's a little bit of difference between the building muscle vs. strength, but one thing is clear: there's a correlation between muscle mass and strength. A 2016 study published in Osteoporosis International shows that, as you age, you lose muscle mass and strength.
Strength vs. Size
Athletes who compete in weight-class sports like boxing or wrestling can use the discrepancy in size and strength to their advantage. A 2017 study published in Frontiers in Physiology shows that if your goal is to get stronger while gaining as little muscle mass as possible, you should focus on lifting heavy weights with fewer reps instead of lighter weights with more reps.
Even if you simply want to get stronger while avoiding getting bulky, you can focus on heavy weights with fewer reps. Again, you'll build muscle, but your strength will increase faster than if you were just lifting lighter weights.
What Makes Muscles Different?
It doesn't make sense that there might be a difference between muscle size and strength until you consider how muscles work. Once you understand what makes one muscle stronger than another, it's easier to see why training with heavy weights improves strength more than training with light weights.
Muscles are more complex than they appear. They're made of numerous bands of fibrous tissue, similar to a rope. Ropes are made of small threads wrapped together to form bigger threads.
Muscles are built the same way. Bundles of fibers form bigger bundles. Each bundle of fiber has a nerve ending that carries an electrical signal from your brain or spinal cord down to the muscle which makes it contract.
Different Types of Muscle Fibers
There are different types of muscle fibers distributed throughout each muscle and three major categories of muscle fiber types. The amount of each fiber type you have in your muscles is mostly a result of genetics. Training can alter it slightly.
Slow-Twitch Muscle Fibers
The first muscle fiber type, which is considered the weakest, is called a Type 1 fiber. If you don't use more power than necessary, it's the first to be activated when you do something like lifting weights or shaking someone's hand.
Since Type 1 fibers are slow, they don't use much energy, which makes them perfect for endurance events like running or swimming. If your muscle has a high concentration of these fibers, you'll likely excel in endurance events.
Fast-Twitch Muscle Fibers
Intermediate Muscle Fibers
In between slow and fast fibers are intermediate, also known as Type 2 A. These are a sort of hybrid fiber that isn't too fast or slow. They don't burn out too fast but won't last forever. Interestingly, many Type 2 X fibers convert to this more efficient Type 2 A fiber when you start training.
The percentage of each fiber type you have in your muscle helps determine how strong the muscle is. If you have more Type 2 X fibers, you'll be stronger than someone with more Type 1 fibers.
Nerves Make Muscles Work
The muscle itself is only half the equation. The nerve that makes the muscle contract is equally important. There are many nerves going into your muscles that control small areas of muscle fibers, allowing you to have more control of your muscles.
Imagine if you had only one nerve going into your muscle. You wouldn't be able to shake someone's hand without crushing it or eat dinner without spilling everything. You need to be able to control your muscles and use only a little bit at a time.
This ability to recruit individual sections of your muscle at a time to conserve energy and avoid hurting others with wild movements is called motor unit recruitment. In weightlifting, the greater the weight you need to lift, the more motor units you need to use.
Maximizing Your Muscle's Potential
So, the amount of muscle you have doesn't necessarily determine your strength. Your nerves have to learn how to coordinate to make the most of the muscle you're building, which is another reason why training is so important.
Psyching Yourself Out
The difference between lifting heavy weights and light weights might also be psychological. Lifting a heavy weight can be intimidating, and light weights won't prepare you for the sensation of handling something heavy. For that reason, it may simply be a difference in mindset between people who lift light weights for many repetitions and people who lift heavy weights for only a few reps.
- Frontiers in Physiology: Are the Hypertrophic Adaptations to High- and Low-Load Resistance Training Muscle Fiber Type Specific?
- European Journal of Sport Science: Effects of Different Intensities of Resistance Training With Equated Volume Load on Muscle Strength and Hypertrophy
- Osteoporosis International: Age-Associated Declines in Muscle Mass, Strength, Power, and Physical Performance: Impact on Fear of Falling and Quality of Life
- American Council on Exercise: How to Select the Right Intensity and Repetitions for Your Clients
- Human Kinetics: Strength Training Results in Measurable Changes in Motor Unit Recruitment
- Elite FTS: Muscle Fiber Types and Training
- Frontiers in Physiology: Greater Neural Adaptations Following High- vs. Low-Load Resistance Training
- National Cancer Institute: Structure of Skeletal Muscle
- National Strength and Conditioning Association: Muscle Activation and Strength Training
- ISSA Online: Type IIa Muscle Fibers: Training for Explosiveness
- Open Oregon State: 10.5 Types of Muscle Fibers
- Nia Shanks: How to Banish the Fear of Lifting Weights