When you weight train, your goals might be two-fold: to get stronger and to increase the size of your muscles. If you don’t want to boost the size of your muscles, you at least want to reduce the age-related loss of muscle tissue. However, muscle size and muscle strength are two distinct entities and you might wonder how closely they correlate. Are larger muscles necessarily stronger and if you gain muscle size, do you gain a proportional amount of strength?
Muscle Strength and Muscle Size: How They Differ
The size of a muscle is related to the volume of muscle tissue it has. Muscles are composed of muscle fibers of two main types, fast-twitch fibers, and slow-twitch fibers. Depending upon the type of training, more slow-twitch or fast-twitch fibers will be activated. In response to the demands of exercise, the muscle fibers adapt to the stress placed on them. If you do predominantly endurance exercise or work your muscles against light resistance for long periods of time, slow-twitch muscles will adapt more than the fast-twitch fibers. Slow-twitch fibers typically adapt by increasing the number of mitochondria inside the fiber since slow-twitch muscles are optimized for endurance. More mitochondria increase the ability of muscle fibers to sustain sub-maximal exercise. With strength or power work, the fast-twitch muscle fibers adapt disproportionately since they’re optimized for strength and power. They adapt by increasing in size.
Muscle size depends on the total volume of muscle tissue rather than the functionality of that tissue. In contrast, muscle strength refers to the capacity of a skeletal muscle to contract and generate force. You measure muscle size differently than muscle strength. For example, imaging studies, such as a DEXA scan, MRI, or CT scanning, measure the tissue components and can distinguish between muscle and fat tissue. In contrast, you determine muscle strength, the maximal ability of a muscle to generate force, indirectly by measuring one-rep max. One-rep max is the maximal force a muscle can generate for a single repetition. Another instrument researchers use in research studies is a dynamometer, a device that measures grip strength.
You might assume that muscle strength and muscle mass are directly correlated. Yes, there is a correlation between the two but it’s not a direct one. When you build muscle strength, your muscles also become larger, but there’s also a neurological component to strength gains. You become stronger before your muscles grow in size. This happens because strength training increases the efficiency with which electrical signals are sent to your muscles to tell them to contract. This increased efficiency occurs during the first few weeks of training and makes the muscle capable of generating more force. It’s too early for an increase in muscle size, so the gains come from neurological adaptations rather than an increase in contractile tissue. Therefore, strength has a functional component that’s independent of the quantity of muscle tissue.
The impact muscle strength and mass have on health also suggests muscle strength and size aren’t correlated on a one to one basis. Studies that followed older people over a long period of time show that declines in muscle strength are linked with greater mortality than is the age-related loss of muscle size.
Can You Increase Muscle Size without Gaining Strength and Vice Versa?
Since the initial strength gains you get from strength training happen before the muscles have had time to grow, you can gain a certain amount of strength without changing the size of your muscles. Muscle tissue changes in size partially due to gains in contractile elements but also from an increase in the size of non-contractile elements in the cytoplasm of muscle fibers. Greater neurological efficiency enhances muscle strength without changing muscle size, but these gains are limited as the nervous system can only improve its efficiency so much. Further strength gains will only come after months of training as the muscles grow in size. Yet, it clearly shows that strength gains can occur independently of gains in muscle volume.
Have you noticed how bodybuilders typically have more muscle size than powerlifters? Yet, powerlifters are often stronger than their bodybuilding counterparts. The way they train is different too. Powerlifters focus only on maximizing strength whereas bodybuilders gain strength but are more focused on building muscle size. Bodybuilding guys and gals want well-defined muscles that “pop” and are aesthetically pleasing. So, they train to achieve those gains.
The powerlifter achieves his or her objective by lifting near their one-rep max. Because they’re lifting so heavy, they can only do a few reps, usually 1 to 4 repetitions before the muscle fails. This style of training is ideal for building strength, but it’s not as effective for building muscle. That’s where hypertrophy training comes in.
Hypertrophy Training: Training for Muscle Size
Hypertrophy gains are maximized by training at a lower percentage of one-rep max. Most bodybuilders lift at 60 to 80% of their one-rep max and do 3 sets of 6 to 10 reps of each exercise. Using a lighter weight maximizes the amount of volume the bodybuilder can do, and volume is important for boosting muscle size. As the powerlifter knows, you can build strength without a proportional increase in muscle size. So, they focus on heavy lifts and lower volume.
There’s a “sweet spot” for hypertrophy gains. If you choose a weight that’s too heavy, you won’t achieve enough volume to maximize hypertrophy. Yet, you can also go too light. If you select a weight that’s not challenging, the muscles won’t be challenged enough to make adaptations. There are studies that show lifting light weights can hypertrophy the muscle, as long as do enough reps to achieve near muscle failure. But you’ll have to do a lot of reps to exhaust the muscles if you’re using a light weight. For many people, that’s time prohibitive!
For hypertrophy training, rest periods between sets are longer too. It’s not unusual for a powerlifter to pause 3 to 5 minutes after a set. You need longer rest periods when lifting at a high percentage of one-rep max as a heavy resistance places more stress on the nervous system and you need more recovery time.
The Bottom Line
You can gain muscle strength without boosting the size of a muscle due to neurological adaptations. This happens when you first start training. Even after you train for a while, strength and hypertrophy gains aren’t always proportional to one another. But, over time, your strength gains will be limited unless your muscles increase in size. That’s because bigger muscle fibers with more contractile elements can if everything else is equal, generate more force. Hopefully, this article gives you a better idea of how you can tweak your own workouts to optimize strength or hypertrophy gains.
· PLoS One. 2014; 9(11): e111810.
· Rev. Bras. Geriatr. Gerontol., Rio de Janeiro, 2016; 19(2):257-264.
· Science Daily. “Why Strength Depends on More Than Muscle”
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