Is the person with the biggest muscles always able to lift the most weight? Not necessarily. Although a muscle with a larger cross-sectional area has a strength advantage over a smaller muscle, other factors also determine how much a person can lift. If you increase the size of your muscles, you have more surface area to lift or push against heavy resistance. Yet, you’ve probably known people who didn’t have large muscles or even a lot of muscle definition who were able to lift a significant amount of weight. Why might that be?
It’s tempting to attribute such discrepancies between muscle size and strength to genetics. No doubt, some people do have a genetic advantage when it comes to strength but what accounts for that genetic advantage? Let’s look at strength and from a physiological standpoint. When you first begin strength training you may discover you’re stronger after only 8 to 10 weeks of training, before your muscles have had a chance to increase in size. During this time before you see a change in muscle size, neural adaptations are taking place. In other words, the way your muscles and nervous system communicate is changing.
As you may know, the functional unit that mediates communication between the brain and muscle is the motor unit. A motor unit is made up of an alpha motor neuron, nerve cells that connect with one or more muscle fibers and are directly responsible for muscle contraction. The more motor units your nervous system is able to activate when you lift against resistance – the more force your muscles can generate and the stronger you’ll be.
Early Adaptations to Strength Training
Just how DOES neural adaptation take place? Early in strength training, your brain becomes better at synchronizing motor unit contractions and more skilled at recruiting multiple motor units at the same time. Motor unit firing rate also increases and the firing becomes more synchronized. As a result, you can generate more force even without changing the size of your muscle. Your brain is more efficient at using the resources you already have.
You also have inhibitory reflexes designed to protect your muscles against injury. For example, if you tried to lift a weight that was too heavy, the inhibitory reflexes since the excessive tension your muscles are generating and send and signal your brain. In response, your brain fires a command to reflexively relax the muscle as a protective mechanism against injury.
Golgi tendon organs, or GTO, are the primary receptors that sense changes in muscle tension and communicate this information to the brain. These receptors are aptly located at the junction where muscles insert into tendons. You also have other inhibitory neurons or nerve cells in your spinal cord. These neurons block excessive force production by reducing the rate at which alpha motor neurons fire.
Another way neural adaptation takes place is the Golgi tendon organs change their threshold a bit so they don’t fire as easily in response to increased force production. Therefore, they don’t inhibit force generation as much. This disinhibition allows you to produce more force in a muscle relative to what you could before training. Remember, neural adaptations happen early before your muscles increase in size.
Structural Adaptations to Strength Training
In contrast to neural adaptations to strength training, which is independent of muscle size, structural adaptations, or changes to the size of the muscle, also take place, although these changes lag behind neural adaptations. It’s only after you’ve trained for more than 10 weeks that you start to see muscle hypertrophy or enlargement of the muscle. Muscles grow through an increase in the size muscle fiber size, a process called hypertrophy. Although neural adaptations predominate in the beginning, muscle hypertrophy prevails as training progresses.
Don’t forget, your muscles are made up of slow-twitch muscle fibers and fast-twitch muscle fibers. Strength training targets your fast-twitch muscle fibers, ones that can generate great force but tire quickly. If you have more fast-twitch fibers relative to slow-twitch ones, you have an advantage in terms of generating strength.
That’s where genetics enter the equation. Most of us have roughly equal quantities of fast-twitch and slow-twitch fibers but some individuals have more of one type than the other. If you have a higher proportion of fast-twitch fibers genetically, you have some advantage in terms of strength and power development. Powerlifters and sprinters tend to have a higher ratio of fast-twitch fibers to slow twitch ones.
Other Factors that Influence Strength
How your tendons insert into your bones also affects how much weight you can lift. If a tendon inserts into the muscle at a point further from the joint, you can generate more force than if the tendon inserts closer. This is another factor influenced by genetics. The length of your arms and legs are factors too. People with shorter arms are at an advantage because they have more “leverage” when lifting.
As you’re aware, gender is a factor. Men are stronger than women, particularly in the upper body. That’s partially because women have less of their lean body mass in the upper half relative to men. Age, too, influences strength development and strength. Due to anabolic resistance and hormonal factors, older people have more difficulty building strength and mass and may need more protein to maximize gains they get.
The Bottom Line
No doubt, there IS a correlation between the cross-sectional area of a muscle and how much you can lift with, but neural factors also play a role, especially early in a training program. Don’t forget, you need to gradually increase the load on your muscles over time to keep developing strength. Also, if your primary goal is strength development, lifting at a high percentage of your one-rep max (85% to 95%) during some training sessions will maximize strength development. No matter how old you are, how you’re built, or what your genetics are, you can become stronger through resistance training.
References:
Periodization Training for Sports, Third Edition by Tudor Bompa, Ph.D. and Carlo Buzzichelli. Neuromuscular Adaptations to Strength Training.
Strength and Conditioning Research. “Muscle Fiber Type”
Br J Sports Med. 2006 Oct; 40(10): 822-823. doi: 10.1136/bjsm.2006.029116.
European Journal of Applied Physiology and Occupational Physiology. March 1993, Volume 66, Issue 3, pp 254-262.
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