What Do We Mean By Muscle Strengthening?

Muscle strengthening is a big topic in the media these days, and it’s not just for bodybuilders anymore. The importance of building and maintaining muscle strength has been emphasized for athletes, older folks, people recovering from injuries, women, and many other populations. But what do we mean when we say muscle strengthening? In this article, we’ll take a look at what muscle strengthening is, what happens when we strengthen muscle tissue, and what some of the benefits are.

What is muscle contraction?

Depending on our particular context, when we say muscle strengthening, we probably think of lifting weights at the gym. Lifting weights is one type of strength training. But it’s not the only kind of muscle strength, because shortening to contract is not the only type of muscle action.

Let’s start with the basics and briefly review skeletal muscle contractions. Remember that muscles don’t just contract and shorten. Muscles can act in several different ways. When a muscle shortens when we contract it, that’s called a concentric contraction. A muscle can also lengthen during a contraction. That’s called an eccentric contraction. Finally, we can contract a muscle in situations where it doesn’t change length at all. That’s called an isometric contraction.

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If we’re thinking about muscle strength, concentric muscle contractions are what happen when we lift a dumbbell at the gym to do a bicep curl. Isometric contractions are what your biceps muscles are doing when you hold the dumbbell without moving it anywhere along the way. Eccentric contractions are what your biceps muscles are doing when you slowly lower the dumbbell back down. Each of those situations calls for a different kind of muscle strength. Additionally, there are other, more specific situations where we rely on muscle strength, like the dynamic muscle strength that we need to run up a steep hill, for example.

Regardless of the type of contraction, when our muscles are acting, muscle cells are firing and using up ATP, or energy, at a cellular level, to do work. At a cellular level, when we challenge skeletal muscle tissue by using it, we have a fair idea of what happens. When our nervous system cues a muscle cell to activate through the release of calcium, the individual muscle cell proteins, actin and myosin, are attracted to each other like two magnets. The amount of muscle force is the total of each of the muscle cells that are activating at the same time to do a muscle contraction.

What is muscle strengthening?

Perhaps surprisingly, however, when we zoom out to a more macro level, our understanding of what happens when we feel stronger or show measurable gains on one or more strength tests is more murky. As with an increase in flexibility, an increase in strength comes from more than one type of change in our body. Those changes are both in the tissue itself and in our nervous system. Science doesn’t have a complete explanation of exactly what happens physiologically when we have the felt sense that we feel stronger.

Hypertrophy and muscle strength

When we strengthen muscles, at least some of the time, hypertrophy occurs. Hypertrophy is the name for an increase in muscle cell size. Increasing tension on our muscles is often correlated with an increase in the size of muscle cells. Interestingly, we can also increase muscle size without increasing strength.

The increases we experience in muscle mass are not always correlated with increases in muscle strength. Muscles can increase in size for different reasons. The number of microfibrils can increase, or the fluid volume inside the muscle can increase. An increase in the number of microfibrils is associated with increased strength, but an increase in fluid volume alone is not.

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The nervous system and muscle strength

Additionally, when we increase muscle strength in a way that we see an increase in measurements of strength, changes in our nervous system that affect nerve to muscle communication also happen. A recent review paper from 2018 (Suchomel et al., 2018) specifically reported aspects of nerve to muscle communication, including “motor unit recruitment, rate coding, motor unit synchronization, and neuromuscular inhibition.” While these actions are more technical than we can cover here, what’s important to understand is that our nervous system also has a role to play in muscle strengthening.

Applying muscle strength research

Although every aspect of muscle strengthening physiology might not be worked out by researchers yet, we do know that the type of resistance training you might already do at the gym or in a fitness class focused on strength-building is effective at building muscle strength. Many research studies agreed, as you might expect, that greater load and frequency led to greater increases in muscle strength.

Why strengthen our muscles?

Although we may not yet have a complete explanation of what happens physiologically when we strengthen our muscles, it’s clear that there are benefits associated with measurable gains in many types of strength. Research found that increased muscle strength was correlated with many aspects of health and wellness, from reductions in diabetes symptoms, decreased obesity, increased longevity, and improved fibromyalgia symptoms, to decreased chances of a cancer diagnosis. All of those are great reasons to keep up with our favorite activities for maintaining muscle strength.