What happens when we lift weights?

Chris Beardsley
Jul 20, 2017 · 4 min read

When we go to the gym, and lift weights regularly for more than a few weeks at a time, good things start to happen.

Some of these changes we can see from the outside.

First of all, we notice an increase in the amount of weight we are lifting. The number of plates on the barbell will increase, or the pin on the weight stack will drop down another level.

Secondly, we start to see changes in the mirror. Our muscles get larger, and their appearance will change slightly. We look better!

In sports science, we call these changes “strength gains” and muscular hypertrophy, respectively.

But there are also changes on the inside.

These changes are hidden, and we cannot see them. Even so, they have important implications for how strength training can be used to improve sports performance.

How do we know about these hidden changes?

Decades ago, scientists began searching for these hidden changes, because of two experimental observations.

Firstly, they realized that the strength gains were proportionally larger than the increases in muscle size.

So something on the inside, that we cannot see, must also be changing. Otherwise, the relative changes in strength and muscle size would be the same.

Secondly, they observed that the strength gains for a given muscle group were quite specific to the exercise performed in training.

In other words, strength gains were greater when tested using the exact same exercise as used in training, and were smaller when tested using a slightly different exercise for the same muscle group.

This finding was the really important one.

So what are these specific effects?

How are strength gains specific?

Over many years, scientists discovered that strength gains were specific in many different ways, as shown below:

In each case, the improvements in strength were greater when the strength test was the same as the type of movement used during training. There was still a degree of “transfer” to other, similar movements, but the increase in strength that was measured was smaller.

Later, while investigating the hidden changes that underpinned each of these effects, researchers found two surprising results.

Firstly, they found that there were lots of hidden changes that caused these specific effects, and not just one.

Secondly, they found that the hidden changes that caused specific gains in strength differed, depending on which aspect of the exercise was changed. For example, the hidden changes causing specific strength gains for (3) the joint range of motion moved, were not the same as the hidden change producing specific strength gains for (7) the amount of stability.

What are these hidden changes, which make strength specific?

While some people like to think of strength being determined by muscle size and either neural drive or coordination, the reality is that there are lots of factors that have a meaningful impact.

Indeed, there are dozens of hidden changes that can affect the amount of strength that is gained in any of the specific ways. Here are some of the most important ones:

I’ll stop there!

Some of these hidden changes have very obvious effects on a given type of specific strength, while others require more effort to figure out.

For example, increases in the number of capillaries, buffering capacity, and rate of ion transport inside the muscle are all ways in which repetition strength is selectively improved.

In contrast, increases in synergist activation along with decreases in antagonist activation are actually the main factors responsible for strength gains on unstable surfaces.

And proportionally greater maximum strength gains are probably caused by several factors, including greater increases in agonist muscle activation, tendon stiffness, lateral force transmission, and coordination.

What is the takeaway?

When thinking about strength training, we tend to focus more on the changes that we can detect from the outside (strength gains and hypertrophy), and forget the amazing, but *hidden* changes that occur on the inside.

Yet, these hidden changes are essential for developing strength for improving sports performance, because they improve the ability of muscles to produce force under the same conditions as in athletic movements, without increasing muscle size, which has the adverse effect of increasing bodyweight.

Chris Beardsley

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This is how strength training works