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:
1. Contraction mode = whether the weight was lifted only, or lowered only
2. Velocity = the speed used to lift the weight
3. Joint angle = the point in the exercise range of motion at which muscle force is greatest
4. Load = the number of reps that can be done with a weight
5. External load type = type of resistance used (weight or elastic resistance)
6. Force vector = direction that force is produced, relative to the body
7. Stability = how stable the exercise is (free weights or machines)
8. Muscle = the muscle group trained
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:
1. Increase in muscle fiber diameter (hypertrophy)
2. Increase in muscle fiber length (sarcomerogenesis)
3. Increase in the angle of the muscle fibers inside the muscle (pennation angle)
4. Different increases in fiber diameter, fiber length, and pennation angle at different parts of a muscle (regional hypertrophy)
5. Shift in muscle fiber type (from type IIX to type IIA)
6. Increase in the amount of force transmitted laterally from the muscle fiber to surrounding collagen tissues
7. Increase in the stiffness of surrounding collagen tissues
8. Increase in tendon stiffness
9. Increase in activation of the prime mover muscles (agonists)
10. Earlier and faster activation of the prime mover muscles(agonists)
11. Increase in activation of the prime mover muscles (agonists) at some joint angles, and not at others
12. Decrease in the activation of the opposing muscles (antagonists)
13. Increase in the activation of synergists, to allow the body to be positioned more effectively for force production
14. Improvements in coordination of a movement, by increased motor skill
15. Increase in the number of capillaries (supplying blood) inside the muscle
16. Changes in buffering capacity and rate of ion transport inside a muscle fiber
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.