Why does lowering and not lifting weights produce unique adaptations?
Eccentric training is a type of strength training in which we just use the lowering phase of the exercise.
Instead of lifting and lowering a weight in sequence, we perform the lowering phase from the top, stop, and then return the weight to the starting point without lifting it, before beginning again.
What is different after eccentric training?
Two things happen after eccentric training that are different from after a similar program of normal strength training:
- Eccentric training causes larger gains in maximum lifting strength (and also in maximum isometric strength) in comparison with normal strength training.
- After eccentric training, the gains in maximum lowering strength (the heaviest weight than can be lowered under control over a set number of seconds) are larger than the gains in maximum lifting strength (the heaviest weight than can be lifted).
Let’s look at each of these in turn.
Why does eccentric training cause larger gains in maximum lifting strength than normal strength training?
Eccentric training causes larger gains in maximum lifting strength than normal strength training *mainly* because the weight used is heavier.
Eccentric training also changes the angle of peak torque to longer muscle lengths, and this can improve force production against the resistance provided by inertial mass, because the strength curve involves a peak contraction at long muscle lengths. However, this is likely of lesser importance, and only applies to strength tested when moving a weight, and not under other conditions.
Anyway, eccentric training involves lowering weights, and not lifting them. And this is why the weights used are heavier. In fact, when we lower a weight under control (over 3 seconds, for example), the maximum weight (one repetition-maximum) we can use is approximately 25–30% larger than the heaviest weight we can lift.
Therefore, the mechanical loading on the whole muscle-tendon unit is higher during eccentric training. This greater mechanical loading on the whole muscle-tendon unit could cause any of the following adaptations that we know increase maximum lifting strength, including:
- Increased tendon stiffness
- Increases in the amount of lateral force transmission inside the muscle
- Increases in the activation of the prime mover muscles
- Increases in load-specific coordination
Since eccentric training usually causes more muscle soreness and damage after exercise, the changes in lateral force transmission may be particularly important.
When muscle fibers are badly damaged and can no longer transmit force along their whole length, they form new lateral attachments to the surrounding collagen at the site of the damage. Force at this point is now transmitted entirely laterally, and this allows the fiber to continue contributing to muscle force, despite being damaged.
Even after the fiber has been fully repaired, these new lateral attachments remain, which means that maximum lifting strength is subsequently increased.
Why is lowering strength increased by even more than lifting strength?
Even though eccentric training causes bigger increases in maximum lifting strength than normal strength training, it produces even larger gains in maximum lowering strength.
So the ratio of maximum lowering strength to maximum lifting strength increases after eccentric training. And therefore we say that eccentric training causes “eccentric-specific” strength gains.
Why does this happen?
There are many possibilities, as follows:
- Increases in the amount of lateral force transmission within the muscle
- Increases in muscle collagen content
- Increases in titin molecule content inside muscle fibers
- Increased spinal excitability, causing improved transmission of neural drive in the lowering phase
- Improved motor control in the lowering phase
Changes in lateral force transmission, muscle collagen content, and the titin molecule content all “work” by increasing active muscle stiffness (stiffness is the amount of force needed to produce a given length change). The increase in muscle stiffness probably helps to increase maximum lowering strength, but does not contribute as much to maximal lifting strength, and this thereby produces eccentric-specific strength gains.
Spinal excitability can be reduced by the actions of muscle spindles (sensory receptors inside the muscle that detect changes in length and speed). If the signals from these sensory receptors can be suppressed after eccentric training (perhaps by signals from Golgi tendon organs, which are receptors that respond to high forces), then the transmission of neural drive in the lowering phase might be increased.
Changes in motor control in the lowering phase happen because lowering actions are controlled by our brains in a different way from lifting actions. With normal strength training, this ability is not challenged because the weights are too light, but with eccentric training we can create a greater stimulus, and therefore a larger adaptation.
What is the takeaway?
Eccentric training allows us to use much heavier loads than normal strength training, which leads to greater gains in maximum lifting strength, likely by means of several mechanisms.
Yet, the gains in maximum lowering strength after eccentric training are even larger than the gains in maximum lifting strength, which means that they are eccentric-specific. Eccentric-specific strength gains probably happen through mechanisms that increase muscle stiffness, and through mechanisms that improve motor control and neural drive in the lowering action.
While similar gains in maximum lifting strength might be achievable after normal strength training (albeit over a longer period of time), it is impossible to achieve eccentric-specific strength gains without doing eccentric training.