Why do you need to lift weights quickly, to get fast?

If you enjoy this article, you will like my first book (see on Amazon).

When we follow a strength training program, we can choose any weight we want, relative to the heaviest load we can lift. This weight can range from an empty bar to our one repetition maximum (1RM).

The amount of weight on the bar affects the *type* of results we achieve, because it determines the speed we can move. This is because the speed we move affects the adaptations that happen inside the central nervous system and inside our muscles after training.

If we choose a heavy weight, we have to move slowly. This produces adaptations that help us exert high forces at slow velocities, which is what we need for lifting heavy weights.

If we choose a light weight, we can move very quickly. This produces adaptations that help us exert high forces at fast velocities, assuming we do move as fast as possible. And is what we need for improving speed.

Let me explain what those different adaptations are.

Why does lifting heavy weights lead to greater maximum strength gains?

When we lift heavy weights, we are *forced* to use a slow speed.

Even when we try and move as fast as possible, we still move the weight slowly.

This slow, but still *maximal* speed is key for producing adaptations that lead to improved maximal strength, because it simultaneously recruits all motor units while also allowing a maximal number of actin-myosin bindings inside the individual muscle fibers.

We can *partially* replicate this situation inside the muscle by using lighter weights while training to muscular failure. This also produces full motor unit recruitment while simultaneously creating a maximal number of actin-myosin bindings inside individual muscle fibers.

However, the effect is not identical, because lifting a light weight to failure involves a lot of fatigue, and this means that many of the motor units are not actually producing very much force by the time full motor unit recruitment is reached.

This has two key implications.

Firstly, it means the tension on the *whole* muscle is never high, and this means that the tendon and the internal structure of the muscle itself are never challenged.

Secondly, it means that neural drive to the muscle is only maximal for a short period of time at the end of the set, as muscular failure approaches. When lifting a heavy weight, motor unit recruitment is high from the first rep.

How does lifting heavy weights lead to greater maximum strength gains?

When we lift heavy weights, we achieve greater gains in maximum strength than when we lift light weights, because of:

  • increased activation (neural drive) of the prime mover muscles
  • increased lateral force transmission within the muscle
  • increased tendon stiffness
  • increased load-specific coordination

If you studied sports science, you will have been taught that lifting heavy weights produces its superior gains in maximum strength through larger increases in neural drive and perhaps also through (load-specific) coordination.

While this is true, it is certainly not the whole picture.

In fact, changes inside the muscle almost certainly also contribute.

Increases in lateral force transmission within the muscle probably occur to a greater extent after lifting heavy weights, because of an increase in the number of costameres, which are the structures that attach the muscle fiber to its surrounding collagen.

Lifting heavy weights probably also increases tendon stiffness, which is why rate of force development is also typically only increased after training with heavy loads, and not after training with light loads to failure.

Why does lifting light weights quickly lead to greater high-velocity strength gains?

When we lift light weights, we can move very quickly.

When we lift a light weight as fast as possible, we produce a certain amount of force. This force is always less than the maximal force we can produce at slower speeds against heavier weights, because of the force-velocity relationship.

The force-velocity relationship states that as velocity increases, our ability to produce force decreases. The faster we move, the less force we can produce.

This happens because force is produced by actin-myosin bindings (called crossbridges) inside muscle fibers. The more crossbridges that are in place within a muscle fiber at any one time, the more force is produced. At faster speeds, the number of attached crossbridges decreases, because they have to detach more quickly at the end of their working stroke to accommodate the faster fiber contraction velocity.

To compensate for this reduced ability to produce force by each individual muscle fiber during high-velocity movements, neural drive is massively increased. Motor unit recruitment is full despite the light weight, and rate coding is *many* times higher than when we lift heavy weights.

Lifting weights quickly therefore involves a much *larger* neural stimulus but a much *smaller* tension on each muscle fiber compared to lifting heavy weights, and this produces totally different adaptations.

How does lifting light weights quickly lead to greater high-velocity strength gains?

When we lift light weights quickly, we achieve greater gains in high-velocity strength than when we lift heavy weights, because of:

  • greater retention of type IIX fibers
  • increased muscle fiber contractile velocity
  • increased activation (neural drive) of the prime mover muscles, but mainly in the early phase
  • increased activation levels of the opposing muscles
  • increased velocity-specific coordination

Type IIX fibers are faster than type IIA fibers. Type IIX fibers convert to type IIA fibers quickly after we start strength training, but the effect is smaller when we lift light weights quickly. This may be because of the smaller duration of time for which the motor units are activated, because of the faster bar speeds.

Single fiber contractile velocity can be increased by high-velocity strength training with light weights, even when these fibers are stimulated involuntarily in vitro, and even when fibers of the *same type* are compared. We still have no idea how this happens, but it does not happen after heavy strength training.

Even though there are important changes that happen inside the muscle after lifting light weights quickly, the main changes occur inside the central nervous system.

While strength training with heavy loads causes an increase in the activation of the prime movers over the whole exercise range of motion, training with light loads and fast speeds produces increases in prime mover activation in the early phase, almost certainly because of a *very* large increase in rate coding in the first fraction of a second after starting the movement.

Training with light loads and fast speeds also reduces opposing muscle activation, which decreases resistance to the movement. Heavy load strength training tends to *increase* this resistance, probably to increase joint stability, which is what you want when lifting heavy weights.

Finally, even when doing the same exercise, coordination of the agonists, antagonists, and synergists differs with load and speed (despite what you may have been told in school).

So lifting a light weight quickly is like doing a different exercise variation from the same exercise with a heavy load. There is transfer, but it is far from being perfect, so improvements in the coordination of a fast movement will always be greatest after training quickly, with light loads.

What is the takeaway?

Heavy load strength training is very effective for improving low-velocity strength against maximal loads, and it achieves these gains through key adaptations that cannot be achieved any other way. Similarly, fast, light load strength training is very effective for improving high-velocity strength. It achieves this improvement by a totally different set of adaptations that also cannot be replicated by any other type of strength training. Look at the demands of your sport, and choose wisely.

If you enjoyed this article, you will like my first book (see on Amazon).

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