Does Strength Equal Speed?

A closer look at Aagaard, RFD, and what heavy lifting actually does

Photo by nhoizey on Unsplash

Every few months, an older strength paper makes the rounds on social media, usually accompanied by a confident caption suggesting we’ve “been overthinking speed” and that strength alone explains power and velocity.

One paper that often gets used this way is an early study by Per Aagaard from the mid-1990s. The most commonly quoted line is some version of:

• Heavy resistance training has been shown to improve the velocity of maximal unloaded movements.

That sentence is technically true.

It is also very easy to misinterpret.

Let’s slow this down and look at what the research actually shows — and just as importantly, what it does not.

What the original Aagaard work actually studied

The early Aagaard studies examined how different resistance-training approaches affected:

• Maximal force (torque)

• Power output

• Performance across a range of movement velocities

The testing was done using single-joint knee extension tasks under tightly controlled laboratory conditions. This is not a flaw — it’s intentional. Constraining the task allows researchers to study neuromuscular adaptations without the noise of coordination, balance, or skill.

In these settings, heavy resistance training increased maximal force, and that increase shifted the force–velocity relationship upward. As a result, participants were able to move faster during unloaded knee-extension tasks.

That finding is real.

Why that result gets overextended

The problem isn’t the data — it’s the leap people make after the data.

Improved velocity in a single-joint, lab-based task is often treated as evidence that:

• Strength alone explains speed

• Explosive training is unnecessary

• Task specificity doesn’t matter

None of those conclusions were tested in the study.

The paper did not examine:

• Sprinting

• Jumping

• Cutting

• Sport skill transfer

• Time-constrained force expression in chaotic environments

It examined knee extensors producing force under controlled conditions.

That distinction matters.

Where Rate of Force Development (RFD) enters the conversation

This is where later Aagaard work becomes essential context.

In the early 2000s, Aagaard and colleagues shifted focus toward Rate of Force Development (RFD) — how quickly force is produced, not just how much force is available.

This matters because most athletic and protective movements occur within very short time windows (often <200 ms). In those windows, peak strength may never be reached.

Later research showed:

• Maximal strength contributes strongly to late-phase force production

• Early RFD is heavily influenced by neural drive, motor unit discharge rate, and intent

• Training that emphasizes rapid force expression tends to improve early RFD more efficiently than heavy slow lifting alone

In other words:

Strength raises the ceiling, but RFD determines how much of that strength you can access in time.

This doesn’t contradict the earlier findings — it completes them.

Why heavy lifting can improve speed (and why that’s not the whole story)

Heavy resistance training can improve speed-related outcomes because:

• It increases maximal force capacity

• It improves later-phase force expression

• It reduces the relative effort required for submaximal tasks

These effects are especially pronounced in less-trained individuals, where neural and strength adaptations occur quickly.

But as training age increases:

• Gains from heavy lifting alone tend to plateau

• Improvements in early RFD become more dependent on how force is applied, not just how much force exists

• Intent, velocity, and task demands matter more

This is why modern strength and conditioning rarely treats “strength” as a single quality.

The practical takeaway

The research does not support the idea that strength and speed are the same thing — nor does it suggest they should be trained in isolation from one another.

A more accurate summary would be:

• Maximal strength is foundational

• RFD and power are time-dependent expressions of that strength

• Training adaptations are specific to how force is produced and practiced

Heavy lifting is valuable.

Explosive intent is valuable.

Task specificity is valuable.

The mistake is pretending one of these replaces the others.

Why this matters clinically and athletically

Oversimplifying strength as a catch-all explanation:

• Encourages one-size-fits-all programming

• Obscures why some strong people still struggle with speed or reactivity

• Makes it harder to explain plateaus to patients and athletes

A more nuanced view helps us:

• Program more intelligently

• Explain progress more honestly

• Avoid turning good research into bad dogma

Final thought

Old papers aren’t wrong — they’re just incomplete when stripped of context.

Strength is powerful.

But how fast you can use it depends on how you train it.