Push-Off in Running: Science, Belief, and a Persistent Confusion of Cause and Effect

For decades, runners and coaches have been taught a simple explanation of running: we move forward by pushing off the ground with the support leg.

It feels obvious.
It looks obvious.
It kind of makes sense.

And that is precisely why it has survived for so long.

 

A man would rather believe in what he prefers.
— René Descartes

 

But intuition and sensation are not mechanics. They can be very deceptive. When examined carefully, the push-off explanation turns out to be less a scientific conclusion than a misunderstanding of what we feel and what actually causes motion.

How Push-Off Became “Obvious” Without Ever Being Proven

Before addressing push-off directly, it is important to acknowledge a broader issue in movement science. As Professor Mark Latash noted, despite impressive technical progress, biomechanics still struggles to provide clear, reliable recommendations for practitioners, and intuition often outweighs scientific guidance.

Running exemplifies this problem. Although we can describe running in great detail, the mechanism behind it has remained poorly understood. Peter Cavanagh pointed this out when he observed that, even with modern technology, biomechanics was still trying to answer questions posed many decades earlier.

In this gap between measurement and understanding, early assumptions were allowed to solidify into belief.

The push-off idea did not emerge from direct proof. It emerged because runners experience strong pressure under the foot during ground contact and instinctively interpret that sensation as active effort. The faster or harder the run, the stronger the pressure—and the more convincing the interpretation becomes.

This is where the fundamental mistake begins.

The Core Error: Confusing Effect With Cause

Pressure under the foot is not evidence of pushing.
It is a reaction to changes in velocity of the body’s center of mass.

As running speed increases, momentum changes more rapidly during support. According to basic physics, greater changes in velocity require greater ground reaction forces. These forces are felt as pressure under the foot.

But pressure is an effect, not a cause.

The sensation is real. The interpretation is wrong.

Mistaking pressure for propulsion is a classic confusion of cause and effect, and it forms the psychological foundation of the push-off belief.

What the Evidence Actually Shows

When objective measurements replaced sensation-based interpretation, they consistently contradicted the push-off model.

→ Electromyographic studies beginning in the 1970s showed that the muscles assumed to produce push-off—especially the quadriceps—are largely inactive during the phase when propulsion is supposed to occur. Activity of the leg extensors decreases before toe-off rather than increasing. This contradiction became known as the Extensor Paradox.

→ Independent biomechanical studies of sprinting by N. A. Fesenko and V.V. Tupa arrived at closely related conclusions from movement analysis. Their work showed that full extension of the support leg is not necessary for effective running and that many traditional drills emphasizing exaggerated extension and push-off lack biomechanical justification. The movement pattern itself does not depend on extension-driven propulsion.

→ Mechanical principles reinforce these findings. Muscles are internal forces, and internal forces cannot change the momentum of the body’s center of mass. To move forward, an external force is required. In running, the only available external force is gravity.

→ Kinematic analysis further undermines the push-off idea through unavoidable geometrical and anatomical constraints. As described by Zatsiorsky, joint mechanics impose two limits: geometrically, the effectiveness of joint motion decreases as a limb approaches full extension; anatomically, velocity is reduced before full extension to avoid catastrophic injury. As a result, maximal effective motion occurs well before full extension.

→ This pattern appears across sports. In throwing and skating, contact ends before full extension is reached, and full extension occurs only after contact has been lost. Running follows the same rule. Analyses show that skilled runners—both humans and animals—use a takeoff pattern with minimal contribution from leg extension, emphasizing rotational movement instead. Even elite sprinters demonstrate high leg rotation velocities without unusually high extension velocities.

→ Performance data point in the same direction. As running speed increases, vertical work decreases. Better runners rise less, not more, and their takeoff angles become lower rather than higher. If push-off were the driving mechanism, the opposite pattern would be expected.

→ Finally, time itself presents a constraint. In elite sprinting, total ground contact lasts only a few hundredths of a second. The supposed propulsive phase occupies a time window too short to be meaningfully controlled by the nervous system. A mechanism that cannot be controlled cannot serve as the basis of technique.

→ Even studies of high jumping reinforce this conclusion. Vertical velocity increases only until ground reaction force drops to approximately one body weight—long before full extension of the leg. Extension continues, but acceleration does not. Extension is present, but it is not the cause.

Conclusion: Clearing the Ground for a Better Explanation

Push-off is not the engine of running. It is a misinterpretation of sensation—a confusion of effect with cause.

The pressure felt under the foot reflects changes in velocity and interaction with the ground, not a propulsive action that drives the runner forward. Muscle activity patterns, mechanical laws, anatomical constraints, and performance data all point in the same direction.

As Thomas Kuhn observed, paradigms often persist not because they are correct, but because people become accustomed to interpreting familiar data through them.

My position is simple: running requires a more logical explanation—one that is consistent with physics, observable in real movement, and usable in practice.

Replacing belief with logic is progress.