blank

Extensor Paradox

ex·ten·sor
/ikˈstensər/
noun
Anatomy

a muscle whose contraction extends or straightens a limb or other part of the body.

noun: extensor; plural noun: extensors; noun: extensor muscle; plural noun: extensor muscles

Origin
blank
early 18th century: from late Latin, from extens- ‘stretched out’, from the verb extendere (see extend).

par·a·dox
/ˈperəˌdäks/
noun
a seemingly absurd or self-contradictory statement or proposition that when investigated or explained may prove to be well founded or true.

Origin
mid 16th century (originally denoting a statement contrary to accepted opinion): via late Latin from Greek paradoxon ‘contrary (opinion)’, neuter adjective used as a noun, from para- ‘distinct from’ + doxa ‘opinion’.

The Extensor Paradox

The extensor paradox refers to the seemingly counterintuitive observation that the muscles responsible for extending the leg, primarily the quadriceps, are inactive during the “push-off phase” of running, despite this phase being traditionally considered crucial for generating forward propulsion. This finding challenges the conventional view of running as a series of muscular pushes and provides further evidence to support the concept of gravity as the primary driving force.

Electromyography (EMG) data, which measures the electrical activity of muscles, has consistently revealed an “electrical silence” in the leg extensor muscles during the push-off phase, indicating a lack of significant muscle contraction. This finding has been termed a paradox because it contradicts the intuitive notion that the extensor muscles should be working hardest when the leg is extending to propel the runner forward.

This apparent paradox can be explained by recognizing gravity’s dominant role in running. It is proposed that instead of actively pushing off the ground, runners should utilize gravity’s pull by falling forward. As the body falls forward, the leg extensor muscles do not need to contract forcefully because gravity is already providing the necessary force for forward propulsion. This idea is further supported by the falling rod model described in the research, which demonstrates how the angle of a runner’s forward fall determines the horizontal acceleration produced by gravity.

Research data suggests that the extensor muscles’ primary function during running is to absorb the impact of landing and to stabilize the leg as the body weight passes over the support foot. As the center of mass moves ahead of the support foot, gravity takes over as the primary propulsive force, rendering forceful contraction of the extensor muscles unnecessary.

Significance of the Extensor Paradox

The extensor paradox is significant for several reasons:

  • Supports Gravity-Based Running Paradigm: It provides evidence against the traditional push-off model of running and supports the concept of gravity as the primary motive force.
  • Highlights Efficiency of Pose Method: The findings align with the Pose Method of running, which emphasizes a controlled fall facilitated by a forward shift of body’s COG and a pulling action of the foot from the ground. This technique minimizes reliance on forceful muscular contractions and maximizes the utilization of gravity’s pull.
  • Explains “Electrical Silence” of Extensors: The paradox explains the lack of significant electrical activity in the leg extensor muscles during push-off, which would be puzzling under the traditional running model.
  • Underscores Importance of Technique: The extensor paradox emphasizes the importance of proper running technique for optimizing efficiency and minimizing muscular effort.

Dr. Romanov postulates that the extensor paradox, far from being a true paradox, is a natural consequence of the body’s adaptation to running within a gravitational field. By accepting and understanding this concept, runners can refine their technique to leverage gravity’s might, minimizing unnecessary muscular effort and enhancing their overall running efficiency.


Additional Reading

Return to Glossary

Our Glossary will help you understand Human Movement better! Take a look.

Glossary