Lombard's Paradox describes a paradox

Paradox

Similar to Circular reasoning, A paradox is a seemingly true statement or group of statements that lead to a contradiction or a situation which seems to defy logic or intuition...

ical muscular contraction in humans. When rising to stand from a sitting

Sitting

Sitting is a rest position supported by the buttocks or thighs where the torso is more or less upright.- Sitting on the floor :The most common way of sitting on the floor involves bending the knees...

 or squatting position

Squatting position

Squatting is a posture where the weight of the body is on the feet but the knees are bent either fully or partially . In contrast, sitting, involves taking the weight of the body, at least in part, on the buttocks against the ground or a horizontal object such as a chair seat...

, both the hamstrings and quadriceps contract at the same time, despite their being antagonists

Antagonist (muscle)

Most muscles work in pairs, and when a muscle works it needs to have an agonist and an antagonist, unless the muscle's natural state is opposite to that which is produced by the muscle, example Sphincter ani externus muscle....

 to each other.

The rectus femoris biarticular muscle

Biarticular muscle

Biarticular muscles are muscles that cross two joints rather than just one, such as the hamstrings which cross both the hip and the knee. The function of these muscles is complex and often depends upon both their anatomy and the activity of other muscles at the joints in question...

 acting over the hip has a smaller hip moment arm than the hamstrings. However, the rectus femoris moment arm is greater over the knee than the hamstring knee moment. This means that contraction from both rectus femoris and hamstrings will result in hip and knee extension. Hip extension also adds a passive stretch component to rectus femoris, which results in a knee extension force. This paradox allows for efficient movement, especially during gait

Gait (human)

Human gait is the way locomotion is achieved using human limbs. Different gaits are characterized by differences in limb movement patterns, overall velocity, forces, kinetic and potential energy cycles, and changes in the contact with the surface .- Foot strike :One variable in different gaits is...

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