Kinesiolgy

Acromioclavicular Joint (AC Joint) Overview and Injuries

The abbreviation AC or AC joint stands for the acromioclavicular joint. The acromioclavicular is one of the three articulations of the shoulder girdle. See the shoulder complex for a general overview of the shoulder girdle and its joints.

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Close-Packed Position (joints)

A close-packed position in a synovial joint is the position in which the joint surfaces become fully congruent and their area of contact is at a maximum. This position has been described as a "screwed in" or "screwed home" position, where the joint is tightly compressed and the ligaments and joint capsule are tense, allowing no more movement. This type of position results in the bones being "locked together" is essence, as if not joint existed between them, allowing them to transmit static forces most efficiently because the joint is extremely stable.

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What is the Frontal Plane?

The frontal plane is one of several anatomical planes which are used as positional references in biomechanics, kinesiology, anatomy, and related fields. They are especially useful for describing movements. The frontal plane, also called the coronal or lateral plane, is an imaginary plane (a flat, two-dimensional surface) that passes through one side of the body to the other and divides the body into front and back halfs (anterior and posterior). It is perpendicular to any sagittal plane. Many different frontal planes can be imagined to pass through the body, but we usually refer to the frontal plane intersecting the midpoint or center of gravity of the body, to divide it into equal front and back halves. This is the cardinal frontal plane. While there can be many frontal planes, there is only one cardinal frontal plane.

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Is the Hamstring to Quadriceps Strength Ratio Really Important?

Many strength trainees, bodybuilders, and exercisers are told that there should be a certain ratio between the strength of their hamstring and quadriceps muscles. Called the H/Q ratio and reported to be anywhere from .50 to .75 with a normative value of .60, the strength ratio of this important agonist/antagonist pairing is considered essential to the stability of the knee joint and to prevent ACL and other injuries. It is also sometimes thought to be predictive of those at risk for hamstring strain.

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Anatomical Direction Terms: A Glossary and Reference

Directional terms are widespread in all references concerning human performance, including anatomy, kinesiology, sports medicine, athletic training; and strength and bodybuilding coaching. At first, these terms can be confusing to the student of strength training but they are easy to understand once the fundamentals are studied.

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Flat Back Posture

In the "flat back"1 postural alignment, the cervical spine is slightly extended, the upper thoracic spine is in flexion, the lower thoracic straight, the lumber straight (flexed) and the pelvis is posteriorly tilted. Bibliography item kendall not found. See Muscles: Testing and Function, with Posture and Pain by Kendall, et al.

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Muscle Roles: What is an Agonist, Antagonist, Stabilizer, Fixator or Neutralizer Muscle?

Perhaps the biggest misunderstanding about how skeletal muscles function to produce the body's movements concerns their particular role. Most people think that a muscle performs ONE particular and very defined role and that they always perform this role. This is not how it works. Muscles must work together to produce different bodily movements and a particular muscle's role may change depending on the movement.

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The Shoulder Complex: Demystifying the Shoulder with Eric Beard

The shoulder joint itself is known as the glenohumeral joint. It is a multi-axial ball and socket enarthrodial joint. This joint is the articulation between the glenoid fossa of the scapula and the head of the humerus. This is the area that most people think of as the shoulder joint. The humerus is, however, one bone of the shoulder.

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Ideal Postural Alignment (Normal Posture)

In this postural alignment the neck is slightly extended, the upper back is in slight flexion, and the lower back is in slight extension.1 The slightly extended inward curve of the neck (cervical spine) and lower back (lumbar spine) is referred to as lordotic. In this way a normal slightly arched position of the neck and lumbar in a position of lordosis. However, this term is generally meant to mean a hyper-extended or over-arched position.

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Knees Over Toes Myth

This Knees Over Toes thread contains information debunking the prevelant myth that the knees should never travel past the toes in a squat or lunge.

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Weak Links Versus Sticking Points

A common misnomer and mixup: in other words this one derives from a mix of misnaming and confusion. In this case, however, rather than sticking points and weak links being confused themselves, it is their RELATIONSHIP that is confused.

All this leads to an analysis of lifts based on muscular contributions at certain portions of the lift: an approach that sometimes has merits but creates false assumptions about what sticking points are versus what biomechanical weak links are.

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The Kinetic Chain: Open Versus Closed

The concept of the kinetic chain was purportedly introduced in 1955 by Arthur Steindler in his important book Kinesiology of the HUMAN BODY UNDER NORMAL AND PATHOLOGYICAL CONDITIONS. He wrote:

"We designate an open kinetic chain a combination in which the terminal joint is free. The waving of the hand is an open kinetic chain in which the action of the shoulder joint, the elbow joint, and the wrist joint are successively involved.

A closed kinetic chain, on the other hand, is one in which the terminal joint meets with some considerable external resistance which prohibits or restrains its free motion. Eventually, the external resistance may be overcome and the peripheral portion of the joint may move against this resistance, for instance, in pushing a cart or lifting a load; or the external resistance is absolute, in which case the proximal part moves against the peripheral, as for instance, in chinning oneself on a horizontal bar; or the limitations of the muscular effort may assert itself both peripherally and proximally and may be insurmountable, in which case no visible motion is produced. Only in the latter instance is the kinetic chain strictly and absolutely closed.

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