Anatomy and Kinesiology: Body Position and Joint Movement

Introduction
Anatomical Position
Anatomical Planes of Motion and Axes
Center of Gravity, Line of Gravity, and Postural Alignment
Joint Movement
References

 

Introduction

Human movement primarily involves two principles biomechanics and kinesiology. Biomechanics is the study of motion and causes of motion of living things, using a branch of physics known as mechanics. It forms the basis for documenting human motion (kinematics) and the causes of that motion (kinetics). Kinesiology, also known as human kinetic, is the scientific study of human movement. It's primarily based on three fields of science biomechanics, musculoskeletal anatomy, and neuromuscular physiology. Kinesiology addresses physiological, mechanical, and psychological mechanisms, and includes the study of gait, posture and body alignment, ergonomics, sports, exercise movements, and activities of daily living (ADL). In order to understand these principles you must first gain an understanding of the anatomical position, planes of motion, center of gravity, line of gravity, postural alignment and joint movement.


Anatomical Position


Anatomical position is a universally accepted reference position used to described regions and spatial relationships of the human body and to refer to body positions [1]. When in the anatomical position, the body is erect with feet together and the upper limbs positioned at the side, palms of the hand facing forward, thumbs facing away from the body, and fingers extended. Figure 1 shows me in the anatomical position. The definitions of the standard anatomical locations and positions are list in Table 1 below.

Term Definition
Anterior The front of the body
Posterior The back of the body
Superficial Located close to or on the surface of the body
Deep Below the surface of the body
Proximal Closer to the reference point
Distal Farther from the reference point
Superior Toward the head; higher
Inferior Away from the head; lower
Medial Toward the midline of the body
Lateral Away from the midline of the body; to the side
Ipsilateral On the same side
Contralateral On the opposite side
Unilateral One side
Bilateral Both sides
Prone Lying face down
Supine Lying face up
Valgus Distal segment of a joint deviates laterally. ( e.g. knock-kneed)
Varus Distal segment of a joint deviates medially. ( e.g. bow-legged)
Arm The region of the body from the shoulder to the elbow
Forearm The region of the body from the elbow to the wrist
Thigh The region of the body from the hip to the knee
Leg The region of the body from the knee to the ankle
Table 1

 

Anatomical Planes of Motion and Axes

There are three cardinal anatomical planes that pass through the body - sagittal (anteroposterior), frontal (coronal), and transverse (horizontal). The sagittal plane divides the the body into the left and right side. The frontal plane divides the body front (anterior) and back (posterior) portions. The transverse plane divides the body into the upper (superior) and lower (inferior) portions [1]. Each plane is perpendicular to the other. When movement occurs in a plane, it must rotate about an axis that has a 90 degree relationship to the plane. During activities of daily living (ADL), exercise, and sports, movement usually occurs in more than one plane at a given joint. Understanding planes and axes of the body is useful for describing the major body movements and instrumental when designing effective exercise programs. Figure 2 shows me being dissected into the three planes. Table 2 below depicts the planes of motion and their axes of rotation.

Plane Description of Plane Axis of Rotation Description of Axis Movement
Sagittal
(Anteroposterial)
Divides the body into
right and left halves
Frontal Runs medial / lateral Flexion
Extension
Hyperflexion
Hyperextension
Frontal
(Coronal or
Lateral)
Divides the body into
anterior and posterior
halves
Sagittal Runs anterior / posterior Abduction
Adduction
Lateral Flexion
Transverse
(Horizontal)
Divides the body into
superior and inferior
halves
Vertical
(longitudinal or
long)
Runs superior / inferior Internal Rotation
External Rotation
Horizontal Abduction
Horizontal Adduction
Table 2

 

Center of Gravity, Line of Gravity, and Postural Alignment

The center of gravity (COG) of an object such as the body is a theoretical point where the the weight force of the object can be considered to act. It is the point where the three planes intersect. It is the point of exact center where the body freely rotates, and the body weight is equal on all sides. When you are standing in a neutral position such as the anatomical position your center of gravity is approximately at the second sacral vertebra. The COG changes as you move away from the anatomical position.

The line of gravity (LOG) of the body is an imaginary vertical line passing through the center of gravity. It helps define proper body alignment and posture using various superficial landmarks from the head, upper extremity, trunk, and lower extremity regions as a guide. It is the downward direction of the force of gravity of the body. Think of this as a vertical force towards the center of the earth. The base of support (BOS) is the area of contact between the body and the support surface.

It is important to understand these principles as the affect balance, stability and postural alignment. Proper postural alignment helps prevent injuries during activities of daily living, exercise, or sport. It can improving your skill and performance in athlete events. I write more about this in the Biomechanics Section

 

Joint Movement

Joint movement can be described by its spatial movement pattern in relationship to the body in terms of the anatomical position. The joint type will dictate how it can move and in what plane or planes the movement occurs. For example, the hip joint allows several movements in all three planes, while the knee joint allows only two movement types in one plan. I describe these movements in detail for each major joint in other articles. For now, it is useful to understand the terms used to describe joint movement. They are listed in Table 3 below.

Movement Type Description Examples
Flexion Movement that decreases the joint angle, usually anteriorly in the sagittal plane Shoulder, knee, elbow, hip movement
Extension Movement the increases the joint angle, usually posteriorly in the sagittal plane. Shoulder, knee, elbow, hip movement
Abduction Movement away the midline of the body, usually in the frontal plane Shoulder, wrist, hip movement
Adduction Movement toward the midline of the body, usually in the frontal plane Shoulder, wrist, hip movement
Horizontal Abduction Movement away the midline of the body in the transverse plane Shoulder, wrist, hip movement
Horizontal Adduction Movement toward the midline of the body in the transverse plane Shoulder, wrist, hip movement
Internal (medial) Rotation Rotation toward away the midline of the body in the transverse plane Shoulder, hip movement
External (lateral) Adduction Rotation toward the midline of the body in the transverse plane Shoulder, hip movement
Lateral Flexion (right or left) Movement away the midline of the body in the frontal plane Neck, trunk movement
Rotation (right or left) Right or left rotation in the transverse plane Neck, trunk movement
Elevation Movement of the scapula (shoulder girdle) superiorly in the frontal plane Scapula movement
Depression Movement of the scapula (shoulder girdle) inferiorly in the frontal plane Scapula movement
Retraction Movement of the scapula (shoulder girdle) toward the spine in the transverse plane Scapula movement
Protraction Movement of the scapula (shoulder girdle) away from the spine in the transverse plane Scapula movement
Upward Rotation Superior and lateral movement of the inferior angle of the scapula (shoulder girdle)
in the frontal plane
Scapula movement
Downward Rotation Inferior and medial movement of the inferior angle of the scapula (shoulder girdle)
in the frontal plane
Scapula movement
Circumduction A compound circular movement involving flexion, extension, abduction, and adduction Shoulder, hip movement
Radial Deviation Abduction of the wrist in the frontal plane. (Same as abduction) Wrist movement
Ulnar Deviation Adduction of the wrist in the frontal plane. (Same as adduction) Wrist movement
Opposition Diagonal movement of the thumb across the palm of the hand to make contact with the
5th digit
Thumb movement
Eversion Abduction of the ankle Ankle movement
Inversion Adduction of the ankle Ankle movement
Dorsiflexion Flexing the ankle so that the foot moves anteriorly in the sagittal plane Ankle movement
Plantarflexion Extending the ankle so that the foot moves posteriorly in the sagittal plane Ankle movement
Pronation (foot / ankle) Combined movements of abduction and eversion resulting in lowering of the medial
(inner) margin of the foot.
Foot / ankle movement - Running on the inner edge of the foot.
Supination (foot / ankle) Combined movements of adduction and inversion resulting in raising of the medial
(inner) margin of the foot.
Foot / ankle movement - Running on the outer edge of the foot.
Table 3

 

References

1. Kendall F, McCreary E. Muscles: Testing and Function. 4th ed. Philadelphia: Lippincott Williams & Wilkins; 1993 In: ACSM's Resource for the Personal Trainer, 3rd ed. Thompson, W.R. ed. Baltimore: Lippincott Williams & Wilkins, 2010: 37-40.

 

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