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Forces Compression: push Tension: pull Shear: slide Torsion: rotate or twist Muscle Movement Classification Agonist A muscle that causes motion. Antagonist A muscle that can move the joint opposite to the movement produced by the agonist. Target The primary muscle intended for exercise. Synergist A muscle that assists another muscle to accomplish a movement. Stabilizer A muscle that contracts with no significant movement to maintain a posture or fixate a joint. Dynamic Stabilizer A biarticulate muscle that simultaneously shortens at the target joint and lengthens at the adjacent joint with no appreciable difference in length. Dynamic stabilization occurs during many compound movements. The dynamic stabilizer may assists in joint stabilization by countering the rotator force of an agonist. See example diagram: Hamstring weakness regarding hamstring's role in knee integrety (during squat or leg press) Antagonist Stabilizer A muscle that contracts to maintain the tension potential of a biarticulate muscle at the adjacent joint. The antagonist stabilizer may be contracted throughout or at only one extreme of the movement. The Antagonist Stabilizer are activated during many isolated exercises when biarticulate muscles are utilized. The Antagonist Stabilizer may assist in joint stabilization by countering the rotator force of an agonist. For example, the Rectus Femoris contracts during lying leg curl to counter dislocating forces of Hamstrings. See knee flexion abduction force vector diagram (Rectus Femoris and Tibialis Anterior).   Antagonist Stabilizers also act to maintain postural alignment of joints, including the vertebral column and pelvis. For example, Rectus Abdominis and Obliques counters the Erector Spinae's pull on spine during exercise like the Deadlift or Squat. This counter force prevents hyperextension of the spine, maintaining the tension potiential of the Erector Spinae. Muscle Attachments Origin (b): muscle attachment that moves least, generally more proximal. Insertion (a): muscle attachment that moves most, generally more distal. Articulation Uniarticulate A muscle that crosses one joint Biarticulate A muscle that crosses two joints Triarticulate A muscle that can move three joints Contraction Isotonic The contraction of a muscle with movement against a natural resistance. Isotonic actually means 'same tension', which is not the case with a muscle that changes in length and natural biomechanics that produce a dynamic resistance curve. This misnomer has prompted authors to propose alternative terms, such as dynamic tension or dynamic contraction. Isokinetic The contraction of a muscle against concomitant force at a constant speed. Diagnostic strength equipment implement isokinetic tension to more accurately measure strength at varying joint angles. Concentric The contraction of a muscle resulting in its shortening. Eccentric The contraction of a muscle during its lengthening. Dynamic The contractions of a muscle resulting in movement. Concentric and eccentric contraction are considered dynamic movements. Isometric The contraction of a muscle without significant movement, also referred to as static tension. Also see Isometric Training.

Tension Curve Gravity Dependant A relative large change of muscular tension is required throughout the range of motion. Muscular tension is greatest when the resistance's line of action is perpendicular to body's lever arm. Gravity dependant exercises may have various resistance curves (described below) including: bell shaped, ascending, and descending. See Gravity Vectors. Kreighbaum and Barthels (1996) classify pulleys and levers as 'gravity dependant' resistance machines alluding they merely redirect the user's applied force and do not alter the amount of resistance torque within the ROM. Fleck and Kraemer (2004) classify pulleys and levers as 'variable resistance' machines suggesting attempting to match the user's strength curve is only one purpose of variable resistance equipment. It appears equipment manufactures, most notably, Hammer Strength Equipment, position the lever to compliment the user's strength curve. See variable resistance below. Variable Resistance A relative continuous muscular tension required throughout the range of motion during a movement. Cams and variable resistance levers typically have a varying tension curve which attempt to match the user's strength curve by a preset resistance curve. Nautilus is the most famous for pioneering the variable resistance cam. Strive Fitness Equipment has designed their equipment to permit the adjustment of the cam to varying training stimulus or match the user's specific training goals. Bell Shaped A tension curve in which the muscular tension required increases then decreases. Many gravity dependant exercises tend to have a bell shaped resistance curve where muscular tension is greatest in middle of the exercise. Also see Gravity Vectors. Ascending (Peak) / A tension curve in which the muscular tension required increases throughout the range of motion until the end of concentric contraction. Also see ROM Criteria. Descending \ A tension curve in which the muscular tension required decreases throughout the range of motion until the end of concentric contraction. Resistance Curve An exercise's characteristic change of force throughout its range of motion. Also see Angle of Pull and Muscle. Anatomical Locations Anatomical position: body upright, feet together, arms hanging at sides, palms facing forward, thumbs facing away from body, fingers extended. See Anatomical Position. Anterior (ventral): Toward front Posterior (dorsal): Toward back Distal: (a) farther away from reference point, or (b) away from vertex of head Proximal: (a) closer to reference point, or (b) toward vertex of head Inferior: away from vertex of head Superior: toward vertex of head Lateral: away from sagittal midline of body Medial: toward sagittal midline of body Movement Abduction: Lateral movement away from the midline of the body Adduction: Medial movement toward the midline of the body Circumduction: circular movement (combining flexion, extension, adduction, and abduction) with no shaft rotation Extension: Straightening the joint resulting in an increase of angle Eversion: Moving sole of foot away from medial plane Flexion: Bending the joint resulting in a decrease of angle Hyperextension: extending the joint beyond anatomical position Inversion: Moving sole of foot toward medial plane Pronation: Internal rotation resulting in appendage facing downward Protrusion: Moving anteriorly (e.g.: chin out) Supination: External rotation resulting in appendage facing upward Retrusion: Moving posteriorly (e.g.: chin in) Rotation: Rotary movement around the longitudinal axis of the bone Force Origin Active: Movement or force occurring under segments own force. Passive: Movement or force occurring under out side force. Scapulohumeral Rhythm The motions of the scapula, clavicle, and humorous working together to achieve full elevation of the arm. Shoulder elevation involves humeral movement (glenohumeral joint) scapular movement (scapulothoracic joint) When the arm is fully elevated by abduction or flexion two thirds of the motion occurs in the glenohumeral joint other third occurs between the scapula and thorax. This coordinated movement is called Scapulohumeral rhythm. Initial 30 degrees of abduction/flexion is primarily glenohumeral supraspinatus initiates first few degrees of shoulder abduction see shoulder abduction force vector diagram Remaining elevation glenohumeral and scapulothoracic joints move simultaneously 2:1 ratio of glenohumeral to scapulothoracic movement Purposes of Scapulohumeral rhythm Preserves length tension relationship Prevents impingement between the humerus and acromion See example Shoulder Press. Newton's Laws of Motion Law of inertia A body in motion tends to remain in motion at the same speed in a straight line; a body at rest tens to remain at rest unless acted on by a force. Law of acceleration A change in the acceleration of a body occurs in the same direction as the force that cased it. The change in acceleration is directly proportional to the force causing it and inversely proportional to the mass of the body. Law of reaction For every action there is an opposite and equal reaction