Movement is generally referenced from the anatomical position in a plane and about an axis.

There are 3 cardinal planes and 3 cardinal axes

1. Sagital plane splits the body into left and right

2. The transverse plane splits the body into up and down

3. The frontal plane splits the body into front and back

There are two fundamental movements of a segment possible in each plane. This is determined by the distal segment orientation in relation to joint position.

Fundamental movements of a segment relate the segment motion only to rotation about an axis in a plane. Fundamental movements of a joint relate the rotation of one segment to the rotation of another.

1. Stretch: 2 forces pull or 1 is anchored and the other pulls

2. Compress: 2 pressing or 1 anchored and 1 with a force

3. Shear: like pushing skin; 1 side can be anchored

4. Bend: 1 side is stretched and 1 side is compressed, like pushing on a finger

Ɛ = ΔL/L. It is usually given as a percent so there is no units

1. What type of material it is

2. The modulus of elasticity

1. determining the cross sectional area of a specimen

2. Clamping specimen to testing hardware

3. Determining the load rate

4. Properly pre-conditioning the specimen

5. Reducing the in-vivo environment as far as temperature, hydration, innervations, and kinematics/kinetics are concerned.

1. protect internal organs

2. allow for locomotion

3. provide stability

4. Site for RBC production

The axial skeleton has 80 bones

The appendicular skeleton has 126

1. Superficial: made of 2 layers (surface and deeper). The surface layer has flat bundles of collagen fibers which are crimped. The deep layer has dense collagen fibers lying parallel to the joint surface. The superficial zone contains a high percentage of water.

2. Transitional: Contains large diamete collagen fiberrs that lie parallel tothe joint surface, but less parallel than in the superficial zone

3. The deep zone: large number of large collagen bundles running perpendicular to the joint surface. There is a high proteoglycan content and low water content

4. Calcified: marks the transition from cartilage to stiffer subchondral bone. The collagen fibers from deep zone anchor the cartilage to the bone by fixing themselves into the subchondral bone

Tendons attach muscle to bone and transmits tensile loads from muscle to bone

   A tendon transmits force from the associated muscle to the bone. It connects to the muscle at the myotendinous junction. Tendons are surrounded by a loose connective tissue that forms a sheath that protects the tendon during gliding.

Both tendons and ligaments are dense connective tissue referred to as parallel-fibered collagenous tissue. They are sparsely vascularized which makes it difficult to repair and regenerate. They are compose largely of collagen and function best in tension. The great mechanical stability of collagen gives tendons and ligaments their strength and flexibility. They both consist of relatively few cells called fibroblasts (20%) and an extra-cellular matrix (80%). Although they are made of the same material, they are built differently.

·         Zone 1- at the end of the tendon

·         Zone 2 – The collagen fibers intermesh with fibro-cartilage

·         Zone 3 – Fibro-cartilage becomes mineralized fibro-cartilage

·         Zone 4 – Mineralized fibrocartilage merges into cortical bone

Both tendons and ligaments are viscoelastic structures. Tendons are strong to sustain high tensile forces resulting from muscle contraction. Tendons are flexible enough to angulate around bony surfaces to change direction of muscle pull. Ligaments are pliable and flexible allowing natural movements of bones. Ligaments are sufficiently strong and inextensible to offer resistance to applied forces. They both sustain predominantly tensile loads.

Under normal conditions in vivo, tendons and ligaments are stressed only to about 1/3 of P_max which is the safety factor. The upper limit for physiological strain in tendons and ligaments is from 2 to 5% (during running and jumping). Experiments in sheep suggest that, during normal activity, a tendon in vivo is subjected to less than ¼ of its ultimate stress.

Injury mechanisms for tendons and ligaments are similar. When a ligament is subjected to loading that exceeds the physiological range, micro failure takes place even before the yield point. When P_lim is exceeded, the ligament begins to undergo gross failure and the joint begins to displace abnormally.

Category 1 of ligament injuries ­– produce negligible clinical symptoms but some pain and no joint instability

Category 2 – produce severe pain, some joint instability; progressive failure of collagen fibers; strength and stiffness decreases by 50%

Category 3 – severe pain during trauma but less afterward; joint completely unstable; most collagen fibers are ruptured

Aging causes physical properties of collagen closely associated with number and quality of cross-links. During maturation, number and quality of cross-links increases thus increasing tensile strength. As aging progresses, collagen reaches a plateau to strength and stiffness eventually decreasing

Immobilization causes tissues to remodel in response to mechanical demands. Physical training increases tensile strength in tendons and ligament-bone interface.

Nonsteroidal and anti-inflammatory drugs are frequently used in the treatment of musculoskeletal conditions. It’s used in treatment of soft-tissue inflammatory disorders. Studies have shown that treatment with these drugs (indomethacin) increased tensile strength of tendon (i.e. increase total collagen content). Short-term administration of these drugs would not hurt tendon healing and would increase the rate of biomechanical restoration of the tissue. As strength increases, the tendons become stiffer.

In terms of structure, there are two types of joints. Joints in which the articular surfaces of the bones are united by fibrous tissue or cartilage are fibrous or cartilaginous joints. Joints in which the articular surfaces are not attached to each other but are held in contact by a sleeve of fibrous tissue supported by ligaments are called synovial joints.

Fibrous joints are called syndesmosis joints. The degree of movement is determined by the amount of fibrous tissue between the articular surfaces. In general, the smaller the amount of fibrous tissue the more limited the movement.  Two types of fibrous joints are membraneous and sutural

There are two types of cartilaginous joints: synchondroses, symphyses.

Each articular surface is covered by hyaline cartilage. Hyaline cartilage enhances cartilage because there is a small coefficient of friction (.0025).

The type of movement in a joint depends on the type of the joint and the shape of the articular surfaces. Degrees of freedom – with respect to the joint axes, there are 6 degrees of freedom. The 6 DOF are: 3 linear directions (along each axis) and 3 rotations (about each axes). Not all synovial joints have all six DOF. In multi-joint movements, the DOF in the segmental chain is the sum of the DOF in all joints.

Joint stability refers to the strength of the bond between the bones. The stronger the bone, the more stable the joint. Joint flexibility refers to the degree of movement in the joint. In general, the greater stability of the joint, the lower flexibility of the joint.

The condyloid joint allows movement in two directions. The saddle joint allows flex/ext, ab/adduction and circumduction. Rotation joint allows a rotation about the longitudinal axis of bone. The hinge joint allows only one movement, flex/ext.  Gliding joint allows short gliding movements in many directions not around any specific axis. Ball and socket joint allows movement about an indefinite number of axes. Allow flex/ext, ab/ad, circumduction, and int/ext rotation.

Skeletal muscle attaches to the skeleton and causes movement. This type of muscle is the most abundant tissue in the human body (accounting for 40-45% of total body weight). There are 430 skeletal muscles found in pairs on the right and left sides of the body.  The most vigorous movements are produced by fewer than 80 pairs.

The structural unit of skeletal muscle is the fiber which are long cylindrical cells with many nuclei. Fibers range in thickness from 10 to 100 um and in length from about 1 to 30cm. Each fiber is covered by loose connective tissue called endomysium. Fibers are organized into various size bundles called fascicles which are covered by the perimysium. Surrounding the whole muscle is fascia called the epimysium.

Each muscle fiber is composed of myofibrils (the contracting element of the muscle). The myofibrils lie parallel to each other within the sarcoplasm of the muscle fiber. Myofibrils vary in number depending on the diameter of the fiber.

The theory of muscle contraction that is most widely held is the sliding filament theory which says the actin and myosin slide towards the center. There is an active shortening of the sarcomere which results from the relative movement of the acting and myosin filaments past on another (each filament retains its original length). The force of contraction is developed by the myosin heads (or cross-bridges) in the region of overlap (A band). This movement of the cross-bridges in contact with the actin filaments produces a sliding of the actin towards the center of the sarcomere.

An electrical impulse causes an action potential which releases ACH and opens up a gate. Sodium (+) rushes in and Potassium (-) rushes out which depolarizes this. This triggers sarcomere to release Ca+ which floods the actin and myosin. These bind to troponin and pulls it off the actin.

·         There are 5 different shapes of parallel fiber arrangements: flat, fusiform, strap, radiate, and convergent

o   The fiber force in a parallel muscle fiber arrangement is in the same direction as the musculature which results in a greater range of shortening and greater movement velocity.

·         In a pennate arrangement, the fibers run diagonally with respect to a central tendon running the length of the muscle. The general shape of a pennate muscle is feather-like with fascicles being short and at an angle to the length of the muscle. The force generate by each fiber is in a different direction than the muscle force. The fibers are shorts and the change in individual fiber length is not equal to the change in muscle length. Pennate muscles have a large cross sectional area and generate more strength than parallel muscle fibers.

·         There are three types of pennate muscles: unipennate, bipennate, multipennate.

·         Type 1 slow twitch fibers – slow contraction times for prolonged, low intensity work

·         type IIa fast twitch oxidative glycolytic – can sustain activity for long periods of contract with a burst of activity and then fatigue

·         type IIb fast twitch glycolytic – generate rapid force production and then fatigue quickly.

The motor unit is the functional unit of a skeletal muscle. A motor unit includes a single motor neuron and all of the fibers innervated by it (this is the smallest part of the muscle that can be made to contract independently). When stimulated, all muscle fibers in a motor unit respond as one (i.e. all-or-none response). The number of muscle fibers forming a motor unit closely related to the degree of control required of the muscle. In small muscles that perform fine movement, the motor unit may contain less than a dozen muscle fibers. In large muscles that perform coarse movements, the motor unit may contain from 1000 to 2000 muscle fibers.

• In a concentric contraction muscles develop sufficient tension to overcome the resistance (muscle shortens while developing tension). In eccentric contraction muscles cannot develop sufficient tension to overcome the resistance (muscle lengthens while developing tension). In isometric contraction muscles develop sufficient tension to balance the resistance (muscle length stays the same while developing tension).

Length-tension relationship states that the force that a muscle can generate varies with the length at which it is held when stimulated. If the relationship is measured in a whole muscle, the tension produced by both active and passive components must be considered.

In the force time relationship, the force generated by a muscle is proportional to the contraction time. The longer the contraction time, the greater the force developed up to the point of maximum tension.

Increasing the temperature increases the conduction velocity across the sarcolemma thus increasing the frequency of stimulation and the muscle force. Increasing the temp also causes greater activity of muscle metabolism thus increasing the efficiency of contraction. Muscle performs more work when it shortens immediately after being stretched from a concentrically contracted state. This may be a result of the elastic energy stored during stretching and also due to energy stored in the contractile tissue.