Module 2: Biomechanics

2.1 Skeletal and Muscular Systems

The skeletal system can be divided into two parts, the axial skeleton and the appendicular skeleton. The axial skeleton includes the skull, spinal column, ribs and sternum. The appendicular skeleton includes everything else (the shoulder complex, arms, hips and legs).

Must Know:Not every bone in the body needs to be memorized, as there are two hundred and six of them. However, the location of the major bones of the body should be known. These include:

Phalanges (fingers and toes) Ulna (forearm, closest to the body in anatomical position/hands facing

forward) Radius (forearm, furthest from the body in anatomical position) Humerus (upper arm) Clavicle (collar bone) Cranium (skull/head) Mandible (jaw) Sternum and ribs (breast bone) Pelvis (hip, each side of which includes the ilium, ischium and pubis) Femur (thigh) Tibia (larger bone of the lower leg, medial to fibula) Fibula (smaller bone of the lower leg, lateral to tibia) Talus (ankle) Calcaneus (heel)

The bones of the spine are important to know as well. From the top of the spine there are, in order:

Seven cervical vertebrae Twelve thoracic vertebrae Five lumbar vertebrae Five sacral vertebrae (these are fused together)

There are three major types of joints, fibrous joints, cartilaginous joints and synovial joints. Fibrous joints, such as the sutures within the skull, allow little to know movement. Cartilaginous joints allow some movement and are found between the vertebrae as intervertebral discs.

The joint type we are most familiar with are synovial joints (like the elbow or knee), which allow considerable movement. Synovial joints can further be divided into uniaxial (allow movement in one plane of motion such as the elbow), biaxial (allow movement in two planes of motion such as the ankle) and multi-axial joints (such as the hip which allows movement in all three planes of motion).

Major joints of the body:Ankle- biaxial Knee- uniaxialHip- multi-axialShoulder-multi-axialElbow-uniaxialWrist-biaxial

Must Know:Like the skeletal system, there are too many individual muscles to memorize. However, the location of the major muscles of the body should be known. These include:

Gastrocnemius and soleus muscles (calf muscles on posterior of lower leg, responsible for ankle plantar flexion)

Tibialis anterior (anterior of lower leg, responsible for ankle dorsiflexion) Quadriceps (includes vastus medialis, vastus intermedius, vastus lateralis

and rectus femoris, located on anterior of thigh, responsible for knee extension)

Hamstrings (includes semimembranosus, semitendinosus and biceps femoris, located on posterior thigh, responsible for knee flexion)

Gluteus maximus (located on posterior of hip, responsible for hip extension) Latissimus dorsi (located on back, responsible for shoulder horizontal

abduction, extension and adduction) Pectoralis major (located on chest, responsible for shoulder horizontal

adduction and flexion) Deltoids (includes posterior, medial and anterior, responsible for shoulder

flexion and abduction) Biceps brachii (anterior of upper arm, responsible for elbow flexion) Triceps brachii (posterior of upper arm, responsible for elbow extension)

Muscles attach in two positions, the origin and the insertion. The origin is the proximal attachment, meaning that this attachment is closer to the center of the body. The insertion is the distal attachment, meaning that this attachment is further away from the center of the body.

During a movement, muscles can perform one of three roles:Agonist: the primary mover of the exercise, during a biceps curl this role would be served by the biceps brachii muscle.Antagonist: the muscle that directly opposes the movement, during a biceps curl this role would be served by the triceps brachii muscle.Synergist: the muscle(s) that function either as secondary movers (muscles that aid in the movement) or stabilizers (muscles that stabilize the joints surrounding the moving joint), during a biceps curl the secondary mover includes the brachialis muscles and the stabilizers include the muscles that surround the shoulder and wrist joints.

2.2 Anatomical Planes and Movement

Anatomical position is defined as standing upright with the hands at the sides with the palms facing forward. All movements are described from this position.

The sagittal plane cuts the body into right and left halves, the frontal plane cuts the body into posterior and anterior halves and the transverse plane cuts the body into top (superior) and bottom (inferior) halves.

Common Question:What plane of motion is a movement performed in?

Sagittal plane movements include any forward, backward, vertical or downward motions. Includes running, jumping, squats and bench press.

Frontal (coronal) plane movements include any side-to-side or lateral motions. Includes jumping jacks, side shuffles and dumbbell lateral raises.

Transverse plane movements include any rotational movements. Includes a golf or baseball swing and any twisting motions.

Must Know:

Movement Definition Joint(s) Plane of Motion

Flexion Angle between bones increases Knee, hip, shoulder, elbow, lower back and neck

Sagittal

Extension Angle between bones decreases Knee, hip, shoulder, elbow, lower back and neck

Sagittal

Abduction Movement away from the mid-line Hip, shoulder FrontalAdduction Movement toward the mid-line Hip, shoulder FrontalLeft Tilt Movement away from the mid-line

of the body to the leftNeck, lower back

Frontal

Right Tilt Movement away from the mid-line of the body to the right

Neck, lower back

Frontal

Internal Rotation

Rotational toward the mid-line Hip, shoulder Transverse

External Rotation

Rotation away from the mid-line Hip, Shoulder Transverse

Horizontal Abduction

Movement away from the mid-line with the limb at ninety degrees

Hip, Shoulder Transverse

Horizontal Adduction

Movement toward the mid-line with the limb at ninety degrees

Hip, Shoulder Transverse

Left Rotation

Counter-clockwise rotation Neck, lower back

Transverse

Right Rotation

Clockwise rotation Neck, lower back

Transverse

Dorsiflexion

Movement of the toes toward the shin

Ankle Sagittal

Plantar Flexion

Movement of the toes away from the shin

Ankle Sagittal

Ulnar Deviation

Movement of the hand toward the mid-line

Wrist Frontal

Radial Deviation

Movement of the hand away from the mid-line

Wrist Frontal

Inversion Movement of the foot toward the mid-line

Ankle Frontal

Eversion Movement of the foot away from the mid-line

Ankle Frontal

2.3 The Lever System

Movement occurs when muscle pulls on bone, rotating it about a joint. Another way to look at it is that movement occurs when force acts on a lever about an axis (fulcrum). The perpendicular distance between this axis and point of force application is called the moment arm. Typically two forces acting on lever, they are known as the force or effort arm and the resistance arm. As there are two forces, there are also two moment arms.

As a lever is rotating about an axis, rotational force will be produced. This rotational force is called torque, which is the product of the force and the moment arm.

Key Point:Torque = Force x Moment arm

There are three types of levers: Type I - the force arm and resistance arm are on different sides of the

fulcrum. Type II- the resistance arm is between the force arm and fulcrum. Type III- the force arm is between the resistance arm and fulcrum.

Mechanical advantage is the ratio of the moment arm through which an applied force acts to that through which a resistive force acts. A mechanical advantage greater than 1.0 allows the applied (muscular) force to be less than the resistive force in order to produce an equal amount of torque. A mechanical advantage of less than 1.0 is a disadvantage and requires the applied force to be greater than the resistive force to produce an equal amount of torque.

Key Point:Type I levers can be mechanically advantageous or disadvantageous depending on the length of the moment arms. Type II levers will always be at a mechanical advantage because the force arm will always be greater than the resistance arm. Type III levers will always be at a mechanical disadvantage because the resistance arm will always be greater than the force arm.

Mechanical advantage can be increased in two ways: increase the length of the force arm, or decrease the length of the resistance arm. Strength differences between

Type I Lever

Type II Lever

Type III Lever

individuals with similar training backgrounds and muscle mass can be accounted for due to differences in tendon insertion. Those with tendon insertions further away from a joint can produce less muscular force to produce the same amount of torque.

During real world movements both the resistance and force arm will change through the range of motion. For example, during a biceps curl both the perpendicular distance between the center of mass of the dumbbell and the elbow joint and the perpendicular distance between the elbow joint and biceps tendon insertion will increase from the bottom of the movement until the elbow is at ninety degrees and will decrease from this point to the top of the movement. Therefore the mechanical advantage of this lever will continually change throughout the range of motion.

The position of the movement where the mechanical advantage is the lowest is referred to as the “sticking point”. It is in this position where the muscular force must be the greatest in order to produce enough torque to continue the movement.

The human body has evolved some structures to improve its mechanical advantage. For example, the patella causes the force arm to produce more torque by increasing the perpendicular distance between the quadriceps tendon and the knee joint. Without the patella, the knee joint would have to produce much more force during knee extension.

Most of the joints of the human body are third class levers. Therefore, most of the movements humans perform are at a mechanical disadvantage. However, the need to produce more muscular force to overcome external resistance does come with a distinct benefit. Because the resistance arm is always greater than the force arm, small displacements of the force arm while cause larger displacements of the resistance arm. In other words, a small change in muscle length leads to big changes in joint or limb position. This lack of mechanical advantage actually results in a large speed advantage.

Resistance machines sometimes use cam levers that will alter the pattern of resistance arm length throughout the range of motion.

2.4 Resistance Systems and Injury Prevention

To describe movement, the variables of force, work and power are used. Force can be derived from many sources (see below). Work is used to quantify the amount of force needed to complete a movement, or series of movement. Work is the product of force and distance (W = F x d). Power is the rate of work (P = W / time or P = (F x d) / time) and can also be expressed as the produce of force and velocity (P = F x v).

Gravity is the most common source of resistance, or force in strength and conditioning and is utilized during bodyweight, free weight and weight stack training. In this context force is the product of mass and acceleration (F = m x a). This dictates that overcoming inertia, or changing the speed of a mass (whether from a static position or after already moving) requires additional force.

Friction is another resistance source and can be observed during sled pushes or moving one surface over the other. The force needed to overcome friction is derived from the normal force of the object (the vertical line of mass) and the coefficient of friction (k) (F = F(n) x k). The coefficient of friction is based on the roughness of the

surface. Ice would have a low coefficient of friction and pavement would have a high coefficient of friction.

Two other common forms of resistance that are found in resistance training equipment are fluid and elastic resistance. Both of these involve variable resistance in which velocity (fluid resistance) and distance (elastic resistance). The force produced through fluid resistance is a product of velocity and a constant, k, that is based on the viscosity of the fluid (F = v x k). The force produced with elastic resistance is a product of an elastic coefficient of resistant, k, and the distance the elastic is stretched (F = d x k).

Common areas of injury during training are the shoulders, knees and lower back. The shoulder is prone to injury during weight training because of its structure and the forces to which it is subjected. Shoulder injury risk can be reduced by performing a warm up with relatively light weights, following a program that exercises the shoulders in a balanced way and exercising at a controlled speed.

The knee is prone to injury because of its location between two long levers. To prevent knee injuries one should always perform a sufficient warm-up, utilize appropriate loads and minimize the use of wraps to the heaviest sets.

The low back is the most common area of injury. Prevention steps include: flatten the back during the lift to stabilize the lumbar spine (be sure not to hyperextend the back), increase the intra-abdominal pressure to stabilize the spine. This can be accomplished with conscious effort, use of a weight belt or with the valsalva maneuver.

A weight belt should only be used for structural exercises (those that load the axial spine directly such as squats or the deadlift) and only for heavy resistance sets (not warm-up sets). The valsalva maneuver is performed by holding the breath in order to create a fluid ball within the torso to stabilize the spine. Anyone who has high blood pressure or CV disease should avoid the valsalva maneuver.

Must Know:Reducing the Risk of Strength Training Injuries

Perform one or more warm-up sets with relatively light weights, particularly for exercises that involve extensive use of the shoulder or knee.

Perform basic exercises through a full ROM. Use relatively light weights when introducing new exercises or resuming

training after a layoff of two or more weeks. Do not ignore pain in or around the joints. Never attempt lifting maximal loads without proper preparation, which

includes technique instruction in the exercise movement and practice with lighter weights.

Performing several variations of an exercise results in more complete muscle development and joint stability.

Take care when incorporating plyometric drills into a training program.

Stages of Tissue HealingInflammation (Occurs during the 2-3 days after the injury)

Exhibited by pain, swelling, redness Decreased collagen synthesis occurs during this time

Repair (Occurs during the 2-3 Days to 2 Months after the injury) Collagen fiber production is the main healing process Stage is marked by decreased collagen fiber organization Decreased number of inflammatory cells shown during stage

Remodeling (Occurs during the 2-4 Months after injury) Proper collagen fiber alignment occurs Results in increased tissue strength

Common Question:What is the rehabilitative strategy during each stage of tissue healing and what other training can occur during the stage?

Inflammation Stage Goal of stage is prevention of new tissue disruptions and prolonged

inflammation with the use of relative rest and passive modalities Function of cardiorespiratory and surrounding neuromusculoskeletal

systems must be maintained by training other areas No active exercise for the injured area (for unaffected areas only)

Repair Stage Goal of stage is prevention of excessive muscle atrophy and joint

deterioration of the injured area Function of the neuromusculoskeletal and cardiorespiratory systems must

be maintained by training other areas Possible exercise options for injured area include:

o Submaximal isometric, isokinetic and isotonic exerciseo Balance and proprioceptive training activities

Remodeling Stage Goal of stage is optimization of tissue function Progressive loading of neuromusculoskeletal and cardiorespiratory systems

as needed (begin to integrate injured area) Possible exercise options for injured area include:

o Joint angle specific strengtheningo Velocity specific muscle activityo Closed and open kinetic chain exerciseso Proprioceptive training activities

Module 2 Practice Questions

1. Which of the following is the best example of a multiaxial joint?

A. Ankle

B. Elbow

C. Hip

D. Wrist

2. During the toe off during a running stride, what is the function of the tibialis anterior?

A. an agonist

B. a synergist

C. an antagonist

D. a prime mover

3. What is the mechanical advantage of a second class lever?

A. equal to one

B. greater than one

C. less than one

D. equal to one half

4. The anatomical plane that dissects the body into right and left halves is known as which of the following?

A. sagittal plane

B. transverse plane

C. frontal plane

D. movement plane

5. Tom is working out with a free-weight training system. Which of the following best describes the type of resistance he experiences as he exercises?

A. elastic

B. electronic

C. fluid

D. gravity

6. Margaret has severe edema and pain immediately following an injury. These are signs of this phase of tissue healing:

A. inflammation

B. repair

C. remodeling

D. return

7. Dwayne is pushing a plate weight across the rubber floor of the weight room. Which form of resistance is he utilizing during this exercise?

A. electronic

B. gravity

C. elastic

D. friction

8. Bob applied 100 newtons of force to a sled over 20 yards in a time of 10 seconds and Tom applied 50 newtons of force for 30 yards in a time of 15 seconds. Who produced the most power?

A. Bob

B. Tom

C. They produced the same amount of power

D. There is not enough information to answer this question

9. Which of the following axis of rotation in a first class lever?

A. fulcrum

B. lever

C. moment arm

D. force arm

10. How would you describe the lever system in which the muscle and resistive forces act on the same side of the fulcrum and the moment arm of the resistive force is longer than the moment arm of the muscle?

A. first class lever

B. second class lever

C. third class lever

D. all of the above

11. Jack has suffered a knee injury. In which phase of healing is it recommended that he begin sport-specific movements and speeds?

A. inflammation phase

B. repair phase

C. remodeling phase

D. any of the above

12. The long jump primarily takes place in which anatomical plane?

A. sagittal

B. frontal

C. transverse

D. static

13. Which movement is the knee making during the downward phase of the front lunge?

A. extension

B. flexion

C. abduction

D. adduction

14. Which of the following joint movements takes place in the transverse plane?

A. flexion

B. adduction

C. extension

D. horizontal adduction

15. Which of the following examples would increase the speed advantage of a muscle?

A. increasing the muscular force

B. decreasing the perpendicular distance between the joint and the tendon insertion

C. increasing the resistance

D. increasing the perpendicular distance between the joint and the tendon insertion

16. What happens to the force required to move an elastic band as the band is stretched?

A. decreases

B. remains the same

C. increases

D. becomes nothing

17. During which stage are the only exercises allowed are those that will not affect the injured limb?

A. inflammation stage

B. repair stage

C. remodel stage

D. reuse stage

18. Which of the following upper leg muscle groups and types of muscle actions are associated with the upward phase of the face down lying leg curl exercise?

Primary Muscle Group Primary Muscle Action

I. flexors eccentric

II. extensors eccentric

III. flexors concentric

IV. extensors concentric

A. II and III only

B. I and IV only

C. I and III only

D. II and IV only

19. Which of the following is an example of a uniaxial joint?

A. ankle

B. hip

C. thumb

D. knee

20. Which of the following would involve a cartilaginous joint?

A. the joint between the femur and the fibula

B. the joint between two plates of the skull

C. the joint between two cervical vertebrae

D. the joint between the humerus and the shoulder girdle

Module 2 Practice Question Answers

1. C (Module 2.1)

2. C (Module 2.1)

3. B (Module 2.3)

4. A (Module 2.2)

5. D (Module 2.4)

6. A (Module 2.4)

7. D (Module 2.4)

8. A (Module 2.4)

9. A (Module 2.3)

10. C (Module 2.3)

11. C (Module 2.4)

12. A (Module 2.2)

13. B (Module 2.2)

14. D (Module 2.2)

15. B (Module 2.3)

16. C (Module 2.4)

17. A (Module 2.4)

18. A (Module 2.2)

19. D (Module 2.1)

20. C (Module 2.1)