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THE BIOMECHANICS OF RESISTANCE EXERCISE

ESSENTIALS OF STRENGTH TRAINING AND CONDITIONING CHAPTER 4

THE BIOMECHANICS OF RESISTANCE EXERCISE

The musculoskeletal system• The skeleton – (muscles can only pull on bones)

– there are 206 bones in the human body.• Axial skeleton – skull/cranium, vertebral column,

ribs, and sternum.• Appendicular skeleton – scapula, clavicle,

humerus, radius, ulna, and wrist and hand bones, os coxa, femur, patella, tibia, fibula, and ankle and foot bones.

THE BIOMECHANICS OF RESISTANCE EXERCISE• Joints – allow movement between bones.• Fibrous joint – no movement.• Cartilaginous joint – limited movement.• Synovial joint – full movement.• Hyaline cartilage – covers the end of the bones

that make up synovial joints.• Synovial fluid – is found in the joint capsule of a

synovial joint. • Synovial joints can be classified into three

groups.

THE BIOMECHANICS OF RESISTANCE EXERCISE1. Uniaxial – rotation occurs about one axis.2. Biaxial – rotation occurs around two perpendicular axes.3. Multiaxial – rotation occurs around all three perpendicular

axes.• Vertebral column – is your back bone and allows movement

to occur.

THE BIOMECHANICS OF RESISTANCE EXERCISE• Cervical vertebrae – 7 bones in the neck region.• Thoracic vertebrae – 12 bones in the upper and middle back

region.• Lumber vertebrae – 5 bones in the lower back region.• Sacrum – rear part of the pelvis.• Coccyx – tail bone.

THE BIOMECHANICS OF RESISTANCE EXERCISESkeletal musculature• All movements involve more than one muscle.• Prime mover – (agonist) the muscle most

directly involved.• Antagonist – muscle in direct opposition to the

agonist. Can be thought of as a break, especially at the end of the range of motion. Protection.

• Synergist – assists indirectly in a movement. Hold scapula in place to allow upper arm movements.

THE BIOMECHANICS OF RESISTANCE EXERCISE

Levers of the musculoskeletal system• First class lever – seesaw. R/F/E• Second class lever – wheel barrow. F/R/E• Third class lever – elbow – curls. F/E/R

• During actual movement the class of lever is determined by the arbitrary decision of where the fulcrum lies.

THE BIOMECHANICS OF RESISTANCE EXERCISEVariations in tendon insertion• If the tendon is further away from the fulcrum

what will happen?

Anatomical planes of the human body• Anatomical position• Sagittal plane – right and left• Frontal plane – anterior and posterior• Transverse plane – superior and inferior

THE BIOMECHANICS OF RESISTANCE EXERCISEBiomechanical factors in human strength• Muscle Cross-Sectional Area

• All else being equal, the force a muscle can exert is related to its CSA rather than to its volume.

• Arrangement of Muscle Fibres• Pennate muscle.• Angle of pennation – no more than 15 degrees.

THE BIOMECHANICS OF RESISTANCE EXERCISEBiomechanical factors in human strength

• Provides some enhancement of force capability for muscle contraction at high speed, particularly at the extremes of the ROM.

• Muscle Length• Muscles can generate the greatest force at its resting length.

THE BIOMECHANICS OF RESISTANCE EXERCISE

Back Injury• Erector Spinae muscles work as cables, such as

a suspension bridge.• All upper body movements must be

transferred to the ground via the back and legs.

• This put the back into a mechanical disadvantage, and therefore must generate forces much greater than the weight of the object being lifted.

THE BIOMECHANICS OF RESISTANCE EXERCISEBack Injury• 85% to 90% of disk herniation's occur in L4 to S1.• With improper technique the force on the lower back could

be as high as 10 times the weight being lifted.• Therefore the back should be in an arched position, as

opposed to a rounded position.

THE BIOMECHANICS OF RESISTANCE EXERCISEIntraabdominal Pressure• The diaphragm and deep muscles of the torso increase the

intraabdominal pressure.• The abdomen is made up mainly of fluid, fluid ball.• This fluid ball assists the athlete in lifting the weight by

supporting the vertebral column.

THE BIOMECHANICS OF RESISTANCE EXERCISE

Intraabdominal Pressure• This is done by performing the Valsalva

manoeuvre, holding one’s breath.• This increases the rigidity of the entire torso.• Dangers are – decreased blood return to the

heart, elevate blood pressure.• To reduce the side effects one must keep the

airway open, breath out slowly during the hardest part of the lift.