Muscle Biomechanics

faster

faster

the _ the contraction concentrically, the weaker we are

increases

maximum velocity _ as maximum force increases

actin-myosin

the force comes from the _ overlap

maximum

in the middle of range of motion for joint, muscles produce _ force because of maximum actin-myosin overlap

shorter; longer

at _ resting lengths, force comes from actin and myosin bonds

at _ resting lengths, force comes from fibers and elastic tension in passive tissues

stretch-shortening cycle

An eccentric contraction following immediately by a concentric contraction

Takes advantage of two musculoskeletal traits:

• Elastic recoil of the passive tissues (SEC and PEC) of the muscle-tendon unit

• Stretch reflex: activating the muscle that has been stretched (muscle spindles)

muscle power

muscle force x contraction velocity

1/3

peak power occurs at the most concave part of the curve at _ max force and velocity

increases

• Moderately elevated temperature _ speed of nerve and muscle function, shifting the F-V curve upwards

• Most efficient temp:  101.3

EMD

is significantly longer in children

• time needed to take the slack to of the tendons

fast twitch

delay = 20 ms

slow twitch

delay = 100ms

torque

we more commonly assess the amount of _ a muscle group can generate at a joint

cross sectional, training

The tension generating capability of a muscle is related to its _ area and its _ state

90 N/cm²

a muscle can generate _ of force

rotary component

• Perpendicular to the bone

• Causes motion to occur

stabilizing component

• Parallel to the bone

• Brings the two articular surfaces closer together

purpose of patella

to increase the mechanical advantage of the quadriceps muscles by increasing the rotary component

electromyography (EMG)

• Recording the electrical stimulus (input) from the nerve into the muscle

• Measures neural activity not force

• no defined pattern

Electrode Examples:

• cabled “hard wired” system

• wireless/telemetric system - cabes

• fine wire EMG electrodes

myalgia

muscle pain from any disorder

myopathy

Any disease of muscle

strain

Tearing of a muscle

sarcopenia

The wasting of muscle tissue and decrease in strength associated with aging

cachexia

The wasting of muscle tissue associated with disease

cramps

moderate to severe muscle spasms and pain. 

• Usually attributed to electrolyte imbalances, Ca and Mg deficiencies, or dehydration

DOMS

Pain and swelling 24-72 hours after strenuous exercise related to microtearing of the muscle tissue

• eccentric exercise causes most soreness

contusions

Muscle bruises caused by compressive forces sustained during impacts

myositis ossificans

calcifications of muscle tissue caused by repeated or serious contusions

• Body will resorb in about 2 months

Rhabdomyolysis

• Caused by crushing or extremely destructive exercise

• If a large number of muscles are crushed, myoglobin will pour into the bloodstream

• Will clog kidneys, leading to kidney failure and ultimately heart failure

muscular dystrophy

• A category of diseases, not one disease

• Hereditary

• Usually diagnosed in childhood

• Muscles lack a protein, “dystrophin”

• This results in a weakened sarcolemma

• If the sacrolemma tears, the muscle cannot function

• No known cure

Duchenne’s muscular dystrophy

• Most common type of muscular dystrophy

• Mainly in males (1:3500 boys) because it is inherited via X chromosome.

• Onset between 2 and 10 years

• Victims rarely live past 20 years

myotonic dystrophy

• Onset between birth and age 60

• Slow progressing

• Victims have muscle spasms, muscle weakness, and heart arrythymia

fibromyalgia

• Idiopathic chronic pain syndrome

• Symptoms include musculoskeletal pain, fatigue, sleep disorders, and headache

• Affects 2% of people, mostly women

• Pain must be present in at least 11 of 18 trigger points

• Treated with antidepressants, pain medication, and exercise