KNPE 453 CH 6 Fatigue and muscle soreness

For unit 1 quiz 5/6

Fatigue

Two definitions:

• Decrements in muscular performance with continued effort, accompanied by sensations and tiredness

• Inability to maintain required power output to continue muscular work at given intensity

Some examples: lactate threshold, ventilatory threshold

Reversible by rest

Is task dependent

Complex phenomenon

Type, intensity of exercise

Muscle fiber type

Training status, diet

Major causes of fatigue

PCr and glycogen depletion

Accumulation of metabolic by-products (lactate, H+, Pi)

Failure of contractile mechanisms in muscle fibers

Altered Neural control of muscle contraction

PCr depletion

Coincides with fatigue

• PCr used for short term, high intensity effort

• PCr depletion can occur in <15s

• PCr depletes more quickly than total ATP

Pacing helps prevent

Peripheral fatigue

Glycogen depletion

Reserves are limited and deplete quickly

Correlated with fatigue

• Related to total glycogen depletion

• Unrelated to rate of glycogen depletion

Depletes for quickly with high intensity

Depletes more quickly during first few minutes of exercise versus later stages

Peripheral fatigue

When does the body want to burn fat?

When its also burning carbohydrates

When is fat metabolism greatly impaired?

With glycogen depletion

Metabolic by-products

Inorganic phosphate (Pi): from rapid breakdown of PCr, ATP

• accumulated during intense, short-term exercise

• excess directly impairs contractile function of myofibrils (Pi can enter sarcoplasmic reticulum and impair Ca release) Ca++ release, C++ function, ATP breakdown

Heat alters metabolic rate

• increased rate of carbohydrate utilization, glycogen depletion

• high muscle temp may impair muscle function

Hydrogen ions accumulate during brief, high-intensity exercise

• H+ accumulation causes a decrease in muscle pH (acidosis) (pH = 6.4 prevents further glycogen breakdown)

Neural transmission

Failure may occur at neruomuscular junction, preventing muscle activation

Possible causes of neural transmission failure

Decrease in ACh synthesis and release

Altered ACh breakdown in synapse

Increase in muscle fiber stimulus theshold

Altered muscle resting membrane potential 

Central nervous sytem

Undoubtedly plays a role in fatigue but not fully understood yet

Central fatigue

Conscious aspect of fiber recruitment

Stress of exhaustive exercise may be too much

Subconscious or conscious unwillingness to endure more pain

Discomfort of fatigue = warning sign

Elite athletes learn proper pacing, tolerate fatigue

Delayed-onset muscle soreness

DOMS

1-2 days after exercise bout

Ranges from stiffness to severe, restrictive pain

Major cause of DOMS

Eccentric contractions

Performing any type of unaccustomed eccentric contractions

Not caused by and increase in blood lactate concentrations

DOMS and structural damage 

Indicated by muscle enzymes in blood (z-line streaming and micro tears in sarcolemma)

Sarcomere z-disks

Anchoring points of contact for contractile proteins