Physiology Ch.6: Fatigue, Muscle Soreness, and Muscle Cramps

What is fatigue?

decrements in muscular performance with continued effort, accompanied by sensations of tiredness

or inability to maintain the required power output to continue muscular work at a given intensity

it is reversible by rest (distinguishes fatigue from muscle weakness/damage)

What are the four major causes of fatigue?

decreased energy available from metabolism, accumulation of metabolic by-products, altered neural control of muscle contraction, and psychobiological aspects 

What is PCr depletion?

It coincides with fatigue, used for short term high intensity effort, depletes more quickly than total ATP, it limits ability to replace ATP, ATP concentration also decreases, and pacing helps defer it. 

What is glycogen depletion? 

glycogen reserves limited, depletion is correlated with fatigue, depleted more quickly with high intensity 

What is depletion in diff. muscle groups?

In activity specific muscles: depletion is fastest. recruited earliest and longest for given task

How is the rate of fatigue dependent on exercise?

the rate of fatigue of each fiber is dependent on exercise intensity. Type 1 fibers (light/moderate intensity), type 2a fibers (moderate/high intensity), type 2x fibers (maximal intensity)

What is depletion and blood glucose? 

The muscle glycogen is depleted first. the liver glycogen goes turns glucose into blood. As muscle glycogen decreases, lover glycogenolysis increases. Muscle glycogen depletion and hypoglyemia=feeling of fatigue. 

What is Pi metabolic by-product?

It is from rapid breakdown of PCr, ATP.

What is lactic acid?

product of anaerobic glycolysis, undergoes constant turnover, recycled to provide energy

WHat is H+ acculumation 

causes muscle acidosis, lactic acid turns into lactate and H+. Short duration, high intensity 

What are the buffers for metabolic by-products?

help muscle pH but not enough, minimize drop in pH (7.1 to 6.5, not to 1.5).

What is pH level is lower than 6.9?

It inhibits glycolytic enzymes. slows ATP synthesis

What is pH equals 6.4? 

it prevents further glycogen breakdown. Rapid decrease in ATP. 

What is intracellular buffer?

beta alanine. potential side effect: tingling 

What is extracellular buffer?

sodium bicarbonate (aka baking soda). Potential side effect: GI distress

What is development of muscle inefficiency?

a major determinant of fatigue and task fatigue. Impairments in ATP production and turnover.

What is reactive oxygen species accumulation? 

impaired mitochondrial function, slower rate of PCr recovery, reduction in oxidative ATP production

What is neural transmission?

failure may occur at neuromuscular junction, preventing muscle activation. Fatigue may inhibit Ca2+ release from SR.

What are some possible causes of neural transmission?

reduced ACh synthesis and release, altered ACh breakdown in synapse, increase in muscle fiber stimulus threshold, altered muscle resting membrane potential

What is the role of CNS in fatigue?

Not fully understood. conscious aspect of fiber recruitment.

What is the conscious aspect of fiber recruitment? 

stress of exhaustive exercise may be too much. person may be subconsciously or consciously unwilling to endure more pain. discomfort or fatigue is a warning sign. elite athletes learn proper pacing, tolerate fatigue.

How does supplementation caffeine work?

supp. increases feelings of energy, focus, wakefulness, and as such as implications for sports performance. These changes are acute but do not seem to cause improved training results over time.

What are the small to moderate benefits of caffeine use?

muscular endurance, movement velocity, muscular strength, sprinting, jumping, and throwing performance. It binds to adenosine antagonist receptors in the brain and keeps them from activating. Effects depend on genome and how your body metabolizes caffeine. 

What are the psychological aspects? 

The conscious decision to terminate activity. Heat alters metabolic rate. Time to fatigue changs with ambient temp. 

What is the conscious decision to terminate activity?

Interaction between perception of effort and motivation. Self-talk as a strategy to reduce fatigue.

What is the heat alters metabolic rate?

Increases rate of carb utilization. Hastens glycogen depletion. High muscle temp. may impair muscle function.

What is the time to fatigue change? 

time to exhaustion is longest at 11C (50F). Time to exhaustion is shortest at 31C (88F). Muscle precooling prolongs exercise. 

What is pre-cooling?

Ex: ice water immersion, ice vests, ice packs, ice water consumption

Effect: slightly impaired single effort sprint performance, but improved endurance performance when in hot environments

What is post-cooling?

Ex: cryotherapy machine, ice baths

Effect: reduced DOMS, reduced perceived fatigue at 24 hrs. No change to blood markers or symptoms at 48 hrs plus

What is the link between energy expenditure and fatigue? 

tolerable duration of high-intentsity exercise. Highest metabolic rate maintained entirely by oxidative metabolism. Correlated with performance in events lasting from 2 min to 2 hr. 

What is muscle soreness? 

Result of exhaustive or high-intensity exercise, esp. performed for first time. It can be felt anytime. Acute soreness during and immediately after exercise. DOMS 1 to 2 days later 

What is acute muscle soreness? 

Felt during or immediately following strenuous or novel exercise. Accumulation of metabolic by-products (H+). Tissue edema (plasma fluid into the interstitial space). Edema creates acute muscle swelling. Disappears in minutes to hours.  

What is DOMS?

delayed-onset muscle soreness. Appears 1 to 2 days after exercise bout. Ranges from stiffness to severe, restrictive pain. Major cause: eccentric contractions. Ex: level-run pain is less than down-hill run pain. It is not caused by increased blood lactate concentration.

How do you determine structural damage?

Indicated by muscle enzymes in blood. Concentractions increase 2 to 10 times after heavy training. Onsets of DOMS parallels onset of increase muscle enzymes in blood.

What are the sarcomere z-disks?

Anchoring points of contact for contractile proteins. Transmit force when muscle fibers contract. Z-disk, myofilament damage seen after eccentric work.

What is the connection between DOMS and inflammation?

Connection between inflammation and soreness. (white blood cells defend body. The count increases with soreness). Substances released initiate inflammation (damaged muscle cells attract neutrophils, which release attractant chemicals. Released substances stimulate pain nerves)

What is muscle damage?

may contribute indirectly to growth by stimulating satellite cell activation and releasing growth factors.

What is muscle hypertrophy?

it can occur without major damage (in repeated bout effect, where soreness/damage reduces but growth still continues). Excess damage can actually intefere with recovery and blunt training adaptations.

Muscle damage might play a role but its not required and too much may be counterproductive 

What are the three factors DOMS loses strength from?

physical disruption of muscle, failure in excitation which is contraction coupling, and loss of contractile protein.

What are some strategies to reduce DOMS?

minimize eccentric work early in training, start with low-intensity and increase gradually, start with high-intensity exhaustive training, and gentle stretching or repeated bouts of exercise

What are exercise-associated muscle cramps? 

localized to overworked muscle, lack of conditioning; improper training and depletion of muscle energy stores. Induced by electrical stimulation, treated with stretching. Reduced by changing excitatory properties of the alpha motor neuron 

What about spicy foods? 

like chili peppers, can provide cramp relief by overwhelming sensory receptors in the mouth and esophagus, which in turn calms the hyperexcited alpha motor neurons responsible for the cramp

What is the neuromuscular control theory? 

it is altered control between motor neuron and muscle. The central origin is hyperexcitable motor neurons. The peripheral origin is spontaneous discharges of motor nerves. the risk factors: age, cramping history, increased exercise intensity and duration, and lact of fitness 

What is the electrolyte depletion theory?

Heat cramps are often associated with large sweat and electrolyte losses, especially sodium and chloride. Treatment: high-sodium solution, ice, massage