WK10 ( CH 19) - Factors Affecting Performance

Question 1

Discuss the role the CNS plays in fatigue.

Answer 1

Increases in CNS arousal facilitate motor unit recruitment to increase strength and alter the state of fatigue. Best estimates suggest that CNS plays a minor role ( about 10%) of fatigue experienced. It should be noted that one kind of central fatigue is the feedback from type III AND IV afferent nerves.

Question 2

Discuss the role of the PNS during fatigue. Both Neural and Mechanical factors.

Answer 2

Neural Factors:
NMJ: action potentials can reach the sarcolemma even in a fatigued state that suggests that the NMJ is not the site of fatigue.

Sarcolemma and T-Tubules: during repeated stimulation of the sarcolemma there can be a reduction in the size and frequency of action potential’s. An action potential block CAN occur in the t-tubule to result in less Ca+2 being released from the sarcoplasmic reticulum.

Mechanical: High concentration of H+ can reduce force per cross-bridge, reduce generated at Ca+2 concentration ( due to H+ interfering with Ca+2 binding), Inhibit SR release. Fatigue is related to concentrations of ADP v ATP, accumulation of Pi and ADP contributes to acute muscle fatigue.

Question 3

Explain the effect of free radicals on exercising muscle.

Answer 3

Prolonged exercise can produce free radicals which can overwhelm cellular anti-oxidants resulting in oxidative damage to tissue. Exercise-Induced damage is a main contributor to acute muscle fatigue.

Question 4

List the limiting factors of all out exercise in anaerobic performances: both ultra short term ( less than or equal to 10 seconds) and short term (10-180 seconds)

Answer 4

Ultra short term: skill, muscular power ( ATP-PCr), fiber type and distribution, and motivation

Short term: shift from mostly anaerobic to 60% aerobic at 180 seconds, ATP produced by anaerobic glycolysis. Accumulation of H+.

Question 5

List the limiting factors of all out exercise in aerobic performances: moderate length ( 3-20 minutes ), Intermediate ( 21-60 min), Long ( 1-4 hours)

Answer 5

Moderate: since exercise lasting this long uses primarily aerobic systems, anything interfering with oxygen delivery would negatively impact performance. Limited by the cardiovascular system and the mitochondrial content of muscle fiber.

Intermediate: lactate threshold, higher number of type I fibers are associated with better bioenergetic economy and lactate threshold.

Long Term: environmental factors as muscle and liver glycogen is depleted, physiological ability to deal with heat, humidity