Chapter 14 Neuromuscular Fatigue

Key Concepts

accumulation hypothesis central fatigue depletion hypothesis electromyography (EMG) electronic integrator glycogen depletion integration muscle action potential (MAP)muscle action potential (MAP) neuromuscular fatigue peripheral fatigue phosphagen depletion planimetry qualitative electromyographyqualitative electromyography quantitative electromyographyquantitative electromyography runner’s wall Setchenov phenomenonSetchenov phenomenon

Review Questions

Which is more fatiguing: continuous isometric muscle actions or intermittent isometric muscle actions? Why? Continuous isometric muscle actions are more fatiguing because they occlude circulation, whereas intermittent isometric muscle actions allow blood to flow to the muscle.

What conclusion did Bigland-Ritchie et al. reach regarding the source of fatigue? Both central and peripheral fatigue are important factors in loss of muscle force, and there are many individual differences involved.

Mechanisms underlying central fatigue occur mainly where? –Brain Mechanisms underlying peripheral fatigue occur mainly within what? –Motor units

Which is more useful: a passive rest break or a pause with diverting activity? A break with diverting activity. This is referred to as the Setchenov phenomenon.

What are three factors that contribute to central fatigue? Sensory feedback from working muscles Accumulation of ammonia Increase in serotonin in the brain

Explain the accumulation hypothesis. It describes the fatigue-causing effects of the buildup of metabolites within muscle fibers. What metabolites are significant in the accumulation hypothesis? Lactate, inorganic phosphate, and ammonia

What happens as a result of lactate buildup? It interferes with muscle contraction in the following ways: –calcium release from the sarcoplasmic reticulum –actin–myosin binding –ATP breakdown –ATP production

How does the depletion hypothesis explain peripheral fatigue? This hypothesis states that fatigue results from the depletion of the phosphagens or glycogen, which are used to produce ATP.

When does phosphagen depletion occur? –During very high intensity activity When does glycogen depletion occur? –During moderate-intensity activity over a long period of time

What is the most likely explanation for runner’s wall? It is likely caused by glycogen depletion in the most active fibers of the quadriceps muscles.

What role does temperature play in muscle fatigue? Muscle fatigue occurs at both low and high muscle temperatures. At high temperatures, metabolites accumulate rapidly in the muscle. Low muscle temperatures may affect neuromuscular electrical transmission or the contractile properties of the muscle.

What has EMG shown regarding the quantification of electrical activity within the skeletal muscles during submaximal fatiguing tasks? Electrical activity increases over time Why does this occur? The increase results from the recruitment of additional motor units and increases in motor unit firing rates.

Useful Websites

Neuromuscular Research Center Electromyography Fundamentals Neurohaven—EMG EMG htm