Biomaterial Database

Respiratory muscle fatigue during exercise: implications for performance. 1996

B D Johnson, and E A Aaron, and M A Babcock, and J A Dempsey

Department of Internal Medicine, Mayo Clinic and Foundation, Rochester, MN 55905, USA.

Heavy whole-body exercise, requiring a 10- to 15-fold increase in minute ventilation, encroaches on the capacities of the respiratory muscle system to respond. Recently, using the technique of bilateral phrenic nerve stimulation, it has been shown that heavy endurance exercise (> 85% of VO2max) lasting > 8-10 min causes diaphragmatic fatigue (15-30% reduction in transdiaphragmatic pressures when electrically stimulated at low frequencies [1-20 Hz] supramaximally). The fatigue appears to be due to an interaction of diaphragmatic work (i.e., pressure production) combined with effects related to exercise intensity (i.e., increased blood flow competition with the locomotor muscles and increased production of metabolic by-products) and requires > 60 min for recovery. Fitness (i.e., as implied from VO2max) appears to allow greater diaphragmatic work for a similar degree of fatigue. Unloading the respiratory muscles (with helium/oxygen gas or using a pressure-assist device) during heavy exercise < 90-95% of VO2max does not appear to alter exercise time, VO2max, or minute ventilation, implying that respiratory muscle fatigue plays little role in altering human performance at these work intensities. However, unloading the respiratory system with helium at work intensities > 90-95% of VO2max has been shown to improve exercise time. This would imply that respiratory muscle fatigue may play a role in limiting human performance at the extremes of human performance or that other factors related to the respiratory system (i.e., alterations in the sensation of dyspnea or mechanical load) may play an important role.

UI	MeSH Term	Description	Entries
D010101	Oxygen Consumption	The rate at which oxygen is used by a tissue; microliters of oxygen STPD used per milligram of tissue per hour; the rate at which oxygen enters the blood from alveolar gas, equal in the steady state to the consumption of oxygen by tissue metabolism throughout the body. (Stedman, 25th ed, p346)	Consumption, Oxygen,Consumptions, Oxygen,Oxygen Consumptions
D010791	Phrenic Nerve	The motor nerve of the diaphragm. The phrenic nerve fibers originate in the cervical spinal column (mostly C4) and travel through the cervical plexus to the diaphragm.	Nerve, Phrenic,Nerves, Phrenic,Phrenic Nerves
D010807	Physical Endurance	The time span between the beginning of physical activity by an individual and the termination because of exhaustion.	Endurance, Physical,Physical Stamina,Stamina, Physical
D010809	Physical Fitness	The ability to carry out daily tasks and perform physical activities in a highly functional state, often as a result of physical conditioning.	Fitness, Physical
D012132	Respiratory Muscles	These include the muscles of the DIAPHRAGM and the INTERCOSTAL MUSCLES.	Ventilatory Muscles,Respiratory Muscle,Muscle, Respiratory,Muscle, Ventilatory,Muscles, Respiratory,Muscles, Ventilatory,Ventilatory Muscle
D003964	Diaphragm	The musculofibrous partition that separates the THORACIC CAVITY from the ABDOMINAL CAVITY. Contraction of the diaphragm increases the volume of the thoracic cavity aiding INHALATION.	Respiratory Diaphragm,Diaphragm, Respiratory,Diaphragms,Diaphragms, Respiratory,Respiratory Diaphragms
D004558	Electric Stimulation	Use of electric potential or currents to elicit biological responses.	Stimulation, Electric,Electrical Stimulation,Electric Stimulations,Electrical Stimulations,Stimulation, Electrical,Stimulations, Electric,Stimulations, Electrical
D006801	Humans	Members of the species Homo sapiens.	Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D015444	Exercise	Physical activity which is usually regular and done with the intention of improving or maintaining PHYSICAL FITNESS or HEALTH. Contrast with PHYSICAL EXERTION which is concerned largely with the physiologic and metabolic response to energy expenditure.	Aerobic Exercise,Exercise, Aerobic,Exercise, Isometric,Exercise, Physical,Isometric Exercise,Physical Activity,Acute Exercise,Exercise Training,Activities, Physical,Activity, Physical,Acute Exercises,Aerobic Exercises,Exercise Trainings,Exercise, Acute,Exercises,Exercises, Acute,Exercises, Aerobic,Exercises, Isometric,Exercises, Physical,Isometric Exercises,Physical Activities,Physical Exercise,Physical Exercises,Training, Exercise,Trainings, Exercise
D018763	Muscle Fatigue	A state arrived at through prolonged and strong contraction of a muscle. Studies in athletes during prolonged submaximal exercise have shown that muscle fatigue increases in almost direct proportion to the rate of muscle glycogen depletion. Muscle fatigue in short-term maximal exercise is associated with oxygen lack and an increased level of blood and muscle lactic acid, and an accompanying increase in hydrogen-ion concentration in the exercised muscle.	Fatigue, Muscle,Muscular Fatigue,Fatigue, Muscular