Running endurance in 27-h-fasted humans.
Nine male marathon runners were exercised to exhaustion to determine the effects of a 27-h fast on endurance performance. Each subject completed two exercise tests at the same treadmill speed (set at 70% maximal O2 uptake), one following a 27-h fast and one 3 h after a preexercise meal, in random order. Fasting caused a 44.7 +/- 5.8% (SE) decrease in endurance performance (P less than 0.01). Blood, muscle, psychological, and ventilatory data were examined to determine the cause of the decreased performance. Fasting caused significant increases in O2 uptake (9.3 +/- 2.0%), heart rate (8.4 +/- 2.4%), and rating of perceived exertion, ventilation, and psychological fatigue, evident within the first 60 min of exercise. There were no differences in plasma glucose or epinephrine levels. Muscle glycogen degraded at the same rate (0.482 +/- 0.146 vs. 0.470 +/- 0.281 mumol.g-1.min-1 in the nonfasted and fasted tests, respectively) despite lower respiratory exchange ratio and elevated free fatty acid levels, which may partially explain the elevated O2 uptake. Lactate, insulin, and norepinephrine were all increased in the fasted test (P less than 0.05). The increase in norepinephrine (r = 0.79, P less than 0.01), the diameter of type I muscle fibers (r = 0.70, P less than 0.05), and ending insulin levels (r = -0.88, P less than 0.01) were correlated with endurance time in the fasted state. Fatigue in endurance running for 27-h fasted humans appears to be related to a combination of physiological, psychological, metabolic, and hormonal changes.
Nieman
D C
DC
Center for Health Promotion, Loma Linda University, California 92350.
Carlson
K A
KA
Brandstater
M E
ME
Naegele
R T
RT
Blankenship
J W
JW
D000328:Adult; D001786:Blood Glucose / Q000032:analysis; D005215:Fasting / Q000523:psychology; D005221:Fatigue; D005934:Glucagon / Q000097:blood; D006003:Glycogen / Q000032:analysis; D006339:Heart Rate; D006801:Humans; D007328:Insulin / Q000097:blood; D007773:Lactates / Q000097:blood; D008297:Male; D009132:Muscles / Q000032:analysis; D010100:Oxygen / Q000502:physiology; D010807:Physical Endurance; D012420:Running; D013997:Time Factors
D001786:Blood Glucose; D007328:Insulin; D007773:Lactates; D006003:Glycogen; D005934:Glucagon; D010100:Oxygen