Increased plasma FFA uptake and oxidation during prolonged exercise in trained vs. untrained humans

Abstract

We studied the effect of local muscle adaptations on free fatty acid (FFA) metabolism during prolonged exercise in trained and untrained subjects. Six trained (T) and six untrained (UT) young human males exercised for 3 h at 60% of their individual maximal dynamic knee extension capacity. The contribution of blood and plasma metabolites as well as intramuscular substrates to oxidative metabolism in the thigh was calculated from arteriovenous differences and femoral-venous blood flow as well as from muscle biopsies in subjects that were continuously infused with [1-14C]palmitate. Arterial plasma FFA concentration increased over time in both T and UT. Fractional uptake of FFA across the thigh remained unchanged over time in T (15%) but decreased in UT (from 15 to 7%), especially during the last hour of exercise. Thus FFA uptake increased linearly over time in T (96 +/- 20 to 213 +/- 20 mumol.min-1.kg-1), whereas it leveled off after 2 h in UT (74 +/- 16 to 133 +/- 46) even though FFA delivery increased similarly in T and UT. Percentage oxidation was similar in T and UT; thus total FFA oxidation was higher in T. Glucose uptake increased in both groups over time and was significantly higher in UT during the last hour of exercise. In conclusion, during prolonged knee extension exercise, FFA uptake increases linearly with FFA delivery in the trained thigh, whereas in the untrained thigh uptake becomes saturated with time. This difference partly explains the increased lipid oxidation in T vs. UT and suggests, furthermore, that local muscle adaptations to training are important for the utilization of FFA during prolonged exercise.

AMPKα2deficiency uncovers time dependency in the regulation of contraction-induced palmitate and glucose uptake in mouse muscle

“…Perfusate samples collected during the perfusion were analyzed to determine FA, glucose, and lactate con- (46,48,49). An ABL-5 analyzer (Radiometer America, Westlake, OH) was used to determine PCO2, PO2, and pH.…”

Skeletal muscle substrate metabolism during exercise: methodological considerations

“…The a-v difference gives the net exchange, but this value is not sufficient to evaluate the rate at which FA are utilized by the muscle, since it may not be totally oxidized immediately. Tracer studies reveal that 60-90 % may be oxidized (Havel et al 1967;Hagenfeldt & Wahren, 1968, 1972Ahlborg et al 1974;Dagenais et al 1976;Turcotte et al 1992). The variation among studies is quite large, which probably relates to the variation in intensity and duration of the exercise as well as the training status of the subjects.…”

“…It is worth emphasizing that only a very small proportion of the FFA offered to the active muscle is taken up by the muscle (at rest approximately 45 %, with exercise approximately 8-15 %; Hagenfeldt & Wahren, 1968;Ahlborg et al 1974;Dagenais et al 1976;Essén et al 1977;Turcotte et al 1992). This percentage is not markedly increased in endurance-trained muscle or when the supply of CHO is limited (Turcotte et al 1992). This implies major limitations in uptake and/or utilization of FA by human skeletal muscle, which are only overcome to a very minor extent by endurance training.…”

An Evaluation of Exercise and Training on Muscle Lipid Metabolism

“…exertion; free fatty acid; glucose; lactate; crossover concept; substrate shuttling EFFECTS OF EXERCISE intensity and training state on muscle lipid metabolism in humans are unclear, as the relatively few studies have utilized different experimental approaches. Some investigations have employed isotopic tracers and indirect calorimetry (25,29,33), whereas others have utilized arteriovenous (a-v) balance methods (17,22,35) and muscle biopsies (18,22 …”

“…isotopic tracers and indirect calorimetry (25,29,33), whereas others have utilized arteriovenous (a-v) balance methods (17,22,35) and muscle biopsies (18,22). In addition, longitudinal and cross-sectional designs have been employed that have tested trained and untrained subjects at either the same absolute or relative exercise intensity, but rarely both.…”