An Evaluation of Exercise and Training on Muscle Lipid Metabolism

Abstract

. Evaluation of exercise and training on muscle lipid metabolism. Am. J. Physiol. 276 (Endocrinol. Metab. 39): E106-E117, 1999.-To evaluate the hypothesis that endurance training increases intramuscular triglyceride (IMTG) oxidation, we studied leg net free fatty acid (FFA) and glycerol exchange during 1 h of cycle ergometry at two intensities before training [45 and 65% of peak rate of oxygen consumption (V O 2 peak )] and after training [65% pretraining V O 2 peak , same absolute workload (ABT), and 65% posttraining V O 2 peak , same relative intensity (RLT)]. Nine male subjects (178.1 Ϯ 2.5 cm, 81.8 Ϯ 3.3 kg, 27.4 Ϯ 2.0 yr) were tested before and after 9 wk of cycle ergometer training, five times per week at 75% V O 2 peak . The power output that elicited 66.1 Ϯ 1.1% of V O 2 peak before training elicited 54.0 Ϯ 1.7% after training due to a 14.6 Ϯ 3.1% increase in V O 2 peak . Training significantly (P Ͻ 0.05) decreased pulmonary respiratory exchange ratio (RER) values at ABT (0.96 Ϯ 0.01 at 65% pre-vs. 0.93 Ϯ 0.01 posttraining) but not RLT (0.95 Ϯ 0.01). After training, leg respiratory quotient (RQ) was not significantly different at either ABT (0.98 Ϯ 0.02 pre-vs. 0.98 Ϯ 0.03 posttraining) or RLT (1.01 Ϯ 0.02). Net FFA uptake was increased at RLT but not ABT after training. FFA fractional extraction was not significantly different after training or at any exercise intensity. Net glycerol release, and therefore IMTG lipolysis calculated from three times net glycerol release, did not change from rest to exercise or at ABT but decreased at the same RLT after training. Muscle biopsies revealed minor muscle triglyceride changes during exercise. Simultaneous measurements of leg RQ, net FFA uptake, and glycerol release by working legs indicated no change in leg FFA oxidation, FFA uptake, or IMTG lipolysis during leg cycling exercise that elicits 65% pre-and 54% posttraining V O 2 peak . Training increases working muscle FFA uptake at 65% V O 2 peak , but high RER and RQ values at all work intensities indicate that FFA and IMTG are of secondary importance as fuels in moderate and greaterintensity exercise. 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

Long-standing, insulin-treated type 2 diabetes patients with complications respond well to short-term resistance and interval exercise training

“…In accordance, improvements in insulin sensitivity following resistancetype exercise training (27)(28)(29) have been shown to occur independent of structural changes in skeletal muscle and/ or IMCL and/or glycogen contents (33). Previous studies have either reported no change (76)(77)(78), a decrease (79) or even an increase (80,81) in IMCL content after exercise training. As such, we expand on previous findings that the reported improvements in physical fitness, muscle strength as well as the attenuated rise in EIR are not necessarily accompanied by significant changes in muscle fibre-type characteristics, MUOX and/or muscle lipid and/or glycogen content.…”

Skeletal muscle low attenuation area and maximal fat oxidation rate during submaximal exercise in male obese individuals

“…This is probably explained by the fact that TG, stored in deep AT, first has to be hydrolyzed into FFA and then transported from the AT to the site of oxidation (mitochondrion) within the muscle fiber. Exercise training often 3,33,34 but not always 35 increases the amount of muscle TG. In accordance with the positive correlation found in the present study between VO 2max and FATOX max (Table 2), endurance training also increases fat oxidation rate during exercise.…”

Disassociation of muscle triglyceride content and insulin sensitivity after exercise training in patients with Type 2 diabetes

“…The effects of exercise training on TG m content in healthy subjects are equivocal, with some studies reporting an increase [11,24,25], decrease [26] or no [9,10,27] after short-term (6-12 weeks) endurance exercise. In our investigation, exercise training had little effect on TG m concentrations in control subjects, but resulted in a substantial overall decrease in patients with Type 2 diabetes.…”