Muscle glycogen recovery after exercise during glucose and fuctose intake monitored by 13C-NMR

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Reduction in muscle glycogen and protein utilization with glucose feeding during exercise.

Effects of feeding glucose on substrate metabolism during cycling were studied. Trained (60.0 +/- 1.9 mL x kg(-1) x min(-1)) males (N = 5) completed two 75 min, 80% VO(2max) trials: 125 g 13(C)-glucose CHO); 13(C)-glucose tracer, 10 g (C). During warm-up (30 min 30% VO2max) 2 . 2 g 13(C)-glucose was given as bicarbonate pool primer. Breath samples and blood glucose were analyzed for 13(C/12)C with IRMS. Protein oxidation was estimated from urine and sweat urea. Indirect calorimetry (protein corrected) and 13(C/12)C enrichment in expired CO(2)and blood glucose allowed exogenous (Gexo), endogenous (Gendo), muscle (Gmuscle), and liver glucose oxidation calculations. During exercise (75 min) in CHO versus C (respectively): protein oxidation was lower (6.8 +/- 2.7, 18.8 +/- 5.9 g; P = 0.01); Gendo was reduced (71.2 +/- 3.8, 80.7 +/- 5.7% P = 0.01); Gmuscle was reduced (55.3 +/- 6.1, 65.9 +/- 6.0%; P = 0.01) compensated by increased Gexo(58.3 +/- 2.1, 3.87 +/- 0.85 g; P = 0.000002). Glucose ingestion during exercise can spare endogenous protein and carbohydrate, in fed cyclists, without glycogen depletion

Muscle glycogen recovery after exercise during glucose and fructose intake monitored by C-13-NMR

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Similar metabolic response to lower- versus upper-body interval exercise or endurance exercise

Purpose. To compare energy use and substrate partitioning arising from repeated lower versus upper-body sprints, or endurance exercise, across a 24-h period. Methods. Twelve untrained males (24 ± 4 y) completed three trials in randomized order: (1) repeated sprints (five 30-s Wingate, 4.5-min recovery) on a cycle ergometer (SITLegs); (2) 50-min continuous cycling at 65% V̇O2max (END); (3) repeated sprints on an arm-crank ergometer (SITArms). Respiratory gas exchange was assessed before and during exercise, and at eight points across 22 h of recovery. Results. Metabolic rate was elevated to greater extent in the first 8 h after SITLegs than SITArms (by 0.8 ± 1.1 kJ/min, p = 0.03), and tended to be greater than END (by 0.7 ± 1.3 kJ/min, p = 0.08). Total 24-h energy use (exercise + recovery) was equivalent between SITLegs and END (p = 0.55), and SITLegs and SITArms (p = 0.13), but 24-h fat use was higher with SITLegs than END (by 26 ± 38 g, p = 0.04) and SITArms (by 27 ± 43 g, p = 0.05), whereas carbohydrate use was higher with SITArms than SITLegs (by 32 ± 51 g, p = 0.05). Plasma volume-corrected post-exercise and fasting glucose and lipid concentrations were unchanged. Conclusion. Despite much lower energy use during five sprints than 50-min continuous exercise, 24-h energy use was not reliably different. However, (i) fat metabolism was greater after sprints, and (ii) carbohydrate metabolism was greater in the hours after sprints with arms than legs, while 24-h energy usage was comparable. Thus, sprints using arms or legs may be an important adjunct exercise mode for metabolic health