Non-technical summary After 30 years of endeavour, this is the first study to show that muscle carnitine content can be increased in humans by dietary means and, perhaps more importantly, that carnitine plays a dual role in skeletal muscle fuel metabolism that is exercise intensity dependent. Specifically, we have shown that increasing muscle total carnitine content reduces muscle carbohydrate use during low intensity exercise, consistent with an increase in muscle lipid utilisation. However, during high intensity exercise muscle carnitine loading results in a better matching of glycolytic, pyruvate dehydrogenase complex and mitochondrial flux, thereby reducing muscle anaerobic energy generation. Collectively, these metabolic effects resulted in a reduced perception of effort and increased work output during a validated exercise performance test. These findings have significant implications for athletic performance and pathophysiological conditions where fat oxidation is impaired or anaerobic ATP production is increased during exercise. AbstractWe have previously shown that insulin increases muscle total carnitine (TC) content during acute I.V. L-carnitine infusion. Here we determined the effects of chronic L-carnitine and carbohydrate (CHO; to elevate serum insulin) ingestion on muscle TC content and exercise metabolism and performance in humans. On three visits, each separated by 12 weeks, 14 healthy male volunteers (age 25.9 ± 2.1 years, BMI 23.0 ± 0.8 kg m −2 ) performed an exercise test comprising 30 min cycling at 50%V O 2 max , 30 min at 80%V O 2 max , then a 30 min work output performance trial. Muscle biopsies were obtained at rest and after exercise at 50% and 80%V O 2 max on each occasion. Following visit one, volunteers ingested either 80 g of CHO (Control) or 2 g of L-carnitine-L-tartrate and 80 g of CHO (Carnitine) twice daily for 24 weeks in a randomised, double blind manner. All significant effects reported occurred after 24 weeks. Muscle TC increased from basal by 21% in Carnitine (P < 0.05), and was unchanged in Control. At 50%V O 2 max , the Carnitine group utilised 55% less muscle glycogen compared to Control (P < 0.05) and 31% less pyruvate dehydrogenase complex (PDC) activation compared to before supplementation (P < 0.05). Conversely, at 80%V O 2 max , muscle PDC activation was 38% higher (P < 0.05), acetylcarnitine content showed a trend to be 16% greater (P < 0.10), muscle lactate content was 44% lower (P < 0.05) and the muscle PCr/ATP ratio was better maintained (P < 0.05) in Carnitine compared to Control. The Carnitine group increased work output 11% from baseline in the performance trial, while Control showed no change. This is the first demonstration that human muscle TC can be increased by dietary means and results in muscle glycogen sparing during low intensity exercise (consistent with an increase in lipid utilisation) and a better matching of glycolytic, PDC and mitochondrial flux during high intensity exercise, thereby reducing muscle anaerobic ATP production. Furthermore, these...

IMN is beneficial in reducing postoperative infectious and noninfectious complications and shortening hospital stay in patients undergoing major open gastrointestinal surgery.

Obesity is increasing, yet despite the necessity of maintaining muscle mass and function with age, the effect of obesity on muscle protein turnover in older adults remains unknown. Eleven obese (BMI 31.9 6 1.1 kg $ m 22) and 15 healthy-weight (BMI 23.4 6 0.3 kg $ m 22) older men (55-75 years old) participated in a study that determined muscle protein synthesis (MPS) and leg protein breakdown (LPB) under postabsorptive (hypoinsulinemic-euglycemic clamp) and postprandial (hyperinsulinemic hyperaminoacidemiceuglycemic clamp) conditions. Obesity was associated with systemic inflammation, greater leg fat mass, and patterns of mRNA expression consistent with muscle deconditioning, whereas leg lean mass, strength, and work done during maximal exercise were no different. Under postabsorptive conditions, MPS and LPB were equivalent between groups, whereas insulin and amino acid administration increased MPS in only healthy-weight subjects and was associated with lower leg glucose disposal (LGD) (63%) in obese men. Blunting of MPS in the obese men was offset by an apparent decline in LPB, which was absent in healthy-weight subjects. Lower postprandial LGD in obese subjects and blunting of MPS responses to amino acids suggest that obesity in older adults is associated with diminished muscle metabolic quality. This does not, however, appear to be associated with lower leg lean mass or strength.