Leucine kinetics in endurance-trained humans

Abstract

This study compared whole-body leucine kinetics in endurance-trained (TRN) and sedentary (SED) control subjects. Eleven men and women (6 TRN, 5 SED) underwent a 6-h primed, constant-rate infusion of L-[1-13C]leucine. Leucine turnover and oxidation were measured using tracer dilution and by measuring 13C enrichment of expired CO2 combined with respiratory calorimetry. Whole-body leucine turnover was greater in the TRN subjects (P less than 0.004; TRN 98.3 +/- 5.0, SED 75.3 +/- 4.2 mumol.kg-1.h-1; mean +/- SE), but there was no difference between groups in leucine oxidation (TRN 13.1 +/- 0.97, SED 11.5 +/- 0.48 mumol.kg-1.h-1). Thus more leucine turnover was available for nonoxidative utilization. In addition, the TRN subjects had higher resting energy expenditures compared with the SED group, and when all subjects were included in the analysis, there was a significant correlation between energy expenditure and protein turnover (n = 11, R = 0.61, P = 0.05). Therefore the heightened resting energy expenditure in the TRN subjects may be accounted for by an increased whole-body protein turnover. These results suggest that endurance training results in increased leucine and/or protein turnover, which may contribute to the increased resting energy expenditure observed in these subjects.

Level of dietary protein impacts whole body protein turnover in trained males at rest

“…Discrepancies between these studies highlight the importance of considering individuals who differ in training state and in the volume and intensity of training as distinct populations, especially when making protein recommendations for persons who endurance train. Because amino acid oxidation increases with increasing exercise intensity and duration [3,5,29], it could be assumed that this would result in differences in WBPTO when looking at differences in long-term training.…”

Discriminant Serum Biochemical Parameters in Top Class Marathon Performances.

“…However, the biological functions of proteins and amino acids are not primarily energetic, at rest as well as during exercise [34,35], but the plasma amino acid pool may decrease with exercise because they are involved in neoglucogenesis [36]. Normally, endurance training increases leucine and/or protein turnover [37], but it also attenuates amino acid oxidation, whatever the exercise intensity [15]. Our results are in accordance with this increased amino acid and protein turnover in relation to training and performance level.…”

A critical review of recommendations to increase dietary protein requirements in the habitually active

“…Aerobic training causes an enhanced metabolic efficiency of protein used at the whole-body level. Table 1 (18,55,69,70) outlines that the absolute amount of whole-body protein oxidised during a 1 h (62) Leucine oxidation (µmol/kg body weight per h) Fig. 2.…”

“…As outlined in Fig. 3 it can be divided into: (1) (55) Assuming 590·0 mmol leucine in each g of whole-body protein (18) This cyclist would oxidise 6·77 g of whole-body protein during a 1 h workout (52 mmol £ 77 kg £ 1 h ¼ 6·77 g) † By contrast, the daily need (using recommended changes in protein RDA from 0·8 to 1·4 g/kg) would require this same athlete to consume an additional 46·2 g protein per d (77 kg £ 0·8 g/kg ¼ 62 g/kg ! 77 kg £ 1·4 g/kg ¼ 108 g/kg)…”