Combined ingestion of protein and free leucine with carbohydrate increases postexercise muscle protein synthesis in vivo in male subjects
René Koopman,1 Anton J. M. Wagenmakers,4 Ralph J. F. Manders,1 Antoine H. G. Zorenc,1 Joan M. G. Senden,1 Marchel Gorselink,3 Hans A. Keizer,2 and Luc J. C. van Loon1,2
 
Departments of 1Human Biology and 2Movement Sciences, Nutrition Research Institute Maastricht, Maastricht University, Maastricht; 3Numico Research BV, Wageningen, The Netherlands; and 4School of Sport and Exercise Sciences, University of Birmingham, Birmingham, United Kingdom
 
Submitted 1 September 2004 ; accepted in final form 22 November 2004  
 
...
In conclusion, the combined ingestion of protein and leucine with carbohydrate improves whole body protein balance during recovery from resistance exercise compared with the ingestion of carbohydrate or carbohydrate with protein. The combined ingestion of both leucine and protein with carbohydrate augments postexercise mixed muscle protein synthesis compared with the ingestion of only carbohydrate. The present data indicate that the additional ingestion of free leucine in combination with protein and carbohydrate likely represents an effective strategy to increase muscle anabolism following resistance exercise.

Strength and body composition changes associated with leucine
supplementation and resistance training
 
T. Ispoglou & R. F. G. J. King Leeds Metropolitan University, UK
 
Evidence to support fue role of leucíne as an ergogenic aid and
supplement to enhance muscle growth during resistance training is
limited (Koopman et al., 2005: American Journal 01 Physiology:
Endocrinology and Metabolism, 288, E645 - E653). Leucine alone
can enhance protein synthesis (Anthony et al., 2000: Joumal 01
Nutrition, 130, 2413-2419) while resistance exercise has been shown
to increase protein synthesis and breakdown (Biolo et al., 1995:
American Joumal 01 Physiology, 268, E514-E520). The
aim of this stUdy was to investigate the effects of combined daily
and post-exercise leucine supplementation on strength and body
composition during 12 weeks of training.
 
After approval was granted by the local ethics cornmittee, 26
untrained men were matched and allocated to one of two groups of
supplementation (placebo: n = 13, mean age 28.2 years, s = 7.3;
leucine, n= 13, mean age 28.5 years, s=O.O). Participants trained
twice per week in eight exercises and ingested daily either 4 g of
leucine or lactose. Five-repetition maximum strength (5-RM) was
assessed every 4 weeks. Fat-free mass was measured using dual-energy
X-ray absorptiometry, multi-frequency bioelectrical impedance, and
total body potassium.
 
There were increases in 5-RM strength ofleg press (P= 0.001), bench
press (P= 0.001), preacher curls (P= 0.000), and triceps press (P=
0.000) (two-way analysis ofvariance); total strength (sum of 5-RM in
eight exercises) gains in the leucine group were greater than those
in the placebo group (t12 = -2.508, two-tailed P=0.028). Total fat-
free mass was greater than pre-exercise values for both the placebo
(P= 0.005) and leucine (P= 0.002) groups.
 
There was an increase (P < 0.05) in fat-free mass of
the arms, legs, and trunk regions of the leucine group, and algo in
the arms and legs of the placebo group; the mean gains in trunk fat-
free mass were 0.3 kg (s=0.8) for the placebo group (P=0.176) and 0.8
kg (s= 1.1) for the leucine group (P=0.031).
 
Our results demonstrate that leucine supplementation improved
strength performance to a greater extent than placebo in specific
exercises; the total percentage gains were 31.2% (s=6.1) and 41%
(s=8.6) for the placebo and leucine groups respectively. Greater
gains in trunk fat-free mass accompanied the group with the highest
strength gains. The results suggest that leucine supplementation
combined with resistance training improves strength and fat-free mass.

L’alanine circulante provenant en grande partie du pyruvate (donc du métabolisme
musculaire du glucose), la conversion de l’alanine en glucose ne représente
en fait qu’un recyclage de carbone d’origine glucidique – l’alanine n’est donc en
quelque sorte qu’un « glucide déguisé ». En revanche, la majeure partie de la glutamine
provient de la conversion d’autres acides aminés : aussi la conversion de
la glutamine en glucose représente-t-elle une « vraie » production de néoglucose
à partir de carbone d’origine protéique, ce qui fait que la glutamine joue un rôle
plus important que l’alanine dans la gluconéogenèse [34].