PJ. Intake of low-dose leucine-rich essential amino acids stimulates muscle anabolism equivalently to bolus whey protein in older women at rest and after exercise. Am J Physiol Endocrinol Metab 308: E1056-E1065, 2015. First published March 31, 2015; doi:10.1152/ajpendo.00481.2014.-Dysregulated anabolic responses to nutrition/exercise may contribute to sarcopenia; however, these characteristics are poorly defined in female populations. We determined the effects of two feeding regimes in older women (66 Ϯ 2.5 yr; n ϭ 8/group): bolus whey protein (WP-20 g) or novel low-dose leucine-enriched essential amino acids (EAA) [LEAA; 3 g (40% leucine)]. Using [ 13 C6]phenylalanine infusions, we quantified muscle (MPS) and albumin (APS) protein synthesis at baseline and in response to both feeding (FED) and feeding plus exercise (FED-EX; 6 ϫ 8 knee extensions at 75% 1-repetition maximum). We also quantified plasma insulin/AA concentrations, whole leg (LBF)/muscle microvascular blood flow (MBF), and muscle anabolic signaling by phosphoimmunoblotting. Plasma insulinemia and EAA/aemia were markedly greater after WP than LEAA (P Ͻ 0.001). Neither LEAA nor WP modified LBF in response to FED or FED-EX, whereas MBF increased to a similar extent in both groups only after FED-EX (P Ͻ 0.05). In response to FED, both WP and LEAA equally stimulated MPS 0 -2 h (P Ͻ 0.05), abating thereafter (0 -4 h, P Ͼ 0.05). In contrast, after FED-EX, MPS increased at 0 -2 h and remained elevated at 0 -4 h (P Ͻ 0.05) with both WP and LEAA. No anabolic signals quantifiably increased after FED, but p70 S6K1 Thr 389 increased after FED-EX (2 h, P Ͻ 0.05). APS increased similarly after WP and LEAA. Older women remain subtly responsive to nutrition Ϯ exercise. Intriguingly though, bolus WP offers no trophic advantage over LEAA. skeletal muscle; blood flow; protein synthesis; aging; amino acids; exercise ILL HEALTH ASSOCIATED WITH AGING represents a major socioeconomic burden, especially given shifting demographics toward a more aged, populous world. In particular, the loss of skeletal muscle mass associated with aging, or sarcopenia, is a major clinical issue. For instance, not only are there established links between low muscle mass and all-cause mortality per se (1), but also, lower skeletal muscle mass associated with sarcopenia leads to increased frailty, risk of falls, sedentarism, poor quality of life, and prevalence of metabolic comorbidities (17, 53).The two major extrinsic influences over muscle mass are nutrition and physical activity. For example, oral intake of protein-based foods containing essential amino acids (EAA) leads to a transient (2-3 h; see Ref.2) stimulation of muscle protein synthesis (MPS) in younger men. This brief increase in MPS above postabsorptive rates serves the purpose of replenishing protein stores lost during fasting, ensuring preservation of muscle protein mass. Similarly, physical activity is a prerequisite for maintenance of a healthy muscle mass. For example, inactivity (6, 20) causes muscle atrophy by inducing "anabo...

. (2017) Effects of leucine-enriched essential amino acid and whey protein bolus dosing upon skeletal muscle protein synthesis at rest and after exercise in older women. Clinical Nutrition . ISSN 1532-1983 Access from the University of Nottingham repository: http://eprints.nottingham.ac.uk/47938/1/1-s2.0-S0261561417313407-mainae.pdf Copyright and reuse:The Nottingham ePrints service makes this work by researchers of the University of Nottingham available open access under the following conditions. This article is made available under the Creative Commons Attribution licence and may be reused according to the conditions of the licence. For more details see: http://creativecommons.org/licenses/by/2.5/ A note on versions:The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription.For more information, please contact eprints@nottingham.ac.uk Methods: Twenty-four older women (65 ± 1 y) received (N ¼ 8/group) 1.5 g leucine-enriched EAA supplements (LEAA_1.5), 6 g LEAA (LEAA_6) in comparison to 40 g WP. A primed constant I.V infusion of 13 C 6 -phenylalanine was used to determine MPS at baseline and in response to feeding (FED) and feedingplus-exercise (FED-EX; 6 Â 8 unilateral leg extensions; 75%1-RM). We quantified plasma insulin/AA concentrations, leg femoral blood flow (LBF)/muscle microvascular blood flow (MBF), and anabolic signalling via immunoblotting. Results: Plasma insulineamia and EAAemia were greater and more prolonged with WP than LEAA, although LEAA_6 peaked at similar levels to WP. Neither LEAA or WP modified LBF or MBF. FED increased MPS similarly in the LEAA_1.5, LEAA_6 and WP (P < 0.05) groups over 0e2 h, with MPS significantly higher than basal in the LEAA_6 and WP groups only over 0e4 h. However, FED-EX increased MPS similarly across all the groups from 0 to 4 h (P < 0.05). Only p-p70S6K1 increased with WP at 2 h in FED (P < 0.05), and at 2/4 h in FED-EX (P < 0.05). Conclusions: In conclusion, LEAA_1.5, despite only providing 0.6 g of leucine, robustly (perhaps maximally) stimulated MPS, with negligible trophic advantage of greater doses of LEAA or even to 40 g WP. Highlighting that composition of EAA, in particular the presence of leucine rather than amount is most crucial for anabolism.