glycine, have been shown to be essential for the synthesis of new collagen ( Li & Wu, 2018 ), with in vitro and in vivo work demonstrating the potential benefit of glycine and proline availability at times around exercise when synthetic machinery is upregulated. Recently, we reported increases in
Rebekah D. Alcock, Gregory C. Shaw and Louise M. Burke
Webb A. Smith, Andrew C. Fry, Lesley C. Tschume and Richard J. Bloomer
The purpose of this study was to evaluate the effect of glycine propionyl-Lcarnitine (GPLC) supplementation and endurance training for 8 wk on aerobicand anaerobic-exercise performance in healthy men and women (age 18–44 yr). Participants were randomly assigned to 1 of 3 groups: placebo (n = 9), 1 g/d GPLC (n = 11), or 3 g/d GPLC (n = 12), in a double-blind fashion. Muscle carnitine (vastus lateralis), VO2peak, exercise time to fatigue, anaerobic threshold, anaerobic power, and total work were measured at baseline and after an 8-wk aerobic-training program. There were no statistical differences (p > .05) between or within the 3 groups for any performance-related variable or muscle carnitine concentrations after 8 wk of supplementation and training. These results suggest that up to 3 g/d GPLC for 8 wk in conjunction with aerobic-exercise training is ineffective for increasing muscle carnitine content and has no significant effects on aerobic- or anaerobic-exercise performance.
Lukas Beis, Yaser Mohammad, Chris Easton and Yannis P. Pitsiladis
Oral supplementation with glycine-arginine-α-ketoisocaproic acid (GAKIC) has previously been shown to improve exhaustive high-intensity exercise performance. There are no controlled studies involving GAKIC supplementation in well-trained subjects. The aim of the current study was to examine the effects of GAKIC supplementation on fatigue during high-intensity, repeated cycle sprints in trained cyclists. After at least 2 familiarization trials, 10 well-trained male cyclists completed 2 supramaximal sprint tests each involving 10 sprints of 10 s separated by 50-s rest intervals on an electrically braked cycle ergometer. Subjects ingested 11.2 g of GAKIC or placebo (Pl) during a period of 45 min before the 2 experimental trials, administered in a randomized and double-blind fashion. Peak power declined from the 1st sprint (M ± SD; Pl 1,332 ± 307 W, GAKIC 1,367 ± 342 W) to the 10th sprint (Pl 1,091 ± 229 W, GAKIC 1,061 ± 272 W) and did not differ between conditions (p = .88). Mean power declined from the 1st sprint (Pl 892 ± 151 W, GAKIC 892 ± 153 W) to the 10th sprint (Pl 766 ± 120 W, GAKIC 752 ± 138 W) and did not differ between conditions (p = .96). The fatigue index remained at ~38% throughout the series of sprints and did not differ between conditions (p = .99). Heart rate and ratings of perceived exertion increased from the 1st sprint to the 10th sprint and did not differ between conditions (p = .11 and p = .83, respectively). In contrast to previous studies in untrained individuals, these results suggest that GAKIC has no ergogenic effect on repeated bouts of high-intensity exercise in trained individuals.
Christopher Tack, Faye Shorthouse and Lindsy Kass
( Greenwald et al., 1990 ); two assessing vitamin C ( Hung et al., 2013 ; Ömeroğlu et al., 2009 ); one assessing taurine ( Akdemir et al., 2015 ); two assessing glycine ( Vieira et al., 2015a ; Vieira et al., 2015b ); and two assessing nutrient complexes, which included various supplements (e
Anthony D. Mahon and Brian W. Timmons
Exercise metabolism in children has traditionally been assessed using the respiratory exchange ratio (RER) to determine the contributions of fat and carbohydrate to the exercise energy demands. Although easily measured, RER measurements have limitations. Other methods to assess metabolism such as the obtainment of a muscle biopsy and the use of nuclear magnetic resonance spectroscopy carry ethical and feasibility concerns, respectively, which limit their use in studies involving children. Stable isotopes, used routinely in studies involving adults, can also be applied in studies involving children in an ethical and feasible manner. Two common stable isotopes used in metabolic studies involving children include carbon-13 (13C) and nitrogen-15 (15N). 13C-glucose can be used to study carbohydrate metabolism and 15N-glycine can be used to assess protein metabolism. This article reviews the use of 13C-glucose and 15N-glycine to study exercise metabolism in children, considers some of the associated ethical aspects, explains the general methodology involved in administering these isotopes and the resources required, and describes studies involving children utilizing these methods. Finally, suggestions for future research are provided to encourage further use of these techniques.
Dana M. Lis and Keith Baar
behind their hype. Gelatin and HC have a similar amino acid profile and are particularly high in glycine, proline, hydroxyproline, hydroxylysine, and arginine ( Eastoe, 1955 ). Gelatin is isolated from the collagen within the skin, tendons, ligaments, and bone of cattle, fish, or pigs through boiling
Graeme L. Close, Craig Sale, Keith Baar and Stephane Bermon
increase in collagen function with increasing doses of copper. Therefore, the goal for copper intake should approximate the RDA of ∼1 mg·kg −1 ·day −1 . Glycine Fibrillar collagens are a repeating tripeptide of glycine-X-proline/hydroxyproline, where X represents any amino acid other than glycine and
Megan Colletto and Nancy Rodriguez
overnight using the end-product method with oral administration of 15 N-glycine and subsequent urine collection as previously described ( Assimon & Stein, 1992 ; Bolster, Pikosky, McCarthy, & Rodriguez, 2001 ). In brief, powdered 15 N-glycine (2 mg·kg body weight, 98 + atom percent enrichment; Cambridge
Thiago Correa Porto Gonçalves, Atila Alexandre Trapé, Jhennyfer Aline Lima Rodrigues, Simone Sakagute Tavares and Carlos Roberto Bueno Junior
al., 2001 ; Snyder et al., 2006 ). Two single-nucleotide polymorphisms of the β 2 -AR gene have been investigated and are related to the extracellular part of the receptor: 16A<G, with a change of arginine (Arg) to glycine (Gly) at amino acid 16, and 27C<G, with a change of glutamic acid (Gln) to glutamine
Rebekah D. Alcock, Gregory C. Shaw, Nicolin Tee, Marijke Welvaert and Louise M. Burke
glycine), as well as unique dipeptides and tripeptides ( Baar, 2017 ; Curtis, 2016 ; Schunck et al., 2013 ; Shaw et al., 2017 ; Smith et al., 2007 ). This has contributed to the marketing of “collagen-support” products for tendon/ligament health or repair, with guidance that athletes should consume