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Adolescent, female, and masters athletes have unique nutritional requirements as a consequence of undertaking daily training and competition in addition to the specific demands of age- and gender-related physiological changes. Dietary education and recommendations for these special population athletes require a focus on eating for long-term health, with special consideration given to "at-risk" dietary patterns and nutrients (e.g., sustained restricted eating, low calcium, vitamin D and/or iron intakes relative to requirements). Recent research highlighting strategies to address age-related changes in protein metabolism and the development of tools to assist in the management of Relative Energy Deficiency in Sport are of particular relevance to special population athletes. Whenever possible, special population athletes should be encouraged to meet their nutrient needs by the consumption of whole foods rather than supplements. The recommendation of dietary supplements (particularly to young athletes) overemphasizes their ability to manipulate performance in comparison with other training/dietary strategies. [ABSTRACT FROM AUTHOR]

Am J Physiol Regul Integr Comp Physiol 298' R25-R33, 2010. First published November 11, 2009; doi: 10.1152/ajpregu.00524.2009.--Exercise-induced expression of peroxisome proliferator-activated receptor gamma coactivator-l[alpha] (PGC-1[alpha] is dramatically inhibited in mice pretreated with a [beta]-adrenergic receptor ([beta]-AR) antagonist, suggesting that [beta]-ARs play an important role in the regulation of skeletal muscle PGC-1[alpha] expression, and potentially, mitochondrial biogenesis. Accordingly, we hypothesized that acute [beta]-AR stimulation would induce transcriptional pathways involved in skeletal muscle mitochondrial biogenesis in humans. Whole body protein turnover (WBPT), myofibrillar protein synthesis (MyPS), skeletal muscle mitochondfial protein synthesis (MiPS), and mitochondrial biogenic signaling were determined in samples of vastus lateralis obtained on two separate occasions in 10 young adult males following 1 h of continuous intravenous administration of saline (CON) or a nonspecific [beta]-AR agonist [isoproterenol (ISO): 12 ng x kg fat free [mass.sup.-l] x [min.sup.-1]], combined with coinfusion of [1,2] [sup.13]C-leucine. [beta]-AR stimulation induced appreciable increases in heart rate and systolic blood pressure (both P < 0.001) but did not affect mitochondrial biogenic signaling (no change in PGC-1[alpha], TFAM, NRF-1, NRF-2, COX, or NADHox expression via RT-PCR; P > 0.05). Additionally, MiPS [CON: 0.099 [+ or -] 0.[O.sub.2]8, ISO: 0.074 [+ or -] 0.046 (mean [+ or -] SD); P > 0.05] and MyPS (CON: 0.059 [+ or -] 0.008, ISO: 0.055 [+ or -] 0.009; P > 0.05), as well as measures of WBPT were unaffected. On the basis of this investigation, we conclude that acute intravenous [beta]-AR stimulation does not increase mitochondrial protein synthesis or biogenesis signals in skeletal muscle. stable isotopes; sympathetic nervous system; isoproterenol; skeletal muscle

We investigated the effect of resistance exercise and feeding on the activation of signaling proteins involved in translation initiation. Nine young men (23.7 [+ or -] 0.41 yr; BMI = 25.5 [+ or -] 1.0 kg/[m.sup.2]; means [+ or -] SE) were tested twice after they performed a strenuous bout of unilateral resistance exercise, such that their contralateral leg acted as a nonexercised comparator, in either the fasted and fed [1,000 kJ, each 90 min (3 doses): 10 g protein, 41 g carbohydrate, 4 g fat] states. Muscle biopsies were obtained 6 h postexercise from both legs, resulting in four experimental conditions: rest-fasted, rest-fed, exercise-fasted, and exercise-fed. Feeding increased PKB/Akt (Ser473) phosphorylation (P < 0.05), while exercise increased the phosphorylation of Akt and the downstream 70 kDa $6 protein kinase ([p70.sup.S6K1], Thr389) and ribosomal protein $6 (rpS6, Ser235/236, Ser240/244; all P < 0.05). The combination of resistance exercise and feeding increased the phosphorylation of [p70.sup.S6Kl] (Thr389) and rpS6 (Ser240/244) above exercise alone (P < 0.05). Exercise also reduced phosphorylation of the catalytic epsilon subunit of eukaryotic initiation factor 2B (elF2B[epsilon], Ser540; P < 0.05). Mammalian target of rapamycin (mTOR, Ser2448), glycogen synthase kinase-3[beta] (GSK-3[beta], Ser9), and focal adhesion kinase (FAK, [Tyr.sup.576/577]) phosphorylation were unaffected by either feeding or resistance exercise (all P > 0.14). In summary, feeding resulted in phosphorylation of Akt, while resistance exercise stimulated phosphorylation of Akt, [p70.sup.S6K1], rpS6, and dephosphorylation elF2B[epsilon] with a synergistic effect of feeding and exercise on [p70.sup.S6K1] and its downstream target rpS6. We conclude that resistance exercise potentiates the effect of feeding on the phosphorylation and presumably activation of critical proteins involved in the regulation of muscle protein synthesis in young men. hypertrophy; lean body mass; protein accretion; weightlifting

Ten healthy young men (21.0 [+ or -] 1.5 yr, 1.79 [+ or -] 0.1 m, 82.7 [+ or -] 14.7 kg, means [+ or -] SD) participated in 8 wk of intense unilateral resistance training (knee extension exercise) such that one leg was trained (T) and the other acted as an untrained (UT) control. After the 8 wk of unilateral training, infusions of L-[ring-[d.sub.5]]phenylalanine, L-[ring-[sup.13][C.sub.6]]phenylalanine, and [d.sub.3]-[alpha]-ketoisocaproic acid were used to measure mixed muscle protein synthesis in the T and UT legs by the direct incorporation method [fractional synthetic rate (FSR)]. Protein synthesis was determined at rest as well as 4 h and 28 h after an acute bout of resistance exercise performed at the same intensity relative to the gain in single repetition maximum before and after training. Training increased mean muscle fiber cross-sectional area only in the T leg (type I: 16 [+ or -] 10%; type II: 20 [+ or -] 19%, P < 0.05). Acute resistance exercise increased muscle protein FSR in both legs at 4 h (T: 162 [+ or -] 76%; UT: 108 [+ or -] 62%, P < 0.01 vs. rest) with the increase in the T leg being significantly higher than in the UT leg at this time (P < 0.01). At 28 h postexercise, FSR in the T leg had returned to resting levels; however, the rate of protein synthesis in the UT leg remained elevated above resting (70 [+ or -] 49%, P < 0.01). We conclude that resistance training attenuates the protein synthetic response to acute resistance exercise, despite higher initial increases in FSR, by shortening the duration for which protein synthesis is elevated. hypertrophy; feeding; weight lifting

We aimed to determine the impact of intense resistance training, designed to increase lean body mass (LBM), on both fasted and fed whole body protein kinetics in untrained young men. Twelve healthy males (22 [+ or -] 2 y of age; B M I, 24.3 [+ or -] 2.4kg/[m.sup.2]) participated in a 12-wk (5-d/wk) resistance training program. Before and after training, a primed constant infusion of [1[-.sup.13] C] leucine was used to measure whole body leucine turnover, protein breakdown, and nonoxidative leucine disposal in the fasted and fed states. Participants were studied during 5-d controlled diet periods that provided a moderate protein intake [1.4 g/(kg body wt.d)]. We estimated protein turnover and nitrogen balance. Training increased LBM (61.6 [+ or -] 6.9 vs. 64.8 [+ or -] 6.7 kg, P

We aimed to determine whether there were differences in the extent and time course of skeletal muscle myofibrillar protein synthesis (MPS) and muscle collagen protein synthesis (CPS) in human skeletal muscle in an 8.5-h period after bouts of maximal muscle shortening (SC; average peak torque = 225 [+ or -] 7 N*m, means [+ or -] SE) or lengthening contractions (LC; average peak torque = 299 [ + or -] 18 N*m) with equivalent work performed in each mode. Eight healthy young men (21.9 [+ or -] 0.6 yr, body mass index 24.9 [+ or -] 1.3 kg/[m.sup.2]) performed 6 sets of 10 maximal unilateral LC of the knee extensors on an isokinetic dynamometer. With the contralateral leg, they then performed 6 sets of maximal unilateral SC with work matched to the total work performed during LC (10.9 [+ or -] 0.7 vs. 10.9 [+ or -] 0.8 kJ, P = 0.83). After exercise, the participants consumed small intermittent meals to provide 0.1 g*[kg.sup.-1] * [h.sup.-1] of protein and carbohydrate. Prior exercise elevated MPS above rest in both conditions, but there was a more rapid rise after LC (P < 0.01). The increases (P < 0.001) in CPS above rest were identical for both SC and LC and likely represent a remodeling of the myofibrillar basement membrane. Therefore, a more rapid rise in MPS after maximal LC could translate into greater protein accretion and muscle hypertrophy during chronic resistance training utilizing maximal LC. eccentric; concentric; resistance exercise; z-band streaming

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