Citrulline has been proposed as an ergogenic aid, leading to an interest in watermelon given its high citrulline concentration. The aim of this study was to determine the effects of a single, pre-exercise dose of l-citrulline, watermelon juice, or a placebo on the total maximum number of repetitions completed over 5 sets, time to exhaustion, maximal oxygen consumption (VO2max), anaerobic threshold, and flow-mediated vasodilation. A randomised double-blind within-participants study design was used to examine these effects among 22 participants (n = 11 males). Supplementation included either a 7.5% sucrose drink containing 6 g of l-citrulline, 710 mL of watermelon juice (~1.0 g citrulline), or a 7.5% sucrose placebo drink. Supplementation was administered 1 or 2 h before exercise testing to investigate a timing effect. There was no significant effect between the three supplements for the total number of repetitions, time to exhaustion, VO2max, anaerobic threshold, or flow-mediated vasodilation. There was also no interaction observed relative to gender or supplement timing (P > 0.05). A single dose of l-citrulline or watermelon juice as a pre-exercise supplement appears to be ineffective in improving exercise performance; however, greater doses of l-citrulline have been shown to be safe and are currently left unexamined.

Defining mechanisms that maintain tissue stem cells during homeostasis, stress, and aging is important for improving tissue regeneration and repair and enhancing cancer therapies. Here, we show that Id1 is induced in hematopoietic stem cells (HSCs) by cytokines that promote HSC proliferation and differentiation, suggesting that it functions in stress hematopoiesis. Genetic ablation of Id1 increases HSC self-renewal in serial bone marrow transplantation (BMT) assays, correlating with decreases in HSC proliferation, mitochondrial biogenesis, and reactive oxygen species (ROS) production. Id1 HSCs have a quiescent molecular signature and harbor less DNA damage than control HSCs. Cytokines produced in the hematopoietic microenvironment after γ-irradiation induce Id1 expression. Id1 HSCs display a blunted proliferative response to such cytokines and other inducers of chronic proliferation including genotoxic and inflammatory stress and aging, protecting them from chronic stress and exhaustion. Thus, targeting Id1 may be therapeutically useful for improving HSC survival and function during BMT, chronic stress, and aging.

Gadomski, SJ, Ratamess, NA, and Cutrufello, PT. Range of motion adaptations in powerlifters. J Strength Cond Res 32(11): 3020–3028, 2018—The aim of this study was to investigate range of motion (ROM) and training patterns in powerlifters. Upper- and lower-extremity passive ROMs were assessed through goniometry in 15 male powerlifters (35.3 ± 13.7 years) and 15 age-matched controls (34.9 ± 14.6 years). The Apley scratch test and modified Thomas test were used to assess ROM across multiple joints. Training frequency, stretching frequency, and exercise selection were recorded using questionnaires. Passive glenohumeral (GH) extension, internal rotation, and external rotation ROM were significantly decreased in powerlifters (p < 0.050). Powerlifters displayed decreased ROM in the Apley scratch test in both dominant (p = 0.015) and nondominant (p = 0.025) arms. However, knee extension angle was markedly improved in powerlifters (20.3 ± 7.3°) compared with controls (29.9 ± 6.2°; p < 0.001). Bench press and bench press variations accounted for 74.8% of all upper-body exercises, whereas back squat and deadlift accounted for 79.7% of all lower-body exercises in powerlifters' training programs. To determine whether existing ROM adaptations were seen in elite powerlifters, the powerlifting cohort was split into 3 groups based on Wilks score: <400 (low), 400–500 (intermediate), and >500 (high). GH ROM limitations were more pronounced in elite powerlifters (Wilks >500), who had more powerlifting experience (p = 0.048) and greater lean body mass (p = 0.040). Overall, powerlifters displayed decreased GH ROM, but increased hamstring ROM, after training programs that were heavily focused on the bench press, back squat, and deadlift.

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