Increasing dietary nitrate (NO3-) through beetroot juice (BRJ) supplementation elicits acute ergogenic benefits. However, it is unknown whether chronic NO3- supplementation can enhance resistance training (RT) adaptations in middle-aged and older individuals. Therefore, we sought to determine whether 12 weeks of combined RT and NO3- supplementation enhanced hypertrophic, vascular, strength, and skeletal muscle angiogenesis adaptations in this population. Twenty-eight apparently healthy, untrained men and women (56±7 years old, 29.1±5.3 kg/m2 body mass index) completed 12 weeks of supervised full-body RT (2x/week) while ingesting either BRJ (140 mL daily, providing 800 mg NO3-; n=14 with 7M/7W) or NO3--depleted BRJ placebo (PLA; n=14 with 7M/7W). Participants underwent a whole-body dual-energy x-ray absorptiometry scan, right mid-thigh ultrasonography for muscle imaging, right leg popliteal artery flow-mediated dilation (FMD) assessments, a biopsy of the right mid-thigh vastus lateralis, and strength testing prior to and following the 12-week intervention. Biopsy analyses included a NO3-/nitrite (NOx) fluorometric assay, immunoblotting for proteins involved in angiogenesis, and immunohistochemistry to quantify fiber type-specific capillaries and cross-sectional areas. Muscle NOx values did not significantly change: +15.4% in BRJ (p=0.073) and +7.8% (p=0.514) in PLA. Both groups significantly improved measures related to muscle hypertrophy, strength, and FMD. However, no significant group × time interactions were observed for whole-body lean mass, mid-thigh muscle cross-sectional area, popliteal artery FMD outcomes, or histological or molecular markers. In conclusion, BRJ supplementation does not enhance RT adaptations in middle-aged and older adults.

Acute nitrate-rich beet root juice supplementation has been shown to improve aspects of endurance exercise performance. These effects may, in part, be due to nitric oxide-mediated effects on skeletal muscle contractility and mitochondrial function. However, no studies have investigated the effects of chronic nitrate supplementation with resistance training (RT) on molecular markers of mitochondrial adaptation and redox state within the skeletal muscle of middle aged and older adults. Likewise, whether supplementation affects functional RT outcomes in this population is unresolved. In the current study, 27 participants (56±7 years old, 85.9±20.6 kg, 36.1±8.3 percent body fat) were block-randomized to consume either a nitrate-depleted (Placebo) or nitrate-rich (~13 mmol) beet root juice (Nitrate) daily and complete 12 weeks of supervised total body RT (2 days per week). Vastus lateralis (VL) biopsies and measurements of leg extensor peak force, strength-endurance, and fatigue were obtained prior to training and ~72 hours following the last training bout. In all participants, training increased VL citrate synthase activity (i.e., mitochondrial content), certain proteins indicative of mitochondrial biogenesis and dynamics, and most leg extensor performance variables. However, Nitrate supplementation did not confer additional benefits with any of the outcomes. In conclusion, increased dietary nitrate consumption in older adults engaged in RT does not alter muscle mitochondrial or redox state variables. Moreover, while RT enhanced leg extensor peak force, strength-endurance, and fatigue outcomes, no additional benefits were observed with Nitrate supplementation.

Background/Objectives: Higher energy and carbohydrate intakes have been hypothesized to enhance resistance training adaptations, yet empirical evidence remains mixed. The purpose of this study was to investigate whether supplemental carbohydrate–energy intake improves muscle hypertrophy and strength. Methods: Twenty resistance-trained men (26.7 ± 4.9 years old, 9.7 ± 6.1 years training experience) completed a quasi-randomized, double-blinded, counterbalanced crossover trial. Participants consumed either a daily protein-only supplement (30 g protein, 4 g carbohydrate) or a daily protein-plus-carbohydrate supplement (30 g protein, 54 g carbohydrate) for 8 weeks each, followed by crossover, while continuing their habitual training and nutrition. Primary outcomes included lean mass obtained using dual-energy X-ray absorptiometry, muscle thickness and cross-sectional area obtained via ultrasound, back squat one-repetition maximum, fatigue index, and knee extensor peak torque. Differences in estimated marginal means, controlling for order and phase effects, were analyzed via linear mixed models, with first-phase-only ANCOVAs as sensitivity analyses. Results: The carbohydrate–protein condition resulted in significantly higher daily energy (+485 kcal/d; p = 0.017) and carbohydrate intake (+33 g/d; p = 0.043) than the protein-only condition, with no differences in protein or fat intake or training volume. No significant differences between conditions were observed for any outcome, including in the sensitivity analyses. Conclusions: Modest supplemental carbohydrate–energy intake did not significantly augment muscle hypertrophy, fatigue resistance or strength in trained men within our study context. More high-powered research is needed to determine how much and under which circumstances carbohydrate–energy intake affects resistance training adaptations.