Limited effects of dietary nitrate supplementation with resistance training on skeletal muscle and vascular outcomes and in middle-aged and older adults

Increasing dietary nitrate (NO 3 - ) through beetroot juice (BRJ) supplementation elicits acute ergogenic benefits. However, it is unknown whether chronic 3 - 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 3 - 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/m 2 body mass index) completed 12 weeks of supervised full-body RT (2x/week) while ingesting either BRJ (140 mL daily, providing 800 mg 3 - ; n=14 with 7M/7W) or 3 - -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 3 - /nitrite (NO x ) fluorometric assay, immunoblotting for proteins involved in angiogenesis, and immunohistochemistry to quantify fiber type-specific capillaries and cross-sectional areas. Muscle NO x 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, these preliminary data on a limited number of participants indicate BRJ supplementation does not enhance RT adaptations in middle-aged and older adults.