The effects of chronic beetroot juice supplementation with resistance training on skeletal muscle mitochondrial and redox markers in middle-aged and older adults

Abstract Purpose Acute nitrate-rich beetroot juice (BRJ) 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 BRJ supplementation with resistance training (RT) on molecular markers of mitochondrial adaptation and redox state within the skeletal muscle of older adults. Likewise, whether supplementation affects functional outcomes in this population is unresolved. Methods In the current study, 27 older adults (56 ± 7 years old, 85.9 ± 20.6 kg, 36.1 ± 8.3% body fat) were block-randomized to consume either a nitrate-depleted (Placebo) or nitrate-rich (~ 13 mmol) BRJ 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 h following the last training bout. Results In all participants, RT increased VL citrate synthase activity (i.e., mitochondrial content), certain proteins indicative of mitochondrial biogenesis and dynamics, and most leg extensor performance variables. However, BRJ supplementation did not confer additional benefits with any of the outcomes. Conclusions RT in middle-aged and older adults dynamically alters muscle mitochondrial markers and knee extensor performance variables, albeit increased dietary BRJ consumption does not confer additional benefits.