The Effects of Chronic Nitrate Supplementation with Resistance Training on Skeletal Muscle Mitochondrial and Redox Markers in 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.