BEETter AGING: Short-Term Dietary Nitrate Supplementation Enhances Muscle Contractile Properties in Older But Not in Young Adults.

Abstract

Dietary nitrate (NO 3- ) supplementation has been shown to improve skeletal muscle contractile function and reduce fatigue, potentially due to alterations in skeletal muscle Ca 2+ handling/sensitivity. Because aging muscle can have impaired Ca 2+ handling, the aim of the study was to evaluate the effects of dietary NO 3- supplementation on muscle contractile properties in young and older adults. Eleven older (69 ± 4 yr, O) and 11 young (26 ± 2 yr, YG) adults consumed either NO 3- -rich beetroot juice (BR) or placebo (PLA), for 7 d. After supplementations, plantar flexors of dominant leg were evaluated as follow: a) maximal voluntary isometric contraction (MVIC), b) potentiated single twitches (Tw pot ) and double twitches electrical stimulations at the frequency of 100 Hz (Db 100 ) on the tibial posterior nerve, c) a fatigue isometric (70% of MVIC) test until exhaustion. The force-frequency relationship was assessed with trains of electrical pulses across a wide range of frequencies on the muscle belly of the nondominant leg. BR supplementation increased plasma [NO 3- ] and nitrite [NO 2- ] in both O and YG compared with PLA (more than sevenfold; all P ≤ 0.02). No changes were observed in MVC, Tw pot , and Db 100 force after BR compared with PLA in both YG and O. Only in O, Db 100 area under the curve (-7 ± 6 N·s change from PLA) and half relaxation time (-0.05 ± 0.06 s change from PLA) were significantly reduced, and time to exhaustion (+32 ± 43 s change from PLA) was significantly longer (all P < 0.02) after BR. In O, BR also significantly increased submaximal force produced by trains of electrical pulses ( P < 0.001). NO 3- supplementation positively affects muscle contractile proprieties, submaximal electrically evoked force production, and fatigue resistance in older adults, whereas these positive results were not found in young.