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

Abstract

Purpose: Dietary nitrate (NO3-) supplementation has been shown to improve skeletal muscle contractile function and reduce fatigue, potentially due to alterations in skeletal muscle Ca2+ handling/sensitivity. Since aging muscle can have impaired Ca2+ handling, the aim of the study was to evaluate the effects of dietary NO3- supplementation on muscle contractile properties in young and older adults.

Methods: Eleven older (69 ± 4 yrs, O) and 11 young (26 ± 2 yrs, YG) adults consumed either NO3--rich beetroot juice (BR) or placebo (PLA), for 7 days. After supplementations, plantar flexors of dominant leg were evaluated as follow: a) maximal voluntary isometric contraction (MVIC); b) potentiated single twitches (Twpot) and double twitches electrical stimulations at the frequency of 100 Hz (Db100) 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 non-dominant leg.

Results: BR supplementation increased plasma [NO3-] and nitrite [NO2-] in both O and YG compared to PLA (more than 7-fold; all P ≤ 0.02). No changes were observed in MVC, Twpot, and Db100 force after BR compared to PLA in both YG and O. Only in O, Db100 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).

Conclusions: NO3- supplementation positively affects muscle contractile proprieties, submaximal electrically evoked force production and fatigue resistance in older adults while these positive results were not found in young.