Acute effect of dietary nitrate on forearm muscle oxygenation, blood volume and strength in older adults: A randomized clinical trial.

Abstract

Both recovery time of post-exercise muscle oxygenation and muscle strength decline with aging. Although beetroot consumption has been shown to improve muscle oxygenation and exercise performance in adults, these effects in the elderly has not been addressed. The aim of the present study was to evaluate the effect of a beetroot-based gel (BG) on muscle O2 saturation, blood volume (tHb) and handgrip strength in the elderly in response to handgrip exercise. In a randomized crossover double-blind design, twelve older subjects consumed BG (100 g of beetroot-based gel containing ~ 12 mmol nitrate) or PLA (100 g of nitrate-depleted gel nitrate-depleted). The subjects performed a rhythmic handgrip exercise which consisted of a one 1-min set at 30% of the maximal voluntary contraction (MVC) of each subject, followed by a 1 min recovery. The muscle oxygenation parameters and tHb were continuously monitored by using near-infrared spectroscopy. MVC was evaluated at baseline, immediately after exercise, and 30 min afterwards. The muscle O2 resaturation rate during exercise recovery was greater in the BG when compared to PLA condition (1.43 ± 0.77 vs 1.02 ± 0.48%.s-1; P < 0.05). Significant increase was observed in tHb during exercise recovery (10.25 ± 5.47 vs 6.72 ± 4.55 μM; P < 0.05) and significant reduction of handgrip strength decline was observed 30 min after exercise in BG (- 0.24 ± 0.18 vs—0.39 ± 0.20 N; P < 0.05). In summary, a single dose of a beetroot-based gel speeds up muscle O2 resaturation, increases blood volume and improves recovery of handgrip strength after handgrip exercise in older adults.