Combined effects of ischemic preconditioning and nitrate supplementation on submaximal cycling exercise and time-trial performance

Ischemic preconditioning (IPC) and dietary nitrate supplementation (DN) have both been shown to modulate nitric oxide (NO) availability. Despite the possibility of a synergistic response, the combined effects of IPC and DN during exercise have yet to be explored.

PURPOSE: To determine the effects of IPC alone and in combination with DN on the physiological responses to submaximal cycling and time trial (TT) performance.

METHODS: Following an initial maximal exercise test, nine competitive male cyclists (34 ± 6 Yr, V[Combining Dot Above]O_2peak: 55 ± 4 mL/kg/min) completed a baseline trial (BASE), and two experimental trials in a double-blind randomized cross-over design. Exercise trials comprised 6 min of cycling at 80% of the ventilatory threshold, followed by a 16.1 km TT. In the experimental trials participants received either 500 mg of DN (chard gel) or a NO₃^--depleted placebo (PLA) 90 min before completing three cycles of bilateral lower limb IPC at 180 mmHg. Venous blood samples were collected pre- and post-IPC to determine changes in plasma nitrite [NO₂^-]. V[Combining Dot Above]O₂ and HR were continuously monitored during submaximal exercise.

RESULTS: Full arterial occlusion was confirmed via coloured Doppler in all trials. Prior to IPC, plasma [NO₂^-] was higher in DN (774 ± 179 nM, P=0.047) than BASE (576 ± 170 nM) and PLA (544 ± 126 nM, P=0.752). Following IPC plasma [NO₂^-] increased in PLA (Δ104 ± 149 nM, d=0.70) and DN (Δ42 ± 90 nM, d=0.47), but not significantly (both P>0.2). In the DN trial, resting V[Combining Dot Above]O₂ was significantly lower compared to BASE (314 ± 69 vs. 367 ± 30 mL/min, P=0.02) and tended to be lower during exercise (P=0.066). Resting V[Combining Dot Above]O₂ was also lower in PLA than BASE (323 ± 62 mL/min, P=0.01) and during exercise (2783 ± 262 vs. 3013 ± 342 mL/min, P=0.04). HR was not significantly different in submaximal exercise (P=0.842). Completion time of TT was not different between conditions (BASE: 1336 ± 73 s, PLA: 1344 ± 88 s, DN: 1344 ± 76 s, P=0.69). Compared to BASE (171 ± 4 bpm), HR was lower following DN (166 ± 4 bpm, P=0.02) but was not different in PLA (169 ± 4 bpm, P=0.60).

CONCLUSION: In the present study, IPC with or without DN, altered a number of physiological responses during rest and submaximal exercise, potentially mediated by an increase in plasma [NO₂^-]. Despite this, there was no evidence for an additive effect and neither intervention altered TT performance.