Increase in Maximal Cycling Power With Acute Dietary Nitrate Supplementation

Abstract

Muscle-shortening velocity and hence power have been shown to increase in the presence of nitric oxide (NO). NO availability increases after consuming nitrate (NO3-). Ingestion of NO3-rich beetroot juice (BRJ) has increased muscle power in untrained adults.

Purpose: This study determined whether NO3- supplementation could acutely enhance maximal power in trained athletes.

Methods: In this double-blind, crossover study, 13 trained athletes performed maximal inertial-load cycling trials (3-4 s) immediately before (PRE) and after (POST) consuming either NO3-rich (NO3) or NO3-depleted (PLA) BRJ to assess acute changes (ie, within the same day) in maximal power (PMAX) and optimal pedaling rate (RPMopt). Participants also performed maximal isokinetic cycling (30 s) to assess performance differences after supplementation.

Results: 2 x 2 repeated-measures ANOVA indicated a greater increase in PMAX from PRE to POST NO3 (PRE 1160 ± 301 W to POST 1229 ± 317 W) than with PLA (PRE 1191 ± 298 W to POST 1213 ± 300 W) (P = .009; ηp2 = 0.45). A paired t-test verified a greater relative change in PMAX after NO3 (6.0% ± 2.6%) than with PLA (2.0% ± 3.8%) (P = .014; d = 1.21). RPMopt remained unchanged from PRE (123 ± 14 rpm) to POST PLA (122 ± 14 rpm) but increased from PRE (120 ± 14 rpm) to POST NO3 (127 ± 13 rpm) (P = .043; ηp2 = 0.30). There was no relative change in RPMopt after PLA (-0.3% ± 4.1%), but there was an increase after NO3 (6.5% ± 11.4%) (P = .049; d = 0.79). No differences were observed between the 30-s isokinetic trials.

Conclusions: Acute NO3- supplementation can enhance maximal muscle power in trained athletes. These findings may particularly benefit power-sport athletes who perform brief explosive actions.

Keywords: beetroot juice; ergogenic aid; inertial load; muscle power; nitric oxide.

Figures

Figure 1

Trained athletes practiced maximal cycling sprints for 1 or 3 d. *Specifically, cyclists require 1 d of familiarization while untrained cyclists (i.e., athletes from other sports) require 3 d of familiarization to reliably produce maximal power on an inertial-load cycle ergometer. Participants warmed-up for 5 min at 90 rpm and at their self-elected intensity, and then rehearsed four maximal cycling trials (3-4 s). During the final day of familiarization, participants rehearsed a highly-fatiguing maximal cycling trial lasting 30 s on a separate isokinetic cycle ergometer. The beetroot juice (BRJ) supplementation trials occurred across two experimental days. Immediately prior to BRJ supplementation (PRE), participants warmed-up, and then performed four maximal cycling trials. They were then issued either nitrate-rich (NO3) or nitrate-depleted (PLA) BRJ. Participants rested without sleeping, exercising, or eating, but water was permitted, for ~2.5 h and then they repeated the morning protocol to assess acute changes in maximal cycling power after BRJ supplementation (POST), with the addition of a 30 s maximal cycling sprint. **The only difference between experimental days was ingestion of either NO3 or PLA.

Figure 2

The inertial-load method measures power (W) across a variety of pedal rates (rpm) in a single maximal cycling effort. Curves drawn with closed and open circles illustrate changes in the power-pedal rate relationships achieved by competitive athletes (n=13) immediately before (PRE) and ~2.5 h after (POST) consuming beetroot juice (BRJ), respectively. Individual data points represent power and corresponding pedal rates of single pedal revolutions occurring immediately before and after the revolution eliciting peak power and optimal pedal rate (enlarged circles) at the apex of each curve. Panels A and B illustrate acute changes in power and pedal rate from PRE to POST after consuming nitrate-depleted (PLA) and nitrate-rich (NO3) BRJ, respectively. Both panels display an upward shift in the power-pedal rate curve from PRE to POST, indicating an acute increase in maximal power after both PLA and NO3 (*p<0.001; ή2=0.83), but NO3 induced a greater rising power (†p=0.009; ή2=0.45). The rightward shift in the power-pedal rate curve in panel B indicates that there was an acute increase in optimal pedal rate from PRE to POST NO3 (‡p=0.043; ή2=0.30). Note: Values are represented as means. SD error bars were removed for clarity.

Figure 3

Acute relative changes in maximal power (%ΔPMAX) after consuming concentrated beetroot juice (BRJ) that was either depleted (PLA; open bar) or rich (NO3; closed bar) in dietary nitrate. %ΔPMAX was significantly greater after NO3 compared to PLA (*p=0.014; d=1.21). Note: Values represent mean±SD.