REDUCED IMPROVES OXYGEN
Oxygen is vital to release the energy that powers muscle. Athletes are under constant energy demand, especially during submaximal exercise (~85% of max heart rate). Increasing oxygen availability can enhance muscle efficiency.
The first study investigating nitrate supplementation (not beetroot juice) and exercise efficiency found a decrease in oxygen use during a multi-stage test on a bike. On average, nitrate supplementation increased resting blood nitrite levels (the precursor to nitric oxide—the molecule responsible for physiological benefits) by 82% and decreased VO2 by 5% (Larsen et al., 2007). This study showed the benefits of nitrate supplementation; however, dietary nitrate supplementation from beetroot juice is a safer approach.
THE RESULTS FOR BEETROOT JUICE:
Moderate-intensity exercise: steady-state VO2 reduced by 5%
High-intensity exercise: nitrates delayed the time to reach peak VO2—increasing time to exhaustion by 16% (11.3 min for beetroot vs. 9.7 min for placebo)
In 2010 Bailey et al. followed up with another study to explore why dietary nitrate supplementation helps reduce the need for oxygen during of exercise. Seven men drank either 500 ml/day of beetroot juice or placebo for six consecutive days. The men completed low- and high-intensity step exercise tests on the final three days.
THE RESULTS FOR BEETROOT JUICE DRINKERS:
Low-intensity exercise: decreased submaximal VO2
High-intensity exercise: increased time to exhaustion by 25%
Beetroot juice can also improve oxygen when walking and running. In 2011 Lansley et al. had nine healthy, physically active men to drink 500 ml/day of beetroot juice or placebo for six days. On days 4 and 5, the men completed treadmill exercise tests. On day 6, they completed knee-extension exercise tests.
Compared to a placebo, beetroot juice lowered the use of oxygen:
Walking: 0.87±0.12 l/min for placebo and 0.70±0.10 l/min for beetroot juice
Moderate-intensity running: 2.26±0.27 l/min for placebo and 2.10± 0.28 l/min for beetroot juice
Severe-intensity running: 3.77±0.57 l/min for placebo and 3.50±0.62 l/min for beetroot juice
Beetroot juice led to a 15% increase in time to exhaustion during severe-intensity running (7.6±1.5 min for placebo and 8.7±1.8 min for beetroot juice) (Lansley, Winyard, Fulford, et al., 2011).
WHY IS THIS IMPORTANT? Endurance performance depends on muscle efficiency. An improvement in muscle efficiency leads to the ability to work longer for the same amount of energy input—this increases tolerance to exercise. Beetroot juice can improve time-to-exhaustion with no adverse effects. The reduced need for oxygen in low-intensity exercise may be due to a lower energy (i.e., adenosine triphosphate) cost of muscle contraction. Beetroot juice allows athletes to better tolerate high-intensity exercise for a longer period of time.
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