Did Popeye© know something about nitrates?

In 1930s, Popeye became so popular for his incredible strength due to ingestion of a can of spinach that immediately increased muscular strength and power. Recent studies suggest a physiological relevance of nitrates (abundant in green leafy vegetables, such as spinach) in skeletal muscle fibers. Nitrate seem to reduce O2 cost of exercise and enhance mechanical efficiency. PURPOSE: No studies have investigated if nitrates supplementation enhances muscle strength and anaerobic performance as well. METHODS: Seven healthy male subjects (age 25 2 years) participated in a randomized double-blind cross-over study and were tested before (PRE) and after 6 days of 0.5 l/day spinach juice (5.5 mol/day nitrate) (SPINACH) or placebo (PLACEBO). The following tests were carried out: a) maximal voluntary isometric contraction (MVC) of knee extensors; b) fatiguing, intermittent sub-maximal (75% MVC) isometric knee extension; c) Wingate 30s test (W30s); d) Repeated Sprint Ability test (RSA) comprising one set of 5 × 6-s maximal sprints with 24 s of passive recovery between repetitions. During the isometric exercises, EMG of vastus lateralis and biceps femoris was recorded. Blood lactate (La) was obtained at rest and after exercise on a mechanically braked cycle ergometer. RESULTS: Relative to PRE, in PLACEBO there were not significant differences for the investigated variables. In contrast, SPINACH vs. PLACEBO: a) Maximal voluntary torque of knee extensors was not significantly different (187 ± 13 vs. 189 ± 13 Nm, p<0.05); total muscle work, estimated as the sum of impulses generated during the fatiguing sub-maximal contractions, was significantly higher (361 ± 69 vs. 254 ± 57 Nm*s*kg-1, p<0.05). b) During W30s mean power was significantly higher (541 ± 22 vs. 506 ± 19 W, p<0.05) and fatigue index was significantly lower (40.4 ± 1.8 vs. 45.9 ± 2.9 %, p<0.05). Lapeak was not significantly different. As for RSA, peak power was significantly higher during the 3rd, 4th and 5th repetition. CONCLUSIONS: A moderate dietary dose of nitrates significantly enhanced variables of anaerobic performance in humans. These effects could be due both to a reduction of ATP cost and to an increase of ATP oxidative production. Although Popeye didn’t know anything about nitrate, we can hypothesize that nitrates could be the “force” of Popeye’s spinach.