I cycle on and off this drink throughout the year for no other reason than simply using it when I need it and not using it when I don't need it. When I'm in 'season' and I'm hitting bodybuilding hard and road cycling hard this drink is part of my daily regimen. I have used this drink (by witness account) on long road cycling rides to power through tough parts of the ride and to overcome cramping and fatigue. I mix about 1-2 ounces in an 8-10 ounce glass of water.

The modern name for this drink is Apple Cider Vinegar, aka ACV or ACV shake. The original name of this drink as used in ancient times was Posca...

Posca was increasingly heavily used by the Roman army during the Republican period when it became a standard beverage for soldiers. The drinking of quality wine was considered a sign of indiscipline, to the point that some generals banned imported vintage wine altogether. Appian records both posca and wine as being among the provisions of the army of Lucullus in his Spanish campaign of 153 BC. It had evidently become part of the customary rations by the 1st century AD; the Christian Gospels describe Roman soldiers offering Jesus sour wine on a sponge (flavoured with hyssop, an aromatic flower, according to the Gospel of John) during the Crucifixion. 

The Historia Augusta records that by Hadrian's time sour wine was a standard part of the normal "camp fare" (cibus castrensis). A decree of 360 AD instructed the lower ranks of the army to drink posca and wine on alternate days.

Although it was primarily associated with soldiers and the lower classes, some higher-ranked Romans also drank posca to express solidarity with their troops. 

Military Benefits

According to Plutarch, Cato the Elder was particularly noted for liking posca. Girolamo Cardano, in his Encomium Neronis, Basel (1562), attributed the superiority of the Roman armies to only three factors: the great quantities of levies, their sturdiness and ability to carry heavy weights due to training, and good foods such as salted pork, cheese and the use of posca as a drink.[3]

Vinegar history provides many examples of this liquid's usefulness to everyday soldiers. Diluted vinegar has been used as a strengthening and energizing tonic by the military throughout the ages. Roman soldiers called this refreshing drink "posca", and used it regularly as did the Japanese samurai. The addition of vinegar to drinking water had the additional benefit of killing any infectious agents that might have been present.

Throughout history the antiseptic nature of vinegar has been used to clean and disinfect soldiers wounds and thus speed up wound healing. Apple cider vinegar was used to this effect during the American civil war and as late as world war one.

References:

1) https://en.wikipedia.org/wiki/Posca

2) http://www.apple-cider-vinegar-benefits.com/vinegar-history.html

3) Cardano, Girolamo. Nero, An Exemplary Life (translated by Angelo Paratico) pp.185-6, Inkstone Books, Hong Kong, 2012. ISBN 978-988-99939-6-2