"Grab the big toe by thumb, the forefinger and the middle finger. And whirl the big toe for 10 times. This stimulation heals the high pressure and the low pressure.

Also, giving appropriate stimulation to these three (parts of the) toe makes the liver and kidney strong .

Of course, to massage for all of the toes is also good for health."

This was from a magazine article 'Ninja Kenkō-hō Hi Sakusen Hichibuku Goshinjutsu'(忍者 健康法秘作戦 秘致武九護身術) - Ninja health method secret strategy) published circa 1972 (translated by Takeharu Nakadai).