The machine, which was installed this week as a promotion for next year's Winter Olympics in Sochi, will issue a one-way ticket to anyone who does 30 squats in 2 minutes.
Russia's RIA Novosti news service said the mini-workout works out to one squat per ruble for a 30-ruble (90 cents) ticket.
The report did not say whether the system has a way of verifying passengers keep their end of the bargain.
The machine was installed at the Vystavochnaya station in downtown Moscow. Tickets at the system's 189 other stations still require cash.