If you apply this on sports betting, say, you place a $20-bet on Barcelona and you lose. You double on your next bet and you win. It doesn't mean you recovered your $20 loss. It may happen that you won on a 1.20 bet, meaning you only won $8 from your $40 bet, which further means you still have a net loss of $12.
That's why you need to increase the bet, what you're playing is not Martingale, you simply "flat betting" using the same amount.
For a 1.5 you need to double, for a 1.25 you need to quadruple, and this will soon spiral out of control, especially with a favorite.
Look how this scenario turned out:
Good old gambler fallacy and why martingale is a bad idea!
It's, therefore, going to be a different version of Martingale, if we can still call it as such. Martingale is basically doubling your next bet every time you lose. But since the goal of which is to recover all your previous losses and even make a profit by just a single bet, and you can't apply this to sports betting because of different odds, you have to make modifications. You're forced to more than double, even triple, your next bet. That's essentially a deviation from the Martingale system. And that would require you to have a much bigger bankroll or else you'd go bankrupt much faster.