Momentum strategies have never performed well during periods of high volatility, writes Mark Hulbert. : When will momentum regain the big mo? I am referring to investment strategies that favor top-performing stocks and avoid those at the bottom. According to the standard academic definition of momentum in the U.S. stock market, the approach has been struggling for over a decade. That standard definition keys off stocks’ performance from 12 months previously to one month previously. The chart below reflects the performance of a portfolio containing the 10% of U.S. stocks with the best returns over that trailing period.