Zac Efron’s former personal trainer says 2 common ab exercises are a waste of time. Here’s what he recommends instead. fitness Zac Efron’s former personal trainer says 2 common ab exercises are a waste of time. Here’s what he recommends instead. Rachel Hosie | Insider December 5, 2022 Hanging knee-raises work the hip-flexors more than the abs, Patrick Murphy, who trained Zac Efron for "Baywatch,"...Read More