Zac Efron [1] knows the value of a good workout buddy. We're fairly sure that his YouTube series "Gym Time" [2] is just a clever way to work out with as many fun people as possible; see his videos with Alexandra Daddario [3], Nina Dobrev [4], and a group of Victoria's Secret models [5] for our supporting evidence.

His latest workout with YouTube star Liza Koshy might go down as the most entertaining one yet. There are subtle High School Musical [6] references, so many high-fives, and a deep Q & A session while balancing on a stability ball (as one does). The workout itself? It's no joke. Zac and Liza go through some challenging plank and glute bridge variations [7], forward and backward lunges, and battle rope sequences [8] before ending with a stability ball plank. Check out the full workout above to get all their moves and a healthy dose of gym buddy FOMO.