Liu is also a fan of isometric pull-ups or chin-ups where you hold your chin above the bar.
Place both of your hands on a pull-up bar with your palms facing away from you (pull-up) or facing toward you (chin-up).
With a neutral spine and your abs engaged, pull yourself up so that your chin is just above the bar.
Hold this position, and focus on engageing your back muscles and keeping your shoulders pressed down away from your ears.
Liu suggests starting with 10- to 15-second holds where you can maintain tension in your upper back and core, then work your way up to 30- to 45-second holds.
To make this move a bit easier, stand on a chair or stable surface and jump up so that your chin is above the bar (meaning you don't have to do an actual pull-up or chin-up before going into your isometric hold).
You can also do this hold with a large resistance band around the bar (like you'd use if you were doing assisted pull-ups), placing your foot in the bottom of the band and pulling yourself up that way.