Get a gym. Commonly known as skullcrushers, lying triceps extensions are a great way to isolate your triceps muscles. Lying Triceps Extensions. Instructions Lying back on a bench with dumbbells in each hand, your arms fully extended overhead. Thanks in advance. This exercise, like dumbbell kickbacks, also work the muscle similarly to tricep pushdowns, just by again putting your body in a different position. The alternating dumbbell triceps extension is an isolating single-joint exercise used to increase size and strength throughout the triceps. I need an alternative to lying tricep extensions.. an exercise that I could get the same (or better) results from. Lying Dumbbell Tricep Extension. Lying Dumbbell Tricep Extensions. Otherwise, close-grip press is good or overhead extensions. I use a Crossbow (by Weider) which can handle many exercises, but I have no "free" weights. This is one of my personal favorites!