If you're a guy who works out, doing push-ups on a decline with a stable surface fires up your triceps the most — more than using shaky suspension straps like TRX when your body is already at a steep angle.

If you're a guy who works out, doing push-ups with TRX straps might make your chest muscles work harder than regular push-ups—especially when you're more upright, like on a slight incline.

If you're a guy who works out, doing push-ups with your feet elevated (like on a bench) makes your shoulders, arms, and upper back work way harder than regular or uphill push-ups — the steeper the angle, the harder those muscles have to work.

If you're a guy who works out, doing push-ups at a 30-degree downward angle makes your shoulder-stabilizing muscles work way harder—up to 2.5 times more—than flat push-ups, no matter if you're on solid ground or using suspension straps.

If you're used to lifting weights, your triceps work harder during shoulder presses when you use a barbell on a solid bench than when you use dumbbells on a wobbly ball — the more stable the setup, the more your main muscles have to engage.

Pressing a barbell in front of your head works your triceps more than doing it behind your neck, because of how your body has to balance and where the weight is pulling.