Triceps pushdown is one of the first exercises most lifters learn, and for a good reason. pushdowns, also knows as tricep extensions are a great and simple exercise that isolates your triceps and builds strength and mass.
The triceps make up most of your arm, so if you want big arms, you have to train them hard. Just like its name, the triceps are consisted of three muscles, all working together to achieve elbow extension.
Using a cable gives you an added benefit over free weights - it provides steady resistance throughout the full range of motion, keeping the tension on your muscles all the time.
Instead of standing up straight, tilt your torso forward 30 degrees. doing pushdown while standing up straight limits your range of motion, in a way that the long head of the tricep muscle is left out, the muscle that is responsible for shoulder extension. Which means, you only train part of your triceps. Tilting your body will give you full range of motion, and will engage the whole three muscles consisting your triceps.
You can to the tricep pushdown with a straight bar, v bar or with a rope, each has it own benefits. Although all attachments target all three heads of the triceps, there are some minor differences. The rope attachment enables you to target fibers deep within the triceps and to move through a fuller range of motion when you straighten your wrists at the bottom of the exercise, it will also give you slightly more tricep activation than the bar. Using a v-bar emphasizes the outer portion of the triceps muscle and the lateral head, while a straight bar puts greater emphasis on the long head.
Keep your upper arms close to your body in the same position and your core tight. Try to move your body as less as possible. Moving your elbows will engage your shoulders and reduce the pressure on your triceps.