Hold a single-arm handle in one hand in front of you on a high cable attachment with the elbow flexed and palm facing down. Keeping the trunk braced tightly, and the elbow close to the side, extend the elbow maximally, then return to the top under control.
 
Purpose
The tricep pushdown is an effective way to isolate the triceps for strengthening elbow extension and general elbow stability. Training a single arm at a time helps develop and preserve symmetry side to side.
 
Programming
Generally sets of 6-15 reps are appropriate.