When working the back of your arms you want to work the muscle in a variety of movements. Push the muscle to it highest performance to see the benefits. To get lean arm go high reps and medium weight. To build use heavier weight and remember always go at your own fitness level. The triceps need to be worked often to see the results you want.
Here are a few exercises that I like to use with my clients.
- Lunge triceps kick
- Same position but palms up
- Triceps over head