For this exercise, you need a band of rubber exercise tubing. Use low-resistance tubing until you become familiar with the exercise.
Grasp one handle of the tubing in each hand. Position the tubing behind your back and under each armpit. Increase the tension on the tubing by wrapping it around each hand several times.
Stand with your feet shoulder-width apart. Hold the handles at shoulder height with palms turned down. Your elbows should be at shoulder level and bent at 90-degree angles.
Keeping your hands at shoulder level or slightly below, press the handles forward until you extend your arms fully. Do not lock your elbows; keep them relaxed. Hold briefly, then slowly return to the start position. Count one-two-three while pressing out, one-two on the pause, and one-two-three-four on the return. One-two-three. One-two. One-two-three-four.
When you are comfortable with the exercise, increase the resistance of the tubing until you can do 18 to 20 repetitions using proper form. To increase resistance, shorten the tubing by wrapping it around each hand, or choose a higher resistance tubing. Once you can achieve 25 or more repetitions, increase the resistance to bring you back to the 18-to-20-repetition target zone.