Sit up straight and grab a dumbbell with both hands. Raise it above your head so it's vertical and in line with your spine. Brace your core and lower the weight behind your head until your forearms touch your biceps; then press back up to the start, keeping your upper arms stationary.
Perform 8-12 reps.
Sit with your knees 2ft apart and feet flat. Hold a dumbbell in each hand, palms up, and lean forwards so your forearms rest on your thighs and wrists hang over your knees. Using your wrists only, curl the weights up as high as possible. Now rotate to a palms-down position and bend your wrists up.
Sitting on the edge of a bench, hold a dumbbell in each hand, letting your arms hang by your sides. Keep your back straight and curl the weights up until your thumbs are near your shoulders. Squeeze, then lower. Now rotate your wrists so your palms face backwards and curl again.
Do 8-12 reps, alternating grips.
Lie back on an incline bench and hold a light dumbbell over your head in your left hand, palms facing in. Support the arm with your right hand. Bend your left arm to lower the weight to your right shoulder; don't bend your wrists. Raise it back up.
Do 12 reps, then switch arms.
Stand holding light dumbbells by your thighs with your palms facing each other. Keep your arms straight, then slowly raise them in front of you at eye level and point to the 10 o'clock and 2 o'clock positions. Slowly lower back down again. Do 8-12 reps to cap off your arm muscle.
Try this workout as part of a complete 28-day plan.