Resisted shoulder flexion in sitting - long lever (Shoulder flexion strengthening, with band, arm straight, sitting)

Sit upright in a chair with your hands relaxed by your sides.
Hold one end of a resistance band in your hand with the other end securely under your foot or tied around the chair.
Leading with your thumb, lift your weaker arm up, keeping your elbow straight.
Hold this position before returning your arm back down to your side.
Ensure you do not hunch your shoulder during this exercise.