Different products require the ability to reach one or both arms out from the body. This reaching can either occur in front of and above the body (to put on a hat), or out to the sides (to reach objects while sitting at a desk).

Reaching becomes more difficult as the arm moves further away from the rest position or when two arms have to reach out simultaneously.

The relative ability to position the hands compared to the head and body depends on the range of motion of the elbow and shoulder joints. The absolute position that each hand can reach to is also influenced by ergonomic factors such as body height and arm length, together with considerations such as wheelchair use.

Age-related conditions such as arthritis can cause reductions in joint mobility and stiffness leading to limited reaching ability. The distance that people can reach out to might be significantly less than the length of their arms.

Temporary injuries such as a broken or bruised arm or collarbone will also affect the distance a person can reach to.