We are familiar with mobility concerns, but even there we often are looking at just the most obvious. Mobility definitely involves moving about and getting around, and we look for someone's ability to do it without assistance or what they might need to help them do this, such as a cane, walker, wheelchair, or other device.
However, mobility includes so much more. It involves every joint in the body. When evaluating or considering mobility, there are the toes, ankles, knees, hips, spine, elbows, wrists, fingers, shoulders, and neck. All are important, and when one part of this system is weakened or affected, the ability to get around or maneuver suffers accordingly.
Balance, stamina, and coordination - while technically part of the sensory system - affect mobility because a person must be able to get around while maintaining full control. If they feel, in anyway, that they can't complete a particular motion because of a lack of well-being, they are not going to have effective mobility.
Reach is related. Closet shelves, upper cabinets, lower cabinets, door handles, drawer pulls, light switches and controls, faucets, shower heads, windows, and even more in a home are dependent upon someone's reach to access and use them as they have been intended.
There are three main factors that affect someone's reaching ability. The first is physical in that they can't straighten the hand of arm enough toward the object they are intending to grasp. Range of motion is part of this also, as the ability of their should joint and muscles must allow for the arm to be fully extended in the desired direction.
When someone can't fully raise or extend their arm over their head (pointing upward), or out in front of them parallel to the floor, or what is termed functional reach where the arm is at a 120-degree angle with the torso, they are not able to obtain and retrieve items as easily as they could if their reach was not limited.
The second one also is physical. someone might not have the height necessary to reach items in the home that are located at higher levels - ceiling fixtures to change a light bulb, items on the top shelf, or dusting door frames, for instance.
Regardless of someone's range of motion or ability to fully extend their hand and arm, their physical height may limit what they can reach. They may want to get something located in a high place and otherwise be able to reach it, but without the assistance or a stool or small ladder, they won't be able to reach or access it.
The third is a physical issue in the home. Someone can't reach the window to open or close it because there is a piece of furniture or a cabinet in front of it that blocks their reach - even with full extension of their arms. It could be a wall control, outlet, switch, or other operational element in the home that is blocked or obstructed by a furnishing in the home.
Collectively, the are limitations to a person's reach - most of them beyond their control - that need to be factored into a home design or aging-in-place modification.