Two Great Myths Of Ergonomic Mouse Design
Every culture develops its own myths, and the “culture” of ergonomics is no exception. Today let’s take a hard look at two major myths of ergonomic mouse design.
You may not have heard these myths repeated in words, but you have probably seen their results without realizing it. One or the other is reflected, to some extent, in nearly all ergonomic mouse designs on the market today.
Myth #1: The more you use your arm and shoulder vs. your hand, the better.
The arm and shoulder are big parts, with big muscles and tendons. Big parts are harder to injure than small ones, so it’s natural to conclude that as much work as possible should be assigned to this “stronger” section of the arm. There’s just one problem with that approach.
As we showed previously (see The Homunculus And The Ergonomic Mouse), the arm lacks precision and dexterity compared to the hand. This can result in stress and shoulder injuries over time, which is the exact opposite of what an ergonomic mouse is supposed to achieve.
The answer is not to load up the hand again, but to get the entire structure – shoulder, arm, and hand – moving freely and working together. This was confirmed by the scientific work of Zhai (Zhai, Milgram, Buxton, 1996). This study showed that an effective computer mouse should rely on all parts of the upper limb working in synergy, rather than depending on one particular limb segment such as the shoulder.
Myth #2: Beware, my son, the Pinch Force Monster
A good myth is incomplete without a scary monster, so ergonomics provides us with one of those too. This repetitive-stress Grendel is called the Pinch Force Monster, and he has been feared ever since medical endoscope operators began to report sore hands.
A bit of background: operating an endoscope requires regular squeezing pressure on a scissors-like grip with significant resistance. Not surprisingly, this repetitive action can result in hand stress and injuries over time.
Since the action of clicking a vertical mouse superficially resembles the “pinch grip” of the endoscope, many well-meaning ergonomic professionals have concluded that vertical mousing must be harmful. But this conclusion overlooks two crucial differentiating factors: the type of grip, and the degree of force involved.
The two principal hand grips, defined by Dr. Napier more than fifty years ago, are known as “power grip” and “precision grip.” The power grip involves pushing against the palm and is classified as a static muscle activity. The precision grip, roughly described by holding a pencil, involves more dynamic muscle activity and thus tends to be less stressful.
The DXT ergonomic mouse design utilizes this pencil-like precision grip for most mousing activities. Sometimes – for example during drag-and-drop – a type of pinch grip is called for. But even then, the low degree of required pressure renders the Pinch Force Monster harmless. Studies show that repetitive grip is indeed harmful, but only if that grip applies a force of at least 10 Newtons (about 2.2 pounds). The maximum pressure required when using a DXT mouse is just 0.73 Newtons – barely 7% of the danger threshold.
The first ergonomic mouse design myth we looked at today is an oversimplification, trying to fix a complicated motion problem by immobilizing the “trouble spot.” Transferring work to your shoulder seems to help for awhile, but the lack of dexterity in that area will soon tell in terms of stress. The entire upper limb should be kept as free as possible, liberating its amazing design to distribute stress while accomplishing work.
Our second myth is based on a real problem, but if we look carefully, we can see that it has been misapplied to ergonomic mice. The Pinch Force Monster is real, but he belongs in an entirely different story. Myths are fine for repeating around a campfire, but not so good for informing decisions about your health.
When considering an ergonomic mouse, be sure that your choice is based entirely on facts.