Assessment of the Musculoskeletal Load of the Trapezius and Deltoid Muscles during Hand Activity

deltoid muscle

Stabilization of Hand Required for High Precision Tasks

During fundamental research and field research we noted the significance of a relaxed hand and forearm to operate a computer mouse. Gripping and pinching as well as reaching for the mouse showed to have severe negative effects on the upper extremity.

We require our hands to perform a great number of varying tasks with the mouse which requires high precision. Although Professor Van Zwieten, Department of Anatomy, BioMed, University of Hasselt mentions the possible risk of moving from the wrist in his paper “Hand Positions in scrolling, as related to PC-workers’ dystonia and treatment of dystonia by means of vibrostimulation and external shock waves therapy” (2009) we sometimes have to.

Danuta Roman-Liu, et al.

Higher precision requires stabilization of hand and forearm to minimize stress. It is from this perspective that we are pleased to be able to refer to the paper by Danuta Roman-Liu, et al. Department of Ergonomics, Central Institute for Labour Protection, Warsaw, Poland.

“Assessment of the musculoskeletal load of the trapezius and deltoid muscles during hand activity.” (2001). In this publication the following is mentioned:

First, higher precision of a task in which only the hand is involved, requires accuracy of movements which means more stabilization of the upper extremity and thus higher muscle tension. Furthermore, in view of the difficulty and possibly the complexity of the task a higher muscular tension can be expected.

No Effect on the Deltoid Muscle

Where is the Deltoid muscle?

The resulting muscle loads due to the performed task influences the tension of the trapezius muscle. Contrary to what is generally thought the study proves that there is no effect on the deltoid muscle.

It should be noted that the lower the level of force used, the more precise a difficult task can be executed. As a consequence, when the forearm is not supported, a higher tension of the descending part of the trapezius muscle results. We herewith refer to the paper by Professor Han Ming Chen of National Taiwan University “The effect on forearm and shoulder muscle activity in using different slanted computer mice” (2007) and our team of Erasmus University Medical Centre “Result of the use of a hand supporting computer mouse by patients with neck and shoulder complaints” (2006).

Support the forearm

So this publication proves the need to support the forearm when working with a computer mouse.

Hand Support when using a computer mouse


Carpal Tunnel Syndrome Explained

Carpal Tunnel Syndrome
Today, more and more people world wide realise that it is important to support your hand when using a computer mouse. If you’re using a mouse that doesn’t fully support your hand, you may eventually experience serious neural effects.

This short video explains why that happens: when you push your hand on the desk and force it in a gripping, claw-like position, your wrist is forced in an awkward, bent position. Tendons may become irritated and swollen.

Pins and Needles

This causes excessive pressure on the median nerve which controls your hand and fingers. First you will notice a feeling of “pins and needles” in the fingers, followed by loss of sensation and even a burning pain. This phenomenon is generally called carpal tunnel syndrome. The shape of the HandShoe Mouse provides full support of the hand and fingers to prevent this harmful pressure on the wrist. Please be aware that, even after providing relief from this pressure, the nerve stays tender and may still provoke pins and needles for weeks afterwards. But when you keep using this truly ergonomic mouse you should feel the difference!

Watch the short video:

Prevent Carpal Tunnel Syndrome? Go to the HandShoe Mouse website.

What Causes Carpal Tunnel Syndrome?

In our ergonomic mouse research during the development of the HandShoe Mouse we noted a few significant sources of flow restriction in arm and hand.
On our main ergonomic mouse website we address this on the first page in the Research section.

A restricted blood flow to the arms could be caused by excessive gripping and pinching when you use a standard (not ergonomic) mouse. This may lead to a contraction of the deep neck muscles and thereby a closing of the Costoclavicular gate which is explained on the HandShoe Mouse Research page:

In line with this phenomenon is the complaint of Carpal Tunnel Syndrome.
One of the causes must be assumed to be a restriction of the lymphatic flow.
See the picture below, which shows the  lymphatic system as well as the main artery.
Some people believe you can prevent Carpal Tunnel Syndrome by means of excercises.

lymphatic flow

But it is not so much the exercises which could provide relief.
You have to tackle the source of the problem and one of the sources identified by our university based research is the Costoclavicular Gate.

The image presented here shows this gate and the artery. The lymphatic system is shown in black on the right.

The gate is affected by the space between the first rib and the clavicular bone.

Deep neck muscles

Deep neck muscle tension

Deep neck muscle tension will narrow this gate. The image on the left shows the deep neck muscles. In other words, it is the general tension in the deep neck muscles (more specific Scaleni) which is a major source of complaints which are generally referred to as Carpal Tunnel Syndrome.

It should be noted that by using the HandShoe Mouse you prevent excessive gripping and pinching. In general you should be aware that you do not grip excessively

This also applies to handling tools like screw drivers and hammers as well as cutlery, pencils, the steering wheel of your car etc.