Those who have served in the military and were required to stand rigidly at attention for long periods are familiar with the tendency to faint under these circumstances. This can be explained simply due to the lack of sufficient blood reaching the brain. It is a well-known medical fact that movement of the legs and ankles promotes blood flow to the upper body cavity. If this movement does not occur, under conditions such as standing rigidly at attention, it is possible that insufficient blood will flow from the legs and fainting will occur. What is not well known is that only a small amount of movement in the leg-ankle region greatly assists in moving the blood upward which should be of interest to barbers, dentists, production-line operators, and others who must stand for extended periods.
The objective of this paper is to describe an ergonomically designed floor mat that assists in producing muscle activity in the legs. Ergonomically designed means the product is engineered to incorporate beneficial features that result from the study of the interaction of the worker and the work environment. The following topics will be discussed.
1. Requirements for proper design
2. Construction and manufacture
3. Medical documentation
4. Market research results
Requirements for proper design
Veins in the leg are fitted with valves similar to those in the heart. Muscles adjacent to the veins contract and squeeze blood upward from the valve to valve. Medical texts refer to this as the “peripheral venous pump” or the “second heart”. The floor mat with variable terrain (VT) causes the stander to move sufficiently in a comfortable fashion so that there is more muscle activity and more blood flow occurs compared to standing on a flat surface.
Dr. Charles Brantingham, a podiatrist, realized the potential benefits of a floor surface designed to assist the ankle and leg in the pumping action. After doing some experimental work, which I will describe later, he and his colleagues applied for and received a patent. This concept-patent describes various types of construction that will produce a variable terrain. Standing on the variable terrain, the foot will be at an angle with the horizontal. A cross section of one form of the variable terrain shows how the foot will be at this angle, approximately three degrees, because of the special construction. When there is a slight shift of the foot, the variable terrain will cause the foot to move through the angle. A flat surface does not allow such movement. This small movement causes ankle and leg muscles to contract and expand, which in turn causes veins to be squeezed, resulting in blood moving from valve to valve.
Improved blood flow will have beneficial effects on the body. There should be less feeling of fatigue because of reduced congestion of blood and better removal of waste products associated with fatigue. In some people there may be a reduced tendency to varicosities since there should be less pooling of blood at the venous valves. Pooling of blood at these sites can result in extension of the veins. This can cause the valves to be incompetent and result in varicose veins.
Increased muscle activity also improves muscle tone. It might be expected that this increased muscle activity itself would result in more fatigue. This is not the case as the low level of muscle activity is distributed in a non-repetitive fashion to result in little or no feeling of fatigue.
Construction and Manufacture
Mats are presently manufactured by using a simple molding technique. The desired wear surface such as polyvinyl chloride, rubber or carpet is placed upside-down in the mold. A mixture of MDI based isocyanate an polyol is distributed on the back of the wear surface. The lid of the mold, which has the VT design in it, is closed and clamped. Demolding can take place as soon as the foam is tough enough to handle.
While many combinations of wear surfaces and foams are possible, it must be understood that a feeling of softness and comfort is an important aspect of making acceptable mats. Therefore, the right combination of wear surface and foam needs to be specified to achieve muscle activity and a comfortable feel. There is a patent pending on mat constructions that satisfies both of these requirements.
The mat now being test marketed has a 65-mil thick polyvinylchloride wear surface over a half-inch-thick flexible polyurethane foam. Foam density is approximately 6 lbs/ft3 in the mat and approximately 3 lbs/ft3 in the free rise state. Compression set is no more than 45 percent compression. The foam has been formulated to pass the DOC-FF-70 Flame Test.
The human foot is more suitable for functioning on a variable terrain than on a flat surface. This does not mean the foot is not adapted to flat surfaces; clearly it is. However, little of the earth’s natural surface is flat. Therefore, it seems logical that during the evolution of the human foot, there was more contact with variable terrain that with flat surfaces.
With this in mind, Brantingham et al. reported results from a study that used electromyographic (EMG) readings from certain leg muscles when subjects were standing on a flat hard surface and then on a variable terrain. These early results showed increased muscle activity on variable terrain. Later, C.N. Moss used an invasive technique employing an intravenous catheter to measure blood-pressure changes at the ankle in four subjects. All subjects experienced a drop in blood pressure during “normal standing” compared with standing still. Normal standing permits the subject to shift positions at will. Note that the blood pressure is about 50 cm less when walking than when standing.
Patent rights to the technology were purchased by Armstrong, and studies were initiated at the Pennsylvania College of Podiatric Medicine, Philadelphia, to confirm the earlier work. EMG measurements on 26 muscles with nine subjects demonstrated that there is more activity on the VT surface than on an equivalent flat surface. An equivalent flat surface is the same as the VT surface except that it does not have the ribbed design molded into the urethane foam back.
Thermograms using infrared photographs of the calf of subjects also verified more activity on the VT surface. The blue portions of photographs show that, where there is more blood flow and more muscle activity, temperatures are higher. Subjects standing on the flat surface tend to have lower leg temperatures as seen by the greater red areas on the photographs.
An application was made to the American Podiatric Medical Association seeking its acceptance of this product. The procedure for acceptance requires the manufacturer to fully describe the product construction, list claims that will be made, indicate how these claims will be supported, and agree not to change the product so that it will no longer function as claimed. The Scientific Committee requested several reviews during the one-year process. A letter announcing the award of the Seal of Acceptance was received for the product now known as Standers Choice® Health Mat.
Market Research Results
Market research evaluations were completed in 1985. The first double blind study initially involved nine industrial mercantile locations, of which five completed the entire program. Complete sets of data were obtained from, 30 participants who rated the comfort of the VT mat significantly higher than that of flat mats. Curiously, the preference for either mat was not significant. Apparently both mats were such a vast improvement over the previous surface that the participant would have taken either mat to improve their lot.
A second double blind study involved 18 operators in a large beauty salon. Thirteen of the participants preferred the VT mat, citing reduced feeling of fatigue. Five preferred the flat mat, but most of these indicated there was not much difference.
To date more than seven thousand mats have been sold or distributed in the test market program. A large collection of solicited and unsolicited positive comments has been accumulated. Frequently workers say they will not give up the mats and in fact will take the mats with them if their job locations are changed.
In summary, the VT concept can best be delivered to the standing worker in the form of a mat using a suitable wear surface and flexible urethane foam backing. This structure has been shown to provide beneficial effects to workers who must stand for relatively long periods. Medical and market research studies support the claim that use of the mat can have a physiological benefit, and users find the mats promote more comfort and less fatigue.