FAQ Compression testing
Summarized for you: all frequently asked questions on the subject of compression testing.
Yet don’t hesitate to contact us in case you have additional questions. We’ll be happy to help!
The state of the science
- 1. What studies have there been so far on the effectiveness of compression textiles and what where the findings?
Here we have confined ourselves to the following two studies, or rather, referred to these studies as being representative:
- 1. Efficacy of Compression Socks to Enhance Recovery in Distance Athletes - Sport and Art 2(2): 15-18, 2014 - DOI: 10.13189/saj.2014.020201 - Lauran Fletcher1, Scot Raab2, Sonya Sanderson1,*, Luke Vargo1 1Department of Kinesiology and Physical Education, Valdosta State University, Valdosta, 31698, GA, United States 2Department of Physical Therapy and Athletic Training, Northern Arizona University, Flagstaff, 86011, AZ, United States *Corresponding Author: email@example.com http://www.hrpub.org/download/20140105/SAJ1-19901529.pdf
- 2. Initial study on the increase in performance due to sports textiles with compressive properties (IGF No. 16868 N). Hohenstein Institut für Textilinnovation gGmbH Schloss Hohenstein 74357 Bönnigheim – Head: Prof. Dr. Stefan Mecheels
Project Leader Martin Harnisch (firstname.lastname@example.org). The IGF project 16868 N by the research association Forschungskuratorium Textil e.V., Reinhardtstraße 12-14, 10117 Berlin, was financed through the AiF within the framework of the programme for promotion of cooperative industrial research and development (IGF) by the German Federal Ministry of Economics and Technology based on a resolution by the German Bundestag.
The studies carried out so far took very different approaches, so that it is difficult if not impossible to compare the findings. The general trend of the results suggests that any positive effects cannot be proven to be significant (which is not to say that some individual products do not have very positive effects). However, what does seem certain is that wearing compression clothing/hosiery has no negative consequences. It also appears to be clear that the vast majority of participants in the studies took a very positive view of the effect of compression.
- 2. Is research into the effectiveness of compression textiles still going on?
We can assume that more studies are being carried out, because the results so far do not satisfy either the supporters or the critics.
- 3. Are there any findings about how compression affects the physical performance of sportsmen and -women?
This question has been addressed in many studies. In some cases, the volunteers reported their subjective impression that the effect was positive. Objectively, however, no significant effects were recorded, at least not for most of the volunteers. In particular cases, the situation may be quite different.
- 5. What benefits does the quality label "Compression" offer me as a consumer or retailer?
The details on the quality label have been assessed by an independent body according to consistent standards. The products have to meet minimum requirements for their compressive effect. The quality label also shows the compression profile of the product, i.e. whether the compression gradually increases or decreases or stays the same. This ensures that the products are suitable for their intended area of use, as sports or travel socks, and that the claims made about them are correct.
- 4. What benefits does the quality label "Compression" offer me as a manufacturer?
The Hohenstein quality label provides objective confirmation of the stated compressive effect, provided by an independent and internationally recognised test institute. The compressive effect can also be monitored and confirmed over a longer period by follow-up testing. The quality label differentiates you from the competition, and consistency in testing ensures that products can be compared objectively. The label is also recognised and valid internationally, and available in various different languages.
- 6. What requirements must a product satisfy in order to be awarded the "Compression" quality label?
Among other things, this depends on whether the textile being tested is for use in the sport or travel sector. For travel socks, there must be a minimum pressure of 10 mmHg, the pressure must decrease (upwards from the ankle) and the pressure at the top must meet certain requirements. For sports use, the minimum pressure is also 10 mmHg, but the manufacturer decides on the pressure profile. The product passes the test provided the pressure profile is as claimed. The entire range of sizes, and the dimensions for each, are required for the measuring process.
- 7. How exactly does the compression testing process work?
HOSY consists of 20 individual tensile testing components, over which the product being tested - a sock or bandage or even perhaps a shirt - is pulled taut and then stretched to the specified extent. When the given circumference is reached, the force that was required is measured and converted into a pressure value. As well as tables showing the results, a chart showing the compression and pressure profile is also produced.
Click here for further information on the test methodology.
- 8. Are the pressures that are measured expressed in relation to the pressures that occur as the textiles are being worn, or can they be so expressed?
Because the HOSY device can reproduce virtually all shapes and sizes, it is very easy for the results of the measuring process to be applied to real use situations. Since we always measure all the (garment) sizes for a product, the results are always applicable to all the different sizes.
- 9. How long does testing take?
Because of the high international demand, testing is currently taking about 3 weeks. It is very important to us that we always maintain the same high testing standard. That is why our compression testing is all carried out by experienced staff using our HOSY (Hohenstein System) at our site in Bönnigheim (Germany).
- 10. What kind of fibre types are generally used in compression textiles?
In principle, any yarn can be knitted in such a way that it creates a certain compressive effect. In compression textiles, though, using elastic yarns like elastane increases this effect.
- 11. Are there also compression textiles made of natural fibres, and can you test these for pressure in the same way?
Yes, natural fibres are often used for medical compression textiles, but here again always in combination with elastic yarns to produce the compressive effect. They may also be used in other sectors.
- 12. When measuring compression and the pressure profile, do you also take account of different types of material and seam position (in the case of clothing that is not knitted in the round)? If so, how? (For example, the knees of tights).
The HOSY measurements are carried out over the complete length of the finished garment, so any differences in compression resulting from different materials or seam positions are taken into account. In practice, this means that any different pressure zones in the circumference of the garment (where such an effect occurs) cannot be measured, but the lengthways ones are very clearly identified.
- 13. Are there any other compression testing devices as well as the HOSY (Hohenstein System)?
Various different test systems are in use around the world. The HOSY test device developed at the Hohenstein Institute in the early 1980s established itself in the field of medical compression hosiery and is specified in the relevant standards such as RAL and DIN. On account of its unique flexibility in terms of the possible sizes, lengths and shapes, we think HOSY is the best solution for non-medical compression products, too.
Click here for further information on the HOSY.
- 14. Doesn't the compressive effect depend on how much the garment is ultimately stretched on the body, i.e. on the garment size and the size of the wearer's limbs?
That's quite right. One of the quality features of our compression testing is that the whole range of sizes is tested, for precisely that reason. During the testing with HOSY, they are stretched to the extent defined for each part of the body for that garment size. In this way we can ensure that the pressure complies with the same specifications across all sizes.
- 15. A compression hosiery product is a 3D object, but during the testing the stocking is only stretched in two dimensions.
Isn't there a mismatch there?
During measurement using the HOSY (Hohenstein System), the test piece is stretched to the extent specified for that (garment) size. The forces required for that stretching are mathematically converted so that they equate to the pressure on a three-dimensional object.
- 16. Do you also record movements, so that you can model the level of compression during movement?
No, we don't do that at the moment. But you could certainly, for example, measure a stocking several times using different combinations of measurements, and so create a kind of "dynamic profile" which would then be very close to what happens during movement.
- 17. How do you work out the pressure exerted by a test piece if you are measuring the tensile force?
We measure the force at intervals of 5 cm along the entire length of the test piece. From these values, using the Laplace formula among others, our experts can calculate the pressure that is exerted on the body in relation to the circumference. In the end, this enables them to work out the pressure profile over the complete length, at any particular point.
Travel, sport & wellness
- 18. Which factors affect the pressure profile of sportswear?
In general, the pressure profile depends on the garment and the material, while the compressive effect of a material depends in turn on the type of knit and the yarns that are used. The kinds of compression and pressure profile that are suitable for particular types of sport have not yet been defined, due to the lack of data from scientific studies.
- 19. Is there a maximum level of compression for sportswear?
So far there are no specifications for that, because the findings from scientific studies don't yet allow any conclusions to be drawn. Furthermore, the requirements could very much depend on the type of sport itself. In general, we recommend that hosiery where the compressive effect is the same as that for medical hosiery should be designed like medical hosiery in terms of its essential parameters.
Nor should the question of comfort be overlooked, both when wearing the garments and when taking them on and off – but here the customer decides whether a product is accepted or rejected.
- 20. Is sportswear that exerts a high pressure only suitable for a particular age group?
No. The pressure itself is, so to speak, age-neutral, it's currently more a question of personal preference – whether the athlete prefers higher or more moderate pressure.
- 21. Can the testing show the compressive effect on different muscle groups? Or are there different test scenarios for different parts of the body?
Of course, you can look at legs, arms etc. separately, but the principles of the test procedure are always the same. You can only look at the compressive effect on specific muscle groups if they are located along the length of the test piece, such as the calf and thigh muscles.