**Analysis for Objective Evaluation the Stress of the Hand Hand**

**Analysis for Objective Evaluation the Stress of the** 

DOI: 10.5772/intechopen.71474

Aydin Ünlü, Peter Gust and Frank Mersch Aydin Ünlü, Peter Gust and Frank Mersch Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.71474

#### **Abstract**

The hand is constantly in contact with products and therefore stressed differently. Heavy stress is the cause of unpleasant sensation and can lead to common hand diseases in the worst case. The chapter starts with the description of hand diseases and with methods to determination of hand stress. Subsequently, the chapter is continued with a literature review of hand stress analysis refer to objectively methods. In the main part, two objective methods are developed and presented to analyze the hand stress. These methods allow the simulation and the measurement of hand stress. Compared to the classical approach, the results of the objective methods show a higher accuracy in faster review of hand stress. Finally, the chapter ends with a discussion of the results and gives opportunities to improve the hand model and the measurement system.

**Keywords:** pressure pain threshold (PPT), pressure discomfort threshold (PDT), digital hand model, handle design parameters, hand stress, hand tissue strain, wrist strain, hand posture, Job Strain Index (JSI), strain variables, sensor glove, JSI-system

## **1. Introduction**

#### **1.1. Hand diseases**

People are constantly in contact with products and thereby stressed differently. In particular, high power transmissions, short rest periods as well as incorrect postures influence the health [1]. In this case, typical diseases may occur due to high stress. In the worst case, diseases in the wrist, for example, arthrosis can be caused by an incorrect estimation. An arthrosis on the wrist leads to a painful restriction of the mobility of the wrist. An anomaly of the compressive stress in the wrist is being held responsible for the high joint wear and the joint pain. An arthrosis at the thumb saddle is called as rhizarthrose [2].

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**Figure 1** shows a deformed joint site. The symptoms can only be alleviated by minimally invasive joint cleansing or by the severing of painful nerve fibers. In a last step, there remains in some cases only a partial stiffening of the carpal bones—or the supply of individual finger joints by arthroplasty or prosthetic. In the case of joint cleansing, a needle is inserted into the joint capsule. If the injection is deeply injected into the thumb saddle joint, the palmarextending tendon of the flexor carpi radials can be injured [3].

limited to few positions. Therefore, Job Strain Index (JSI) by [6] is often determined for the evaluation of the hand strain. With regard to the development of a system to objectify hand

The JSI method was published by [6] and deals with the evaluation of hand strain. Thereto, a manual work was observed for 3 min, and a so-called Job Strain Index (JSI) was calculated. The determination of the JSI is based on the estimate of six strain variables and on the multipliers determined by those. The strain variable, intensity of exertion (IE) refers to the maximum effort that can be exerted by a human being [10]. Hand-dependent maximum gripping forces by [7] can help to determine the effort. The strain variables, duration of exertion (DE) and efforts per minute (EM) result from the formulas for the maximum effort. For the estimation of hand/wrist posture (HWP), angle limits for the wrist extension (E), flexion (F) and ulnar deviation (D) are specified. The comparison of the JSI with the limits shows the risks of

**frequents**

10–29% (1) 4–8 (1) Good (1) Slow (1) 1–2 (0.5)

1 Light (1) <10% (0.5) <4 (0.5) Very good (1) Very slow (1) <1 (0.25)

3 Hard (6) 30–49% (1.5) 9–14 (1.5) Fair (1.5) Fair (1) 2–4 (0.75) 4 Very hard (9) 50–79% (2) 15–19 (2) Bad (2) Fast (1.5) 4–8 (1) 5 Near maximal (13) 80–100% (3) ≥20 (3) Very bad (3) Very fast (2) ≥8 (1.5)

**Hand posture Work speed Work duration**

Analysis for Objective Evaluation the Stress of the Hand http://dx.doi.org/10.5772/intechopen.71474 19

To provide early ergonomic criteria for product design, digital hand models can be used for the simulation of hand stress. Digital hand models are generated by computer representations of the hand and can be simulated using either the multibody systems method (MBS) or the finite element method (FEM). It is also possible to couple the methods of FEM and MBS. In contrast to MBS models, FEM models are deformable and can calculate mechanical stresses such as pressure in certain parts of the body. MBS models consist of rigid non-deformable bodies connected to one another by kinematic joints. Using the MBS method, it is only possible to determine the kinematics of the body and the contact forces. These data are used, for example, as input data for FEM simulation [8]. Often the hand models are simulated as part models because of their complexity. This includes, for example, simulating finger models. For example, [9] developed a combined FEM and MBS finger

the hand health. **Table 1** shows a template for determining the multipliers.

strain, this chapter focuses on the JSI method.

**Rating Exertion intensity Exertion duration Exertion** 

**2. Literature review**

JSI = EI × ED × EF × HP × WS × WD

**Table 1.** Template of JSI-determination.

2 Somewhat hard (3)

**2.1. Simulation-models to determine the hand stress**

A novel therapy involves a stabilization by kinesio-taping. In addition to the massage effects, that stimulate the flow of blood and lymph. The elastic adhesive tape supports joint functions. The influence of the tapes on the tensions corrects muscular imbalances so that a balance between the muscle groups can arise again. The stimulation of the proprioceptors in the joints ensures a better sense of movement. By stimulating the receptors, pain in the joint is relieved [4].

#### **1.2. Determination of hand stress**

In the application of hand-held products, the user is under different stress factors. These stress factors cause in human's strains, depending on individual characteristics and abilities. Stress means the physical characteristics of the work situation, for example, a force transmission on the hand. Strain, in contrast, refers to the reactions such as hand pain [5].

In most cases monitoring methods are used to determine the hand strain. These monitoring methods are based on the scoring of certain stressful situations. Thereby valid low scores lead to low strain. But in the most monitoring methods the level of detail of the hand is

**Figure 1.** Computed-tomography of a rhizarthrosis.

limited to few positions. Therefore, Job Strain Index (JSI) by [6] is often determined for the evaluation of the hand strain. With regard to the development of a system to objectify hand strain, this chapter focuses on the JSI method.

The JSI method was published by [6] and deals with the evaluation of hand strain. Thereto, a manual work was observed for 3 min, and a so-called Job Strain Index (JSI) was calculated. The determination of the JSI is based on the estimate of six strain variables and on the multipliers determined by those. The strain variable, intensity of exertion (IE) refers to the maximum effort that can be exerted by a human being [10]. Hand-dependent maximum gripping forces by [7] can help to determine the effort. The strain variables, duration of exertion (DE) and efforts per minute (EM) result from the formulas for the maximum effort. For the estimation of hand/wrist posture (HWP), angle limits for the wrist extension (E), flexion (F) and ulnar deviation (D) are specified. The comparison of the JSI with the limits shows the risks of the hand health. **Table 1** shows a template for determining the multipliers.


**Table 1.** Template of JSI-determination.
