Elsevier

Applied Ergonomics

Volume 33, Issue 5, September 2002, Pages 477-484
Applied Ergonomics

A comparison of the effects of floor mats and shoe in-soles on standing fatigue

https://doi.org/10.1016/S0003-6870(02)00027-3Get rights and content

Abstract

In assembly line positions and other occupations, employees experience pain and discomfort associated with long periods of standing. Modifying flooring is a common intervention method used to alleviate problems associated with constrained standing. This study investigated the effects of four different standing conditions upon assembly workers’ perception of general fatigue and discomfort associated with various body parts following 1 week of 8-h days of exposure to each condition. The four standing conditions were (1) on hard floor, (2) on a floor mat, (3) wearing shoe in-soles, and (4) wearing shoe in-soles while standing on a floor mat. Questions were asked regarding general fatigue and discomfort. In general, the mat, in-soles and combined conditions were more comfortable than standing on hard floor. Moderately strong correlations were found for the variables of height, age and job tenure. Shorter individuals experienced greater discomfort in the upper leg and low back when standing on a mat and when wearing in-soles. The older workers and those with more job seniority reported greater discomfort associated with body joints when standing on the hard floor and when standing on the floor mat. No significant differences in fatigue or discomfort were found when comparing the overall effects of using the floor mat to wearing the shoe in-soles or the combined condition.

Introduction

Prolonged standing is common in many manufacturing and service occupations such as assembly work, drill press operator, and cashier. Research literature suggests it is also the direct cause of pain and discomfort. Several countries have described and quantified this as an ergonomic problem of significant magnitude. The American Podiatric Association reported that 83% of the US industrial workforce had foot or lower leg problems such as discomfort, pain or orthopedic deformities. A survey of Australian workers reported that 91% had foot problems and 49% specifically complained of painful feet (Marr and Quine, 1993). In the Danish working population, the 1 year prevalence of low back and feet complaints had been reported to be approximately 40% and 12%, respectively (Biering-Sorensen, 1985). A Switzerland study corroborated these findings, reporting the prevalence of back problems among workers subjected to prolonged standing to be 39% and leg problems 23% (Buchberger, 1993).

The impact of discomfort and disorders associated with long-term standing on health insurance, absenteeism, productivity and well-being is substantial (Marras et al., 1995; Sommerich et al., 1993). Preventing musculoskeletal disorders in the workplace has become a top priority in many countries. Increased attention has focused on ergonomic interventions for solutions. This involves fitting the work environment to the worker. Commonly chosen ergonomic intervention methods to reduce pain and discomfort associated with prolonged standing is the alteration of the flooring on which workers stand, and the use of in-soles in footwear. However, little scientific evidence exists regarding the effectiveness of these intervention methods. The studies that have been done have primarily used subjective rating of fatigue and discomfort while standing in controlled laboratory settings. A few studies have incorporated objective measures such as leg volume changes, skin temperature readings, and electromyographic muscle responses. Collectively, the results of these studies present with mixed and sometimes conflicting results.

Discomfort has consistently been reported to increase over time with standing, and generally appears to be greatest at the feet, becoming progressively less from the feet up (Konz et al., 1990; Redfern and Chaffin, 1988; Zhang et al., 1991). There appears to be a “threshold value” above which there is a pronounced risk for increase in discomfort. Buckle et al. (1986) suggested this corresponds to above 30% of the working day while Ryan (1989) showed a value of about 45–50% for regular symptoms in lower extremity and feet, and about 25% for low back pain.

Much of the discomfort is purported to be from venous pooling and maintained static postural muscle contractions (Brantingham et al., 1970; Konz et al., 1990; Winkel and Jorgensen, 1986). The venous pooling is a result of a lack of contract-relax leg muscle activity which ordinarily prevents the blood from accumulating in the lower extremities. The reduced blood supply on gravity-loaded muscles accelerates muscle fatigue and pain due to an accumulation of metabolites in muscles (Edwards, 1988). An accumulation of metabolites has been reported to lead to activation of nociceptive muscle afferents which may result in muscle hypersensitivity (Djupsjobacka et al., 1994; Djupsjobacka et al., 1995; Johansson et al., 1993). Significantly higher leg and foot skin temperatures and lower heart rates have also been reported as effects of prolonged standing (Rys and Konz, 1990). This supports the physiological basis for hampered circulation.

Various other objective measures such as blood pressure, center of pressure displacement, electromyographical recordings of muscle activity, and task performance have been studied to further explore physiological models that could explain discomfort and fatigue due to prolonged standing. Only a handful of these studies have been reported, and the results were mixed. Lack of consensus on the exact underlying physiological causes of discomfort and fatigue associated with prolonged standing makes it very difficult to design and recommend the most effective ergonomic interventions.

One popular ergonomic intervention has been to modify the flooring in an attempt to alleviate the problems associated with constrained standing. It is not uncommon to see workers themselves padding the floor or putting down cardboard to reduce stress and tiredness in their low backs or legs. Cushioned mats or so-called “anti-fatigue” mats on the market are claimed to alleviate or reduce fatigue from standing. Certain types of shoes or shoe in-soles are suggested in sales promotion advertisements as having the same beneficial effects of preventing pain and discomfort associated with prolonged standing. The positive effects on local circulation in the legs and the contractile pattern of the postural muscles reported by mats and shoe in-soles is still not clear; moreover it is unknown in which job situations the effects of these products are most important (Hansen et al., 1998).

Scientific investigations studying the effects of flooring and shoe in-soles on workers’ fatigue levels have used psychophysical, physiological and biomechanical data collection methods to quantify the effects of these conditions on low back and lower extremity symptoms during prolonged standing. Results of investigations thus far have given conflicting information (Kim et al., 1994).

The premise behind “anti-fatigue” mats is simple. These mats are engineered to make the body naturally and imperceptibly sway, which encourages subtle movement by calf and leg muscles. This promotes blood flow and keeps blood from stagnating in the veins, which causes workers to feel fatigued. The characteristics of thickness and stiffness of mats have been studied to determine the most beneficial properties. Redfern and Chaffin (1995) found that in general, softer materials caused less perceived tiredness; however, one extremely soft floor resulted in higher ratings of tiredness. Harder flooring materials caused greater discomfort. The 3/8″–5/8″ thick mats had the lowest rating for overall tiredness, which was 50% lower than the rating for the concrete floor.

Foot volume, foot and calf temperature, electromyograph (EMG), heart rate, force platform and video recordings have been used to assess the physiological and biomechanical effects of mats (Brantingham et al., 1970; Cook et al., 1993; Jorgensen et al., 1993; Kim et al., 1994; Madeleine et al., 1998; Rys and Konz (1990), Rys and Konz (1994)). However, physiological and biomechanical findings related to standing on a soft or a hard surface are still controversial. Zhang et al. (1991) combined subjective ratings with physiological and biomechanical measures in an attempt to identify flooring and shoe effects on fatigue and discomfort. The duration of standing was found to have the largest effect. Stuart-Buttle et al. (1993) used EMG measures of the lower extremity during standing to determine the effect of floor compliance. They found no differences in spectral characteristics of leg EMGs when floor compliance was varied. Mats appeared to reduce localized muscle fatigue in the erector spinae muscles only. This fatigue reduction was observed only with the more compressible of two mats. These results imply that localized muscular fatigue in the leg may not be relieved with “anti-fatigue” mats, and some mats may only benefit the back (Kim et al., 1994).

Rys and Konz (1994) concluded that mats are more comfortable than concrete and that mats with 6% compression from the body weight are more comfortable than mats with 18% compression. Konz et al. (1990), found that the best-rated mats were the least compressible. It is difficult to compare these studies however, due to their inadequate reporting of mat properties.

Rys and Konz (1988), Rys and Konz (1989), Rys and Konz (1990) compared standing on concrete with standing on other floor surfaces. Foot volume was recorded in all studies but consistently failed to produce significant results. Heart rate was found to be significant in the 1988 study which compared concrete to carpeting.

The question is often asked as to whether shoe in-soles are more beneficial than floor mats. Shoe in-soles are sometimes perceived as “mobile mats”.

Shoe in-soles have been proven to effectively improve comfort and reduce back, leg, and foot pain in individuals who must stand throughout their workday (Basford and Smith, 1988). Viscoelastic inserts have been reported to decrease symptoms in patients with degenerative joint disorders (Voloshin and Wosk, 1981) and chronic low back pain (Wosk and Voloshin, 1985). This is supported by Redfern and Chaffin (1995) who found that subjects scored in-soles among the three highest in comfort ratings among seven different flooring conditions.

Like floor mats, the physical properties of shoe in-soles have been studied as well. Pratt et al. (1986) examined five different types of shoe in-sole materials using force plate recordings and an accelerometer to record shock absorption. The viscoelastic material was determined to be superior. He also found the viscoelastic material's shock attenuating properties performed well after 1 year of use. Another study evaluated materials to find that the “moderately deformable” materials were best. These included Neoprene –R425N, Plastazote-Low density, Aliplast-6A, Aliplast-4E, Ethafoam, Evazote, and Poron-20125 (Campbell et al., 1982).

Tooms et al. (1987) studied the effects of shoe in-soles on back and leg discomfort in a group of nursing students. The students reported a significant peripheral shift in pain location from back to lower extremity; the viscoelastic group showed significant changes in duration of post-work pain and frequency of pain during the workday.

Only one study has been found that compared the effects of different types of mats and shoe in-soles on perception of tiredness, fatigue and discomfort for workers required to stand while performing their jobs (Redfern and Chaffin, 1995). It was also the only study found that assessed standing effects for greater than a 4-h period. This study used a small sample size of 14 subjects and did not test for the combined effect of wearing in-soles while standing on mats, a condition occasionally chosen by workers themselves.

The purpose of this study was to compare the effects of floor mats and shoe in-soles on workers’ perceptions of tiredness, fatigue and discomfort following 8-h shifts of continuous standing including a combined condition with both floor mats and shoe in-soles.

Section snippets

Subjects

Twenty-seven factory workers (9 males and 18 females), all of whom held assembly line positions within a large Midwest United States manufacturing plant initially agreed to participate in this study. The critical criteria for subject selection was that subjects’ jobs required them to stand continuously throughout their 8-h shift. The types of jobs were similar: they required similar postures and work-rest cycles, minimal walking, and constant standing. Subjects worked in light assembly

Means and standard deviations

Table 2 depicts the means and standard deviations of the subjects’ perceptions of firmness of standing surface, level of general fatigue and level of fatigue specifically associated with the legs following exposure to each of the standing conditions. The highest ratings for firmness, general fatigue and leg fatigue were reported when standing on wood floor. Table 3 reveals the means and standard deviations for discomfort ratings associated with specific body parts following exposure to the four

Discussion

Moderately strong correlations were found for the variables of height, age, and job tenure for discomfort associated with various body parts and their exposure to the different types of standing conditions. Shorter subjects reported greater general fatigue, and greater specific discomfort associated with the lower legs, knees and upper back while standing on hard floor. These subjects also experienced greater discomfort in their upper legs and low backs when exposed to standing on a mat for a

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