Pairwise comparisons found that forefoot cushioning and arch support VAS measures were stable from the first session and from the second session for overall comfort and arch cushioning. Measures of both heel dimensions were stable from the third session (see Table, Supplemental Digital Content 3, which illustrates tests of simple effects resulting from significant main effects, http://links.lww.com/MSS/A35). Overall comfort measures obtained from session 1 differed only from those obtained from session 4 (2.92 mm, range = 0.22-5.62 mm), whereas session 1 measures of arch cushioning differed from those obtained from session 3 (4.39 mm, range = 1.74-7.55 mm), session 4 (4.9 mm, range = 1.74-8.06 mm), and session 5 (3.92 mm, range = 0.76-7.08 mm). However, in point estimates of effect, all of these differences were small. Heel cushioning and support measures obtained from sessions 1 and 2 both differed from those obtained from sessions 3, 4, and 5 (see Table, Supplemental Digital Content 3, which illustrates significant pairwise comparisons, http://links.lww.com/MSS/A35), and although the point estimates of effect are relatively larger than all other dimensions, as they are <0.6, they are still small.
Using the data-derived method involved 16 significant pairwise comparisons with SEM ranging from 7.08 to 9.59 mm (Table 5). On the basis of these data, 9.59 mm represents the change required for a clinically meaningful change in comfort. Asking subjects for meaningful change resulted in three subjects nominating 5 mm, one subject nominating 7 mm, four nominating 10 mm, and the remaining two nominating 15 and 25 mm. The mean of these values, representing the anchor-based MCID, is 10.2 mm.
Experiment 2: Ranking Scales
Friedman ANOVA found no differences between sessions (χ2(4) = 1.138, P = 0.888). Post hoc Wilcoxon signed-rank tests showed no difference between walking and jogging (t = 124.5, P = 0.446, r = 0.01).
Evaluation of Comfort Scale Dimensions
Subjects' responses for the major influences in their overall comfort judgments were categorized by theme (Table 6). In short, all subjects responded that their overall comfort was influenced by arch comfort. One subject also nominated the forefoot as an important factor.
Linear stepwise regression found a combination of heel cushioning and support, forefoot cushioning, and arch cushioning to explain 69% of the overall comfort model. Heel cushioning was found to have the highest correlation with overall comfort (r = 0.726) and an adjusted r2 of 0.526. Heel support was also very highly correlated with overall comfort (r = 0.722) and slightly increased the adjusted r2 value of the linear regression model (0.539). Arch support had the lowest correlation with overall comfort and, through the stepwise process, was excluded from the model.
The purpose of this investigation was to determine the most reliable measures of footwear comfort from three commonly used scales. We found the ranking scale to be the most reliable because no differences in relative shoe comfort were found between sessions or gait. Of the rating scales, a 100-mm VAS was more stable than a seven-point Likert scale on measuring the same outcomes. Because of this finding, the Likert scale was excluded from further analysis.
VAS measures of overall comfort and arch cushioning required a minimum of two sessions to produce reliable measures. Heel cushioning and support measures were reliable from the third session. These findings are different from those of Mundermann et al. (12), who recommended four to six consecutive sessions for reliable comfort measures. Their methodology included comfort measures obtained from novel inserts; thus, it cannot be ascertained if the additional time requirement was due to the scale or adjusting to the inserts.
In using a VAS, an MCID is an important indicator of meaningful change. Subject-derived and data-derived methods of establishing MCID produced very similar results of 10.2 and 9.59 mm, respectively. We believe that either of these amounts is a valid indicator of meaningful change. In applying these amounts to pairwise comparisons, not only were the ES obtained from statistically significant differences all found to be small (<0.6, >0.2), they were all less than both nominated MCID. Therefore, the statistically significant differences found in this study are not clinically relevant.
The second aim of the investigation was to determine which dimension of footwear comfort influenced subjects' perceptions of overall comfort. When questioned, all subjects in our investigation responded that the most important influence on overall comfort was arch comfort. Forefoot comfort was also indicated by one subject. In a study of 20 Hong Kong Chinese women, Au and Goonetilleke (1) also found that the forefoot and arch contributed to comfort and that the difference between an uncomfortable and comfortable forefoot and arch could be clearly indentified. In contrast, the present investigation found that the heel was not identified as an important comfort consideration despite its contribution to the overall comfort model. Au and Goonetilleke (1) found that rearfoot comfort measures obtained from comfortable and uncomfortable shoes were not significantly different. This suggests that individuals prioritize other areas of the foot and, as demonstrated in regression modeling, heel cushioning and support measures are encompassed in measures of overall comfort.
It must be acknowledged that the features identified by this investigation are not the only factors that can affect shoe comfort. Shoe fit (8,11,24) and aesthetics (1,23) have also been identified as important factors, particularly at the point of sale, and require individuals to have different shoes. Arch height, the length of the first toe, breadth of the ball of the foot, and instep circumference differ between men and women (24). Small differences have been found in hallux height and in the angle of the metatarsal-phalangeal joint between Japanese-Korean and North American cohorts (8). Aesthetics is a dominant factor in the choice of shoe for both normal (1) and pathological (23) cohorts. By using the subjects' own shoe, rather than a standard shoe, we were able to build on these findings by suggesting specific components of the shoe that influence the comfort construct. Similar findings occurred between the work of Au and Goonetilleke (1) involving a Hong Kong Chinese female cohort wearing dress shoes and the present study with a cohort of both genders and a variety of ethnic backgrounds wearing sports shoes. Because of this, we are confident that, although different people will require different shoe designs (either for cosmetic or for fit reasons), ensuring arch and forefoot comfort is essential.
This is the first study to compare comfort measure scales, to suggest important dimensions to use when measuring footwear comfort, and to propose an MCID for a comfort VAS. Establishing these findings involved asking subjects up to 480 comfort questions for five consecutive days. We acknowledge that subjects could develop fatigue as the study progressed. However, in such case, we would expect reliability of responses to decrease in latter sessions. We found reliability was constant during the last 3 days for all measures and conclude that our subjects did not experience survey fatigue.
A ranking scale measuring overall comfort produced the most reliable footwear comfort measures. This was followed by a 100-mm VAS measuring overall comfort, forefoot arch and heel cushioning, and arch and heel support. A seven-point Likert scale produced the least reliable results. Using a ranking scale provides information regarding the relative comfort of footwear and is useful with two or more items. A VAS is required if information is needed regarding the amount or change in comfort. If a VAS were to be used, measures of overall comfort, forefoot and arch cushioning, and arch support obtained during two sessions will provide reliable information. In doing so, 10.2 and 9.59 mm can be used to identify MCID in footwear comfort.
Financial support for this research was received from the Australian Research Council (Australian Research Council Linkage Project grant LP0668233). K.M. is supported by an Australian Research Council Australian Postgraduate Award Industry. Vasyli International provided the inserts used in this study.
The authors report no conflicts of interest.
The results of this study do not constitute endorsement by the American College of Sports Medicine.
The authors thank Prof. Michael Martin and Dr. Steven Stern (School of Finance and Applied Statistics, the Australian National University, Canberra, Australia) for their statistical guidance.
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VISUAL ANALOG SCALE; RANKING SCALE; MINIMAL CLINICALLY IMPORTANT DIFFERENCE; SHOES
Supplemental Digital Content
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