1. 2 Dipartimento di Bioingegneria, Politecnico di Milano, Milano, Italy.
Effect of high-heeled shoes on three-dimensional body Center of Mass displacement during walking
Sidequersky F.V. 1, Annoni I. 1, Mapelli A. 1, Lenci B. 1, Colangelo V. 1,2, Sforza C. 1
1 Dipartimento di Scienze Biomediche per la Salute, Università degli Studi di Milano, Milano, Italy.
2 Dipartimento di Bioingegneria, Politecnico di Milano, Milano, Italy.
INTRODUCTION
Although millions of women daily wear high-heeled shoes, their negative effects on the development of degenerative joint disease are well known [1, 2, 3]. Anyway, there is not yet a complete knowledge of the changes of the body center of mass (CoM) position due to heel height. The purpose of the study was to quantitatively compare the 3D displacement of the CoM [4], also focusing on its upper and lower components, during flat-heeled and high-heeled gait.
Wilcoxon signed rank test was used to test differences of CoM displacement between flat-heeled and high-heeled gaits, whereas two-way ANOVA for repeated measures was used to test differences of CoM position variability between the two gait modalities and among the three gait events.
RESULTS
High-heeled gait was characterized by a significantly lower CoM at R heel strike (p=0.024, median difference: 0.6%) and L heel strike (p=0.030, median difference: 1.1%). The same findings were also observed for uCoM (p=0.042, p=0.038 respectively) and lCoM (p=0.004, p=0.005 respectively) (Fig. 3). No significant differences were found at R toe off. In addition, a significant forward displacement of the lCoM in high-heeled gait was observed at each of the three stages (R heel strike, p=0.017, median difference: 6 mm; L heel strike, p=0.034, median difference: 9 mm; R toe off, p=0.003, median difference: 15 mm). Similar results were found for the whole CoM (p=0.024, p=0.038, p=0.004 respectively). The uCoM in high-heeled gait, instead, was significantly more anterior than in flat-heeled gait only at R toe off (p=0.024, median difference: 6 mm) (Fig. 4). On average, intra-individual variability of CoM coordinates did not change significantly in none of the three gait events, nor between the two gait modalities (p>0.05): the median of the 11 subjects’ SDs ranged between 3 and 4 mm in the anterior-posterior direction, between 0.3 and 0.5% in vertical direction, between 16 and 18 mm in medio-lateral direction.
MATERIALS AND METHODS
11 women (mean age, 24 years) without gait dysfunction participated in the study. They performed 10 trials with high-heeled shoes (at least 8 cm) and 10 with flat-heeled shoes (at most 1 cm). Nine infrared TV-cameras, with a sampling frequency of 60 Hz, were positioned beyond the perimeter of a working volume of 520 (length) x 210 (height) x 180 (depth) cm. For each subject, 14 reflective markers were attached on specific body landmarks: left and right tragion, acromion, olecranum, ulna styloid process, great trochanter, femur lateral epicondyle, lateral malleolus (Fig.1a), and then their 3D coordinates were recorded by an optoelectronic system (SMART-E, BTS S.p.a, Garbagnate Milanese, Italy) [5, 6]. These markers allowed the body segmentation in 10 independent masses [7]: a head, a torso, two arms and two forearms constituted the upper body; two upper legs and two lower legs constituted the lower body (Fig. 1b). After the system calibration, the 3D marker coordinates were reconstructed with an average error of 0.63 mm (SD, 0.7 mm).
Figure 1 a. Subject with markers positioned on anatomical landmarks. a b
Figure 1 b. Segmental model of the human body.
Figure 3. Mean±SD of the lower CoM vertical displacement at right heel strike. W-test: p<0.05.
Figure 4. Mean±SD of the upper CoM anterior-posterior displacement at right toe off. W-test: p<0.05
Figure 2. Spatial decomposition of total CoM in the gait cycle with (red) and without (blue) heels. Mean values ±1SD of a tested subject.
Using mean anthropometric data previously collected [8], including the mass distribution within the segments and the locations of their centers of mass, the whole body CoM was computed by means of weighted average. The body CoM was separately evaluated in its anterior-posterior, vertical and medio-lateral displacements in each normalized stride cycle (Fig.2). In particular, for both flat-heeled and high-heeled gait: CoM anterior-posterior coordinate was related to the simultaneous position of the center of pelvis; its vertical component, normalized to leg length, started from the plane passing across the malleoli when soles were in full contact with the ground; CoM medio-lateral coordinate was related to the gait direction. Each subject’s mean and standard deviation (SD) of the three CoM coordinates were extracted for right (R) heel strike, left (L) heel strike and right toe off for both flat-heeled and high-heeled trials. Additionally, all these computations were separately applied to the upper (uCoM) and lower (lCoM) components of the whole body CoM.
DISCUSSION
Our findings confirm that wearing high-heeled shoes significantly change the normal displacement of the human CoM (both its components). In particular, the lower and more anterior CoM position could be seen as the biomechanical adaptation of the body posture in order to maintain a dynamic balance and avoid falls. In the future, these data will be integrated with inter-segmental angular relationships, and used to estimate the metabolic cost of high-heeled gait.
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