# Influence of feet clearance and angle on healthy subjects' balance stability

A. Mouzat, Michel Dabonneville, Pierre, Raphael Bertrand, Philippe Vaslin

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A. Mouzat, Michel Dabonneville, Pierre, Raphael Bertrand, Philippe Vaslin. Influence of feet clearance and angle on healthy subjects' balance stability. XVIIth Congress of the International Society of Biomechanics, ETH Zürich, Jul 2001, Zürich, Switzerland. pp.138. hal-05000146

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Submitted on 27 Mar 2025

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# Influence of Feet Clearance and Angle on Healthy Subjects' Balance Stability

A. Mouzat<fnref n="1" />, M. Dabonneville<fnref n="2" />, P. Bertrand<fnref n="1" />, P. Vaslin<fnref n="2" />

## Introduction

Only a few studies explored the influence of the feet positions on the balance stability of subjects standing upright with open-eyes on a force-plate (Okubo et al., 1979; Kirby et al., 1987). They noticed a decrease of the total path length (L) of the center of pressure (COP) along with the increase of the clearance or the angle between feet. This decrease was also significant and more important in the medio-lateral (Ly) than in the fore-and-aft (Lx) direction. The purpose of the present study was to systematically investigate the influence of feet clearance and angle when the subject stands upright with open-eyes on the COP's path lengths (L : total length, Lx : fore-and-aft length, Ly : medio-lateral length) as well as on the fore-and-aft (Sx) and medio-lateral (Sy) dispersions of the COP around its mean position, and on the area (A95) of the 95 % confidence ellipse (Takagi, 1985).

## Methods

The statokinesigrams of 25 healthy men (23.8 +/- 3.6 years) with eyes opened were recorded on an AMTI force-plate. The subjects' feet positions were controlled by a special frame fixed on the force-plate which allowed to impose four clearances (0, 0.02, 0.1 and 0.2 m) together with four angles (0°, 15°, 30° and 45°). For each subject, the testing order of the 16 feet positions was randomized. L, Lx and Ly were calculated from data recorded during the same period (20 s) and at the same sampling rate (respectively 10 and 100 Hz) as Okubo and Kirby, while Sx, Sy and A95 were calculated from data recorded at a sampling rate of 100 Hz during 20 s.

## Results & Discussion

All these parameters have been then compared with a two-factors (clearance and angle) ANOVA (Table 1) and a Scheffe post-test.

<table><caption>**Table 1:** ANOVA results (n.s. : non significant ; * : P < 0.05 ; ** : P < 0.01 ; *** : P < 0.001)</caption><thead><tr><th>Factors</th><th>L</th><th>Lx</th><th>Ly</th><th>Sx</th><th>Sy</th><th>A95</th></tr></thead><tbody><tr><td>Clearance</td><td>n.s.</td><td>n.s.</td><td>n.s.</td><td>**</td><td>***</td><td>***</td></tr><tr><td>Angle</td><td>n.s.</td><td>n.s.</td><td>n.s.</td><td>n.s.</td><td>**</td><td>**</td></tr></tbody></table>

The variation of feet clearance had no significant effect on L, Lx and Ly. But the increase of feet clearance from 0 to 0.2 m induced a significant decrease (P < 0.05) of Sx (15 %), Sy (61 %) and A95 (67 %) (Figure 1).

<figure><img src="image_2.png" /><figcaption>**Figure 1:** Feet clearance's effects on the six calculated parameters : L, Lx, Ly, Sx, Sy, A95.</figcaption></figure>

<footnote n="1">¹ LAPSCO UPRESA CNRS 6024, Université Blaise Pascal, Clermont-Ferrand/France</footnote>

<footnote n="2">² LIMOS FRE CNRS 2239, Université Blaise Pascal, Clermont-Ferrand/France</footnote>
The increase of feet angle from 0° to 45° had only a significant effect (P < 0.05) on Sy (17 %) and A95 (23 %) and induced no variation of L, Lx, Ly and Sx (Figure 2).

<figure><img src="image_3.png" /><figcaption>**Figure 2** : Feet angle's effects on the six calculated parameters : L, Lx, Ly, Sx, Sy, A95.</figcaption></figure>

Then we compared our results with Okubo's and Kirby's using a Student t-test. No significant difference was found between previous and present results on L, Lx and Ly for the same feet positions (P > 0.05) (Table 2).

<table><caption>**Table 2** : Student t-test results (n.s. : non significant ; n.r. : no result)</caption><thead><tr><th>Authors</th><th colspan="3">Okubo</th><th>Kirby</th></tr><tr><th>Feet position (clearance-angle)</th><th>0 m-0°</th><th>0 m-30°</th><th>0.10 m-0°</th><th>0 m-0°</th></tr></thead><tbody><tr><th>L</th><td>n.s.</td><td>n.s.</td><td>n.s.</td><td>n.r.</td></tr><tr><th>Lx</th><td>n.s.</td><td>n.s.</td><td>n.s.</td><td>n.s.</td></tr><tr><th>Ly</th><td>n.s.</td><td>n.s.</td><td>n.s.</td><td>n.s.</td></tr></tbody></table>

These results confirm and extend those of Okubo and Kirby while showing that the increase of feet clearance and angle significantly improves healthy subjects' balance stability in open-eyes condition. Moreover they show that feet clearance has a higher influence on stability than feet angle (Table 3). For both factors however this improvement is mainly due to the decrease of the medio-lateral dispersion of the COP which reveals a better lateral stability (Figure 1, Figure 2).

<table><caption>**Table 3** : Decrease percentage of Sx, Sy and A95 induced by the increase of clearance (from 0 to 0.2m) and angle (from 0° to 45°)</caption><thead><tr><th rowspan="2">Parameters<br>Factors</th><th colspan="2">Sx</th><th colspan="2">Sy</th><th colspan="2">A95</th></tr><tr><th>Clearance</th><th>Angle</th><th>Clearance</th><th>Angle</th><th>Clearance</th><th>Angle</th></tr></thead><tbody><tr><td>Decrease percentage</td><td>15%</td><td>0%</td><td>61%</td><td>17%</td><td>67%</td><td>23%</td></tr><tr><td>Difference Clearance Angle</td><td colspan="2">15%</td><td colspan="2">44%</td><td colspan="2">44%</td></tr></tbody></table>

Among the 16 positions tested in the present study, the smallest confidence ellipses were obtained when the feet were spread with a clearance of 0.2 m and oriented at angles of 0° and 30°. So these two positions seem to be the most efficient ones with regard to the balance stability of healthy subjects in upright stance. Could they thus be used as reference positions for further studies on balance stability of other subjects with various characteristics ?

## References

* Okubo J. et al. *Agressologie*, **20**, 2, 127-132, 1979.

* Kirby R.L. et al. *J. Biomech.*, **20**, 4, 423-427, 1987.

* Takagi A. et al. in : IGARASHI, *Vestibular and visual control of posture and locomotion equilibrium*, 74-79, Black (eds.), 1985.