4 RESULTS
4.2 G AIT ADJUSTMENT ON DIFFERENT FLOOR CONDITIONS
In this study, we used RCOF, foot-ramp angle, three-dimensional motion of pelvic and COM as main variables to evaluate the effects induced by floor
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materials on locomotion. The required coefficient of friction (RCOF) was obtained by dividing the horizontal ground reaction force by the vertical ground reaction force at heel strike during walking. The effects of floor condition on RCOF are presented in Figure 14. The data of young participants indicated that peak required coefficients of friction were significant greater in the transition conditions than those in the consistent conditions (P < 0.05). Compared to that in the plane-wood condition, peak RCOF increased by 5.8% when the subjects walked from plane-wood to PVC floor. Compared with walking under consistent condition of rough-ceramic floor, the peak RCOF under transition condition from rough-ceramic to PVC increased by 10.4%. Walked under plane-wood and ceramic both had significant difference between consistent condition and transition condition.
Figure 14 Peak RCOFs on different floor conditions. Peak required coefficient of friction were significant greater in the transition condition than in the
corresponding consistent condition (PW: plane wood, RC: rough ceramic,*P <
0.05, **P < 0.01).
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5.8 10.4
The results reveal that transition from one floor material to another with lower coefficient would cause higher peak RCOF. And with larger COF-difference between two continuous floor materials, peak RCOF increased more. The higher RCOF values mean that participants used larger horizontal foot forces during walking.
Figure 15 and Figure 16 illustrate the peak RCOF on different floor conditions of fifty-two years-old male and seventy-one years-old female, respectively. As observed in Figure 15, data of middle-aged male present the same adjusting strategy as young participants. The peak required coefficient of friction is greater when walked on the transition condition than walked on the consistent condition.
Figure 15 Peak RCOF of 52 years-old male on different floor conditions. Peak required coefficient of friction was greater in the transition condition than in the consistent condition (PW: plane wood, RC: rough ceramic).
While walked on plane-wood to PVC floor condition, peak required coefficient of friction was 5.7% larger than walked on plane-wood floor condition. For walked on the consistent condition of rough-ceramic, peak required coefficient of friction increased 2.2% when walked on transition condition. However, the increase of peak required coefficient of friction when walked on plane-wood to PVC and rough-ceramic to PVC had no significant difference (P > 0.05).
Figure 16 Peak RCOF of 71 years-old female on different floor conditions. Peak required coefficient of friction was lower in the transition condition than in the consistent condition. (PW: plane wood, RC: rough ceramic *P < 0.05).
Unlike young and middle-aged participants, data of seventy-one years-old female showed different adjusting strategy (see Figure 16). The peak required coefficient of friction is decreased in the transition condition than in the consistent condition. Compared to that in the consistent condition of plane-wood, peak required coefficient of friction reduced 4.6% while walked on plane-wood
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to PVC. For consistent condition of rough-ceramic, peak required coefficient of friction reduced 11.8% when walked on transition rough-ceramic to PVC. We find statistically significant difference (P < 0.05) only between rough-ceramic and rough-ceramic to PVC.
Foot angle at heel strike obtained from position data of reflective markers at metatarsal and heel. Negative values are plantar-flexion, positive valures are dorsi-flexion. Figure 17 shows FootAngHC of young participants, the number at x-axis shows the different of COF between floor materials. Compare with walked on the consistent condition of plane-wood, FootAngHC decreased about 30% when young participants walked from higher-COF floor materials to lower-COF floor. And walked from rough-ceramic to PVC floor, with larger COF-difference, shows more decrease of FootAngHC. Compared to that walked on the consistent condition of plane-wood condition, FootAngHC decreased 28.9% while walked from plane-wood to PVC, and decreased 31.5% while walked from rough-ceramic tile to PVC. In addition, walked from plane-wood to PVC and walked from rough-wood to PVC had significant difference (P < 0.05 and P < 0.01, respectively) comparing with walked on consistent condition of plane-wood.
Figure 17 Foot-ramp angle at heel strike on different floor conditions. Foot-ramp angle at heel strike decreased in transition condition. (PW: plane wood, RC:
rough ceramic, COF-diff.: COF difference between two contiguous floor materials. *P < 0.05, **P < 0.01)
Figure 18 shows peak right pelvic tilt angle on consistent and transition conditions. The numbers in the bracket show the difference of COF between floor materials (COF on front material minus COF of back material). In transition condition, less peak anterior pelvic tilt angle is observed as compared to walking on the same floor material in consistent condition. Compared to that in the consistent condition, peak pelvic tilt angle in three transition conditions all decreased significantly. However, the amount of decrease did not rise with the difference of COF.
COF-diff. (—) (0.095) (—) (0.108)
28.9% * 31.5% **
COF-diff. (—) (0.095) (—) (0.108)
* **
Figure 18 Peak right pelvic anterior tilt on different floor conditions (young participants). Pelvic anterior tilt angle decreased significantly in transition conditions. (PW: plane wood, RC: rough ceramic, COF-diff.: COF difference between two contiguous floor materials. *P < 0.05, **P < 0.01)
Figure 19 shows peak right pelvic tilt angle of fifty-two years-old male on consistent and transition conditions. The COF-diff number shows the difference of COF between floor materials (COF on front material minus COF of back material), and the number below zero presents the condition that transition from low-COF to high-COF floor. The results show no general effect of floor transition. Walks from low-COF to high-COF floor induce significantly increase (P<0.01) of peak pelvic tilt angel on plane-wood, but not on rough-ceramic surface. Compared with that in the consistent condition of rough-ceramic, peak pelvic tilt angle even decrease slightly when walk from PVC to rough-ceramic.
In addition, compared to the each consistent condition, peak pelvic tilt angle decreased when walked on plane-wood to PVC (compared to consistent condition of plane-wood) but increased when walked on rough-ceramic to PVC (compared to consistent condition of rough-ceramic). However, the amount of
COF-diff. (—) (0.095) (—) (0.108)
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decrease did not rise with the difference of COF.
Figure 19 Peak right pelvic anterior tilt on different floor conditions (fifty-two years-old male). Pelvic anterior tilt angle increased significantly when walk from low-COF to high-COF floor. (PW: plane wood, RC: rough ceramic, COF-diff.: COF difference between two contiguous floor materials. **P < 0.01)
COM was calculated by the position of each marker point and the anthropometry data. We used the motion of COM in medial-lateral direction to indicate gait stability. Figure 20 shows the COM motion in the medial-lateral direction while walked on plane-wood floor and from plane-wood to PVC floor.
The time period shown in the figure was from the 50% of gait cycle before right heel contacted the material above the force platform to the 50% of gait cycle after the right heel contacted the material above the force platform. The figure indicates that for young participants, the excursion of COM in medial-lateral direction is slightly but significantly (P<0.05) larger when walked on
＊＊
COF-diff. (-0.095) (—) (0.095) (-0.108) (—) (0.108)
plane-wood to PVC compared to that walked on consistent condition of plane-wood.
Figure 20 Motion of COM in medial-lateral direction on plane wood and plane wood to PVC (young participants). Moving range of COM in medial-lateral direction slightly but significantly larger when walking on plane wood compared to walking on plane wood to PVC.
Figure 21 illustrates mean COM trajectory in the medial-lateral direction of middle-aged participant’s (fifty-two year-olds male) on plane-wood and form plane-wood to PVC. The time period shown was the same as in Figure 20. The amplitude of the lateral motion was also slightly larger when walked on plane wood as compared to walked on plane-wood to PVC.
50% 70% 90% 100% 10% 30% 50%
Heel Contact
Figure 21 Motion of COMy in the medial lateral direction on plane wood and from plane wood to PVC (participant 1, fifty-two year-olds male). Moving range of COM in medial-lateral direction slightly but significantly larger when walked on plane wood compared to walked on plane wood to PVC.