Mediolateral foot placement control can be trained: Older adults learn to walk more stable, when ankle moments are constrained

Abstract

Falls are a problem, especially for older adults. Placing our feet accurately relative to the center-of-mass helps us to prevent falling during gait. The degree of foot placement control with respect to the center-of mass kinematic state is decreased in older as compared to young adults. Here, we attempted to train mediolateral foot placement control in healthy older adults. Ten older adults trained by walking on shoes with a narrow ridge underneath (LesSchuh), restricting mediolateral center-of-pressure shifts. As a training effect, we expected improved foot placement control during normal walking. A training session consisted of a normal walking condition, followed by a training condition on LesSchuh and finally an after-effect condition. Participants performed six of such training sessions, spread across three weeks. As a control, before the first training session, we included two similar sessions, but on normal shoes only. We evaluated whether a training effect was observed across sessions and weeks in a repeated-measures design. Whilst walking with LesSchuh, the magnitude of foot placement error reduced half-a-millimeter between sessions within a week (cohen's d = 0.394). As a training effect in normal walking, the magnitude of foot placement errors was significantly lower compared to the control week, by one millimeter in weeks 2 (cohen's d = 0.686) and 3 (cohen's d = 0.780) and by two millimeters in week 4 (cohen's d = 0.875). Local dynamic stability of normal walking also improved significantly. More precise foot placement may thus have led to improved stability. It remains to be determined whether the training effects were the result of walking on LesSchuh or from repeated treadmill walking itself. Moreover, enhancement of mechanisms beyond the scope of our outcome measures may have improved stability. At the retention test, gait stability returned to similar levels as in the control week. Yet, a reduction in foot placement error persisted.

Fig 1. Experimental design.

Each week consisted of two (training) sessions. In week 1, participants walked only on normal shoes. In weeks 2–4, they walked on normal shoes in the Normal walking and After-effect conditions, but on LesSchuh (Fig 2) in the Training condition (shaded blue area). In weeks 2–4, the widths of the ridges underneath the shoes were 2.0, 1.5 and 1.0 cm respectively. In week 6, we performed a retention test. We collected data during all sessions.

Fig 2. LesSchuh.

The narrow ridge underneath the sole constrains mediolateral shifts in the center of pressure. The width of the ridge in the figure is one centimeter.

Fig 3. Treadmill with safety harness.

Fig 4. Scores on the Short Physical Performance Battery (SPPB).

Higher scores represent better physical performance. Red circles represent individual data points. The green line represents the threshold [30] above which participants are in the safe zone.

Fig 5. Scores on the Falls Efficacy Scale-International (FES-I).

Red circles represent individual data points. Higher scores mean a more serious concern of falling.

Fig 6. The degree of foot placement control across measurement sessions.

Fig 7. Magnitude of foot placement error (i.e. standard deviation of residual) in meters across measurement sessions.

Fig 8. Gait stability across measurement sessions.

Fig 9. Step width across measurement sessions.

Fig 10. Stride time across measurement sessions.

Fig 11. Magnitude of foot pacement placement error in meters retention.

Fig 12. Gait stability retention.

Fig 13. Main results: Training effects on foot placement control and gait stability.

Fig 14. The degree of foot placement control.

The degree of foot placement control (R²) can be altered in different ways. In all panels we see fictive data of the foot placement model. As a simplification we have drawn the linear relationship for one of the predictors (it can be either CoM position or velocity). Panel A shows a foot placement model with a “high” foot placement error, a “low” CoM variance and a “small” slope. In panels B-D, we illustrate respectively how a “low” error, a “high” CoM variance and a “steep” slope increase the R² of this model.