Stepping biomechanics of the transition into stair descent in naturalistic homes using instrumented insoles

Introduction:

Stair falls frequently occur during the transition from level walking to stair descent. Laboratory research indicates that the demands of transition steps are different to continuous descent, yet these findings have not been confirmed in home environments where most falls occur.

Using instrumented insoles in naturalistic experimental homes, this early-translational study quantified biomechanical differences between transitional and continuous descent and explored the influence of lighting conditions.

Method:

Five participants descended a 14-step staircase in an experimental home under bright and dim lighting; three trials per condition in a randomised order. An insole inertial measurement unit (Walk With Path) quantified absolute foot angle in sagittal (+ve: below horizontal) and transverse (+ve: out-toeing) planes at initial contact, and peak vertical foot acceleration during loading of the 1-step transition (Step1, right foot), 2-step transition (Step2, left foot), and continuous descent. 

Results:

Sagittal and transverse-plane foot angles were significantly lower in both transition steps than continuous descent (p<0.05). Group mean angles did not differ between lighting conditions for any step, but sagittal-plane variability on Step1 was greater in dim light (IQR: 4.14° bright vs 12.1° dim).

No significant differences in peak loading acceleration were found between steps or lighting conditions (p>0.05). However, variability was greater in the transitions than continuous descent, and was greater on Step1 in the bright than dim condition (IQR: 18.89ms-2 bright vs 10.91ms-2 dim). 

Conclusion:

This novel, early-translational study found more neutral foot angles and greater loading variability during level-to-stair transition than during continuous descent. These behaviours are associated with known fall risk factors, so may contribute falls during stair transitions. The changes in movement variability in dim lighting warrant further investigation to understand their interacting effects on safety.

Wearable sensors show promise for measuring stair biomechanics and can enhance future research understanding fall mechanisms and intervention effectiveness in real-world settings.