Tone Entropy Analysis of Augmented Information Effects on Toe-Ground Clearance When Walking.

Minimum toe clearance (MTC) is an event approximately mid-swing in the walking cycle that is critical for preventing unintended foot contact with surface irregularities ("tripping"). Treadmill-based gait training for older adults was undertaken using real-time augmented information to increase foot-ground clearance at MTC (MTC height). Ten young (Y) (Age: 23±2 year) and ten older (O) (Age: 76±9 year) participants undertook 10 min preferred speed treadmill walking (baseline) followed by 20 min with MTC height information (training) and 10 min without augmented information (retention). Three-dimensional lower limb position was sampled at 100 Hz from which MTC height was computed for each step cycle. MTC height data were analyzed using traditional descriptive statistics (mean and SD) and by computing tone (T) and entropy (E) to show, respectively, cycle-to-cycle changes to MTC height and the informational content of the MTC height time-series. There were significant ( ) age-group differences in T-E values of MTC height; Baseline ( Older=-5.40±2.00 (T); 6.63±0.23 (E); Young = -3.00±0.89 (T); 6.20±0.51 (E)), Training ( Older=-5.05±3.45 (T); 6.46±0.42 (E); Young = -2.55±0.67 (T); 6.75±0.39 (E)) Retention ( Older=-3.77±2.59 (T); 6.38±0.46 (E); Young = -2.55±0.67 (T); 6.26±0.39 (E)). Relative to baseline, tone value was significantly ( ) reduced and entropy was elevated in training and vice versa in retention phase for the young group but no significant trends were observed for older group. T and E measures of MTC height considered separately discriminated the age groups only in baseline but distinctive "clusters" were observed in tone versus entropy plots indicating characteristically different patterns of MTC adjustment over step cycles. Treadmill training with MTC height augmented information is a practical intervention for reducing tripping in older people and others with gait impairments. T-E analysis is useful for identifying characteristics of lower limb control with ageing that have not been previously recognized in studies employing traditional statistical analysis of the MTC event.