The shank-thigh (S-T) MARP group results were statistically significant for both factors (shoe traction × obstacle) during all the three periods (stance, braking, and propulsion; and ). The S-T MARP values were significantly larger for the high traction shoe, and decreased as the obstacle height increased in both shoes. Specifically, the decrease in the S-T MARP values was symmetrical between obstacle conditions for the stance and the propulsive periods in both shoes. However, for the braking period this decrease was only noticeable from the level walking to the 10% obstacle conditions; the post-hoc analysis showed no statistical differences between the obstacle conditions. Regarding the foot-shank (F-S) MARP group results, no statistically significant differences were found between conditions.
Group means (M) and standard deviations (SD) for MARP and DP.
F-ratios from the two-way ANOVA with repeated measures on both factors: shoe traction (s) × obstacles (o).
The DP group results were statistically significant for both S-T and F-S segmental relationships for all three periods analyzed regarding the obstacle factor ( and ). For the shoe factor all S-T segmental relationships were significant, while for the F-S only the propulsive period was significantly different. All the DP group results increased in value as the obstacle height increased for both shoes. Furthermore, the S-T DP results were larger for the low traction shoes for all periods.
Graphically, the thigh segment during the stance phase showed a segmental reversal which occurs towards the later part of stance (). Functionally, every time that a trajectory goes through zero a segmental reversal is observed. It is worth noting that the thigh exhibited a fairly constant velocity during the middle part of the stance period, especially in the no obstacle conditions. Constant velocity is depicted by flat horizontal sections. However, spatial aspects of the phase portraits expressed the same general shape from one condition to the next. However, in level-walking (0% obstacle) and low-obstacle (10%) conditions, low traction shoes caused an additional curve segment to be developed within the original pattern during late stance. The shank segment phase portraits revealed no reversals, indicating a backward only rotation around the knee joint during the stance phase of walking (). However, the foot behaved differently than the other lower extremity segments (). The foot segment during stance displayed a cusp shape. Cusps in the foot trajectory path, when the velocity is near zero, indicate sudden interruption in the movement pattern. This is due to the fact that the foot remained flat on the ground for a period of time during midstance. The foot trajectories were more similar geometrically between conditions; however, the angular velocity of the foot segment appeared to increase during the later part of the stance period in the high traction condition, as compared to the low traction situation. This observation was graphically visible thought a more pronounced concave-down configuration during the later portion of the stance phase.
Phase portraits (or phase planes) of the sagittal (a) thigh, (b) shank, and (c) foot motions from a representative trial for all conditions during stance. Black solid lines: low traction shoes; grey solid lines: high traction shoes.
The group mean ensemble foot-shank (F-S) and shank-thigh (S-T) relative phase curves for the stance period are displayed in . In general, it can be observed that segmental relative phase relationships are non linear i.e., neither in-phase (~0° values) nor out-of-phase (~180° values) by a constant magnitude during stance. In addition, during level-walking, F-S and S-T relative phases began differently than for obstacle conditions. Indeed, both segmental relative phases began around 0° for the no obstacle conditions, whereas F-S relative phase began around −25° and S-T relative phase around +50° for the obstacle conditions. Therefore, the effect of the obstacle on the relative phase caused the segments to be more out of phase at touchdown.
Figure 2 Relative phase curves for the sagittal foot-shank (a) and shank-thigh (b) segmental relationships from the same representative trial for all conditions during stance. Each curve is an ensemble average over all trials. The standard deviation curves are (more ...)
The group mean ensemble F-S relative phase curves had similar configurations for all conditions (). All curves began with negative values (or negative zero values for the level-walking conditions) that indicated that the shank was leading the foot (i.e., the shank was moving faster in phase space) during the first initial portion of stance. Early in stance, the relationship between the foot and shank reversed. Reversal in the relationship between the two segments was evident by the local minimum in the relative phase graph. The positive slope after the local minimum indicated that the foot was leading the shank segment (i.e., the foot was moving faster in phase space). During mid-stance, the foot-shank relationship became more out of phase, and the foot clearly was leading the shank (positive values: 25–50°). Moreover, there was not a distinct (unique) local maximum in the F-S relative phase. In fact, inspection of the F-S relative phase curve indicated that there were multiple fluctuations during midstance. Local minimums and maximums suggest a change in direction of the relationship between the two segments. During the late portions of the stance, the relationship between the foot and shank became progressively in-phase.
The group mean ensemble S-T relative phase curves also displayed quite similar trends (). For the obstacle conditions, all curves began with positive values that indicated that the shank was leading the thigh. Immediately after the shank-thigh relationship became more in-phase (0°) during mid-stance. During late stance, the relationship between the shank and thigh became progressively out of phase with the thigh leading. A slightly different segmental relationship occurred for the level-walking conditions. As previously mentioned, the S-T segments began more in-phase (i.e., close to zero degree). However, early in stance the relative phase became more-out-of-phase with the thigh leading the shank before returning to a more in-phase relationship throughout the middle portion of the stance period. During late stance, the relationship became progressively out of phase, similarly to what was observed in the obstacle conditions.