A Forward Dynamic Modelling Investigation of Cause-and-Effect Relationships in Single Support Phase of Human Walking

Modeling and Analysis of Foot Function in Human Gait Using a Two-Degrees-of-Freedom Inverted Pendulum Model with an Arced Foot

Gait models are important for the design and control of lower limb exoskeletons. The inverted pendulum model has advantages in simplicity and computational efficiency, but it also has the limitations of oversimplification and lack of realism. This paper proposes a two-degrees-of-freedom (DOF) inverted pendulum walking model by considering the knee joints for describing the characteristics of human gait. A new parameter, roll factor, is defined to express foot function in the model, and the relationships between the roll factor and gait parameters are investigated. Experiments were conducted to verify the model by testing seven healthy adults at different walking speeds. The results demonstrate that the roll factor has a strong relationship with other gait kinematics parameters, so it can be used as a simple parameter for expressing gait kinematics. In addition, the roll factor can be used to identify walking styles with high accuracy, including small broken step walking at 99.57%, inefficient walking at 98.14%, and normal walking at 99.43%.

THE RELIABILITY OF A NOVEL HEEL-RISE TEST VERSUS GONIOMETRY TO ASSESS PLANTARFLEXION RANGE OF MOTION

BACKGROUND

Ankle plantarflexion (PF) active range of motion (ROM) is traditionally assessed in a non-weight-bearing (NWB) position with a universal goniometer. However, a convenient, reliable, low-cost means of assessing functional PF active ROM in a weight-bearing (WB) position has yet to be established.

PURPOSE

To compare the intra- and interrater reliability of PF active ROM measurements obtained from a goniometric NWB assessment, and a functional heel-rise test (FHRT) performed in WB.

STUDY DESIGN

Reliability study.

METHODS

Two physical therapy student examiners, blinded to each other's measurements, assessed PF active ROM through a NWB goniometric technique and a FHRT on all subjects within the same test session. Intra- and interrater reliability values were calculated using an intraclass correlation coefficient (ICC_2,1, ICC_2,k) and 95% confidence intervals. Standard error of measurement (SEM) and minimal detectable change (MDC) were recorded for each method.

RESULTS

43 healthy participants (mean ± SD, age: 22.7 ± 1.7 years, height: 1.7 ± 0.1 m, mass: 77.8 ± 17.2 kg) completed testing procedures. The within-session intrarater reliability (ICC_2,1) estimates were observed for goniometry (right: 0.96, left: 0.95 - 0.97) and FHRT (right: 0.99, left: 0.99), as well as the interrater reliability (ICC_2,k) of goniometry (right: 0.79, left: 0.79) and FHRT (right: 0.79, left: 0.87). Goniometry SEM (3.3 - 3.6 °) and MDC (9.2 - 9.8 °) were observed, in addition to FHRT SEM (0.6 cm) and MDC (1.6 - 1.7 cm). A weak correlation was found between FHRT and goniometric measurements (r = -0.03 - 0.13).

CONCLUSIONS

The FHRT was found to have good to excellent intra- and interrater reliability, similar to goniometric measurement. The lack of agreement between these measurements requires further exploration of a WB assessment of ankle PF active ROM.

LEVEL OF EVIDENCE

2b.

A Lagrange-based generalised formulation for the equations of motion of simple walking models

Simple 2D models of walking often approximate the human body to multi-link dynamic systems, where body segments are represented by rigid links connected by frictionless hinge joints. Performing forward dynamics on the equations of motion (EOM) of these systems can be used to simulate their movement. However, deriving these equations can be time consuming. Using Lagrangian mechanics, a generalised formulation for the EOM of n-link open-loop chains is derived. This can be used for single support walking models. This has an advantage over Newton-Euler mechanics in that it is independent of coordinate system and prior knowledge of the ground reaction force (GRF) is not required. Alternative strategies, such as optimisation algorithms, can be used to estimate joint activation and simulate motion. The application of Lagrange multipliers, to enforce motion constraints, is used to adapt this general formulation for application to closed-loop chains. This can be used for double support walking models. Finally, inverse dynamics are used to calculate the GRF for these general n-link chains. The necessary constraint forces to maintain a closed-loop chain, calculated from the Lagrange multipliers, are one solution to the indeterminate problem of GRF distribution in double support models. An example of this method's application is given, whereby an optimiser estimates the joint moments by tracking kinematic data.