At L. Hof

Human bipedal gait requires active control of mediolateral dynamic balance to stay upright. The margin of stability is considered a measure of dynamic balance, and larger margins are by many authors assumed to reflect better balance control. The inverted pendulum model of gait indicates that changes in the mediolateral margin of stability are related to changes in bilateral single support times. We propose updated equations for the mediolateral margin of stability in temporally symmetric and asymmetric gait, which now include the single support times of both legs. Based on these equations, we study the relation between bilateral single support times and the mediolateral margin of stability in symmetric, asymmetric, and adaptive human gait. In all conditions, the mediolateral margin of stability during walking followed predictably from bilateral single support times, whereas foot placement co-varied less with the mediolateral margin of stability. Overall, these results demonstrate that the bilateral temporal regulation of gait profoundly affects the mediolateral margin of stability. By exploiting the passive dynamics of bipedal gait, bilateral temporal control may be an efficient mechanism to safeguard dynamic stability during walking, and keep an inherently unstable moving human body upright.

Lateral stability during gait is of utmost importance to maintain balance. This was studied on human subjects walking on a treadmill who were given 100-ms perturbations of known magnitude and timing with respect to the gait cycle by means of a computer-controlled pneumatic device. This method has the advantage that the same perturbations can be given at different phases of the stride cycle, thereby allowing an analysis of the phase dependency of the responses in the primary muscles involved. After an inward push, e.g., a push toward the left during right stance, the left foot in the step to follow is placed more to the left (outward strategy). The hypothesis was that this movement is caused by automatic unvoluntary muscle activity. This turned out to be the case: the abduction movement follows EMG responses in the left abductor muscle, gluteus medius, in response to the push. Two responses, with latencies of 100 and 170 ms, and a late reaction >270 ms can be discerned. All three responses are phase dependent; they show facilitation in swing and no response in stance, in contrast to the normal walking activity (background). This independence of the background activity suggests a premotoneuronal gating of these responses, reminiscent of phase-dependent modulation of electrically elicited reflexes. It is concluded that facilitating pathways are opened independent of normal background activation to enable appropriate actions to restore balance after a mediolateral perturbation.

In this study we investigated how leading limb angles combined with active ankle moments of a sound ankle or passive stiffness of a prosthetic ankle, influence the center of mass (CoM) velocity during the single limb support phase in gait termination. Also, we studied how the trailing limb velocity influences the CoM velocity during this phase. We analyzed force plate data from a group of experienced transfermoral (TF) amputee subjects using a prosthetic limb, and the outcome from a two-dimensional mathematical forward dynamics model. We found that when leading with the sound limb, the subjects came almost to a full stop in the single limb support phase, without the use of the prosthetic limb. When leading with the prosthetic limb, the CoM deceleration was less in a relatively short single limb support phase, with a fast forward swing of the trailing sound limb. Slowing down the heavier trailing sound limb, compared to the prosthetic limb, results in a relatively larger braking force at the end of the swing phase. The simulations showed that only narrow ranges of leading limb angle and ankle moments could be used to achieve the same CoM velocities with the mathematical model as the average start and end velocities of the prosthetic limb user. We conclude that users of prosthetic limbs have a narrow range of options for the dynamics variables to achieve a target CoM velocity. The lack of active control in the passive prosthetic ankle prevents the TF amputee subjects from producing sufficient braking force when terminating gait with the prosthetic limb leading, forcing the subjects to use both limbs as a functional unit, in which the sound limb is mostly responsible for the gait termination.

Background Enhancement of physical activities is an important goal in rehabilitation programmes for patients with chronic musculoskeletal pain (CMP). A relationship between activity level and psychological factors is suggested but studied scarcely. Aim To explore the relationship between the activity level and psychological factors in patients with CMP. Methods Study design is cross-sectional, explorative. Participants are patients with CMP, included for outpatient multidisciplinary pain rehabilitation. Measures Activity level was measured by the RT3 accelerometer during 1 week; pain intensity was measured with a 100-mm visual analogue scale; depression, somatization and distress were measured with Symptom Checklist-90-Revised (SCL-90-R), coping strategy with the Utrecht Coping List (UCL, scales active coping, passive coping, avoiding), fear of movement measured with Tampa Scale of Kinesiophobia (TSK), scale activity avoidance. Depending on data distribution, correlations between the mean number of activity counts and psychological factors were tested with Pearson or Spearman correlation coefficients. Results Fifty three patients were included: age mean 39.9 years [standard deviation (SD) 11.3]; activity counts per day mean 198,243 (SD 78,000); pain intensity mean 58 (SD 27.7); SCL-90-R mean 149.4 (SD 42.5); UCL active coping mean 17.9 (SD 3.7); UCL passive coping mean 12.3 (SD 3.7); UCL avoiding mean 15.3 (SD 3.0); TSK total mean 35.4 (SD 7.4); TSK activity avoidance mean 16.9 SD (4.7). Correlations between psychological factors and the mean number of activity counts per day ranged from r = –0.27 to r = 0.01 and were all non-significant (p ≥ 0.05). Conclusion Psychological factors and activity level were unrelated in patients with CMP.

In this study, conditions that enable a prosthetic knee flexion strategy in transfemoral amputee subjects during obstacle avoidance were investigated. This study explored the hip torque principle and the static ground principle as object avoidance strategies. A prosthetic limb simulator device was used to study the influence of applied hip torques and static ground friction on the prosthetic foot trajectory. Inverse dynamics were used to calculate the energy produced by the hip joint. A two-dimensional forward dynamics model was used to investigate the relation between obstacle-foot distance and the necessary hip torques utilized during obstacle avoidance. The study showed that a prosthetic knee flexion strategy was facilitated by the use of ground friction and by larger active hip torques. This strategy required more energy produced by the hip compared to a knee extension strategy. We conclude that when an amputee maintains enough distance between the distal tip of the foot and the obstacle during stance, he or she produces sufficiently high, yet feasible, hip torques and uses static ground friction, the amputee satisfies the conditions for enable stepping over an obstacle using a knee flexion strategy.

In this study, the occurrences of stabilizing and destabilizing external moments of force on a prosthetic knee during stance, in the first steps after gait initiation, in inexperienced users were investigated. Primary aim was to identify the differences in the external moments during gait initiation with the sound leg leading and the prosthetic leg leading. A prosthetic leg simulator device, with a flexible knee, was used to test able-bodied subject, with no walking aid experience. Inverse dynamics calculations were preformed to calculate the external moments. The subjects learned to control the prosthetic leg within 100 steps, without walking aids, evoking similar patterns of external moments of force during the steps after the gait initiation, either with their sound leg loading or prosthetic leg leading. Critical phases in which a sudden flexion of the knee can occur were found just after heelstrike and just before toe off, in which the external moment of force was close to the internal moment produced by a knee extension aiding spring in the opposite direction.