Bilateral temporal control determines mediolateral margins of stability in symmetric and asymmetric human walking.

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.

Force production parameters as behavioural measures for anger expression and control: The Method of Stamp Strike Shout.

This study presents first test results of a new performance-based, psychomotor method to measure anger expression and control, based on voice expression and physical force production in directional movement of arms and legs, called the Method of Stamp Strike Shout (MSSS). Recorded are the standardized impact of stamping on a force plate, hitting a punching bag, and the amplitude of shouting in a microphone at various force levels. The premise is, that these body behaviours stand for the 'urge to act or shout' that belongs to anger-related emotions. The MSSS is meant to be applied in addition to potentially biased self-report questionnaires and has been designed for diagnostic as well as therapeutic purposes in clinical practice. First, this paper focusses on the instrumentation, internal structure and reliability of the MSSS. An explorative study in a student sample (n = 104) shows correlation patterns between increasing and decreasing levels of force production within each subtest (Stamp, Strike and Shout) and between the three subtests. We found excellent internal consistency of the three subtests and high test-retest reliability. The parameters of increasing and decreasing force levels form the slopes of what we call a force pyramid. To adjust for the clustering within persons, aggregated outcomes were calculated: sum scores per subtest as an indication of total force produced, two linear contrast scores to indicate the rate of increase / decrease, and two quadratic contrast scores as measures of the curvature of the slopes. On all subtests, all aggregated scores showed differences between men and women, also when controlled for weight. To test the validity of the MSSS, the second part of the paper examines the relationship between force parameters and anger coping style, measured by the Self-Expression and Control Scale (SECS). The results suggest that the Shout subtest was the most sensitive indicator for anger coping style, showing negative correlations with Anger In, for women as well as men. For women, higher amplitude was also associated with higher Anger Out and lower amplitude with higher Anger Control. The Stamp subtest showed weak positive correlations with the Anger In subscales, whereas no correlations were found on the Strike subtest. Further, a more robust comparison was made between two groups of participants who reported to have an internalizing versus an externalizing anger coping style. Results indicated that internalizing women as well as men used less force than externalizing participants on all three subtests, especially on the Shout subtest. This was confirmed by lower mean sum scores on the Shout subtest for internalizing women compared with externalizing women. No differences in linear contrast scores were shown between internalizing and externalizing participants. The quadratic contrast scores suggested differences of the curvation of the slopes between women with more or less anger control when stamping, and men with more or less anger control when striking. As this is an explorative study, findings should be interpreted with caution.

Staying in dynamic balance on a prosthetic limb: A leg to stand on?

With the loss of a lower limb, amputees lack the active muscle empowered control of the ankle that is important for balance control. We examined single-leg stance on prosthesis vs. sound limb balancing on narrow ridges in transtibial amputees. When balancing on the prosthetic limb, the lateral displacement of the center of pressure was reduced and was compensated by an increase in counter-rotation. We show that single-leg stance on a prosthetic limb can be compared to balancing on a narrow ridge. Standing on a prosthetic limb involves the same balance mechanisms as balancing on narrow ridges of 40-mm to 20-mm width. Yet, the ability to balance on a narrow ridge with the sound limb was only a weak predictor for an amputee's ability to stand on the prosthetic limb. Balancing in single-leg stance on a prosthetic limb is not a common activity. The ability to compensate with the sound limb may therefore be functionally more important than the ability to stay in dynamic balance on the prosthetic limb.

A stricter condition for standing balance after unexpected perturbations.

In order to account for the dynamic nature of balance, the concept of the 'extrapolated centre of mass' XcoM has been introduced (Hof et al., 2005). The law for standing balance was then formulated as: the XcoM should remain within the Base of Support (BoS). This law, however, does not take into account that the centre of pressure (CoP) needs time to displace due to various neural and mechanical delays. The theory is extended to include the finite reaction- and displacement time of the CoP. Experimental results on humans standing on two feet undergoing sudden postural perturbations are presented. In this case it turns out that the area of the effective BoS is only a fraction, some 30%, of the area of the static BoS.

Intravenous immunoglobulin therapy in dermatology: an update.

Intravenous immunoglobulin (IVIG) is a fractioned blood product consisting of IgG antibodies which was first used in antibody deficiency disorders. It is increasingly being used for several inflammatory and autoimmune conditions. IVIG can also be used in a wide range of dermatological diseases which are difficult to treat including autoimmune bullous skin diseases and toxic epidermal necrolysis. The use of IVIG in dermatological disorders is discussed in this article.

Controlling horizontal deceleration during gait termination in transfemoral amputees: measurements and simulations.

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.

The relative contributions of the prosthetic and sound limb to balance control in unilateral transtibial amputees.

In unilateral transtibial amputees maintenance of standing balance is compromised due to the lack of active ankle control in the prosthetic limb. The purpose of this study is to disentangle the contribution of the prosthetic and sound limb to balance control following waist-pull perturbations. We compared the contribution of the hip and ankle joints to balance control of 15 unilateral transtibial amputees and 13 able-bodied controls after been externally perturbed through release of a pulling force. Perturbations were applied in four different directions. Outcome measure was the proportion of joint moment integrated over time generated by the hip and ankle joints in order to restore static stability after perturbation. Analyses revealed that perturbations in backward/forward direction were recovered mainly by the ankle strategy. The amputees compensated for the absence of active ankle control in the prosthetic limb by increasing the ankle moment in the sound limb. Interestingly, the passive properties of the prosthetic foot contributed to balance control, which has important implications for prosthetic fitting and standing stability in lower limb amputees. Amputees and controls resisted perturbations in medio-lateral direction by generating the necessary hip moments. Finally, these findings are discussed with respect to prosthetic design and rehabilitation processes.

Stabilizing moments of force on a prosthetic knee during stance in the first steps after gait initiation.

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.

Principles of obstacle avoidance with a transfemoral prosthetic limb.

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.

Core muscle response times and postural reactions in soccer players and nonplayers.

UNLABELLED: Decreased core stability has been suggested to be associated with a higher occurrence of lower extremity injuries and low back pain. In a physical contact sport like soccer, direction-specific muscle reflex responses are crucial in maintaining core stability. Delayed core muscle response times repeatedly have been reported in patients with low back pain, but no study has compared core muscle reflex latencies and postural control between soccer players and less active nonplayers. PURPOSE: The goal of this study was to investigate whether soccer players will exhibit shorter average core muscle reflex latencies along with less postural sway in response to a sudden trunk perturbation compared with nonplayers. A second goal was to see whether postural control measures are a valid, more practical alternative for the use of surface EMG in measuring reflexive core neuromuscular control. METHODS: Sudden trunk loading in the frontal and sagittal plane was used in 10 high-level amateur soccer players and 11 less active nonplayers to study core muscle reflex latencies, using surface EMG of six major trunk muscles. Simultaneously, kinematic response data of a balance seat were obtained using gyroscopes measuring seat angular velocity. RESULTS: Soccer players demonstrated shorter reflex latencies compared with nonplayers for the rectus abdominis, erector spinae, and externus obliquus muscles in response to sagittal plane perturbations. These shorter reflex latencies went along with greater seat movement in response to sudden trunk loading, with moderate correlations between the two measures. CONCLUSIONS: The results showing shorter reflex latencies and greater balancing movements for soccer players add to the debate whether more postural sway is an appropriate indicator of having less neuromuscular control.

Over rough and smooth: amputee gait on an irregular surface.

When negotiating irregular surfaces, the control of dynamic stability is challenged. In this study, we compared the adjustments in stepping behaviour and arm-swing of 18 unilateral transtibial amputees and 17 able-bodied participants when walking on flat and irregular surfaces. Experimental findings revealed that unilateral transtibial amputees reduced their gait velocity only slightly when walking on irregular surfaces. Analyses of the temporal gait characteristics, i.e. stride time, stance time, double-support time and step frequency, showed no statistically significant adjustments. Interestingly, the amputees did not increase the stability margins for lateral balance which were calculated based on the concept of the "extrapolated center of mass". Furthermore, they did not increase their step width, which was already wide when walking on the flat surface. However, amputees did increase the lateral component of relative arm-swing velocity in order to walk stable on irregular surfaces.

Determining asymmetry of roll-over shapes in prosthetic walking.

How does the inherent asymmetry of the locomotor system in people with lower-limb amputation affect the ankle-foot roll-over shape of prosthetic walking? In a single-case design, we evaluated the walking patterns of six people with lower-limb amputation (3 transtibial and 3 transfemoral) and three matched nondisabled controls. We analyzed the walking patterns in terms of roll-over characteristics and spatial and temporal factors. We determined the level of asymmetry by roll-over shape comparison (root-mean-square distance) as well as differences in radius of curvature. In addition, we calculated ratios to determine spatial and temporal asymmetries and described different aspects of asymmetry of roll-over shapes. All participants showed some level of asymmetry in roll-over shape, even the nondisabled controls. Furthermore, we found good intralimb reproducibility for the group as a whole. With respect to spatial and temporal factors, the participants with transtibial amputation had a quite symmetrical gait pattern, while the gait in the participants with transfemoral amputation was more asymmetrical. The individual ankle-foot roll-over shapes provide additional insight into the marked individual adjustments occurring during the stance phase of the nondisabled limb. The two methods we present are suitable for determining asymmetry of roll-over shapes; both methods should be used complementarily.

The Narrow Ridge Balance Test: a measure for one-leg lateral balance control.

The assessment of balance capacity for people with widely different balance abilities is an important issue in clinical practice. We propose the narrow ridge balance test as a sensitive tool to assess one-leg balance capacity. In this test, participants are asked to perform single-leg stance on ridges of gradually decreasing width (100, 80, 60, 40, 20, 10, and 4mm). An outcome measure was developed, base on time in balance in relation to the gradually decreasing ridge width. To evaluate the sensitivity and discriminating power of the test, we applied it to two groups of participants, a group of young participants (age 20-30 years) and group of healthy elderly participants (age 60-80 years). The test showed to sensitively differentiate between the two groups, showing lower scores for the elderly. Furthermore, the test appeared to identify large within-group differences. A special feature of this setup is that the difficulty of the test increases with the balance capacity of the participant. In this way, each participant is exposed to the maximally challenging task, and a broader variety of balance control mechanisms come into play. Finally, the outcome score of the new test was contrasted to conventional measures of standing balance, showing good agreement.

Balance recovery after an evoked forward fall in unilateral transtibial amputees.

Falls are a common and potentially dangerous event, especially in amputees. In this study, we compared the mechanisms of balance recovery of 17 unilateral transtibial amputees and 17 matched able-bodied controls after being released from a forward-inclined orientation of 10%. Kinematic analysis revealed statistically significant differences in response time and knee flexion at heel-strike between both groups. However, there were no statistically significant differences in step length of the leading and trailing limb, swing time of the leading limb, and maximal knee flexion during swing. In the amputees, we found spatial and temporal differences when recovering with the sound versus prosthetic limb first. When leading with the prosthetic limb, they responded faster and also the interval between heel-strike of the leading and trailing limb was shorter. Furthermore, amputees made a longer step and showed less knee flexion at heel-strike when leading with the prosthetic limb. Interestingly, amputees as a group had no specific limb preference, prosthetic or sound, to recover after a forward fall, despite the asymmetry in their locomotor system. Analyses of dynamic stability (extrapolated center of mass) revealed that the amputees were equally efficient in recovering from an impending fall as controls, irrespective whether they lead with their prosthetic or sound limb. We suggest that in amputee rehabilitation, balance recovery after a fall should be trained with both sides, as this can increase confidence in fall-prone situations.

Comparative roll-over analysis of prosthetic feet.

A prosthetic foot is a key element of a prosthetic leg, literally forming the basis for a stable and efficient amputee gait. We determined the roll-over characteristics of a broad range of prosthetic feet and examined the effect of a variety of shoes on these characteristics. The body weight of a person acting on a prosthetic foot during roll-over was emulated by means of an inverted pendulum-like apparatus. Parameters measured were the effective radius of curvature, the forward travel of the center of pressure, and the instantaneous radius of curvature of the prosthetic feet. Finally, we discuss how these parameters relate to amputee gait.

Gait adjustments in obstacle crossing, gait initiation and gait termination after a recent lower limb amputation.

OBJECTIVE: To describe the adjustments in gait characteristics of obstacle crossing, gait initiation and gait termination that occur in subjects with a recent lower limb amputation during the rehabilitation process. DESIGN: Prospective and descriptive study. SUBJECTS: Fourteen subjects with a recent transfemoral, knee disarticulation or transtibial amputation. METHODS: Subjects stepped over an obstacle and initiated and terminated gait at four different times during the rehabilitation process. OUTCOME MEASURES: Success rate, gait velocity and lower limb joint angles in obstacle crossing, centre of pressure shift and peak anteroposterior ground reaction force in gait initiation and termination. RESULTS: In obstacle crossing amputees increased success rate, gait velocity and swing knee flexion of the prosthetic limb. Knee flexion in transfemoral and knee disarticulation amputees was not sufficient for safe obstacle crossing, which resulted in a circumduction strategy. In gait initiation and termination amputees increased the anteroposterior ground reaction force and the centre of pressure shift in the mediolateral direction in both tasks. Throughout the rehabilitation process the centre of pressure was shifted anteriorly before single-limb stance on the trailing prosthetic limb in gait initiation, whereas in gait termination the centre of pressure in single-limb stance remained posterior when leading with the prosthetic limb. CONCLUSION: Subjects with a recent amputation develop adjustment strategies to improve obstacle crossing, gait initiation and gait termination. Innovations in prosthetic design or training methods may ease the learning process of these tasks.

Foot and ankle compression improves joint position sense but not bipedal stance in older people.

This study investigates the effects of foot and ankle compression on joint position sense (JPS) and balance in older people and young adults. 12 independently living healthy older persons (77-93 years) were recruited from a senior accommodation facility. 15 young adults (19-24 years) also participated. Compression was applied at the ankles and feet using medical compression hosiery. The mean velocity of the centre of pressure (CoP) displacements and the root mean square of the CoP velocity in both anteroposterior and mediolateral directions, were measured with a foot pressure plate. In older people, ankle compression was associated with an improvement of JPS towards normal values. However, a concurrent deterioration of their balance was found. In young adults compression had no effect on either JPS or balance.

The importance of sensory-motor control in providing core stability: implications for measurement and training.

Although the hip musculature is found to be very important in connecting the core to the lower extremities and in transferring forces from and to the core, it is proposed to leave the hip musculature out of consideration when talking about the concept of core stability. A low level of co-contraction of the trunk muscles is important for core stability. It provides a level of stiffness, which gives sufficient stability against minor perturbations. Next to this stiffness, direction-specific muscle reflex responses are also important in providing core stability, particularly when encountering sudden perturbations. It appears that most trunk muscles, both the local and global stabilization system, must work coherently to achieve core stability. The contributions of the various trunk muscles depend on the task being performed. In the search for a precise balance between the amount of stability and mobility, the role of sensory-motor control is much more important than the role of strength or endurance of the trunk muscles. The CNS creates a stable foundation for movement of the extremities through co-contraction of particular muscles. Appropriate muscle recruitment and timing is extremely important in providing core stability. No clear evidence has been found for a positive relationship between core stability and physical performance and more research in this area is needed. On the other hand, with respect to the relationship between core stability and injury, several studies have found an association between a decreased stability and a higher risk of sustaining a low back or knee injury. Subjects with such injuries have been shown to demonstrate impaired postural control, delayed muscle reflex responses following sudden trunk unloading and abnormal trunk muscle recruitment patterns. In addition, various relationships have been demonstrated between core stability, balance performance and activation characteristics of the trunk muscles. Most importantly, a significant correlation was found between poor balance performance in a sitting balance task and delayed firing of the trunk muscles during sudden perturbation. It was suggested that both phenomena are caused by proprioceptive deficits. The importance of sensory-motor control has implications for the development of measurement and training protocols. It has been shown that challenging propriocepsis during training activities, for example, by making use of unstable surfaces, leads to increased demands on trunk muscles, thereby improving core stability and balance. Various tests to directly or indirectly measure neuromuscular control and coordination have been developed and are discussed in the present article. Sitting balance performance and trunk muscle response times may be good indicators of core stability. In light of this, it would be interesting to quantify core stability using a sitting balance task, for example by making use of accelerometry. Further research is required to develop training programmes and evaluation methods that are suitable for various target groups.