By Dr Marie-Louise Bird.

Vitamin D plays an important role in musculoskeletal health, with low levels of vitamin D associated with muscle weakness and poor postural balance. When vitamin D levels are high, they suppress parathyroid hormone (PTH) release explaining why low levels of vitamin D are often found in combination with high levels of PTH. The primary function of PTH is to control calcium levels with the blood. While high levels of PTH are associated with morbidity and mortality in older adults, the specific roles of this hormone on fall risk factors (like balance and gait instability) is less clear. This study was undertaken to gain further insight into the relationship between vitamin D, PTH and physical fall risk factors.

This observational cohort study recruited 122 women (61 pairs of twins >45 years of age) as part of a larger study designed to examine environmental and heritable features of gait and balance. We collected data on dynamic balance, gait, and blood serum levels of vitamin D, PTH and calcium. Serum concentrations were divided into tertiles for association with fall risk factors. High levels of PTH and low levels of vitamin D were both associated with gait instability (increased time in double support during the gait cycle). Low levels of vitamin D was associated with poor dynamic balance as measured by a rapid stepping test.

Low serum vitamin D and high PTH negatively influence measures of physical fall risk in middle age and older women. Importantly, this relationship was not just found in elderly women – our study included women from 47 years of age. This research leads us to think that there may be critical cut off levels of vitamin D and PTH with respect to accidental falls, but further research is needed to validate and clarify this complex issue. Additionally, the role of high levels of PTH without low levels of vitamin D appears more frequently than previously thought, and the independent role of PTH warrants further investigation.

Figure: Parathyroid hormone levels are positively associated with double support duration during walking. As published in Bird et al. Gait Posture 2018.

Publication

Bird, M. L., El Haber, N., Batchelor, F., Hill, K. D, & Wark, J. D. (2018). Vitamin D and parathyroid hormone are associated with gait instability and poor balance performance in mid-age to older aged women. Gait & Posture, 59, 71-75. Doi: https://doi.org/10.1016/j.gaitpost.2017.09.036

About the Author

By Keisuke Hirata. 

Walking on a split-belt treadmill (Figure 1A) is a well-established method to investigate motor adaptation during locomotor tasks. Although previous studies reported the symmetry of step length as a critical measure of adaptation, the relative contribution of the lower limb joints remains unclear. This is relevant because clarifying the effect of split-belt training on joints and preselecting patients to be applied. In this study, we measured the hip, knee, and ankle joint angles using a motion capture system during split-belt treadmill walking to determine which joints facilitate adaptation of gait (Figure 1B).

Ten healthy young adults participated in the study. They walked under a symmetric and asymmetric condition on a split-belt treadmill. During the symmetric condition, both belts moved at 0.9 m/s. In asymmetric condition, one belt moved at 0.9 m/s while the other moved at 1.8 m/s (Figure 1C). After a 3-min adaptation period, participants walked with symmetric step length, which was consistent with results from previous studies. Our kinematic analysis showed that the left and right knee and ankle joint angles were asymmetric when the foot made initial contact, while the hip joint angles remained symmetric (Figure 1D). Our result suggests that the more forward foot contact position of the faster side was due to increased extension of the knee, but not the hip.

Our findings suggest that people mainly alter their knee joint angles to adapt to split-belt treadmill walking. This increases our understanding of gait adaptation. It is also clinically relevant since researchers and clinicians are starting to use the split-belt paradigm as a rehabilitation tool. Our results suggest that they should consider the function of each of the patient’s joints as the results of the split-belt rehabilitation may be limited for patients with impaired knee joints.

Publication

Hirata K, Kokubun T, Miyazawa T, Yokoyama H, Kubota K, Sonoo M, Hanawa H, Kanemura N (2018). Contribution of lower limb joint movement in adapting to re-establish step length symmetry during split-belt treadmill walking. J Med Biol Eng. doi: https://doi.org/10.1007/s40846-018-0456-0

Figure 1. A: The experiment was performed on a split-belt treadmill, where a left and a right belt can move at different speeds. B: Definitions of the angles and step length at foot contact. C: Gait protocol and data collection periods; the two belts started at similar speed for 1 minute, after which the fast side belt speed was increased. D: Joint angles at foot contact during initial contact of the leg on the slow (top left) and fast (bottom left) side of the treadmill during the last 10 strides in the asymmetric condition, and a typical example of the lower joint angles at foot contact on the fast and slow side during the experimental (right).

About the Author

By Dr Patricia van de Walle and Dr Pieter Meyns.

Toddlers learn to walk with their arms in an elevated position. As gait matures, a reciprocal arm swing with the hands at the height of the hips and both arms alongside the trunk quickly appears. Arm swing is an integral part of typical walking, most likely with the goal of minimizing energy expenditure and optimizing stability. However, arm swing is not always well coordinated in patient populations, where often the position of the arms remains elevated. This altered arm swing can be the result of compensation strategies, altered gross motor function or a combination of both, and compromises the role of arm swing during typical walking. There are several movement disorders in children that affect not only lower but also upper limb movements during walking. As such, age-related reference data of arm movements during walking are imperative to allow clinicians to assess whether deviations are related to immaturity or whether they are caused by an underlying pathology or need for compensation.

Gait data of 102 participants between 3 to 35 years old was collected using a full-body marker set (Vicon, Plug-In-Gait; Figure 1A). This gait data was analysed for five age-groups: young children (3-6y), children (6-10y), pubertal children (10-14y), adolescents (14-19y) and adults (19-35y). Age-related changes in arm movements were compared using continuous joint angular waveforms, and as mean joint angle position and range of motion of shoulder, elbow and wrist in different anatomical planes. The overall shape of the arm movement patterns was comparable across all age groups (Figure 1B) with lower variability in the older age groups. At the shoulder, a larger mean extension angle was seen in the two youngest groups compared to the older children and adults. The range of shoulder axial rotation was significantly larger in adults compared to all other age groups. In the two youngest groups, a higher mean elbow flexion and wrist extension angle was found.

Natural arm swing patterns were present at the age of three but showed maturation (i.e. change to adult-like values) and/or fine-tuning (i.e. decrease of variability) in all joints and planes. Some remnants of the elevated arm position were observed until the age of ten years (e.g. increased shoulder abduction and decreased elbow flexion range of motion) where others already disappeared at the age of six years (e.g. increased mean shoulder extension and elbow flexion position). In conclusion, age-specific reference data should be used when clinically assessing arm swing during walking in pediatric pathologies.  

Figure 1: Marker setup and normative joint angle data.  A) Plugin gait total body marker placement. B) Group average of the joint angles over the gait cycle in sagittal (shoulder, elbow, wrist; + = flexion), transversal (shoulder; + = internal rotation) and coronal plane (shoulder and wrist; + = abduction). Black line (adults); blue line (adolescents); red line (pubertal children), green line (children); yellow line (young children). Significant differences between the joint angular profiles between age groups (SPM-d1; ANOVA) are presented by a grey rectangle: * p<0.05, ** p<0.01, *** p<0.001

Publication
Van de Walle, P., Meyns, P., Desloovere, K., De Rijck, J., Kenis, J., Verbecque, E., … & Hallemans, A. (2018). Age-related changes in arm motion during typical gait. Gait & posture, 66, 51-57. https://doi.org/10.1016/j.gaitpost.2018.07.176

This article resulted from combined expertise of motion analysts/researchers at the Clinical Motion Analysis Laboratory, Cerebral Palsy Reference centre UZ Leuven, and three Belgian Universities i.e. UAntwerp, UHasselt and KU Leuven.

About the Author

By Dr Jenna Yentes.

Have you ever noticed that doing the same thing over and over can become tiring or mind numbing after a while? The same may be true for our movements. Nikolai Bernstein has been credited for the statement, “repetition without repetition”; meaning that even when you are repeating a movement, you are never doing it exactly in the same way. Historically, research had considered this variation to be an error, assuming that each repetition of movement should be exactly like the last. Our recent editorial, “Movement variability: A perspective on success in sports, health, and life” explores this notion.

Our editorial supports a growing point of view that variation within the repetitions of movement is healthy. Variation in movement allows for a flexible strategy that can adapt to changes in the environment. Others have gone on to propose that the loss of variation in movement is indicative of pathology or injury. It is now well established that loss of variation in heart rate variability is indicative of mortality. In some populations, changes in heart rate variability are better indicators of mortality than conventional, clinical measurements. On the other side of the spectrum, introduction of variation into learning a new skill via practice schedules or tasks, as well as recovering from an injury (therapy), has led to reductions in the amount of time it takes to learn a new skill or recover. A seminal example of how variation within breathing movement improved patient outcomes is provided in pulmonary medicine. Variation in timing of mechanical ventilation has led to improvements in alveolar recruitment, ventilation/perfusion matching and systemic oxygenation, suggesting improved breathing performance. In sports, there is a body of literature that suggests that variation within team dynamics can identify expert, skilled, and novice athletes.

We suggest that humans possess variation to be successful, not only in the task at hand, but even further in an array of environments. If one only wants to be successful at the task at hand, then limiting variation may be required. However, if the inherent variation exists for the purpose of being flexible and adaptable, possibly variation is truly the essential ingredient for health. For example, standing with limited movement or sway may be required to steady one’s gaze for dart throwing. However, in order to hit the bullseye numerous times, one may need to be able to alter their sway pattern or posture to adapt to the task at hand. As pointed out in the editorial, although we may have embraced the idea of variation as an essential ingredient of human behaviour, “our societal attitudes are still directed toward ignoring the essential implications of this variability” (pp.758).

Figure 1. A loss of variability is indicative of pathology or injury. This has been shown in both the amount of variability and the variation within the repetitions of movement. As can be seen in the figure to the right, the same movement is being performed; however, there is a variation within the movement patterns as well as the amount of variability. In the case to the left, the onset of a pathology or injury can reduce the flexibility within the movement patterns, leading to decreased variability.

Publication

Mukherjee MM, Yentes JM*. Movement variability: A perspective on success in sports, health, and life. Scandinavian Journal of Medicine and Science in Sports, 28(3):758-759, 2018. PMC5831508. https://onlinelibrary.wiley.com/doi/abs/10.1111/sms.13038

About the Author

Age-related changes to the musculoskeletal and neurological systems can predispose older adults to a greater fall risk than their younger counterparts. This multifaceted nature of sensory and motor degradation raises the question: how do older adults responses to destabilizing events, such as slips and trips, differ from healthy younger individuals? We tested this by perturbing older and young adults during gait initiation, the transition between quiet stance and dynamic gait. It is well described that transitional movements are more difficult for older adults due to greater postural demands. We predicted that older adults would have greater difficulty recovering from the destabilizing event and that this would result in a greater risk for future falls. We hope that the resultant information could be used to inform fall prevention strategies aimed at reducing high risk postural responses.

To simulate real-world slips and trips, we utilized a robotic moving platform to deliver perturbations. The platform motion occurred as the participant initiated a step, during push-off, similar to a real-world slip on a low friction surface. This motion was known to cause a destabilizing event, however not strong enough to cause a fall. Perturbations occurred in random to the left, right, backward, and forward directions, making them unpredictable to the participant. Motion tracking equipment was utilized to recreate a 3D model of participant responses. For simplicity, only results from mediolateral (left/right) perturbations will be discussed. Following mediolateral perturbations, we observed significant differences in the stepping patterns of older adults relative to young adult participants. On average older adults took shorter, narrower, and quicker steps than the younger adults. As a result, these altered step patterns demonstrated by older adults required more steps to return to forward motion. This strategy is concerning, as taking a series of small steps is  associated with a higher risk for falls. This rapid reaction may not provide as much ‘stability’ as the coordinated postural response observed in the younger adults.

Future research should aim to determine if these responses can be modulated through exercise intervention or training paradigms specific to a robotic platform. This research could provide a proactive falls prevention intervention aimed to improve reactionary balance when older adults are faced with a destabilizing trip or slip. However, further knowledge is needed to determine if the skills learnt on a perturbation platform are transferable to a real-world slip or trip.

Figure 1: Older adult participant initiating gait on the robotic platform.
Publication

Shulman, D., Spencer, A., Vallis, L.A., 2018. Age-related alterations in reactive stepping following unexpected mediolateral perturbations during gait initiation. Gait & Posture 64, 130–134. https://doi.org/10.1016/j.gaitpost.2018.05.035

About the Author

After stroke, asymmetrical stepping and standing balance is commonly observed when weight bearing or spatiotemporal parameters are measured. These asymmetries are thought to circumvent stroke-related impairments and enable stroke survivors to walk and maintain their balance while standing. However, at the same time, motor planning is also impaired in stroke survivors which impacts the integration of incoming sensory information during functional daily movements and standing balance performance. This process is not well understood but could explain stroke-induced asymmetries. Movement-related cortical potentials (MRCPs) – measured using electroencephalography (EEG) – can be used to estimate motor planning processes in the cortex. After a stroke, longer duration and larger amplitude MRCPs are detected for planning paretic hand movements compared with the non-paretic hand. These differences to the MRCP are thought to reflect the longer time and greater cognitive effort needed to plan a movement, respectively. The aim of this study was to examine motor planning via MRCPs to understand whether motor planning can be attributed to difficulties with stepping and balance after a stroke.

Self-initiated stepping was performed by participants with sub-acute stroke with the paretic and non-paretic legs. Both EEG and electromyography recorded brain and muscle activity, with movement onset identified by electro-goniometers affixed to the lateral knees. There were no significant differences in stepping performance between legs or in MRCP measures (p ≥ 0.069, Figure). However, when the paretic leg was stepping, the burst onset of the biceps femoris (or hamstring) muscle influenced the MRCP amplitude (p = 0.024; Figure).

This indicates that cortical planning for initiating stepping is similar between legs after a stroke. Between-leg symmetry may indicate that a portion of the motor planning is actually to prepare for the movement as a whole (e.g. walking). Comparable motor programs may be needed to plan the shifting of the centre of mass, irrespective of whether it is to plan stepping of the paretic or non-paretic legs. It is likely that the motor plan required for stepping reflects this pattern in the sub-acute phase after stroke. The earlier hamstring muscle activity in the paretic leg may then be associated with a lower cognitive effort as measured by the MRCP. The MRCP may therefore be an important process for the timing of muscle preparation for initiating stepping in stroke survivors.

Figure: In panel A, no differences are seen between the paretic and non-paretic legs for step duration, movement related cortical potential (MRCP) amplitude or biceps femoris (BF) onset. Bars indicate standard deviations. In panel B, higher cognitive effort (MRCP amplitude) related to later onset of BF burst in the paretic leg stepping condition. Data points above the horizontal line indicate individuals with the onset of BF burst after knee flexion, and points below the line specify individuals that show a BF burst in advance of knee flexion. Smaller MRCP amplitudes were found in those with earlier onset BF suggesting that lower cognitive effort is required with an anticipatory burst of hamstring muscle activity.

Publication

• Peters S, Ivanova TK, Lakhani B, Boyd LA, Staines WR, Handy TC, Garland SJ. Symmetry of cortical planning for initiating stepping in sub-acute stroke. Clinical Neurophysiology. 2018 Apr;129(4):787-796. doi: 10.1016/j.clinph.2018.01.018. Epub 2018 Feb 1.

About the Author

Difficulty with turning while walking is a common and delibitating problem for individuals with Parkinson’s disease (PD). A possible explanation for this problem may be the inability to adequately regulate step width during the turn. Although the characteristics of turning impairments in PD are well documented, few studies have investigated how step width is regulated during turning. Dopaminergic medication is commonly prescribed to decrease the severity of PD symptoms and has been shown to improve gait. However, it is unclear whether and how dopaminergic medication affects turning ability. Therefore, this study aimed to compare regulation of step width during pre- and unplanned walking turns in individuals with PD to healthy controls and to investigate whether dopaminergic medication improves step width regulation or not.

Seventeen individuals with PD (ON and OFF dopaminergic medication) and 17 healthy controls performed each of the following three tasks, presented randomly: walking and turning 180° to the right or left, and walking straight. To evaluate both proactive and reactive turning behavior, the task was visually cued before starting to walk (preplanned turns) or at one step before reaching the turning point (unplanned turns). Walking kinematics were measured by 3D motion analysis. Turns initiated with the step and spin strategy (see example in Figure 1A-B) were analysed separately. Our findings reveal that both individuals with PD and controls alternated their step width while turning, i.e. from wide-to-narrow-to-wide base of support for the step strategy and narrow-to-wide-to-narrow base of support for the spin strategy (Figure 2A-B). However, irrespective of turning strategy, individuals with PD turned with narrower steps whilst using crossing steps (i.e. step width closer to a value of zero). The effects of dopaminergic medication were sparse; significant interaction effects were found for the step strategy (Figure 2A) but post-hoc testing did not reveal any significant differences between PD OFF and ON.

To conclude, problems regulating step width while executing cross-over steps with a narrow base of support appears to be a critical feature for turning in PD. This finding could reflect a safety strategy among individuals with PD in order to decrease the postural demands associated with the drastic change of base of support while performing crossing steps. As dopaminergic medication showed limited effect on step width regulation, rehabilitation plays an important role to promote safe turning strategies with a specific emphasis on sustaining a wide support base.

Figure 1. Schematic drawing of A) the step strategy (i.e. first turning step ipsilateral to the turning direction) and B) the spin strategy (i.e. first turning step contralateral to the turning direction) during a right turn. Note that similar to straight walking, the step strategy leads to positive step width as the base of support is widened, whereas the spin strategy results in a narrow or negative step width as the turning foot crosses over and lands close to or medial to the line of progression of the internal leg.

Figure 2. Step width (meter) of three turning steps for PD-OFF, PD-ON and the control group while using A) the step and B) spin strategy to initiate pre- and unplanned turns. Positive values reflect widening of the base of support whereas negative values reflect crossing-over of the base of support. Error bars represent 95% confidence interval. *p ≤ .025; **p ≤ .01.

Publication

Conradsson D, Paquette C, Lökk J, Franzén E. Pre- and unplanned walking turns in Parkinson’s disease – Effects of dopaminergic medication. Neuroscience. 26;341:18-26. 2017

http://doi.org/10.1016/j.neuroscience.2016.11.016

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