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

Lower limb spasticity is a common consequence of stroke. The persistent muscle overactivity, paresis, increased stretch sensitivity and altered tissue properties, which characterize spasticity, affect the ability to effectively modulate muscle activity. In turn, the ability to control the position of the centre of mass is altered and may lead to an increased likelihood of falling. Because unilateral impairments are common after stroke (Figure 1A), posturographic measures quantifying the contributions of each limb to balance control may have utility in characterizing specific deficits in spatio-temporal parameters of control. More importantly, there is an added need to use these measures to characterize change in balance control over time, as a way of informing clinical decision-making. Precise quantitative measures of changes in individual limb contributions to balance control over time have the potential of providing specific and sensitive information on the efficacy of interventions.

Using data that tracked recovery over a 2-year window, we retrospectively analyzed changes in balance-related outcomes that took individual-limb contributions to balance into consideration over time, to characterize the natural time course of balance recovery in individuals with post-stroke spasticity. Inter-limb synchronization (the amount of similarity in forward and backward sway between the left and right legs over a 30 second trial) was determined by calculating the peak of the cross-correlation function between the anteroposterior centre of pressure traces on 2 force plates (one for each leg). Spatial symmetry, weight-bearing symmetry, and Berg Balance Scale scores were also tracked. Hierarchical growth curve modelling was used to estimate the recovery trajectories of 92 stroke-survivors with (n=45) and without (n=47) post-stroke spasticity of the lower limb (assessed as Modified Ashworth Scale ≥ 1 at the ankle alone with or without knee spasticity). Separate trajectories were modelled for individuals with and without spasticity. Models were additionally generated based on the severity of spasticity. These analyses identified early improvement followed by a slowing and plateau in rates of recovery. Individuals with spasticity had greater deficits than those individuals without spasticity, but the recovery trajectories between groups did not differ. Inter-limb synchronization was negatively influenced by the severity of spasticity (Figure 1B).

Spasticity affects balance control by reducing the extent of inter-limb synchronization of the centres of pressure. This reduction in synchronization persists well into the recovery window. Further research is needed to determine whether these recovery trajectories can be modified with interventions that aim to reduce spasticity or enhance motor recovery of the lower limbs. From this perspective, the information derived from this study can serve as indicators of the natural time course of recovery using specific metrics of balance control.

Figure 1. A) Typical example of a stabilogram of the affected (left) and less-affected (right) legs of an individual with lower limb spasticity. B) Comparison of recovery trajectories on 3 outcome measures for individuals with (left) and without (right) lower limb spasticity after stroke.

Publication

Singer JC, Nishihara K, Mochizuki G (2016). Does post-stroke lower limb spasticity influence the recovery of standing balance control? A multilevel growth model of stability control measures over two years. Neurorehabilitation and Neural Repair, 30(7):626-634. http://journals.sagepub.com/doi/pdf/10.1177/1545968315613862

About the Author

Perhaps you, like many members of our ISPGR community, have been engaged in the development and evaluation of interventions to improve postural balance and ambulation? Most likely, this was for frail members of our society who have an increased risk of falling due to reduced muscle strength/power, or in patient populations who suffer from musculoskeletal disease or degeneration?  In that case it is unlikely that you often venture into the sports medicine literature, let alone literature that establishes a theoretical framework for sport scientists who are engaged in the daily monitoring of elite athletes. In this blog, I would like to offer some creative ideas on how to evaluate physiological adaptations from a strength training programme for the frail elderly person, or how to monitor neuromechanical adaptations from ballroom dancing classes for the baby boomers.

In our recent perspective paper in Sports Medicine, we reviewed some of the sports science and sports medical literature on the recent developments of player load monitoring. The scientific field of player load monitoring has grown rapidly, and we believed that there was a lack of theoretical framework to justify the daily monitoring of a vast amount of variables in sports environments, ranging from subjective ratings of perceived exertion to a host of complicated derivatives from GPS-based position tracking. Historically, this has been the domain of exercise physiologists, who have gained extensive knowledge on physiological processes and the effects of different types of training regimes. Very few biomechanists have looked into this, and the knowledge on so-called ‘mechanobiological’ adaptations from training and exercise is still very limited. In order to address this important knowledge gap, we developed a theoretical framework that firstly separates a biomechanical load-adaptation pathway from the physiological load-adaptation pathway (see Figure). Secondly, the framework helps to identify observations that are associated with the external load (how is the body moving through and interacting with its environment), and observations that represent internal load (what is the stress on the internal structures and systems). The availability (and affordability) of wearable sensor technologies has made it possible to monitor external load more easily. Monitoring of the internal load and of the adaptations that are constantly taking place as a consequence of those loads, however, remain a huge challenge. For example, whilst sports scientists embrace the concept of supercompensation to explain the progressive physiological benefits from training and exercise, there are few experimental observations available that allow one to monitor this wonderful phenomenon actually taking place. Therefore, our perspective paper also addresses the practical implications and to some extent the pitfalls around measuring loads and adaptation outside a laboratory, some of which may well apply to other contexts than elite athlete monitoring.

Figure: A theoretical framework that separates a physiological load-adaptation pathway (left) from a biomechanical load-adaptation pathway (right). Measures that are indicative of what the body is doing (external load) are also separated from measures that represent the internal consequences to our body (internal load). Eventually, this internal load will cause adaptations which can be associated to each of these pathways, even if not exclusively so.

We hope that our perspective paper will assist the ISPGR community to consider using established methodologies from sports and exercise contexts into more clinical applications. For example, technologies developed by (and for) sports science could be used to evaluate physical loads due to therapeutic interventions. Or, established ratings of perceived effort multiplied by session time, may well be a useful tool in exercise programmes for the elderly or patient populations. Finally, we hope that the complex systems approaches to evaluate intricate interactions between various types of loads and load-adaptation pathways, could provide members of the ISPGR community with new ideas to better interrogate the multifactorial responses to multi-component exercise programmes within their clinical trials.

Publication

Vanrenterghem, J., Nedergaard, N.J., Robinson, M.A., Drust, B. (2017) Training load monitoring in team sports : A novel framework separating physiological and biomechanical load-adaptation pathways. Sports Medicine, Published Online First.

About the Author

People who have had a stroke fall frequently. Many previous studies with older adults have found that exercise, particularly balance training, reduces fall risk. However, comparable studies in stroke survivors indicate that similar exercise training does not prevents falls in this group. People fall when they fail to recover from a loss of balance. Recently, studies have found that ‘perturbation-based balance training’ (PBT), which involves people experiencing repeated balance losses, can improve control of reactions to a loss of balance. Some studies have found that PBT reduces fall rates in healthy older adults or in people with Parkinson’s disease. We wanted to know if PBT could reduce fall rates in people with sub-acute stroke.

Physiotherapists at our institution had started PBT with some of their eligible clients as part of routine care for stroke rehabilitation. Therefore, we conducted a non-randomized study to establish the benefit of PBT compared to non-PBT rehabilitation. We recruited participants with sub-acute stroke at discharge from in-patient rehabilitation if they completed PBT during their routine rehabilitation. We then asked these individuals to report any falls that they experienced in the following six months. We compared fall rates to a matched historical control group who were recruited for another study before physiotherapists had implemented PBT, but who also reported falls in daily life for six months after discharge. Five (out of 31) participants in the PBT group reported 10 falls in the six months post-discharge, whereas ten (out of 31) participants in the historical control group reported 31 falls in the six months. The fall rates in the PBT group were significantly lower than in the control group, when accounting for some characteristics that differed between the two groups at baseline.

The results of this study suggest that PBT might help to prevent falls in people with sub-acute stroke. Because the study was not randomized, the results should be interpreted with some caution. However, since the results are consistent with other studies showing reduced fall rates with PBT, the evidence from this study may be sufficient to recommend PBT in clinical practice. Other studies of PBT used programmable treadmills or custom-built moving platforms to provide the balance perturbations in training. In the current study, the physiotherapist provided manual perturbations (e.g., push or pull; see Figure). This meant that PBT only required equipment that is already in most physiotherapy practices. For this reason, we think it would be relatively easy to implement our PBT program in other settings.

Figure: Physiotherapist delivers a rightward pull perturbation while the participant walks over foam obstacles.

Publication

Mansfield A, Schinkel-Ivy A, Danells CJ, Aqui A, Aryan R, Biasin L, DePaul VG, Inness EL. Does perturbation training prevent falls after discharge from stroke rehabilitation? A prospective cohort study with historical control. J Stroke Cerebrovasc Dis. 2017; doi: 10.1016/j.strokecerebrovasdis.2017.04.041

About the Author

People with Parkinson disease (PD) often report difficulty walking as an early and troublesome problem.  Emergence of gait problems is considered a red flag indicating onset of disability, and can contribute to reduced quality of life.  Gait in people with PD is often slower, with reduced stride lengths and increased variability that may be attributed to loss of ability to maintain a steady gait rhythm.  To address this loss of rhythmicity, many studies have employed use of external rhythmic cues, such as music or a metronome, to help stabilize gait.  However, we know very little about the impact of self-generated rhythmic cues, such as singing, on gait.  The goal of this study was to test the feasibility of singing during walking in people with PD, gathering preliminary evidence regarding the efficacy of this novel cueing technique.

Twenty-three people with Parkinson disease participated.  Each person walked at their normal, comfortable pace for the Baseline condition, which was used to determine preferred walking cadence.  Cue rate, or beats per minute of the song, was then set to match preferred cadence.  Participants then walked in three cued conditions and a dual task condition (see Figure).  When walking to music, participants maintained velocity but increased spatial and temporal variability.  Variability was further increased when participants walked while singing along to music.  Singing in the absence of music, however, did not increase variability.  In contrast, when dual tasking (i.e. completing a word generation task while walking) participants showed reductions in velocity along with large increases in variability.

Of all the conditions tested, singing was the only cue condition that did not result in increased variability.  We think that matching a self-generated rhythm may facilitate rhythmicity more than matching an external cue.  Future work should explore use of faster cueing rates and use of mental rather than overt singing, in addition to determining the utility of singing during walking in everyday, real-world situations. If singing continues to hold promise in future studies, this could represent a substantial advance as singing is universally available, inexpensive, and adaptable.

Copyright

The ISPGR blog applies Creative Commons Attribution (CC BY) license to figure and text of the article.

https://creativecommons.org/licenses/by/4.0/

Publication

Harrison, E. C., McNeely, M. E., & Earhart, G. M. (2017). The feasibility of singing to improve gait in Parkinson disease. Gait & Posture, 53, 224-229.

https://www.ncbi.nlm.nih.gov/pubmed/28226309

About the Author

Following anterior cruciate ligament (ACL) rupture, reconstructive surgery (ALCR) is often performed to mechanically stabilise the knee, however functional and neuromuscular deficits can persist long after surgery. Impaired single-limb balance control when standing on the ACLR limb compared to healthy individuals has been reported by other groups. Building on these findings, the current study aimed to generate new knowledge as to whether similar balance deficits exist between injured and contralateral uninjured limbs, one year post-surgery, which is typically the time when patients are permitted to return to sport. Uncovering balance deficits in patients who have undergone ACLR is clinically important information, which may help to identify a risk factor with the capacity to predict ACL re-rupture or contralateral injury, and advance rehabilitation strategies post-surgery.

Our study investigated 100 adults who had undergone a primary hamstring-tendon ACLR in the 12 months prior to testing. Participants performed challenging tasks of static single-limb balance, with eyes closed, whilst standing on the ACLR and uninjured limb. Traditional measures of centre of pressure movement (excursion, velocity) in anterior-posterior and mediolateral directions were collected over 20 seconds, using a Nintendo Wii Balance Board (Figure 1). We were also interested in exploring possible associations between patients who presented with concomitant injury (chondral lesions) or underwent ‘additional’ surgeries (meniscectomy) at the time of ACLR, and balance ability, one year following reconstruction. We found that single-limb standing balance did not differ between the ACLR and uninjured limb for any of the centre of pressure measures of interest (all P values >0.686). Whilst 71 participants were reported to have concomitant injury/surgeries, these factors were not associated with measures of balance ability (all P values >0.213).

Findings reported in our article extend, and concur with, prior evidence indicating the absence of balance deficits between the injured and uninjured limbs during less challenging unilateral balance tasks, where visual information was available (i.e. quiet standing with eyes open). However, in the context of wider evidence, which demonstrates that patients who have undergone ACLR show poorer balance control relative to their healthy counterparts, our results point to the suggestion that bilateral balance deficits may exist in this clinical population. For health professionals involved in the management of patients following ACL injury and ACLR, our research implies that clinical assessments of balance, and interventions designed to enhance balance ability, should consider both the injured and uninjured limbs, within the early stages of post-ACLR rehabilitation strategies.

Figure 1: Standing balance test procedures and Nintendo Wii output (centre of pressure movement)

Publication

Hatton AL, Crossley KM, Clark RA, Whitehead TS, Morris HG, Culvenor AG. Between-leg differences in challenging single-limb balance performance one year following anterior cruciate ligament reconstruction. Gait & Posture 2017 52:22-25. http://dx.doi.org/10.1016/j.gaitpost.2016.11.013

About the Author

The prevalence of falls in older adults is huge: one out of every 3 adults aged 65 years or older will fall at least once per year. These numbers are even higher in neurodegenerative conditions such as in Parkinson’s disease and in people with cognitive impairments.  Recent studies showed that certain aspects of cognition, especially executive function, are critical for safe ambulation.  This makes sense intuitively if we imagine the cognitive skills needed just to cross a busy intersection or to negotiate obstacles. We aimed to use virtual reality to safely train the motor aspects that are important for fall risk, while also implicitly teaching participants to improve cognitive functions vital to safe ambulation.

We carried out a randomized controlled trial at five clinical centers. Adults aged 60−90 years with a high risk of falls, i.e., two or more falls in the 6 months before the study, and with varied motor and cognitive deficits were randomly assigned to receive 6 weeks of treadmill training plus VR or treadmill training alone. Both groups aimed to train three times per week for 6 weeks, with each session lasting about 45 minutes. The VR system consisted of a motion-capture camera and a computer-generated simulation that includes real-life challenges such as obstacles, multiple pathways, and distracters that requires continual adjustment of the stepping pattern. The subject’s gait was measured in real-time and projected on into the VR that was displayed on a large screen. The primary outcome was the incident rate of falls during the 6 months after the end of training.

Data from 282 participants (VR group n=154, and treadmill training alone group n=148) was analyzed. Before training, the falls incident rate was similar in both training arms. Six months after the end of training, the rate decreased in both groups, but it was 42% significantly lower in the treadmill training plus VR group, compared to the treadmill training alone group (figure 1).

Figure 1:  On the left is a picture of the Virtual Reality setting. The user walks on the treadmill while engaging in tasks in the virtual scene. The figure on the right shows the reduction in incident fall rate ,6 months post intervention , in the treadmill  training plus virtual reality group compared to the active control group of treadmill training.

The study has important implications for research and clinical practice. Treadmill training plus VR successfully reduced in fall rates in a diverse group of older adults at high risk for falls. Adherence and participation were very high, no serious adverse events were observed, and participants reported high satisfaction and enjoyment. This RCT demonstrates the added value of the VR component and suggests that this approach could be a viable option for improving motor-cognitive function and reducing fall risk in older adults.

Publication

Addition of a non-immersive virtual reality component to treadmill training to reduce fall risk in older adults (V-TIME): a randomized controlled trial.

Mirelman A, Rochester L, Maidan I, Del Din S, Alcock L, Nieuwhof F, Rikkert MO, Bloem BR, Pelosin E, Avanzino L, Abbruzzese G, Dockx K, Bekkers E, Giladi N, Nieuwboer A, Hausdorff JM.Lancet. 2016 Sep 17;388(10050):1170-82. doi: 10.1016/S0140-6736(16)31325-3.

http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(16)31325-3/abstract

About the Author

Every year about 500,000 people become disabled as a result of spinal cord injuries (SCI). The communication lines between the brain and spinal cord below the injury are cut or dramatically diminished, depending on the severity of the event, which leads to a range of motor disabilities.

It is possible to access the surviving circuits and pathways to alleviate these deficits via epidural electrical stimulation (EES). Walking requires the activation of spatially distributed spinal motor circuits following precise temporal sequences that are continuously adjusted through sensory feedback. Therefore, current neuromodulation therapies – which deliver stimulation to restricted spinal cord locations and remain constant throughout gait execution – are not optimal. In the present work, we argued that targeted stimulation in space and time of the spinal cord, matching the natural dynamics of spinal motor circuit activation, can restore walking and improve motor control after spinal cord injury.

We first conducted anatomical and functional experiments to visualize the spatiotemporal pattern of hindlimb motoneuron activation in intact rats (Figure 1a). We found that walking involves the alternating activation of spatially restricted hotspots underlying extensor versus flexor muscle synergies. We then developed neuromodulation strategies that specifically target proprioceptive feedback circuits in the dorsal roots in order to access these hotspots. Computer simulations determined the optimal electrode locations to recruit specific subsets of dorsal roots. These results steered the design of spatially selective spinal implants and real–time control software to modulate extensor versus flexor muscle synergies with precise temporal resolution adjusted through movement feedback. This conceptually new stimulation strategy reinforced extension versus flexion components for each hindlimb independently and improved a range of important gait features after complete SCI (see Figure 1b).

We considered that spinal implants designed to activate the proprioceptive afferents projecting to the identified flexor and extensor hot spots would engage muscle synergies encoders related to extension and flexion. Our results showed that tailored spinal implants targeting specific subset of dorsal roots with electrodes enabled a gradual control over the degree of flexion and extension on the left and right hindlimbs. Although challenges lie ahead, we believe that spatiotemporal neuromodulation of the spinal cord will become a viable way to accelerate and augment functional recovery in humans with SCI.

Figure 1: Spatiotemporal neuromodulation reproduces the natural pattern of motoneuron activation. From left to right and top to down. (a) Tracer injections into muscles spanning each hindlimb joint, to visualize the spatial location of hindlimb motoneurons. We decomposed the muscle activity during locomotion recorded in all the traced muscles into functional models (muscle synergies). To link muscle synergies to the activation of the burst (‘hotspot’) of motoneuron activity, we extracted the spinal map for each synergy independently. A model of spinal segments showing the temporal sequence underlying the recruitment of muscle synergies and the corresponding activation of extensor and flexor hot spots. (b) Rats received complete SCI at T7 and a spinal implant with conventional midline electrodes (black) and spatially selective lateral electrodes (blue and red). Locomotion in rats on a treadmill without stimulation and with continuous neuromodulation applied over the midline of lumbar and sacral segments (black electrodes) and during spatiotemporal neuromodulation (blue and red electrodes). On the right the results for an intact rat is showed.

Publication

Wenger N, Moraud EM, Gandar J, Musienko P, Capogrosso M, Baud L, Le Goff CG, Barraud Q, Pavlova N, Dominici N, Minev IR, Asboth L, Hirsch A, Duis S, Kreider J, Mortera A, Haverbeck O, Kraus S, Schmitz F, DiGiovanna J, van den Brand R, Bloch J, Detemple P, Lacour SP, Bézard E, Micera S, Courtine G (2016). “Spatiotemporal neuromodulation therapies engaging muscle synergies improve motor control after spinal cord injury.” Nature Medicine. Feb;22(2):138-45. http://www.nature.com/nm/journal/v22/n2/full/nm.4025.html

About the Author