Impact of ageing, fall history and exercise on postural reflexes following unpredictable perturbations: A systematic review and meta-analyses

Age-related changes in muscle coordination patterns of stepping responses to recover from loss of balance

INTRODUCTION

Reactive stepping capacity to recover from a loss of balance declines with aging, which increases the risk of falling. To gain insight into the underlying mechanisms, we investigated whether muscle coordination patterns of reactive stepping differed between healthy young and older individuals.

METHODS

We performed a cross-sectional study between 15 healthy young and 14 healthy older adults. They recovered from 200 multidirectional platform translations that evoked reactive stepping responses. We determined spatiotemporal step variables and used muscle synergy analysis to characterize stance- and swing-leg muscle coordination patterns from the start of perturbation until foot landing.

RESULTS

We observed delayed step onsets in older individuals, without further spatiotemporal differences. Muscle synergy structure was not different between young and older individuals, but age-related differences were observed in the time-varying synergy activation patterns. In anterior-posterior directions, the older individuals demonstrated significantly enhanced early swing-leg synergy activation consistent with non-stepping behavior. In addition, around step onset they demonstrated increased levels of synergy coactivation (mainly around the ankle) in lateral and anterior directions, which did not appear to hamper foot clearance.

CONCLUSION

Although synergy structure was not affected by age, the delayed step onsets and the enhanced early synergy recruitment point at a relative bias towards non-stepping behavior in older adults. They may need more time for accumulating information on the direction of perturbation and making the corresponding sensorimotor transformations before initiating the step. Future work may investigate whether perturbation-based training improves these age-related deficits.

Treadmill induced belt-accelerations may not accurately evoke the muscle responses to obstacle trips in older people

BACKGROUND

Treadmill belt-accelerations are a commonly utilised surrogate for tripping, but their physiological validity is unknown. This study examined if a treadmill belt-acceleration induces lower limb muscle activation responses similar to a trip on a walkway.

METHODS

38 older people (65+ years) experienced one treadmill belt-acceleration and one walkway obstacle trip in random order. Muscle responses were assessed bilaterally using surface electromyography on the rectus femoris (RF), tibialis anterior (TA), semitendinosus (ST) and gastrocnemius medial head (GM). Unperturbed muscle activity, post-perturbation onset latency, peak magnitude, time to peak and co-contraction index (CCI) were examined.

RESULTS

Muscle activity in the right ST was greater during unperturbed walking on the treadmill compared to walkway (P=0.011). Compared to a treadmill belt-acceleration, a walkway trip elicited faster onset latencies in all muscles; greater peak magnitudes in the left RF, TA, GM and right GM; faster time to peaks in the left TA and right GM; and lower knee and ankle muscle CCI (P<0.05).

CONCLUSIONS

Walkway trips and treadmill belt-accelerations elicit distinct muscle activation patterns. While walkway trips induced faster and larger muscle responses, treadmill belt-accelerations involved greater co-contraction. Therefore, treadmill belt-accelerations may not accurately simulate the muscle responses to trips.

Age-Related Dysfunction in Balance: A Comprehensive Review of Causes, Consequences, and Interventions

This review delves into the multifaceted aspects of age-related balance changes, highlighting their prevalence, underlying causes, and the impact they have on the elderly population. Central to this discussion is the exploration of various physiological changes that occur with aging, such as alterations in the vestibular, visual, proprioceptive systems, and musculoskeletal degeneration. We examine the role of neurological disorders, cognitive decline, and medication side effects in exacerbating balance issues. The review underscores the significance of early detection and effective intervention strategies in mitigating the risks associated with balance problems, such as falls and reduced mobility. It discusses the effectiveness of diverse intervention strategies, including exercise programs, rehabilitation techniques, and technological advancements like virtual reality, wearable devices, and telemedicine. Additionally, the review stresses the importance of a holistic approach in managing balance disorders, encompassing medication review, addressing comorbidities, and environmental modifications. The paper also presents future research directions, emphasizing the need for a deeper understanding of the complex mechanisms underlying balance changes with aging and the potential of emerging technologies and interdisciplinary approaches in enhancing assessment and intervention methods. This comprehensive review aims to provide valuable insights for healthcare providers, researchers, and policymakers in developing targeted strategies to improve the quality of life and ensure the well-being of the aging population.

Combined Reactive and Volitional Step Training Improves Balance Recovery and Stepping Reaction Time in People With Parkinson's Disease: A Randomised Controlled Trial

BACKGROUND

Falls are frequent and devastating events for people with Parkinson's disease (PD). Here, we investigated whether laboratory-based reactive step training combined with home-based volitional step training was effective in improving balance recovery and stepping ability in people with PD.

METHODS

Forty-four people with idiopathic PD were randomized into intervention or control groups. Intervention participants performed unsupervised volitional step training using home-based exergames (80+ minutes/week) for 12 weeks and attended reactive step training sessions in which they were exposed to slip and trip perturbations at 4 and 8 weeks. Control participants continued their usual activities. Primary outcomes were balance recovery following an induced-trip/slip and choice stepping reaction time (CSRT) at the 12-week reassessment. Secondary outcomes comprised sensorimotor, balance, cognitive, psychological, complex stepping (inhibitory CSRT and Stroop Stepping Test [SST]), gait measures, and falls experienced in everyday life.

RESULTS

At reassessment, the intervention group had significantly fewer total laboratory-induced falls and faster CSRT compared to the control group (P < .05). The intervention group also had significantly faster inhibitory CSRT and SST movement times and made fewer mistakes in the SST (P < .05). There were no significant differences in the rate of every day falls or other secondary outcome measures between the groups.

CONCLUSION

Combined volitional and reactive step training improved balance recovery from an induced-perturbation, voluntary stepping time, and stepping accuracy in cognitively challenging tests in people with PD. Further research is required to determine whether such combined step training can prevent daily-life falls in this population.

[Muscle activation times facing to a perturbation in patients with early-stage Parkinson's disease]

OBJECTIVES

Parkinson's disease (PD) generates a high incidence of falls, however, there is little evidence of instabilities in the initial stages. This investigation sought to compare the muscle activation times in patients with initial PD against a postural disturbance vs. a control group.

MATERIALS AND METHODS

The electromyographic activity (EMG) of 10 patients with PD in early stages (61.3 ±3.8 years) and a control group of 10 adults (62.2 ±3.0 year) was evaluated. The participants were subjected to a surface disturbance, which generated a stabilization response. The test was performed under 2conditions: eyes open (OA) v/s eyes closed (OC). Trunk (spinal erector) and lower extremity (soleus, tibialis anterior, femoral biceps, femoral rectus, adductor magnus, gluteus medius) muscle activation time was analyzed using surface EMG.

RESULTS

The PD group showed faster response times compared to the control group in the soleus muscle in OC (P=.04). This same muscle showed differences when comparing OA vs. OC only in the PD group (P=.04), showing a shorter response time in the OC condition. When comparing the spinal erector muscle, the PD group showed slower response times in the OA (P=.02) and OC (P=.04) conditions compared to the control group.

CONCLUSIONS

Muscle activation times show that people with PD respond slower in the trunk muscles, while activation times decrease at the distal level. In the early stages, the slower responses at the trunk level could explain the onset of instability postural in these patients.

Immediate and Long-Term Effectiveness of Proprioceptive Neuromuscular Facilitation and Static Stretching on Joint Range of Motion, Flexibility, and Electromyographic Activity of Knee Muscles in Older Adults

Introduction and Objective: Previously, various stretching techniques were compared to study their effects on the different physiological parameters of hamstring muscles in the elderly population. There is no research that compares the immediate and long-term effects of proprioceptive neuromuscular facilitation-contract–relax (PNF-CR) and static stretching (SS) techniques on knee range of motion (ROM), hamstring flexibility, and knee flexor muscle EMG activity in the elderly. This study intends to compare the same. Methods: A total of 30 males aged 55–75 years were randomly assigned into the PNF-CR group (n = 10), SS group (n = 10), and control group (n = 10). The PNF-CR group received four trials of the contract–relax technique, the SS group received passive stretching of an 80 s duration by the therapist, and the control group received no intervention. A total of 12 sessions were given during the four-week period. Knee range of motion, electromyographic activity of the biceps femoris, and the sit-and-reach test were taken for the dominant side thrice: pre-intervention, immediately after stretching, and after the training period. Results: A statistically significant difference was observed in the maximum voluntary isometric contraction (MVIC) of biceps femoris between the PNF and the control groups (p = 0.01) after four weeks of intervention. The knee ROM and hamstring flexibility for the PNF group showed significant improvement immediately post-test (p = 0.01) and after four weeks of training (p = 0.07 and p = 0.001). SS showed significant results for both ROM and flexibility after four weeks of intervention (p = 0.001), and significant immediate post-test improvements were seen for ROM only (p = 0.007). Conclusions: PNF stretching has an immediate, as well as long-term, effect on knee ROM and hamstring flexibility, whereas it has only a long-term effect on muscle electromyographic activity. SS has an immediate, as well as long-term, effect on knee ROM and only a long-term effect on hamstring flexibility, without any immediate or long-term effects on muscle electromyographic activity.

Impact of pathological conditions on postural reflex latency and adaptability following unpredictable perturbations: A systematic review and meta-analysis

BACKGROUND

Pathological conditions can impair responses to postural perturbations and increase risk of falls.

RESEARCH QUESTION

To what extent are postural reflexes impaired in people with pathological conditions and can exercise interventions shorten postural reflexes?

METHODS

MEDLINE, EMBASE, Scopus, SportDiscus and Web of Science were systematically searched for articles comparing muscle activation onset latency in people with pathological conditions to healthy controls following unpredictable perturbations including the effect of exercise interventions (registration: CRD42020170861).

RESULTS

Fifty-three articles were included for systematic review. Significant delays in muscle activity onset following perturbations were evident in people with multiple sclerosis (n = 7, mean difference [MD]: 22 ms, 95% confidence interval [CI]: 11, 33), stroke (n = 10, MD: 34 ms, 95% CI: 19, 49), diabetes (n = 2, MD: 19 ms, 95% CI: 10, 27), HIV (n = 3, MD: 9 ms, 95% CI: 4, 14), incomplete spinal cord injury (n = 2, MD: 57 ms, 95% CI: 33, 80) and back and knee pain (n = 7, MD: 12 ms, 95% CI: 6, 18), but not in people with Parkinson's disease (n = 10) or cerebellar dysfunction (n = 4). Following exercise interventions, the paretic limb of stroke survivors (n = 3) displayed significantly faster muscle activation onset latency compared to pre-exercise (MD: -13 ms, 95% CI: -24, -4), with no significant changes in Parkinson's disease (n = 3).

CONCLUSIONS

This systematic review demonstrated that postural reflexes are significantly delayed in people with multiple sclerosis (+22 ms), stroke (+34 ms), diabetes (+19 ms), HIV (+9 ms), incomplete spinal cord injury (+57 ms), back and knee pain (+12 ms); pathological conditions characterized by impaired sensation or neural function. In contrast, timing of postural reflexes was not impaired in people with Parkinson's disease and cerebellar dysfunction, confirming the limited involvement of supraspinal structures. The meta-analysis showed exercise interventions can significantly shorten postural reflex latencies in stroke survivors (-14 ms), but more research is needed to confirm this finding and in people with other pathological conditions.