The use of neuromuscular electrical stimulation (NMES) for managing the complications of ageing related to reduced exercise participation
Introduction
As the global population ages, the number of older adults who require long term care is rapidly increasing with figures estimated to double by 2050 [1]. This age-related loss of functional independence is associated with chronic and insidious conditions which can negatively alter the neuromuscular and cardiovascular systems. These alterations lead to the progressive loss of muscle mass, strength, aerobic capacity and eventually physical function [2]. The accompanying functional deficits can impair an individual’s ability to carry out activities of daily living, and place that individual below a threshold for functional independence [3].
Regular exercise has been shown to delay degenerative processes in senescent muscle [4]. As such, older adults are currently recommended to engage in exercise to prevent morbidity and maintain independence [5]. However, exercise participation is poor in older adults, with those aged 70–79 years old 50% less likely than their 50–59 years old counterparts to engage in sufficient levels [6]. Although this drop-off in activity levels can in part be linked to factors such as a lack of interest, many older individuals often cannot exercise due to inadequate functional capacity and underlying comorbidities such as pain and chronic illness [7], [8], [9]. These limiting factors highlight a need for alternatives to voluntary exercise to reduce the functional deficits associated with age-related alterations in activity patterns [3], [10]. Assistive technologies such as neuromuscular electrical stimulation (NMES) have previously been used successfully to target both the neuromuscular and cardiovascular systems in healthy young and older adults and clinical populations [11], [12], [13], and could be an effective alternative to voluntary exercise in older adults.
A growing body of evidence demonstrates the efficacy of NMES in athletes and both young and older adults [14], [15], [16]. In its current state NMES is used as both a training and rehabilitation tool, and in particular during or after periods of limb immobilisation or disuse [17]. NMES is generally delivered in static positions with no functional movement, differing it from functional electrical stimulation (FES) which is most commonly used in spinal cord injured patients to generate functional movements [18]. However, although NMES can be effective, it does suffer from three main limitations; excessive discomfort, limited spatial recruitment of motor units and the early onset of fatigue due to the high metabolic demand and repeated activation of the same motor units [19]. These limitations can compromise treatment effectiveness. A complete insight into the physiological and methodological considerations of NMES is beyond the scope of this paper and the reader is directed to the following review [19].
These limitations of NMES have led to the development of a multipath delivery system (multiple current pathways) in combination with the use of larger electrodes integrated into wearable garments (Fig. 1) which can disperse current density to allow for higher NMES exercise intensities at a given amount of discomfort [20], [21]. This can lead to improved treatment effectiveness, and subsequently better in-patient and home-based exercise and rehabilitation. However, despite these improvements in exercise delivery, NMES currently suffers from poor clinical acceptability [22], and patient engagement and adherence to unsupervised NMES sessions is generally poor. In addition, technology-based exercise supports such as biofeedback and gamification can assist health behaviour change [23], [24], and have potential to improve the clinical acceptability of NMES.
Therefore, this review is concerned with the recent progress which has been made in demonstrating the effectiveness of NMES for improving the neuromuscular and cardiovascular systems of older adults and explaining the potential for leveraging digital supports to enhance its implementation. In the first sections, age-related functional and physiological changes will be described. The following sections will give an overview of current exercise recommendations and the application of NMES technologies. Finally, we will discuss how applying supportive digital techniques to create innovative models of NMES delivery could hold promise as therapeutic alternatives to voluntary exercise to attenuate age-related reductions in physical function.
Section snippets
Methodology
A literature search was performed in PubMed and Google Scholar with the following key terms: “electrical stimulation” OR “neuromuscular electrical stimulation” OR “electromyostimulation” OR “electrostimulation” AND “ageing” OR “elderly” OR “senior”. A second search used the following terms: “gamification” OR “biofeedback” OR “user-centred design” AND “neuromuscular electrical stimulation” OR “electrostimulation” OR “rehabilitation” OR “exercise”. The search was limited to English language
Ageing and skeletal muscle structure and function
Sarcopenia, the age-related loss of muscle mass and strength is a hallmark of the ageing process [25], and is seen in 15% to 50% of older adults [26]. Muscle mass loss can range from 3 to 10% per decade between the ages of 30 and 70 years with this increasing to 15% per decade thereafter [27]. Muscle strength is mostly maintained until 50 years old, where after a decline in strength of 5% per year has been reported [28]. The strength deficits observed in older adults can be explained partly by
Ageing and the cardiovascular system
Cardiorespiratory fitness, defined as the ability of the cardiovascular and respiratory systems to provide working muscles with oxygen during sustained physical activity is generally expressed as peak oxygen uptake (VO2peak) [41], and is considered an independent predictor of future all-cause mortality in older adults [42]. Cardiorespiratory fitness declines progressively with age and is viewed as a strong predictor of functional capacity [43]. Cross sectional studies have observed typical
Current exercise recommendations
The American College of Sports medicine (ACSM) currently recommends that over 65’s engage in 150mins/week of moderate intensity aerobic exercise, and resistance training (RT) 2x/week to promote and maintain health [50]. The benefits of regular aerobic exercise and RT in older adults are widely recognised [51], [52]. Despite this, inactivity amongst the elderly is high. Objective data collected from accelerometers provides alarming results suggesting only 5% of over 65’s achieve recommended
Neuromuscular electrical stimulation – an alternative therapy to voluntary exercise?
Neuromuscular electrical stimulation (NMES) involves controlled muscle contractions generated by electrical impulses, which are delivered directly to the target muscle through surface electrodes (Fig. 1.) and a small, battery operated NMES unit [57]. Commonly stimulated muscles include the quadriceps and hamstrings, and impulses are delivered at high enough intensities to generate visible muscle contractions [17]. Due to its ability to induce fused tetanic contractions, high frequency NMES
Challenges to the use of NMES
Neuromuscular electrical stimulation is used in both clinical and research settings [22], but its implementation into regular clinical practice as an exercise intervention remains difficult. One commonly-reported limiting factor is discomfort felt during electrically evoked contractions [79], [80]. Variables such as gender, skin-fold thickness and coping style can influence this perception of discomfort [61]. This issue can be mitigated somewhat by increasing electrode size, therefore
Supports to use of NMES
Commencing any exercise regime can be a challenging experience for older adults, and many will need additional psychological, social and physical supports to facilitate full participation in the exercise intervention [89], [90], [91]. A large body of research is being conducted into techniques designed to support individuals to engage in this kind of behavioural change and overcome the most common barriers to exercise [92], [93], [94]. It is evident that there is a requirement for supportive
Conclusion
The multi-systemic effects of ageing and its underlying comorbidities and the associated decrease in activity levels can leave older adults both at risk of loss of functional independence, and the inability to participate in the exercise that is necessary to mitigate this risk. NMES appears a feasible and safe alternative to voluntary exercise for the most at-risk older adults, but in its current state suffers from poor clinical acceptability. Challenges to using NMES in a clinical population
Contributors
Dominic O’Connor and Louise Brennan are both primary authors.
All authors were responsible for the design and development of the review.
Dominic O’Connor and Louise Brennan drafted the paper.
Brian Caulfield critically reviewed the manuscript.
Conflict of interest
The authors declare that they have no conflict of interest.
Funding
Dominic O’Connor and Louise Brennan are supported by a grant from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement no. 722012.
Provenance and peer review
This article has undergone peer review.
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