Trunk Muscle Training Augmented with Neuromuscular Electrical Stimulation Appears to Improve Function in Older Adults with Chronic Low Back Pain: A Randomized Preliminary Trial
-“Clinically important reductions in pain of greater than 2 points on a numeric pain rating scale during the course of the trial. But, only the TMT+NMES group had clinically important improvements in both performance-based and self-reported measures of function. In terms of the participants’ global rating of functional improvement at 6-months, the TMT+NMES group improved by 73.9%.”
-“In conclusion, this preliminary investigation has demonstrated that TMT+NMES is a safe and acceptable intervention that may have the potential to improve physical function in older adults with chronic LBP. It is particularly interesting to note that TMT+NMES appears to have the potential to result in longer term functional improvements than our passive control approach which was grounded in the use of passive treatments. ”
Hicks, G. E., Sions, J. M., Velasco, T. O., & Manal, T. J. (2016, October). Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4935645/
Low back pain (LBP) is the most frequently reported musculoskeletal problem and the third most frequently reported symptom of any kind in people over the age of 75.1-2 In fact, 17.3% of all visits to physicians for LBP involve individuals over the age of 65.1, 3-4 As evidence of the societal impact of LBP in older adults, between 1991 and 2002, Medicare data indicates a 132% increase in LBP patients and a 387% increase in related charges for LBP.5 Despite the fact that LBP is a common problem for older adults and is associated with poor outcomes in this vulnerable age group6-9, little research has focused on LBP in people over the age of 65.1, 10 With minimal research available, clinicians are left without clear evidence-based guidance as to how they should manage older adults with LBP.
Although all older adults are at some risk for mobility limitations, it is becoming clear that those with significant LBP may be at a greater risk for functional decline. Reid et al. have demonstrated that restricting LBP is independently associated with declines in walking speed and chair rise performance in older adults.7 Hicks and colleagues have shown that a single report of moderate-severe LBP is associated with greater decline in function over three years among otherwise healthy older adults.9 With mounting evidence that older adults with LBP are at greater risk of decreased physical performance, it is becoming clear that management of LBP in the geriatric population should not only focus on pain reduction, but on improvement of physical function.
Recent work has demonstrated that older adults with poor trunk muscle composition (higher levels of intramuscular fat infiltration) appear to have a greater risk of reduced mobility-related function over a three-year timespan, especially in those with higher levels of LBP severity.8-9 Further, those individuals with the most severe LBP also had the highest levels of fat infiltration.8-9 Taken together, these factors indicate that a thoughtfully designed exercise program targeting the trunk muscles may be able to both improve physical function and reduce pain. While trunk muscle training (TMT) has been used in younger LBP groups, it is unproven in older adults and, alone, may not be sufficient to substantially improve physical function and symptoms, given the compromised state of aged muscle.
Typically, aged muscle has undergone a reduction in the total number of muscle fibers and a preferential atrophy of fast, type II muscle fibers, which results in slower muscle contractile properties.11-13 Age-related altered motor unit discharge rates may be linked to the slower contractile properties as well.14-15 The sub-maximal or endurance-focused approach to training trunk muscles that is used for improving trunk stability in patients with LBP will primarily recruit slow, type I muscle fibers and will likely do little to induce muscle hypertrophy or change the ratio of muscle to fat in the trunk musculature. As a result, there is a need for examining ways to augment volitional exercise in older adults since the proportion of type II muscle fibers is known to decrease with aging, along with a concomitant decrease in muscle force-production capacity.13 Type II fibers provide greater force production than type I fibers and are important for sudden bursts of muscle activation. Volitional muscle contractions appear to utilize type I muscle fibers more readily and to a greater extent than type II fibers, and type II fibers most likely are not approaching their maximum force production capabilities even during near maximal voluntary contractions.16-18 Volitional exercise performed even at near maximum intensities may not provide enough tension through the atrophied type II fibers to induce hypertrophy of these fibers. There is mounting evidence to suggest that aged skeletal muscle does not hypertrophy with resistance training in the same way that younger muscle does19-21; and, as a result, aged muscle requires a higher training dose to increase muscle size.22-25
Neuromuscular electrical stimulation (NMES) has been shown to recruit type II muscle fibers and to induce increases in muscle strength.26-29 Although NMES has been traditionally used for muscle strengthening in young, physically active individuals, several studies have shown that it can also increase strength and function and is well tolerated in older patients.30-33 Therefore, it is possible that TMT augmented with NMES may provide greater improvements in muscle composition and performance than a volitional program alone, thus enhancing the opportunity for reducing functional limitations. Treatment of chronic LBP in older adults using an exercise intervention has been hypothesized as a way to prevent functional decline and the development of frailty; however, this hypothesis has yet to be experimentally explored or confirmed.
The objectives of this preliminary trial were: (1) to evaluate the feasibility and safety of an NMES-augmented trunk muscle training program (TMT+NMES) in older adults with chronic LBP, (2) to investigate whether TMT+NMES could improve physical function and pain compared with a passive control intervention in older adults with chronic LBP, and (3) to determine effect sizes to inform future trials. In this preliminary trial, the first objective was focused on exploring issues relevant to the feasibility of conducting a larger trial of the proposed intervention (i.e. treatment adherence, study attrition and safety); whereas, the second and third objectives were more aligned with typical pilot study issues (i.e. assessing whether treatment effects are consistent with investigator expectations). Altogether, the feasibility and pilot components of this preliminary trial will allow us to determine whether a large-scale trial of TMT+NMES is warranted.