Neuromuscular Impairments Contributing to Persistently Poor and Declining Lower-Extremity Mobility Among Older Adults: New Findings Informing Geriatric Rehabilitation

Abstract

Objective To identify neuromuscular impairments most predictive of unfavorable mobility outcomes in late-life. Design Longitudinal cohort study. Setting Research clinic. Participants Community-dwelling primary care patients aged ≥65 years (N=391) with self-reported mobility modifications, randomly selected from a research registry. Intervention(s) Not applicable. Main Outcome Measure(s) Categories of decline in and persistently poor mobility across baseline, 1 and 2 years of follow-up in the Lower-Extremity Function scales of the Late-Life Function and Disability Instrument. The following categories of impairment were assessed as potential predictors of mobility change: strength (leg strength), speed of movement (leg velocity, reaction time, rapid leg coordination), ROM (knee flexion/knee extension/ankle ROM), asymmetry (asymmetry of leg strength and knee flexion/extension ROM measures), and trunk stability (trunk extensor endurance, kyphosis). Results The largest effect sizes were found for baseline weaker leg strength (OR [95% CI]: 3.45 [1.72-6.95]), trunk extensor endurance (2.98 [1.56-5.70]), and slower leg velocity (2.35 [1.21-4.58]) predicting a greater likelihood of persistently poor function over 2 years. Baseline weaker leg strength, trunk extensor endurance, and restricted knee flexion motion also predicted a greater likelihood of decline in function (1.72 [1.10-2.70], 1.83 [1.13-2.95], 2.03 [1.24-3.35]). Conclusion Older adults exhibiting poor mobility may be prime candidates for rehabilitation focused on improving these impairments. These findings lay the ground work for developing interventions aimed at optimizing rehabilitative care and disability prevention and highlight the importance of both well-recognized (leg strength) and novel impairments (leg velocity, trunk extensor muscle endurance).

Knee extensor power asymmetry is unrelated to functional mobility of older adults

“…Similarly, Straight and colleagues (2016) demonstrated that leg extension power asymmetry was weakly correlated to 6-minute walk, timed up-and-go, and 30-s chair stand tests and was an independent predictor of overall lower-extremity function only after controlling for total leg power, age, comorbidities, physical activity and adiposity. Longitudinal data from the Boston RISE study demonstrated that weaker leg strength was associated with a nearly two-fold likelihood of declining lower-extremity function, yet strength asymmetry was not (Ward, Beauchamp et al 2016). Taken together, these results suggest that the asymmetry of strength and power is only marginally related to the functional mobility of older adults.…”

“…It should be noted that previous investigations of strength and power asymmetry in older adults have used a range of testing modalities including pneumatic resistance, the Nottingham Power Rig, and isokinetic dynamometry, and, some studies measured knee extensor asymmetry whereas others measured whole-leg asymmetry (Skelton, Kennedy et al 2002, Portegijs, Sipila et al 2005, Perry, Carville et al 2007, Carabello, Reid et al 2010, LaRoche, Cook et al 2012, Bean, Latham et al 2013, Straight, Brady et al 2016, Ward, Beauchamp et al 2016). These studies are therefore not directly comparable because of the task-specificity of asymmetry and the use of compensatory mechanisms that may mask single-joint strength and power asymmetries during whole-leg exercises (Bond, Cook et al 2017).…”

“…Using the Nottingham power rig, Portegijs et al showed in older women that maximal walking velocity was slowest in those that demonstrated poor leg extensor power and high asymmetry and that each variable was an independent predictor of walking velocity (Portegijs, Sipila et al 2005). When leg press strength was assessed using pneumatic resistance, Ward and colleagues showed that despite their older adult sample possessing 20% strength asymmetry, a larger magnitude of asymmetry was not a predictor of decline in self-reported lower-extremity function, whereas weaker leg strength was (Ward, Beauchamp et al 2016). …”

Age-specific differences in the time-frequency representation of surface electromyographic data recorded during a submaximal cyclic back extension exercise: a promising biomarker to detect early signs of sarcopenia

“…Studying the neuromuscular functional decline of the lumbar back extensors muscles would be particularly promising, because these muscles have a higher than average rate of muscle loss with 2.5% per year [19]. In addition, poor back extension strength and endurance was found to be predictive of future falls, impaired mobility, frailty, and the need for institutionalization in older adults [20][21][22][23]. Recent observations by this research group found the surface electromyographic (SEMG) based measures of back muscle fatigue capable of identifying early agedependent changes in individuals who did not demonstrate a major back strength decline with aging [24].…”

The rehabilitation enhancing aging through connected health (REACH) study: study protocol for a quasi-experimental clinical trial

“…In a recently published clinical demonstration project evaluating a rehabilitative care program addressing mobility problems under Medicare reimbursement guidelines, robust improvements in mobility were observed even after accounting for health factors that might impede progress such as pain or cognitive impairment. This program targeted specific neuromuscular impairments identified as relevant to mobility and focused on other important elements such as principles of behavioral change [ 5 – 7 ]. However, limitations with program engagement and retention of patients were observed due to the frequency of outpatient visits required (average 10–12) and transportation limitations given that these patients manifested mobility limitations.…”