Central activation, muscle performance, and physical function in men infected with human immunodeficiency virus

Abstract

Loss of muscle mass and limitations in activity have been reported in persons infected with human immunodeficiency virus (HIV), even those who are otherwise asymptomatic. The extent to which factors other than muscle atrophy impair muscle performance has not been addressed in depth. The purpose of this study was to determine the extent of neuromuscular activation of the knee extensors and ankle dorsiflexors of 27 men infected with HIV receiving antiretroviral therapy and its relationship to muscle performance. The central activation ratio (CAR) was determined using superimposed electrical stimulation during maximum voluntary contractions. In addition to force and power measurements, muscle cross-sectional area and composition was evaluated using computed tomography. Aerobic capacity was determined from treadmill exercise testing. Eleven of the subjects had an impaired ability to activate the knee extensors (CAR = 0.72 ± 0.12) that was associated with weakness and decreased specific force. The reduced central activation was not associated with muscle area, body composition, aerobic capacity, CD4 count, or medication regimen. Those individuals with low central activation had higher HIV-1 viral loads and were more likely to have a history of AIDS-defining illness. These results suggest the possibility of a different mechanism contributing to muscle impairment in the current treatment era that is associated with impairment of central motor function rather than atrophy. Further investigation is warranted in a larger, more diverse population before more definitive claims are made.Keywords central activation; electrical stimulation; HIV infection; muscle cross-sectional area Loss of skeletal muscle mass has a significant impact on functional performance, independent function, and associated quality of life in persons infected with the human immunodeficiency virus (HIV).1 , 36 Since highly active antiretroviral therapy (HAART) became the standard of care for HIV infection in 1995, the incidence of wasting (involuntary weight loss >10% ideal body weight) has declined, although it is still common.29 , 49 In the era of HAART, recent work indicates that HIV-associated weight loss is primarily due to fat 26,32 Identifying the factors beyond the reduction of muscle mass that contribute to impaired muscle function is required for optimizing the design of rehabilitation strategies to improve muscle strength and functional capacity in this chronically ill patient population.One factor that can reduce muscle force production in the absence of muscle atrophy is an impairment of central activation (i.e., the ability to activate the available muscle mass). Central activation failure has been shown to contribute significantly to muscle weakness in other clinical populations, e.g., in persons with osteoarthritis, cerebral palsy, or previous knee arthroplasty,14 , 31 , 39 and to negatively influence the relationship between muscle strength and physical function.14 The role of central activation in muscle performance in persons...

The Frequency of Low Muscle Mass and Its Overlap With Low Bone Mineral Density and Lipodystrophy in Individuals With HIV—A Pilot Study Using DXA Total Body Composition Analysis

“…Mirroring this, researchers have also looked past muscle mass and wasting in individuals with HIV. Results also indicate that others factors apart from muscle atrophy contribute to impaired muscle function in this population (27). More recently, Note: With the higher cutoff, less medication classes were positively associated with LD.…”

Changes of functional status and volume of triceps brachii measured by magnetic resonance imaging after maximal resistance training

“…MIPAV was used to analyze images on a personal computer workstation (23). This program calculates the surface area (in mm 2 ) of the manually selected region of interest (24,25). Briefly, for each axial image, the crosssectional area (CSA) of the triceps brachii muscle was Figure 1.…”

Paradoxical contractile properties in the knee extensors of HIV-infected men treated with antiretroviral therapy

“…The neuromuscular function of middle-aged HIV+ individuals treated with ART has recently been reported (Scott et al 2007;Oursler et al 2009). In 1 study, HIV+ subjects with higher viral loads and histories of AIDS-defining illnesses exhibited weakness during maximum volitional contractions (MVC) of the knee extensors, compared with other HIV+ subjects.…”

“…In 1 study, HIV+ subjects with higher viral loads and histories of AIDS-defining illnesses exhibited weakness during maximum volitional contractions (MVC) of the knee extensors, compared with other HIV+ subjects. This weakness was not related to atrophy, but rather to impaired central drive, as assessed by the central activation ratio (CAR) (Scott et al 2007). The purpose of this investigation was to evaluate the contractile responses of muscles of HIV+ individuals and to compare them with those of age-matched controls.…”

“…To our knowledge, this aspect of neuromuscular physiology has not been reported in an HIV+ population. In this brief communication, we examine muscle function in HIV+ individuals by evaluating the force (torque)-frequency relationship in the knee extensors of a subset of the population from previous studies (Oursler et al 2006;Scott et al 2007), and comparing it with that of a matched control group. Because the force-frequency relationship is largely a function of the rates of force generation and relaxation, we also report on these contractile properties.…”