Muscle power failure in mobility-limited older adults: preserved single fiber function despite lower whole muscle size, quality and rate of neuromuscular activation

Abstract

This study investigated the physiological and gender determinants of the age-related loss of muscle power in 31 healthy middle-aged adults (aged 40–55 years), 28 healthy older adults (70–85 years) and 34 mobility-limited older adults (70–85 years). We hypothesized that leg extensor muscle power would be significantly lower in mobility-limited elders relative to both healthy groups and sought to characterize the physiological mechanisms associated with the reduction of muscle power with aging. Computed tomography was utilized to assess mid-thigh body composition and calculate specific muscle power and strength. Surface electromyography was used to assess rate of neuromuscular activation and muscle biopsies were taken to evaluate single muscle fiber contractile properties. Peak muscle power, strength, muscle cross-sectional area, specific muscle power and rate of neuromuscular activation were significantly lower among mobility-limited elders compared to both healthy groups (P ≤ 0.05). Mobility-limited older participants had greater deposits of intermuscular adipose tissue (P < 0.001). Single fiber contractile properties of type I and type IIA muscle fibers were preserved in mobility-limited elders relative to both healthy groups. Male gender was associated with greater decrements in peak and specific muscle power among mobility-limited participants. Impairments in the rate of neuromuscular activation and concomitant reductions in muscle quality are important physiological mechanisms contributing to muscle power deficits and mobility limitations. The dissociation between age-related changes at the whole muscle and single fiber level suggest that, even among older adults with overt mobility problems, contractile properties of surviving muscle fibers are preserved in an attempt to maintain overall muscle function.

Non-Discriminant Relationships between Leg Muscle Strength, Mass and Gait Performance in Healthy Young and Old Adults

“…gait speed of 0.8 m/s, a 0.17-kg greater dietinduced increase in muscle mass versus control did not improve gait speed ( p = 0.46 for between-group differences) and performance in a composite mobility test ( p = 0.51) [30] . While muscle power compared with leg strength may be functionally more relevant to gait speed [31] , at 3-year follow-up, declines of muscle size, strength, power, and scores in a composite mobility test were similar [32] . In addition, leg press power correlated with functional status as weakly ( r = 0.64, p < 0.001) [33] as muscle strength correlated with gait speed in the present study (range r = 0.55-0.63, p < 0.05; Table 2 , Fig.…”

Body Composition, Muscle Capacity, and Physical Function in Older Adults: An Integrated Conceptual Model

“…Furthermore, muscle power has been found to be more important to activities of daily living than muscle strength (Bean et al, 2002;Foldvari et al, 2000), because many activities (stair climbing, lifting one's body from a bed or chair, and carrying groceries) require greater use of muscle power relative to muscle strength. Across all age groups, men have greater muscle power than women (Bassey et al, 1992;Caserotti, Aagaard, Simonsen, & Puggaard, 2001;Metter et al, 1997;Reid et al, 2012). However, the rate of decline in muscle power is greater in men (3%) than women (1.7%; Skelton, Greig, Davies, & Young, 1994).…”

“…Sex also affects each of these factors and contributes to differences in PF between men and women. For example, in comparison with older men, older women tend to have higher amounts of body fat (Jankowski et al, 2008;Valentine, Misic, Rosengren, Woods, & Evans, 2009), lower muscle quality (Reid et al, 2012), and poorer PF Millán-Calenti et al, 2010;Murtagh & Hubert, 2004;Valentine, Misic, et al, 2009). More specifically, between the ages of 70 and 90, the proportion of disabled women increased from 22% to 81%, whereas the proportion of disabled men only increased from 15% to 57% (Leveille, Penninx, Melzer, Izmirlian, & Guralnik, 2000).…”

Análises proteômicas do tendão calcâneo sob efeito do envelhecimento e treinamento de força

“…O processo de envelhecer culmina na deterioração progressiva da integridade estrutural e funções fisiológicas (Kavathia et al, 2009;. As perdas inerentes à força e resistência, juntamente com alterações na arquitetura muscular e propriedades tendíneas, são muito visíveis com o avanço da idade (Morse, Thom, Birch, et al, 2005;Morse, Thom, Reeves, et al, 2005;Onambele et al, 2006;Reid et al, 2012).…”

“…O processo de envelhecer culmina na deterioração progressiva da integridade estrutural e funções fisiológicas (Kavathia et al, 2009;. As perdas inerentes à força e resistência, juntamente com alterações na arquitetura muscular e propriedades tendíneas, são muito visíveis com o 6 avanço da idade (Morse, Thom, Birch, et al, 2005; Morse, Thom, Reeves, et al, 2005;Onambele et al, 2006;Reid et al, 2012).Grande parte dessas variáveis pode tornar o desempenho motor fragilizado.Ações rotineiras, como coordenar os movimentos corpóreos, ficar em pé, sentar e se locomover, são afetadas, ocasionando visíveis diminuições da interação do indivíduo senil com o meio em que vive (Frolkis et al, 1976;Dudhia et al, 2007).Estudos realizados em animais e humanos visam a esclarecer aspectos morfológicos e biomoleculares do tecido tendíneo, causadores das alterações referidas acima. Resultados prévios, oriundos de populações de ratos e coelhos, mostraram diminuição do número de fibras espessas de colágeno em TC, causada pela atrofia durante a senescência (Nakagawa et al, 1994), diminuição do diâmetro das fibras de colágeno (Chen et al, 2006), juntamente com uma capacidade de proliferação celular e metabolismo dos fibroblastos (componentes celulares básicos dos tendões) diminuídos.…”