Reference values for vastus lateralis fiber size and type in healthy subjects over 40 years old: a systematic review and metaanalysis

Abstract

Skeletal muscle atrophy is a major systemic impairment in chronic diseases. Yet its determinants have been hard to identify because a clear research definition has not been agreed upon. The reduction in muscle fiber cross-sectional area (CSA) is a widely acknowledged marker of muscle atrophy, but no reference values for the muscle fiber CSA at the age of the onset of chronic disease have ever been published. Thus, we aimed to systematically review the studies providing data on fiber CSA and fiber type proportion in the vastus lateralis of the quadriceps of healthy subjects (age >40 yr) and then to pool and analyze the data from the selected studies to determine reference values for fiber CSA. We followed the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) and identified 19 studies, including 423 subjects that matched the inclusion criteria. On the basis of fiber type and gender, the mean fiber CSA and the lower limits of normal (LLNs) were (%type I*60) + 1,743 μm(2) and (%type I*60) - 718 μm(2), respectively, for men; and (%type I*70) + 139 μm(2) and (%type I*70) - 1,485 μm(2), respectively, for women. There was no significant heterogeneity among subgroups of fiber type and gender. The pooled type I fiber proportion was 50.3% (LLN = 32.9%). In multivariate analysis, fiber CSA was significantly correlated with Vo2 peak (r = 190.92; P = 0.03), and type I fiber proportion was correlated with age (r = -0.024; P = 0.005), body mass index (r = 0.096; P = 0.005), and Vo2 peak (r = -0.053; P = 0.005). Our metaanalysis of a homogeneous set of studies is the first to provide valuable LLNs for fiber CSA according to fiber type and gender. This analysis will be improved by prospective assessment in well-characterized healthy subjects.

Effect of endurance versus resistance training on quadriceps muscle dysfunction in COPD: a pilot study

“…Based on studies of the muscular adaptations to exercise in COPD compared to healthy age-matched subjects, it seems that RT could increase cross-sectional area22 and muscle mass,4 whereas ET appears to increase muscle oxidative capacity 10,11,23. In the present study, the proportion of type I fibers at baseline was low compared to reference values established in a healthy elderly population,24 and although not as low as observed in severe COPD,21 the results were similar to results from studies of milder staged COPD 25,26. Even though our results did not show an increase in type I fiber proportion after ET, there appears to be a potential for an adaptation toward a more oxidative muscle phenotype after aerobic training in COPD 3,25.…”

Skeletal muscle myofilament adaptations to aging, disease, and disuse and their effects on whole muscle performance in older adult humans

“…Studies examining whole vastus lateralis muscle indicate that the age-related reduction in muscle size is due to fibers being lost and a decrease in CSA, especially in MHC II fibers (Lexell et al, 1988; Lexell and Downham, 1991; Lexell, 1995). In contrast, a recent metaanalysis, which did not include skinned fiber results, indicates CSA is unchanged with age, but is larger with higher physical activity levels (Gouzi et al, 2013). Thus, the variation in CSA with age between the various studies may be due to other confounding factors.…”

Human skeletal muscle metabolic economy in vivo: effects of contraction intensity, age, and mobility impairment

“…As such, it can be hypothesized that in mixed muscle, ME will decrease with increasing contraction intensity, as a greater proportion of less efficient, type II fibers are recruited to contribute to force production. Although conflicting evidence exists (3,63,70), an inverse relationship between contraction intensity and ME has been observed in young adults, along with an association between average ME and type II fiber area (34).With advanced age, there can be a modest shift in fiber type toward a greater proportion of type I fibers (23,35,55,56,77), suggesting that older muscle may be inherently more economical than young on the basis of fiber-type composition. It can be further hypothesized that a lower proportion of type II fibers in older muscle (23,35,55,56,77) should protect against a decline in ME with increasing contraction intensity, as rela-…”

“…It can be further hypothesized that a lower proportion of type II fibers in older muscle (23,35,55,56,77) should protect against a decline in ME with increasing contraction intensity, as rela-…”

“…With advanced age, there can be a modest shift in fiber type toward a greater proportion of type I fibers (23,35,55,56,77), suggesting that older muscle may be inherently more economical than young on the basis of fiber-type composition. It can be further hypothesized that a lower proportion of type II fibers in older muscle (23,35,55,56,77) should protect against a decline in ME with increasing contraction intensity, as rela-tively fewer type II fibers would contribute to force production at greater intensities in older adults.…”