title: Pennation angle does not influence the age-related differences in echo intensity of the medial gastrocnemius.
abstract: The reflection of an ultrasound (US) wave is strongest when the propagation direction of the wave is perpendicular to muscle fascicles. Thus, it is possible that muscle echo intensity (EI), a gray-scale US measure of muscle quality, may be influenced by the angulation of muscle fascicles. Therefore, the purpose of this study was to determine if age-related differences in muscle EI values are influenced by differences in pennation angle (PA). Medial gastrocnemius EI and PA were examined using panoramic US imaging in 24 young (19.8 ± 1.7 y) and 21 older (69.3 ± 3.3 y) men. The young men had lower EI values (young = 74.1 ± 6.3 a.u., older = 89.1 ± 8.8 a.u.) and a greater PA (young = 20.0 ± 2.9°; older = 17.2 ± 2.5°) compared with the older men (p < 0.01). In addition, there was a negative relationship (r = -0.473, p < 0.01) between PA and EI with both groups combined, but no significant relationship when the young (r = -0.334, p = 0.111) and older (r = -0.147, p = 0.525) men were examined separately. An analysis of covariance revealed that muscle EI values remained different (p < 0.01) between age groups after adjustment for differences in PA. Thus, after statistically adjusting the mean EI values for the differences in PA, there were still significant age-related differences in EI. These findings may provide further support that the age-related changes in muscle EI values reflect changes in tissue composition (i.e., increase in intramuscular fat and/or connective tissue) commonly reported in older adults.
authors.affiliation: Neuromuscular Research Laboratory, Department of Exercise and Sport Science, University of North Carolina-Chapel Hill, Chapel Hill, North Carolina, USA. Electronic address: edryan@email.unc.edu.
authors.forename: Eric D
authors.initials: ED
authors.lastname: Ryan
authors.affiliation: Neuromuscular Research Laboratory, Department of Exercise and Sport Science, University of North Carolina-Chapel Hill, Chapel Hill, North Carolina, USA; Valencell, Inc., Raleigh, North Carolina, USA.
authors.forename: Joseph G
authors.initials: JG
authors.lastname: Rosenberg
authors.affiliation: Neuromuscular Research Laboratory, Department of Exercise and Sport Science, University of North Carolina-Chapel Hill, Chapel Hill, North Carolina, USA.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Scharville
authors.affiliation: Neuromuscular Research Laboratory, Department of Exercise and Sport Science, University of North Carolina-Chapel Hill, Chapel Hill, North Carolina, USA; Human Performance Laboratory, Department of Health, Exercise, and Sport Sciences, Texas Tech University, Lubbock, Texas, USA.
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Sobolewski
authors.affiliation: Neuromuscular Research Laboratory, Department of Exercise and Sport Science, University of North Carolina-Chapel Hill, Chapel Hill, North Carolina, USA.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Tweedell
authors.affiliation: Neuromuscular Research Laboratory, Department of Exercise and Sport Science, University of North Carolina-Chapel Hill, Chapel Hill, North Carolina, USA.
authors.forename: Craig R
authors.initials: CR
authors.lastname: Kleinberg
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging*; D014463:Ultrasonography; D055815:Young Adult
keywords: Aging; Muscle architecture; Muscle quality; Ultrasound