Quantity versus quality: Age-related differences in muscle volume, intramuscular fat, and mechanical properties in the triceps surae

Sabrina Pinel; Nicole Y Kelp; Jessica M Bugeja; Bart Bolsterlee; François Hug; Taylor J M Dick

doi:10.1016/j.exger.2021.111594

Quantity versus quality: Age-related differences in muscle volume, intramuscular fat, and mechanical properties in the triceps surae

Exp Gerontol. 2021 Dec:156:111594. doi: 10.1016/j.exger.2021.111594. Epub 2021 Oct 18.

Authors

Sabrina Pinel¹, Nicole Y Kelp², Jessica M Bugeja³, Bart Bolsterlee⁴, François Hug⁵, Taylor J M Dick⁶

Affiliations

¹ The University of Queensland, School of Biomedical Sciences, Brisbane, Queensland, Australia; The University of Groningen, Faculty of Medicine, Groningen, The Netherlands.
² The University of Queensland, School of Biomedical Sciences, Brisbane, Queensland, Australia.
³ The University of Queensland, School of Information Technology and Electrical Engineering, Brisbane, Queensland, Australia; Australian e-Health Research Centre, CSIRO Health and Biosecurity, Brisbane, Queensland, Australia.
⁴ Neuroscience Research Australia (NeuRA), Randwick, New South Wales, Australia; University of New South Wales, Randwick, New South Wales, Australia; Queensland University of Technology, School of Mechanical, Medical and Process Engineering, Brisbane, Queensland, Australia.
⁵ The University of Queensland, School of Biomedical Sciences, Brisbane, Queensland, Australia; University of New South Wales, Graduate School of Biomedical Engineering, Randwick, New South Wales, Australia; Institut Universitaire de France (IUF), Paris, France; Université Côte d'Azur, LAMHESS, Nice, France.
⁶ The University of Queensland, School of Biomedical Sciences, Brisbane, Queensland, Australia. Electronic address: t.dick@uq.edu.au.

PMID: 34673171
DOI: 10.1016/j.exger.2021.111594

Abstract

With aging comes reductions in the quality and size of skeletal muscle. These changes influence the force-generating capacity of skeletal muscle and contribute to movement deficits that accompany aging. Although declines in strength remain a significant barrier to mobility in older adults, the association between age-related changes in muscle structure and function remain unresolved. In this study, we compared age-related differences in (i) muscle volume and architecture, (ii) the quantity and distribution of intramuscular fat, and (iii) muscle shear modulus (an index of stiffness) in the triceps surae in 21 younger (24.6 ± 4.3 years) and 15 older (70.4 ± 2.4 years) healthy adults. Additionally, we explored the relationship between muscle volume, architecture, intramuscular fat and ankle plantar flexion strength in young and older adults. Magnetic resonance imaging was used to determine muscle volume and intramuscular fat content. B-mode ultrasound was used to quantify muscle architecture, shear-wave elastography was used to measure shear modulus, and ankle strength was measured during maximal isometric plantar flexion contractions. We found that older adults displayed higher levels of intramuscular fat yet similar muscle volumes in the medial (MG) and lateral gastrocnemius (LG) and soleus, compared to younger adults. These age-related higher levels of intramuscular fat were associated with lower muscle shear modulus in the LG and MG. We also found that muscle physiological cross-sectional area (PCSA) that accounted for age-associated differences in intramuscular fat showed a modest increase in its association with ankle strength compared to PCSA that did not account for fat content. This highlights that skeletal muscle fat infiltration plays a role in age-related strength deficits, but does not fully explain the age-related loss in muscle strength, suggesting that other factors play a more significant role.

Keywords: B-mode ultrasound; Fascicle length; Magnetic resonance imaging; Muscle stiffness; Shear wave elastography; Skeletal muscle.

MeSH terms

Aged
Ankle Joint / physiology
Humans
Isometric Contraction* / physiology
Leg
Muscle Strength / physiology
Muscle, Skeletal* / physiology