Magnetic resonance elastography (MRE) shows significant reduction of thigh muscle stiffness in healthy older adults

Paul Kennedy,Colin Brown,Edwin J.R Van Beek,Eric Barnhill,Carolyn Anne Greig,Neil Roberts,Calum Gray

doi:10.1007/s11357-019-00147-2

Abstract

Determining the effect of ageing on thigh muscle stiffness using magnetic resonance elastography (MRE) and investigate whether fat fraction and muscle cross-sectional area (CSA) are related to stiffness. Six healthy older adults in their eighth and ninth decade and eight healthy young men were recruited and underwent a 3 T MRI protocol including MRE and Dixon fat fraction imaging. Muscle stiffness, fat fraction and muscle CSA were calculated in ROIs corresponding to the four quadriceps muscles (i.e. vastus lateralis (VL), vastus medialis (VM), vastus intermedius (VI), rectus femoris (RF)), combined quadriceps, combined hamstrings and adductors and whole thigh. Muscle stiffness was significantly reduced (p < 0.05) in the older group in all measured ROIs except the VI (p = 0.573) and RF (p = 0.081). Similarly, mean fat fraction was significantly increased (p < 0.05) in the older group over all ROIs with the exception of the VI (p = 0.059) and VL muscle groups (p = 0.142). Muscle CSA was significantly reduced in older participants in the VM (p = 0.003) and the combined quadriceps (p = 0.001), hamstrings and adductors (p = 0.008) and whole thigh (p = 0.003). Over the whole thigh, stiffness was significantly negatively correlated with fat fraction (r = − 0.560, p = 0.037) and positively correlated with CSA (r = 0.749, p = 0.002). Stepwise regression analysis revealed that age was the most significant predictor of muscle stiffness (p = 0.001). These results suggest that muscle stiffness is significantly decreased in healthy older adults. Muscle fat fraction and muscle CSA are also significantly changed in older adults; however, age is the most significant predictor of muscle stiffness.

Highlights

Age-related effects on skeletal muscle include loss of muscle mass and decline in muscle force production, defined as sarcopenia, (Cruz-Jentoft et al 2010) and increased fat accumulation within the muscle (Marcus et al 2010)
magnetic resonance elastography (MRE) measurements of magnitude of the complex modulus, |G*|, indicated lower mean stiffness in all Regions of interest (ROIs) in the older group compared to the young group (Table 1), of which a significant difference was found in VL (1.57 ± 0.42 kPa vs 2.20 ± 0.39 kPa, p = 0.02) and VM (1.70 ± 0.43 kPa vs 2.30 ± 0.52 kPa, p = 0.043) muscle groups, quadriceps (1.60 ± 0.34 kPa versus 2.04 ± 0.23 kPa, p = 0.043), combined hamstrings and adductors (1.46 ± 0.24 kPa versus 1.70 ± 0.13 kPa, p = 0.043) and whole thigh (1.52 ± 0.17 kPa versus 1.86 ± 0.14 kPa, p = 0.005, Fig. 4a)
Muscle cross-sectional area (CSA) showed a similar direction of change to the stiffness measurements, in that mean CSAwas lower in the older compared to the younger group over all measured ROIs (Table 1)

Summary

Introduction

Age-related effects on skeletal muscle include loss of muscle mass and decline in muscle force production, defined as sarcopenia, (Cruz-Jentoft et al 2010) and increased fat accumulation within the muscle (Marcus et al 2010). The change in muscle stiffness with age is less well described. Radiographic measurement of muscle stiffness includes contributions from muscle fibres, inter- and intramuscular fat and extracellular matrix (ECM) which supports the fibre bundles. Changes in each of these constituent parts may affect the overall stiffness measurement of the muscle. The effect of ageing on muscle mechanical properties has been studied in ex vivo animal models (Wood et al 2014) and revealed significantly increased extracellular matrix (ECM) stiffness in older rats.

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