Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC205
Muscle to Bone ratio as an intra-individual indicator of sarcopaenia
T. Maden-Wilkinson1, J. S. McPhee1, J. Rittweger1,2, D. A. Jones1, H. Degens1,2
1. Institute for Biomedical Research into Human Movement and Health, Manchester Metropolitan University, Manchester, United Kingdom. 2. Institiute of Aerospace Medicine, German Aerospace Center, Cologne, Germany.
The decline in muscle mass and strength during ageing and its consequences for health and quality of life have been well documented. However, the data on which this is based are largely from cross-sectional studies and it is difficult to acquire longitudinal data over a 70-year time span. The implicit assumption of the cross-sectional studies is that the muscles of the older subjects in their twenties were of a similar size to those of the present-day 20-year olds. The challenge is to find a way of relating the present state of the muscle to what it might have been in the past by relating the muscle size to some standard that shows little, if any, changes in adulthood. The femoral cross sectional area might be such a standard as it changes little, across the adult lifespan. Therefore, the muscle mass to bone area ratio might be an indicator of extent of age-related muscle atrophy. To investigate this, 21 young (22.4±3.0 yrs) and 20 elderly (71.4±4.6 yrs) men completed an MRI scan (Esaote, 0.25-T; G-Scan) and maximal isometric voluntary knee extension contractions (MVC). For MRI, cross-sectional slices were obtained perpendicular to the thigh at 25mm intervals from the distal the proximal ends of the femur using a turbo-3D T1-weighted protocol. Quadriceps muscle (Qcsa) and femur cross sectional area (Fcsa) were determined in each slice. The maximum Qcsa may be representative for the maximal force the muscle can generate, while the risk of fracture might be highest where the Fcsa is smallest. Therefore the ratio between the smallest Fcsa and maximum Qcsa was represented as the muscle: bone ratio. Student’s t-tests were used to compare the groups and Pearson correlation coefficients were used to determine relationships between variables. Data are presented as mean ± SD. We observed no difference in smallest Fcsa (Y: 6.09±0.8cm2 vs. O: 6.27±0.87 cm2 p=0.52), cortical (p=0.86) or trabecular (p=0.46) bone CSA between young and old. Compared with young, elderly had a smaller maximal Qcsa (p<0.0001) and MVC torque (O: 160±34 Nm vs. Y: 263±44 Nm, p<0.0001). The muscle: bone ratio in elderly was 9.6±1.4 and in young it was 14.0±1.5 conferring a 32% lower muscle: bone ratio in elderly men (p<0.0001). Muscle: bone ratio correlated significantly in both Y and O groups (see figure; p<0.01). In conclusion, we report here that muscle and bone cross sectional areas are correlated in young subjects. The fact that femur cross sectional area was similar in young and older subjects while muscle size was smaller in old suggests that the bone size may be used to determine the extent to which the older muscle has deteriorated with age. This circumvents, to some extent, the difficulty of conducting long term longitudinal studies of muscle deterioration with age. The same technique may also be useful in clinical studies of conditions where muscle atrophy can occur.
Where applicable, experiments conform with Society ethical requirements