Proceedings of The Physiological Society

Physiology 2016 (Dublin, Ireland) (2016) Proc Physiol Soc 37, PCB150

Poster Communications

A 5-yr longitudinal study of quadriceps physiological cross sectional area, voluntary activation and in vivo specific force of older men and women

J. Cameron1, H. Degens1, D. Jones1, J. McPhee1

1. Healthcare Sciences, Manchester Metropolitan University, MANCHESTER, United Kingdom.

Background: Loss of strength is one of the most recognisable features of advancing older age and has been termed dynapenia. It may be due to lower muscle mass (sarcopenia), reduced voluntary activation, or lower specific force (force per physiological cross-sectional area (PCSA)). Methods: To investigate, 12 older men and 13 older women (mean ± SD age at baseline 71±4 yrs) who were all relatively active and healthy provided written informed consent and completed measurements at baseline and again 5 yr later. Maximal voluntary isometric knee extension force (MVC) was measured at 90 degree knee angle. The interpolated twitch technique was applied to assess the level of voluntary activation and ultrasound was used to measure fascicle length and pennation angle of each of the quadriceps muscles during MVC. The volume of each quadriceps component muscle and the patella tendon moment arm were estimated from magnetic resonance imaging. PCSA for each muscle was estimated from muscle volume/fascicle length. Quadriceps specific force was estimated from: (MVC/patellar tendon moment arm) / (quadriceps PCSA * the cosine of the fascicle pennation angle). Results: Compared with baseline, MVC (12%, p=0.001), voluntary activation (6%, p=0.003) and PCSA (5%, p<0.0005) were reduced and the in vivo specific force was 7% lower at follow-up compared with baseline (p=0.027). After accounting for the reduced voluntary activation by estimating the force that could be produced if the muscle was fully activated, there was no difference in specific force between baseline and follow-up (p=0.693). Conclusion: These results show that strength was lost at around 2% per year, while PCSA and voluntary activation declined at rates of around 1% per year. The change in muscle size (PCSA) and the reduced neural activation equally contributed to the loss of strength and there was no apparent loss of ‘muscle quality', as evidenced by the specific force when corrected for activation levels.

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