Abstract
Studies have revealed an age-related decrease in the ability to produce force as well as an increase in the contractile stiffness and passive stress of single muscle fibres. However, further insight into age-related changes to the passive properties of human skeletal muscles is needed. The aim of this study was to characterize single muscle fibre passive properties from young and old males across a physiologic range of sarcomere lengths (SLs). Ten young ([YM]: mean age: 25.4years) and ten old ([OM]: mean age: 68.9years) males participated. Vastus lateralis muscles were biopsied and 182 fibres were tested and analyzed (90 YM and 92 OM) using a cumulative stretch-relaxation protocol. Passive mechanical characteristics of each fibre were obtained by fitting the integral of the logistic function to experimental stress-SL data. Muscle fibres from older individuals had significantly greater passive elastic moduli at short SL (1.9-2.65μm) compared with young (p<0.05). This resulted in a significantly larger passive stress for SLs between 2.1μm and 3.55μm for older individuals when compared with young (p<0.05). These results provide novel insight into the length dependency of changes in single muscle fibre passive mechanical properties with age.
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