INTRODUCTION: The aim of this cross-sectional study was to concurrently assess musculo-articular stiffness (MAS) and muscle stiffness (MS) of the knee extensors in younger and older individuals. METHODS: Fourteen young (22.1 ± 3.0 years old) and 12 older (65.4 ± 5.7 years old) men were tested for maximal voluntary contraction (MVC), rate of torque development (RTD), muscle thickness, MAS, and MS of knee extensors. RESULTS: MVC, RTD, and muscle thickness were higher in the younger group (288.6 vs. 194.3 Nm, 1319.5 vs. 787.0 Nm s(-1), 23.1 vs. 17.7 mm, respectively, P < 0.05). MAS normalized to the load supported (30% of MVC) was not different between groups (87.9 vs. 88.5 Nm(-1) kg(-1)), whereas the older group exhibited a higher level of normalized MS (23.2 vs. 18.6 Nm(-1) kg(-1), P < 0.05). CONCLUSIONS: Determinants of MS have been highlighted along with their role in elevated MS. The unaltered level of MAS, which is functionally important in an aging population, might be achieved through a decrease in tendon stiffness.
INTRODUCTION: The aim of this cross-sectional study was to concurrently assess musculo-articular stiffness (MAS) and muscle stiffness (MS) of the knee extensors in younger and older individuals. METHODS: Fourteen young (22.1 ± 3.0 years old) and 12 older (65.4 ± 5.7 years old) men were tested for maximal voluntary contraction (MVC), rate of torque development (RTD), muscle thickness, MAS, and MS of knee extensors. RESULTS: MVC, RTD, and muscle thickness were higher in the younger group (288.6 vs. 194.3 Nm, 1319.5 vs. 787.0 Nm s(-1), 23.1 vs. 17.7 mm, respectively, P < 0.05). MAS normalized to the load supported (30% of MVC) was not different between groups (87.9 vs. 88.5 Nm(-1) kg(-1)), whereas the older group exhibited a higher level of normalized MS (23.2 vs. 18.6 Nm(-1) kg(-1), P < 0.05). CONCLUSIONS: Determinants of MS have been highlighted along with their role in elevated MS. The unaltered level of MAS, which is functionally important in an aging population, might be achieved through a decrease in tendon stiffness.