کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
6270981 | 1614746 | 2016 | 10 صفحه PDF | دانلود رایگان |
- Age-related strength loss is frequently accompanied by reduced firing rates of motor units.
- Previously, soleus rates were not lower despite plantar flexion strength decrements.
- Here we found plantar flexion strength was 46% lower for older men than young.
- Motor unit firing rates in both gastrocnemii were not affected by age.
- In this muscle group, firing rates are well-maintained despite large strength differences.
The triceps surae comprises an important group of muscles for human posture and gait. The soleus unlike other limb muscles shows atypical lower firing rates in both old and young adults across various voluntary strength levels, including maximal contractions. The other portion of the triceps surae, the gastrocnemii has not been explored in aging, and despite anatomic, histochemical and age-related morphological differences, they share many common functions with soleus. During multiple visits, 10 active young (23-33Â years) and 10 active old participants (76-86Â years) performed a series of plantar flexor isometric contractions at a range of contraction intensities including maximal voluntary contraction (MVC) with tungsten microelectrodes inserted into the lateral (LG) and medial (MG) gastrocnemius. Despite equal and near maximal voluntary activation (VA) (â¼98%), MVC torque was â¼46% lower, twitch tension was â¼34% lower, and contractile speed was â¼15% slower in the old men compared with the young. At all isometric torque levels tested (25, 50, 75 and 100% MVC) there were no statistically significant differences in mean motor unit firing rates (MUFRs) between young and old men. In both groups, the range of mean MU firing rates was similar (â¼8Â Hz at 25% MVC to â¼22Â Hz at 100% MVC). The structural age-related changes in the gastrocnemii are not reflected in neural drive adaptations, indicating that MUFRs may not be a common feature with aging and other factors such as habitual use or anatomical location may be influential.
Journal: Neuroscience - Volume 330, 25 August 2016, Pages 376-385