Abstract：
:Following active muscle lengthening, steady-state isometric force is elevated compared with an isometric contraction without prior lengthening for the same muscle length and activation level. This property of muscle contraction is known as residual force enhancement (RFE). Here, we aimed to determine whether neural factors may mask some of the mechanical benefits of RFE on plantar flexion torque production. Inherent to lengthening contractions is an increase in cortical and spinal-mediated inhibition, while knee flexion places the medial gastrocnemius at a neuromechanical disadvantage. Neuromuscular properties of the plantar flexors were investigated with a Humac Norm dynamometer in 10 males (∼27 years) with a flexed (90°) and extended (180°) knee and with or without calcaneal tendon vibration (frequency range: 80-110 Hz). There was no effect for vibration (p > 0.05), but there was an effect for knee angle (p < 0.05) such that there was a 2 fold increase in RFE with the knee flexed compared with extended. During submaximal torque matching, following active lengthening there was an activation reduction (electromyography; EMG) of 7.2 and 4.7% with the knee flexed and extended, respectively for soleus as compared with the reference isometric contraction, but no difference for the medial gastrocnemius. Despite attempting to excite Ia input onto the plantar flexor motor neuron pool, vibration had no influence on RFE. Surprisingly, RFE was elevated more for the knee flexed than extended, which was possibly owing to the activation differences across the disparate muscles of the triceps surae during the plantar flexion task.
journal_name
J Biomechjournal_title
Journal of biomechanicsauthors
Dalton BH,Contento VS,Power GAdoi
10.1016/j.jbiomech.2018.07.019subject
Has Abstractpub_date
2018-09-10 00:00:00pages
70-76eissn
0021-9290issn
1873-2380pii
S0021-9290(18)30528-1journal_volume
78pub_type
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