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Methods to Quantify Pharmacologically Induced Alterations in Motor Function in Human Incomplete SCI
Published on: April 18, 2011
Changes in muscle activity with increase in leg stiffness during hopping
Hiroaki Hobara1, Kazuyuki Kanosue, Shuji Suzuki
1Graduate School of Human Sciences, Waseda University, Tokorozawa, Saitama, Japan. h_hobara@moegi.waseda.jp
Neuroscience Letters
|March 21, 2007
Summary
This study reveals that leg stiffness during hopping is primarily controlled by muscle preactivation and stretch reflexes, not antagonistic muscle co-contraction. This finding clarifies the neural basis of spring-like leg mechanics in locomotion.
Area of Science:
- Biomechanics
- Neuroscience
- Human Locomotion
Background:
- Mammalian locomotion exhibits spring-like leg behavior, but its underlying neural control is not fully understood.
- Leg stiffness is a key parameter influencing the efficiency and stability of locomotion.
Purpose of the Study:
- To investigate the neural mechanisms regulating leg stiffness during human hopping.
- To differentiate the roles of muscle preactivation, stretch reflexes, and antagonistic muscle activity in controlling leg stiffness.
Main Methods:
- Seven male subjects performed two-legged hopping with preferred and short ground contact times.
- Leg stiffness was calculated using a spring-mass model based on kinematic data.
- Electromyographic (EMG) activity of medial gastrocnemius (MG), soleus (SOL), and tibialis anterior (TA) muscles was recorded.
Main Results:
- Leg stiffness was significantly higher during short contact time (SCT) hopping compared to preferred contact time (PCT).
- SCT hopping showed increased pre- and post-landing EMG activity in MG and SOL muscles.
- Tibialis anterior (TA) activity was lower during SCT, particularly post-landing, compared to PCT.
Conclusions:
- Leg stiffness is regulated by adjustments in centrally programmed muscle preactivation and short-latency stretch reflexes of the triceps surae.
- Co-contraction of the antagonistic tibialis anterior muscle plays a minimal role in modulating leg stiffness during hopping.
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