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Early structural adaptations to unloading in the human calf muscles
O R Seynnes1, C N Maganaris, M D de Boer
1Institute for Biomedical Research into Human Movement and Health, Manchester Metropolitan University, Alsager, UK. o.seynnes@mmu.ac.uk
Acta Physiologica (Oxford, England)
|February 13, 2008
Summary
Muscle architecture rapidly remodels within 14 days of lower limb unloading, mitigating muscle force loss. These adaptations in fascicle length and pennation angle help preserve muscle function during unloading.
Area of Science:
- Exercise Physiology
- Muscle Biology
- Biomechanics
Background:
- Unilateral lower limb suspension (ULLS) is a model for studying muscle unloading.
- Muscle torque and architecture are crucial for physical function.
- Understanding adaptations to unloading is vital for rehabilitation and space travel.
Purpose of the Study:
- To investigate the impact of 3-week ULLS on muscle torque.
- To examine changes in muscle architecture, including volume, fascicle length, and pennation angle.
- To correlate muscle architectural changes with muscle torque and physiological cross-sectional area (PCSA).
Main Methods:
- Eight healthy men underwent 3 weeks of ULLS.
- Measurements included plantarflexion maximal voluntary contraction (MVC), muscle volume (VOL), fascicle length (L(f)), pennation angle (theta), PCSA, and EMG.
- Assessments were performed on days 14 and 23 of ULLS.
Main Results:
- MVC and soleus (SOL) EMG decreased by 10% and 29% by day 14.
- Muscle volume of SOL, gastrocnemius medialis (GM), and gastrocnemius lateralis (GL) decreased significantly.
- GL fascicle length and pennation angle reduced, leading to a 3% decrease in GL PCSA by day 14, which persisted.
Conclusions:
- Rapid muscle architecture remodeling occurs within 14 days of lower limb unloading.
- Adaptations in muscle architecture mitigate the decline in PCSA.
- These changes may protect against greater muscle force loss during unloading.
