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First published online June 27, 2008
Journal of Experimental Biology 211, 2336-2345 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.017640

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Scaling of muscle architecture and fiber types in the rat hindlimb

Carolyn M. Eng¹, Laura H. Smallwood¹, Maria Pia Rainiero², Michele Lahey¹, Samuel R. Ward² and Richard L. Lieber^1,*

¹ Departments of Orthopaedic Surgery and Bioengineering, University of California and Veterans Administration Medical Centers, San Diego, CA, USA
² Department of Radiology, University of California and Veterans Administration Medical Centers, San Diego, CA, USA

View larger version (87K): [in this window] [in a new window]   Fig. 1. Lateral view of a rat hindlimb transected above the lumbar spine, with muscle X indicated by the arrow. The origin of the muscle is on the craniolateral pelvis and its insertion on the craniomedial tibia. Scale bar, 10 mm.

View larger version (8K): [in this window] [in a new window]   Fig. 2. Scatter plot of fiber length and physiological cross-sectional area (PCSA) in the muscles of the rat hindlimb. Muscles included psoas, gluteus superficialis (GSup), gluteus medius (GMed), adductor brevis (AddB), adductor longus (AddL), adductor magnus (AddM), adductor tertius (AddT), rectus femoris (RF), vastus intermedius (VI), vastus lateralis (VL), vastus medialis (VM), biceps femoris (BF), semitendinosus (ST), semimembranosus (SM), muscle X, cranial head of gracilis (GRcr), caudal head of gracilis (GRca), medial head of gastrocnemius (GMH), lateral head of gastrocnemius (GLH), plantaris (PLA), soleus (SOL), tibialis posterior (TP), flexor digitorum longus (FDL), flexor hallucis longus (FHL), peroneus longus (PL), peroneus brevis (PB), tibialis anterior (TA), extensor digitorum longus (EDL), and extensor hallucis longus (EHL). Typically studied rat muscles are represented by filled triangles; all other muscles are represented by open squares.

View larger version (20K): [in this window] [in a new window]   Fig. 3. Comparison of mass (A), fiber length (B) and total physiological cross-sectional area (PCSA; C) across functional muscle groups in the rat hindlimb. Flexors at the hip, knee and ankle are shown as solid bars, whereas the extensors are shown as hatched bars. The functional groups include hip flexors (N=2 muscles), hip extensors (N=6), knee flexors (N=9), knee extensors (N=4), dorsiflexors (N=3) and plantarflexors (N=9). *Significant difference between muscle groups at each joint (P<0.05).

View larger version (14K): [in this window] [in a new window]   Fig. 4. Comparison of myosin heavy chain isoform percentages for each functional muscle group (color coded, see key) in the rat hindlimb.

View larger version (8K): [in this window] [in a new window]   Fig. 5. Semi log-transformed plot of relationship of fiber-length-to-muscle-length ratio (Lf/Lm ratio) and body mass in adductor longus (AddL), lateral head of gastrocnemius (GLH), soleus (SOL), flexor digitorum longus (FDL) and tibialis anterior (TA). The Lf/Lm ratio of all muscles scales negatively with increasing body mass, meaning that larger animals generate relatively smaller fiber excursions than smaller animals. This is especially true for the TA and SOL, both of which have larger scaling exponents than the other muscles.

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