P17 The topography of hypertrophy: how muscle architecture changes with strength training.
Eguchi J, Bolsterlee B, Thom JM and Herbert RD
- NeuRA, Sydney, New South Wales, Australia
- University of New South Wales, Sydney, New South Wales, Australia
Background. Progressive resistance training (PRT) changes muscle architecture [1]. Training-induced changes in muscle architecture have been measured previously using two-dimensional ultrasound imaging, which is prone to projection errors [2]. We used diffusion tensor imaging (DTI; an MRI technique) to investigate three-dimensional architectural changes in the human quadriceps following PRT.
Methods. Eleven healthy young adults completed eight weeks of PRT (leg press and leg extension). Anatomical MRI and DTI scans were obtained before and after training. Mean fascicle lengths, pennation angles, volume and physiological cross-sectional area (PCSA) were obtained from the rectus femoris (RF), vastus lateralis (VL), vastus intermedius (VI) and vastus medialis (VM) muscles using procedures described elsewhere [3].
Results. Mean isometric strength increased by 11.8 ± 14.2% (p<0.05). Volume increased (p<0.01) in all muscles, ranging from 11.1% in VI to 14.1% in VL. Fascicle length increased (p<0.01) by 13.3% in VM, by 18.6% in VI and by 22.1% in RF, and did not change significantly in VL. Only the VL changed its PCSA (13.1% increase, p<0.05). Pennation angles and summed PCSA did not change significantly. Isometric strength change did not correlate with summed PCSA change (r=0.33; p=0.32).
Discussion. This is the first DTI-based study on PRT-induced changes in muscle architecture. The data corroborate previous findings made with ultrasound that fascicles increase in length following PRT. Surprisingly, PCSA change was not related to isometric strength change. Muscle volume increased by a similar amount to fascicle length.
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