Regional hypertrophy in the human quadriceps following progressive resistance training
Bolsterlee B, Eguchi J, Thom JM and Herbert RD
NeuRA, Sydney, New South Wales, Australia
University of New South Wales, Sydney, New South Wales, Australia
Background
Muscles have complex three-dimensional (3D) shapes, and may remodel in complex 3D patterns when their structure adapts in response to progressive resistance training (PRT) [1]. We used magnetic resonance imaging (MRI) to study regional changes in muscle cross-sectional area (CSA) following PRT.
Methods
mDixon MRI scans of the upper legs were obtained from 11 healthy young adults (9 female) before and after 8 weeks of PRT of the knee extensors. 3D models of the vastus lateralis (VL), vastus intermedius (VI), vastus medialis (VM) and rectus femoris (RF) were created. CSAs were measured before and after training at 1% intervals of femur length. Changes in absolute and relative CSA were grouped by region in distal, middle and proximal thirds of the leg.
Results
CSA increased in all muscles and all regions by, on average, 13%. In all muscles, the relative increase in CSA was largest in the distal third, ranging from 13% in the VI to 24% in RF. In the VL and VI, the absolute increase was larger in the middle third than in the distal third by a factor of 1.8 and 1.6 times, respectively. Conversely, in the VM, the distal third grew 1.9 times more than the middle third.
Discussion
All regions and muscles increased in CSA after PRT, but patterns of hypertrophy differed strongly between muscles and regions. Further analyses showed that mid-thigh CSAs, as measured with ultrasound in this group, reflected the overall shape change of the muscles poorly.
1. Narici MV et al. (1996) Human quadriceps cross-sectional area, torque and neural activation during 6 months strength training. Acta Phys Scan 157(2), 175-186.