More Experience = More Growth

More Experience - More Growth
Intro
Little is known about muscle fiber recruitment patterns in complex weight training exercises like the barbell squat during multiple repetitions, and if there is any difference in these activation patterns among different populations. This study compared the relative activation of the vastus lateralis (VL) and the vastus medialis muscles in the legs of subjects with different training experience during the barbell squat.
Trial & Data
Nine (9) trained and seven (7) untrained subjects performed 2 1RM tests and another workout using 85% of 1RM to failure. They performed these workouts with surface electrodes placed on their quads to record and assess muscular recruitment and activation patterns of the VL and VM muscles. The data was digitally filtered, rectified and integrated (IEMG) to compare each rep of the multi rep exercise workout to the 1 RM day workouts.
Results
Results showed that while the VL muscle was recruited similarly between the experienced and inexperienced trainers, the VM muscle was recruited differently. The experienced weight trainers recruited more VM fibers and to a far greater extent than the inexperienced lifters. This is an interesting finding and explains how people do incur knee soreness and injury. An imbalance between the VL and VM muscles is a major cause/contributor of many knee problems.
Loading the knee joint, such as in the squat, exposes and compounds the weakness to cause possible future problems. No surprise the experienced lifters were stronger in their 1RMs, however they also performed far more repetitions during their 85% of 1RM squats. In doing so they recruited far more muscle fibers during the process. The researchers concluded that while recruiting more muscles fibers generates more force, the ability to recruit more fibers to exert more force is a learned skill that experienced trainers possess. Also, that recruitment pattern follows a different activation pattern from novice to experienced lifters.

Ref: The relationship between training status and intensity on muscle activation and relative submaximal lifting capacity during the back squat. J.Strength & Cond. Res; 14 (2):175-181.