Knee Extension & Squats - 2 studies.

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QuantumPositron

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The Journal of Strength and Conditioning Research: Vol. 9, No. 3, pp. 182–187.
Effect of Foot Position on the Electromyographical Activity of the Superficial Quadriceps Muscles During the Parallel Squat and Knee Extension
Joseph F. Signorile, Keith Kwiatkowski, John F. Caruso, and Bobby Robertson

Human Performance Laboratory, Department of Exercise and Sport Sciences, University of Miami, Coral Gables, Florida 33124

ABSTRACT

Many strength trainers believe that varying the foot position during the parallel squat or knee extension can target specific muscles of the quadriceps group. To test this theory, 10 men performed 3 parallel squats at added resistance equal to their body weight and 3 knee extensions at 8- to 10-RM resistance under 3 treatment conditions: toes pointed out, lateral rotation of the tibia ®; toes straight forward, no rotation of the tibia (N); and inward, medial rotation of the tibia (MR). Lifts were separated by a 5-min rest. Bipolar surface electrodes placed on the bellies of the v. lateralis and v. medialis and on the lateral and medial portions of the rectus femoris revealed no significant differences in electrical activity for any muscle due to changes in foot position during the squat. During the knee extension, however, LR produced a significantly greater mean rmsEMG than the other foot positions across all muscles. Thus for the squat a lifter should choose the most stable and comfortable position. For the knee extension, however, maintaining a laterally rotated position is best.
 
The Journal of Strength and Conditioning Research: Vol. 8, No. 3, pp. 178–183.
An Electromyographical Comparison of the Squat and Knee Extension Exercises
Joseph F. Signorile

Department of Exercise and Sport Sciences, University of Miami, Coral Gables, Florida 33124
Brad Weber and Brad Roll

Athletics Department, University of Miami, Coral Gables, Florida 33124
John F. Caruso, Ilka Lowensteyn, and Arlette C. Perry

Department of Exercise and Sport Sciences, University of Miami, Coral Gables, Florida 33124

ABSTRACT

The seated knee extension is commonly used with the parallel squat to promote balance between the vastus medialis (VM) and vastus lateralis (VL). No controlled studies have examined the relative contributions of each muscle during these exercises, so this study employed EMG analysis to determine their contributions. Ten experienced lifters performed squats and knee extensions at their 10-RM. Sets were separated by 15 min rest and the order of performance was reversed between sessions, which were 1 week apart. EMG was collected on the VL and VM of the dominant leg during the first and last repetition of each exercise. Since EMG activity differed significantly between the two testing days, each was analyzed separately. No significant differences were found between the root mean square of the amplitude of the EMG for the VL and VM during either exercise. The parallel squat elicited more electrical activity than the knee extension in both muscles, and the downward shift in frequency of the EMG signal was greater for both the VM and VL during the parallel squat. The results question the value of the knee extension as a supplemental exercise in this case.
 
This is a weeny bit OT:
<div>
(bosbik @ Feb. 07 2008,09:34)</div><div id="QUOTEHEAD">QUOTE</div><div id="QUOTE">i got a question.... is it ok to put some leverage/angle on your heels when squatting?</div>
You can do it and it won't kill you BUT by doing so you will be closing your knee angle at the lowest point in the squat thus shortening your hamstrings and adductors and reducing their potential for contraction.

Most folks resort to using a block either because they see others doing it and/or because they can do a full squat more comfortably by doing so. However, if you do this you are robbing yourself of the important hamstring stretch. Full squats, with feet flat on the floor, will help to address any lack of flexibility in the hamstrings and adductors if you persevere with them; it may take a few weeks or a month but your flexibility will improve and then you will benefit from a stronger drive out of the hole.

If at all possible, do try to get hold of a copy of Starting Strength by Mark Rippetoe and read the chapter on squats (well, read all of it!
smile.gif
) as it will help you understand the mechanics of the movement better and sort out any other areas of poor form that you may have.
 
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