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EMG STUDY #1

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Extension Exercises:
The "Psoas Paradox"

Lower back irritation and 
abdominal strength exercises

The "Lombard’s Paradox"
and the chair squat

Abdominal musculature during 
a chair squat

Biomechanical Principles to be Investigated
The role of multi-joint muscles at the pelvic girdle, hip and knee joints; the effects of various neutralizing or stabilizing synergies on multi-joint muscle functions

Purpose
Multi-joint muscles are capable of performing motions at more than one joint along an open or closed kinetic chain (e.g., psoas major, sartorius, hamstrings, peroneals, etc.).  Generally speaking, a two-joint muscle (i.e., with a single origin and insertion) pulls both of its lever segment attachments equally toward the center of the belly of the muscle.  If a single joint action is desired, other muscles must also generate tension to create a neutralizing or stabilizing synergy at the appropriate proximal or distal joint location.  Proper execution of various lower extremity callisthenic and weight lifting exercises involves stabilization of the lumbar-pelvic girdle segment.  Why?  This lab will investigate the function of the psoas major during the performance of select sit-up exercises and the function of hamstring muscles when performing a chair squat. 

Rationale
The incidence of low back injury from improper execution of a variety of callisthenic exercises is completely preventable by effective instruction and, therefore, inexcusable.  Understanding the importance of trunk stabilization during the performance of open and closed chain lower extremity activities is the key learning objective to be conveyed to students, athletes, patients and clients.