View Full Version : [Re: PP127: Sit-ups and Hip Flexor Paradox]

04-24-2002, 08:13 AM
Thank you Dr. Siff for bringing up an interesting and long standing
controversy. One of the best studies I have seen that
investigates this issue is:

Juker D, McGill S, Kropf P, Steffen T. Quantitative intramuscular
myoelectric activity of lumbar portions of psoas and the
abdominal wall during a wide variety of tasks. Med Sci Sports Exerc

Juker et al's abstract

PURPOSE: Since most previous reports of EMG activation profiles from
psoas and the abdominal wall have been qualitative, the objective of
this work was to document myoelectric activity from these deep muscles.
This knowledge is required to assist in choosing specific training
exercises and for making rehabilitation decisions that require knowledge
of normalized and calibrated muscle activation levels in different
tasks. METHODS: Intramuscular EMG was collected from five men and three
women, in whom amplitudes were normalized to maximum contraction efforts
and reported over a wide variety of clinical and rehabilitation tasks.
Electrodes were inserted into vertebral portions of psoas and the three
layers of the abdominal wall. Normalized signal amplitudes were reported
as peak levels and time histories. RESULTS: All forms of sit-ups
activated psoas (15-35% MVC) more than the curl-up (10%); psoas was not
highly activated during barbell lifting of loads up to 100 kg ( 16%
MVC); psoas was most active during maximal hip flexion efforts; push-ups
activated psoas up to 25% MVC. Several isometric abdominal exercises
were evaluated using the criteria of maximizing abdominal activation
while minimizing psoas activity: the side (bridge) support exercise
proved the best training method for the abdominal wall. CONCLUSIONS:
Consideration of deep muscle activity, provided in this report, is
important for choosing the most appropriate rehabilitation and training
program for an individual. Specific guidance is provided for choosing
the best abdominal exercise, together with activation profiles during
lifting, during twisting, and during hip rotation.
Specific to the P&P activity of the psoas (expressed at a percent of MVC
for each of 2 sets of electrodes, respectively) was for the following
straight-leg sit-ups 15 +/- 12, 24 +/- 7
bent-knee sit-ups 17 +/- 10, 28 +/- 7
press-heel sit-ups 28 +/-23, 34 +/- 18
bent-knee curl-up 7 +/- 8, 10 +/- 14 -

I think of special note is that pressing the heels into the ground while
doing a sit up has been proposed as a way to eliminate psoas activity
during sit-ups. Obviously that did not work in this study. On the
other hand the bent knee curl up does appear to limit psoas activity.
Of the "abs" exercises, the ones that produced the highest levels of
activity in the psoas were:

straight leg raise 35 +/-20, 33 +/- 8
right hand to left knee 56 +/- 28, 58 +/- 16

__________________________________________________ ___________________
Stephen M. Perle, D.C.
Associate Professor of Clinical Sciences
University of Bridgeport College of Chiropractic
Bridgeport, CT 06601

__________________________________________________ ___________________
Ignorance more frequently begets confidence than does knowledge:
it is those who know little, and not those who know much,
who so positively assert that this or that problem will never
be solved by science. Charles Darwin

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