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

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  • [Re: PP127: Sit-ups and Hip Flexor Paradox]

    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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