Another common myth about abdominal workouts...
Over the past few years, numerous routines and techniques have
been promoted as a way to make your abdominal workouts more effective.
Bending your knees during the sit-up, for example, is recommended
as a way to reduce the activity of the muscles that flex your hip.
This is supposed to reduce the stress to your lower back, and lead
to greater isolation of the abdominals.
It's a myth that's very popular today, despite research
showing that moving the legs from straight to bent actually increases
hip flexor activity.
Pressing your heels into the floor during the sit-up is also said
to "disable" the psoas. The psoas is one of the muscles
responsible for flexing your hips. A reduction in psoas activity
is thought to "isolate" your abdominals and reduce the
risk of injury to the spine.
Press-heel sit-ups are performed like a typical bent-knee sit-up.
The only difference is that as you raise your upper body, you press
your heels into the floor.
The press-heel sit-up does have a reputation as the best way to
"isolate" your abdominals. Yet, there's very little evidence
to show that it reduces psoas activity in the slightest.
In fact, a research team from the University of Bern in Switzerland
has found that the exact opposite occurs!
The study, carried in the journal Medicine and Science in Sports
and Exercise, compared a number of different abdominal exercises
using electrodes inserted into vertebral portions of the psoas and
three layers of the abdominal wall.
The study shows clearly that muscle activity in the psoas is slightly
higher during the press-heel sit-up compared to the bent-knee sit-up.
In other words, pressing your heels into the floor during the bent
knee sit-up appears to increase psoas activity.
One of the other "secrets" revealed in the study was
that the muscles on both sides of your waist (called the obliques)
are highly active during both the press-heel sit-up and the bent-knee
sit-up.
To "tone" these muscles, most people add a small twist
to the end of a sit-up, which actually serves very little purpose.
If you do want to work the obliques a little harder during the
sit-up, twisting movements are most effective when the twist is
initiated at the start, rather than at the end of
a sit-up.
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Reference
Juker, D., McGill, S., Kropf, P., & Steffen, T. (1998) Quantitative
intramuscular myoelectric activity of lumbar portions of psoas and
the abdominal wall during a wide variety of tasks. Medicine
and Science in Sports and Exercise, 30, 301-310
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