Recently a student asked me the following offline question. My response may
be of some interest here. Any further comments are welcome.
<<What is you view, Dr Siff, on the use of timed sit-ups as a measure of
muscle endurance? The definition of muscle endurance says: it is the ability
for the muscle to repeatedly exert itself till exhaustion. Now with timed
sit-ups, strong, but not really fit guys can do1 or 2 minutes easily without
being exhausted at all. I don't even think that this limited time even allows
the muscles to exert themselves to exhaustion.>>
***Several comments:
1. Why do anyone wish to test abdominal endurance when these muscles serve
the primary purpose of stabilisation, a quality which depends on strength,
not endurance? I have often spoken at conferences about this issue and
rarely come across a single exercise scientist who has tested the 1RM (1
repetition maximum) or even the 5RM of the abdominal muscles.
2. Why test the abdominals and not a larger number of muscles? Since the
principle of specificity is involved in human function, testing the
abdominals alone cannot be extrapolated to apply to overall muscle endurance.
3. Rapid execution of situps strongly and reflexively recruits the hip
flexors and the abdominals, so that this test can hardly be regarded as a
test of abdominal muscle endurance, especially since this test usually is
done with the subject's feet restrained. Rapidity of rebound can also
involve the use of stored elastic energy and distort the picture of what
exact process is involved in this so-called "endurance" activity.
4. There are two major categories of muscle endurance, namely static and
dynamic endurance. The usual rapid test does not give any information of
endurance under static or very slow (quasi-isometric) muscle action (which
may be involved in stabilising the trunk in strength sports such as rugby,
weightlifting, wrestling, gymnastics , judo, etc).
5. Often the limitation to this sort of movement is local muscle ischaemia,
since the continuous strenuous activity tends to inhibit blood flow, so that
it may be difficult to distinguish between true local muscle endurance and
the effects of local ischaemia or impaired blood flow.
6. Another limitation is the fact that every subject has a different RPE
(Rating of Perceived Effort) of any exercise, so that some folk can continue
an action for much longer than others because of mental, rather than physical
qualities.
7. The time element does not specifically test for endurance. Instead it
tends to estimate the mean power over a certain interval (work done per unit
time).
8. Since all exercise involves an element of motor skill (and situp tests
are no exception), it is important for all subjects to achieve comparable
levels of skill if we are to compare performances of isolated muscles.
9. Strength and endurance performance is often a function of bodymass
(generally, the heavier one is, the lower one's relative strength), so are we
justified in comparing the unadjusted performances of subjects of different
bodymass?
10. The leverages involved in trunk flexion differ from person to person, so
that a person with a highly efficient lever system is intrinsically better
equipped to produce strength and power than someone with a less advantageous
lever system.
So, in summary, I agree with any misgivings about using the traditional timed
situp test as a way of assessing human muscle endurance and wonder why its
use has persisted for so long.
Dr Mel C Siff
Denver, USA
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(413) 832-9446 (FAX)
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