Recently there has been an abundance of advice to minimise impact loading on
the body by the use of various walking or climbing machines, in particular
the new generation of so-called "elliptical trainers".
These "elliptical" trainers are designed solely on the faulty and exaggerated
premise that all impulsive or impact training is harmful to the body. Any
form of exercise that is too intense or too prolonged for the current state
of your body may be damaging, not simply all forms of impulsive or ballistic
exercise. In fact, a good deal of research reveals that osteoarthritis and
degeneration of the joints is more commonly associated with inactivity or
prolonged non-impulsive activity than well-controlled impulsive or impact
activity. Some other reports suggest that the typical type of mid-air karate
or TaeBo punching and kicking without a target actually being struck may
cause more joint and soft tissue damage than actions involving contact with a
target.
Here is a relevant extract from my book, "Facts & Fallacies of Fitness"
(page 58) - this material was written by a biomechanics colleague of mine who
spent years researching the effects of impulsive and non-impulsive actions on
the joints of animals and humans.
Since quite a few of the contentious topics that regularly arise for
discussion here are also analysed in this book, the Table of Contents may be
of interest to those who enjoy dissecting current exercise methods and
beliefs - see this web page:
http://24.16.71.95/SPORTSCI/JANUARY/textbooks_by_m_c_siff.htm
MYTH: All Impact Loading Training should be Avoided
These most interesting remarks are what my colleague, Dr Mark Swanepoel (also
formely from the University of Witwatersrand, S Africa), sent to me about the
well-meaning, but misleading avoidance of impact loading and its implications
for joint integrity. They are highly relevant, not only to the use of many
endurance training machines, but also to the entire popular fitness
philosophy of avoiding all ballistic or impulsive exercise.
“I am suspicious of exercise machines that control both displacement and load
simultaneously. They must be physiologically appropriate for a very small
sector of the population, if anyone. Unless performances on various exercise
machines become recognized competitive events, machines that do not offer the
athlete some freedom in the speed of muscle usage and contraction versus
displacement, cannot possibly be a good way to prepare the body for
competition.
Dr Seedhom of Leeds University and his postgraduate students such as Drs Tony
Swann and Nelson Chen have investigated joint useage and degradation. Their
work, taken as a whole together with that of such workers as Drs Bullough and
Goodfellow of Oxford, and Kempson, demonstrates conclusively that joints
subjected to ‘heavy impacts’, such as the ankle, are relatively free from
osteoarthrosis in old age, and those that are subjected to much lower loading
experience a greater incidence of cartilage fibrillation and osteoarthrosis.
In fact, as one progresses up the lower limb, from the ankle, to the knee, on
to the hip, and then to the lumbar apophyseal joints, so the extent of
fibrillation increases at any given age. The reason appears to be that the
cartilage of joints subjected to regular ‘peaky’ loading with relatively high
joint contact stresses, is much stiffer and better able to endure the odd
exceptional load, than softer cartilage that is lowly loaded.
There are now many new exercise machines on the market (such as Elliptical
Trainers or Pendulum Walkers) that are advertised as being ‘low’ or even
‘zero’ impact machines, including one horrific device that subjects the lower
limbs to a centripetal acceleration about a fixed horizontal axis through the
hips, with the knees locked straight. My problem is that joint cartilage and
muscles subjected to such activities will certainly not adapt appropriately
for normal walking, running and stair climbing, and that people using such
unphysiological exercise devices may be letting themselves in for serious
joint trouble later in life.
The catch is that because the market for such devices is relatively modern,
we have no studies of the long-term effects of using them. Should
biomechanists be setting up some sort of body that investigates exercise
machines, and award their ‘mark of approval’ to decent ones, while
withholding their blessing from the bad? Should biomechanists not try to
establish the long term effects of various exercise machines using
experimental and control groups?
Having seen ankle, knee, and lumbar apophyseal joints myself, I fully
support in essence the hypothesis advanced by Bullough and Goodfellow, and
later by Seedhom independently, i.e. that joint cartilage subjected to
regular repetitive loading due to vigorous exercise is healthy and remains
so, while cartilage that is only heavily loaded now and then softens, (i.e.
proteoglycan production decreases), the collagen network loses its cohesion,
and the cartilage then becomes damaged due to the inevitable odd heavy load.
Healthy cartilage is cartilage that is subjected to repetitive, physiological
loading regularly, and this includes full proper joint motion during
exercise. Of course, impact loading should be built up gradually, but there
is nothing bad about impact loading per se - cartilage ‘loves’ to be loaded
properly, and it is the cartilage of the ankle that is least subject to
fibrillation.
Zero impact machines that hold joints immobile while subjecting them to
compression, and variations on this theme - are bound to be very bad for the
health of chondrocytes and cartilage metabolism. Soft, irregularly loaded
cartilage, is cartilage that eventually deteriorates. Walking and running
are healthy exercises for joints, provided that footwear is not worn and a
suitable running surface is present, or that footwear is very carefully
chosen so as not to alter the natural loading of the foot significantly.”
References that support the above essay are the following:
Seedhom B & Wright V Is repetitive loading a cause of osteoarthrosis? J
Orthop Rheum 1988, 1: 79-87
Seedhom B & Swann AC Biomechanics of the osteoarthritic knee. Pendragon
Papers No. 1, Proc of workshop at the Duke of Cornwall Dept of Rheum, Royal
Cornwall Hospital, Truro, Cornwall, Oct 1985
Seedhom B, Takeda T, Tsubuku M & Wright V Mechanical factors and
patello-femoral osteoathritis. Ann Rhem Dis 1977, 38: 307-316
Bullough P, Goodfellow J & O'Connor J The relationship between degenerative
changes and load-bearing in the human hip. 1973
Meachim G & Fergie I Morphological patterns of articular cartilage
fibrillation. J Path 115: 231-240
Swann AC The effect of mechanical stress on the stiffness of articular
cartilage and its role in the aetiology of osteoarthrosis. PhD thesis,
School of Medicine, Univ of Leeds, UK 1988
Kempson G Mechanical properties of articular cartilage and their
relationship to matrix degradation with age. Ann Rheum Dis 1975, 34, Suppl
2: 111-113
Kempson G, Freeman M & Swanson S The determination of a creep modulus for
articular cartilage from indentation tests on the human femoral head. J
Biomech 1971, 4: 239-250
Swanepoel MW, Adams L & Smeathers J Human lumbar apophyseal joint damage
and intervertebral disc degeneration. Ann Rheum Dis 1995, 54: 182-188.
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Dr Mel C Siff
Denver, USA
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