Elliptical Trainers

[Guest guest]

Periodically we are asked questions about the value or effect of non-impact

exercise such as that provided by machines such as " elliptical trainers " .

Read the following extracts from my " Facts & Fallacies of Fitness " book, then

make any comments which you may like to share with us:

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Suspended walking machines are safer than walking or running

[siff M C Facts & Fallacies of Fitness 2002, pp 57-58]

Impressive-looking suspended pendulum 'skywalking' machines enjoy a degree of

popularity among members of the public who believe infomercial claims on TV

that these devices are as effective as normal walking or running and much

safer. Insofar as they protect one from the vagaries of motorists on the

road, they definitely are safer than road running, but they impose patterns

of movement on the body which do not emulate those of free walking or

running.

They rely predominantly on the hip flexors and extensors, thereby largely

eliminating the propulsion offered by the thigh muscles and plantarflexor

muscles of the lower limbs. Since flexion of the knee does not take place in

'skywalking', the quadriceps and hamstrings are neglected. The tilting of

the pelvis facilitated by gluteus medius during normal walking and running

does not take place on 'skywalkers'. This device also eliminates involvement

of the adductors and abductors of the thigh, as well as the lateral rotators

of the thigh (such as piriformis, gemellus and obturator muscles).

Not only does this serious neglect of many major walking and running muscles

diminish the training effect drastically, the altered patterns of movement

and the absence of non contact phases with the ground can impose more stress

on the hips and lumbar spine. The supposed benefit of completely eliminating

impact loading of the body actually constitutes a serious disadvantage of

'skywalking', because the impact of well-controlled running and walking

offers an important strengthening effect on the skeleton and certain soft

tissues such as the spinal discs, cartilages and knee menisci. In other

words, the claims about 'skywalkers' need to be seriously questioned.

My colleague, Dr Mark Swanepoel, who also taught alongside me in the School

of Mechanical Engineering at the University of the Witwatersrand had some

highly relevant comments to make about this type of machine (given in the

next essay).

All impact loading training should be avoided?

These most interesting remarks are what Dr Mark Swanepoel 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 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 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 & 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 & 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, 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

http://groups.yahoo.com/group/Supertraining/