Passive movements have a far less extensive physiological, and therefore also a far less extensive therapeutic, effect than active movements.

Passive movements cannot claim any important value as regards the development and shape of the bones and skeleton.

The definite dilatation of the blood vessels in the muscles during active movements is not found in passive movements, and therefore the strong repletive and depletive effect upon the circulation which active movements possess and the effect upon the nutritive condition of the muscles are done away with.

The passively shortened muscle does not thicken as much as that contracted actively, and does not press so firmly upon the veins as the latter. This factor in active movements, so beneficial to the circulation, is therefore less in passive movements.

Passive movements exercise the muscles only to a very limited extent. The muscle's power of stretching and elasticity are called into play, but it is not so in regard to its power to change by its own work chemically stored vital force into movement and heat. In resting muscle and in passively moved muscle, just as in other tissues, as we all know, an "internal" parenchymatous respiration takes place by which oxygen is taken up, carbon dioxide given off, and more complex molecules break up into simpler molecules with production of heat. But although metabolism in a passively moved muscle, owing to increased circulation (see below), must be somewhat more rapid than in a resting muscle, it certainly reaches only an inconsiderable fraction of the metabolism of an actively working muscle.

An interesting fact worth mentioning was, however, noticed by Schmulewitz, namely, that muscle, like elastic, becomes warmer to a certain extent on being drawn out.

By the absence of muscle work in passive movements the formation of those products which stimulate the centres for circulation and respiration is to a large extent absent, as also the consequent marked effect upon the activity of these organs. The enormous therapeutic effect of active movements, especially of "terrain cures" for weak hearts and other forms of cardiac insufficiency, is absent from passive mechano-therapy in so far as we aim at strengthening the heart. With regard to this I must allow that passive movements, by their effect upon the venous circulation mentioned below, facilitate the work of the heart. But this is quite another matter, and not nearly so valuable as the therapy of exercise, which by means of active movements can affect the heart itself. "Chest-lifting" is one of the movements most often used in Swedish gymnastics, and quite the most advertised as regards its effects. Nor can it be denied that it increases the ventilation of the lung - in other words, causes deeper inspiration and expiration, and thus has a similar effect upon respiration and circulation. But a fairly observant person receiving chest-lifting for, e.g., a quarter of an hour, and afterwards walking uphill at a moderate pace for the same length of time, will obtain a vivid impression of the much greater effect of the walk than of the chest-lifting upon the ventilation of the lung, upon the heart-beat, systole and diastole, and upon the whole circulation for that matter.

From the above it is clear that passive movements only to a limited extent affect internal respiration, metabolism, and the production of heat.

It must be allowed, in spite of the lack of experimental evidence, that the effect of passive movements upon the tension of the fascia, upon the size of Braune's spaces and upon the "venous pumps," is much less than that of active movements. This very important difference depends chiefly upon the fact that the muscles which act upon the fascia by their shortening in active movements owing to their power of contractility when influenced by the will contract strongly, but in passive movements they contract with considerably less strength.

By the stretching of the veins, and by the compression of the blood vessels of the spleen, liver and other vessels of the abdomen during certain movements (see above), passive movements have certainly as strong an effect as active movements of the same extent.

Passive movements in medical gymnastics are of greatest value in the treatment of joint affections. By means of passive movements we can stretch shrunken joint capsules, ligaments and contractions, separate parts of synovial membrane which after long contact have become adherent to each other, as well as stretch or tear adhesions which have formed and other more or less organised inflammatory products. We thus prevent the changes which result from too prolonged fixation - shortening of soft parts, especially the troublesome atrophic shortening of muscle, formation of blood vessels and connective tissue, and finally adhesion and ossification of cartilage and consequent destruction of the joint. Lastly, by passive movements we can restore mobility of tendons and muscles which have become partially adherent to their sheaths as the result of prolonged uninterrupted rest or of inflammatory conditions.

On the other hand, stretching alone will not fully restore the length of a trophically shortened muscle. If one does not resort to orthopaedics or surgery one must partially rupture the shortened muscles, treatment which is only possible in the case of the smaller muscles (see Muscle Contractures).

It is also worth noting that, with regard to contractures in the lower extremities, one ought not to spend too much time and work over passive movements. What these accomplish may also be brought about by the partly active, partly, in a sense, passive, movements of walking, and the patient will always prefer the pain caused by himself to that caused by others.