Physiotherapist use an Ultrasound machine to vibrate the body’s cells. This vibration increases the rate of cellular activity and stimulates small blood vessels to open up. Ultrasound treatment has may different physiological effect on a cellular level.

The “ultra-“ refers to the high pitch and rate of sound waves which is used as to accelerate the healing process. Ultrasonic waves are produced by the machine and applied to the affected area by using a treatment head (Probe like part with a metal front). This transmits the sound waves from the machine to the skin by using a gel to ensure the sound waves are transferred to deep tissues, to help speed up injury recovery. Ultrasound tends to be most effective on tissues with a higher collagen density (such as ligaments and tendons).

Physiotherapist’s use of Ultrasound is popular mainly due to the wide variety of uses, and depth of research backing up its effectiveness.

The future of healing your tissue

Ultrasound (US) is a form of mechanical energy (not electrical). Mechanical vibration at increasing frequencies is known as sound energy. The normal human sound range is from 16 Hz to something approaching 15-20,000 Hz (in children and young adults). Beyond this upper limit, the mechanical vibration is known as ultrasound. The frequencies used in therapy are typically between 1.0 and 3.0 MHz (1 MHz = 1 million cycles per second).

Sound waves are longitudinal waves consisting of areas of compression and rarefaction. Particles of a material, when exposed to a sound wave will oscillate about a fixed point rather than move with the wave itself. As the energy within the sound wave is passed to the material, it will cause oscillation of the particles of that material. Clearly any increase in the molecular vibration in the tissue can result in heat generation, and ultrasound can be used to produce thermal changes in the tissues.

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Demonstration of physiotherapy treatment called ultrasound

Therapeutic Ultrasound & Tissue Healing

One of the therapeutic effects for which ultrasound has been used is in relation to tissue healing. It is suggested that the application of US to injured tissues will, amongst other things, speed the rate of healing & enhance the quality of the repair.

The therapeutic effects of US are generally divided into:


In thermal mode, US will be most effective in heating the dense collagenous tissues and will require a relatively high intensity, preferably in continuous mode to achieve this effect.

Among the more effectively heated tissues are periosteum, collagenous tissues (ligament, tendon & fascia) & fibrotic muscle. If the temperature of the damaged tissues is raised to 40‑45°C, then a hyperaemia will result, the effect of which will be therapeutic. In addition, temperatures in this range are also thought to help in initiating the resolution of chronic inflammatory states


This phenomenon is known to affect diffusion rates & membrane permeability. Sodium ion permeability is altered resulting in changes in the cell membrane potential. Calcium ion transport is modified which in turn leads to an alteration in the enzyme control mechanisms of various metabolic processes, especially concerning protein synthesis & cellular secretions.

The result of the combined effects of stable cavitation and acoustic streaming is that the cell membrane becomes ‘excited’ (up regulates), thus increasing the activity levels of the whole cell. The US energy acts as a trigger for this process, but it is the increased cellular activity which is in effect responsible for the therapeutic benefits

Effects of Ultrasound

  • Accelerated healing
  • Numbing effect (less pain)
  • Ease muscle spasm
  • Reduce inflammation
  • Improve blood supply
  • Stimulate bone healing
  • Reduce swelling
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What does it feel like?

Ultrasound therapy isn’t painful, but you may feel a little tingling sensations or heat. Treatments tend to last anywhere between 3 and 8 minutes, depending on the size and depth of the structure being treated.

Ultrasound treatment causes your body’s cells to vibrate. Sometimes these cells and fluid vibrate so quickly causing the feeling of warmth. The treatment head is kept in motion throughout the treatment, to avoid the risk of burns to the underlying tissue.

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Why Ultrasound treatment helps?

  • Healing of the tissue
  • Improved blood flow to the area
  • Reduce swelling
  • Reduce inflammation
  • Breaking up scar tissue
  • Reduced pain

The physiological effects of Ultrasound:

The ultrasound waves cause the tissues in the body to alternately compress and expand which results in small changes to the shape of the cells.

The ultrasound waves cause the tissues to heat up. This has several useful effects:

  •  Increased blood flow to the area. Blood brings oxygen which is needed for healing and removes waste products caused by injury.
  • Increased metabolism (the chemical processes happening within the cells). More energy release, means faster healing.
  • Stimulates collagen production. Collagen is one of the building blocks of muscles, tendons and ligaments
  • Increased extensibility of connective tissue, e.g. ligaments and tendons – it makes them more stretchy. This is when treating scar tissue and old injuries.
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Ultrasound treatment of patient

Ultrasound Therapy

Ultrasound has been used as a treatment modality for sports injuries by therapists over the last 50 years.

How does ultrasound work?

Ultrasonic waves or sound waves of a high frequency that is not audible to the human ear are produced by means of mechanical vibration in the metal treatment head of the ultrasound machine. The treatment head is then moved over the surface of the skin in the region of the injury transmitting the energy into the tissues.

When sound waves come into contact with air it causes a dissipation of the waves, and so a special ultrasound gel is placed on the skin to ensure maximal contact between the treatment head and the surface of the skin and to provide a medium through with the sound waves can travel. Ultrasound can also be applied under water which is also a medium for ultrasound waves to travel through.

Effects of therapeutic ultrasound

The effects of therapeutic ultrasound are still being disputed. To date, there is still very little evidence to explain how ultrasound causes a therapeutic effect in injured tissue. Nevertheless practitioners world wide continue to use this treatment modality relying on personal experience rather than scientific evidence. Below are a number of the theories by which ultrasound is proposed to cause a therapeutic effect.

Thermal effect:

As the ultrasound waves pass from the treatment head into the skin they cause the vibration of the surrounding tissues, particularly those that contain collagen. This increased vibration leads to the production of heat within the tissue. In most cases this cannot be felt by the patient themselves. This increase in temperature may cause an increase in the extensibility of structures such as ligaments, tendons, scar tissue and fibrous joint capsules. In addition, heating may also help to reduce pain and muscle spasm and promote the healing process.

Effects on the inflammatory and repair processes:

One of the greatest proposed benefits of ultrasound therapy is that it is thought to reduce the healing time of certain soft tissue injuries.

Ultrasound is thought to accelerate the normal resolution time of the inflammatory process by attracting more mast cells to the site of injury. This may cause an increase in blood flow which can be beneficial in the sub-acute phase of tissue injury. As blood flow may be increased it is not advised to use ultrasound immediately after injury.

Ultrasound may also stimulate the production of more collagen which is the main protein component in soft tissue such as tendons and ligaments. Hence ultrasound may accelerate the the proliferative phase of tissue healing. It is thought to improve the extensibility of mature collagen and so can have a positive effect to on fibrous scar tissue which may form after an injury.

Application of ultrasound:

Ultrasound is normally applied by use of a small metal treatment head which emits the ultrasonic beam. This is moved continuously over the skin for approximately 3-5 mins. Treatments may be repeated 1-2 times daily in more acute injuries and less frequently in chronic cases.

Ultrasound dosage can be varied either in intensity or frequency of the ultrasound beam. Simply speaking lower frequency application provides a greater depth of penetration and so is used in cases where the injured tissue is suspected to be deeply situated. Conversely, higher frequency doses are used for structures that are closer to the surface of skin.

Contraindications of ultrasound

As ultrasound is thought to affect the tissue repair process and so it is also highly possible that it may affect diseased tissue tissue in an abnormal fashion. In addition the proposed increase in blood may also function in spreading malignancies around the body. Therefore a number of contraindications should be followed when using therapeutic ultrasound:

Do not use if the patient suffers from:

  • Malignant or cancerous tissue
  • Acute infections
  • Risk of haemorrhage
  • Severely ischeamic tissue
  • Recent history if venous thrombosis
  • Exposed neural tissue
  • Suspicion of a bone fracture
  • If the patient is pregnant
  • Do not use in the region of the gonads (sex organs), the active bone growth plates of children, or the eye.
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