During your physiotherapy sessions, your therapist is led to choose from various modalities to reduce your pain. His choice may be for an electrotherapy device, such as TENS (Transcutaneous Electrical Nerve Stimulation).
The TENS, combined with other manual therapy modalities, is effective in the short-term reduction of acute pain related to trauma, such as an ankle sprain, and chronic pain such as long-standing low back pain .
The physiotherapist will decide, depending on the condition presented, what will be the parameters to enter the device in order to properly treat the pain. Indeed, the action mechanism of the TENS will be modified according to the data that will be entered.
They are two main action mechanisms:
- Gate activation
- Endogenous opiates
Have you ever rubbed your knee after hitting it on something? TENS uses the same principle; By adjusting the parameters of the TENS, the machine stimulates the skin and the sensitive nerves near the painful area. This comes to numb the pain and it becomes less detectable by the brain. In acute pain, sensory nerves that specifically transmit pain (D and C fibres) are irritated and send their unpleasant message to a section of the spinal cord, which in turn passes it on to the brain. This same section of the spinal cord receives the sensory nerves which transmit the sensations of touch / vibration / numbness ( ẞ and fibres). By adjusting the parameters of the TENS adequately, it is able to numb the ẞ and fibres. This great non-painful stimulation ensures that the section of the spinal cord that is irritated by the pain of the injury will be over-stimulated by numbness, which will inhibit the sensation of pain in the brain. The sensation felt under the electrodes is a very strong but not painful numbness.
Thus, the brain feels less pain, because the numbness of the TENS “tricks” the brain by inhibiting pain at the level of the spinal cord.
This method is used in chronic pain cases. It is known that during chronic pain, changes in the plasticity (ability to change) of the brain occur. Then, the use of the mechanism seen above will not be effective, because this one acts only at the level of the spinal cord. Thus, by modifying the parameters of the TENS, it is possible to stimulate other sensory fibers which will act directly on the brain. In this way, a substance, called endogenous opiates, will be secreted and will act as a powerful analgesic directly in the “computer” of pain that is the brain.
The advantage of this method is that the analgesic effects persist longer, about 6 hours, but it is noteworthy that this is more painful on the skin where the electrodes are positioned.
The therapist will strategically place electrodes at the painful area to be treated and gradually increase the intensity according to the patient’s tolerance. A very strong numbing sensation, but still comfortable to treat acute pain. To treat chronic pain, reaching the pain threshold is recommended.
TENS has clinically proven itself as a temporary analgesic. It is not, however a “magical” device. Indeed, other interventions in manual therapy and adequate specific exercises must be applied jointly in order to optimize the effectiveness of the physiotherapy treatments.