Superficial Heating Modalities Overview

Study Notes

Superficial heating modalities are methods that increase the temperature of the skin and superficial subcutaneous tissue.
These modalities are used to:
- Heat superficial joints with minimal soft tissue covering
- Produce a heating effect in deeper structures like muscles through a reflex mechanism
- Increase the extensibility of collagen tissue by heating it

The extent of temperature rise, the rate of energy addition, and the volume of tissue exposed influence physiological changes.
Therapeutic heating levels are between 40°C and 45°C.
- Hyperemia occurs at these temperature limits.
Increased rate of temperature rise:
- Can lead to tissue damage.

For every 10°C increase in tissue temperature, the chemical activity in cells and metabolic rate increase two to threefold.
This increase in chemical reaction rate leads to increased oxygen uptake.

Increased tissue temperature causes vasodilation, leading to increased blood flow.
Vasodilation occurs due to:
- Axon reflex
- Release of chemical mediators (histamine, prostaglandins)
- Local cord reflexes

Heat is used to provide analgesia and assist with pain and muscle spasm resolution.
Heat elevates the pain threshold by altering nerve conduction velocity and changing muscle spindle firing rates.
- Increased muscle temperature to 42°C decreases type II afferent firing and increases Ib afferent firing from the Golgi tendon organ.
  - This decreases tonic extrafusal fiber activity.
- Superficial heating only reduces gamma efferent activity, causing less muscle spasm.

Heating and stretching can alter the viscoelastic properties of connective tissues.
- This allows residual elongation of connective tissues after stretching and releasing.