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Physical modalities (heat, cold, ultrasound, TENS) and therapeutic exercise
Each physical modality has its own depth of action and contraindications: superficial heat warms a few centimetres, ultrasound heats deep down to bone, and diathermy is forbidden near metal and pacemakers — and the exam question is almost always "what is forbidden for this patient".
Why it matters in the exam
Superficial heat (hot packs, paraffin, infrared) reduces pain and stiffness and increases flexibility before stretching. Deep heat: therapeutic ultrasound especially heats the bone-tendon and ligament interface, and shortwave or microwave diathermy. General contraindications to heat: insensate skin, poor blood supply, bleeding tendency, acute inflammation and oedema, malignancy in the area, and a patient who cannot report pain. Ultrasound is forbidden over a pregnant uterus, over the eyes and testes, over malignancy and over an exposed spinal cord after laminectomy, and used with care over growth plates; it is allowed over metal implants. Diathermy is forbidden with metal, a pacemaker or an electronic implant.
Cold reduces pain, swelling, muscle spasm and nerve conduction velocity; it is forbidden in Raynaud phenomenon, cold urticaria, cryoglobulinaemia and ischaemia. TENS reduces pain by "gate control" and release of endogenous opioids; it is forbidden over the carotid sinus, over a pregnant uterus and in a patient with a demand pacemaker (or used with great care). Neuromuscular electrical stimulation (NMES) is used to strengthen muscles and prevent atrophy.
Therapeutic exercise: in isometric contraction muscle length does not change; in isotonic concentric contraction the muscle shortens, and in eccentric contraction it lengthens under load — producing more force for less energy and causing more delayed muscle soreness, and it is the basis of treatment for tendinopathy (for example of the Achilles tendon). In isokinetic contraction speed is constant and a special device is needed. An "open chain" exercise — the distal limb is free (for example seated knee extension); a "closed chain" exercise — the distal limb is fixed (squat), with less shear force on a reconstructed ACL. Principles of strengthening: progressive overload and specificity.
Key points
- Superficial heat — superficial; ultrasound — deep.
- Diathermy is forbidden with metal and pacemakers.
- Cold — pain and swelling; not in Raynaud.
- TENS — not over the carotid sinus or a pregnant uterus.
- Eccentric — tendinopathy; closed chain — ACL.
Summary table
| Modality | Depth or action | Forbidden in | Allowed or note |
|---|---|---|---|
| Superficial heat | Superficial layers | Insensate skin, ischaemia, bleeding, malignancy | Before stretching |
| Ultrasound | Deep heat, bone-tendon interface | Pregnant uterus, eyes, testes, malignancy, exposed spinal cord | Allowed over metal implants |
| Diathermy | Deep heat | Metal, pacemaker, electronic implant | — |
| Cold | Reduces pain, swelling and conduction | Raynaud, cold urticaria, cryoglobulinaemia | Acute injury |
| TENS | Gate control | Carotid sinus, pregnant uterus, demand pacemaker | Chronic and acute pain |
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Sources
- Braddom's Physical Medicine and Rehabilitation, 6th edition (2021) — Physical Agent Modalities; Therapeutic Exercise
- DeLisa's Physical Medicine and Rehabilitation: Principles and Practice, 6th edition (2019) — Therapeutic heat and cold, electrical stimulation
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.