Definitions, Heat, Ice

Receptors

• Mechanoreceptors → detect mechanical stimuli such as touch, pressure, movement, and tension.

• Baroreceptors → detect changes in blood pressure.

• Chemoreceptors → detect chemicals or changes in chemical substances.

• Thermoreceptors → detect changes in temperature.

• Photoreceptors → detect light and are involved in vision.

Pain gate fibres

• A-delta fibres → larger and faster-conducting due to their thin myelin covering.

  • Responsible for sharp, well-localised pain that occurs first.

  • Activated by mechanical and thermal stimuli.

  • Are free nerve endings that detect painful pressure and temperature stimuli.

• A-alpha fibres → primary sensory receptors of the muscle spindle and Golgi tendon organ.

• A-beta fibres → act as secondary receptors of the muscle spindle and contribute to cutaneous mechanoreception (sensation from the skin).

Cryotherapy

• Cryotherapy → uses cold to lower local tissue temperature.

• Common cold modalities include:

  • Cold packs

  • Ice massage

  • Cold baths

  • Vapocoolant sprays

  • Cold compression units

• Physiological effects of cold:

  • ↓ Pain

  • ↓ Blood flow

  • ↓ Edema (swelling)

  • ↓ Inflammation

  • ↓ Muscle spasm

  • ↓ Metabolic demand

Effects of heat (10)

Physiological effects of heat

• Core temp: 37°C

  • Hypothermia: <35°C

  • Hyperthermia: >39°C

• Thermoregulation: controlled by CNS.

• Surface temp: varies widely depending on multiple factors.

Localised effects of heat depend on:

• Tissue volume + characteristics

• Ability to dissipate heat (blood supply)

• Rate of temp rise

• Temperature tissue reaches

Cellular:

• ↑ temp → ↑ chemical reactions + metabolic activity (13% ↑ per 1°C)

• ↑ O₂/nutrient requirements + ↑ waste products

• Activity ↑ to a peak, then declines.

• >45°C → protein damage → cellular destruction/burns

Circulation:

• Skin → vasodilation → ↑ blood flow/redness

• Deep tissue → vasoconstriction from blood diversion to surface

• BUT ↑ muscle metabolism → vasodilation

• Depth of heating affects these processes.

Collagen:

• Heat changes viscoelastic properties → may facilitate stretch (evidence conflicting).

Muscle tone:

• Heat may ↓ increased muscle tone from peripheral mechanisms.

• ↑ Golgi tendon organ firing → ↑ inhibition.

Pain:

• May ↓ pain from muscle spasm/ischaemia.

• ↑ nerve conduction velocity may affect pain mechanisms.

Performance:

• Muscle strength ↓ immediately after heating

• May ↑ above pre-treatment levels 2 hrs later.

Healing:

• Heat ↑ bleeding, oedema, chemical activity + nociception.

• At 38.6°C: ↑ O₂ uptake + blood flow → ↑ O₂, nutrients + white cells.

• Early healing: potentially detrimental.

• Later healing: potentially beneficial.

Systemic:

• Generalised vasodilation + possible ↑ core temp

• ↓ splanchnic blood flow → heat transported to surface

• Sweating → cooling

• Humidity → sweating less effective

• Risks: heat illness, swelling, rash, water/salt deficiency

• Heat stroke: >41°C → CNS control systems fail.

Effects of heat table

Modalities of heat therapy: WAX

• Paraffin wax + mineral oil in a temperature-controlled bath: 42–50°C.

• Wax is better tolerated than water at the same temp because it has a lower specific heat → releases less energy when cooling.

• Limb is dipped + withdrawn repeatedly to let wax set: 6–12 times.

• Then wrapped in an insulating layer.

• Wax can be cleaned + reused.

• Do NOT put used wax directly back into the bath.

Indications:

• Softens adhesions + scars on skin

• Proliferative & remodelling stages of healing

Contraindications / Precautions

• Wounds

• Wax contamination

• Allergy

• Acute dermatitis → may be worsened

• Defective thermal sensation

• Highly flammable → requires safety measures

• Wax can make the floor very slippery.

Modalities of heat therapy: HOT PACKS

Dry packs/pads

• E.g. heat-retentive gels, hot water bottles, wheat/microwave bags

• Final temp: ~40–42°C

Moist packs/pads

• Immersed/kept in hot water (hydrocollator)

• Cool more quickly than dry packs → may need replacement during treatment.

Modalities of heat therapy: Radiant Heat (Infrared Lamp)

• Superficial thermal agent

• Uses electromagnetic radiation between microwaves + light → produces heating.

• Limited evidence for efficacy in:

  • Pain → old studies; recent work suggests ↑ nerve conduction → may ↑ nociception.

  • Joint stiffness → evidence based on 1 study / 2 participants.

  • Skin lesions e.g. fungal infections.

• NOT for open wounds → can cause further damage.

Modalities of heat therapy: HYDROTHERAPY

Whirlpool Baths

• Use hot water to heat tissue.

• Allow localised treatment.

• Water temp: 36–41°C.

• Water movement stimulates skin receptors → may activate the pain gate mechanism.

Hazards & Detrimental Effects

• Impaired sensation → ↑ risk of burns.

• Faulty equipment → ↑ risk of burns/injury.

• Contact techniques + wounds → risk of infection + further tissue damage.

• Open wounds → heat can cause further damage.

• Fertility: heating may temporarily lower sperm count.

• Infants: risk of apnoea.

• Elderly: risk of dehydration, dizziness + headaches.

Contraindications & Precautions

Absolute contraindications:

• Lack of thermal sensitivity

• Recent bleeding/haemorrhage in area

• Devitalised skin e.g. after deep X-ray treatment

• Certain skin conditions e.g. skin carcinomas

Use caution with:

• Impaired local circulation

• Damaged/infected tissue → risk of breakdown

Before applying heat:

• Perform a thermal skin test

• Check equipment

• Educate patient on expected sensations.

Cryotherapy

Cryotherapy

• Cryotherapy = local/general cooling of the body for therapeutic purposes.

• Involves transfer of energy away from the tissue.

• Cooling depends on:

  • Temperature difference between surfaces

  • Thermal conductivity of tissue

  • Duration of application

  • Size of area being cooled

Physiological effects of cooling

Physiological Effects of Cold

• ↓ Majority of cellular processes (freezing causes damage).

• Vasoconstriction of cutaneous vessels → CIVD (cold-induced vasodilation) may follow.

• Peripheral nervous system: ↓ nociceptive effects via competing impulses.

• At 4°C: nerves stop firing.

• ↓ Blood flow in muscle + deep tissue.

• Muscle: ↓ time to contraction, same force.

• ↓ Muscle tone.

• Tissue repair: cold has both positive + negative effects.

Cold — Inflammatory Phase

• Very effective during the inflammation stage of healing in soft-tissue injuries.

• Promotes vasoconstriction + more viscid blood.

• Pressure over wound → haemostasis.

• Prolonged/intense cooling → delays clotting.

• Prompt cooling of skin burns → reduces tissue damage.

• Cooling ↓:

  • Swelling

  • Production of irritants

  • Pain

  • Cell necrosis reactions

  • Nociceptor firing speed.

Efficacy of Cryotherapy

Evidence supports cryotherapy for:

• Pain

• Muscle spasm

• Muscle spasticity

• Chronic inflammation + joint effusion

Cryotherapy modalities

Commercial Cold Packs

• Plastic bags containing water + anti-freezing solids.

• Silica gel is most common.

• Stored at −5 to −10°C.

• Apply for ~20 min.

• Cover with a towel → reduces risk of ice burn.

• Towel should be wet, not frozen.

🧊 Cryo/Cuff

• Provides compression + ice therapy.

• ↓ Swelling + pain and may ↓ need for analgesia.

• Can provide cryotherapy for hours.

• 3 main parts:

  • Cuff: pouch filled with ice-cold water.

  • Tube: connects cuff → canister; allows water exchange.

  • Canister: holds ice + water.

• Replace ice every 6–8 hours.

Ice Immersion

• Cold tap water + flaked ice: 50:50

• Temperature: 16–18°C

• Duration: 15–20 min

• Agitate water every 5 min

• If water is 10°C: intermittent immersion → 1 min at a time

• Mainly used for extremities.

Cold Packs

• Flaked ice folded in damp terry-towelling.

• Towel may be wrapped in a plastic sheet.

• Duration: ~20 min.

• Water/run-off water creates an insulating layer → keeps skin at 5–10°C.

• Neater method: flaked ice in plastic → wrapped in towel.

• Oil on skin ↓ risk of ice burn.

Ice Massage

• Solid ice block on a wooden stick or in a polystyrene cup.

• Muscle stimulus:

  • Stroke for 4 sec over the same dermatome as the muscle being activated.

  • Commonly used in Bell’s palsy → stroked over the cheek.

• Can also be used over trigger points.

• Pain management: slow circular movements over an area up to 15 cm².

Cold — Hazards & Detrimental Effects

• Ice burns:

  • Mild → erythema + tenderness for a few hours; subsides after 1–2 days.

  • Severe → fatty necrosis + frostbite, lasting up to 3 weeks.

• Neural damage to superficial nerves → axonotmesis.

• ↑ Collagen stiffness → consider this when planning mobilisation (MOB).

Cold — Precautions

• Open wounds

• Hypertension or hypotension

• Poor thermal/heat sensation → perform thermal skin test

• Avoid treating very large areas → risk of systemic effects

• Monitor all treatments for signs of cold burns.

Cold — Contraindications

• Acute febrile illness

• Cardiac disease

• Peripheral vascular disease

• Vasospasm / Raynaud’s disease

• Cryoglobinaemia → abnormal blood proteins react at low temperatures → may block vessels

• Cold urticaria → hives/swollen skin triggered by cold

• Patient dislikes cold

• Axonotmesis → peripheral nerve injury

• Sensory deficiency → cooling causes partial sensory loss → ↑ risk of tissue damage.