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Physical Modalities are physical agents that produce a specific therapeutic response. This review focuses on most commonly used physical modalities including heat (superficial and deep heat), cold, sound, electricity, mechanical forces and light.

Superficial heat

  • Commonly used superficial heat modalities include: hot packs, heating pads, paraffin bath, infrared and fluidotherapy. The heat penetration is usually less than 1 cm.1
  • Physiologic effects of heat: pain relief, increase in local blood flow, metabolism and elasticity of connective tissues.2 Heat increases bleeding and edema and may exacerbate acute inflammation.
  • Methods of heat transfer: conduction is transfer of heat between two objects at different temperature through direct contact (example: hot packs, paraffin bath); convection is transfer of heat by fluid circulation (liquid or gas) over the surface of a body (example: fluidotherapy); conversion is changing of one energy form into another (example: ultrasound, radiant heat)
  • Indications: Heat is usually used for subacute and chronic conditions, can reduce pain and muscle spasm, relax skeletal muscles, and decrease joint stiffness.
  • Contraindications: patients with peripheral vascular disease, bleeding disorder, local malignancy, acute inflammation or trauma, edema, infection, open wounds, over large scars, patients with impaired sensation (neuropathy) or impaired ability to communicate (dementia or dysphasia).

Deep heat

  • Deep heat modalities include ultrasound, shortwave diathermy (SWD) and microwave diathermy (MWD). Heat penetration can be 3-5 cm or more without overheating underlying subcutaneous tissue or skin.
  • Ultrasound is the most commonly used deep heating agent. The ultrasound machine converts electrical energy into acoustic energy via the piezoelectric effect. The physiologic effects of ultrasound can be divided into thermal and non-thermal effects (cavitation, acoustic streaming, and standing waves). Ultrasound has been widely used in the treatment of various soft tissue disorders including bursitis, tendinitis, degenerative arthritis, musculoskeletal pain, contractures, and promotes wound healing.3
  • Ultrasound contraindications: Besides the superficial heat contraindications above, specific ultrasound contraindications include: over eyes, pregnant uterus, malignant area, near the heart, brain or spine, laminectomy sites, epiphyseal plates of children and patients with pacemakers.
  • Ultrasound precautions: metal plates, screws, pins, external fixators, and joint replacement components.
  • SWD and MWD convert electromagnetic energy to thermal energy. SWD has good bone penetration, commonly used to heat large area of deep tissues and within the joints, such as hip, knee or ankle. MWD has more superficial heat penetration compared to SWD and ultrasound. It is commonly used to heat superficial muscles and shallow joints.
  • SWD and MWD contraindications: metal items, contact lenses, gravid or menstruating uterus, and skeletal immaturity. MWD increase the chance of miscarriages among pregnant therapists.4


  • Common cold modalities include cold packs, ice massage, cold baths, vapocoolant sprays, and cold compression units. These modalities lower local tissue temperature.
  • Physiologic effects of cold: decreases pain, blood flow, edema, inflammation, muscle spasm, and metabolic demand.2
  • Depth of penetration depends on the intensity and duration of cold application. At least 15 minutes is necessary to achieve analgesia effect, 20 minutes is the usually recommended treatment duration.5 Treatment time for ice message is usually 7-10 minutes. Vapocoolant sprays use Fluori-Methane spray to produce abrupt temperature change over a small surface area. The spray can stimulate Aβ fibers to reduce painful arc and decrease muscle spasm.
  • Indications: acute inflammation and edema, spasticity, pain, arthritis, bursitis, muscle strain and ligament sprain, muscle spasm, and myofascial trigger points.
  • Contraindications: Hypersensitivity or poor tolerance to cold, Raynaud’s disease and phenomenon, peripheral vascular disease, open wounds, cryoglobulinemia, paroxysmal cold hemoglobinuria, patients with impaired sensation (neuropathy) or impaired ability to communicate (dementia or dysphasia).


  • This modality uses electricity to stimulate nerve or muscle via electrodes.
  • Common types of electrotherapy: transcutaneous nerve stimulation (TENS), interferential therapy (IFT), neuromuscular electrical stimulation (NMES), and iontophoresis.
  • Indications: acute and chronic pain, neuromuscular disease, joint effusion and edema, disuse muscle atrophy, wound and bone healing.
  • Contraindications: over carotid sinus, heart, pregnant uterus or infected area, pacemakers, AICDs, battery operative implant devices (intrathecal pumps, spinal cord simulators, etc.), seizure disorder, active hemorrhage, malignancy, circulatory impairments, arterial or venous thrombosis, thrombophlebitis, decreased sensation, and atrophic skin.6
  • Mechanism of action for pain reduction: There are two postulated theories. First, by stimulating large myelinated afferent, A-beta fibers can block the transmission of pain signals to the brain (gate control theory). Secondly, electrical stimulation stimulates body’s production and release of endogenous opioids and neurotransmitters. High frequency (HF) and low frequency (LF) TENS activate different opioid receptors. LF TENS activate mu receptors while HF TENS activate delta receptors. As most opioid analgesics work on mu-opioid receptors, HF TENS is more effective in treating opioid tolerant patients.7

Mechanical force

  • Spinal traction and deep message are two commonly used examples.
  • Physiological effect and mechanism of action: spinal traction can provide a pulling force to the spine, cause vertebral joint distraction, and provide stretching to the ligament, muscle and facet joint5, reduction of compression and nerve root and disc irritation.
  • Indications: Disc herniation with nerve impingement, spondylolisthesis, narrowed intervertebral foramen, degenerative facet joints, joint hypomobility, discogenic pain, and muscle spasm.5
  • Contraindications of spinal traction: spine malignancy, osteoporosis, osteomyelitis, fracture, instability (Rheumatoid arthritis, Down syndrome, Marfan syndrome, Ehlers-Danlos syndrome, atlantoaxial subluxation), cord compression, congenital spinal deformity, acute sprain or strain, pregnancy, uncontrolled HTN, and cardiovascular disease.

Light therapy

  • Low level energy Laser therapy (LLLT) uses low-powered laser light to produce a biological response in tissue.
  • Mechanism of action: It does not produce thermal effect. Exact mechanism is still under investigation. It is proposed to affect fibroblast function and accelerate connective tissue repair.8 Some research suggests LLLT has anti-inflammatory effect by reducing prostaglandin synthesis.9
  • Indications: It is commonly used to decrease acute and chronic pain and inflammation10,11, stimulate collagen metabolism and promote wound healing.12
  • Contraindications and precautions: Treatment over malignancy, irradiation of the neck region in hyperhidrosis, epilepsy, exposure of the retina, and exposure of the abdomen during pregnancy.13


Paraffin bath

  • Paraffin wax and mineral oil mix in a 7:1 or 6:1 ratio
  • Treatment temperature is between 126 °F to 130 °F (52.5 °C to 54.4 °C)
  • Three techniques:
    Dipping: Dip body parts into paraffin bath and then quickly remove to build coating of wax, repeat 7-12 times, followed by wrapping in wax paper or plastic bag, then cover with towels
    Immersion: Serial dips is followed by immersion in the paraffin bath for 30 minutes
    Brushing: A brush is used to apply paraffin to large body parts.
  • Treatment duration is 20- 30 minutes
  • Commonly used to heat irregular surface such as hands and feet
  • Commonly used for rheumatoid arthritis, osteoarthritis, contractures and scleroderma
  • Contraindicated if patient has open wounds, abrasions or skin infections


  • Hot air is blown through a container holding fine cellulose particles. It is a type of superficial dry heat
  • Temperature range is between 115 °F to 120 °F (46.1 °C to 48.9 °C)
  • Provide desensitization effect by agitation of particles
  • Range of motion exercises are allowed during treatment
  • Should be avoided in infected wounds
  • Commonly used to heat hands, wrists, and arms to decrease pain, edema and stiffness

Radiant heat (Infrared lamps)

  • Light energy is absorbed through skin and converted to superficial heat (depth of penetration <1 cm)
  • Distance from the lamp to skin is usually 20 inches and applied for 20 minutes
  • Heating effectiveness decreases dramatically as the distance from body to lamp increases
  • Dry heat, commonly used for patients who cannot tolerate the weight of hot packs
  • Precautions: burn precautions, light sensitivity, skin drying, use of photosensitizing medications

Ultrasound (US)

  • Mode: continuous vs pulsed. Continued US provides mainly thermal effects while pulsed US emphasizes nonthermal effect
  • Frequency: 0.8-3 MHz. Low frequency US has better heat penetration while high frequency US produce more thermal effect in the superficial area
  • Intensity: determines the strength of the treatment, the upper limit is 3.0 W/cm2
  • Duration: 5-10 minutes per site with a stroking technique
  • Ultrasound gel is needed as a coupling medium. When treating uneven surfaces, the body part can be immersed in degassed water
  • Low-intensity pulsed ultrasound (LIPUS) treatment was shown to promote wound healing and can stimulate bone healing in fresh fractures.14

Phonophoresis (Sonophoresis)

  • Use ultrasound to drive medications into and through skin by increasing cell permeability
  • Treatment parameters: pulsed mode, 1 MHz frequency, stroking techniques, and treat for 5 minutes per site
  • Medications: Corticosteroids or anesthetics (lidocaine)
  • Common uses: Osteoarthritis, bursitis, tendinitis, tenosynovitis, epicondylitis, fasciitis and rapid skin anesthesia

Shortwave Diathermy (SWD)

  • Converts radio wave electromagnetic energy to thermal energy
  • The most commonly used frequency is 27.12 MHz
  • Treatment duration: 20-30 minutes for one body area
  • SWD units can use either capacitor electrodes or inducer cable electrodes

Microwave Diathermy

  • Converts microwave energy to thermal energy
  • Frequency: 915 to 2,456 MHz
  • More superficial heat penetration compared to US and SWD: 1-4 cm

Extrascorporeal Shock Wave Therapy (ESWT)

  • Use high intensity pulsed mechanical waves to treat musculoskeletal disorders
  • Does not produce thermal effect
  • Approved by FDA in the US for treatment of plantar fasciitis and tennis elbow

Cold packs

  • Use of commercial cold pack or ice packs
  • Cover with towel and do not let skin come in direct contact with cold pack
  • Treatment time: onset of numbness is around 20 minutes

Cold compression units

  • Use circulating cold water attached to an intermittent pump unit to provide pneumatic compression
  • Primarily used to treat acute musculoskeletal injury with soft tissue swelling or used after surgical procedures
  • Temperature: 45°F (7.2°C)
  • Pressure: Up to 60 mmHg

Ice massage

  • Treatment time: 7-10 minutes
  • Commonly used over small areas by using gentle stroking motions

Vapocoolant sprays

  • “Spray-and-stretch” technique is commonly used: Apply the spray in one direction parallel to muscle fibers at a rate of 4 inches/sec while the muscle is passively stretched
  • Precautions: skin irritation and local freezing

Low-Level Laser Therapy (LLLT)

  • LLLT delivers minimal energies (between 1 and 4 Joules)
  • The depth of penetration is determined by its wavelength
  • The laser probe is applied perpendicular to the targeted treatment area
  • There is no standard treatment protocol

Transcutaneous Nerve Stimulation (TENS)

  • A TENS units is a pocket-size programmable device to apply electrical stimulation through wires and electrodes attached to the patient’s skin
  • Stimulates nerve fibers and provides symptomatic relief of pain
  • Treatment time is normally 30 minutes to 1 hour per session
  • There are different types of stimulators: conventional, acupuncture, hyperstimulation, pulsed and modulated
  • A systematic review found TENS was no more effective than sham or placebo in treating chronic low back pain.15
  • TENS has been found be effective in treating neuropathic pain is spinal cord injury patients16 and painful diabetic peripheral polyneuropathy.17

Neuromuscular Electrical Stimulation (NMES)

  • Application of electrical stimulation above the motor threshold to cause a muscle contraction
  • Can be utilized as therapeutic muscle stimulation or functional electrical stimulation (FES).
  • Therapeutic muscle stimulation: repetitive simulation to paralyzed muscle to minimize atrophy and maintain range of motion
  • FES: Uses electrical stimulation to assist patient in performing a functional task
  • Indications: Muscle strengthening, neuromuscular re-education, cardiovascular conditioning, prevent disuse atrophy, osteoporosis, venous thrombosis, spasticity management, shoulder subluxation in hemiplegic limb, phrenic nerve pacing and urinary incontinence


  • Uses low electrical current to deliver substance bearing a charge through the skin
  • Drives a drug across the skin barrier.
  • Commonly used medications: anti-inflammatory agents like steroids
  • Indications: plantar fasciitis, tendonitis, and bursitis

Spinal traction

  • Provides a pulling force to the cervical or lumbar spine by using manual techniques or pulley system or special device
  • Sustained vs intermittent traction
  • For cervical traction, the neck is flexed between 20-30 degrees while the patient in a sitting or supine position. More than 20 lbs. is applied intermittently for a minimum of 7 seconds of traction time with subsequent rest time. The traction duration is 20-25 minutes. Up to 50 lbs. is needed to cause intervertebral disc separation.5
  • For lumbar traction, the most common position is supine with hip and knees flexed to 90 degrees; > 50 lbs. is required for posterior vertebral separation and >100 lbs. is needed for anterior separation
  • Treatment duration is typically 20 minutes.


The use of therapeutic modalities in rehabilitation has been present for centuries, but there is lack of strong evidence to support its effectiveness and how to use them effectively. Well designed and high qualities of studies are needed, including placebo-controlled or sham-controlled trials as well as trials of comparative effectiveness and trials of combination therapies.


LLLT (low level laser therapy) is a relatively new therapeutic modality. LLLT received FDA approval in 2002 for the treatment of pain associated with carpal tunnel syndrome and in 2004 for iliotibial band syndrome. Most studies have focused on pain management and wound healing. Recently, the effects of LLLT on nerve tissue have been investigated.18,19 However, the literature on LLLT effectiveness is conflicting. More research is needed to further investigate its effectiveness and to determine optimal treatment parameters.1


  1. Fischer E, Solomon S. Physiological responses to heat and cold. In: Licht S, ed. Therapeutic Heat and Cold. 2nd Revised ed. New Haven: E. Licht; 1965:126-169.
  2. Malanga GA, Yan N, Stark J. Mechanisms and efficacy of heat and cold therapies for musculoskeletal injury. Postgraduate medicine. 2015;127(1):57-65.
  3. Dyson M. Role of ultrasound in wound healing. In: McCullough JM, Kloth L, Feedar JA, eds. Wound Healing: Alternatives in Management. 2nd ed. Philadelphia, PA: F.A. Davis Company; 1995:318-345.
  4. Ouellet-Hellstrom R, Stewart WF. Miscarriages among female physical therapists who report using radio- and microwave-frequency electromagnetic radiation. American journal of epidemiology. 1993;138(10):775-786.
  5. Chen W-S, Annaswamy TM, Yang W, Wang T-G. Physical Agent Modalities. In: Cifu DX, ed. Braddom’s Physical Medicine and Rehabilitation. 5th ed. Philadelphia, PA: Elsevier; 2015:369-396.
  6. Strax TE, Grabois M, Gonzalez P, Escaldi SV, Reyna M, Cuccurullo SJ. Physical Modalities, Therapeutic Exercise, Extended Bedrest, and Aging Effects. In: Cuccurullo SJ, ed. Physical Medicine and Rehabilitation Board Review. 3rd ed. New York, NY: Demos Medical; 2014:621-656.
  7. Leonard G, Cloutier C, Marchand S. Reduced analgesic effect of acupuncture-like TENS but not conventional TENS in opioid-treated patients. The journal of pain : official journal of the American Pain Society. 2011;12(2):213-221.
  8. Kreisler M, Christoffers AB, Al-Haj H, Willershausen B, d’Hoedt B. Low level 809-nm diode laser-induced in vitro stimulation of the proliferation of human gingival fibroblasts. Lasers in surgery and medicine. 2002;30(5):365-369.
  9. Sakurai Y, Yamaguchi M, Abiko Y. Inhibitory effect of low-level laser irradiation on LPS-stimulated prostaglandin E2 production and cyclooxygenase-2 in human gingival fibroblasts. European journal of oral sciences. 2000;108(1):29-34.
  10. Huang Z, Ma J, Chen J, Shen B, Pei F, Kraus VB. The effectiveness of low-level laser therapy for nonspecific chronic low back pain: a systematic review and meta-analysis. Arthritis research & therapy. 2015;17:360.
  11. Bjordal JM, Johnson MI, Iversen V, Aimbire F, Lopes-Martins RA. Low-level laser therapy in acute pain: a systematic review of possible mechanisms of action and clinical effects in randomized placebo-controlled trials. Photomedicine and laser surgery. 2006;24(2):158-168.
  12. Mester E, Spiry T, Szende B, Tota JG. Effect of laser rays on wound healing. American journal of surgery. 1971;122(4):532-535.
  13. Navratil L, Kymplova J. Contraindications in noninvasive laser therapy: truth and fiction. Journal of clinical laser medicine & surgery. 2002;20(6):341-343.
  14. Bashardoust Tajali S, Houghton P, MacDermid JC, Grewal R. Effects of low-intensity pulsed ultrasound therapy on fracture healing: a systematic review and meta-analysis. Am J Phys Med Rehabil. 2012;91(4):349-367.
  15. Khadilkar A, Milne S, Brosseau L, et al. Transcutaneous electrical nerve stimulation for the treatment of chronic low back pain: a systematic review. Spine. 2005;30(23):2657-2666.
  16. Celik EC, Erhan B, Gunduz B, Lakse E. The effect of low-frequency TENS in the treatment of neuropathic pain in patients with spinal cord injury. Spinal cord. 2013;51(4):334-337.
  17. Forst T, Nguyen M, Forst S, Disselhoff B, Pohlmann T, Pfutzner A. Impact of low frequency transcutaneous electrical nerve stimulation on symptomatic diabetic neuropathy using the new Salutaris device. Diabetes, nutrition & metabolism. 2004;17(3):163-168.
  18. Hashmi JT, Huang YY, Osmani BZ, Sharma SK, Naeser MA, Hamblin MR. Role of low-level laser therapy in neurorehabilitation. PM & R : the journal of injury, function, and rehabilitation. 2010;2(12 Suppl 2):S292-305.
  19. Rochkind S. The role of laser phototherapy in nerve tissue regeneration and repair: research development with perspective for clinical application. Proceedings of the World Association of Laser Therapy; 2004; Sao Paolo, Brazil.\

Author Disclosure

Thiru M. Annaswamy, MD
Nothing to Disclose

Li Liu, MD
Nothing to Disclose