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A 2019 prospective crossover study by Acevedo et al. (Frontiers in Veterinary Science) examined the thermal and extensibility effects of 3.3 MHz therapeutic ultrasound on the calcaneal tendon in 10 healthy anesthetized hound dogs. Four protocols (continuous and 20% pulsed at 1.0 and 1.5 W/cm² for 10 minutes) were tested while tendon temperature was monitored via thermistor needle. Continuous ultrasound at 1.5 W/cm² produced the greatest heating (mean +3.5°C, peak +4.1°C), with most of the rise occurring in the first 3 minutes and rapid cooling afterward. Pulsed modes caused minimal temperature change (<1.7°C). In a separate phase, 10 minutes of continuous 1.5 W/cm² ultrasound increased tarsal flexion by 6.6° (a 5% gain indicating improved tendon extensibility), but the effect was transient and returned to baseline within 5 minutes. The authors concluded that continuous ultrasound safely heats canine tendon and that stretching exercises must be performed immediately during or right after treatment to capture the short “stretching window.”

Core Differences in Application 

•  Continuous wave (100% duty cycle): Delivers uninterrupted energy → thermal effects dominate. Raises tissue temperature 3–4°C+ in collagen-rich structures (tendons, ligaments, joint capsules). Ideal for chronic stiffness, scar remodeling, contractures, or pre-stretching. Requires vigilant monitoring and transducer movement to avoid hotspots. Most heating occurs in the first 3 minutes; sessions are often shorter (3–8 min).

•  Pulsed wave (typically 10–50% duty cycle): Intermittent bursts with cooling periods → non-thermal/mechanical effects dominate (cavitation, acoustic streaming). Minimal heating; promotes cell permeability, protein synthesis, inflammation resolution, and tissue repair. Safer for acute/subacute injuries, edema, or fresh soft-tissue lesions. Sessions can be longer with lower total energy.

Key Takeaways Across Settings

Both modes use the same frequencies (1 MHz deep, 3 MHz superficial) and require coupling gel with slow circular transducer motion. Continuous is thermal-first (chronic conditions); pulsed is repair-first (acute conditions). Overlap exists depending on intensity and duration, but pulsed is generally preferred when heat could worsen inflammation.

Research Validation by Pathology

Evidence is mixed/moderate-quality but pathology-specific:

•  Knee OA: Pulsed ultrasound outperforms for both pain and function; continuous helps pain only.

•  Tendinopathies (e.g., lateral epicondylitis, Achilles/calcaneal): Both modes reduce pain and improve grip/ROM, but pulsed is safer acutely and may better support repair.

•  Acute soft-tissue injuries: Pulsed preferred for non-thermal healing mechanisms.

•  Chronic stiffness/contractures: Continuous provides the targeted heating needed for extensibility.

Benefits are dose-dependent and strongest in collagen-dense tissues. High-quality RCTs remain limited; ultrasound is best used adjunctively with exercise and manual therapy.

Final Clinical Perspective

Knowing the purpose of ultrasound therapy—thermal heating versus non-thermal repair—is essential before accepting any single study (including the canine calcaneal tendon paper above) at face value. Tissue type, acuity of injury, and the exact parameters matter. A deeper understanding of continuous versus pulsed mechanisms empowers clinicians to interpret research critically, tailor protocols to the individual patient or animal, and avoid suboptimal or even counterproductive application. Always match the mode to the clinical goal rather than defaulting to “what the study used.”

Reference List 

1.Acevedo B, Millis DL, Levine D, Guevara JL. Effect of Therapeutic Ultrasound on Calcaneal Tendon Heating and Extensibility in Dogs. Front Vet Sci. 2019;6:185. doi:10.3389/fvets.2019.00185. 

2.Zeng C, Li H, Yang T, et al. Effectiveness of continuous and pulsed ultrasound for the management of knee osteoarthritis: a systematic review and network meta-analysis. Osteoarthritis Cartilage. 2014;22(8):1090-1099. 

3.Physiopedia. Therapeutic Ultrasound. Accessed 2026. physio-pedia.com

4.Ünver HH, et al. Comparing the efficacy of continuous and pulsed ultrasound treatments in lateral epicondylitis: A randomized controlled trial. Turk J Phys Med Rehab. 2021.  

5.Armagan O, et al. Effects of placebo-controlled continuous and pulsed ultrasound treatments in carpal tunnel syndrome. Clinics (Sao Paulo). 2014;69(8):524-528.