Connective tissues surrounding joints (such as tendons, ligaments, joint capsule, adhesions, and skin) are viscoelastic, and often shorten in response to trauma and prolonged immobilization. Static Progressive Stretch (SPS) and dynamic splinting are two fundamentally different techniques used to permanently lengthen shortened connective tissues.

SPS is the incremental, periodic application of stress relaxation (SR) loading. In SR loading, tissue is stretched and held at a constant length, and the amount of force is reduced over time. Therapists often apply SPS manually when treating stiff tissues. JAS devices provide SPS for home use, as an adjunct to clinic therapy.

By contrast, dynamic splinting uses creep-based loading rather than stretch relaxation. In creep-based loading, tissues are continually elongated over time with the application of constant force. Dynamic splints are spring-loaded, tension controlled devices and are available through various manufacturers.

Biomechanical and clinical research proves that stress relaxation/SPS achieves permanent soft tissue elongation faster than creep/dynamic splinting. The proven JAS SPS protocol requires three 30-minute sessions per day to achieve steady and permanent gains in joint ROM. By comparison, dynamic splinting requires 8 to 12 hours per day of continuous wear time to achieve results. This prolonged wear time leads to poor patient compliance, and can lead to secondary complications of joint pain and skin breakdown. (See the Research section for a listing of clinical studies.)