An “ISO device” most commonly refers to one of two things: an electrical isolation device used in medical settings to protect patients from dangerous current, or an isokinetic exercise device used in physical rehabilitation to test and rebuild muscle strength. The term also occasionally comes up in reference to ISO-certified medical devices, though that describes a quality standard rather than a specific piece of equipment. Here’s what each one does and why it matters.
Electrical Isolation Devices in Healthcare
An electrical isolation device separates a patient-connected circuit from the main power supply so that stray electrical current can’t reach the patient’s body. This is critical in hospitals because patients are often vulnerable in ways healthy people aren’t: they may have catheters, electrode leads, or other conductive paths that bypass the skin’s natural resistance. A current as small as 10 microamperes delivered directly to heart tissue can trigger a fatal heart rhythm called ventricular fibrillation. For comparison, 80 milliamperes (8,000 times more) is needed to cause the same problem through intact skin on an arm-to-arm path.
Isolated power systems eliminate the risk of electric shock from leakage current, which is the small amount of unintended current that flows through or along the surface of electrical insulation. Canadian medical regulations cap allowable leakage current at 100 microamperes for patient-connected equipment under fault conditions. International standards from the IEC allow up to 500 microamperes under the same conditions, though many safety experts recommend the stricter 100-microampere limit.
How Electrical Isolation Works
There are three main physical methods used to achieve this separation. Optical isolation uses light (typically through components called optocouplers) to transmit signals between circuits with no direct electrical connection. Capacitive isolation passes signals through electric fields using capacitors. Inductive isolation uses transformers to transmit signals via magnetic fields. All three accomplish the same goal: allowing data and power to move between circuits while keeping dangerous current paths physically broken.
In operating rooms and intensive care units, isolation transformers sit between the building’s power supply and the equipment plugged in near patients. If a fault develops in any connected device, the isolated system prevents current from finding a path through the patient’s body to ground.
Isokinetic Exercise Devices
An isokinetic device is a motorized machine that controls the speed of a movement while measuring how much force your muscles produce. The core concept is straightforward: no matter how hard you push or pull, the machine locks the movement to a constant speed set by a therapist. If you push harder, the machine resists more. If you ease up, the resistance drops. This creates a unique training condition where the muscle works at maximum capacity throughout the entire range of motion, not just at the strongest point.
The machine accomplishes this through a braking mechanism, often a magnetic particle brake, that modulates resistance in real time. A control system continuously monitors the speed of the moving limb and adjusts the brake’s counter-torque to keep that speed constant. The result is precise, measurable data on the torque your muscles generate at every angle of the movement.
Clinical Uses
Isokinetic devices have been used in rehabilitation and performance testing for roughly 60 years, with their popularity peaking in the 1980s as research confirmed their value for knee injury assessment. They remain a standard tool today, particularly for evaluating recovery after surgery. The knee is the most commonly tested joint because of how frequently it’s injured and how easily it fits the machine’s setup.
After anterior cruciate ligament (ACL) reconstruction, for example, clinicians use isokinetic testing to measure quadriceps strength in the repaired leg compared to the uninjured leg. Research from the 2020s has established that reaching 90% or better strength compared to the opposite knee is one of the key benchmarks used to determine whether a patient can safely return to sport. Studies consistently show that quadriceps strength deficits persist for extended periods after ACL injuries and reconstructions, making objective measurement essential rather than relying on how the knee “feels.”
Beyond the knee, isokinetic devices can test strength, power, and endurance at the shoulder, ankle, hip, and other joints. They’re used following meniscus repair, rotator cuff surgery, and various musculoskeletal injuries where knowing exact strength deficits guides the next phase of rehab.
ISO-Certified Medical Devices
Sometimes “ISO device” refers to a medical device manufactured under ISO 13485, the international quality management standard for medical device companies. This isn’t a type of equipment. It’s a certification that the manufacturer follows specific processes for designing, producing, and tracking their products throughout their lifecycle. The U.S. Food and Drug Administration now incorporates ISO 13485:2016 as the foundational framework for its own quality system regulation, meaning manufacturers selling in the U.S. must meet these requirements. The standard specifically requires risk management at every stage, from initial design through production and post-market monitoring.
If you see “ISO” on a medical device’s packaging or documentation, it typically signals compliance with this manufacturing standard rather than describing what the device does.