The MEDX and Keiser difference

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About Medx – Perfecting the testing of human strength, endurance and range of motion.

Arthur Jones is the legendary founder of Nautilus. In 1986, he founded MedX to perfect the testing of human strength, endurance and range of motion. After years of development and testing, validated by independent research teams at the University of Florida, MedX perfected its medical Lumbar Extension machine. It has since helped tens of thousands of people around the world reduce or eliminate their back pain while increasing their function and quality of life.

Subsequent developments produced the MedX Cervical Extension, Rotary Neck and Torso, and Knee/Hamstring machines, providing the medical community with the first tools capable of producing specific and accurate tests of functional ability along with the finest source of rehabilitative exercise.

MedX applied the knowledge gained from its medical machines to the design of a full line of exercise-only machines. These machines incorporated MedX’s patented compound weight stack which produces less friction and enables several hundred levels of available resistance in increments of 2ft-lbs. This feature reduces user strain and, for the first time, made it possible for individuals to select the exact level of resistance required regardless of their strength.

MedX created exercise versions of its medical machines and branded them the Core Spinal Fitness System™ In less than 20 minutes, twice a week, these five machines focus on the strength, stability, flexibility and endurance of the body’s core, providing a solid foundation for whole body strength.



How it works

Keiser’s singular, foundational focus on improving human performance has resulted in the development of products designed to revolutionize fitness and wellness. Iron and weight stacks have shown results, but they have reached their limits. Keiser represents a fundamental change in approach for challenging and exceeding the status quo.


The rate at which work is done (Power = Work ÷ Time). In the world of fitness, this is defined as the speed in which the resistance (weight) is moved. Power = Force (strength) x Velocity (speed). Training can only be considered functional if it is done at speed. Keiser has created the technology that allows users to train at speed, on every machine, for every movement.

CNS/NMS Training

Keiser pneumatic equipment provides the ability to train the brain and develop more than muscle. Science has proven that the brain “records” the movements you make and the speed at which you make them (muscle memory). Keiser helps retrain the user’s central nervous system and neuromuscular system, allowing for slow training/slow performance or fast training/fast performance.


Keiser’s equipment solutions and programs are developed with the full spectrum of users in mind, from the performance athlete to the older adult.

  • Unilateral or bilateral movements
  • Zero lb/kg starting resistance on most machines
  • Consistent resistance at any speed, from slow to explosive
  • True functional training for strength at any speed
  • Heavy negatives and heavy positives
  • Small-increment, 1lb resistance increases
  • Simple, push-button controls
  • Easy step in, (not up) design


Keiser maximizes muscular and neuromuscular output while minimizing stress on the joints and connective tissue, resulting in a reduced risk of injury.

  • Negligible shock loading to connective tissues and joints
  • Consistent variable resistance curve at any speed