Microprocessor-controlled exercise equipment that uses a servomotor has the capability to adjust the applied resistive load based on position, velocity, and acceleration. One method of applying the resistive load consists of applying a greater load during the eccentric phase of the exercise motion (muscles actively lengthening) than during the concentric phase of the motion (muscles actively shortening). This technique, called eccentric overloading, can improve the benefits of a strength training session significantly. Although the exercise device can alternate between concentric and eccentric loading based solely on the direction of the bar movement, this is undesirable for several reasons. First, when the velocity is close to zero, the system would rapidly switch between the eccentric and concentric loads. Second, if the exerciser is unable to complete a lift with the concentric load and wishes to lower the bar, the system would apply the high eccentric load, which is highly undesirable. Thus, it is necessary for the system to know the limits of the movement (range of motion, ROM) so that the system can identify when the user has completed the lift and the eccentric load can be properly applied.

Furthermore, it is desirable that the system only applies the resistive load when the exerciser has the bar within the exercise ROM, and applies a minimal base load when the user picks up the bar from the start position. For example, if the exerciser performs bicep curls with 100 pounds, then it would be ergonomically undesirable to require the exerciser to pick up the bar from ground level with 100 pounds applied. It would be greatly advantageous if the system applies a much lower force of, say, 20 pounds while the exerciser picks up the bar, and then applies the full 100 pounds only while the user is performing the bicep curls.

For these reasons, the system needs to adjust to the exerciser's ROM and have the capability of engaging and disengaging the load based on the exerciser's interaction with the bar. In order to maximize the user's experience and to minimize the time spent adjusting the equipment, it is beneficial if the ROM is measured automatically, and if the user can engage and disengage the resistive load with minimal interactions with a user interface. Fully automated exercise microprocessor-based equipment is not currently in use, and the control algorithms for such exercise devices have not yet been developed.

The algorithm developed in this work allows a system to automatically measure an exerciser's ROM and apply the desired eccentric and concentric forces while exercises are performed. The exerciser is able to engage and disengage the resistive load while maintaining the proper exercise position, and without the need to interact with a user interface.

The algorithm does not apply the eccentric load if the user does not complete the concentric lift for safety reasons, and it only applies the load within the ROM. The user only has to hold the bar steady for a number of seconds and the load will be released. The user can then “pick up” the load again by lowering the bar and raising it again. These intuitive methods for engaging and disengaging the resistive forces save time and decrease the chance of injuries.

This work was done by Douwe Bruinsma of TDA Research, Inc. for Glenn Research Center. NASA is seeking partners to further develop this technology through joint cooperative research and development. For more information about this technology and to explore opportunities, please contact http://technology.grc.nasa.gov . LEW-19343-1

NASA Tech Briefs Magazine

This article first appeared in the February, 2017 issue of NASA Tech Briefs Magazine.

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