Clinical Applications of Iso-Inertial, Eccentric-Overload (YoYo™) Resistance Exercise

Abstract

In the quest for a viable non-gravity dependent method to "lift weights" in space, our laboratory introduced iso-inertial resistance (YoYo™) exercise using spinning flywheel(s), more than 25 years ago. After being thoroughly tested in individuals subjected to various established spaceflight analogs, a multi-mode YoYo™ exercise apparatus was eventually installed on the International Space Station in 2009. The method, applicable to any muscle group, provides accommodated resistance and optimal muscle loading through the full range of motion of concentric actions, and brief episodes of eccentric overload. This exercise intervention has found terrestrial applications and shown success in enhancing sports performance and preventing injury and aiding neurological or orthopedic rehabilitation. Research has proven that this technique offers unique physiological responses not possible with other exercise hardware solutions. This paper provides a brief overview of research that has made use, and explored the efficacy, of this method in healthy sedentary or physically active individuals and populations suffering from muscle wasting, disease or injury. While the collective evidence to date suggests YoYo™ offers a potent stimulus to optimize the benefits of resistance exercise, systematic research to support clinical use of this method has only begun to emerge. Thus, we also offer perspectives on unresolved issues, unexplored applications for clinical conditions, and how this particular exercise paradigm could be implemented in future clinical research and eventually being prescribed. Fields of particular interest are those aimed at promoting muscle health by preventing injury or combating muscle wasting and neurological or metabolic dysfunction due to aging or illness, or those serving in rehabilitation following trauma and/or surgery.

Keywords: clinical trials; eccentric training; flywheel exercise; rehabilitation; skeletal muscle; strength training.

Figure 1

Typical smoothed torque values across a set of 7 maximal repetitions of YoYo™ knee extension exercise in young healthy men. Black line denotes torque; gray line denotes knee angle. Typically, torque increases over the initial three repetitions, whereas from the fourth or fifth repetition, peak torque typically decreases due to fatigue.

Figure 2

Cartoon depicting YoYo™ Leg Press employed in a virtual reality environment. Full arrows highlight the direction of the muscle force during concentric and eccentric actions vs. the direction of the movement; dashed arrows represent the cross-talk between the central nervous system and the skeletal muscle.