Oval rings oriented to achieve the highest pedaling load at the horizontal crank position per the Rotor and Q ring designs have been around since at least the 1930s and probably before that. That fad does indeed come and go.

Shimano's engineers analyzed the running stride as it pertains to cycling and recognized that the human leg has evolved to deliver maximum force most efficiently with a less acute knee angle, i.e., with the leg closer to full extension, than that seen with circular rings, let alone Rotor or Q rings. In addition, they recognized that the proportion of time spent delivering power is lower per running stride than per pedal revolution with circular rings (let alone Rotor, or Q rings).

Biopace rings are designed to mimic the mechanics of running by increasing the effective gear ratio at the point in the pedal stroke that corresponds to the running foot strike and also increasing the rest period per stroke. The compromise is that the design works best at up to the average running pace of 90 to 95 strides per minute and less well at higher cadences.

Biopace was reviewed in the various bike magazines at the time of its introduction as a brilliant advance in the ergonomics of cycling. Then, after 6 months or so, the reviewers started hearing complaints from racers about the uneven pedal stroke interfering with high-cadence attacks and sprints.

Since the only thing that sells more magazines than "It rules!" is "It sucks!," the benefits of Biopace for the majority of riders for most riding were thereafter ignored, and the design was vilified. The benefits are subtle, and subtle doesn't sell.

The Rotor/Q ring design appeals to common sense; the advantages of the Biopace design are nonintuitive. Common sense isn't always reliable; that's why science was invented. Turn your Biopace rings to any orientation you like, but give the Shimano engineers credit for knowing what they were doing.