Five years after Spitz’s dazzling, biorhythm-fueled performance, Reggie Jackson hit home runs on his final four swings of the World Series, each blast coming off a different pitcher. However, Jackson’s biorhythm cycles were all at their nadir.

Biorhythmist Russ Streiffert had a retort for this seeming refutation of the theory. Streiffert posited that since Jackson’s cycles were all at their low point, he benefited from being recharged and synchronized. To summarize, negative days can be positive. And positive phase days can be negative, since much energy has been expended. Sort of how “good” and “bad” can both mean excellent, I suppose.

In the ballpark of ad hoc hypotheses, Streiffert had hit a grand slam. An even more creative ploy is asserting that some people are a-biorhythmic. So if the person’s results aren’t what the chart shows they should be, biorhythmists can make this claim. Taking the Get Out Of Jail free card even further, we learn that some people are a-biorhythmic just some of the time. Those times coincide with whenever biorhythm theory isn’t confirmed. These ad hoc hypotheses make biorhythm claims untestable and, thus, not scientific. They also make them unverifiable and, indeed, no biorhythm proponent has ever published a paper in a peer-reviewed journal.

Wilhelm Fliess first devised the idea as an offshoot of numerology in the 19th Century. Fliess was fixated with 23 and 28, so he chose those as the number of days in the cycle. A person’s fitness, alertness, and so on would be determined by these rhythms. Despite the hormonal differences in males and females, he gave both genders the same rhythm. This glaring error has never been addressed. It is also problematic that everyone would have the same rhythm despite the diversity in physiology among the population. Also left unexplained is why the cycle would begin at birth.

About a century after Fliess, 33 days become the more popular number. Others have proposed 38, 43, and 53 day cycles. While the methods were overhauled, the results were kept, which is a pseudoscience giveaway. The main idea is that one’s biorhythm foretells what kind of day is ahead. Where one is at in the cycle will determine what attributes are conferred, be it increased agility or susceptibly to illness. The worst day is when all cycles are in a transition phase. These are called Critical Days and they occur about thrice monthly. Rather than pouring over the mounds of data necessary to see if there is a connection, proponents are content to point out Clark Gable had a heart attack on such a day.

Even worse, some biorhythmists count the day before and after a Critical Day as being just as pernicious. This bumps the number of danger days to just past one in four, making any supposed comparison between those days and misfortune statistically meaningless.

Biorhythm proponents advocate keeping a daily log. This would be potentially more valid if the subjects recorded how each day went, then checked their biorhythm charts. Instead, people scan the chart first, then see what happens. This opens them to self-fulfilling prophecies and subjective validation.

This was best demonstrated by Patron Saint of Skeptics, James Randi. He had proponent George Thommen prepare some biorhythm charts. Then a subject followed it for two months and reported a 90 percent success rate. Randi then revealed the subject had been given Randi’s chart. Randi said this was by mistake and the “real” chart was given, with the subject finding it even more accurate. A second ruse was revealed, as this chart was really done for Randi’s secretary. Who knows, maybe Thommen would have detected Randi’s trickery if his alert cycle had been ascending.