Michael Bahrke, co-editor of the 2002 book Performance-Enhancing Substances in Sport and Exercise and former project director for a large National Institute of Drug Abuse study on anabolic steroid use, offers this insight.

During the 2006 Tour de France, Floyd Landis's ratio of testosterone to epitestosterone (an inactive steroid isomer of testosterone), the so-called T/E ratio, was higher than 4 to 1, the limit considered by the World Anti-Doping Agency (WADA) as proof of steroid use. (Some reports say Landis's level was as high as 11 to 1.) Later, additional investigation using carbon isotope ratio testing revealed a foreign, prohibited substance as the likely source for the positive test.

Because Landis previously tested within the acceptable ratio limit, speculation as to why a spike in the ratio occurred centered around the possible use of a testosterone patch or gel, which typically provide a relatively low dose of testosterone.

Is it possible a small, single dose of testosterone produced such a quick recuperative effect resulting in a sensational turnaround in performance? Physiologically speaking, most likely not. But it is feasible that the improved performance could have come as a result of a shift in mood level.

Although research indicates that use of large doses of testosterone can significantly increase muscular strength within six to 12 weeks of administration, it is not clear if the performance-enhancing benefits are evident following shorter periods of administration, such as within a few days. One recent study, however, found significant effects in muscular strength (one repetition maximum) and cycle performance (10-second sprint) following three weeks of testosterone administration. Surprisingly, almost half of the subjects (four of nine) remained under the current WADA T/E ratio limit despite receiving testosterone injections. (Additional research is needed to determine if similar results can be produced employing even shorter administration periods, such as within 24 to 72 hours.)

At this time, and with large doses of testosterone, most researchers, clinicians and recipients would generally consider the performance-enhancing effects—especially increases in muscle strength, endurance and size, as well as mood changes and recuperative abilities—to manifest following chronic (that is, weeks of) administration rather than acute, or within hours of, administration. In other words, testosterone would not be used so much for recovery and increased work output during a single Tour stage as it would be for maintenance and improved performance over the course of the entire race.