Question: It seems as though everyone has a single-speed mountain bike to train on these days. Am I missing out on something?
Single-speed (SS) training isn't just for dedicated single speed racers. All bike racers interested in improving their weaknesses in a fun and specific way can benefit from riding and training on a single speed.
In the image below, you can view a Quadrant Analysis (QA) that was generated using Power-Tap data collected from one rider on both a geared mountain bike (in yellow), and a single-speed mountain bike (in red). This QA compares the physical demands of each mountain bike (MTB) ride. The rides were also similar in intensity (about IF .8).
Each point within the QA plot shows the pedal force and pedal speed (think cadence—the vertical line corresponds to a cadence of 85). QA helps to identify the neuromuscular demands of a cycling genre. What's striking in this plot are the relative differences between SS MTB and geared MTB demands in terms of force and cadence. The iso-power lines illustrate that when pedal speed (cadence) gets very low, pedal forces must be very high to maintain power.