One of my friends, doing her first sprint triathlon, had a theory that basically states that since she will be on the bike a lot longer than she will be swimming or running, she should devote a lot more of her training time to the bike. Is this a good philosophy to go by?
The question of "which sport should I focus on most in my triathlon training" is very common, and a difficult question to answer. More often than not an athlete will want to focus on their favorite sport, which is often the bike, by justifying most of their time during the triathlon will be spent on this sport. This seems the logical and obvious, but it's not quite that simple.
Triathlon is an interesting sport to coach. Triathlon coaches are challenged with a sport that consists of three very different individual sports, and inevitably athletes who have varied needs and wants in terms of how to train each of these sub-sports while properly addressing triathlon as the stand-alone event for which the athlete is preparing.
We can't simply look at each sub-sport through the narrow perspective of duration. Yes, during any triathlon the greatest portion of time will be spent on the bike, but, not necessarily the greatest portion of effort.
While there is no proven formula to compare sport-to-sport demands, a basic rule of thumb is that cycling effort is about a 3:1 ratio when compared to running. Meaning, an hour of running is roughly equivalent to 3 hours of riding. Obviously nutrition, hydration, and athletic background are factors as well, but, for most athletes a 3:1 bike-to-run-effort ratio is pretty dependable.
Therefore, when looking at sprint triathlon, a mid-pack athlete might expect to spend 45 minutes on the bike and 25 to 30 minutes on the run. So, the run represents more than our 3:1 ratio and closer to 2:1. Also, the run is the final event which drives up its energy demands.
Thus, we could argue triathlon training should focus more on the run, right? Ah, but here we run into other issues.