Riding inside can build all the fitness you need to perform at your best in outdoor events. There’s no doubt cyclists or triathletes can accomplish all of the high-intensity interval work their outdoor-only counterparts would normally do throughout the year. But particularly with the current focus on polarized training and reverse periodization, high-intensity interval work is typically only 10–20 percent of an athlete’s total annual workload. The other 80+ percent is low- to moderate-intensity endurance riding, and that’s the harder part to replicate entirely indoors. With the emergence of Zwift and other interactive apps, “free riding” at an endurance pace is more appealing than it used to be, and the rise of e-racing is making it possible to feed your competitive drive without riding outside.
Most cyclists and triathletes, however, are training indoors with the intent to participate or compete in events outdoors. The most common scenario is using a mixture of indoor and outdoor training sessions to maximize your available training time. More and more, the percentage of overall training being completed indoors is growing, and training primarily indoors can have both positive and negative impacts on outdoor performance.
The advantage of indoor fitness is the level of control we have over the amount and distribution of intensity. If you want precision in training, you can’t beat riding structured workouts indoors on a smart trainer in erg mode. At the end of a week or a month of training, your power files and training data will be close to perfect because your motivation and willpower played no part in determining your performance. As I have mentioned before, this is also a significant disadvantage to training indoors with erg mode, because you risk losing or not developing the internal drive and expertise for self-pacing.
Perfect training files don’t necessarily equate to optimal preparation for real-world cycling performances. In the Dark Ages, when cyclists and triathletes only rode indoors when they absolutely needed to, the transition back to outdoor group rides and races was pretty seamless. The outdoor skills might have gotten a bit rusty but came back quickly. Now that athletes are spending more and more time riding inside (and building tremendous fitness indoors), there has been a significant dissociation between fitness and skill.
If you have spent hours and hours on a smart trainer or plugged in to Zwift, The Sufferfest, TrainerRoad, Rouvy, FulGaz, or any of the other indoor cycling apps, you may very well have the fitness and power to ride in an outdoor peloton at 30 mph. To be successful and safe in that environment, however, you need the handling skills to ride shoulder to shoulder at that speed, to brake appropriately before corners, and to take good lines through turns. Without those skills, it’s like putting a bunch of brand-new drivers into Ferraris and having them go out on the track with people who have been driving Ferraris for 10 years. Everyone on the track has similar horsepower, but only some know how to drive the car.