There is an old quote from Fausto Coppi, the most successful Italian professional cyclist racing in the mid-twentieth century, in which he reportedly suggested to “ride a bike, ride a bike, ride a bike”.
When it comes to getting fit, cycling training can be relatively simple and, especially for beginners, training volume is the most influential factor. As such the suggestion to “ride a bike, ride a bike, ride a bike” might well be all that’s needed. Having said that, any efforts to further improve your fitness level should consider a well planned distribution of training load: the right mix of volume and intensity. If training volume can easily be tracked with a measure of time (hours) or distance (kilometres) ridden each week (for example, pro cyclists ride on average more than 20 hours per week), defining intensity might be trickier.
Around a century ago exercise intensity was categorised as either “easy” or “hard”. Then, from the 60s the concept of threshold(s) was introduced (link to a commentary paper) leading to exercise intensity being categorised in three zones: moderate (below threshold), heavy (threshold), and severe (above threshold). It’s fair to say that the use of the term “threshold” can be quite confusing, in fact there have been more than 25 different definitions published in research papers over the years.
Nowadays some training software and/or coaches use up to 5 or 7 training zones, but the concept of threshold is still the core idea behind these multilayered methods. The good news is that, from a practical point of view, there are some valid ways to recognise your threshold based on simple methods. A couple of examples are the Talk Test (link to research paper) and Borg’s rating of perceived effort (link to research paper). The Talk Test requires to exercise while talking and to define whether it’s possible to talk in full sentences, talking in short phrases, or talking in single words. These three different “conditions” are aligned with the above mentioned exercise intensities: moderate, heavy, and severe.
Another simple approach is to use Borg’s scale (0-10) to rate the individual perception of effort. According to Borg’s scale, 3/10 corresponds to a “moderate” effort, 5/10 “heavy” and 7/10 “very strong”, effectively matching the above mentioned moderate, heavy and severe intensities. Despite its apparent simplicity, this is a scientific valid method to determine training intensities.
As for how much threshold is needed, that is much bigger question for another day!