Rhythms in Software Development
In Fartlek - Increasing your Sustainable Pace, Erik Meade uses the fartlek concept to talk about sustainable pace in software development. However, the notion of fartlek comes from training e.g., runners. That is, the combination of short, intense work interspersed with longer, lower intensity work increases an athlete's ability to perform both in terms of their base level and their peak performance.
So, in terms of training software developers to become more proficient, there is some validity in intensive learning situations so as to point out the need to improve our ways of doing things. However, the fartlek metaphor doesn't really work in the software development world because the stress of high pressure work doesn't e.g, make us more capable of sustaining a faster base pace or increase our peak performance. The facts are clear that the stress induces worse results and more work (due to the need to e.g., fix the bugs introduced as a consequence of trying to ameliorate the stress) both in the short term and over time.
A more appropriate metaphor for what Erik is talking about is the notion of rhythm. Humans, both individuals and groups, function in rhythms. The rhythms come in various granularities such as daily, weekly, seasonally, etc. and various types such as mental, physical, emotional, and spiritual. In my experience, software developers and managers (and the myriad, inhumane "methodologies" that are used) not only tend to ignore the rhythms in our lives but actively fight against them.
For example, one key aspect in the perennial war between computer "languages for dumb people" and "languages for smart people" is how the language designers choose to either put various kinds of straitjackets on people or give folks plenty of rope to hang themselves with. :-)
The key manifestation of rhythm in agile practices is, IMHO, actually the notion of (very) short cycles, both individually in terms of individual task management (via, e.g., TDD) and group project management (i.e., XP's "iterations" and Scrum's "sprints"). The rapid cycling provides the hooks, if you will, of perceiving the reality of what's been accomplished (or not) and choosing how to adjust moving forward.
I leave it, for now, as an exercise for the reader to delve into how the notion of rhythm fits into the software itself and the systems that we create with that software.