By integrating many different types of problems that a student has to solve together, you increase learning.
That’s the basic concept behind interleaving. It is like weaving, except instead of weaving various threads of fabric together, you are weaving various threads of information together.
In the paper by Rohrer, et al. called The benefit of interleaved mathematics practice is not limited to superficially similar kinds of problems, the authors attempt to show that the research on this kind of thing is applicable to a classroom setting (or in our case, a gym setting!). (I discussed another paper of Rohrer’s here.)
Here’s the abstract (bold is mine):
Most mathematics assignments consist of a group of problems requiring the same strategy. For example, a lesson on the quadratic formula is typically followed by a block of problems requiring students to use that formula, which means that students know the appropriate strategy before they read each problem. In an alternative approach, different kinds of problems appear in an interleaved order, which requires students to choose the strategy on the basis of the problem itself. In the classroom-based experiment reported here, grade 7 students (n = 140) received blocked or interleaved practice over a nine-week period, followed two weeks later by an unannounced test. The mean test scores were greater for material learned by interleaved practice rather than by blocked practice (72% vs. 38%, d = 1.05). This interleaving effect was observed even though the different kinds of problems were superficially dissimilar from each other, whereas previous interleaved mathematics studies had required students to learn nearly identical kinds of problems. We conclude that interleaving improves mathematics learning not only by improving discrimination between different kinds of problems, but also by strengthening the association between each kind of problem and its corresponding strategy.
So by making students solve different kinds of problems, going back and forth between each kind, the students got better at distinguishing between each kind, and they were better able to apply the right problem-solving-strategy to the problem in front of them.
In short, interleaving made the students better problems solvers, and this worked at least as well when the types of problems were quite different from one another.
In a gym setting you can think of it this way. It’s like learning how to snatch and squat at the same time — two exercises which are remarkably different in approach. Rather than learning the snatch and clean at the same time — two exercises that are superficially quite similar.
I’d make a further claim based upon my own experience that it might be better to keep the types of problems different — by keeping the kinds of problems very different, it will make the learning of what makes them different more clear when you go back and forth. Perhaps over time, this may help the student learn what makes the superficially similar lifts (like snatches and cleans) more different than they appear at the outset by giving them practice at the art of analytics — seeing differences that are subtle and similarities that are obscured by superficial variance.
Now go lift something heavy,