Where’s the rationale for training the upstroke of the cycling action? Is there any scientific evidence to back it up?
In Jeffrey P. Broker’s chapter 5 article on Cycling Biomechanics: Road and Mountain in the second edition of Edmund R. Burke’s book High-Tech Cycling he states on page 133:
Cyclists of all abilities exhibit negative effective forces (i.e., forces applied to the pedal perpendicular to the crank, but in opposition to crank rotation) during the upstroke (180-360 degrees) in steady state cycling. As we have recognised at the Olympic training centre, cyclists correctly sense that they lift or pull the leg up during recovery, but do not lift the leg as fast as the pedal is rising. Thus, the pedal actually helps lift the leg.
Compared to recreational cyclists, elite cyclists generally have reduced negative force effectiveness during the upstroke, and typically, the region of the upstroke during which they exhibit these negative effective forces is reduced.
This final statement gives the rational for training the upstroke musculature. It is possible to improve cycling efficiency by reducing the negative effective forces on the upstroke by using training techniques that train the upstroke musculature.
This can include single leg drills, single leg hill climbing, over gear training, and my personal favourite, and possibly the most effective, over gear training with powercranks.
In my opinion, if you use powercranks at normal crank lengths, this is the only time you should really be using them in your training.