When I first got PCs, I focused on synchronizing the pedals, and then on building muscle. In all of that I realized that wile the right foot, for example, is pressing down the left foot doesn't need to pull up with the same force, but rather just with the same speed. This means that hip flexors, hamstrings, etc. won't get as strong as quads, jsut strong enough to maintain the same speed as the down stroke.

Once I realized this I decided to do some drills to force the weaker muscles to get stronger than the minimum required to match the speed of the downstroke. These may be covered in various videos.

Standing leg isolations 1. I found that an upstroke could be accomplished by hamstrings, or hip flexors, or some combination of both. In may case, I tend to lift with my hip flexors. I found that if I stood up and moved my hips and torso slightly forward, that would force my hamstrings to do all the work in the upstroke. I hope that by isloating the hamstrings, I can have a little more power throughout my rides.

Standing leg isolations 2. This is roughly the same as above but I move my hips back so that I'm over the saddle. This allows me to isolate the hip flexors.

Alternating leg isolations. The videos the rider a rider alternating every 5 pedal strokes. I prefer to do two different modifications. On hilly rides, I alternate every 10 pedal strokes, and on shorter, flatter rides I alternate every mile or so. The idle leg can get cold and stiff, so I can't spend too much time between alternating.

Continuous pedaling. When I first started riding medium distances on my PCs I wouuld ride for a minute then coast for about 10 seconds to let my legs rest. I did two things to address this. On flat roads, I pick a landmark in the distance (telephone pole, parked car) and refuse to stop pedaling until I pass the landmark. No matter how it burns, I keep pedaling. I think that it's better to weed out bad habits early. The second thing I started to do is to find a long grade - it doesn't have to be steep - and do repeats on it. The repeats force me to continue to pedal even when I want a rest. When I first started using PCs, I was on a medium grade and I decided to take a little break. I pulled over, and unclipped my pedals. The problem, I found was that it was nearly impossible to clip back in going uphill. I ended up walking to a street sign, holding it with one hand while clipping in and then got going again. All told, it would have been better to keep pedaling thorugh the discomfort and to avoid that hassle. That was the last time I unclipped on a hill.