I'm a runner and almost non-cyclist. Once a year or two I participate in the XC race consisting of running-cycling-running. Approximately 6 km + 20 km + 1.7 km. (3.7 mile + 12 mile + 1 mile). Comparing races of different years it is clear that I became better runner, but cycling speed is more or less unchanged. Heart rate for cycling part decreased by ~10 beats, but lactate in the thighs does not allow to go faster. 21:30 min for running and 45:30 for cycling, it's best running time and 5-6 min more than best cycling times, and this is an amateur race without cyclists.
Are the muscles that are used for cycling are useful for the running uphill sections? I'm pretty weak in the uphill running (and even walking) and in general physically
If cycling and running are different, why post-cycling running so hard, slow and... specifically broken? May it be useful to run after such a hit to the running form/technique?