Thanks for writing on the forum. We hope to use the forum to share knowledge and yours are a fairly common questions.
Sorry to hear that your Rainier climb didn’t succeed. Although, from the sounds of it there were some valuable lessons. We often learn more from our failures than our successes. Despite not being able to run it seems that your fitness was not an issue on Rainier. So, you have shown yourself that you can prepare without much running by using alternative training. That should be comforting unless you have aspirations to run more anyway. I’ll come back to that in a bit but first……
The high HRs you saw were likely caused by lack of acclimatization to both the heat and the altitude. When your core temp rises the capillaries in your skin dilate which shunts valuable blood to the skin for cooling and away from the working muscles. That means the heart has to beat faster to keep the O2 supply to the muscles high enough. Similarly when you are not acclimated to higher elevations your heart will need to beat faster to make up for the shortfall in O2 at the muscles. I doubt you were well acclimated to either so it makes complete sense to me that you saw higher HRs.
As for running. Throughout our evolution running was an advantageous trait that was selected for and passed on to the next generation. Those that were not good a running didn’t fair well and had less chance to pass their genes on. For the past few thousand years we’ve been at the top of the food chain and don’t need to run down our next meal or out run that sabre tooth tiger. So, not all humans are natural runners any longer. Many need to learn to run. The chances are good that you too can learn to run well and injury free. Baring any serious bio-mechanical defects that place you as an outlier on the Bell curve, that is. Find a good running coach and or a very good PT to do some gait analysis and maybe provide corrective help.
I believe that you need to get 100 miles of running into your legs before you can safely train by running. The connective tissues such as tendons and facia are very poorly vascularized. As a consequence they are very slow to adapt when new stress is placed on them. The most common running injuries involve the lower legs and the most common reason is “too much, too soon”.
We have had good success with our coached clients using a run/walk progression that very gradually increases running duration while shortening the interspersed walk duration during their workouts. For many who have never been able to run without injury or who have not run regularly for years it may take months to accumulate those 100 miles. Ramping up too fast will put you into cycle of injury, recovery, re-injury. Your’s sounds like a classic case of this.
While the actual run/walk progression must be constructed for each individual, a general rule of thumb is: Don’t increase run segment length more than 10% per week. And, do not increase total running time by more than 15% over 3 week.
Running, especially mountain running, seems to transfer very well over to mountaineering and alpine climbing. We have decades of anecdotal experience seeing this evidence. The reveres is not true. Mountain climbing does not transfer to running well at all. Economy is the main reason. Swedish researchers found that economy differences between good and poor runners can easily exceed 40%! That means for any given pace it could be coasting your 40% more energy and O2 consumption then a good runner. No one has that kind of aerobic capacity to waste.
I hope this helps