(TL;DR at bottom) I haven't done anything in fitness training, in a dedicated way, for many years, up till deciding a couple of months ago that it was long since time I did. So then I started to put a little regimen together, nothing too strenuous to start with. I quickly found myself able to increase this workout, and have been very pleased with my progress, even in so short a time. It has especially been a long time since I did any kind of running. Part of the reason for this is that I have a little 'dodginess' in one knee that made it awkward to run. The most I ever did was a short jog to get across a busy road, for instance. Even then, I found that I would jog on the balls of my feet/toes, I think to help reduce impact transferring up through the knee. Or whatever, but that's how I found I would do it. Now, I have found that I have built some strength about the knee, and have been running up and down the stairs as part of my new regime (I'm nothing if not unorthodox! lol), which has advanced this greatly. But what I really want to be able to do is proper jogging/running, for a proper cardio-vascular workout if nothing else. So with my new-found ability, I decided to test myself with some jogging on the spot, just to see how far I had come - didn't want to try going out for a jog straight away, partly, I admit, due to self-consciousness, but also in case I did myself an injury and would then find it difficult to get home. I'm glad I did! What I did at home, was 30mins jogging on the spot. I had planned to do just 15, but found I felt quite capable of keeping going, so it got to 20mins, then 25, then finally decided that 30 had given me a decent workout, bit sweaty, a little tired. I did the whole thing on balls of feet/toes. Felt fine, no worries, was actually very happy with my progress. Next day, the calf muscles in both legs were very stiff and painful. Clearly now, I'd overdone it. I have been hobbling about for the last couple of days, and only now are things improving - going to give it a day or two more before carefully going back to exercise. TL;DR So I have a couple of very basic questions about running, strange as it may seem to many: 1. Is it a bad idea to run on the balls of the feet/toes? 2. If my body is not going to give me any warnings or signals whilst exercising that I am overdoing it, how on earth am I going to set my exercise limits?! Help!