After skipping for about a month, I noticed a slight discomfort in my knees. Nothing major, but noticeable. I skip with decent cross-training shoes on, on a carpet covered concrete floor. Concerned about the pain until I could secure a decent, high-density foam mat, I turned to jogging to build my cardio. The first run went excellent, considering I hadn't ran in years. However after the second run, my knees were burning. I only ran 3k and wore a decent pair of Nike running shoes. The next day, tapping on my lower knee joint resulted in a very uncomfortable sensation. I decided not to run or skip for a week. Over the course of the week, the "resting state" discomfort/pain in my knees did decrease, however any time I'd run a few steps, run up stairs, or jump and land flat footed, there was a noticeable aching in the lower knee joint. Not a sharp pain or a jolt, but an ache. At the close of the week-off (today, August 3rd) I tried skipping. After a few minutes, the aching was noticeable to the point that I was losing my focus and not skipping well. So I stopped. Is it normal to experience deep aching in the knees after only two jogs? Am I on the road to having fuxxed knees? Some sound advice would really be appreciated.