I just got back into jogging about a month ago and I'm up to 10 miles per week. When I jog at about 5.5-6mph my heart rate soars to 90% of my max after about 12-15 minutes at this pace, after 30 minutes I slow down to a walk at about 3.5mph, it then takes me about 6-10 minutes to bring my heart rate down to 65%. Does this just mean I'm out of shape and should maybe race walk, keeping my heart rate in a more normal 70-80% range? I'm 5-10 190lbs.