I hiked for two days in the mountains, distance more than 3.75 miles elevation gain of 3900 ft with a 30 lb backpack. GPS was spotty and the activity function did not appear to be working. It kept showing as a completed activity when I was out of GPS range. Since I would have had to stop hiking frequently I did not save it. The Garmin did not track the steps, floors climbed or heartrate exertion level for either hike. I have had the Garmin for six months and it has seemed to track my daily data fairly accurately including biking and hiking but I have usually been in areas where there is access to GPS. I have installed the most recent update. Any suggestions are welcome even if there is a better option than the 4s.