hi, im 23, not overweight (actually a bit skinny), non smoker.just had a full medical and heart, bp etc. are perfectly normal. but ive never done regular exercise in my life.i'm determined to get fit, but right now i cant run for more than about minute without a break.and 70 year old dudes were overtaking me today and its embarassing.whats the best way to build my fitness level quickly but without exhausting myself?
Walk uphill and lift weights. You'll notice the difference in a week! Start on a treadmill walking at like 2.0 incline, 3.0 speed, and stay on for 26 minutes (that's how long it takes to start burning fat). Each week, up the time by a few minutes and the speed by a couple notches. Start by working out every other day, then four times a week, and keep moving up.
Do NOT forget to get plenty of sleep and drink lots of water... continue eating healthy and you'll notice the physical results in about six weeks.