A good subject..having spent more hours than I would care to recall trying to keep in shape, may I suggest a couple of things which have worked for me [ sixty years young and still learning ]..
Point One: experiment to find the type of exercise YOU ENJOY. For some, it will be jogging or hiking, for others it will be swimming, for others it will be aerobics, tai chi, boxing, weights, etc etc...
which leads to..
Point Two: fitness is a full time job. If you don't believe it, start your favorite exercise regime, practice religiously for a month or so,... and then drop off for a few weeks. Your decline in fitness will be depressing, which leads you back to Point One.
Point Three: Consistency and Persistency... I see a lot of guys at my local gym come and go... dead keen for a couple of weeks, and then they drop away. Instant results are the stuff of dreams and slick marketing.
Point Four: You need a goal... may be it is losing/gaining weight... being able to beat your son at squash... [ mine ] or whatever... otherwise boredom sets in...
Point Five: related to Four... tailor your fitness regime to your pastime... for me it is seakayaking... and all the gym work I do means very little if I don't spend time with my butt in my kayak, actually paddling. Call it 'match' fitness, and it sure helps your mental attitude under stress.
my 0.02c
Peter Rattenbury, Australia.
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"Serve in Love; live by Faith"