Exercise reduces feelings of stress by design. Remember the stress response is also known as the "fight or flight response" and both "fighting" and "fleeing" are great exercise. Exercise allows the release of endorphins which are key in turning off the stress response. Exercise also improves your circulation-- improved circulation to the brain helps memory and mood. Improved circulation to the skin helps skin look more youthful and improves appearance (and it won't cost hundreds of dollars a bottle) Improved circulation to the genitals reduces the risk or severity of impotence in men and improves arousal in women, and has been demonstrated to improve sexual function in both sexes.
Exercise improves sleep, exercising, at least 2 hours prior to bedtime, will help you fall asleep faster and stay asleep through the night and improves sleep quality. Sleep of course is imperative to good health.
Physical activity also reduces the risk of certain cancers, namely breast, colon, and possibly endometrial and lung cancers may all be reduced by regular physical activity.
In all my years in healthcare the healthiest older people enjoyed some type of physical activity, My very active older patients (70-80 years old) look many years younger and have very few health problems, and rarely, if ever, complain of the "aches and pains" that other people seem to have. They all enjoy their activities and besides the obvious health benefits, it serves as I for one, wish to age like them.
So why do we resist? I see too many people think of exercise as a punishment for being overweight or for eating. Exercise is a reward for the body you love, it is a gift you give yourself. If you can't phathom the idea of working out after WORK -- go play! Research what is available in your area, take tennis lessons, play racquetball, soccer, go dancing. A walk around the block can be refreshing, Play your favorite music or take the time to reflect on things you are grateful for. Being in Nature also helps relieve stress -- Enjoy a hike or bike ride in a local trail.
Whatever you choose to do, you're on the right track by starting some physical activity, start slowly if you've been sedentary up until now. Don't exercise right before bedtime, and if you are at risk for heart disease or if you have heart disease be sure to talk to your healthcare provider first.