How much exercise is really enough for a 45-year-old man?

Staying active and exercising enough can be a difficult thing to do when combined with a 40-hour work week and an active family/social life. The American College of Sports Medicine gives guidelines for how much exercise and what intensity is enough to stay physically healthy. Its recommendations are as follows:

• Exercise three to five days each week
• Warm up for five to ten minutes prior to exercise
• Maintain your exercise intensity for 30 to 45 minutes
• Gradually decrease the intensity of your workout, then stretch to cool down during the last five to ten minutes
• If weight loss is your major goal, then participate in your aerobic activity at least 30 minutes for five days each week.

So, based on these guidelines, it sounds like you're doing a good job at four days per week, but be sure to balance the time between aerobic and strength training in order to maintain or increase your lean muscle mass while losing fat mass. Metabolism doesn't slow with age, but rather as a result of losing lean muscle mass. Aerobic conditioning is excellent for endurance and reducing cardiovascular disease risks; and strength training is essential for maintaining muscle mass and bone density.