What Is the Max Amount of Time You Can Exercise Per Day?

With all the benefits of exercise, more must be better, right? Not always. Believe it or not, even exercise can be harmful when you do it excessively.

It's not uncommon for competitive athletes to spend hours a day training for their sport. Even recreational marathoners, cyclists and triathletes may have a very demanding training schedule with several long training sessions each week.

There's nothing wrong with putting in the time. The human body is capable of withstanding great amounts of physical stress, which allows people to carry out amazing feats of endurance. However, how much your body can withstand depends on several factors:

Conditioning: This is the strength of your musculoskeletal, cardiorespiratory and cardiovascular systems and their ability to handle stress. The more you train, the more these systems can handle and the better conditioned you become. The more conditioned you are, the longer you can exercise.

Type of activity: Brisk walking is a lot less hard on the body than sprinting. You can walk for hours a day, but most people can't sprint for as long a time.

Physiological makeup: Endurance athletes may have different physiological characteristics that can enable them to go the extra mile. For example, according to the American Council on Exercise, some people have more of a particular muscle fiber called Type 1, or slow-twitch, muscle fibers.

Slow-twitch fibers are able to provide their own energy source and can therefore sustain activity for an extended period of time. This is in contrast to Type 2 or fast-twitch muscles, which are better able to handle short-lived but more powerful explosive movements.

People tend to be dominant in one or the other type of muscle fiber, especially if they have been training in a specific sport. Endurance runners, for example, are slow-twitch dominant and can typically exercise far longer than power lifters, who are fast-twitch dominant.

Read more: How Many Times Should I Exercise Per Week?

How much you can exercise and how much you should exercise are two different subjects. You can exercise as much as you are able and have the time for. But you should only exercise as much as is safe for your body.

Overexercising often leads to overreaching syndrome, or the more severe overtraining syndrome. In both conditions, the body is not getting enough rest to recover from the amount of physical activity it's doing.

According to an article in the March/April 2015 issue of the American College of Sports Medicine's Health & Fitness Journal, more than 125 signs and symptoms of these conditions have been identified. The most common include:

• Persistent heavy, stiff and sore muscles.
• Persistent fatigue and feeling washed out.
• Increased frequency of infections, colds and headaches.
  
• Chronic injuries.
• Disturbed sleep.
• Poor mental concentration and restlessness.
• Irritability.
• Depression.
• Abnormally high or low heart rate.
  
• Loss of appetite.
• Weight loss.
• Change in bowel habits.

If you experience one or more of these symptoms, it may be a sign you're exercising too much. The first line of treatment is rest. For more severe cases, a complete break from activity may be necessary. To prevent overreaching or overtraining, ACSM's Health & Fitness Journal recommends the following:

• Listen to your body and take a break when you need to.
• Don't increase your training volume or intensity by more than 10 percent each week.
• Alternate periods of intense training with periods of less intense training or rest.
• Rest for 24 to 72 hours between strength workouts.
• Get high-quality sleep and nutrition and stay hydrated.

The U.S. Department of Health and Human Services' physical activity guidelines for adults recommends that all adults get at least 150 minutes of moderate-intensity exercise or 75 minutes of vigorous cardiovascular exercise each week.

For further benefits, you can aim for 300 minutes of moderate-intensity or 150 minutes of vigorous-intensity cardio each week. That's about an hour on the treadmill at a steady moderate pace five days a week or five 30-minute stair-climbing or rowing sessions weekly.

In addition, adults should aim to strength train all their major muscle groups twice a week. You can do two total-body workouts or divide your routine into splits, doing lower body twice weekly and upper body twice weekly. Some people may spend 30 minutes doing a few sets of a few exercises, and some might spend a couple of hours doing more sets and more exercises.

As long as you as you listen to your body and take steps to avoid overtraining, you can do as much exercise as your schedule allows.

Read more: 7 Reasons to Do Moderate-Intensity Exercise More Often