Do you dread going to the gym for what feels like hours at a stretch? Or do you avoid working out altogether because you just don't have the time? Then what I'm about to tell you should be music to your ears: sometimes when it comes to exercise, less is more.

It's becoming increasingly clear that too much exercise, particularly long bouts of cardio, can cause more harm than good.

And while most Americans would be well served to exercise more, there's probably no need to work out for more than 45 minutes or so at a time, as long as you exercise correctly and efficiently. In fact, one of the most effective exercises I know of takes just 20 minutes for the whole workout (I'll explain more below)...

When Good Exercise Goes Bad...

Getting your heart pumping with regular cardio exercise is important. As your heart rate rises, the amount of oxygen in your blood improves, and endorphins, which act as natural painkillers, increase.

Meanwhile, aerobic exercise activates your immune system, helps your heart pump blood more efficiently, and increases your stamina over time. But there is a cut off point to these benefits, and if you push your cardio session too long it can actually harm your body, leading to:

• A catabolic state, in which your tissues break down
• Excess cortisol (stress hormone) release, which not only contributes to catabolism but also chronic disease
• Microscopic tears in muscle fibers (which will have trouble healing if you continue over-exercising) and increased risk of injuries
• A weakened immune system
• Insomnia, especially if your workout is in the afternoon or evening

Research emerging over the past several years has now given us a whole new understanding of what your body requires in terms of exercise, and many of our past notions have been turned upside-down. It's now clear that exercising too much can be a serious blow to your health.

Too Much Cardio Can Even Damage Your Heart

One of the best examples of the risks of over-exercising can be gleaned from marathon runners. Running a marathon is often seen as the epitome of fitness and the ultimate show of endurance. But it puts an extraordinary stress on your heart.

According to a study presented at the Canadian Cardiovascular Congress 2010 in Montreal, regular exercise reduces cardiovascular risk by a factor of two or three. But the extended vigorous exercise performed during a marathon raises cardiac risk by seven-fold! Long-distance running also leads to high levels of inflammation that may trigger cardiac eventsⁱ and damage your heart long after the marathon is over.

In a study published in the Journal of Applied Physiology,ⁱⁱ researchers recruited a group of extremely fit older men. All of them were members of the 100 Marathon club, meaning athletes who had completed a minimum of 100 marathons. If running marathons provided cardiovascular benefit this would certainly be the group you would want to seriously examine. So what did they find?

Half of the older lifelong athletes showed some heart muscle scarring as a result, and they were specifically the men who had trained the longest and hardest.

Research has also revealed heart scarring after elite cardio training. Published in the journal Circulation,ⁱⁱⁱ an animal study was designed to mimic the strenuous daily exercise load of serious marathoners over the course of 10 years. All the rats had normal, healthy hearts at the outset of the study, but by the end most of them had developed "diffuse scarring and some structural changes, similar to the changes seen in the human endurance athletes."

Yet another study showed that long-term endurance athletes suffer from diminished function of the right ventricle of the heart after endurance racing.^iv They also had increased blood levels of cardiac enzymes, which are markers for heart injury, and 12 percent of the athletes had detectable scar tissue on their heart muscle one week post-race. So it is more than likely that if you over-exercise you will do your body great harm.

Ideally, to get the most benefits you need to push your body hard enough for a challenge while allowing adequate time for recovery and repair to take place. It turns out that one of the best ways to do this is to follow a fitness regimen that mimics the movements of our hunter-gatherer ancestors, which included short bursts of high-intensity activities -- but not long-distance running such as is required to complete a marathon or even an hour on the treadmill.

Short Bursts of High-Intensity Exercise Gives You More Benefits in Less Time

Earlier I mentioned an incredibly efficient workout that you can complete in just 20 minutes. I was referring to Peak Fitness. After a three-minute warm up, you raise your heart rate up to your anaerobic threshold for 20 to 30 seconds (this can be done by sprinting, using an elliptical machine, recumbent bike, etc.), followed by a 90-second recovery period. Then repeat that cycle for a total of eight repetitions, as shown below.

Download Interview Transcript

According to fitness expert Phil Campbell, author of "Ready Set Go," getting cardiovascular benefits requires working all your muscle fibers (you have three different types) and their associated energy systems. Curiously enough, this cannot be achieved with traditional cardio... Your heart has two different metabolic processes:

1. The aerobic, which require oxygen for fuel
2. The anaerobic, which do not require any oxygen

Traditional strength training and cardio exercises work primarily the aerobic process. High-intensity interval training, such as Peak Fitness, on the other hand, work your aerobic AND your anaerobic processes, which is what you need for optimal cardiovascular benefit. As an added boon, when you perform Peak Fitness exercises properly, you will also increase your human growth hormone (HGH), which increases your muscle growth and effectively burns excessive fat. Naturally enhanced HGH release also plays an important part in promoting your overall health and longevity.

When you work out, it is wise to push as hard as you possibly can a few times a week, but you need to wisely gauge your body's tolerance to this stress, and give your body time to recuperate. In fact, you should not do Peak Fitness more than three times a week. If you do, you may actually do more harm than good -- similar to running marathons. I personally do them about once a week if I am doing strength training as this give me enough time to recover. 

You Can Also do High-Intensity Super-Slow Weight Training

Download Interview Transcript

Dr. Doug McGuff, M.D., an emergency room physician, is a proponent of high-intensity interval training using weights, which is purposed to achieve many of the same results as Peak Fitness using cardio equipment. If you watch the interview you will see he advocates even LESS exercise and recommends only using a very intense program once every 7 to 10 days. I am not convinced that this is ideal but it may be, so I still do three workouts a week, two strength training and one Peak Fitness.

In the interview above, he discusses both high-intensity anaerobic-type training, and high-intensity super-slow weight training. He believes you only need 12 minutes of Super Slow type strength training once a week to achieve the same growth hormone production as you would with Peak Fitness! Intensity is key, and, according to Dr. McGuff, when the intensity is really high, the frequency may need to be reduced in order for it to be really productive.

These exercises can be done using either free weights or machines. The benefit of using a quality machine is that it will allow you to focus your mind on the effort, as opposed on the movement.

Dr. McGuff recommends the following five movements:

1. Pull-down (or alternatively chin-up)
2. Chest press
3. Compound row (A pulling motion in the horizontal plane)
4. Overhead press
5. Leg press

Here's a summary of how to perform each exercise:

1. Begin by lifting the weight as slowly and gradually as you can. The first inch should take about two seconds. Since you're depriving yourself of all the momentum of snatching the weight upward, it will be very difficult to complete the full movement in less than 7-10 seconds. (When pushing, stop about 10 to 15 degrees before your limb is fully straightened; smoothly reverse direction)
2. Slowly lower the weight back down
3. Repeat until exhaustion. (Once you reach exhaustion, don't try to heave or jerk the weight to get one last repetition in. Instead, just keep trying to produce the movement, even if it's not 'going' anywhere, for another five seconds or so. If you're using the appropriate amount of weight or resistance, you'll be able to perform four to eight repetitions)
4. Immediately switch to the next exercise for the next target muscle group, and repeat the first three steps. When done in this fashion, your workout will take no more than 12 or 15 minutes.

The Importance of Recovery

You exercise because it makes you feel better, and for most, it helps keep your weight at an optimal level. It's also one of the best treatments for insomnia and reducing insulin resistance, as well as being a wonderful aid in the treatment of depression. So the reasons to exercise are many. If you start slow, and most importantly, listen to your body, you shouldn't run into the problem of exerting yourself excessively.

If you're a serious athlete, however, you may want to reconsider how you train. From my perspective you can train for two goals, either to maximize athletic competitiveness, or train for longevity and increased fertility (especially for women). In my view it is not possible to do both as they have conflicting workout patterns.

As I've discussed before, research has shown that replacing those long cardio sessions with shorter, high-intensity burst-type exercises, such as Peak Fitness, actually produces GREATER results in far less time! But recovery is crucial...

This includes not only resting your body in between workouts but also giving it the proper nutrients it needs in the recovery phase, as your post-workout meal can support or inhibit the health benefits of exercise. For instance, fast-assimilating protein such as high-quality whey protein, eaten within 30 minutes of your workout, will essentially "rescue" your muscle tissue out of the catabolic state and supply it with the proper nutrients to stimulate repair and rejuvenation.

References:

• ⁱ Am J Cardiol. 2001 Oct 15;88(8):918-20, A9
• ⁱⁱ J Appl Physiol. 2011 Jun;110(6):1622-6
• ⁱⁱⁱ Circulation. 2011; 123: 13-22
• ^iv European Heart Journal December 6, 2011 [Epub ahead of print]