Low Intensity Cardio or High Intensity Cardio?

May 2, 2011 by  
Filed under The Fitness Bug


Daniel Offer writes. Offer exercises in the evenings at his local gym and in the surrounding villages when not working on his Facebook emoticons application Emoinstaller. In short, Emoinstaller provides additional Facebook smileys for your Facebook account.

Everyone knows that a good cardiovascular workout improves your general health, and that the results will vary depending on the frequency and intensity which with you exercise. So, which type of workout is right for you?

Cardio routines are classified according to the average heartbeat rate maintained during the session, which is expressed as a percentage of maximum heart rate (MHR), the greatest number of times your heart can beat in a minute.

MHR can be calculated using the following formula: = 206.9 – (0.67 x age)

Low intensity cardio is performed at 60 – 70 % of MHR, and is any kind of exercise that allows you to maintain a comfortable, easy pace throughout the duration of the session.

It is often associated with aerobic / steady state exercise, which is any kind of activity which allows you to keep a regular heart rate for an extended period of time. Examples of low intensity aerobic activities include gardening, a gentle stretching routine, or a long, slow walk or cycle.

It is also possible to do a hybrid aerobic-interval training at low intensity. This kind of exercise involves alternating short periods of low impact aerobic training with short periods of rest, repeated for as long as it takes to reach 20 – 30 minutes of activity in total. When done by untrained beginners, or people who are too overweight to perform bouts of aerobic activity for any length of time, the goal is to increase the level and intensivity of the activity whilst bringing down the amount of time spent resting. This type of training is also used by strength and power athletes during recovery periods in between high intensity training, and is usually referred to as tempo work.

By contrast, high intensity cardio is any type of exercise which challenges your body and leaves you breathless and exhausted. During high intensity cardio your target heart rate zone should be 70 – 80 % of MHR.

Though a high intensity cardio workout can be aerobic, like endurance running, it is most often associated with interval training. High intensity interval training (HIIT) sessions last for 15 – 20 minutes and involve alternating short periods (30 – 90 seconds) of intense activity with longer periods of either total rest, or very low activity.

In the end, whether you’re doing aerobic exercise or interval training, it’s all about how hard you are pushing yourself.

Low intensity cardio vs high intensity cardio

Despite the debate surrounding the advantages and disadvantages of low and high intensity cardio routines, results of studies carried out over the past few years do allow some conclusions to be drawn.

Level of preparation

Low intensity cardio be done by just about anyone at any level of fitness. Little, if any, warm-up is needed, and it´s easier to maintain a steady pace for a long time. It does not need to involve a structured, scheduled workout, you can pick an activity that you already do on a daily basis and simply do it for a bit longer, like walking more or taking the stairs more often.

However, for many people, this type of exercise can get boring as it takes a long session to get significant results, and the only factors you can use to push yourself further and improve on your fitness level are speed, incline and duration.

High intensity cardio is generally considered more interesting because it can be practiced with any activity which allows the intensity level of the exercise to be easily adjusted, like running, cycling, skipping or using a variety of gym equipment. There are also more ways in which you can alter the workout to push your body further (speed, amount of repetitions, length of rest periods, bodyweight vs free weights, exercise duration etc).

However, it requires a moderate to high initial level of fitness and a lot more motivation. If you are not motivated, working at such at high intensities can result in an inconsistent workout schedule, or even burnout.

Health benefits

Even exercising at modest intensities will improve your general level of fitness, increasing your lung capacity and improving your cardiovascular fitness, which in turn lowers ´bad´ (LDL) cholesterol and risk of heart disease, high blood pressure, stroke and diabetes. Improved blood circulation also permits the fatty acids in your bloodstream to move more efficiently into the muscle, meaning that fat is more readily available when you need the fuel.

Exercising regularly is a good way of managing your weight, and it will help your body become more efficient at processing oxygen, allowing your cells to metabolise and burn fat more efficiently. Regular exercise also reduces the number of stress hormones in your system, and seems to produce chemical changes in the body which enhance your psychological fitness and alleviate the symptoms of moderate depression.

However, after some (relatively) small improvement in general fitness and the initial loss of excess fat, the results achieved by low intensity exercise tend to plateau. When this happens, the only way to build on the initial results is to push yourself to do more.

High intensity cardio provides you with all the health benefits associated with low intensity cardio, but it delivers better results, and it also delivers these results faster.

Exercising at high intensities also increases endurance. During periods of great activity, when our body is running out of oxygen, it shifts to from aerobic to anaerobic metabolism. Lactic acid, the end product of this process, begins to accumulate in the muscles as its cells are unable to burn it off quickly enough – that’s the pain that you feel just before muscle fatigue sets in. High intensity training allows you to increase your lactic acid threshold, the point at which the lactic acid begins to accumulate in the muscles, meaning that you can work harder, for longer.

High intensity workouts also boost your metabolism during and after exercise. Every exercise session generates a certain amount of excess post-exercise oxygen consumption (EPOC), sometimes called ´exercise afterburn´. EPOC represents the extra oxygen the body has to consume after a workout just to get the body back to it’s pre-exercise state (replenishing energy and oxygen stores, removing lactate, bringing body temperature and heart beat down to pre-exercise levels, etc).

It can take anywhere from 15 minutes to 48 hours for the body to fully recover to a resting state, depending on the intensity and duration of the workout, as well as the level of fitness and gender of the athlete. A high intensity workout will produce a significantly longer period of EPOC than a low intensity workout, during which oxygen, and calories, are also consumed at higher levels.

Weight loss and the fat-burning zone

Most of the war of words in the low versus high intensity training discussion has been over weight loss and the so-called fat-burning zone.

Though your body always uses fats and carbohydrates, and some protein, as energy sources, the proportion of each substance used changes depending on the intensity of the exercise done.

During periods of low activity, a person´s body uses fat as its primary source of fuel; fat provides over twice the amount of energy than an equivalent amount of carbohydrate or protein, but it takes more time to convert to energy. When operating at higher intensity levels, the body turns towards carbohydrates as a primary fuel source, as they can be converted to energy much faster than fat, making them more readily available for the body’s immediate energy needs.

The fat-burning zone varies per person, but is thought to be around 60 – 70% of MHR, thereby falling in the low to medium intensity exercise range. A person out this zone will burn a higher proportion of fat calories as a percentage of total calories burnt.

However, if you increase the intensity of the exercise you will burn more calories in total, and, depending on the duration of the session, more fat calories.

For example, if a person exercises at 60% MHR for a half hour walk and burns 300 calories, and 50% of those calories are fat calories, they have used up 150 fat calories.

If a person exercises at around 80% MHR for half an hour burns 450 calories, if 40% of those are fat calories, they have used up 180 fat calories. This gives them a higher overall calory burn, and a higher amount of fat calories burnt.

Low intensity cardio is good for initially dropping weight when you are very unfit, and for keeping your weight down. There is also evidence to suggest that, because the low amount of effort involved, it’s easier for people doing low intensity workouts to exercise consistently, and stick to diets.

However, as the overall calory burn from low intensity cardio is much less during the same period of time, if you are serious about losing weight, you will have to put more effort into your exercise routine.

It is also better to vary the type of exercise you do if you want to keep losing weight. Doing a lot of aerobic exercise in particular, allows your body to adapt to the activity and become more efficient at burning calories whilst doing it; this means that you will keep having to increase the amount of time you spend on the same exercise if you want to continue seeing results.

Risk of injury

With exercise always comes a risk of injury. Low intensity cardio however does, in general, present a lower risk of injury than high intensity cardio.

Any kind of endurance training can generate overuse injuries as you are subjecting certain parts of your body to stresses for a long period of time (for example, joggers often have knee injuries). People not interested in improving their endurance levels can avoid this problem by simply changing the type of exercise they are doing.

At high intensity levels there is also the risk of over-training. This is what happens when someone is training excessively and/or not eating properly, and can result in a loss of muscle mass. When the body has exhausted its blood glycogen (carbs), it starts to break down (catabolise) protein, to get the energy it urgently needs; if the person’s diet does not contain enough protein and overall calories to sustain them through their workout, the protein is provided by their muscle tissue.

Performing at a high intensity for too long (which depends on the fitness level of the athlete) has also been shown to increase the levels of catabolic hormones like cortisol in the blood, which can cause the breakdown of muscle tissue.

The results of excessive aerobic training on the body are nicely demonstrated when you consider the thin physique of a marathon runner who has specialized in endurance training, as opposed to the bulkier form of a sprinter who generally trains for short intensive bursts.

Excessive training of a certain muscle group and its supporting muscle groups can also lead to local over-training, sometimes suffered by bodybuilders or strength/power athletes. This is because when you work out at high intensities, you are causing microscopic tears in your muscles, and your body needs both the time and the right nutrients to repair the tissue damage caused by the workout and rebuild bigger, stronger muscle.

The problem can be exacerbated when the person is also dieting to lose fat. The lessened calory intake simply makes the body have to dip further into its fuel reserves, sacrificing more muscle tissue along the way.

Other than persistent pain and stiffness in the muscles and joints, over-training can cause lowered testosterone levels and can lead to psychological problems like depression, irritability, mood swings, insomnia and an inability to concentrate. It can, however, easily be avoided by keeping the intensity of your training program under control.

Studies have also found that long sessions of aerobic training (like long distance running) can lead to the production of free radicals in the body. Unless these are neutralized by antioxidants in the diet, they can damage important cellular structures and accelerate the symptoms of aging. However, regular exercise has also been shown to enhance the body’s antioxidant defense system, so this kind of damage is normally found in “weekend warriors”, people who are generally inactive but sporadically participate in long sessions of physical activity.

Training schedule

Low intensity cardio sessions are generally longer than high intensity ones, as it takes more time to burn the same overall amount of calories. However, as low intensity cardio is mostly low impact, it can be done on a daily basis, depending on the fitness level of the person and the amount of time they have available.

Conversely, high intensity cardio is very time-efficient as the sessions are short and provide rapid results. However, because of the impact that working at high intensities has on the body, this type of workout should not be done daily, as you run the risk of over-training and injury. Unless you are exceedingly fit, it is recommended that you keep your high intensity sessions to 2 or 3 times a week, and have rest periods in between.

If you do want to exercise in between high intensity sessions, doing some low intensity cardio has its advantages: the easy activity keeps the blood flowing and can be psychologically beneficial, and bodybuilders in particular can also use the activity to burn off the extra calories they are eating to keep up their muscle, whilst avoiding the problems which come with over-training.

Which type of cardio workout is for me?

Studies have shown that tailoring a routine to your individual needs is the best way to get results, and the type of cardio that you choose to do should depend on your fitness level and goals. However, the following generalizations can be made.

Low intensity exercise is for:

  • Very overweight people and unfit beginners, and those who are not motivated enough to do more intensive exercise

  • People recovering from injury, and people with certain chronic health problems like congenital heart disease, asthma and arthritis
  • Pregnant women and the elderly
  • People who are trying to burn fat, especially in conjunction with a low-fat diet
  • People wanting to exercise in between high intensity training sessions

High intensity exercise is for people who are moderately to very fit, highly motivated and:

  • Want to lose weight

  • Want to increase their endurance levels
  • Want quick results and are pressed for time
  • Get bored easily

Combining a variety of routines will prevent your body from adapting to any particular type of physical activity, as well as protecting you from overuse injuries and keeping you interested in your workouts.

Whichever type of cardio routine you choose, it should be one you are motivated to do and will be able to sustain.

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