Cardio, intervals and all that.

Fitness now has almost as many fads and passing gimmicks as nutrition and dieting these days. Among these is the old debate about traditional cardio versus new fangled interval training and its variants. Recently, traditional cardio has been receiving very bad press owing to the notion that it encourages your body to store energy as fat, and decreases your heart and lung capacities. Against this notion it is posited that interval training (or its variants, such as Dr Al Sears PACE programme) enable you to burn fat faster and ignite a post workout after burn effect.

However, when fads and fashions rule any debate the problem sometimes lies in the method of debate as much as the topic being being debated. The cardio versus interval controversy may be such a case in point. This has recently been pointed out by Shaun Hadsall, who points out that traditional cardio, threshold intervals and what he terms metabolic bursts, can compliment each other [1],[2],[3] in a more rounded and effective training regimen than just limiting oneself to just one of these approaches.

Cardio

Doing low intensity cardio prior to weight training or high intensity/burst training depletes glycogen stores and robs you of the energy needed to maximise the benefits of the weight training.

However, doing low intensity cardio after weight training when glycogen stores have already been depleted by the weight training or high intensity/burst routine results in more efficient fat burning.

Low intensity cardio strengthens the cardiovascular and pulmonary system through different pathways to high intensity and burst workouts.

High intensity or burst workouts (typical of anaerobic exercise) primarily burn calories both during and after the workout, whereas low intensity cardio training (typical of aerobic exercise) burns calories during the workout.


Ideally, a short period of low intensity cardio following a weight training or high intensity/burst workout routine enhances the fat burning outcome of your training session, while a long cardio workout say once a week gives you the benefits of cardio without the pitfalls of a traditional cardio weighted approach to fitness training.

Threshold interval training

Steady state cardio training lays a basic foundation of endurance and conditions the cardiovascular system through its own pathways which are different from other forms of training. However, limiting your regimen to steady-state cardio, or doing steady-state cardio before other forms of exercise are counter productive.


Breaking down glucose occurs much faster using (anaerobic) threshold intervals than with aerobic exercises. However, when glycolysis takes place during a threshold type of workout it produces metabolic waste products that inhibit muscle contractions, which leads to exhaustion and fatigue. The aerobic system can use these same waste products as fuels, but as soon as exercise intensity crosses a certain threshold, wastes are produced faster than they can be used. That is when you start to feel the lactic burn. That is also why threshold exercises should be done in a series of intervals with rest periods in between. It is this lactate threshold that these exercises are performed at, which is the reason it is called threshold interval training.

Typically, these intervals last between 60 and 180 seconds with a one to two minute rest period in between. Also, ideally a threshold interval session is performed directly after weight training as is the case for traditional cardio, or first thing in the morning when your body is in a fasted state.

Metabolic bursts

The next level of intensity up from threshold intervals is metabolic bursts. These are very hard and short bursts of exercise followed by a period of active recovery to allow the heart rate to relax.

This type of anaerobic (without oxygen) energy system is called the creatine phosphate system. It fuels maximum and near-maximum efforts of these short-bursting types of intervals. 

Only tiny amounts of creatine phosphate are stored in the muscles, so this energy system cannot support efforts lasting much longer than 20 seconds.[3]

They also keep the body’s metabolic rate elevated for 38 to 48 hours after the workout, whereas the aerobic and even the threshold anaerobic routines cause only a slight afterburn effect. However, because of the intensity bursts, you can only do this type of workout at most a couple of times per week. However, their effect is hard to realise with other more traditional forms of training. These include the release of fat burning hormones, the encouragement of energy storage in the muscles rather than in fat cells, enhanced after burn, and enhanced hormonal response. Again, early morning or post strength or bodyweight training are the best times to do them.


In summary, there is not necessarily an opposition between traditional cardio, traditional interval training and metabolic bursts. The main problem with cardio is that many people do it before strength or bodyweight training whereas it should be done after your main muscle routine. The thing about traditional cardio is that it can be performed below the lactate threshold, which means an extended uninterrupted session can be performed. This is ideal after a particularly strenuous strength or bodyweight session has been undertaken, say a lower body workout involving the large muscles.

Doing anaerobic cardio just above the lactate threshold is appropriate when your strength or bodyweight session has not been so strenuous, say an upper body workout. They are also ideal first thing in the morning when your body is in a fasted state, which leads to greater fat burning potential. Metabolic bursts can be done once or twice per week, ideally first thing in the morning, or after say an upper body strength or bodyweight workout.

[1] Ab “Targeted” Interval and Cardio Solution. Private Update #1
[2] Ab “Targeted” Interval and Cardio Solution. Private Update #2
[3] Ab “Targeted” Interval and Cardio Solution. Private Update #3

How to maintain leptin production and sensitivity

According to the guys at Bio Trust, the number one hormone for fat burning is leptin, and maintaining healthy levels of leptin, as well as your bodies sensitivity to it are crucial to a successful fat burning regime.

Joel Marion has outlined some tactics that can be used to promote leptin production and maintain high levels. However, it seems to me that using these tactics require a lot of discipline and practice to get right, as you will see.

1. Leptin production

Leptin is produced in accordance with calorie intake, since it is the main fat burning hormone. Therefore, in order to encourage leptin production it is necessary to take in a lot of calories. Obviously, you cannot keep this up every day - if you did you would soon find that you were storing more calories than you are burning. What it does mean is that if you restrict calories as part of a fat reduction regime, leptin levels will naturally decrease. Therefore, incorporating a 'cheat' day say once per week will give a boost to your flagging leptin levels.

2. Leptin maintenance

Clearly, going back to your restricted calorie regime following a cheat will soon lead to decreasing leptin levels in very short order. The problem then comes down to how to maintain leptin levels in between cheat days. According to Joel Marion, this can be accomplished through 'reverse carbohydrate tapering' - adding an extra small amount of carbohydrates each day in between the cheat days.

Joel Marion recommends an extra 20g of carbohydrates each day following a cheat day so that on day one you would have 20g extra, on day two 40g extra, and so on. Obviously this is the part that requires the discipline and practice since it is necessary  to take enough to maintain leptin levels, while ensuring that it is not so much that it contributes to fat storage.