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.

Insulin, leptin, triglycerides....what ?

It can be a very complicated thing to understand, but it is very important to get it correct if you want to maintain good health as you get older. It is also vital to the understanding of proper metabolic health. A very good article on the subject is one by Byron J. Richards, which can be read in full at the Wellness Resources website. In fact, the site is an extremely good source of information on the issues discussed in this blog.

Here, I will limit myself to quoting verbatim selected passages from the article. This passage pretty much summarises the physiology behind insulin and leptin resistance.

First off, your blood is not a very sweet beverage. Normal fasting blood sugar is slightly less than one teaspoon of sugar in your five or so quarts of blood. What happens when you drink a sugar sweetened Coke that contains 10 teaspoons of sugar?

When you eat any food, even fat, your insulin level will rise. Higher amounts of refined carbohydrates or simple sugars will raise your insulin faster and in higher amounts. The greater the fiber content of your diet, the slower insulin is raised and the more controlled the process.  When you eat a large meal, regardless of the type of calories, it causes a large surge in insulin that is difficult to manage. 

Insulin is a taxicab for calories. Its goal is to take blood sugar, as its passenger, to various locations in your body that want it. It helps if you are active, as some of the sugar is more likely to be wanted by cells in your body, including your many muscle cells. 

Blood sugar is fuel, like gasoline is to a car. Your brain must have a regular supply or your head conks out. Thus, following a meal your insulin taxi’s are busy transporting sugar through your circulation and out to your cells, hoping to find cells that need some sugar.

In a healthy person, insulin drops off a whopping 60 percent of the sugar at your liver, which acts as a warehouse, converting the blood sugar to glycogen for storage. 

Insulin is released by your pancreas in two phases. The first phase is from insulin that is already made and stored in your pancreas, which is just waiting for some food to come along. This is your first wave of taxis coming to pick up the first set of blood sugar passengers. The release of this insulin triggers your pancreas’ beta cells to start making more insulin to deal with the rest of the meal.

As you are eating, some of the insulin transports blood sugar to your white adipose tissue or stored fat. The blood sugar is taken up by fat cells, activating their metabolism, in turn producing the hormone leptin. Leptin now enters your blood and begins traveling up to your brain. The more you eat, the more insulin you make, and the more leptin you make.

When leptin levels get high enough, meaning you have eaten enough, then leptin permeates into your brain and tells your subconscious brain you are full. At the same time, the higher levels of leptin also tell your pancreas that you are full, which turns off the beta cell production of insulin, as no more taxis are needed.

If you ate the right amount of food for your physical activity level, then blood sugar always has some place healthy to go; insulin rises and falls in a controlled manner, as does leptin.

When insulin has too many blood sugar passengers, and cells don’t need any sugar, then insulin stimulates the production of triglycerides, which can become stored fat. This is how you gain weight. Unfortunately, as triglycerides elevate in your blood they get in the way of leptin getting into your brain.  This keeps you eating more than you need to because you don’t yet have a full signal, a problem called leptin resistance.  This encourages even further insulin driven triglyceride formation, making it more likely you will gain weight.

If you stop eating too much and start exercising more, then this simple case issue can improve and will often bounce back to normal function, thus the basic idea of eating less and exercising more to lose weight. 

If you continually eat too much and gain weight, then cells get tired of seeing insulin taxis driving up.  In fact, they shutter their windows and lock their doors; insulin becomes persona non grata. The reason for this rejection of insulin is rather simple.  If the cells take in blood sugar when they can’t use it, because they already have enough, then the extra sugar will caramelize and kill the cell.  Rejecting insulin is a self defensive measure. This is the mechanism behind basic insulin resistance at the cellular level.

If this problem goes on, blood sugar levels continue to rise, insulin resistance gets worse, leptin resistance gets worse, cholesterol levels go up, blood pressure goes up, triglyceride levels go up, and inflammation really starts heating up.  Eventually, this leads to type 2 diabetes, along with many risk factors for heart disease, and then heart and kidney disease lock into place.

The next passage begins to introduce the dietary regimen which is necessary to control the insulin-leptin-trigleride complex.

In normal health, when you haven’t eaten for three hours, insulin levels return to a baseline.  Now your pancreas makes a different hormone called glucagon. This hormone tells your liver to release the sugar (glycogen) it has stored to sustain your blood sugar levels, and as it does this it turns on your liver’s fat burning system. Thus, under the influence of glucagon your liver simultaneously uses sugar and fat to sustain your blood sugar – a true fat burning time that helps clear up stagnating levels of triglycerides in your blood. 

If you snack on anything surpassing 30 calories you will raise insulin, which automatically turns off glucagon, causes fat burning to stop, and blunts the use of sugar that has been stored in your liver.  However, since you haven’t used the stored sugar in your liver, then insulin can’t put more sugar back in your liver as it normally would, meaning it will readily turn blood sugar into fat (even if you snacked on something with no fat). 

You are supposed to get a snack between meals, but it is supposed to come from your liver, not from eating.

The worst things for leptin and insulin are eating between meals, eating large meals, eating low fiber, eating highly refined sugar or refined carbohydrates, not eating enough quality protein, and not exercising. 

If you eat anything after dinner you make matters even worse, because now you reduce the optimal access into your stored fat during sleep, a prime opportunity to burn fat.

When this system is abused and weight is gained, then fat begins to accumulate in excess in your liver. The fat clogs your liver’s metabolism, and reduces the ability of sugar to store in your liver following a meal. This is liver insulin resistance caused by fatty buildup.  This means that you are much more likely to become hypoglycemic or have low blood sugar between meals, because you don’t have enough sugar in your warehouse to use for blood sugar between meals.

This same fatty liver problem also gets in the way of how glucagon would burn fat between meals, causing glucagon to synthesize sugar in an inappropriate and out-of-control manner, making blood sugar go high even though you haven’t eaten. This is why diabetics wake up with very high fasting blood sugar levels.  These are complicated metabolic problems that are more difficult to fix than simple case insulin resistance.

Furthermore, your pancreas starts to tune out leptin, meaning that leptin resistance occurs at the level of beta cells and the beta cells aren’t getting the leptin message to stop making insulin in a timely manner.  This causes extra insulin to be made, which excessively lowers blood sugar by turning sugar to fat, while simultaneously inducing hypoglycemia or low blood sugar symptoms. This makes a person want to eat again two to three hours after the previous meal, in turn making the whole problem worse.

....Additionally, the liver, muscles, and circulation are clogged with accumulating fat. This is like trying to cook a meal in a filthy kitchen, it is going to be challenging. This problem will only gradually improve as weight is lost, it never improves until the weight is lost, and it will always get worse if weight is gained.

A healthy way to maintain your body's insulin and leptin sensitivities is through plenty of exercise and and a good dietary regimen. The author gives a simple five rule guide to diet:-

Rule 1:  Never eat after dinner.  
Rule 2:  Eat three meals a day (do not snack).  
Rule 3:  Do not eat large meals.  
Rule 4:  Eat a breakfast containing protein. 
Rule 5:  Reduce the amount of carbohydrates eaten.

within which it is necessary to observe:-

Dietary fibre, especially soluble fiber, is critical to repair blood sugar problems. Soluble fiber is vital for slowing the rate at which sugar enters your blood, thus enabling your insulin system to function with less stress. It also helps you maintain healthier triglyceride and cholesterol levels. Individuals who struggle with blood sugar issues need 35 to 50 grams of fiber per day, much of it as soluble fiber (a higher level than the 25 grams the government recommends for general health). Higher amounts are also very helpful to curb appetite and support weight loss.

...Protein  is vital in the repair of blood sugar metabolism. A minimal objective for protein intake is three-fourths of your ideal weight in grams of protein per day. To improve insulin function, the key proteins that help are rich in branch chain amino acids – especially leucine. Unlike any other amino acids, leucine directly communicates to insulin, instructing it to work efficiently in muscle. This not only helps preserve your muscle mass as you lose weight, but it also helps your muscles use glucose as fuel, in turn supporting healthy insulin function. Whey protein also helps leptin enter your brain more efficiently, supporting normal insulin function in your nervous system.

The key foods to eliminate are refined carbohydrates, refined sugar, and high fructose corn syrup. Complex carbohydrates and fruit should be eaten at meals, several servings of each per day. Saturated fat and cholesterol-containing foods do not need to be avoided – just don’t eat them in excess.

A further tip given in another article on the same website is

Researchers found that eating low carbohydrates following exercise improved insulin sensitivity, meaning the muscles and liver could more readily take up blood sugar. However, eating a low calorie meal following aerobic exercise did not improve insulin function. This means you should not try to starve yourself in an effort to lose weight. By eating a calorically appropriate meal of mostly protein, fat, and veggies (avoid bread, rice, potatoes, pasta, dessert) following aerobic exercise, you are much more likely to get insulin working in your favor.

Of course, ensuring you get adequate protein2 at the meal before and/or after exercise also helps ensure that you have adequate protein to properly repair and recover from exercise. Individuals who lack dietary protein do not enjoy the progressive improvement in fitness that exercise can provide with proper protein nourishment.

For those out there that want to delve deeper into this subject, the author has published two relevant books namely Mastering Leptin and The Leptin Diet. Also, there are numerous video resources to get you started.