Fuel Usage During Exercise

Below is a very informative article on what types of "fuel" your body uses during different types of exercise. It also looks at how higher intensity, shorter period exercise can actually be more effective at burning calories than longer term, lower intensity exercise. Check it out!

Fuel Usage During Exercise
by: Yuri Elkaim


The type of substrate (fuel) and the rate at which it is utilized during exercise is largely dependent on the intensity and duration of the exercise. During strenuous exercise there is an obligatory demand for carbohydrate (CHO) oxidation that must be met; fat oxidation cannot substitute. In contrast, there is an increase in fat oxidation during prolonged moderate intensity exercise as carbohydrate fuels are depleted. Fats are also more dominant in long duration exercise since fat oxidation requires more oxygen than does carbohydrate oxidation.

Fuel Selection During Exercise

Again, fats are the primary source of fuel for muscle during low-intensity exercise (70% of VO2max). Proteins contribute less than 2% of the substrate used during exercise of less than one hour’s duration but may increase up to 5-15% during the final minutes of exercise lasting 3-5 hours.

At about 40% of VO2max there is a “crossover point” where carbohydrate becomes more dominant than fat in supplying fuel to the muscle. This shift to CHO metabolism is caused by two factors: the recruitment of fast twitch fibers (which are better equipped to metabolize CHOs) and increasing levels of epinephrine in the blood (which contribute to glycogen breakdown). This shift can also be seen when examining the contribution of fat oxidation at various exercise intensities. At 20%, 50%, 80%, and 100% of VO2max, fat oxidation yields 175 kcal/min, 250 kcal/min, 200 kcal/min, and 25 kcal/min, respectively. As such, someone looking to burn more fat during exercise would want to hover in the 50% to 80% VO2max range.




As the duration of exercise increases, there is a greater contribution from fat and less from carbohydrate. This is the result of increased levels of blood lipase, an enzyme that helps break down fat, during low-intensity longer duration exercise.

Muscle Glycogen Utilization

At the onset of most types of exercise, and for the entire duration of very strenuous exercise, muscle glycogen is the primary carbohydrate fuel for muscular work. The intensity of exercise determines the rate at which muscle glycogen is used as a fuel. The heavier the exercise, the faster glycogen is broken down. Furthermore, studies have shown that glycogen is depleted faster from fast-twitch fibers, especially during interval type work .

Historically, it has been thought that increased epinephrine levels in the blood were responsible for the initiation of glycogenolysis (glycogen breakdown). However, other research has shown that the breakdown is also triggered within the muscle itself as a result of increased Calcium ions .

Maintenance of Normal Blood Glucose Levels During Exercise

As glycogen, and thus glucose, is the primary fuel sources during most exercise, it is needs to be remembered that glucose plays a primary role in supplying our vital organs with energy. As such, the body has many systems in place to maintain adequate levels of glucose in the blood during times of inadequate carbohydrate intake (starvation/fasting) and accelerated glucose removal from the blood (exercise). Blood glucose concentration is maintained through four different processes:

• Mobilization of glucose from liver glycogen stores

• Mobilization of fats to spare blood glucose

• Synthesis of new glucose in the liver from amino acids, lactic acid, and glycerol

• Blocking of glucose entry into the cell to force the substitution of fat as a fuel.

These processes are controlled by several “slow” and “fasting” acting hormones such as thyroxine, cortisol, growth hormone, epinephrine/norepinephrine and insulin/glucagon. Maintaining normal blood glucose concentrations is a major task when you consider that the liver may only have 80g of glucose before exercise begins, and the rate of blood glucose oxidation approaches 1g/min in heavy exercise or in prolonged (>3 hours) moderate intensity exercise.




Carbohydrate Replenishment and Diets

This is one of the main reasons why it is recommended to replenish glucose and glycogen levels during activities such as soccer games, marathons, triathlons, 3-5 set tennis match, and so forth. Each of these sporting activities require moderate to high levels of exertion for extended periods of time and thus fuel replenish, mainly via sports drinks, is essential in maintaining physical performance and skill execution.

The effect of carbohydrate intake and diet composition on performance has been heavily studied. The vast majority of studies show that a high carbohydrate diet is essential for those who engage in intense or long duration exercise. For instance, one study had trained subjects run a 30 km race twice, once following a high carbohydrate (CHO) diet and the other time after a mixed diet. The initial muscle glycogen level was 3.5g/100g of muscle following the CHO diet and 1.7g/100g of muscle during following the mixed diet. The best performance of all subjects occurred during the high CHO diet. Although the starting pace was not faster, the additional CHO allowed them to maintain the pace for a longer period of time .

Bear in mind that substrates and hormones can interact and alter certain processes. This is commonly seen when a high glycemix index CHO food is ingested just prior to exercise. In this case, the resulting spike in blood glucose elicits a rise in insulin levels. As a result, fat mobilization is reduced (due to insulin’s anabolic effect on fats) forcing the muscle to use additional muscle glycogen. This is not desired if you are looking to sustain a given exercise intensity for prolonged periods of time.

Putting It All Together

The common misconception is that to lose weight you must stay in your “fat burning zone”. Even though there is some truth to this statement, it is inaccurate in the sense that losing weight is about burning as many calories as possible. As such, exercising at a higher intensity for moderate durations would be most effective in burning calories. It is important to remember that a calorie is a calorie regardless of its source and since 1 lb of fat is equivalent to 3500 calories, calorie-reducing exercise regimens are most suitable for those looking to lose weight.

Such exercise programs can take the form of interval work, where a bout of high-intensity exercise is combined with a bout of low-intensity. This type of training of has been shown to elevate the body’s metabolism for up to 16 hours post-exercise. It also fosters the maintenance of lean body mass while stimulating the release of lipase – a good thing since maintaining muscle and losing fat should be the goal. Having said this, I would also recommend implementing longer duration low-intensity exercise as well for it’s aforementioned benefits on fat oxidation. However, ensure to keep the intensity in the 50-80% VO2max range for best results!

References:

Essen et al. (1978). Glycogen depletion of different fiber types in human skeletal muscle during intermittent and continuous exercise. Acta Physiologica Scandinavia, 103: 446-55.

Hultman et al. (1967). Physiological role of muscle glycogen in man with special reference to exercise. In Circulation Research XX and XXI, ed. C.B. Chapman, 1-99 and 1-114. New York: The American Heart Association.

Karlsson, J. & Saltin, B. (1971). Diet, muscle glycogen and endurance performance. Journal of Applied Phsyiology, 31: 203-206.


About The Author
Yuri Elkaim is the owner of Total Wellness Consulting and creator of the only 12 week body shaping fitness program designed for Ipod/Mp3 players. Please visit http://www.myFitterU.com for more info

Strength Training - The Perfect Repetition

I have been a member of a number of gyms throughout my life. While there I have seen thousands upon thousands of other people working out. One thing that I noticed again and again is that many people have terrible form when it comes to strength training and lifting weights. I do not have perfect form at all times, but I have learned the proper way to lift weights to maximize the results and minimize the risk of injury. There is not one single proper way to lift weights, but there are some guidelines that should be followed. I came across this article that did a very good job of detailing what the author calls "the perfect rep". There is some good information in this article, so I have republished it below:

The Perfect Rep: Unlocking The Ultimate Secret For Permanent Effective Training
by: Joey Sheather

This will be the most important piece of information that you will ever read about weight training.

Repetitions… Your entire training career is composed of millions of them. You group them in sets and they are the basis of each workout. Performing them correctly is the difference between success and failure. A perfect repetition, seemingly simple, has many components and is powerfully effective. I am going to explain how to perform the perfect rep and why it is so important.

At the impressionable age of 14 I was lucky enough to be introduced to the world of weight training by a competitive bench presser and ex-Olympic wrestler. He was a cartoonish 5 foot 3, 65 kilo powerhouse with a barrel chest and black pony-tail mullet down to his arse. At his gym in Bellingen he would ensure that I learned and retained precise lifting technique during my first 12 months of training. Thank-you Kevin. Under his supervision I went on to become the Australian School-boys Bench Press Champion at the ripe old of age of 15 with a lift of 87.5 kilograms (192.5 pounds) at a HUGE (laughs) body-weight of 66 kgs (145 lbs). That was after only 6 months of training. Technique and intensity is EVERYTHING!

Kevin sold the gym to a great man called Scott who became a very close friend of mine, a fantastic training partner and the catalyst for my career in Personal Training. He looked somewhat normal in comparison to Kevin sporting a natural, balanced, muscular bodybuilder’s physique. His basic training philosophy was to hit each muscle group from every angle with perfect form designating set and exercise volume in proportion to the size of the muscle group, i.e. back being the most complex and largest received the most exercises while biceps being one of the smallest received the least. I learned a lot from him. Exercise form was always at the fore-front of his teachings.




From Kevin I discovered that each exercise has an optimum movement path to generate maximum power safely. Scott showed me a broad range of exercises and how to apply good technique to each of them for consistent effectiveness and efficiency. I have taken these lessons with me throughout my career and applied them to my training and the hundreds of exercises that I have created myself.

Anyone who knows me will find that I am extremely particular about good exercise technique. I pay very close attention to the body position and movement pattern adjusting fine components so that the exercise is totally optimised. I must annoy the hell out of my clients sometimes. It works though.

WHY IS PERFECT EXERCISE TECHNIQUE SO IMPORTANT?

Reduced Risk Of Injury…

If you are to remain injury-free throughout your training career you must practise safe, tight, controlled lifting technique for every single repetition. If the movement is as close to biomechanical perfection as possible you will receive maximum stimulation with minimum risk. Injuries will halt your progress every time and can be very serious. Any chance to avoid them should be harnessed, implemented and retained.

Decreased ‘Cheating’ And Involvement Of Unrelated Muscle Groups…

If your form is sloppy there is a good chance that you are not hitting the target muscle as completely as you could be. As soon as your technique declines other muscle groups come into play assisting during the lift, often in an unsafe manner. A classic one is allowing your torso to swing during a bicep curl using your lower back, glutes and hamstrings to get the weight up. There is not only the danger of hurting yourself there is also the probability that you are not taking the target muscles to failure. Keep the form tight and you will stimulate the muscle safely and entirely.

Decreased Involvement And Fatigue From Ancillary Muscle Groups…

Related to the last point the execution of a perfect repetition every time will ensure the target muscle is isolated and fully fatigued before the ancillary muscles (assisting muscles) give out. To make this more clear I will describe two examples where this is a common occurrence. Example 1: when you perform a back exercise if you do not focus on engaging and isolating the targeted muscles of the back then the forearms and biceps will crash and burn before the back is fully worked. Example 2: when you perform a chest exercise if you do not focus on isolating the pectorals during the movement then the triceps and anterior deltoids will give out first impeding the progress of the chest. It is easy for ancillary muscles to come into play during an exercise if your form is sloppy because they are there to assist the movement. But because they are smaller and weaker if you do not make sure that the target muscle is completely fatigued first they will always give out holding backyour progress.

Increased Motor Neuron Innervation And Muscle Fiber Activation…

If you isolate the target muscle group and contract it slowly and intensely through the entire movement you will activate the greatest amount of muscle fibers. A safe and full range of motion (ROM) will involve muscle fibers from the origin (initial attachment) right across to the insertion (final attachment) of the muscle. A slow, intense, precise movement during the entire concentric contraction (muscle shortening) and eccentric contraction (muscle lengthening) will innervate more motor neurons ‘firing’ more muscle fibers. This will facilitate a maximum activation of the muscle fibers and total muscle contraction maximizing strength and muscle gain.

Improved Mind-Muscle Connection…

The mind-muscle connection is your ability to feel the target muscle contract completely and under total control during the execution of an exercise. Usually a muscle group that you find difficult to feel and to develop is one that you have a poor mind-muscle connection with. Consistent, strict form on all of your repetitions will help you gain control of these stubborn body-parts. The mind-muscle connection improves when the path from your motor cortex (the control centre of your brain for movement) to the working muscle becomes more efficient.




Improved Focus, Discipline, Intensity And Quality Of Training…

This level of precision for every single repetition that you perform during your workout demands a massive amount discipline, will-power and intensity. You control the movement of every exercise and apparatus as though it were part of your body. Be patient and apply it to all exercises performed until it becomes second nature. By this stage it will feel awkward to train with sloppy technique and you won’t miss it because you will become stronger and more muscular and injury-free.

COMPONENTS OF A REPETITION

1. Starting Point – where the body is in the appropriate position to begin the Repetition.

2. Concentric Contraction – where the muscle shortens as the weight is lifted through the predetermined Range of Motion (ROM). Also called ‘The Positive Phase’.

3. Mid Point – the point of greatest contraction at the top of the Repetition where you pause briefly before releasing the weight.

4. Eccentric Contraction – where the muscle lengthens as the weight is released to the Finishing Point. Also called ‘The Negative Phase’.

5. Finishing Point – same as the Starting Point.

GUIDELINES TO PERFORMING THE PERFECT REP

Learn And Practice Proper Technique…

Take the time to study the extensive step-by-step video exercise descriptions on my website http://www.GlobalWeightTraining.com. They are demonstrations personally performed by me explaining all the muscles involved, the detailed technique and what the repetitions should look like during a set. There are over 300 hundred exercises; learn them before you perform them.

Apply And Maintain Proper Technique…

Once you have learned the exercise guidelines make sure you apply them to your training in the gym precisely and consistently. If you forget how to do something go back to the site and look it up.

Repetition Speed…

The repetition speed should for muscle growth and strength in bodybuilding, shaping and toning and for general health should be medium (1-2 seconds) during the Concentric Contraction (where the weight is lifted) and slow (2-5 seconds) during the Eccentric Contraction (where the weight is released). The exact seconds required for each phase of the repetition depends on the size of the range of motion (ROM) of each individual exercise. Example; Calf exercises have a smaller ROM so the time required to perform the repetitions slowly would be reduced. Squats, on the other hand, have a large ROM so the time required to perform the repetitions slowly would be increased. Performing exercise with speed is not without merit and it is prevalent in functional training, power-training, and sport-specific training but there is an increased risk of tissue injury with the sudden force exerted when lifting. There is also greater focus on the tendons, ligaments, bones and joints rather than the muscles.




Ancillary Muscles And Stabilizers…

You cannot perform an exercise safely or effectively unless your body is positioned in accordance with the guidelines for that exercise. This means that once you are set your ancillary muscles (the direct assisting muscles for the movement) and the stabilizers (the muscles that hold the rest of the body in the correct place) must be engaged so that a perfect repetition is performed every time. This will make your body safe, strong and functional.

Abdominals And Core Muscles…

It doesn’t matter which exercise you are performing your mid-section must be switched on for total maximum gains. The abdominals and the core inner muscles of the spine are the superstructure of the body which holds everything together under the stresses of exercise. They lock you safely into the correct position and maintain it during the set. Engaging them properly will stabilise the body, increase your total strength, increase the strength of the abdominals and core muscles themselves, protect the spine and facilitate the implementation of perfect repetitions for all exercises. * To use your mid-section properly during exercise pull your lower abs in towards the spine, pull in the obliques, contract the entire abdominal complex and lift the chest *

Symmetry And Precision Of Movement…

To be certain that both sides of your body develop evenly you must ensure that each exercise is executed symmetrically. Human bodies are never built with faultless balance and the rigours of life make that deviation from perfect symmetry even more profound. To diminish the impact of this continuing you need to train in front of a mirror as much as possible or utilise the constant critical eye of a training partner. This will allow you to supervise and fine-tune your exercise technique at all times reducing imbalances of strength, muscularity and functionality.

Range Of Motion…

Most of the time you need to use a full range of motion (ROM) to stimulate the all of the muscle fibers from the origin, across the belly (the middle bulk), to the insertion of the muscle. If you cheat and continuously use partial repetitions you will lose flexibility and miss out on muscle and strength gains from the outer angles. There is a limit, however, to how large the ROM should be. It is individual to each exercise and should be large enough for maximum muscle fiber stimulation without causing any joint or tissue injury from over-extension. There are techniques and set sequences that are based on partial repetitions but they have their own strict technique and should be used sparingly for shock tactics and variety.

Breathing…

You need to breathe properly during each repetition to maintain a continuous delivery of oxygen around the body to the working muscles. It will also reduce the build-up of carbon-dioxide. This will give you the energy to power through the set and decrease the onset of blood lactate accumulation (OBLA – that awful burn from lactic acid which is caused from glycogen being burnt for energy without the presence of oxygen). Breathing properly also takes the pressure off your cardio-vascular system facilitating normal function under conditions of high stress from intense exercise. It is important to keep the blood pressure down and unnecessary strain off the body as no-one is unbreakable. Another advantage of full, rhythmic breathing is that it will pace the tempo of your repetitions. You can’t take slow, full breaths if your reps are fast and messy.

BASIC BREATHING TECHNIQUE DURING A REPETITION

1. Take a slow, deep intake of breath as the weight is released (when the target muscle stretches and lengthens during the eccentric contraction).

2. Breath out more forcefully as the weight is lifted (when the target muscle engages and shortens during the concentric contraction)

3. There are alternate breathing techniques but this one is simple and safe so remember: breathe in when the weight is released and breathe out when the weight is lifted.

INTENSITY

Finally we come to my favorite word; Intensity. To cause the greatest amount of muscle fiber damage and to induce growth producing chemistry within the body you need to push each set to absolute failure or beyond. By that I mean that you make sure you grind out each repetition with perfect technique until it is not possible to perform another without losing your form. To go beyond failure you must utilise a training partner or spotter or perform intensity increasing techniques which are described on our website http://www.GlobalWeightTraining.com. You must however maintain precise technique for each repetition throughout the set no matter what your goal is or how far you push yourself.

There you have it my friends. I have given you the key. Place it in the lock and turn it. Don’t look back. There is so much out there to learn, understand and apply to your training. You may get a little lost among it all but if you know how to perform ‘The Perfect Rep’ every time the most basic element of successful training will be with you forever. Good luck and have fun…