Category Archives: Encyclopedia
Waist Circumference
Waist circumference is a measurement that gives an indication of fat related health risk. Although your body composition is an important indication as well. Not everyone has access to a reliable device to measure body composition such as an MRI-scan or DEXA scan or to someone skilled with a skin fold caliper. To measure waist circumference only a flexible measurement tape is needed so it is accessible to practically everyone and not complicated. In addition, body fat is not distributed in the same way for everyone. Two persons with the same relative amount of body fat can store their fat on different locations such as hips or inside the abdomen. Since internal abdominal fat (see also visceral fat) greatly increases risk of developing cardiovascular disease and diabetes mellitus type 2 and more visceral fat corresponds with an increased waistline, this measurement can help indicate whether or not you are at increased risk for developing these disorders.
How to measure waist circumference
Take a flexible measurement tape and put it around your waist. The tape measure should be held above the navel but below the lowest ribs at the narrowest point of the torso. Make sure the tape measure is completely horizontal and that the one who is measured stands upright and relaxed and before measurement breathes out normally. Compare the value with those in Table 1 below to get an indication of developing cardiovascular disease or other fat related conditions.
| Waist circumference norms (in centimetres and inches) | ||
| Men | Women | Risk category |
| Less than 94cm (37 inch) | Less than 80cm (inch) | Low |
| 94-102cm (37-40 inch) | 80-88cm ( inch) | High |
| Greater than 102cm (40 inch) | Greater than 88cm ( inch) | Very high |
Table 1: Waist circumference norms
Note: these norms apply to Caucasian adults and Asian women. Currently not enough data on other ethnic groups is available.
Risk category:
Low: You are not at increased risk of developing lifestyle related diseases such as cardiovascular disease. You can maintain your current lifestyle, although it does not hurt to improve it further.
High: You are at increased risk of developing cardiovascular disease or other lifestyle related diseases. Either improving your diet, decreasing your energy intake or starting strength and endurance training will help losing weight and abdominal fat.
Very high: You are at very high risk of developing lifestyle related diseases. Large changes in lifestyle in multiple areas are necessary to improve your health. Improve your diet, decrease your energy intake, start training to increase muscle mass and improve cardiovascular endurance and exercise more every day.
References:
-Bushman, B. (2011). Assesing Personal Fitness. Complete Guide to Fitness & Health. First Edition. USA Human Kinetics.
-Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults. 2007.
Visceral Fat
Visceral fat is fat that is located around the organs in the abdominal cavity, including around the stomach, intestines, liver and kidneys. It is different in structure than subcutaneous adipose tissue and intramuscular fat and also producessubstances that play an important role in the immune system.
However, an excess of visceral fat also leads to an over-production of these chemicals, and is associated with a greater risk of developing coronary heart disease, type 2 diabetes mellitus, and inflammation-related disorders. A too large amount of visceral fat, is also known as abdominal obesity.
While an excessive amount of visceral fat is common in people that are overweight or obese certainly, it is also possible that people with an apparently healthy BMI have too much visceral fat. As a result these people can have a increased risk on developing the diseases mentioned above.
The amount of visceral fat can be reduced by a healthy lifestyle with a healthy diet and regular, sufficient physical activity and exercise and sufficient sleep. In addition, it has been shown that different types of training not only help reduce the amount of visceral fat but also counteracts the negative effects of too much visceral fat.
Testosterone
Testosterone is an androgen (male sex hormone) that promotes the development of secondary male characteristics during puberty. These include characteristics as a deeper voice, facial hair and an increase in muscle mass. Testosterone stimulates, directly (through testosterone receptors on muscle fibers), and indirectly, (through stimulating Growth Hormone production in the pituitary), hypertrophy. The increase in muscle mass caused by testosterone increases muscle strength. However this is not the only reason muscle strength increases. Testosterone can also bind with receptors on neurons (nerve cells), where it influences the production of neurotransmitter and the structure of nerve cells. Testosterone increases strength not only by increasing muscle mass but by improving muscle activation as well.
Testosterone is primarily produced in the testicles in men, and in the ovaries and adrenal glands in women. Men produce 15-20 times more testosterone than women, and the effect of different training protocols is greater on testosterone levels in men as well. In women, testosterone levels are hardly influenced by strength training or other forms of exercise, which partly explains the lower potential in women for increasing muscle mass.
In addition, an artificial form of testosterone (androgenic anabolic steroids) is used to stimulate muscle strength, hypertrophy and contraction speed, to increase performance in sports and athletic events. Most athletic organizations have banned the use of androgenic anabolic steroids and athletes who are caught using them risk suspension. Moreover, the use of androgenic anabolic steroids increases risk of developing cardiovascular disease and several forms of cancer.
References:
– Baechle, T.R., Earle, W.R. (2008). Endocrine Responses to Resistance Exercise. Essentials of Strength Training and Conditioning. Third Edition. USA. Human Kinetics. -Wilmore, J.H., Costill, D.L., Kenney, W.L. (2008). Ergogenic Aids and Sport. Physiology of Sport and Exercise Fourth Edition. USA Human Kinetics.
Supersets
Superset training is a form of exercise organization in strength training, in which a combination of two exercises are alternated without rest. Many combinations of exercises are possible, but traditionally two antagonistic exercises are combined, which target opposite muscle groups. This way, when performing the second exercise, the muscle groups that were active during the first exercise are allowed a short rest before their second set.
Superset training has several advantages over traditional 3 set per exercise training. Firstly, by combining two exercises without rest, training time is effectively cut in half. Secondly, because the muscles get a shorter rest period, and because they can rest less effectively while other muscles are active during their rest, muscles can not recover as well as during normal training. This results in increased acidification, lactate production and muscle fatigue, which can lead to greater muscle adaptations and muscle growth. Thirdly, due to the same amount of work performed in less time, the body’s work capacity increases and needs more energy during recovery (EPOC), which helps weight loss and improvement in body composition.
Superset training is less suitable for those just starting strength training because training intensity is higher than during regular strength training with rest periods after each set. Superset training is mostly done by combining exercises targeting opposite muscle groups, such as biceps and triceps. However, it is possible to make other combinations as well, such as a standing calf raise and shoulder press (calves and shoulders). As long as muscle groups during one exercise, are not or hardly active during the second exercise, they can effectively be combined into a superset.
Sarcomere
Muscles are responsible for making movements through muscle contractions. Muscles consist of many different fibers, which consist of myofibrills. Myofibrills in turn consist of many sarcomeres in series. A sarcomere is the smallest functional unit in a muscle and is the structure that makes the muscle contraction possible.
A sarcomere consists of thin actin filaments and thick myosine filaments, which can slide past each other when the sarcomere contracts. The actin filaments are connected to the z-lines which form the connections between the sarcomeres in series. The myosin filaments are in the middle of the sarcomere in the center of several actin filaments. Each myosin filament has myosinheads portruding from the filament, which can bind to special binding places on the actin filaments. Through this interaction between actin and myosin filaments, sarcomeres are able to exert force.
When a contraction is started, the myosin heads are activated and form so called cross-bridges by binding at the binding places at the actin filaments. After forming the cross-bridge, the myosinhead pulls at the actin filament, and the filaments slide past each other, shortening the sarcomere. After this, the myosinhead unbinds and returns to its original position, ready to form another crossbridge with the next binding place.
References:
-Wilmore, J.H., Costill, D.L., Kenney, W.L. (2008). Structure and function of exercising muscle. Physiology of Sport and Exercise Fourth Edition. USA Human Kinetics.
Range of Motion
The range of motion is a term which is used to describe the range through which a joint or muscle can move. The range of motion of a joint is dependent on several factors such as the stiffness of tendons or ligaments, activity level, age, gender and structure of the particular joint.
During training it is important to move through an as large as possible part of the available and safe range of motion. This results in a more effective training for the active muscles and flexibility is maintained or even increased. A limited range of motion can be detrimental to performance in sports and is related to developing physical problems such as low back pain. In addition a limited range of motion also increases risk of injury.
See also:
Muscles and Muscle Fiber Types
The limbs of the body are able to move because muscles contract and excert force on the skeleton. Muscles consist of muscle fibers and a single muscle fiber in turn is made up of smaller units called sarcomeres. 
VO2Max
The oxygen uptake or VO2 is the amount of oxygen that the body takes in to supply the oxygen which is required for several physiological processes. The oxygen is absorbed by the blood through the lungs and transported to various tissues throughout the body that require oxygen. At rest most oxygen is consumed by the heart, brains and internal organs. When exercise starts, the VO2 increases (breathing frequency and tidal volume both increase) as exercise intensity increases. The brain still needs the same amount of energt, but the heart and active muscles require the largest part of the oxygen uptake. VO2 will continue to rise as intensity rises until it reaches its maximum value or VO2max. VO2max is often used as a measure of endurance and is seen as the most important determining factor in endurance events such as cycling. The VO2max is often expressed relative to bodyweight (L*min-1*kg-1), but sometimes as an absolute value (L*min-1).
References:
-Guyton, A.C., Hall, J.E. (2000). The Cell and Its Function. Medical Physiology. Tenth Edition. Philadelphia, USA. W.B. Saunders Company.
Obesity
Obesity or adiposity,
is a medical condition which is characterized by a large amount of excess weight due to fat mass. Obesity is defined as a Body Mass Index larger than 30. A BMI of 40 or more is also known as morbid obesity.
Myostatin
Myostatin
Wendy the myostatin deficient dog
is a cytokine which functions as an antagonist for Insulin-like Growth Factor-1. It is therefore a negative regulator of muscle growth. In other words, it causes the breakdown of muscle tissue. It is an essential substance in maintaining balance in protein synthesis and protein breakdown. This is most obvious in animals that have mutations in their DNA, rendering the myostatin gene less active or even completely shutting it down. These animals have an highly increased muscle mass and look like bodybuilders among their species. This reduces muscle function as well, since myostatin also serves to improve muscle quality. However it also plays a major role in diseases such as muscle dystrophy, where myostatin activity is increased and muscle mass decreases progressively.
Muscle Contraction
A muscle consist of sarcomeres which can contract in three different ways, namely concentric, isometric and eccentric. But what is the difference in these types of muscle contraction?
Mitochondrion
The mitochondrion is an important cell organelle. The most important function of a mitochondrion is to generate ATP. The mitochondria are therefore often called the cells’ power plants. Mitochondria are present in almost almost all cells, but the number of mitochondria in a cell depends on the amount of energy the cell needs, and therfore large numbers of mitochondria are present in muscle fibers. The concentration of mitochondria is dependent on muscle fiber type and the demands placed upon the muscle. In addition the number of mitochondria in a muscle fiber adapts to endurance training or low intensity high repetition resistance exercise, which both target the aerobic system and stimulate the mitochondria to replicate.
Maximum Heart Frequency
The maximum heart frequency or maximum heart rate is the highest amount of beats the heart can make in a minute during intense exercise. The heart frequency is strongly dependant on the intensity of the exercise, with higher intensity exercise resulting in an higher heart rate. When the intensity of the exercise is increased up to a point where the heart frequency can not rise any further the maximum heart frequency is reached.
Lactate
Lactate is a substance produced during the anaerobic breakdown of glucose or glycogen. This process is also known as the anaerobic glycolysis. It is continuously produced and can be used to generate more ATP in aerobic metabolism or transported to the liver to be converted to glucose. Contrary to popular belief, lactate is not responsible for metabolic acidosis, or acid buildup in the muscle.
Lactate Threshold
The lactate threshold is the training intensity at which the concentration lactate starts to accumulate in the blood stream. Lactate, or rather lactic-acid, is a by product of the anaerobic glycolysis, which is an system which produces ATP at higher exercise intensities or when the aerobic energy systems are not yet able to generate the necessary ATP.
Interval Training
Interval training is a form of cardiovascular workout which is characterized by periods of higher intensity exercise followed by periods of lower intensity for recovery. In contrast, regular cardiovascular workouts consist of maintaining only one intensity of exercise for a prolonged period. Research has shown that interval training has considerable advantages over conventional cardiovascular training.
Insulin
Insulin is an anabolic hormone which is responsible for transporting excess glucose from the blood into the cells. In healthy person’s blood glucose will rise after a meal rich in carbohydrates. When the blood glucose is high enough, insulin will be secreted from the pancreas’ beta-cells which will transport the glucose to other storage sites, such as the glycogen stores in the muscles or liver, or when those are filled, the fat cells in adipose tissue. It stimulates protein transport into body cells and therefore stimulates muscle hypertrophy. And in addition insulin inhibits the usage of fatty acids to generate energy as well, so the body temporarily depends more on glucose metabolism.
Hypertrophy
Hypertrophy 
is the process of growing tissues. In exercise physiology it normally refers to muscle hypertrophy or the increase of muscle mass. Muscle hypertrophy as a result of training is caused by an increase of cross section of themuscle fibers which form the muscle. This increase is caused by an increase in net protein production.
Growth Hormone
Growth hormone is produced in the anterior pituitary gland. The best known function of growth hormone is stimulating cell growth in almost all tissues, hence the name. Growth in children is regulated by growth hormone. In adults it still has many important functions, not the least of which are inducing muscle growth or hypertrophy, stimulating bone mineralization and increasing lipolysis or fat metabolism.