Factors affecting energy metabolism [] Dauncey, M. Lookup at Google Scholar. Factors affecting energy metabolism. Abstract: Basal metabolic rate BMR is the energy expenditure in a post-absorptive state, 12 hours after the last meal and with the subject at rest in a comfortably warm room. To examine the effects of overeating and undereating on RMR, subjects lived in a calorimeter at 26 degrees C for 27 hours on three occasions--high, medium and low energy intake.
During underfeeding the metabolic rate decreased significantly during the day. Johnstone, A. Factors influencing variation in basal metabolic rate include fat-free mass, fat mass, age and circulating thyroxine, but not sex, circulating leptin or triiodothyronine.
American Journal of Clinical Nutrition, 82, 5, — International Journal of Obesity, 14, 4, — With the popularity of high-intensity interval training rising fast, trainers need to understand the physiological principles that make this training approach so effective, particularly for helping clients overcome plateaus and achieve their weight-loss goals.
The ACE Metabolic Training Workshop provides the tools and information you need to safely offer your clients fun and effective high-intensity metabolic conditioning sessions that will help them shed pounds and keep them coming back for more. There are no prerequisite educational requirements to attend this workshop and registration closes two business days prior to the workshop date. Click here for more information on when this workshop will be offered and how to register, or call , Ext.
Mark P. Kelly, Ph. He has been involved in exercise sciences as an author, presenter, trainer and athlete for more than 25 years. He has been teaching sciences in universities and performing research and physiological assessments in exercise science for more than 20 years.
He currently creates workshops, presentations, webinars and articles to bridge the gap between science and application for trainers and the general public.
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Don't miss out! Save now. Be in a class of your own. Ends soon! Act now. Create your story as an ACE Specialist. Limited time! Talk with an Advisor. October By Mark P. During the first few seconds of intense muscular activity, such as sprinting, tennis serve or weight lift, ATP is maintained at a relatively constant level, but the CP level declines steadily as it is used to replenish the depleted ATP.
After around seconds of intense exercise activity, CP storage is exhausted and an alternative fuel must be used. Their potential total energy yield for a 20 kg muscle man is approximately 4. It has been estimated, however, that the energy cost of a m sprint is about 8 kcal, and if the duration of the sprint is 10s, the power is W So even if the ATP and CP of the entire muscle mass could be used for the sprint, there would be a remaining deficit in energy which has to be provided by glycolysis with the formation of lactic acid.
Carbohydrates blood glucose and glycogen from muscle or liver are the only macronutrients whose potential energy can generate ATP anaerobically as well as aerobically Before either glucose or glycogen can be used to generate energy, it must be converted into a compound called glucosephosphate Figure 2. Conversion of a molecule of glucose requires one molecule of ATP. In the conversion of glycogen, glucosephosphate is formed directly from glucosephosphate with no need for extra energy expenditure.
The anaerobic glycolysis begins once the glucosephosphate is formed and produces pyruvic acid that is converted to lactic acid as an end product. During this process, 3 molecules of ATP are formed from each glucose residue originated from glycogen or 2 molecule of ATP for each molecule of glucose Figure 2.
The anaerobic glycolysis contributes energy during an all-out effort lasting maximum 1 to 2 minutes, and may produce power of around W Unfortunately, this energy system does not produce larger amounts of ATP and cannot generate energy for longer duration activities. Furthermore, the lactic acid production impairs glycolytic action and decreases the muscle fibers' calcium binding capacity which may impede muscle contraction 5. Production of energy in amounts sufficient to support continued muscle activity for longer than 2 minutes requires the input of oxygen.
The rest is being released when pyruvate enters the aerobic pathway of energy production where it is irreversibly converted to acetyl-CoA and degraded within mitocondria in the Krebs cycle Figure 2.
The complete oxidation of 1 mole of glucose produces 36 moles of ATP. The aerobic pathway can also provide ATP by metabolizing fats and proteins. Fat energy reserves are stored in the human body as triglycerides. To release energy, triglycerides must be hydrolyzed lipolysis to fatty acids and glycerol as follows:. Most of the fatty acids that skeletal muscle is exposed to during exercise are derived from subcutaneous adipose tissue, with a small amount derived from plasma triglycerides and intramuscular triglycerides.
Fatty acids released from adipose tissue are transported to the muscle in the plasma where they are bound to albumin. At the muscle site, fatty acids bound to albumin or stored in the core of chylomicrons and very low density lipopoproteins VLDL have to be released prior to transport across the membrane.
In the case of VLDL and chylomicrons, this is achieved by the lipoprotein lipase enzyme. For each carbon fatty acid molecule, ATP are produced. As triglyceride molecule contains three fatty acid molecules, ATP are formed from one triglyceride component Glycerol can also be used to yield a small amount of energy.
Transformed to 3-phosphoglyceraldehyde, it can degrade to pyruvate and enter the Krebs cycle. Glycerol also provides carbon skeletons for glucose synthesis Figure 3. Although the primary fuels contributing to oxidative metabolism during prolonged exercise are fats and carbohydrates, proteins amino-acids can be used as a source of substrate oxidation.
The use of amino-acids as a fuel is increased when other substrates, especially carbohydrate, are not available. Amino acids can be converted to acetyl-CoA or Krebs cycle metabolites to enter the oxidative process, or be synthesized to glucose when glycogen reserves run low Figure 3. In order to enter the pathways of energy production, amino acids are converted to Krebs cycle metabolites.
This conversion requires transamination or deamination of amino acid and consecutive incorporation of nitrogen into urea molecule. Because some energy is spent in this process, the metabolized protein yields 4. Carbohydrates muscle glycogen and plasma glucose and fats plasma fatty acids and intramuscular triglyceride are thus the primary energy sources during exercise. The proportion of their contribution to energy expenditure is determined largely by the intensity and duration of substrate utilization.
At this intensity, the rate of appearance of fatty acids in plasma is very similar to the rate of fatty acid oxidation i. The rate of fatty acid oxidation is determined from direct measures of the rate of appearance Ra of glycerol, which is an index of lipolysis defined as 3 x glycerol Ra, as 3 fatty acids and 1 glycerol molecule are released from 1 triglyceride during lipolysis.
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