In this topic - information on:
How muscles produce energy and burn calories
How your body produces energy from protein, carbohydrate and fat in your diet
The 4 different ways your body replaces used energy to keep you energised
Which is your least and most efficient energy replacement system
As you can imagine the Intensity / effort of exercise does vary the benefits of the exercise.
This when combined with the Frequency, Intensity and Time and Type of exercise (this forms the acronym FITT)
A short explanation of how muscles produce energy and burn calories, to produce movement will help provide an understanding.
This might be a bit technical, and you don’t have to understand it.
It's just nice to get a glimpse of another marvel the body performs – and how exercise aids weight management.
The unit of energy that is used in the body, when muscles contract, is called adenosine triphosphate (ATP)
You may be surprised to learn there are 656 muscles in the body that pull on the skeleton to produce movement.
It is these muscles that are the major user of energy provided by the food and drink (protein, carbohydrate and fat) we consume, which we digest and which in turn enters our blood stream to supply the cells, including muscles.
Our body produces ATP in the mitochondria (element of our cells) by using the protein, carbohydrate and fat in our diet – the process requires all 3 elements.
When a muscle contracts it uses one of phosphates of the energy unit which means the original triphosphate (3 phosphates) becomes adenosine diphosphate (2 phosphates) that is ADP.
It is how the body replaces the used phosphate to become ATP again, ready produce energy in the muscle repeatedly, that is of most interest as this is where energy (calorie burn) is used.
The body’s energy replacement systems, to replace the one phosphate are:
Creatine Phosphate (ATP-CP)
Glucose without oxygen (Anaerobic or Lactic Acid)
Glucose with oxygen (Aerobic)
Fat with, glucose, with oxygen
Our body is truly marvelous!
The body uses all these energy systems for the purpose of meeting the energy demand of the body from the start of any activity through to the highest intensity level of Maximum Heart Rate (MaxHR) exercise.
It is a good idea to read the topic Exercise Intensity and Benefits, along with the information in this topic.
For activities that achieve 60% of MaxHR or greater the energy systems used by duration are:
0 – 10 seconds: Creatine Phosphate (ATP-CP)
20 – 90seconds: Glucose without oxygen (Anaerobic or Lactic Acid)
90 seconds to several minutes: Glucose with oxygen (Aerobic)
More than several minutes: Fat with, glucose, with oxygen
Re-synthesis of ADP to ATP by energy system
Each of the systems have a different level of efficiency, depending on the molecule used in the re-synthesis process.
1. Phosphocreatine system
Quick re-synthesis of ADP to ATP.
Duration - Creatine Phosphate (CP) system does this almost immediately. Body only has short term supply, max 10 seconds.
Recovers for re-use with 3 min rest or active rest.
Waste product - None
1 molecule of CP for 1 molecule of ATP produced.
2. Anaerobic or Lactic Acid System
Duration - 20 – 90seconds
Glucose without oxygen. Glucose in the blood or Glycogen stored in the body used to supply phosphates i.e., Anaerobic Glycolysis.
Waste product - Lactic acid.
1 molecule of Glucose for 2 molecules of ATP produced.
3. Aerobic System: Glucose with oxygen
Duration - 90 seconds to several minutes
Glucose with oxygen. Glucose in the blood or Glycogen stored in the body used to supply phosphates i.e., Aerobic Glycolysis.
Waste products - carbon dioxide and water.
1 molecule of Glucose for 38 molecules of ATP produced.
4. Aerobic System: Fat with oxygen
Duration - From several minutes to hours
This is the dominant energy system used when the Exercise Heart Rate is between 60-80% of Maximum Heart Rate.
Intramuscular fat, or fat transported to the muscle can be used in the energy process. Small amounts of glucose and oxygen needs to be present; Mitochondria breakdown protein, fat, carbohydrates to release energy - carbon dioxide and heat are byproducts.
Waste products - carbon dioxide and water.
1 molecule of fat with glucose, oxygen present produces more than 200 ATP molecules.
This energy system is the most important to use to create the Foundational Cardio Conditioning upon which all other physical benefits can be built.
For an effective exercise session aimed at fat and weight loss, this Aerobic System; Fat with Oxygen is the optimal range to work within. Incorporating variations in exercise intensity, through Interval Training, significantly contributes to fat and weight loss by engaging energy systems that have a higher rate of energy consumption, as noted above.
Again, see the topic Exercise Intensity and Benefits.
Foundational cardio fitness is a measure of how well the heart, lungs, and blood vessels can transport oxygen and nutrients to the muscles during exercise. It is an important component of overall fitness and has been linked to numerous health benefits, including a reduced risk of cardiovascular disease, improved cognitive function, and increased longevity.
Additionally Foundational Cardio Fitness improves the removal of waste, principally carbon dioxide and lactic acid from the muscles, which aids endurance and in turn the potential for further, greater Health, Wellness and Fitness gains.
Again, this is the dominant energy system used when the Exercise Heart Rate is between 60-80% of Maximum Heart Rate, and so is the principle upon which the FitWell aerobic sessions are based.
A summary of the role of Protein
Protein plays a crucial role in the body’s energy systems, although it’s not the primary source of energy. Here’s how it works:
Building and Repairing Tissues: Protein is essential for building and repairing tissues, including muscles, skin, and organs. This process requires energy, indirectly contributing to the body’s overall energy expenditure.
Enzyme Production: Proteins are used to create enzymes, which are vital for metabolic reactions that produce energy. Enzymes help break down nutrients, including carbohydrates and fats, to release energy.
Hormone Regulation: Some hormones, like insulin and adrenaline, are made from proteins. These hormones regulate various body processes, including metabolism and energy production.
Direct Energy Source: In situations where carbohydrates and fats are not available, the body can convert protein into glucose through a process called gluconeogenesis. This provides an alternative energy source, especially during prolonged exercise or fasting.
Maintaining Energy Balance: Protein helps maintain energy balance by regulating appetite and satiety. Consuming protein can help you feel full longer, reducing overall calorie intake and supporting energy levels.
While protein is not the body’s preferred energy source, it plays a supportive role in maintaining and regulating energy systems.
More information see: Exercise Intensity and Benefits
Recommended Reading: What is a Pace Clock - How to use it
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