Jessie Newell by Jessie Newell

This blog will highlight the key topics that are important for you as a fitness professional.

Concepts of Fitness

These are the components that are directly related to health and well-being, as opposed to the things that would improve performance (e.g., agility, speed, reactivity, coordination). While the components of physical fitness are things we NEED to maintain to be healthy, skill-related components are things we may WANT to work on for optimal performance.

  • Muscular strength is defined as how much force one could potentially create during a single given effort. This is important for activities of daily living (ADLs) such as lifting boxes into a car or carrying a child or grandchild. It is vital that we perform regular resistance exercises because we lose muscle mass as we age.
  • Muscular endurance is defined as the ability to resist fatigue over a period of time and is essential for ADLs such as walking across town, mowing the lawn, etc.
  • Cardiovascular endurance is defined as the maximal capacity of the heart, blood vessels, and lungs to deliver oxygen and nutrients to the working muscles so that energy (ATP) can be produced. This is important for ADLs, such as walking, swimming, biking, and hiking, and plays a significant role in reducing the risk of many diseases.
  • Flexibility is the ability to move a joint through a normal range of motion (ROM). We lose mobility for a number of reasons as we age, so it is important that our joints retain ROM.
  • Body composition refers to the distribution of fat mass vs. lean body mass (LBM) that comprises one’s mass (weight). LBM plays a significant role in weight management. By keeping percent body fat in a healthy range, individuals can reduce the risk for health issues such as hypertension, type 2 diabetes, and coronary artery disease.


Energy Systems 

The body needs energy in the form of adenosine triphosphate (ATP) and has three ways of making it during exercise: the phosphagen system, anaerobic glycolysis of carbohydrates, or aerobic or oxidative glycolysis of carbohydrates or fats. Which system the body uses depends on the duration and intensity of the activity performed (this is discussed further in Chapter 5). It is crucial to understand these systems because we need to manipulate the duration and intensity of our clients’ workouts to make sure their programs are specific to their goals. This knowledge can also help address concerns such as how much rest is appropriate in between resistance exercise sets. For a more detailed explanation of the three energy pathways, click here.

  • Phosphagen System: This system is available immediately but can only last a maximum of five to 10 seconds of all-out exertion. It is primarily responsible for quick, powerful movements, and the initiation of high-intensity activities such as sprinting or powerlifting.
  • Anaerobic Glycolysis: This system is available very quickly and can last up to a maximum of approximately three minutes (variable with training—see “Connecting the Dots,” below, for more information), but lactic acid is a byproduct, so it cannot be maintained for long periods. It is primarily responsible for all activities requiring large bursts of energy for relatively more extended periods.
  • Aerobic or Oxidative Glycolysis: This system takes longer to produce ATP, but is most efficient and allows one to go for the most extended duration. This system is responsible for low- to moderate-intensity activities as they can be maintained for long periods. They are also responsible for energy production for ADLs.


Connecting the Dots:

Revisit the anatomy of the muscles and let’s relate this to the muscle fiber types. We have Type I fibers (slow-twitch) that are for slower, more sustainable activities. These fibers mostly derive energy from aerobic glycolysis and are red in color due to a high density in blood vessels. Type II muscle fibers are for faster, shorter duration activities, and consist of two types: Type IIa and Type IIx. Type IIx are the fastest, so they will predominantly derive their energy from the phosphagen system and will be white in color. Type IIa fibers can last for relatively longer periods of time, but will still fatigue within a few minutes. Also known as fast oxidative glycolytic (FOG) fibers, Type IIa fibers can be trained to last longer (anaerobic endurance). Think for a second of the light and dark meat of a chicken, and the activities that a chicken does. The dark meat (legs/thighs) are darker (indicating Type I fibers deriving energy aerobically) because a chicken spends most of its day walking around at a slow, maintainable pace. The breast and wings are lighter meat (indicating Type II muscle fibers and anaerobic energy production) because the only thing a chicken uses them for is a quick burst of “flying” so it doesn’t need to be as vascular.


Ventilatory Thresholds (VT1 and VT2) and VO2:

First and foremost, it’s important to understand the difference between VO2 and Ventilatory Thresholds. This information plays a big role when trying to decide whether to do a VO2 assessment or a ventilatory threshold assessment.

  • VO2 is looking at oxygen consumption. The more efficient a person’s cardiovascular system becomes, the more he or she is able to deliver and utilize oxygen, so we look at this when trying to understand a client’s cardiovascular health.
  • VT1 is the body’s first marked increase of respiration and heart rate and is associated with the lactate threshold (LT) or point at which too much lactic acid accumulates within the muscle and has to be spilled out into the blood to be buffered or broken down to be re-used. Ventilatory thresholds are defined as nonlinear increases in respiration and heart rate (see page 80 of the Essentials of Exercise Science Manual). This is the point when the body must “step it up a notch” to meet the demands of this intensity—you can see by the dotted line what the breathing rate would look like if it increased linearly. It is also the point at which the focus of the breathing changes from needing to draw in more oxygen to needing to blow off excess CO2.
  • VT2 is the second marked increase of intensity and the point at which the breathing rate increases. This point is associated with the onset of blood lactate accumulation (OBLA), where lactic acid is accumulating faster than the body could possibly buffer or break down. Intensity above VT2 will eventually cause the body to fatigue when the lactic acid overwhelms the blood's neutral pH level, and the higher the intensity the faster that accumulation of lactic acid occurs.