Training and The Respiratory system

For information purposes only. Exercise at your own risk

Ever wondered about the science behind cardiovascular fitness? Me neither but in order to understand how to produce effective training routines, an underlying knowledge of basic physiology is essential.

Aerobic endurance refers to the intake, transport and utilisation of oxygen in modern parlance (Smith, 1999). 21% of inspired air is oxygen. Intake begins when air is breathed into the lungs.

Oxygen travels through the pharynx and larynx into the bronchial tubes and then through the bronchioles, into the lungs. air flows into the larynx, past your vocal cords, and down the trachea, which splits into the two primary bronchi—one feeding each lung. From there, the air continues to the ends of the bronchi, which bifurcate like thousands of stems branching from a trunk into about 30,000 tiny terminal “bronchioles” in each lung. At the ends of the bronchioles are tiny grape-like clusters of air sacs known as the alveoli. It is in the alveoli that the gas exchange with blood occurs.

The lungs enable the exchange of gaseous molecules from the environment with molecules in the bloodstream. Though the lungs are very compact; and encompass at total surface area, that is about 40 times larger than the surface area of the entire body.

Alveoli in the lungs enable oxygen to pass into the bloodstream, red blood cells, and carried to the rest of the tissues throughout the body. This is also where waste product carbon dioxide, is removed from the blood stream, allowing it to be expelled from the body.

alveoli are elastic cavities lined with a tiny amount of fluid and a molecule called surfactant, which prevents these airways from collapsing in on themselves. Surrounding the alveoli are networks of tiny capillaries that carry oxygen-depleted blood around the outside of the alveoli. When a tiny portion of air reaches the alveoli, gasses are easily dissolved into the fluid, and then exchanged with molecules in the adjacent bloodstream.

One important feature of the lungs, is the lung epithelium. This is the specialized layer of cells that line the alveoli. The epithelium is held together via what are known as tight junctions. These tight junctions are made up of proteins that insert through the membranes of adjacent cells and link the cells together so tightly that they prevent salt and other small molecules from passing through the gaps between the cells.

As with many aspects of fitness, the most apparent changes in aerobic capacity occur early on in training, and in the very unfit (Sharkey, 1990). Training increases the efficiency of the muscles that are incorporated into breathing, allowing the body utilise more oxygen during exercise. Training also reduces the residual volume (portion of lung capacity that is not utilised) and by increasing the inspiratory reserve volume and vital capacity. See table 1

I. Inspiratory Volumes
A. Inspiratory Reserve Volume (IRV)
1. Maximal inspired volume from end-tidal inspiration
B. Tidal Volume (Vt)
1. Volume inspired and expired with each normal breath
2. Minimum volume: 3 ml/kg
3. Normal volume: 6-7 ml/kg
C. Inspiratory Capacity (IC)
1. Maximal volume inspired from resting expiratory level
2. Calculation: IRV + Vt
II. Expiratory Volumes
A. Expiratory Reserve Volume (ERV)
1. Maximal expired volume from end-tidal inspiration
2. Normal: 25% of Vital Capacity
B. Residual Volume (RV)
1. Volume remaining in lungs after maximal expiration
2. Normal adult: 1.0 to 2.4 Liters
C. Functional Residual Capacity (FRC)
1. Volume remaining in lungs at resting expiratory level
III. Overall Lung Volumes
A. Vital Capacity (VC)
1. Maximal volume expelled after maximal inspiration
B. Total Lung Capacity (TLC)
1. Volume in lungs at end of maximal inspiration
2. Calculation: VC + RV
3. Normal adult: 4-6 Liters

References
A. Rollings (1984) Facts and Formulas, McNaughton & Gunn
B. Marini (1987) Respiratory Medicine, Williams & Wilkins

However, respiratory system functioning, is not usually a limiting factor in endurance performance as ventilation can be increased to a greater extent than cardiovascular function. Overall lung capacity remains relatively unchanged.

Respiratory rate is usually lowered at rest after training, and during submaximal exercise. In contrast, respiratory rate tends to increase at maximal levels after training.
After training, maximal pulmonary ventilation is increased. This is due to an increased tidal volume and respiratory rate at maximal exercise intensity. Typically, this can increase from 120L/min in untrained individuals to about 150L/min in after training.

Gas exchange at the alveoli increases during maximal exercise, and pulmonary blood flow, tends to increase following training, leading to increased lung perfusion. This increases pulmonary diffusion at maximal rates