Minute Ventilation as a Measure of Fitness and Endurance
By: RTM Vital Signs LLC
When exercising, a person will breathe deeper and more often in order to supply the muscles with the oxygen (energy) they need and to remove carbon dioxide (waste). Exercise, over time, will increase the strength and function of muscles, making them more efficient – requiring a lower amount of oxygen to power them or alternately the same amount of oxygen to produce more power from the muscles. Over time, lung capacity improves, muscle efficiency improves, endurance improves, and performance/fitness improves. Fitness is defined as the ability to breathe in enough oxygen to power muscles. Respiratory Rate (RR) alone does not provide information on how much oxygen is taken in during exercise and therefore cannot be used to track improvements in muscle efficiency, the volume of air per breath, called Tidal Volume (TV), is also required. As fitness improves, the volume of air inhaled/exhaled per minute, called Minute Ventilation (MV) increases. RR x TV = MV. If MV is increased by increasing TV, it will have a greater effect on gas exchange than if the same MV is reached by increasing RR.
An average person at rest breathes around 10 breaths per minute with a tidal volume around 500 ml/breath. Thus, a person at rest with a RR = 10 and a TV = 500 ml has a minute ventilation of 5,000 ml or 5 liters/minute. Minute Ventilation commonly exceeds 30+ liters/minute during strenuous exercise. Minute Ventilation (MV) is the critical parameter for fitness and endurance.
As respiratory muscles (diaphragm and intercostals) are strengthened, endurance improves. In fact, there are studies that have shown that separate respiratory (breathing) training resulted in improved endurance and reduced blood lactate levels. Many of these studies are recent have been done within the last 2-5 years and the information/data on respiratory function effects on endurance and performance are emerging (https://www.peakendurancesport.com).
The measurement of minute ventilation (RR x TV) during exercise correlates closely with the body’s production of CO2 and total body cellular metabolism. Thus, the pattern of minute ventilation during everyday living and exercise is an excellent metric that athletes and the general public will use to gauge their overall body fitness. The concept of real-time monitoring of minute ventilation (RR x TV) as a marker for physical fitness will complement the millions of people that currently monitor their heart rate during exercise (cycling, running, playing sports) as a gauge to their physical fitness.
The average person who purchases an Apple watch or Fitbit to track fitness parameters (57 million people in the US alone) does so to improve their fitness – what gets measured gets improved. Respiratory function is a primary parameter of fitness. It hasn’t been included in general public devices because there hasn’t been a way to measure MV. There is currently no wearable product on the market, with a cell phone application, that can monitor and track MV during an individual’s daily activities, exercise, and sleep. RTM fills this gap by providing BOTH the RR and TV in the MV= RR x TV equation.