I. Field of the Invention
This invention relates generally to an apparatus and method for determining an appropriate, individualized exercise regimen to optimize the desired goal of reducing fat or improving cardiovascular performance, and more particularly to a method and apparatus for providing real-time monitoring to assist a subject in matching his/her goal.
II. Discussion of the Prior Art
As described in the Snow et al. U.S. Pat. No. 6,554,776, which is assigned to the applicants' assignee and the contents of which are hereby incorporated by reference, it is well recognized that with increasing exercise, muscles need to burn metabolic substrates to perform mechanical work. Carbohydrates and fat are then typical fuel sources that must be metabolized to provide energy. As a result of this metabolism, oxygen is consumed to provide energy and carbon dioxide is produced as a byproduct. A typical response to exercise is to increase the delivery of oxygen to the working muscles by increasing blood flow that also facilitates the removal of carbon dioxide by delivery to the lungs for excretion. This oxidative process, known as aerobic metabolism, causes a proportional increase in oxygen consumption and carbon dioxide production that is closely coupled with the level of work being performed. Aerobic metabolism uses a mixture of fat and carbohydrate substrates. The respiratory exchange ratio (RER), also sometimes called the respiratory quotient (RQ), represents the amount of carbon dioxide (CO2) produced, divided by the amount of oxygen consumed (VO2). At rest, and with light exercise, the RER generally ranges from 0.7 to 0.85 and is dependent, in part, on the predominant fuel used for cellular metabolism.
As the level of work continues to increase, and the ability to increase the delivery of oxygen to working muscles approaches its maximal limits, alternative methods are activated to supplement the energy produced through aerobic processes. This alternate method, known as anaerobic metabolism, predominantly uses carbohydrate substrates that disproportionately increase carbon dioxide production relative to oxygen consumption. This disproportionate increase is reflected by an increase in the RER from 0.9 to 1.3 or greater.
One of the values of the RER measurement is that it permits identification of the anaerobic threshold (AT) and, therefore, identifies the work rate where aerobic processes are no longer adequate. The term “anaerobic threshold” is based on the hypothesis that at a given workrate, the oxygen supplied to exercising muscles does not meet the oxygen requirements. This imbalance increases anaerobic glycolsis for energy generation, yielding lactate as a metabolic byproduct. The AT is a point during exercise at which ventilation abruptly increases despite linear increases in work rate and oxygen uptake. As described in the Acorn et al. U.S. Pat. No. 5,297,558, exercise prescriptions and protocols for increasing fitness and weight loss are based on knowing or assuming this threshold. Typically, the measurement is made during a baseline test and the exercise prescription is based on the threshold as determined from the RER. However, it is understood that the anaerobic threshold will change during the training period as the cardio respiratory system becomes more efficient and subsequent testing is required to adjust the prescription for the training effect.
In the past, measurement of RER has typically been possible only in laboratory environments using computerized exercise testing systems, such as that described in the Anderson et al. U.S. Pat. No. 4,462,764 and the Howard et al. U.S. Pat. Nos. 5,060,656 and 5,117,674. These devices measure ventilation using airflow, oxygen and carbon dioxide levels using discrete analyzers and a computer is employed to perform computations to determine the oxygen uptake and the carbon dioxide production. The calculation of RER is a secondary calculation. The drawback to this approach for measuring RER is the expense and complexity of integrating three sensors with a computer, aligning the signals time wise and maintaining calibration for all three sensors. The technique of ventilatory gas measurement has a number of potential limitations that hinder its broad applicability. Gas exchange measurement systems are costly and require meticulous maintenance and calibration for optimal use. Personnel who administer tests and interpret results must be trained and proficient in this technique. Finally, the test requires additional cost and time, as well as patient cooperation. Thus, a need exists for a simple, inexpensive sensor or monitor that can be directly employed by an untrained subject during the course of exercise to monitor his/her own RER. In turn, the subject may determine his/her heart rate at a detected AT and then pace his/her exercise by maintaining a heart rate at a predetermined percentage below heart rate at AT if the goal is to burn fat or at a predetermined percentage above heart rate at AT if the goal is improved cardiovascular performance.