Cardiorespiratory Fitness and Health

Now that we have discussed the various methods for measuring body weight, body fat, and fat distribution, it is important to spend some time discussing a fitness-related indicator of health.

Cardiorespiratory fitness (CRF) refers to the integrated ability of the circulatory and respiratory systems to transport oxygen to the mitochondria of skeletal muscle for ATP production required to perform physical work.^[1] Since CRF refers to the functional capacity of numerous body systems, it is often considered a predictor of total body health. Numerous studies have consistently reported that CRF is a strong and independent predictor of cardiovascular disease and all-cause mortality risk. In fact, CRF has been reported to be a more meaningful predictor of morbidity and mortality risk than other conventional risk factors such as hypertension, obesity, hyperlipidemia, type II diabetes, and smoking. A CRF level of <5 METs indicates an elevated risk of mortality, whereas CRF levels of >8 to 10 METs reflect increased survival.^[2] Despite these clinical observations and findings, the importance of CRF in determining one’s CVD/mortality risk can be undermined by healthcare professionals and CVD specialists. While it is useful to measure traditional risk factors such as smoking and obesity, the addition of CRF as a risk factor may allow healthcare professionals to more accurately assess a person’s risk of experiencing adverse health outcomes.

Measuring Cardiorespiratory Fitness

CRF can be measured directly, in the form of maximal oxygen consumption (VO2max), or predicted using the peak oxygen consumption achieved on a treadmill/cycle ergometer exercise test.  Some examples of a predictive VO2max test include the Balke and Ware Treadmill Test and the 6-Minute Walk Test. During the Balke and Ware Treadmill Test, the speed is set to 3 mph for females and 3.3 mph for males at 0% grade. For men, after the first minute, the grade is raised to 2% and then increased by 1% for every minute thereafter. For women, after 3 minutes, the grade is raised by 2.5% and then increased by 2.5% every 3 minutes thereafter. The Balke and Ware is a great test because it can be performed maximally to evaluate cardiac function in clinical settings and submaximally to assess CRF in fitness settings. Additionally, since the speed is kept constant, this test is also appropriate for deconditioned and elderly populations that may experience gait disturbances at high speeds. On the other hand, the 6-Minute Walk Test (6MWT) is a great submaximal field test to use among clinical and older populations. In this test, the distance covered by an individual in 6 minutes is recorded. The American Thoracic Society recommends using a 30 m unimpeded walking course and using a lap counter to keep track of how many laps the individual has completed. The 6MWT is a great option because this test requires minimal equipment and is very easy and quick to administer. Although VO2max or VO2peak measurements are ideal for determining one’s CRF level, not all patients are willing to perform exercise stress tests. For such patients, it may be beneficial to have them fill out self-report physical activity questionnaires. Although self-report questionnaires may not be the most accurate measure of CRF, they can still provide the healthcare professional with a broad understanding of the patient’s CRF levels and disease risk. One such publicly available questionnaire is the International Physical Activity Questionnaire (IPAQ), an open-access 27-item self-report measure of physical activity levels among individuals aged 15 years or older.

 Physical Activity Guidelines and Health

It is also important for clinicians to educate clients on the numerous health benefits associated with exercise beyond weight loss. This is because research has consistently demonstrated that exercise alone is not an effective method for experiencing weight loss. The current Canadian 24- hour Movement Guidelines ^[3] recommend that individuals meet 150 minutes of moderate to vigorous-intensity exercise per week for adults aged 18-64. Following these guidelines is associated with a lower risk of mortality, cardiovascular disease, hypertension, type 2 diabetes, several cancers, anxiety, depression, dementia, weight gain, adverse blood lipid profile. as well as improved bone health, cognition, quality of life and physical function. However, the American College of Sports Medicine (ACSM) states that up to 60 minutes of moderate to vigorous-intensity exercise per day is needed when relying on exercise alone for weight reduction. ^[4]  These ACSM are supported by another research study, in which male participants living with obesity (LWO) demonstrated a 7.5 kg body weight reduction in 3 months in the exercise group, which was comparable with the results seen in the calorie-restricted group. The participants in the exercise group were required to meet a daily 700-calorie energy expenditure goal, which translated to 60 minutes of exercise per day.^[5] Therefore, extremely high volumes of exercise are required to see meaningful reductions in body weight. Additionally, inter-individual differences contribute to the heterogeneity in individual capacity for weight loss in response to exercise interventions. While some individuals achieve clinically significant weight loss, others may experience either minimal to no changes in body weight or even experience some weight gain in response to exercise training without caloric restrictions. However, clinical studies have shown that those who are classified as being overweight or having obesity report no weight loss or modest weight loss (<5 kg) from exercise training but still experience numerous health benefits such as improved cardiorespiratory fitness (CRF), glucose control, endothelial function, lipoprotein particle size, high-density lipoprotein, and overall quality of life.^[6] From this, it can be understood that exercise programs do not always guarantee weight loss. Instead, exercise programs guarantee vast improvements in cardiometabolic health profiles and cardiorespiratory fitness levels independent of weight loss.

Ethnicity-Specific Guidelines

Due to the cumulative effects of modernization and colonization, many Indigenous peoples do not currently meet the 150 minutes per week of moderate-vigorous physical activity recommendations. Researchers have found that cultural land-based activities such as hunting can be used to promote increased physical activity participation among Indigenous peoples. In one study, researchers recruited six middle-aged male hunters of the Esk’etemc Indian Band and recorded their heart rate (HR) and step count on two days of hunting and two days of their daily regimen while living on-reserve, respectively.^[12] The results of the study showed that although there were no significant differences in mean HR and average step count between the hunting and living on-reserve days, the time spent engaging in light, moderate, and vigorous activities was two times greater on the hunting days when compared to the on-reserve days.^[13] Moreover, the greatest health and fitness benefits were derived from successful hunts, as the strenuous task of handling the animal greatly increases exercise intensity.^[14] The results of this study highlight the importance of including culturally appropriate and relevant ways of remaining physically active, such as hunting, in the Canadian Physical Activity Guidelines (CPAG) to increase physical activity participation among diverse cultural groups in Canada.