Cardiorespiratory fitness (CRF) defines the unceasing integrity of the cardiovascular and respiratory systems to support the musculoskeletal system in energy production during sustained physical activity or exercise (Lang, et al., 2018). It is determined by the VO2max – maximum oxygen uptake of an individual. The cardiovascular and respiratory systems work together to enhance this marker. Through numerous stages, oxygen and nutrients are supplied to the cells’ mitochondria while accumulating metabolic by-products of the cell are taken out. This process sustains the cells’ working intensity for longer periods. It also basically determines an individual’s CRF which makes it an important parameter to be assessed during health screening.
Higher levels of physical activity and exercise translate to higher and better cardiorespiratory fitness. This allows for better and more efficient exchange & transport of oxygen, nutrients and waste materials in the cardiovascular and respiratory systems. The cardiovascular network which consists of arteries, veins and capillaries does not get placed as a result. The absence of plaques in blood vessels drastically reduces the risks of hypertension, which is the most common risk factor for heart disease, and stroke and is usually the leading cause of mortality (World Health Organization, 2015). Also, when individuals with pre-existing hypertension achieve an increase in their CRF levels through structured exercise and physical activity, they experience a beneficial reduction of prehypertension and hypertension blood levels.
The risk of stroke is inversely associated with CRF and is evident in both gender and applies to both ischemic and hemorrhagic stroke. Therefore, an increased stroke incidence is linked to a lower CRF level (Hussain, et al., 2018 & Lee, et al., 1999). However, a change in fitness off-sets the risk of stroke incidence. The use of CRF programmes to rehabilitate stroke individuals is crucial in the reduction of risk factors for first and second-time stroke incidents.
Preventing diabetes is a top health issue in the twenty-first century. Obesity and physical inactivity are the key non-genetic predictors of diabetes (Tuomilehto, et al., 2001). Even though current treatments could help control diabetes, they are unable to eradicate all of its negative effects. Hence, it is preferable to prevent diabetes. The major way to do that is to increase cardiorespiratory fitness. This means increasing physical activity and exercise levels. Minor buildups of cardiorespiratory fitness have been linked to clinically substantial reductions in diabetes risk.
Also, individuals with higher cardiorespiratory fitness levels but living with diabetes possess decreased insulin resistance, improved glycemic control and improved lipid profile. Individuals who engaged in lifestyle intervention of moderate-intensity physical activity increased their cardiorespiratory fitness levels which lowered the risk of diabetes by 58% when compared to individuals who did not (McKinney, et al., 2016).
Depression is linked to a lower quality of life in terms of health and a lower level of adherence to medical treatments (Herring, et al., 2012). Furthermore, depression is linked to an elevated risk of cardiovascular morbidity and mortality on its own (Bradley & Rumsfeld, 2015). Depression worsens when the patients show withdrawal from activities such as physical exercise (Shomaker, et al., 2012).
Physical activity and exercise can significantly decrease depressive symptoms by 30% (Herring, et al., 2012) as a result of the antidepressant effect it has on the human brain. Hence, higher CRF levels lower depression effects on the brain. This is supported by fitness interventions aimed at lowing the significant burden associated with depression (Schuch, et al., 2016).
The human brain begins to lose grey matter in about 30 years of life. Grey matter is responsible for memory and thinking. Loss of grey matter could lead to brain diseases such as Alzheimer’s disease which predominately affects the aged. However, an increase in physical activity and CRF maintains cognitive function in older age and promotes healthy ageing by reducing the ageing effects on the human body. This benefit of increased CRF on cognitive function can last for 25 years (Zhu, et al., 2014). Williams, et al. (2017) also linked excellent cardiorespiratory fitness in older adults to a thicker cortex which reduces the rate of age-related cortical atrophy.
Exercise training and physical activity have an induced effect on the cardiorespiratory fitness of individuals (Lavie, Church, Milani, & Earnest, 2011). This can be attributed to the adaptation of the human body – cardiovascular and respiratory systems, in response to the stimuli physical activity places on it. The more stimuli the body receives from physical activity and exercise, the more it adapts to it. Therefore, individuals who frequent physical activity and exercise often have better cardiorespiratory fitness than their sedentary counterparts as a result of the difference in the efficiency of their cardiovascular and respiratory systems. In the same light, athletes also have a higher cardiorespiratory fitness level than non-athletes due to their constant training and the demands of the sports they engage in. Also, on average, males have better cardiorespiratory fitness than females since men are more physically active than females. At the end of the study by Lin, et al. (2015), participants in the exercise training group had higher CRF levels than those in the control group (sedentary group), who had no change or had lower CRF levels.
Ill health is a great impediment to attaining better cardiorespiratory fitness. Patients with comorbidities such as depression, stroke, coronary artery disease and heart failure tend to not engage in physical activity or exercise which decreases the output of their cardiovascular and respiratory systems, thereby, reducing their cardiorespiratory fitness. Active individuals would therefore possess greater cardiorespiratory fitness than individuals affected by ill health.
However, recent data propose that higher cardiorespiratory fitness is associated with improved survival and decreased cardiovascular diseases and other comorbidities including hypertension, diabetes, heart failure and stroke (Al-Mallah, Sakr, & Al-Qunaibet, 2018).
Ageing is the most uncontrollable factor in humans. Ageing brings about reduced efficiency of all body systems. The cardiovascular and respiratory systems are the most susceptible to a decline with ageing which directly leads to a decline in cardiorespiratory fitness. Hakola et al. (2011) observed a 1.6% decrease per year in VO2max in both genders. Thus despite males having better cardiorespiratory fitness than women, they both suffer a reduced cardiorespiratory fitness level. Also, a 5-10% decrement every 10 years in VO2max has been documented for untrained individuals (Fleg, et al., 2005). However, physical activity and exercise may help delay the onset of ageing.
Direct assessment of CRF is deemed the most accurate and often used in research. Individuals wear a face mask with volume and gas concentrations of inspired and expired air directly measured. The test involves either exercising on a treadmill or ergometer bike at an intensity that increases every few minutes until exhaustion and is designed to achieve a maximal effort. However, direct measurement pre-requisites skilled and competent staff, longer processing duration and can only be conducted in a laboratory. This measurement type is usually reserved for athletes due to the demands of their sports. Also, the usage of maximal testing could be contraindicative, especially for elderly individuals and cardiac patients since the test may increase the chance of a heart attack.
Another way to measure CRF is by the use of prediction equations that take into account an individual’s physical activity (PA) level, sex, age, waist circumference, and resting heart rate to provide a reasonable estimate of CRF.
Indirect Measurement involves the use of safe submaximal tests which includes walking, cycling and stepping. It also makes use of simple devices, is easy to be constructed, affordable, can be used for larger participants and saves time. Recognizing these strengths, several submaximal exercise tests have been developed to indirectly measure CRF and choosing the right protocol is not an easy task. Factors to be considered when choosing a submaximal protocol include:
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