Prevalence Of Cardiorespiratory Fitness Research Articles

Refuting the myth of non-response to exercise training: 'non-responders' do respond to higher dose of training.

The prevalence of cardiorespiratory fitness (CRF) non-response gradually declines in healthy individuals exercising 60, 120, 180, 240 or 300min per week for 6weeks. Following a successive identical 6-week training period but comprising 120min of additional exercise per week, CRF non-response is universally abolished. The magnitude of CRF improvement is primarily attributed to changes in haemoglobin mass. The potential for CRF improvement may be present and unveiled with appropriate exercise training stimuli in healthy individuals without exception. One in five adults following physical activity guidelines are reported to not demonstrate any improvement in cardiorespiratory fitness (CRF). Herein, we sought to establish whether CRF non-response to exercise training is dose-dependent, using a between- and within-subject study design. Seventy-eight healthy adults were divided into five groups (1-5) respectively comprising one, two, three, four and five 60min exercise sessions per week but otherwise following an identical 6-week endurance training (ET) programme. Non-response was defined as any change in CRF, determined by maximal incremental exercise power output (Wmax ), within the typical error of measurement (±3.96%). Participants classified as non-responders after the ET intervention completed a successive 6-week ET period including two additional exercise sessions per week. Maximal oxygen consumption (V̇O2 max ), haematology and muscle biopsies were assessed prior to and after each ET period. After the first ET period, Wmax increased (P<0.05) in groups 2, 3, 4 and 5, but not 1. In groups 1, 2, 3, 4 and 5, 69%, 40%, 29%, 0% and 0% of individuals, respectively, were non-responders. After the second ET period, non-response was eliminated in all individuals. The change in V̇O2 max with exercise training independently determined Wmax response (partial correlation coefficient, rpartial ≥0.74, P<0.001). In turn, total haemoglobin mass was the strongest independent determinant of V̇O2 max (rpartial =0.49, P<0.001). In conclusion, individual CRF non-response to exercise training is abolished by increasing the dose of exercise and primarily a function of haematological adaptations in oxygen-carrying capacity.

Prevalence and Cardiovascular Disease Correlates of Low Cardiorespiratory Fitness in Adolescents and Adults

Population surveys indicate that physical activity levels are low in the United States. One consequence of inactivity, low cardiorespiratory fitness, is an established risk factor for cardiovascular disease (CVD) morbidity and mortality, but the prevalence of cardiorespiratory fitness has not been quantified in representative US population samples. To describe the prevalence of low fitness in the US population aged 12 through 49 years and to relate low fitness to CVD risk factors in this population. Inception cohort study using data from the cross-sectional nationally representative National Health and Nutrition Examination Survey 1999-2002. Participants were adolescents (aged 12-19 years; n = 3110) and adults (aged 20-49 years; n = 2205) free from previously diagnosed CVD who underwent submaximal graded exercise treadmill testing to achieve at least 75% to 90% of their age-predicted maximum heart rate. Maximal oxygen consumption (VO2max) was estimated by measuring the heart rate response to reference levels of submaximal work. Low fitness defined using percentile cut points of estimated VO2max from existing external referent populations; anthropometric and other CVD risk factors measured according to standard methods. Low fitness was identified in 33.6% of adolescents (approximately 7.5 million US adolescents) and 13.9% of adults (approximately 8.5 million US adults); the prevalence was similar in adolescent females (34.4%) and males (32.9%) (P = .40) but was higher in adult females (16.2%) than in males (11.8%) (P = .03). Non-Hispanic blacks and Mexican Americans were less fit than non-Hispanic whites. In all age-sex groups, body mass index and waist circumference were inversely associated with fitness; age- and race-adjusted odds ratios of overweight or obesity (body mass index > or =25) ranged from 2.1 to 3.7 (P<.01 for all), comparing persons with low fitness with those with moderate or high fitness. Total cholesterol levels and systolic blood pressure were higher and levels of high-density lipoprotein cholesterol were lower among participants with low vs high fitness. Low fitness in adolescents and adults is common in the US population and is associated with an increased prevalence of CVD risk factors.