Roughly 40 percent of people who engage in guideline-based moderate-intensity continuous exercise for six months do not show a measurable improvement in VO2 max.
"for example, some evidence has shown that moderate-intensity continuous exercise, even for six months or so doing guideline-based evidence, roughly 40 percent of people don't see a measurable improvement in their VO2 max." (said at 0:00:00)
Exercise training trials have documented significant inter-individual variation and apparent 'non-response' in VO2 max following standardized moderate-intensity continuous training (MICT). In the 6-month Dose Response to Exercise in Women (DREW) randomized trial, 44.9% of participants failed to show an increase in VO2 max (change ≤ 0 L/min) at a dose of 4 kcal/kg/week (approximately 50% of the standard physical activity guideline dose), whereas at the standard guideline-concordant dose of 8 kcal/kg/week, the non-response rate was 23.8% (and 19.3% at 12 kcal/kg/week). Subsequent multicenter analyses similarly show that when accounting for technical error of measurement and minimal clinically important differences, a large proportion of individuals undergoing MICT do not show definitive VO2 max increases, though higher exercise volumes or intensities reliably reduce non-response rates.
- context: Volume of exercise and fitness nonresponse in sedentary, postmenopausal women. (Medicine and science in sports and exercise 2009) · cited 161x in the literature
"Participants were randomized to one of three exercise treatment groups (4, 8, or 12 kcal x kg(-1) x wk(-1)) for 6 months. Participants exercised 3-4 d x wk(-1) at 50% V x O 2max... A total of 44.9%, 23.8%, and 19.3% of the 4-, the 8-, and the 12-kcal x kg(-1) x wk(-1) treatment groups (P < 0.0001), respectively, were nonresponders." (abstract, results)
pubmedfull study (doi) - context: A Multi-Center Comparison of O 2peak Trainability Between Interval Training and Moderate I… (Frontiers in physiology 2019) · cited 116x in the literature
"Based on a high threshold for a likely response (technical error of measurement plus the minimal clinically important difference), high-volume HIIT had significantly more (P < 0.01) likely responders (31%) compared to low-volume HIIT/SIT (16%) and MICT (21%)." (abstract, results)
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Prolonged sedentary behavior increases health risks even in individuals who engage in regular exercise.
"that suggest even if you're a committed exerciser, prolonged sedentary is increasing your risk, right?" (said at 0:57:13)
Early systematic reviews and meta-analyses (such as Biswas et al., 2015) reported that prolonged sedentary time was independently associated with cardiovascular disease, type 2 diabetes, cancer, and all-cause mortality, even after adjusting for physical activity. However, subsequent large-scale harmonized meta-analyses have clarified that the risk depends strongly on the volume and intensity of exercise. A harmonized meta-analysis of over 1 million individuals (Ekelund et al., 2016) demonstrated that high levels of moderate-intensity physical activity (approximately 60–75 minutes per day) eliminated the increased all-cause mortality risk associated with sitting more than 8 hours per day (HR 1.04, 95% CI 0.99–1.10), though high TV-viewing time retained some attenuated risk. Similarly, an accelerometer-based meta-analysis (Ekelund et al., 2020) found that 30–40 minutes of moderate-to-vigorous physical activity daily eliminated the excess mortality risk associated with high sedentary time.
- partial: Sedentary time and its association with risk for disease incidence, mortality, and hospita… (Annals of internal medicine 2015) · cited 2719x in the literature
"Significant hazard ratio (HR) associations were found with all-cause mortality (HR, 1.240 [95% CI, 1.090 to 1.410]), cardiovascular disease mortality (HR, 1.179 [CI, 1.106 to 1.257]), cardiovascular disease incidence (HR, 1.143 [CI, 1.002 to 1.729]), cancer mortality (HR, 1.173 [CI, 1.108 to 1.242]), cancer incidence (HR, 1.130 [CI, 1.053 to 1.213]), and type 2 diabetes incidence (HR, 1.910 [CI, 1.642 to 2.222]). Hazard ratios associated with sedentary time and outcomes were generally more pronounced at lower levels of physical activity than at higher levels." (abstract, results, passage verified)
pubmedfull study (doi) - context: Does physical activity attenuate, or even eliminate, the detrimental association of sittin… (Lancet (London, England) 2016) · cited 2724x in the literature
"High levels of moderate intensity physical activity (ie, about 60-75 min per day) seem to eliminate the increased risk of death associated with high sitting time. However, this high activity level attenuates, but does not eliminate the increased risk associated with high TV-viewing time." (abstract, conclusions, passage verified)
pubmedfull study (doi) - context: Joint associations of accelero-meter measured physical activity and sedentary time with al… (British journal of sports medicine 2020) · cited 382x in the literature
"Higher sedentary time is associated with higher mortality in less active individuals when measured by accelerometry. About 30-40 min of MVPA per day attenuate the association between sedentary time and risk of death, which is lower than previous estimates from self-reported data." (abstract, conclusions, passage verified)
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Mechanical shear forces from increased blood flow during exercise cause circulating tumor cells to die in a dose-dependent manner based on exercise intensity.
"So there's evidence that exercise in general—exercise is involved in basically anything that gets your blood flow up—basically those cancer cells die because they're so disrupted and sensitive to the mechanical forces, whereas normal cells are fine. But it seems to also, again, be a dose-dependent effect: the more intense the exercise, the more blood flow that's going quicker, the more intense the effect." (said at 1:16:09)
Evidence supports the concept that hemodynamic shear stress levels corresponding to intense exercise destroy circulating tumor cells (CTCs) while sparing normal blood-like cells in a magnitude-dependent manner. However, this has been demonstrated in vitro using microfluidic circulatory systems simulating human arterial shear stresses (e.g., 60 dyn/cm² during intensive exercise versus 15 dyn/cm² at rest), rather than directly measured in vivo in exercising humans.
- supports: High Shear Stresses under Exercise Condition Destroy Circulating Tumor Cells in a Microflu… (Scientific reports 2017) · cited 202x in the literature
"1) High shear stress of 60 dynes/cm 2 achievable during intensive exercise killed more CTCs than low shear stress of 15 dynes/cm 2 present in human arteries at the resting state. 2) High shear stress caused necrosis in over 90% of CTCs within the first 4 h of circulation. More importantly, the CTCs that survived the first 4 h-circulation, underwent apoptosis during 16-24 h of post-circulation incubation... As high shear stress had much less damaging effects on leukemic cells mimicking the white blood cells, we propose that intensive exercise may be a good strategy for generating high shear stress that can destroy CTCs and prevent cancer metastasis." (abstract, results, passage verified)
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