by Ben Best
Oxygen uptake capacity during maximal physical exercise (aerobic capacity, peak VO2, VO2 max) is an often-used biomarker of physical fitness. Optimal performance occurs at 11ºC ambient temperature, with time to exhaustion decreasing 10−15% at 4ºC or 21ºC [JOURNAL OF THE AMERICAN COLLEGE OF NUTRITION; Maughan,RJ; 26(5):604S-612S (2007)].
Aerobic capacity decline accelerates with age, with the rate of decline increasing from 3-6% per decade in the 20s and 30s to over 20% per decade after age 70 [CIRCULATION; Arena,R; 116(3):329-343 (2007)]. Although people who exercise have higher aerobic capacity (generally in proportion to their amount of exercise), accelerated decline in aerobic capacity with age is seen among exercisers and non-exercisers alike [CIRCULATION; Fleg,JL; 112(5):674-682 (2005)].
A study of male patients in cardiac rehabilitation to increase exercise capacity (aerobic capacity, peak VO2, VO2 max) showed that each 1% increase in exercise capacity was associated with a 2% decrease in mortality [AMERICAN JOURNAL OF CARDIOLOGY; vanhees,L; 76(4):1014-1019 (1995)]. Coronary artery disease patients who showed a high change in exercise capacity after physical training had 60% lower mortality than patients with a low change [AMERICAN JOURNAL OF MEDICINE; Milani,RV; 122(10):931-938 (2009)]. A positive association has been found between exercise capacity (aerobic fitness) and cognitive information processing speed (but not memory) [MEDICINE & SCIENCE IN SPORTS & EXERCISE; Van Boxtel,M; 29(10):1357-1365 (1997)].
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Improvement in cardiovascular health is the most frequently cited health benefit of exercise (often associated with weight loss). As was stated in the previous section, every 1% increase of peak VO2 max from exercise training is associated with a 2% decrease in cardiovascular mortality in coronary artery disease patients [AMERICAN JOURNAL OF CARDIOLOGY; Vanhees,L; 76(14):1014-1019 (1995)]. People with insulin resistance show increased blood pressure, triglycerides, and inflammatory cytokines associated with cardiovascular disease. Exercise has been shown to increase insulin sensitivity (reduce insulin resistance). A study of healthy men who engaged in one-legged exercise for 3 weeks showed a 60% higher insulin-stimulated glucose uptake in the trained leg compared to the untrained leg [DIABETES; Frosig,C; 56(8):2093-2102 (2007)].
Chronic heart failure patients performing moderate leg exercise for 3 months showed reduced endothelial dysfunction in their legs, but not in their arms [CIRCULATION JOURNAL; Kobayashi,N; 67(6):505-510 (2003)]. Another study of chronic heart failure patients in an exercise program showed significant reduction in inflammatory cytokines associated with endothelial dysfunction [EUROPEAN HEART JOURNAL; Adamopoulos,S; 22(9):791-797 (2001)].
A 16-week aerobic exercise program with randomized participant and control adults of three 20-minute stationary bicycle sessions per week eliciting 70% maximal heart rate showed 1% loss of body weight, 5% loss of abdominal fat, 25% drop in plasma triglycerides, 10% increase in peak oxygen uptake (aerobic capacity, VO2max), and 55% increase in PGC−1α gene expression for mitochondrial biogenesis. Insulin resistance was significantly reduced in those aged 40-59, but did not reach statistical significance for those over age 60 [DIABETES; Short,KR; 52(8):1888-1896 (2003)]. Other studies of greater exercise duration or intensity have shown increased insulin sensitivity with exercise for older people. For example, another study showed no difference was detected between the insulin sensitivity of young and old physically trained persons, which was much greater than that of young and old sedentary persons [DIABETES; Lanza,IR; 57(11):2933-2942 (2008)].
A meta-analysis of 52 exercise programs lasting at least 12 weeks (which included 4700 subjects) showed an average 4.6% HDL cholesterol increase, 5.0% LDL cholesterol decrease, and 3.7% triglyceride decrease. Average systolic blood pressure was reduced 3.4 mmHg, and average diastolic blood pressure was reduced 2.4 mmHg [CIRCULATION; Thompson,PD; 107(24):3109-3116 (2003)], but for subjects with high blood pressure the reductions were 7.4 mmHg (systolic) and 5.8 mmHg (diastolic). Human subjects reducing calories by 20% or increasing calorie burning by 20% through exercise for one year. Both the exercise group and the calorie restriction group showed improved diastolic function (left ventricular filling capacity), although the effect was more robust for the calorie restriction group [AMERICAN JOURNAL OF PHYSIOLOGY; Riordan,MM; 294(3):H1174-H1182 (2008)].
Between 4% and 15% cases of myocardial infarction are associated with vigorous exercise — usually in those who were unaccustomed to physical activity. The victims are most often obese male smokers with high plasma lipids [JOURNAL OF THE AMERICAN MEDICAL ASSOCIATION; Giri,S; 282(18):1731-1736 (1999)]. Caffeine equivalent to two cups of coffee has been shown to reduce heart blood flow 11% in an exercise test given to coronary heart disease patients [PLOS ONE Namdar,M; 4(5):e5665 (2009)].
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After 8 weeks of treadmill exercise, old rats showed one-third the nuclear DNA oxidative damage (8-OHdG) in muscle tissue compared to controls — which was attributed to increased DNA repair [PFLUGERS ARCHIV; Radak,Z; 445(2):273-278 (2002)]. Human subjects reducing calories by 20% or increasing calorie burning by 20% through exercise for one year showed a comparable 50% reduction in white blood cell DNA oxidation (8-OHdG) [REJUVENATION RESEARCH; Hofer,T; 11(4):793-799 (2008)]. Long-term volunteer wheel running in rats significantly reduced muscular mitochondrial hydrogen peroxide production [AMERICAN JOURNAL OF PHYSIOLOGY; Judge,S; 289(6):R1564-R1572 (2005)].
Healthy young men given a three-day antioxidant treatment associated with intensity-resistance exercise showed reduced lipid peroxidation (TBARS assay) with 1.8 grams/day N−AcetylCysteine (NAC) (−14%) and 1.2 grams/day α−lipoic acid (−16%), but not with 3 grams/day taurine [JOURNAL OF PHYSIOLOGICAL SCIENCES; Zembron-Lacny,A; 57(6):343-348 (2007)]. A six-day study of healthy young men given 6 grams/day taurine showed reduced exercise-induced DNA damage [AMINO ACIDS; Zhang,M; 26(2):203-207 (2004)].
Elite male Japanese athletes given 300 milligrams/day of CoEnzyme Q10 showed half the serum lipid peroxidation as controls on the fifth day of training camp [BRITISH JOURNAL OF NUTRITION; Kon,M; 100(4):903-909 (2008)]. Healthy volunteers given CoEnzyme Q10 before exercise showed reduced subjective fatigue with 300 milligrams, but not with 100 milligrams [NUTRITION; Mizuno,K; 24(4):293-299 (2008)]. Superoxide dismutase increased 130% in some brain areas of exercized rats [PHARMACOLOGY, BIOCHEMISTRY, AND BEHAVIOR; Somani,SM; 50(4):635-639 (1995)].
Exercise leads to up-regulation of anti-oxidant enzymes. Anti-oxidant supplements can interfere with this enzyme induction for moderate exercise, but for strenuous exercise anti-oxidant supplements can protect against oxidative stress [FREE RADICAL BIOLOGY & MEDICINE; Gomez-Cabrera,M; 44(2):126-131 (2008)]. One thousand IU daily of alpha−tocopherol reduced post-exercise elevation in biomarkers of muscle damage and lipid peroxidation in men [FREE RADICAL BIOLOGY & MEDICINE; Sacheck,JM; 34(12):1575-1588 (2003)].
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Treadmill exercise in old rats was associated with better short-term memory and only one-third the error rate for spatial memory, as well as 4 times the levels of antiapoptosis protein (Bcl-2) expression in brain tissue [EXPERIMENTAL GERONTOLOGY; Kim,S; 45(5):357-365 (2010)]. Running was shown to enhance learning and hippocampal neurogenesis in old mice [JOURNAL OF NEUROSCIENCE; van Praag,H; 25(38):8680-8685 (2005)]. Exercise was shown to induce angiogenesis and increase cerebral blood volume in the motor cortex of exercised rats [NEUROSCIENCE; Swain,RA; 117(4):1037-1046 (2003)]. Similar effects were seen in monkeys subjected to aerobic exercise training [NEUROSCIENCE; Rhyu,IJ; 167(4):1239-1248 (2010)]. Exercise has even been shown to restore hippocampus-dependent memory following experimental ischemic stroke in mice [JOURNAL OF NEUROSCIENCE RESEARCH; Luo,CX; 85(8):1637-1646 (2007)].
Exercise potentiates synaptic function under the direction of Brain-Derived Neurotrophic Factor (BDNF) [BRAIN RESEARCH; Vaynmanus,SS; 1070(1):124-130 (2006)], the production of which is increased by exercise [NEUROCHEMISTRY INTERNATIONAL; Radak,K; 49(4):387-392 (2006)]. Half of a group of 120 adults age 55 to 80 who engaged in aerobic exercise (the control group did stretching exercise) for one year showed improved memory and a 2% increase in hippocampal volume, as opposed to a 1.4% decline in the control group [PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES (USA); Erikson,KI; 108(7):3017-3022 (2011)].
The lactate threshold corresponds to the intensity of exercise at which lactic acid begins to accumulate in the blood stream. The acute effects of exercise have an inverted U-shape on cognitive function. Reaction time is optimal near the lactate threshold [INTERNATIONAL JOURNAL OF SPORTS MEDICINE; Chmura,J; 15(4):172-176 (1994)], and this is evidently optimal for cognitive function in general [JOURNAL OF PHYSIOLOGICAL ANTHROPOLOGY; Kashihara,K; 28(4):155-164 (2009)].
A combination of physical activity and anti-depressant medication was shown to upregulate brain-derived neurotrophic factor in the hippocampus of a rat model of depression [BRAIN BEHAVIOUR RESEARCH; Russo-Neustadt,A; 120(1):87-95 (2001)]. Persons suffering from depression showed more improvement with exercise alone than with anti-depressant medication or a combination of exercise and anti-depressant medication [PSYCHOSOMATIC MEDICINE; Babyak,M; 62(5):633-638 (2000)]. In coronary artery disease patients, exercise training reduced the level of psychological stress to less than half, while reducing mortality [AMERICAN JOURNAL OF MEDICINE; Milani,RV; 122(10):931-938 (2009)].
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A 65-year-old man with high physical activity who has never smoked can expect to live 16.2 years of non-disabled life plus 2 years of disabled life. With low physical activity the same man would expect to live 11 years of non-disabled life plus 2.6 disabled years. If the man had ever smoked, low physical activity would be associated with 9.5 years of non-disabled life and 2 disabled years. Women can expect to live 1-2 years of additional non-disabled life and one year of disabled life above that of a man in the same smoking and physical activity category [AMERICAN JOURNAL OF EPIDEMIOLOGY; Ferrucci,L; 249(7):645-653 (1999)]. Data from the Framingham cohort is more modest: at age 50 high physical activity adds 3.7 (men) or 3.5 (women) years to life expectancy and moderate physical activity adds 1.3 (men) or 1.1 (women) years to life expectancy above low physical activity [ARCHIVES OF INTERNAL MEDICINE; Franco,OH; 165(20):2355-2360 (2005)]. Association does not prove causality, and it could easily be argued that people who are healthier can engage in more physical activity. Intervention studies and animal experiments are more informative than epidemiology.
NAC has proven effective for reducing plasma inflammatory cytokine increase following exercise — presumably through anti-oxidant action [JOURNAL OF APPLIED PHYSIOLOGY; Vassilakopoulos,T; 94(3):1025-1032 (2003)]. NAC also protects against exercise-induced apoptosis of lymphocytes [BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS; Quadrilatero,J; 319(3):894-901 (2004)].
High physical activity in women over age 50 has been associated with a 67% reduction in breast cancer risk [CANCER EPIDEMIOLOGY, BIOMARKERS & PREVENTION; Breslow,RA; 10(7):805-808 (2001)].
Six months of resistance training has been shown to alter gene expression in muscle biopsies of older persons to more closely match those of younger persons [PLOS ONE; Melov,S; 2(5):e465 (2007)].
Previously non-exercising older adults experimentally subjected to a punch biopsy used in dermatological research showed faster wound healing (average 29.2 days) if exercising 3 hours per week for 3 months when compared to non-exercising controls (who averaged 38.9 days) [JOURNALS OF GERONTOLOGY; Emery,CF; 60A(11):1432-1436 (2005)].
Weight loss by overweight persons is associated with increased mortality, but not for many of those who become or remain physically active [INTERNATIONAL JOURNAL OF OBESITY; Ostergaard,JN; 34(4):760-769 (2010)].
Endurance exercise in mtDNA mutator mice induced systemic mitochondrial biogenesis, restoring mitochondrial respiratory capacity, and eliminating premature mortality [PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES (USA); Safdar,A; 108(10):4135-4140 (2011)]. Endurance exercise training increases the size and number of mitochondria in muscles, while also increasing GLUT4 (insulin sensitivity) [JOURNAL OF PHYSIOLOGY AND PHARMACOLOGY; Holloszy,JO; 59(Suppl 7):5-18 (2008)]. The PGC-1α has been identified as an activator of mitochondria biogenesis, and endurance exercise has been shown to activate the PGC-1α gene in human skeletal muscle [JOURNAL OF PHYSIOLOGY: Pilegaard,H; 546(Pt 3):851-858 (2003)].
Telomere length is positively correlated with self-reported levels of exercise [ARCHIVES OF INTERNAL MEDICINE; Cherkas,LF; 168(2):154-158 (2008)]. Similarly, vigorous exercise is associated with protection against the telomere shortening associated with psychological stress [PLOS ONE; Paterman,E; 5(5):e10837 (2010)].
Healthy males given 600 mg/day phosphatidylserine for ten days showed a significant reduction in cortisol and an increased testosterone/cortisol ratio following moderately intense exercise [JOURNAL OF THE INTERNATIONAL SOCIETY OF SPORTS NUTRITION; Starks,MA; 5:11 (2008)]. Healthy active males given 750 mg/day phosphatidylserine for ten days showed a nearly 20% increase in time to exhaustion [MEDICINE & SCIENCE IN SPORTS & MEDICINE; Kingsley,MI; 38(1):64-71 (2006)].
Associations with self-reported exercise leading to improved self-reported sleep are probably mostly due to the good health practices of exercisers, which make them good sleepers. Experimental studies have shown at most a very modest improvement of sleep due to exercise, although exercise is known to reduce anxiety & depression [CLINICS IN SPORTS MEDICINE; Youngstedt,SD; 24(2:355-365 (2005)].
Warmup and stretching before exercise reduces muscle injury by increasing muscle temperature and blood-flow, and increasing the force and length-of-stretch required to produce tear [SPORTS MEDICINE; Woods,K; 37(12):1089-1099 (2007)].
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