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Jan 25 2017

Paper: Physical Activity and Exercise as Medicine among Sedentary Adults

Physical Activity and Exercise as Medicine among Sedentary Adults

Increasing a sedentary person’s physical activity gradually from public health perspective

A small amount of exercise will jumpstart a cycle of continual positive benefits in nearly any sedPhysicalActivityentary individual and set them up for a gradual increasing healthy lifestyle, decreased risk for premature death by adapting to changes in heart rate, building muscle tissue, increased mitochondrial density, and positive neuromuscular adaptations. But before a sedentary person or population of individuals should be prescribed an exercise regimen to move towards this positive route, care must be taken to ensure they do not jump into the exercise program abruptly or at a high intensity.  With a vast majority of Americans overweight or obese – and by correlation, sedentary – most of these sedentary persons develop health complications that arise from excess body fat – adipose tissue – which over time leads to coronary heart disease (CHD), hypertension, and type 2 diabetes. From a public health standpoint, it is this concern that must be addressed when prescribing physical activity and exercise to a generic sedentary population: most will have chronic disease diagnoses that must be first addressed prior to an exercise regimen.

Multiple studies and literature exist that show physical activity and exercise as vastly beneficial for the public’s health (Biddle and Batterham, 2015). Nearly all activity from a short duration low intensity to high intensity training will improve the health of a sedentary individual. In fact, Powers and Howley (2012) point out that the more intense exercise one does, the more health benefits achieved (p. 357). But from a public health perspective having a population of sedentary people exercise suddenly exercise intensely could lead to catastrophic disasters because the majority of the individuals will already have cardiovascular hear disease or other obesity related chorionic illnesses that could be exacerbated on the outset of exercise. 

We know that physical training produces profound effects on the body physiologically – most notably with the cardiovascular and cardiopulmonary systems – overtime as exercise progresses. Specifically, training increases the size of the left ventricle of the heart, producing more blood flow through higher stroke volume output per heart beat strengthening cardiac contractility (Powers and Howley, 2012, p. 287). Oxygen is also extracted from the blood at a higher rate, because during training the number of capillaries that that deliver blood to the muscle increase, and the number of mitochondria in muscles cells increase with training (Powers and Howley, 2012, p. 287).  Studies show that the number of mitochondria in muscle cells start to increase within the first 5 days of training, and mitochondrial density in muscle can double within six weeks of training (Powers and Howley, 2012, p. 289).  As the muscle cell is exercised, the number of capillaries increase, allowing oxygen plus fuel in the form of glucose or Free Fatty Acids (FFA) to be oxidized in the muscle cell (Powers and Howley, 2012, p. 291).

As we can see, it takes time to develop these physiological adaptations in the body, and these are only a couple examples of positive changes that ultimately lead to a healthier person who was previously sedentary.  Numerous changes occur as a person transitions from sedentary to active as blood flow increases, heart becomes stronger, and muscles cells are activated.  A person cannot be expected to conduct strenuous activity right away; it takes time to develop energy pathways, neuromuscular response mechanisms and cardiovascular changes.  More importantly a gradual increase in physical activity and exercise will lessen the possibly negative reactions that might be present with chronic diseases like CHD, type 2 diabetes, or hypertension.

Exercise adaptations in elderly vs younger adults

Exercise among elderly populations over 65 years old can produce positive physiological adaptations in the body just like younger populations, however, certain limitations are present with age. As a person ages, muscle strength declines each year especially over the age of 60 and maximum aerobic power also decreases yearly which can cause lower overall cardiovascular and cardiorespiratory fitness (Powers and Howley, 2012, p. 383).  But this does not mean elderly persons should give up on maintaining fitness. On contrary, elderly populations should either continue exercising if they are part of a fitness program, or they should immediately start a physical activity program to lessen the decline in cardiac output or muscle moss the body undergoes and to decrease the risk factors developed with physical inactivity over time.  A study of older adults aged 68 who participated in a training program produced significant physiological improvements from low-to-moderate-intensity training (Posner, Gorman, Windsor-Landsberg, et al.., 1992).

Elderly populations will have lower resting heart rates (cardiac output), VO2 max, muscle mass, bone density, and overall strength when compared to younger populations, but both still respond to exercise stimulus (Terjung, Zarzeczny, and Yang, 2002). Both populations though show adaptations to exercise in increasing VO2 max, lowering blood pressure, increasing insulin sensitivity, and increases muscle strength (Powers and Howley, 2012, p. 388). But overall values will likely differ between populations because the starting point in elderly would be quite lower, but the training effect is still positive.  If the elderly person was previously sedentary or has obtained any chronic illness, then special care must be taken before exercising that they do not jump into strenuous activity too soon.  They must take special care of diet too, and caution against safety related issues with regard to falls or other possible injuries if they have weakened muscles or low bone density. Overall though, elderly people will still respond in a healthy manner and possibly live longer if participating in any kind of exercise regimen.

The effect of exercise on appetite and body composition.

Exercise has a profound impact on appetite suppression of an individual, especially those who are trying to lose weight.  However, there is a remarked difference between male and female individuals who exercise and perceived hunger.  Scott and Powers (2012), describe several studies where intense exercise in females tended to lead increased appetite while intense exercise in males lead to decreased appetite and decreased weight gain (p. 428). These components are key when proscribing nutrition programs for persons wanting to lose weight or starting a health and fitness routine.  Separate nutrition and exercise programs would need to be developed for male vs female individuals by fitness trainers looking to help clients lose weight.  Though the difference in appetite contains a measured difference, the role of exercise on body composition through eventual more Fat Free Mass (FFM) vs Fat Mass (FM) regardless of male vs female appetite suppression.  If a male exercises intensely and does not feel as hungry as a female, both will still eat to replenish their energy expenditures. Depending on the timing of the male nourishment replenishment, appetite inhibiting hormones such as cholecystokinin (CCK), glucagon-like peptide-1 (GLP-1), peptide tyrosine-tyrosine (PYY) will likely lead to less consumption of calories than he had not exercised, and likely less often. (Blundell, Gibbons, Caudwell, et al., 2011, p. 70).  The female though after intense exercise may still feel a need to eat and will do so, but likely consume less than the male would and probably through homeostasis mechanisms such as basal metabolic heart rate (BMR) and energy expenditure of just said exercise.

            The key role of exercise in appetite suppression though must be addressed more fully with describing changes in body composition as exercise progresses. One set of theories suggest that sedentary or likely obese people and those with excessive adipose tissue (Fat Mass) tend to have weakened leptin response signals, no longer telling the brain to stop eating (Blundell, Gibbons, Caudwell, et al., 2011, p. 70).  The more adipose tissue cells, the less leptin works and the more a person eats.  But during exercise and when exercise is conducted over time, the less fat mass accumulation in the body and more Fat Free Mass (FFM) from the energy expenditure during the exercise.  This results in a change in body composition, and more FFM will change the energy expenditure and BMR in the body, again because of the exercise.  These changes in energy expenditures and a higher BMR means more food is needed to be consumed to maintain the act of “staying alive.”  Combined with the fact that exercise (at least in males) reduces appetite means a cycle of reduced calorie consumption and reduced FM will lead to less weight in overweight individuals, changes in body composition for the better, and better desire to eat more nutritiously.  

            Overall, exercise both reduces appetite and helps control food consumption and which ultimately leads to decreased weight in individuals with obesity related problems including diabetes. (Heden, Ying, and Kanaley, 2016). In addition to appetite suppression, exercise also induces other positive physiological response to the body like “adjustments in blood flow, gastrointestinal hormone response, gastric emptying, muscle cellular metabolism, adipose tissue biochemistry as well as brain activity” (Gibbons, Caudwell, et al., 2011, p. 74). As an individual exercises over time, more oxygen, energy (ATP), proteins and enzymes are delivered to muscles muscle cells, and even more capillaries are created to deliver these items to muscles, heart and throughout the body. Increased metabolism through MBR and muscle response to increased oxygen flow causes muscle cell remodeling – protein synthesis – comes with exercise. Egan and Zierath (2013) point out that over time, “muscle demonstrates remarkable malleability in functional adaptation and remodeling in response to contractile activity” (p. 162). This creates more FFM, and lowers FM and all contributes to the cycle of changes in body composition through exercise. Adipose tissue biochemistry changes include the increase sensitivity of leptin hormone signaling that the body has consumed enough food, and stored amounts are plentiful, while the brain receives signals from elsewhere that the food consumed is enough to replenish energy expenditure. This better balance in the brain helps regulate overall appetite to consume the right amount needed.

Role of altitude and heat, in distance performances of one to four hours’ duration.

Altitude and heat play a significant role in distance performances of long aerobic duration between one and four hours.  At altitude, less air pressure impacts the oxygen extraction out of the blood by muscles tissues due to the lesser number of O2 molecules. As we have learned throughout this physiology textbook, VO2 max plays a significant role in exercise performance. If a person cannot produce enough ATP energy quick enough based on a lower number of oxygen delivery mechanisms altitude, then exercise output will be lowered.  This phenomenon was exemplified in the 1960 Mexico City Olympics held at 7,400 ft altitude; events that relied primarily on aerobic systems for energy produced lower winning times than would have been produced at sea level.

This author has had the luxury of experiencing these physiological effect of altitude on performance after living at 7,200 ft. high in Colorado. During the first year at altitude coming from sea level, any sort of performance in an event took significant more energy and effort to run, in addition to producing slower running times.  However, after three years when competing at sea level and monitoring heart rate, the increase in oxygen concentration during exercise led to extremely fast times, and a very low perceived effort in performance. The cardiac output or work rate of the heart was 20-30 beats per minute slower than had the same effort been run at altitude.  The physiological adaptations that took place at altitude produced huge advantages when returning to sea level and performance bettered.

When exercising for very long distances in the heat, we know that increase external temperature makes it harder for the body to reach homeostasis as it too producing heat and trying to maintain homeostasis by cooling itself down. Heat is created and given off during exercise by muscle contractions, and the more the muscle contracts, the more heat is given off (Powers and Howley, 2012, p. 268).  In a hot environment, the muscle cells themselves become at risk to developing heat-induced muscular fatigue through free radical production during exercise (Powers and Howley, 2012, p. 273). In addition, the cardiovascular system is strained with reduced muscle blood flow as the body is trying to both provide blood to the muscle and move the blood to the exterior near the skin for cooling (Powers and Howley, 2012, p. 273).  With blood and muscle metabolism slowing down in the heat, performance of distances over one two four hours becomes negatively altered.  One study also showed inflammation markers within the gastrointestinal track of individuals who competed in a 5-day ultramarathon stage race in an extremely hot (30-40 degree C) environment and those markers stayed elevated in the blood after the event was completed much longer than a controlled group (Gill, Teixeira, Rama, et al., 2015). This author participated in this same ultramarathon event – Al Andalus Ultimate Trail in Southern Spain – along the same course and same extreme heat conditions and probably had the same rise inflammatory markers in the blood.

Exercising in the heat though should not be all together stopped.  Heat acclimatization can occur when a person gradually exercises in the heat and over time can adapt by producing more heat shock proteins (Powers and Howley, 2012, p. 275).  Other physiological adaptations that occur from purposely exercising in the heat include increased plasma volume, seating earlier, higher sweat rate, reduced salt loss in sweat and reduced skin blood flow (Powers and Howley, 2012, p. 273).  

These positive changes mean that though environmental factors like heat and altitude have a probably negative overall effect of exercising during long distance performances, it is possibly to train and acclimatize to maximize performance potential when compared to others if during competition.  Even if not planning to exercise for over one to four hours, the effects of heat and altitude training on the body would still produce health benefits from lower cardiac output and less stress on the body than if not acclimatized to extreme environments.

 

 

References:

Biddle, S. H., & Batterham, A. M. (2015). High-intensity interval exercise training for public health: a big HIT or shall we HIT it on the head?. International Journal Of Behavioral Nutrition & Physical Activity, 121-8. doi:10.1186/s12966-015-0254-9

Blundell, J. E., Gibbons, C., Caudwell, P., Finlayson, G., & Hopkins, M. (2015). Appetite control and energy balance: impact of exercise. Obesity Reviews, 1667-76. doi:10.1111/obr.12257

Egan, B., & Zierath, J. R. (2013). Exercise metabolism and the molecular regulation of skeletal muscle adaptation. Cell Metabolism, 17(2), 162-184. doi:10.1016/j.cmet.2012.12.012

Gill, S. K., Teixeira, A., Rama, L., Rosado, F., Hankey, J., Scheer, V., & … Costa, R. S. (2015). Circulatory endotoxin concentration and cytokine profile in response to exertional-heat stress during a multi-stage ultra-marathon competition. Exercise Immunology Review, 21114-128.

HEDEN, T. D., YING, L., & KANALEY, J. A. (2016). Impact of Exercise Timing on Appetite Regulation in Individuals with Type 2 Diabetes. Medicine & Science In Sports & Exercise, 48(2), 182-189. doi:10.1249/MSS.0000000000000755

Millar, P. J., & Goodman, J. M. (2014). Exercise as medicine: Role in the management of primary hypertension. Applied Physiology, Nutrition & Metabolism, 39(7), 856-858. doi:10.1139/apnm-2014-0006

Posner, J. D., Gorman, K. M., Windsor-Landsberg, L., Larsen, J., Bleiman, M., Shaw, C., & … Knebl, J. (1992). Low to moderate intensity endurance training in healthy older adults: physiological responses after four months. Journal Of The American Geriatrics Society, 40(1), 1-7.

Powers, S. K., & Howley, E. T. (2012). Exercise physiology: Theory and application to fitness and performance (8th ed.). New York, NY: McGraw Hill.

Terjung, R., Zarzeczny, R., & Yang, H. (2002). Muscle blood flow and mitochondrial function: influence of aging…the following article, from the proceedings of the 11th International Conference on the Biochemistry of Exercise, was originally scheduled to appear in the Supplement to Volume 11 of IJSNEM. International Journal Of Sport Nutrition & Exercise Metabolism, 12(3), 368-378 11p.

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