" IDEAL AMOUNT OF EXERCISE FOR A HEALTHY LIFE : HAVE WE SOLVED THE GOLDILOCKS PROBLEM ? " – REVIEW OF THE LITERATURE CLINICAL

There is an increasing interest in the place of physical activity to counter the increasing risk of non-communicable diseases and its complications in the community. Debate remains just how much exercise is too little, too much or just right to improve health and longevity. This article reviews the present evidence of physical activity on mortality and the possible ideal recommendations on physical activity.

In recent times, there has been an increasing interest in the place of physical activity to counter the ever increasing risk of non-communicable diseases and its complications in the community.However, the debate remains just how much exercise is too little, too much or just right to improve health and longevity.There is no doubt that any amount of exercise is better than none.Exercise is known to reduce risks of many chronic diseases, cancer and premature death (Table 1).The clear majority of these studies show a dose-response association of physical activity in reducing mortality, without any upper limit of safe activity (1-6, 8-13, 15-18, 20-26, 28-30, 32-33, 38-39).Minority of studies show increased risk at the higher end of the activity range, raising concerns whether frequent, strenuous exercise, exceeding current recommendations, can be potentially dangerous and harmful to health and wellbeing contributing to early mortality (7,14) and few studies showed no dose-response association (19,27,31,34,35,36,37). the guidelines have not been very clear whether the recommended amount of exercise represents the minimum or the ideal and also regarding the upper limit of exercise for longevity benefit.
Despite having a reasonable amount of evidence, the recommendation for exercise does not come with clear dosing instructions.The current guidelines call for a minimum of 75 vigorous-intensity or 150 moderateintensity minutes per week (7.5 metabolic equivalent hours per week) of aerobic activity to build and maintain health and fitness (40).Moderate-intensity physical activity requires a moderate amount of effort that noticeably accelerates the breathing and heart rate.Examples of the moderate-intensity physical activity include brisk walking, dancing, bicycling with -light effort (10-12 mph), gardening, housework and domestic chores, active involvement in sport and games with children, walking domestic animals and carrying or moving moderate loads (<20kg).Vigorous-intensity physical activity requires a large amount effort that leads to rapid breathing and a substantial increase in heart rate.Examples of the vigorous-intensity physical activity include running, brisk walking up a hill, bicycling fast (14-16 mph), fast swimming, aerobics, competitive sports and games and carrying or moving heavy loads of >20kg (40).However,

PHYSICAL INACTIVITY KILLS
According to the World Health Organization, physical inactivity has been identified as the fourth-leading risk factor for death for people all around the world (41).The studies have shown that sedentary behaviour can lead to death from cardiovascular events and cancer as well as cause chronic conditions such as Type 2 diabetes.Prolonged sitting, for eight to 12 hours or more a day, increased the risk of developing type 2 diabetes by 90% and sedentary behaviour increases our risk disease or premature death, even if we exercise (42).Researchers from Toronto who analyzed 47 studies demonstrated that sedentary behavior (remaining seated still) outweighs the benefit we get from exercise, can lead to death from cardiovascular events and cancer as well as can cause chronic conditions  (22,191) Relative risks for all-cause mortality in those who were moderately inactive (sedentary job with <0.5 h recreational activity per day or standing job with no recreational activity), moderately active (sedentary job with 0.5-1 h recreational activity per day, or standing job with <0.5 h recreational activity per day, or physical job with no recreational activity) and active (sedentary job with >1 h recreational activity per day, or standing job with >1 h recreational activity per day, or physical job with at least some recreational activity, or heavy manual job), compared with those who were inactive (sedentary job and no recreational activity) were 0.83, 0.68, and 0.68, respectively Lan TY [ Inverse dose-response gradient was observed between physical activity and mortality from less than 500 to 3500 kcal per week, beyond which benefit was only slight ǂ 39 studies related to association of mortality with dose of exercise found during PubMed search "exercise[Title/Abstract]) OR physical activity[Title/Abstract])) AND ((dose[Title/Abstract]) OR amount[Title/Abstract]))) AND mortality[Title/Abstract] * Studies which did not show a dose-response association ** Studies showing increased risk at the higher end of the activity range such as Type 2 diabetes.Prolonged sitting, for eight to 12 hours or more a day, increased the risk of developing type 2 diabetes by 90% and sedentary behaviour increases our risk disease or premature death, even if we exercise (42).Researchers from Toronto who analyzed 47 studies demonstrated that sedentary behavior (remaining seated still) outweighs the benefit we get from exercise, can lead to death from cardiovascular events and cancer as well as can cause chronic conditions such as Type 2 diabetes.Prolonged sitting, for eight to 12 hours or more a day has shown to increase the risk of developing type 2 diabetes by 90%.However, regular exercise can lower the negative health impact of sedentary behaviour.
In the first of the three studies done to study this area, researchers utilized pooled data about people's exercise habits from six large, ongoing health surveys in the National Cancer Institute Cohort Consortium, with information on more than 660,000, mostly middle-aged adults in order to study the mortality benefit with the duration of exercise ( 6).This study included more than 116,000 deaths, with a median follow-up of 14 years.Using this data, the researchers stratified the adults by their weekly exercise time, from those who did not exercise at all to those who worked out for 10 times the current recommendations or more, and

HOW MUCH EXERCISE IS IDEAL?
Three new large-scale studies provide some clarity to the above debate, suggesting that the ideal dosage of exercise for a longer life is a slightly higher than what is currently recommended, but less than many of us might expect.The studies also found that prolonged or intense exercise is unlikely to be harmful and could add years to people's lives (5,6).
Sri Lanka Journal of Diabetes, Endocrinology and Metabolism mortality data for the groups.As expected, the people who did not exercise at all were at the highest risk of premature death.Those who exercised a little, but not meeting the present recommendations, still lowered their risk of premature death by 20%.Those who met guidelines precisely, completing 150 minutes per week of moderate exercise, had 31% less risk of dying during the 14-year period compared with those who never exercised.The ideal for exercise benefits, however, came among those who reached 3 to 5 times the physical activity recommendation, working out moderately, mostly by walking, for 450 minutes per week, or a little more than an hour per day.They were 39% less likely to die prematurely compared to than people who never exercised.Beyond that point, the benefits plateaued, but never significantly declined.Those few individuals engaging in 10 times or more than the recommended exercise dosage, gained almost the same reduction in mortality risk (39% vs. 31%) as people who simply met the guidelines without any increased their risk of dying prematurely.A similar dose-response relationship was also observed for mortality due to cardiovascular disease and to cancer.
The second new study done by the Australian researchers reached a similar conclusion regarding the mortality benefit and the intensity of exercise and mortality (5).For this study, Australian researchers closely examined health survey data for more than 200,000 Australian adults of aged 45 and above to determine how much time each person spent exercising and how much of that exercise qualified as vigorous; running or jogging instead of walking, or playing competitive singles tennis versus a sociable doubles game.During 1.4 million person-years of follow-up, 7435 deaths were registered.They also found that meeting the exercise guidelines substantially reduced the risk of early death, even if someone's exercise was moderate, such as walking.Those who spent up to 30% of their weekly exercise time in vigorous activities were 9% less likely to die prematurely than people who exercised for the same amount of time but always moderately, while those who spent more than 30% of their exercise time in strenuous activities gained an extra 13% reduction in early mortality when compared with people who never exercised.The researchers did not see any increase in mortality, even among those few people completing the largest amounts of intense exercise.
The third study looked at data from the NHANES (National Health and Nutritional Examination Survey) from 1999-2006 in the United States where they followed up the study cohort till 2011 (3).48 different individual physical activities (e.g., swimming, running, bicycling) were assessed.The total moderate-tovigorous physical activity (MVPA) MET-min-month was calculated based on these 48 individual physical activities.Engaging in MVPA even below the minimum recommendation was associated with survival benefits, and the greatest survival effects occurred at a dose of approximately 5 times the minimum recommendation (45% reduction of the risk of all-cause mortality).Although very high levels (e.g., 10 times the minimum recommenddation) of self-reported MVPA did not demonstrate the greatest survival effects, high levels of physical activity did not appear to have harmful effects.These results were comparable with the above two studies.These were not randomized trials and the reliance on people's recall of exercise habits was a major limitation.Therefore, the only conclusion that the researchers could demonstrate was the association of reduced mortality rate with exercise.Still, this association was strong and consistent and the takeaway message seemed straightforward.These studies reinforced a universal conclusion: a modest amount of weekly exercise can produce huge benefits.It has also shown that high levels of exercise appear to carry no excess risks.They also provide important evidence to 'inactive' individuals by showing that modest amounts of activity provide substantial benefits, while reassuring 'very active' individuals of no exercise-associated increase in mortality.

RECOMMENDATIONS
So how could one reduce the time you spend in inactivity that is harmful and optimizes physical activity for a healthy life?Be aware of how much time is spent sedentary and make a goal of reducing that number a little bit each week.Also, make it a goal to stand up or walk around for a minute or three once every half an hour spent sedentary.Anyone who is physically capable of activity should try to reach at least 150 minutes, and a peak of about 450 minutes (3 to 5 times the recommended) of leisure time physical activity per week.Larger doses (10 or more times the minimum) do not seem to be unsafe but with no additional benefit over the above recommendations.
In conclusion, health care professionals should encourage inactive adults to perform leisure time physical activity and do not need to discourage adults who already participate in high-activity levels.Physical activity should be endorsed in clinical and public health activity guidelines to maximize the population benefits of exercise.

Table 1 : Summary of studies on physical activity and mortality
total activity), replacing 1 h/d of sitting with an equal amount of activity was associated with a ǂ Sri Lanka Journal of Diabetes, Endocrinology and Metabolism benefit for both exercise and nonexercise activities.Among more active participants (>2 h/d total activity), replacement of sitting time with purposeful exercise was associated with lower mortality but not with nonexercise activity Wu CY [9] (2015) Participation in higher levels of PA did not show a dose-dependent association with mortality Sri Lanka Journal of Diabetes, Endocrinology and Metabolism