Introduction

Chronic diseases is the name given to a group of diseases which are typically long lasting, non-communicable and often preventable and manageable. All types of chronic diseases are positively impacted by physical activity to varying degrees (Anderson & Durstine, 2019; Warburton et al 2006), and with chronic disease mortality rates rising at such a rapid rate (Murphy et al, 2015), some predictions even suggest that life expectancy may begin to decline for future generations born at some point in the later half of this century (Olshansky et al, 2005).

Physical activity is the most effective modifiable risk factor of chronic disease (Warburton et al, 2006) and with recent findings showing that 32.9% of the UK adult population don’t perform regular exercise (Public health England, 2024), physical activity can function as an effective, non-invasive, tool to minimise chronic disease risk through a number of different mechanisms (Neufer et al, 2015; Ruegsegger et al, 2018).

The purpose of this literature review is to outline the general recommendations for what duration, what type and what intensity exercise will be sufficient for the general population to obtain most of the benefits from physical activity. This literature review will then look into effective methods of prescribing physical activity, which health care professionals can use to increase the chances of patients performing the recommended physical activity and thus experience its benefits.

Cardiovascular disease

The first paper assessing physical activities effects on cardiovascular related mortality rates date back to 1953, when a study by Morris et al (1953) found that in the age bracket of 45-64 those who was physically active experienced less than half of the mortality rates from coronary heart disease compared to those who was not physically active. Since this time it has become more widely accepted that physical activity holds multiple cardiovascular health benefits with many more papers being published which display the benefits of physical activity on cardiovascular disease rates and the mechanisms of which physical activity achieves this (Neufer et al, 2015; Ades et al, 2001; Anderson et al, 2016). A meta analysis by Lacombe et al (2019) found similar results to Morris et al 66 years later. This meta analysis looked at the results of 25 studies with a publication date of 2010 or later. These studies compared the cardiovascular disease risk of self-reported physically active and physically inactive participants, those who reported being physically active were less than half as likely to develop a cardiovascular disease event. One major limitation to the results of this study is that those who reported being physically active may have made other positive lifestyle modifications which may confound the results such as achieving a minimum of 7 hours of sleep per night and eating a wide variety of fruits and vegetables, both of which have been associated with a decreased risk of developing a wide variety of diseases (Kohyama et al, 2021; Slavin et al, 2012).

A randomised control trial conducted by Ross et al (2015) found that high duration high intensity training is best at stimulating improvements in cardiovascular fitness. This study randomly assigned 121 sedentary, middle aged and obese participants to one of three groups. Group one performed 5 low duration low intensity training sessions per week, defined as burning 180 and 300 calories per session for women and men respectively, at 50% of their VO2 max. Group two performed 5 high duration low intensity training sessions per week, defined as burning 360 and 600 calories per session for women and men respectively, at 50% of their VO2 max. Group three performed 5 high duration high intensity training sessions per week, defined as burning 360 and 600 calories per session for women and men respectively, at 75% of their VO2 max. Cardiorespiratory fitness progress was measured using the Exercise Treadmill Test following 24 weeks of the protocol (Miller, 2008). Results showed that 38.5% of those in group one had no improvements in cardiorespiratory fitness (these people were marked as nonresponders), 17.6% of those in group two were nonresponders and 0% of those in group three were nonresponders. This study concluded with the idea that high intensity high duration endurance training is the most beneficial training intensity and duration for cardiovascular health, although their are limitations to this study. One limitation is that the treadmill test uses EKG changes as a gauge for cardiovascular health, however a meta analysis conducted by Warbuton et al (2006) casts doubt on the use of traditional physiological markers as indicators of chronic disease risk and displays how chronic disease risk can be reduced without changes in traditional physiological markers, therefore, individuals may still be able to experience a substantially reduced cardiovascular disease risk with as little as 4 sessions of moderate intensity cardiovascular exercise per week lasting 15-30 minutes per session, even if this doesn’t stimulate any change in traditional physiological markers of chronic disease risk.

The mechanisms of which physical activity achieves a decrease in cardiovascular disease risk is now becoming more clear, including reduced inflammation, increased HDL-cholesterol, body weight reductions, increased myocardial strength, increased oxygen delivery to the body (Ades et al, 2001), endothelial cell regeneration (Moebius-Winkleret al, 2015), hypertrophy of cardiac muscle (Xioa et al, 2014), and increased oxidative metabolism (Hood et al, 2011). 

Metabolic diseases

Metabolic diseases is the term given to a group of health problems, which affect the body’s heart and blood vessels, and increase the risk of diseases such as cancer, osteoporosis and type 2 diabetes (NHS, 2023). 

A meta analysis conducted by Li et al (2016) looked at 71 cohort studies reviewing the relationship between physical activity and cancer mortality rates, this meta analysis displays how the risk of cancer mortality decreases at a rapid rate up to 7.5 metabolic equivalent of tasks (MET) hours per week, equivalent to just 150 minutes of moderate intensity exercise per week (Wang et al, 2019), where chances of cancer mortality was lowered by 14% compared to sedentary individuals. Beyond 7.5 MET hours per week the risk of cancer mortality began to very significantly plateau and it is even speculated that cancer risk may rise, somewhere around 40 MET hours per week. One of the main mechanisms of which physical activity decreases cancer risk is likely through a decrease in chronic inflammation, which is associated with a decrease in chronic disease risk, including cancer (Michels et al, 2021; Beavers et al, 2010). Some evidence suggests that chronic inflammation is likely reduced to a greater extent with resistance training over endurance training (Beavers et al, 2010). 

Physical activity which loads the body, particularly resistance training, has been shown to substantially decrease the risk of osteoporosis (Beck et al, 2001). A research study by Farmer et al (1989) followed 3,595 women aged between 40 and 77 years old for 10 years, of these participants 84 new cases of hip fractures occurred, and it was identified that those who was not physically active were approximately twice as likely to experience a hip fracture compared to those who were physically active. It is believed that bones adapt to the high loads placed on them from physical activity through alterations in bone mass, external geometry, and internal micro-architecture, in what is known as wolff's law (Beck et al, 2001), this results in a decreased risk of osteoporosis (Blake & Fogelmam, 1998).  

Regular physical activity has been shown to decrease type 2 diabetes risk more than metformin (Knowler et al, 2021), which is currently the most commonly prescribed medication for type 2 diabetes (Sterrett et al, 2016). A systematic review conducted by Jeon et al (2007) searched for studies investigating the relationship between physical activity and type 2 diabetes, after some filtering for relevant studies a total of 16 studies was identified and used to draw conclusions from. This systematic review found that as little as 150 minutes of brisk walking per week was enough to decrease the risk of type 2 diabetes by roughly 30% compared to sedentary individuals. Physical activity decreases type 2 diabetes risk via a decrease in blood glucose (Holloszy et al, 2005), physical activity is believed to achieve this through the stimulation of exercise induced GLUT-4 proteins, which allows glucose to enter the cell independent of the insulin receptor (Holloszy et al, 2005). There is also reliable evidence suggesting that resistance type training causes a decreased risk in type 2 diabetes more so than endurance type training (Dunstotan et al, 2005).

Recommendations

Despite physical activities clear benefits towards minimising chronic disease risk (Anderson & Durstine, 2019; Warburton et al, 2006), health care professionals are still far more likely to prescribe patients with more traditional forms of medication over physical activity (Writz et al, 2016; Sterrett et al, 2016; Tu et al, 2018), even if physical activity is more effective, convenient and economical for the patient (Warburton et al, 2006; Jeon et al, 2007; Yang et al, 2006). 

By health care professionals prescribing physical activity as a form of medication patients are far more likely to actually engage in the protocol (Krot & Sousa, 2017). One effective method which health care professionals can use to prescribe physical activity to patients is through Making Every Contact Count (MECC) (Tindale, 2021), this intervention involves a healthcare professional simply suggesting exercise as a form of medication to a patient with every contact they have with the patient (Tindale, 2021). A research study by Keyworth et al (2018) surveyed 1,387 medical professionals and found that 56% of medical professionals perceived that patients would benefit from MECC, however, in only 50% of these cases was MECC delivered, largely due to the unclear guidelines surrounding physical activity.

The NHS guidelines recommend 150 minutes of moderate intensity exercise per week (NHS, 2024), which is likely sufficient to achieve the bulk of the benefits from physical activity towards minimising chronic disease risk (Wang et al, 2019; Jeon et al, 2007). Exercising beyond 150 minutes per week will likely result in diminished returns, although medical professionals should still promote the idea of exercising beyond 150 minutes for those who are willing to do so. Their is yet to be an established peak as to the optimal weekly dosage of physical activity for preventing chronic disease, although their likely is a peak somewhere, and beyond this point individuals will experience a greater risk of chronic disease, likely due to chronic inflammation which has been associated with overtraining (Smith et al, 2004) and has been linked to an increase in chronic disease risk (Michels et al, 2021; Beavers et al, 2010). Future research should aim to identify a peak in physical activity wear beyond this point the risk of chronic diseases increase, although this point will likely not be reached by the vast majority of individuals without the prevalence of chronic injuries making very high amounts of physical activity implausible (Kujala et al, 2003; Ataoğlu et al, 2013).

Conclusion

The evidence towards physical activity as an effective form of medication to decrease the risk of chronic disease is irrefutable (Anderson & Durstine, 2019; Warburton et al 2006), medical professionals should therefore prescribe patients with a minimum of 150 minutes of moderate intensity exercise spaced out throughout the week in accordance with the NHS guidelines (NHS, 2024). Medical professionals should use the MECC method to increase the chances of patients performing the protocol and thus gain the desired benefits (Krot & Sousa, 2017; Keyworth et al, 2018). Exercise should ideally consist of primarily endurance training with the addition of some resistance training, but for those with limited time they likely should perform a large portion of their weekly exercise dose with weight bearing endurance exercises, such as through jogging, so that they can gain more of the benefits which is largely associated with more resistance type training, such as greater blood glucose control and a greater decreased risk of osteoporosis (Dunstotan et al, 2005; Beck et al, 2001), while still achieving the bulk of the benefits from physical activity, which lies in endurance training (Anderson & Durstine, 2019; Warburton et al 2006).

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