Hippocrates in 400BC said that exercise is man’s best medicine, but his message has been lost over time and we became an increasingly sedentary society. Regular exercise is among those factors providing a viable solution to the problem that we are living longer but not healthier. Our body needs movement and forces stimuli to be healthy and many processes are enhanced when we stress our body.

Our body is a complex but perfect system, composed by many parts that work in synergy to ensure our body can correctly perform any action. We have bones that are the pillars for muscle chains and other soft tissues (i.e. tendons, ligaments and fascia) that run from head to feet in our body. In turn, these soft tissues are responsible to hold in place the bones. Take all the soft tissues away and the bones would pile on the floor, as they do not interlock or stack in any kind of stable way. Remove the bones, and your body would do the same. This is our musculoskeletal system (Figure 1).

Figure 1 – The musculoskeletal system. Bones and muscles wok in synergy to allow body’s functions. (From [38])
Every part in our body, including bones and muscles, is composed by cells that have their natural life cycle. During their life, cells can be damaged or die, reason why they need constant replacement to maintain body’s vitality. Ageing is the progressive and inexorable accumulation of molecular and cellular damage which leads to loss of physical function, increasing infirmity, elevated risk of chronic illness, and ultimately death. So, cell replacement is fundamental in maintaining our body in a good state of health and live longer and healthier.

Bone remodeling is a lifelong process where mature bone tissue is removed from the skeleton by osteoclasts (a process called bone resorption) and new bone tissue is formed by osteoblasts (bone formation). Its function is to adjust bone architecture to meet changing mechanical needs and it helps to repair microdamages in bone matrix preventing the accumulation of old bone [1]. The activity of osteoblasts and osteoclasts is modulated by force stimuli [2,3]. Furthermore, sutures also function as intramembranous bone growth site that respond to force stimuli, contributing to the morphogenesis of bones [4].

Figure 2 – Bone remodeling cycle. Osteoclasts are responsible for bone resorption in order to remove old bone cells. Then osteoblasts form new bones. The action of both osteoclasts and osteoblasts is modulated by force stimuli. (From [39])
Where do you think these force stimuli are coming from? From our daily exercise! Regular exercise has effects on bone density, size and shape, resulting in substantial improvements in mechanical strength. Think for example to tennis players showing a playing arm much bigger than the other, like Maria Sharapova in Figure 3. This is the result of major mechanical loading on the playing arm, with greater muscle volume associated to greater bone volume and bone mineral content (20-40% higher) [5,6,7]. With greater bone density, bone fracture risk is reduced [8,9]. This is why physical exercise is a good way for preventing and fighting osteoporosis, where bone weakness increases the risk of broken bones and the morbidity/mortality that ensues [10,11].

Figure 3 – As many other tennis players, Maria Sharapova shows a playing arm much bigger than the other. This is the result of using always the same arm to hit the ball, with greater development of both muscles and bones. (From [40])
Our face is also composed by bones: maxilla is the main bone and it remodels according to force stimuli coming from tongue and teeth in contact (through masseter muscles). Among other factors, many contemporary jaw problems derive from the modern industrial soft high-calorie food, with facial bones that do not develop correctly since missing forces from the chewing effort, with resulting malocclusion [12,13,14].

The same applies to all other bones of the body, including feet: flatfoot and fallen arches, bunions and hallux valgus, hammer toe, blisters, corns and calluses are all problems that arose in the modern life due to the use of modern over cushioned, narrow and heeled shoes [15,16].

Similar processes happens to muscles when we exercise. When greater than normal resistance is placed on a muscle, small microscopic tears occur in the tissue. The area of damage is repaired by satellite cells from outside the muscle fibers that replicate and mature into grown cells, fusing to already existing fibers. This process forms new muscle protein strands, which increases strength and size of the muscle to better cope with similar physical activity in the future [17].

Figure 4 – When exercising, small tears occur in the muscle fibers. Satellite cells duplicate, fusing to already existing fibers and increasing muscle size and strength. (From [41])
The heart is a muscle too, responsible to pump blood through the blood vessels of the circulatory system. Blood provides the body with oxygen and nutrients, as well as assists in the removal of metabolic wastes. When exercising, our cells need more oxygen, so the heart rate increases to supply more blood. Over time the heart improves its function and muscles enhance their ability to extract and use oxygen from blood, with blood pressure that decreases when at rest. This means exercising is a good way to prevent hypertension [18,19,20], with a resulting lower risks of cardiovascular diseases and mortality [21,22,23,24].

Hypertension in mid-life is also linked to development of dementia and Alzheimer’s disease later in life [25,26,27,28]. Indeed, exercising stimulates brain functions: 90% of the brain’s activity is used to balance our body within the gravitational field of earth, in both resting and moving. As Figure 5 highlights, we have nerves throughout our entire body that exploit two functions: 1) signal for muscles and 2) sensory information for the central nervous system. Everything is coordinated by the brain, so it is not surprising that exercising prevents cognitive decline at all ages [29], with a positive relation between fitness and academic achievements [30].

Figure 5 – Nervous system. We have nerves throughout the entire body that are responsible to carry signals for muscles and sensory inputs for the central nervous system. (From [42])
Everyone ages and physical and mental declines can appear normal. However, there are different ways to age. A healthy lifestyle is what keep you younger and exercising is an essential part of it: the sometimes drastic loss of ability that many older people experience is not an inevitable part of ageing.

A sedentary lifestyle is one of the top causes of ill health in the world, contributing to type 2 diabetes, dementia, heart disease, and cancers [31,32]. Many high profile examples exist of healthy older people, but we usually assume that this is down to luck. Better nutrition and more exercise are two important factors that determine lifespan, meaning there is no such thing as luckiness when talking about healthiness.

One major change needed is to challenge and reset the beliefs about what happens to us as we grow older, to know that it is possible to combat some effects not by a drug or potion or elixir of life but by increasing physical, mental, and social activity. This would also reduce the risk of needing social care [33] and overall risk of death [34]: people with a good state of health do not exercise because they are healthy, but they are healthy because they have been exercising for large proportions of their lives, also boosting their immune system [35]. So, if you want to be healthy and live longer, do not be lazy: take care of your body and it will take care of you! And you will be happier too, since physically active people are at a reduced risk of developing depression and anxiety [36,37]. So, be active!



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Other websites

[38] Muscles, by Merck Manual

[39] Describe the process of bone remodeling, by Orthopaedics One

[40] The secret side effect of professional tennis, by Daily Mail

[41] Muscle Physiology

[42] Nervous system highlight, by Shutterstock