Science is not at a point to work out any muscle as wished, for example lung muscles, rib muscles; however, science is a pretty good level more or less to change muscles shape, body shape.
Mild exercise for a young man, will be vigorous for a 50 YEARS WOMAN.
bUT, İN ANY CASE WALKİNG 1 hour a day in fresh air will be good for any one.
Each person might have a knowladgable person who is good to shape any muscle of body such as ribs, but today their salary is very high.
Only a knowladgable educated person will check a body anatomy, muscles to see what muscles requires exercise training. Most man lifts dumpless incorrectly and have a ugly appearance on their neck/shoulder area(figure 1).
Figure 1. Neck shoulder area. Shoulder needs to be trained to risen for better.
Figure 2. Butterfly arm exercise either in water or in a exercising room will give better neck/shoulder area shape, will give wider and risen shoulders.
During exercises either in water or in a exercising room, paying attention to stretch muscles to full-extend will train muscles better.
For example, Michael is very good to stretch muscles to full-extent. His arm, his lung area is stretched to full each time he repeats his stroke. Michael advantage that he is very tall and proportionally has very wide shoulders around his head to pull water easily is a different issue, or is the subject of his easy fast move in water during swimming. This post gives him as a good example of full-stretching of axilla, arm-shoulder lung area muscles. That someone is swimming not necessarily means he/she is benefiting from full-stretching her/his axilla, arms; going in water is not always equal to do best exercise for body. Swimming is a complex activity,and do not necessarily aims to give best shape for any body; specially female's spine posture will not look better when trained only to have too wide back shoulder muscles.
In conclusion, exercise program to train different muscle groups should be tailored to each person problems or body shape.
The exercise program developer not necessarily be the instructor for muscle training.
To diagnose the problem muscles can be done only by a knowladgable, medically educated person. Many perfect exercise to have perfect abdominaL MUSCLES CAN NOT BE done for everyone, because requires elastic bodies. See below photo.
Figure 3. This girl has a genetic advantage to bend her body backwards easily. Such genes are not frequent between humans, preliminary data shows that only 10% or less female can bend her bodies healthily as above backwards bridge position. Bending body backwards is good to strech not only abdominal muscles but also the connective tissue, the ligaments that bind the important organs will be healtier with such movement, ligaments, entire abdominal muscles will be refreshed, healthier, stomach fat will be removed. But, someone with weak spine, weak vertebrae connections should never forse to do such movement.
Thus, each people should be instructed only to exercise to suit their genetic background. Although training may improve some stretching exercise, most people even after years of training will fail to bend their bodies backwards.
Although, walking can be recommended to anyone, some training such as weight lifting, pull-ups, backward-bending should not be tried to force body to injuries.
Same training program may give health to some people with suitable genetic background, but, may hurt some bodies with wrong genes.
An example stretching exercise is to stretch tummy area to decrease fat around tummy. mANY peOPLE SİTTİNG against computer will have loose tummy muscles, or will have fat about their tummies.
if we want a lean, flat strong tummy, then we need to work or stretch the muscles at this area. We want an exercise to stretch the major muscle at tummy area to reduce the fat of this area of body. The major muscle of this area is called Rectus Abdominalis. In general not the person training, but the exercise-program-developer is supposed to locate the fat body related major muscles. sTRECTHİNG any muscle, in this example, rECTUS aBDOMİNALİS will reduce fat around this muscle.
Streching Rectus Abdominalis, or exercising tummy area fat, is best achieved by backward flexion of body about waist. Most people will not be able to do a backward bridge bending, but many will succeed in backward bending by the help of the a supporting wall as shown in Figure 4, (c) , the hands climbs towards floor to bend body further. sTRETCH EXERCİSES HAS THE ADVANTAGE OVER sole muscle exercise that they not only trains muscles but the internal organs at this area. For example tummy exercise by backward bending will also healthly stretch stomach area, female or male reproductive organs, in females for example increase circulation on Uterine, uterine ligaments. 
Figure 4. Tummy exercise. Major tummy muscle(Rectus Abdominalis).
Figure 5. Bending body towards sides will remove fat about waist line, about sides as highligted as blue on this figure. The figure depicts body with muscles.
Figure 6. Some exercises will be done easier with holding a rope or scarf.
Bending body sides is easier when a scarf fabric(shown as pink colored) is hold between hands as shown in figure 6.
Our genes not only changes the body shape at birth, but also in later life limits the bodies to do some exercises. If someone does not use her/his flexibility to do some stretching exercises, the genetic background will not be noticable by someone's appereance(phenotype).
The easiest way to refresh any tissue(any muscle ) is to increase the circulation in entire body as achieved during walking. Walking increases lung circulation of blood and increases the quality of blood reaching any tissue, any muscle. During walking kidneys or any other vital organ is refreshed with increased higher quality blood circulation. For young males walking can be replaced by running activity. But, shoes are very important for both walking and running. Many wrong shoes will damage our foot.
Sometimes,the limitation to do some exercises is because of the bone length, proportions of bone lenght. For example, the exercise 'cross-legged' is done easily by people who has comparatively wide hips and long femur bones. In 'cross-legged' exercise, most of the times limiting reason is not connective tissue or muscle flexibility. 
Figure 7. Cross-legged
The shape of hip muscles will be better by exercise; however, too wide hips can not be narrowed by exercise training. The lenght of bones are genetically determined.
Or breast shape of woman can be improved by diet, sufficient Potassium, sufficient protein, healthy weight, and by doing some certain exercises; however, the shape of breasts, breast muscles mostly determined by genetic factors. Losing too fast weight will cause drooped breasts; Potassium lost, and protein breakdown in female breasts damaging breasts muscles, shape. (If the breasts are too large genetically, even a perfect diet or exercise will not be able to prevent breasts from drooping).
If someone starts doing suddenly very heavy exercises, it is not good for good for health.
It is Heart, Lung, the blood circulation between heart and lung, healthy Kidney that increases the quality of blood (oxygenated blood, ammonium free blood); very fast exercising in a short time, running too fast causes blood muscle, brain or to other vital tissues in bad quality(not reoxygenated), such increase in circulation rather harm bodies, does not improve health in entire body.
In literature increasing blood circulation to striated muscle without increasing its oxygenation is called 'exercise towards anaerobic metabolism'. Myself, I never try to do any exercise to increase circulation of bad quality blood. I try to balance my heart, my lung, my kidney work simultaneously to achieve good quality blood to muscle or to my any vital organs such as brain. Brain requires oxygenated high quality blood.
Sometimes in literature the exercise that sends oxygenated blood(high quality blood) to tissues is called 'aerobic exercise'.
For example, prior to my open sea long distance(10 kms) summer vacation swimmings, I do very long distance walkings(15kms/3 hours day) in fresh-air, under daylight for months to increase my Lung, Kidney, Heart capacity, thus I make sure that when I swim long distance, my muscles, all my tissues are circulated by oxygenated blood; my heart, lung, kidney capacity manages that. I never force my body to swim to increase anaerobic metabolism in my striated muscles. I also continue to my stretching exercises.
Some sports magazines call my walking program prior to swimming as 'cardio exercise', exercises that helps to increase heart output capacity healthly.
InCREASİNG Heart Beat will not always equal to an increase in quality of blood that reaches brain or to other important organs.
Blood pressure, lung inspiration rates/volumes, blood gas levels, blood acidity, fatty-acid level, liver, kidney function etc is also important during exercise.
Increasing heart-beat may help blood Fatty-acids entry into striated muscles as an energy source for, but not necessarily means that brain will have high quality blood.
Heart is a very hardworking organ in our body. During vigorous exercise, such as increasing the speed of walking from 3 kms to 9 kms per hour, heart rate will increase about 30 beats depending on age, leg arm muscle mass, weight etc. Such increase of heart-beat for entire body in general causes a bad effect on nutrition/metabolism of heart cells themselves, a dilemma moment for heart; resting for itself or working for other body tissues.
Heart cells, at normal heart-beat rate will contract, will remove old lipids to replace with newly synthesized lipids if contraction is followed with resting times with enough oxygen. But, if the contraction of muscle cells are too much(if heart beats too much), there remains no sufficient resting times to refresh heart wall (no resting time to increase or regenerate intracellular lipid structures of heart which required for intramyocyte subcompartment calcium stores, future day's contraction/beats of heart).
In other words, by excess heart-beat rate, heart sacrifice its own nutrition for the needs of some muscles in legs, arms etc. Does it worth to sacrifice heart cell's quality by too much heart-beat if in future ultimate organ needed for body, for brain is the heart? The answer is No. Excess heart-beat increases blood fatty-acid levels, increases fatty-acid levels in heart-cells, but does not improve heart-cell usage of Fatty-acid proportional to the fat level in capillary heart vessels. Then, excess free fatty-acids, not used by heart muscle will bind to Sodium and will create harmfull fats in heart coronary arteries. Clogged coronary vessels will cause damages in heart wall(Heart Attack, myocardial infarction, damage in heart muscle-walls).
Heart AFTER too much exercise may sometimes stop to increase heart-beat-rate and the diastolic blood pressure(when the heart is in rest) will increase. The systolic and diastolic blood pressure is also important for healthy exercising to consider. Since systolic blood pressure is regulated not only by heart but by kidney, by many other factors, it is the subject of another post.
If a person eats too much fat before exercise, since exercise itself regardless of what is eaten increases blood fatty-acids levels, the increase in heart-beat further accelerates clogging of heart coronary arteries to damage heart. In blood, the harm of fatty-acids can be decreased by sufficient protein intake, thus high protein, low fat diet is also recommended to exercising times.
I am rather a video, photo person, rather a mathematical scale, exact 'scientific units' person, ı BELİEVE each program should be tailored to each person after scientific check ups by knowledgeable people.
I am thankfull to all photos, videos etc that tells how they are building their bodies whether I approve or not their methods. Such comparisons will help to reach the best exercise program for each gene, for each life.
*during walking exercise hands must be free to allow upper body, shoulder, lung, rib muscles move freely by movement of legs.
