Humans specifically, can last some time without food, several days without water and only a few minutes without oxygen.
As we grow older or if our musculature is locked up, this will diminish our intake or utilization of oxygen. This in turn will affect our overall level of energy and vitality. There is a body of evidence that suggests that the level of planetary oxygen has decreased from what it was many years ago and the amount of pollution in most cities is increasing to an alarming level.
There are modalities such as the many martial arts techniques that teach awareness of the breath and breathing. There are also therapies such as Rebirthing and the general breath therapies that use the breath as the general healing conduit.
When we take a closer look at breathing we notice how it will change accordingly with different emotional states. If for instance we experience a fright then the breathing will momentarily cease. On the other hand there is a state of chronic ill health or pain the breathing will most likely be shallow, with a break between the in and out breath. If you will carefully observe how someone is breathing you will gain and idea of their emotional state.
The idea is that any emotional disturbance is locked into the body's musculature and cellular structure. When this memory is recalled the emotional state of that 'time' and the breathing state associated with it will be reflected in the body. The person can use the breath to heal this 'past' event and so give themselves more energy in the present moment. The in and out breath are connected in a circular fashion. This can heighten the emotional state and then even it out to a state of homeostasis or peaceful balance. This is usually best undertaken with a facilitator to guide the process.
There is a great need for clearing emotional blockages and regaining a state of peace and equilibrium for overall good health. Depending on the state of the person and their willingness to attain greater energy and vitality there are many things possible here.
There are modalities such as qi gong and tai chi whose aim is to create a greater flow of 'chi' (life essence) in and through the body. These work on the more subtle levels of the body energy as well as strengthening the musculature. Yoga, as I understand it, works in a similar fashion.
There are the less subtle exercises like jogging, aerobics and the many sporting options that are available. There is no reason whatsoever for anyone to say that they do not have an option for increasing their lung capacity to some extent. This would be the case even if they were in a wheelchair. The main thing that is necessary is the willingness and awareness to change what one habitually does.
Relaxation is a great help in expanding lung capacity as well as helping release the tight muscles of the chest. This will necessitate a conscious focus on the part of the individual.
When the flow of oxygen is increased in the body much healing and regeneration can occur. Some of this may be painful or it may just entail feeling more energy in the body. The greater quantity of dissolved oxygen in the blood ( to its optimum) will allow more nutrients to be available for regeneration of all areas of the body. The food eaten will be more readily assimilated and smaller amounts will provide greater energy because the 'burning' capacity of the body will be increased.