The Theory of Exercise (yinyoga.com)

All forms of exercise share two features in common: first we must stress the tissues, then we must let the tissues rest. Yang tissues do better when stressed in a yang manner and yin tissues do better when stressed in a yin way. Stress has many negative connotations in our culture because we forget the "rest" part of this equation. But to have no, or little, stress in our life is just as damaging as having too much stress. We need to stress the body, and we need to rest it. There is a yin/yang balance here that leads to health. Too much of anything is not healthy. Yang exercise targets the yang tissues: the muscles. Muscles love to be rhythmically and repetitively moved. Any static holds are brief. The muscles are elastic and can take this type of exercise. However, to apply yang exercise to yin tissues could damage them. Yin tissues, being more plastic, require gentle but long-held stresses. Imagine bending a credit card back and forth one hundred and eight times every morning. It wouldn't take many mornings of this for it to snap in half. The credit card is plastic, just as our ligaments are. To rhythmically bend ligaments over and over again, as some students do when doing drop back from standing into the wheel, can, over time, damage the ligaments, just like the credit card was damaged The warning here is … do not apply yang exercise techniques to yin tissues! Applying a yin exercise to yang tissues could also be damaging! Holding a muscle in a contracted state for a long period of time is called "tetany" [1] and may damage the muscle.

Is it better to tighten muscles (yang) or relax them (yin)? That depends on your intention. We tighten our muscles to protect our joints. We relax our muscles so we can exercise our joints. What is your intention in the pose you are doing?

Many health care professionals shudder at the thought of exercising joints; they have the mistaken view that all exercise is yang exercise. Despite this concern it is possible to exercise ligaments, bones, and joints. In fact, it is necessary. However, being yin tissues means we must exercise them in a yin way. And then, please remember the important second part of this equation - we must let them rest! [2]

There is a lot of research proving the importance of stress and rest beyond just developing strength physically, but it is beyond the scope of this journey to go into it further. [3] 

Link: http://www.yinyoga.com/ys1_0.3_theory_of_exercise.php

Principles of Pilates (Wikipedia)

Philip Friedman and Gail Eisen, two students of Romana Kryzanowska, published the first modern book on Pilates, The Pilates Method of Physical and Mental Conditioning, in 1980 and in it they outlined six "principles of Pilates".^[9] These have been widely adopted—and adapted—by the wider community. The original six principles were concentration, control, center, flow, precision, and breathing.

Concentration

Pilates demands intense focus: "You have to concentrate on what you're doing all the time. And you must concentrate on your entire body for smooth movements."^[10] This is not easy, but in Pilates the way that exercises are done is more important than the exercises themselves.^[10] In 2006 at the Parkinson Center of the Oregon Health and Science University in Portland, Oregon, the concentration factor of the Pilates method was being studied in providing relief from the degenerative symptoms of Parkinson's disease.^[11]

Control

"Contrology" was Joseph Pilates' preferred name for his method and it is based on the idea of muscle control. "Nothing about the Pilates Method is haphazard. The reason you need to concentrate so thoroughly is so you can be in control of every aspect of every moment."^[12] All exercises are done with control with the muscles working to lift against gravity and the resistance of the springs and thereby control the movement of the body and the apparatus. "The Pilates Method teaches you to be in control of your body and not at its mercy."^[13]

Centering

For practitioners to control their bodies, they must have a starting place: the center. The center is the focal point of the Pilates Method.^[14] Many Pilates teachers refer to the group of muscles in the center of the body—encompassing the abdomen, lower and upper back, hips, buttocks, and inner thighs—as the "powerhouse". All movement in Pilates should begin from the powerhouse and flow outward to the limbs.

Flow or efficiency of movement

Pilates aims for elegant sufficiency of movement, creating flow through the use of appropriate transitions. Once precision has been achieved, the exercises are intended to flow within and into each other in order to build strength and stamina. In other words, the Pilates technique asserts that physical energy exerted from the center should coordinate movements of the extremities: Pilates is flowing movement outward from a strong core.^[15]

Precision

Precision is essential to correct Pilates: "concentrate on the correct movements each time you exercise, lest you do them improperly and thus lose all the vital benefits of their value".^[16] The focus is on doing one precise and perfect movement, rather than many halfhearted ones. Pilates is here reflecting common physical culture wisdom: "You will gain more strength from a few energetic, concentrated efforts than from a thousand listless, sluggish movements".^[17] The goal is for this precision to eventually become second nature, and carry over into everyday life as grace and economy of movement.^[18]

Breathing

Breathing is important in the Pilates method. In Return to Life, Pilates devotes a section of his introduction specifically to breathing "bodily house-cleaning with blood circulation".^[19] He saw considerable value in increasing the intake of oxygen and the circulation of this oxygenated blood to every part of the body. This he saw as cleansing and invigorating. Proper full inhalation and complete exhalation were key to this. "Pilates saw forced exhalation as the key to full inhalation."^[20] He advised people to squeeze out the lungs as they would wring a wet towel dry.^[21] In Pilates exercises, the practitioner breathes out with the effort and in on the return.^[22] In order to keep the lower abdominals close to the spine; the breathing needs to be directed laterally, into the lower rib cage. Pilates breathing is described as a posterior lateral breathing, meaning that the practitioner is instructed to breathe deep into the back and sides of his or her rib cage. When practitioners exhale, they are instructed to note the engagement of their deep abdominal and pelvic floor muscles and maintain this engagement as they inhale. Pilates attempts to properly coordinate this breathing practice with movement, including breathing instructions with every exercise. “Above all, learn to breathe correctly.”^[23]

^{Source: http://en.wikipedia.org/wiki/Pilates}

Benefits of Pilates (Wikipedia)

Pilates is a conditioning routine that may help build flexibility, muscle strength, and endurance in the legs, abdominals, arms, hips, and back.^[4] It puts emphasis on spinal and pelvic alignment, breathing, and developing a strong core or center, and improving coordination and balance. Pilates' system allows for different exercises to be modified in range of difficulty from beginning to advanced. Intensity can be increased over time as the body conditions and adapts to the exercises.^[4]

Source: http://en.wikipedia.org/wiki/Pilates

Types of Relaxation Techniques

A) Visualization - is a method of relaxing the mind by picturing a relaxing scene. This may involve imagining spending time in a safe place, picturing a relaxing location such as a beach or a meadow, or imagining releasing stress. 

B) Muscle relaxation - can involve passive progressive muscle relaxation (consciously allowing each muscle group to relax), progressive muscle relaxation (progressively tightening and releasing muscles), or using other methods such as physical movement, massage, or stretching to release muscle tension.

C) Sensory relaxation - involves using the senses (vision, hearing, touch, smell, taste) to relax. This may include using your imagination to picture various sensations, or experiencing different sensations to induce relaxation. It is possible to experience sensations by listening to music, sampling different foods, using aromatherapy, applying heat and cold, etc. 

D) Creative expression relaxation - is the use of creativity to relax. This may involve art, dance, music, writing, putting something together, crafts, or a variety of other creative pursuits.

Source:  http://www.nerdtests.com/mq/uttake.php?id=43458