Stress is an enemy of human lives- one of the strongest myths told to us since ages past. Our real enemy is failure to balance stress with intermittent rest. Subjecting yourself to stress is the only way to systematically get stronger —mentally, physically, emotionally, and spiritually. Few of us do not push ourselves nearly hard enough to realize our potential, nor do we rest, sleep, and renew nearly as deeply or for as long as we should. 

Human body has a standard reaction when it faces a task where performance really matters to goals or well-being: Sympathetic nervous system and the hypothalamus, pituitary and adrenal glands pump stress hormones, adrenaline and cortisol, into the bloodstream. Heartbeat and breathing speed up, and muscles tense. What happens next is what divides healthy stress from harmful stress. People experiencing beneficial or "adaptive" stress feel pumped. Blood vessels dilate, increasing blood flow to help the brain, muscles and limbs meet a challenge, similar to the effects of aerobic exercise, according to research by Wendy Mendes, an associate professor in the department of psychiatry at the University of California, San Francisco, and others. During stress, blood vessels constrict and "you may feel a little dizzy as your blood pressure rises," says Christopher Edwards, director of the behavioral chronic pain management program at Duke University Medical Center. Symptoms are fit of anger, speaking loudly or experience lapses in logical judgment. Hands and feet may grow cold as blood rushes to the body's core. Research shows the heart often beats erratically, just like a seismograph during an earthquake. 

In a stressful situation, alarm systems in the brain trigger the release of hormones that prepare you to fight back or flee the scene. Among other results, these chemicals may boost blood pressure, speed up heart rate and make you breathe faster. They may also affect your ability to learn and remember things. Stress hormones such as adrenaline and cortisol can either facilitate or impair memory, depending on when these hormones are released. Stress hormones may affect memory by strengthening or weakening the connections between nerve cells in the brain.

Hungarian researcher found that “stress” is our body’s natural reaction to change- good and bad.  Even if we’re experiencing good changes our bodies still consider it “stress”.  He went on to coin the term “eustress” to describe good stress as “eustress” and referred to bad stress as “distress.” 

Regular cardiovascular exercise is a form of stress that enhances the heart's ability to efficiently pump blood drops an average of 1 percent a year between the ages of 30 -70, and faster after that. Focusing on one thing for a defined period of time — like counting your breath, working over a demanding task, or even reading a difficult book — you're subjecting your attention to stress. As your mind wanders, the challenge is to return your focus to the breath, or the task, or the book.

Effectively, you're training control of your attention. More intensely you practice, even for short increments of time, the stronger you'll get. 

Let us see the example below

In a study of 50 college students, some were coached to believe that feeling nervous or excited before a presentation could improve performance. A control group did not receive coaching. When students were asked to make a speech about themselves while receiving critical feedback, those who received the coaching showed a healthier physiological response, leading to increased dilation of the arteries and smaller rises in blood pressure than the control group.
In a parallel study, students who received the same coaching before taking graduate entrance exams garnered higherscores on a mock test in the lab and also on the actual exam three months later, compared with controls, according to a study co-authored by Dr. Mendes and published in Journal of Experimental Social Psychology. They also showed higher levels of salivary amylase, a protein marker for adrenaline that is linked toepisodes of beneficial stress.

Completing a challenging task of work, or a tough workout, or an intellectually demanding book, frees us to truly savor and enjoy the period afterwards. It allows us to experience time off not as slacking but as a fully earned opportunity for restoration. Most of us instinctively run from discomfort, but struggle equally to value rest and renewal. We operate instead in a gray zone, rarely fully engaged and rarely totally relaxed. What practice could you add to your life to regularly push beyond your comfort zone — and then deliberately renew?

Increasing the amplitude of your wave — from intense effort to deep renewal — is a definite path to a more fully realized life.