The fundamentals: What you need to know to get started

Muscles
When you decide to move a part of your body, your brain transmits the message to your muscle fibers via your nerves. The fibers respond by contracting, which creates motion. For example, when you contract your biceps, the triceps on the back of your arm relaxes.
Exercises that involve continuous motion, such as rowing, walking, or swimming, result in the rhythmic tightening and releasing of muscle fibers. In addition to moving your body, this process produces a “milking” action that helps move blood through your veins and back to your heart.

Exercise :
While you exercise:
·         Unless you are taking medications, your heart rate can reach 130 to 150 beats per minute (sometimes higher, particularly in young, fit individuals). That nearly doubles the resting norm of 70 to 80 beats per minute for most people.
·         Your heart may pump up to 20 liters of blood per minute (40 liters for well-trained endurance athletes)
·         Your skin and muscles receive 80% of your total blood flow.
·         Millions of capillaries open up to feed muscle fibers.
·         Your lungs pass up to 200 pints of air in and out each minute. When not exercising, the average for most people is 12 pints a minute.

Bones
Throughout your life, your body is constantly building and dismantling bone tissue. This maintains your skeleton by replacing old bone with new bone and frees calcium, the main building block of bone, for other tasks. When the amount of calcium in your blood gets low, your body draws on the reservoir of calcium stored in the bones.
Early in your life, your body builds bone faster than it loses it. But with age, bone is lost more rapidly than it’s formed. Exercise plays a key role in slowing bone loss. Stress increases bone strength and density. Exercises that work against gravity (such as walking, jogging, tennis, basketball, and strength training) provide the greatest benefit.
What can exercise do for you?
Many people spend more than half their waking hours sitting down. And activities that don’t enhance health account for quite a lot of the remainder. This growing trend may cause more trouble than most people realize.

In fact, one study that followed more than 50,000 middle-aged women for six years found that even among women who were avid exercisers, the more television they watched, the more likely they were to gain weight or develop diabetes — regardless of how much physical activity they did. For every two hours the women spent watching television each day, they had a 23% greater risk of becoming obese and a 14% greater risk of developing diabetes. Sitting at work for many hours also heightened their risks for obesity and diabetes. When planning your day, it may be beneficial not only to increase the time you spend exercising but also to try to reduce your “sitting time.” 

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