Twisting or pulling a muscle or tendon can result in a strain. It can also be caused by a single instance of improper lifting or by over stressing the back muscles. A chronic strain usually results from overuse involving prolonged, repetitive movement of the muscles and tendons. In addition, there are several factors that put a person at greater risk for a back strain or sprain, including excessively curving the lower back, being overweight, having weak back or abdominal muscles, and tight hamstrings (muscles in the back of the thighs). Playing sports that involve pushing and pulling—such as weightlifting and football—also increases the risk of a low-back injury. Chronic strains happen slowly over time from prolonged, repetitive overuse of muscles. Chronic strains develop from using the same muscle groups in the same pattern, causing even small stresses to build on one another. Causes of chronic strain include:
Improper body mechanics or using the wrong muscle groups for a task, such as repeatedly lifting heavy objects using your back instead of your legs
Improper sports mechanics or techniques, such as habitually gripping a tennis racket too tightly or an incorrect golf swing
Participation in the same exercises in the same way, day after day
Poor posture
Use of the wrong equipment, such as running shoes without the proper support for your foot type
Answer: The lower respiratory system moves oxygen into the blood; the circulatory system delivers blood to the body.
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