: Muscle fatigue is caused by the accumulation of metabolic waste (like lactic acid) and the depletion of energy stores during prolonged physical activity. Health and Posture

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: Muscles often work in pairs (like the biceps and triceps); when one contracts, the other relaxes to produce movement at a joint.

: Bones grow in length through the division of cartilage cells and in thickness through the periosteum (the outer membrane). Muscular System and Movement

: A lack of physical activity can lead to weakened muscles and cardiovascular issues.

: Bones are made of organic substances (which provide flexibility) and inorganic minerals like calcium (which provide hardness).

: Skeletal muscles (striated) are responsible for voluntary movements, while smooth muscles control internal organs and are involuntary.

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