Answer:
Isotonic contractions maintain constant tension in the muscle as the muscle changes length. This can occur only when a muscle's maximal force of contraction exceeds the total load on the muscle. Isotonic muscle contractions can be either concentric (muscle shortens) or eccentric (muscle lengthens).
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O M G i just did that one on Plato
well anyway i think the answer was the the skin because any thing that invades the body is a threat to the immune system.
