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The force and contraction time relation was studied in twitch isometric contraction of flexor carpi ulnaris muscle (FCU) and triceps surae (TS) in 5-week-old infants, 3-year-old children and adults. Contraction time (CT), duration of the plateau of active state (PAS), and time of the decline of active state (DAS) do not change with increasing force of contraction of FCU in all three age groups and in TS in 5-week-old infants. CT and DAS decrease with increasing force of contraction in 3-year-old children and in adults. PAS remains unchanged with increasing force of TS in 3-year-old children and decreases in adults, but considerably less than CT and DAS. Evidence is adduced supporting the view that CT changes with increasing force of TS depend mainly on the elastic properties of the muscle.
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