Fast muscle fibers are?

Ans. is'd'i.e., Glycolytic(Ref: Principles of medicalphysiolog p. 512)TYPES OF MUSCLE FIBERS:Two fibers types:Type I/red fibersType II/white fibers.Motor unit contains only one muscle fibers type:I.e., All motor unit fibers are either type-I or type II.Hence, named accordingly.CHARACTERISTICS OF MUSCLE FIBER TYPES:Parameters/CharacteristicsType I muscle fiberType II muscle fiberDifference according to fiber typeRed -Due to |ed myoglobin & mitochondrial content.White -Lack myoglobin & have few mitochondria.Subtypes- Nil -Type IIA & Type IIBIIA - Oxidative & glycolytic.IIB - Glycolytic.Usually type IIB fibers refer type II fibers.Other names1. "Slow-twitch" fibers:Due to small fiber length & diameter.Maintain relatively sustained contraction.2. "Slow motor units"Have early recruitment.1. "Fast-twitch" fibers -Sho duration of twitch.Due to bigger diameter & |ed myosin & actin filaments.Generate greater tension comparatively.2. Type IIa/"Fast Fatigue Resistant" (FR) units:Intermediate fatigability.3. Type IIb/"Fast fatigable units":Late recruitment thresholdMetabolismAerobic.Slow oxidative.Anaerobic.Fast glycolytic.Glycolytic capacity &glycogen contentLowHighSarcoplasmic reticulumNormalExtensiveBlood supplyHighNormalMyosin ATPase activityLowHighConduction velocitySlowFastContractile propeiesSlow time to peak tensionType IIa - Fast time to peak tension.Type IIb - Fastest time to peak tension.Type of muscleRed muscles -In muscles required for prolonged contraction.Also with muscles maintaining posture.Back muscles (At back of hip)Gluteus muscles .Calf muscles.White/Pale muscles -Muscles helpful in rapid contractions & finer movements.Hand & extraocular muscles.