Muscle Fibers (Fast/Slow-Twitch Type I, IIa, IIx)

slow twitch (fibers)

Endurance athletes possess large % of

fast twitch (fibers)

Power athletes possess large % of

Aerobic

Process that requires oxygen

slow & fast twitch

Skeletal fibers divided into two general categories based on how quickly they contract

Myoglobin

a protein that carries oxygen in muscle (maintain high level of energy for longer periods)

Fast-twitch Type IIa (fast glycolytic fibers)

also used for strength/power activities, can sustain longer than IIx fibers

glycolytic

breakdown of glucose

Fast-twitch Type IIa (fast glycolytic fibers)

can only sustain activity for less than 30 seconds

anaerobic

does not require oxygen (vs aerobic which means "with air")

type IIx

fast-glycolytic

type IIa

fast-oxidative glycolytic

Fast-twitch Type IIx (fast glycolytic fibers)

high contraction (speed) high Force high Size high Anaerobic low Aerobic low Efficiency low Fatigue (resistance) low Mitochondrial

Fast-twitch Type IIa (fast glycolytic fibers)

highly adaptable endurance training, long-term anaerobic activities i.e. swimming

Slow twitch - Type I fibers

long distance, Endurance athletes, aerobic activities

Type I: Slow-twitch (slow oxidative)

low contraction (speed) low Force low Size low Anaerobic (capacity) high Aerobic high Efficiency high Fatigue (resistance) high Mitochondrial

Aerobic capacity

max oxygen consumption by tissues during exercise

Fast-twitch Type IIa (fast glycolytic fibers)

med contraction (speed) med Force med Size med Anaerobic med Aerobic med Efficiency med Fatigue (resistance) med Mitochondrial content

slow oxidative

muscle fibers resistant to fatigue

mitochondria

powerhouses energy production for a cell (act like digestive system-takes in nutrients, breaks them down, and creates energy for cell)

aerobic metabolism

process of creating energy to fuel muscle activity with oxygen

Speed of Contraction Type I Low Speed of Contraction Type IIa Medium Speed of Contraction Type IIx High Force capacity I Low Force capacity IIa Medium Force capacity IIx High Fatigue resistance I High Fatigue resistance IIa Medium Fatigue resistance IIx Low Mitochondrial content I High Mitochondrial content IIa Medium Mitochondrial content IIx Low Size I Low Size IIa Medium Size IIx High Efficiency I High Efficiency IIa Medium Efficiency IIx Low Aerobic capacity I High Aerobic capacity IIa Medium Aerobic capacity IIx Low Anaerobic capacity I Low Anaerobic capacity IIa Medium Anaerobic capacity IIx High

Fast Twitch Size (diameter) Large Fast Twitch Aerobic/Oxidative Capacity Low Fast Twitch Contraction Speed Fastest/Power Fast Twitch Anaerobic/Glycolytic Capacity Highest Fast Twitch Myoglobin Low Fast Twitch Examples Superficial Gastroc Biceps Fast Twitch Fatigue Resistance Low Slow Twitch Name Type 1 (Oxidative) Slow Twitch Size (diameter) Small Slow Twitch Aerobic/Oxidative capacity -high Slow Twitch Contraction Speed - low Slow Twitch Anerobic/Glycolytic Capacity- Low Slow Twitch Myoglobin- High Slow Twitch Example Soleus Slow Twitch Fatigue Resistance - High

Type IIx -fast-twitch Type IIa-fast-twitch

Fast glycolytic fiber

type II

Fast-twitch

Fast-twitch Type IIx (fast glycolytic fibers)

short-term anaerobic activities i.e. sprinting, lifting heavy weights (activities lasting less than a minute)

Type I

slow twitch

myoglobin

storage of oxygen in muscle cell

aerobic metabolism

use of oxygen by cells