BIOL121: 06/05/2026 (Mendel)

direct phosphorylation

quick regeneration of ATP

ENZYME = creatine kinase, transfers phosphate from CP to ADP (CP+ADP→creatine+ATP) (1CP→1ATP)

no oxygen used, provide for short bursts of energy = 15s (spring runner)

anaerobic pathway

happens when creatine phosphate runs out

glucose → 2 pyruvate

GLYCOLYSIS = 1 glucose → 2 ATP net

pyruvate → lactic acid (byproduct/muscle burn)

ANAEROBIC GLYCOLYSIS = glycolysis+fermentation

longer energy provision (30-40s), NO oxygen used, OUTSIDE mitochondria

aerobic pathway

occurs during rest or moderate exercise

AEROBIC RESPIRATION = glycolysis, mitochondria activity (occurs IN mitochondria)

OXYGEN REQUIRED

32 ATP per glucose, CO2 and H2O

hours of ATP usage

muscle recruitment

motor units with smallest muscle fibers recruited first

larger fibers recruited as stimulus intensity increases

largest motor units activated only for most powerful

muscle tone

constant, slightly contracted state of all muscles

keeps muscle firm, healthy, ready to respond

isotonic contractions

muscle changes in length and moves load

COCENTRIC = muscle shortens doing work (biceps contract to pick up book)

ECCENTRIC = muscle lengthens generating force (laying book down)

isometric contractions

load is grater than max tension muscle can generate

muscle neither shorten nor lengthen

energy for contraction and ATP

ATP supplies energy needed for muscle fiber, depleted in 4-6 seconds, only source for contractile activities, quick regeneration

move and detach cross bridges

pump Ca back in SR

Pump Na+ out and K+ in after excitation-contraction coupling

ATP regeneration

direct phosphorylation of ADP by creatine phosphate (CP): CP + ADP = creatine + 1ATP (15s)

ANAEROBIC PATHWAY = glycolysis (break glucose into 2 pyruvic acid = 2 ATP net gain) and lactic acid formation (byproduct, converted from pyruvic acid)

AEROBIC RESPIRATION = series of chemical reactions occurring in mitochondria requiring oxygen, breaks glucose into CO2, H2O, ATP ( 32 possible)

fatty acids are main fuel after 30min of exercise

lactic acid

diffuses into bloodstream

broken down by liver, delivered by kidneys, burn off for fuel by heart

converted back into pyruvic acid or glucose by liver

yields only 5% as much ATP as aerobic, but 2.5x faster

energy systems used during sports

AEROBIC ENDURANCE = time muscle contracts using aerobic pathways (light to moderate activity for hours)

ANAEROBIC THRESHOLD = point at which muscle metabolism converts to anaerobic pathway

excess postexercise oxygen consumption

return muscle to pre-exercise state:

oxygen reserves replenished

lactic acid reconverted to pyruvic acid

glycogen stores replaced

ATP and creatine phosphate reserves are resynthesized

all require extra oxygen (EPOC/oxygen debt)

force of muscle contractions

depends on number of cross bridges attached

NUMBER MUSCLE FIBERS STIMULATED = more motor units → greater force

RELATIVE SIZE OF FIBERS = bulkier muscle → more tension

FREQUENCY OF STIMULATION = higher frequency/more stimuli, greater force

DEGREE OF MUSCLE STRETCH = sarcomeres 80-120% normal resting length generate more force

less than 80%, filaments overlap too much → force decreases

more than 120%, filaments do not overlap enough → force decreases

muscle fiber type

SLOW OXIDATIVE FIBERS = low-intensity, endurance activities (maintain posture)

FAST OXIDATIVE FIBERS = medium-intensity activities (walking, jogging)

FAST GLYCOLYTIC FIBERS = short-term intense or powerful movements (sprinting)

load and recruitment

LOAD = muscles contract fastest when no load added, greater load → shorter duration of contraction/slower contraction

RECRUITMENT = more motor units contracting, faster longer contraction

aerobic (endurance) exercise

increases muscle capillaries, mitochondria, myoglobin (O2 of muscle) synthesis

results in greater endurance, strength and resistance to fatigue

convert fast glycolytic fibers into fast oxidative fibers (jogging, swimming, biking)

resistance exercise

typically anaerobic (weight lifting, isometric exercise)

muscle hypertrophy, increase in fiber size

increased mitochondria, myofilaments, glycogen stores, connective tissue

increased muscle strength and size