CH 1: structure and function of exercising muscle
Muscle-Fascicle-Muscle fiber-Myofibril
Muscle: made up of bundles of fascicles; surrounded by epimysium
Fascicles: made up of muscle fibers; surrounded by perimysium
Muscle fiber: made up of myofibrils; surrounded by endomysium
Myofibril: made up of actin and myosin; divided into sarcomeres
6 steps of an action potential
1. -70 RMP
2. Na channels open, Na moves into the cell
3. Depolarized to 30 mV, Na channels close
4. Repolarized. K= channels open allowing K+ into the cell
5. Hyperpolarization
6. Back to -70 RMP
ATP-PCr fuel/enzymes/rate/energy produced
fuel: Phosphocreatine
Enzymes: creatine kinase
rate: 10 ATP/ second
Energy produced: 1 mol ATP/ 1 mol PCr
EPOC
Excess Post exercise Oxygen Consumption: occurs when O2 consumed> O2 demand in early recovery
Replenishes ATP/PCr stores, converts lactate to glycogen, replenishes hemo/myoglobin, Clears CO2
Role of Ca/Ach in muscle contraction/action potential
Ca: Binds to troponin and enables actin-myosin contraction
Ach: Binds to Ach receptors which opens up sodium channels, allowing Na+ into the cell which triggers an action potential
6 steps of a muscle contraction
1. AP starts in the brain
2. AP arrives at axon terminal, releases Ach
3. Ach crosses synapse and binds to receptors
4. AP travels down T-tubules
5. Ca is released from the sarcoplasmic reticulum
6. Ca enables actin-myosin contraction
Motor unit
A muscle neuron and the fibers that innervates it
Glycolysis fuel/enzymes/rate/energy produced
fuel: Glucose or glycogen
Enzymes: Phosphofructokinase
Rate: 5 ATP/ second
Energy produced: 2 mol (glucose) or 3 mol (glycogen)/ 1 mol substrate
Direct vs Indirect calorimetry
Direct: Estimates total body expenditure based on heat production- substrate metabolism efficiency
Indirect: Estimates total body expenditure based on O2 used and CO2 produced * main method used in lab settings*
Role of ATP in cross-bridging
Thin and Thick filaments
Thin: Actin: I band: anchored at z disk; contains 3 proteins: Actin, troponin, and tropomyosin
Thick: Myosin: H zone: titan is stabilizer (prevents overstretching); Globular heads: Protrude 360 degrees from thick filament heads, and interacts with actin filaments for contraction
Size Principle
The order of recruitment is directly related to the size of a motor neuron
Oxidative (carbs) fuel/enzymes/rate/energy produced/steps
fuel: glucose or glycogen
enzymes: Isocitrate Dehydrogenase
Rate: 2.5 ATP/ second
Energy produced: 32 (glucose) or 33 (glycogen)/ 1 mol substrate; NADH and FADH2 is also produced
Steps: Glycolysis, Krebs cycle, Electron transport chain
RER and training
RER: Respiratory Exchange Ratio: ratio between rates of CO2 production and O2 usage; predicts substrate use, kilocalories/ O2 efficiency; O2 usage during metabolism depends on the fuel being oxidized ( more carbon atoms in molecules= more O2 needed)
RER CHO=1.0; Fats=0.70
Training allows for: High VO2 max, High lactate threshold (% VO2 max), high economy of effort, high % type 1 fibers- more training allows athlete to compete at a higher percentage of their VO2 max
Na/K pump
When K+ channels open and K+ leaves the cell, it is offset by the Na/K pump; Resting membrane potential is created by the Na/K pump
Role of Actin, Myosin, Troponin, Tropomyosin
Actin: Contains myosin binding site
Myosin: Interacts with actin filaments for contraction
Troponin: Moves tropomyosin; binds to Ca+
Tropomyosin: Covers active site at rest
Golgi Tendon Organs and Muscle Spindles
GTO: Sensitive to tension; initiate relaxation
Muscle Spindles: Sensitive to stretch; initiate contraction
Oxidative (fats) fuel/enzymes/rate/energy produced/steps
Fuel: triglycerides or Free fatty acids (FFAs)
Enzyme: lipase, Acetyl-CoA
rate: 1.5 ATP/ second
Energy produced: 100+ ATP/ 1 FFA
Steps: dependent on how many carbons on FFA- beta oxidation, krebs cycle, electron transport chain
Kcal- O2L conversion
(Kcal/min)/5= (VO2L/min)
Muscle fiber types
Type 1: slow-twitch; high oxidative capacity; fatigue resistant; high aerobic endurance; Recruited for low intensity aerobic exercise and daily activities
Type 11a: fast-twitch; poor aerobic endurance; fatigue quickly; used for short/intense endurance; produce more force than T1
Type 11x: fast-twitch; poor aerobic endurance; fatigue quickly; seldom used for daily activities; used for short/explosive sprints; produce more force than T1
Steps of cross bridge/ power stroke
1. Ca binds to troponin
2. Troponin pulls tropomyosin off binding site
3. Myosin heads pivot and power stroke
4. Myosin binds to actin
Sympathetic vs Parasympathetic
Sympathetic: Fight or flight; predominate during exercise
Parasympathetic: rest and digest; oppose the effects of the sympathetic nervous system
Time/Duration/ overlap of systems
Time- ATP-PCr: 3-15 seconds; Glycolysis: 15 seconds - 2 minutes; Oxidation (carbs) : 90 minutes; Oxidation (fats) : days
All 3 systems interact for all activities; no one system contributes 100%, but 1 system dominates for a given task
Low intensity exercise (below 60% VO2 max): lipids are primary substrate
High intensity exercise (above 75% VO2 max): Carbs are primary substrate
VO2, Lactate threshold with training and effects on performance
Lactate threshold: Point at which blood lactate accumulation increases markedly- lactate production cannot be cleared fast enough- good indicator of potential for endurance athlete
Usually expressed as percentage of VO2 max
Higher lactate threshold=better endurance performance
For 2 athletes with the same VO2 max, the one with the higher lactate threshold will have better performance
The amount of force exerted during a muscular contraction is dependent on...
Type of motor unit recruited, initial length of the muscle, and the neural stimulation