Muscle Physiology

• Anaerobic fermentation enables cells to produce ATP in the absence of oxygen. It yields about 2 ATPs per glucose molecule and lactic acid possible contributing to muscle fatigue
• Aerobic respiration produces far more ATP, does not generate lactic acid, and requires a continual supply of oxygen
• ATP supply depends on the availability of oxygen and organic energy sources like glucose and fatty acids
• At rest and during mild exercise, muscles get their energy from the aerobic respiration of fatty acids. For moderate exercise, muscles get their energy from glycogen stores; for heavy exercise, muscles get their energy from blood glucose
• For immediate energy, creatine phosphokinase catalyzes the transfer of phosphate between creatine and ATP. It obtains P from a phosphate-storage molecule creatine phosphate, and gives it to ADP to create ATP
• Myokinase transfers P from one ADP to another, converting the latter to ATP
• Phosphagen system is the combination of ATP and CP which provides nearly all energy for short bursts of activity
• In anaerobic fermentation, glucose is converted into pyruvate which is converted into lactate 3 instead of acetyl CoA and enters into the citric acid cycle.
• After about 40 seconds of activity, the respiratory and cardiovascular systems start to deliver oxygen fast enough for aerobic respiration to meet most of the muscle's ATP demands. For 30 minutes, energy comes equally from glucose and fatty acids. But after 30 minutes, depletion of glucose causes fatty acids to become the more significant fuel
• Muscle fatigue could be peripheral or central. Peripheral muscle fatigue is the inability of a muscle to maintain force of contraction after prolonged activity. Central fatigue is the mental barrier preventing the drive of motor output
• Muscle fatigue is the progressive weakness from prolonged use of muscles. Fatigue in high-intensity exercise is thought to result from K+ accumulation in the T Tubules reduces excitability; excess ADP and P slow cross-bridge movements, inhibit calcium release, and decrease force production in myofibrils
• Fatigue in low-intensity (long-duration) exercise is thought to result from fuel depletion as glycogen and glucose levels decline, electrolyte loss through sweat can decrease muscle excitability, and central fatigue
• VO2 Max is the point at which the rate of oxygen consumption plateaus and does not increase further with added workload
• The lactate threshold is the maximal oxygen uptake at which a rise in blood lactate levels occurs. It occurs at about 50-70% VO2 max
• Excess Post Exercise Oxygen Consumption (EPOC) is the period in which creatine phosphate and ATP in muscle fibers is resynthesized, myoglobin replaces lost O2, and lactic acid is converted back into glycogen stores and pyruvate.
• Toxin blocks inhibitory nerve impulses from upper motor neurons so excitatory input is continuous at alpha motor neurons
• Muscle cramps result from a state of sustained contraction of a muscle during which the muscle does not relax to its initial length or tension
• Some causes of cramps are: dehydration, and depleted levels of potassium and sodium
• latent period between the end of the muscle action potential and the beginning of muscle tension development represents the time required for release and binding to troponin
• Starling's Law - the amount of tension developed by a sarcomere is proportional to the amount of overlap of filaments or fiber length
• During incomplete tetanus, your muscles go through temporal summation of muscle contractions with small rests in between, but will eventually result in complete tetanus
• Treppe, also known as the staircase effect, is the phenomenon that occurs when initial contractions after a long break are weaker than subsequent
• shiver is an involuntary, summed contractions that release heat
• Isotonic muscle contraction is when the muscle contracts, shortens, and creates enough force to lift the weight
• Isometric contraction is when the muscle contracts, but the muscle does not shorten; creates force without moving the weight
• Eccentric motion is force generation as the muscle lengthens. It is 50% more forceful than concentric motions and often leads to delayed onset muscle soreness