Muscle Fatigue

What causes Muscle Fatigue? Muscle fatigue is a multiplication of factors that lead to decreased physical activity Three things contribute to Muscle Fatigue Phosphagen/ Lactic Acid system Delayed On-set Muscle Soreness Biomolecules use to supply energy

Phosphagen System Body has some ATP within the body, readily available to muscles for work Supply energy needs of working muscle at Only for ~10 seconds Body turns to the Phosphagen System first Involves Creatine Phosphate and Creatine Kinase Short bursts of activity – sprinting Body relies on this pathway

Phosphagen System To replenish the ATP levels quickly, muscle cells use Creatine Phosphate High energy phosphate Enzyme that removes phosphate from C.P. is Creatine Kinase Transfers phosphate from C.P. to ADP  ATP Reaction is reversible re-form Creatine Phosphate to generate more ATP

Lactic Acid System Phosphagen system does not depend much on glucose reserves When activity continues for longer periods of time, body shifts to Lactic Acid Fermentation Involves more chemical reactions than the Phosphogen system Longer time to generate ATP Still Rapid enough to produce ATP to last ~90 sec Produces Lactic Acid as a by product Cause soreness, lead to fatigue later

Aerobic Respiration After ~2 min. of exercise, body shifts to Aerobic respiration Breakdown of gluose… Glucose can come from various places glycogen supplies in muscle & liver, direct absorption from food in small intestine If stores of glucose are finished, body can turn to fatty acids, then proteins Aerobic respiration takes longer than Phosphogen or Lactic acid – but can supply energy for a longer time

In Order, now Start by using free ATP in cells Lasts for less than 5 sec. Next, Phosphagen pathway kicks in Supplies energy for 8 to 10 seconds Involved in rapid acceleration, short-duration exercise If continues, lactic acid pathway starts Builds up Lactic Acid in muscles, causes secondary effect of pain short-distance exercises Finally, aerobic respiration Generate large amounts of ATP Occur in endurance events

Delayed-Onset Muscle Soreness Every time you exercise you are breaking muscle fibers This is normal Breaking down sites where muscle contraction occurs Muscle rebuilds connections, stronger If wait time is not long enough, soreness develops Lactic acid contributes to muscle soreness as well L.A. is what makes your muscles hurt post work-out Lactic acid builds up in the muscle tissue Causes the fatigue and soreness Both result in lower muscular output

How do we tie the animation to what we know?

 Exertion Requires  in ATP Sec. 0 – 3 ATP need comes from stores w/in cells Sec. 3 – 10 ATP need comes from Phosphagen System Creatine Kinase removes phosphate from Creatine Phosphate - forms ATP < 90 – 120 s. ATP forms from Lactic Acid Fermentation Significantly less ATP/glucose (2/1) Leads to fatigue and pain Lactic Acid interferes w/ muscle contraction

>2 min. ATP formed from Aerobic Respiration IF person is working @ AEROBIC CAPACITY Aerobic Capacity – when pyruvates are formed from glycolysis at a rate matched by O2 delivery Aerobic Capacity can be sustained for a long time, depending on your level of conditioning. Factors that affect Aerobic Capacity Heart rate stroke volume Amount of capillaries in body Level of hemoglobin Amount of stored glycogen Lung capacity

What if we wanted to condition in order to burn body fat? What happens when you are running at aerobic capacity and you reach a hill or are pushed by a competitor? Push harder, more effort Body moves over aerobic capacity Compensate by doing more anaerobic respiration What if we wanted to condition in order to burn body fat? Must exercise long enough to lower glycogen stores so body turns to lipids Body requires 4x O2 supply to metabolize fat than carbs. Need low intensity over long periods of time AND have low heart rate

How can we metabolically use fats and proteins?

Carbohydrate Any carbohydrate digested will be converted into glucose Very easily broken down Matter of time needed for digestion & absorption Polysaccharide & Disaccharides digested into monosaccharide in digestive tract All monosaccharide are absorbed in liver – converted to glucose or glycogen

Fats When fats are digested Majority of energy is in the fatty acids Broken down into glycerols and fatty acids (triglycerides) Glycerol is converted to an intermediate & used in Glycolysis Majority of energy is in the fatty acids Break down fatty acid chain into 2-carbon molecule fragments 18 -16 – 14 – 12… Process named β Oxidation 2-Carbon attaches to CoA Makes Acetyl CoA New Acetyl CoA mol. enter Krebs Cycle Only can be processed Aerobically Think about working out…

Fats Huge amount of energy Fat has more energy in bonds than other biomolecule Each 2-carbon chain is converted into an Acetyl CoA For example – A 18-carbon fatty acid can produce 9 Acetyl Co-A Can make 190 ATP from a 18-C Fatty Acid tail!!!!!! Huge amount of energy

Proteins Then, must be Deaminated – amino groups must be removed Proteins can also be used for fuel First – digestive enzymes break proteins into amino acids Amino acids can enter cycle to build biomolecules New amino acids Essential Amino Acids Then, must be Deaminated – amino groups must be removed Nitrogen is further processed as waste products – urea

Proteins Incoming Krebs Cycle molecules can also… Enzymes then convert proteins into intermediates of Glycolysis and the Krebs cycle Can make Acetyl CoA Can make other 4-5 C structures Pyruvate Other structures used in Krebs Cycle Incoming Krebs Cycle molecules can also… Provides building blocks for biosynthesis of every other organic compounds the organism needs Essential amino acids, vitamins, minerals, fatty acids all involved in pathway

When fat reserves are diminished, Protein from body tissue will supply metabolic needs For all cells and tissues Body will degrade itself to maintain metabolic activity When starving, fasting or when there is insufficient carbohydrate/lipids for energy needs… Body uses proteins from body tissues to supply fuel molecules to the brain, nerve cells and red blood cells These cells have the highest energy requirement of all cell types