Muscle Cells and Contraction mitochondria contractile filaments sarcoplasmic reticulum

Muscle Types Type I - “Red”, “Slow” –Contracts relatively slowly –Many mitochondria –Good blood supply Type IIb - “White”, Fast” –Contracts relatively rapidly –Few mitochondria –Poor blood supply –Packed full of contractile filaments

Gentle exercise Type I muscles recruited –good blood supply, heaps of mitochondria Most readily available fuel is glucose –Glucose transporters move to cell surface glucose BLOOD MUSCLE glucose Transporters

Consequences of Glucose Usage Muscle glucose uptake leads to a decrease in blood glucose concentration Need to keep blood glucose constant! –Small change in blood glucose causes... insulin glucagon

Effects of Low Insulin and High Glucagon –Stimulation of glycogen breakdown in liver –Stimulation of fat breakdown in white adipose tissue FAT fatty acids GLYCOGEN glucose fatty acids glucose WAT LIVER

Glucose Recycling Glucose stores (glycogen) are limited –Cannot convert fatty acids into glucose GLUCOSE CONSERVATION AND RECYCLING –Fatty acids substitute for glucose as a fuel –Fatty acids prevent glucose from being wastefully oxidised

Fatty Acid and Glucose Oxidation glucose acetyl CoA CO 2 pyruvate fatty acids GLYCOLYSIS FATTY ACID OXIDATION

Fatty Acid Oxidation inhibits Glucose Oxidation glucose acetyl CoA CO 2 pyruvate fatty acids GLYCOLYSIS FATTY ACID OXIDATION lactate to liver inhibits

WAT LIVER Summary of Gentle Exercise –Initially, glucose is used –Then fatty acids take over and glucose is recycled FAT fatty acids CO 2 GLYCOGEN glucose lactate CO 2 MUSCLE

Moderate Exercise As the pace increases, the rate of fatty acid utilisation increases, but.... –The enzymes that catalyse fatty acid oxidation soon reach their maximum capacity –During running, fatty acid oxidation alone is not sufficient to maintain ATP production –Inhibition on glucose oxidation is removed Glucose oxidation occurs! Less glucose recycling Liver glycogen stores depleted faster

Summary of Moderate Exercise WAT LIVER FAT fatty acids CO 2 GLYCOGEN glucose lactate MUSCLE

Strenuous Exercise –As the intensity of the exercise increases further, muscle glycogen is broken down. WAT LIVER FAT fatty acids CO 2 GLYCOGEN glucose lactate MUSCLE GLYCOGEN

Glycogen Depletion during a Marathon Race Time (hours) Glycogen (mg/g) slower faster

Why Glycogen is Important When glycogen has run out, only fatty acid oxidation can be used for ATP generation Power output is lower when using only fatty acids “Hitting the Wall” Cannot sprint if there’s no glycogen

Strategies Start the event with more glycogen than your competitors Spare the glycogen by making more use of fatty acids Use fatty acids sooner so less glycogen is used in the early stages

Glycogen Supercompensation –After extensive depletion, glycogen resynthesis overshoots Time (days) pre-exercise level

Glycogen Loading - Classical Time (days) HiFATHiCHO –Interrupts training! –Potentially dangerous –Uncomfortable –Character building!

Glycogen Loading - Tapered Time (days) Fits well into normal training No dangerous full glycogen depletion. always High Carbohydrate

Glycogen Sparing Increase the use of fatty acids –Carnitine helps fatty acids enter mitochondria –Training increases the activity of fatty acid oxidation enzymes Start fatty acid release from White Adipose Tissue early –Strong cup of coffee! –NOT glucose drinks BEFORE an event insulinglucagon= inhibition of fatty acid release

Fitness Better cardiovascular system Increased vascularisation of muscles –better oxygen supply –better fuel supply (especially fatty acids) More mitochondria –Higher capacity to burn fatty acids Conversion of Type IIb to Type I?

Sprinting Uses Type IIb muscles –Poor blood supply –Packed full of contractile filaments –Few mitochondria –VERY rapid consumption of ATP Fuel selection problem –Fatty acids? »oxygen supply, mitochondria –Blood Glucose? »transporter recruitment, blood supply

Anaerobic Glycogen Utilisation Inefficient and incomplete High turnover Accumulation of lactate Takes time to stimulate glycogen breakdown GLYCOGEN pyruvate lactate acetyl CoA GLYCOLYSIS ADP ATP to blood stream

Buying time with Creatine Phosphate Less than 5 seconds supply of creatine phosphate –Enough to get glycogen mobilisation going Adrenaline stimulates massive glycogen breakdown. creatine phosphate + ADP  ATP + creatine

Fatigue Role of lactate?? Acidity interferes with many processes –Enzymes involved in glycolysis –Contractile process –Calcium movements All very controversial! –But one things for sure: very low pH and running out of glycogen are definitely bad news –OK, so that was TWO things…

Fatigue 2 Use pH buffers? –Bicarbonate widely used –Certainly works but check with doctor first! Does glycogen ever run out in a sprint? –Not in short events (100 m) –Important in longer events and multi-heat competitions

Does Glycogen run out during Sprinting? Have to ensure adequate glycogen resynthesis between races Rapidly absorbed carbohydrate Time (hours) depleted

Sprint Training Increased power output –Increased cell size –More contractile filaments –STEROIDS! Co-ordination Conversion of Type I to Type IIb? Adequate glycogen stores

Lessons Muscle Contraction –Muscle Types Getting energy from fat and carbohydrate –No work, no energy consumption! –Increase work, increased oxidation of fuel Fuel mix during.... –Walking, Jogging, Running and Sprinting Training effects

How the Fuel Mix Changes LIGHTINTENSE MODERATE Fatty acids CO 2 Fatty acids CO 2 Fatty acids CO 2 Glucose CO 2 Fatty acids CO 2 Glucose CO 2 Fatty acids CO 2 Glucose CO 2 Glycogen CO 2 SPRINTING Glycogen lactate Glycogen lactate Creatine P creatine

Take Home Message! Glycogen is an important fuel to all athletes –Using fatty acids quickly and copiously reduces the use of valuable glycogen Carbohydrate intake has to be high to allow adequate glycogen synthesis