Macronutrient Metabolism in Exercise and Training Chapter 5

Fuel for Exercise The fuel mixture that powers exercise generally depends on: The intensity of effort The duration of effort The exerciser’s fitness status The exerciser’s nutritional status

Bioenergetics Cells need constant supply of ATP Minimal amounts stored for cellular processes Intramuscular Muscular contraction-exercise Constant, large supply

Bioenergetics Formation of ATP (3 metabolic pathways) 1. Phosphocreatine (PC) breakdown ATP-PC system (phosphagen system) 2. Degradation of glucose and glycogen Glycolysis (Glycolytic system) 3. Oxidative phosphorylation Tricarboxylic cycle, Krebs cycle

Bioenergetics Anaerobic pathways (do not involve O2) Aerobic pathway 1. ATP-PC breakdown 2. Anaerobic glycolysis Aerobic pathway Requires O2 2. Aerobic glycolysis 3. Oxidative phosphorylation

Bioenergetics ATP-PC ATP-PCr (30 sec) Activities (examples) Sprints (< 30 sec) High jumping Weight lifting

Bioenergetics Anaerobic Glycolysis – Examples: Lactic acid system (20 or 30 sec to 120 sec) Intermediate in duration Examples: Middle distance running Swimming Basketball

Bioenergetics High intensity exercise – 2 minutes Aerobic sources ATP-PCr (30 sec) Lactic acid systems (30-120 sec) Provide 50% of the energy Aerobic sources

Aerobic Energy Longer duration Requires a steady energy supply Examples: Marathon running Distance swimming or cycling Jogging, hiking, or backpacking Little or no lactic acid buildup

Energy Continuum

Relative Aerobic & Anaerobic Contributions Crossover concept

Sources of Energy for ATP Synthesis Sources of energy for ATP synthesis include: Liver and muscle glycogen Triacylglycerols within adipose tissue and active muscle Amino acids within skeletal muscle donate carbon skeletons

Carbohydrate Use During Exercise Intense anaerobic exercise Muscle glycogen Blood glucose Sustained high levels - aerobic exercise. Glycogen stores Blood glucose – Glycogen breakdown - released from liver

Macronutrient Contributions

Intense Exercise Change in hormone release Stimulation Epinephrine Norepinephrine Glucagon Decreased insulin release Stimulation Glycogen phosphorylase - glycogenolysis p157

Intense Exercise Early stages Later stages Stored muscle glycogen Glycogenolysis of liver stores Blood glucose Blood glucose can supply 30%

300 g gly in leg muscles, 100 g in liver 300 g gly in leg muscles, 100 g in liver. Fat stored in adipose cells in muscle fibers and close to mito.

Moderate and Prolonged Exercise As exercise continues Glucose from the liver becomes major contributor (as muscle glycogen falls; about 2-3 hrs) Fat use increases

CHO & Exercise Sharp uptake of blood glucose during initial stage of exercise, continue to increase as exercise progresses, faster supply of energy

Glycogen Depletion Blood glucose levels fall. Level of fatty acids in the blood increases. Proteins provide an increased contribution to energy. Exercise capacity progressively decreases.

Moderate and Prolonged Exercise Progressive decrease blood glucose, increase fat metabolism fat metabolism increases with similar exercise when glycogen loaded protein use for energy remains higher with glycogen depletion After 2 h exercise capacity decreases to 50% of max, glycogen depleted state.

Fatigue “hitting the wall” Results Fall in muscle/liver glycogen CNS used blood glucose as energy (central fatigue) Increased fat metabolism Fat provides energy at a slower rate Slower rate figure 5.5 FA mobilization and transport, and breakdown takes longer

Trained Muscle Trained muscle So, trained individuals Increased ability to produce ATP (inc. mitochondrial volume) Increased blood supply (capillary density) Increased glycogen storage So, trained individuals Maintain a higher work rate Maintain that workrate for longer periods of time

Dietary Influence Condition 1 (Low carb) Condition 2 (normal) Normal caloric intake – 3 days CHO 5% Lipid 95% Condition 2 (normal) Recommended % CHO, Fat, Pro Condition 3 (high carb) CHO 82%

Dietary Influence

Influence of Diet A carbohydrate-deficient diet Rapid depletion of muscle and liver glycogen. Low carbohydrate levels Intensity decreases to level determined by how well the body mobilizes and oxidizes fat. So, this diet reduces performance

Fat as an Energy Substrate Fat supplies about 50% of the energy Light and moderate exercise. Stored fat Important during the latter stages of prolonged exercise (greater than 2 hours)

Caloric Equivalents CHO and fat contribute equally during moderate exercise, fat gradually increases as glycogen is depleted

Sources of Fat During Exercise Fatty acids released from adipocytes Delivered to muscles as FFA bound to plasma albumin Circulating plasma triacylglycerol Very low-density lipoproteins Chylomicrons Triacylglycerol Within active muscle itself

Lipolysis Hormones activate lipase. These hormones are secreted more during exercise. Epinephrine, Nor-epinephrine, GH Mobilization of FFAs from adipose tissue Trained muscle has an increased ability to utilize fat due to the higher volume of mitochondria

Exercise Training Regular aerobic exercise: Increases the ability to oxidize long-chain fatty acids Improves the uptake of FFAs Increases muscle capillary density Increases size and number of muscle mitochondria SO, at the same workload, after training Fat metabolism is up and CHO metabolism is down Same relative workload (% max), CHO and Fat utilization is the same Goals of endurance training

Exercise Training After training, energy from fat oxidation increases following aerobic training

Protein Use During Exercise Carbohydrate-depleted state Causes significant protein catabolism. Protein utilization rises Endurance Resistance-type exercise.

Protein Use During Exercise Greater use as energy fuel than previously thought Nutritional status Intensity of exercise training or competition. Duration of exercise Certain AAs, the branched-chain amino acids Leucine, Iso-leucine and valine Oxidized directly in skeletal muscle

Exercise and Protein Metabolism Lemon 10.3 maughan increase rates of muscle protein degradation, significant muscle damage with exercise, especially if there is a significant eccentric component.

Protein Use During Exercise Branched-chain amino acids Oxidized in skeletal muscle not the liver. Leucine, isoleucine, valine Make up 1/3 skeletal muscle Important in protein synthesis Seem to be oxidized during longer term endurance exercise side-chains that are non-linear. These are leucine, isoleucine and valine. The combination of these three essential amino acids make up approximately 1/3 of skeletal muscle in the human body, and play an important role in protein synthesis. BCAA’s are currently used clinically to aid in the recovery of burn victims, as well as for supplementation for strength athletes.

Exercise and Protein Metabolism Lemon 10.6 maughan maybe because most of energy is from anaerobic metabolism and muscle glycogen

Exercise and Protein Metabolism Endurance exercise – increased protein need as neg balance occurs

Exercise and Protein Metabolism The data indicate that both endurance and strength athletes need more protein than sedentary