EXSS3071 Week 7 Lecture

Slide 1 – Ice-breaker Case Study

EXSS3071+CHO+fat+and+Sports+Performance+2025+S1.pdf](file-service://file-FZy8HV5AWcieTraTJHWTQW)

• Client profile: 35-y male; runs 2-3 × wk (45-60 min), lifts 1-2 × wk (30-60 min). Half-marathon (21 km) in 4 wk; goal < 120 min.

• Current gaps: no hydration or diet plan; unaware of CHO/fat needs.

• Key variables to monitor: habitual CHO intake (g kg⁻¹ d⁻¹), long-run glycogen depletion, daily energy periodisation, sweat rate & sodium loss, long-run fuelling trials, perceived exertion.

• Discussion points with dietitian: race-day CHO loading (48 h), in-run CHO (30–60 g h⁻¹), caffeine timing, gut-training, fluid schedule; post-run glycogen restoration; body-mass trends.

Slide 2 – Lecture Title & Contributors

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• Topic: Carbohydrate, Fat & Sports Performance.

• Lecturer: Kenneth Daniel (APD, AFHEA). Acknowledges O’Connor, Gifford, Parker, Johnson, Hay.

• Take-away: lecture merges biochemistry with applied sport-nutrition practice.

Slide 3 – “Where Are the Carbohydrates and Fats?”

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• Visual aligns Australian Dietary Guidelines with food groups.

• CHO-rich: grains, fruit, some dairy, starchy veg.

• Fat-rich: oils, nuts/seeds, higher-fat dairy, meats.

• Implication: athletes must combine both macronutrients strategically rather than demonise either.

Slide 4 – Lecture Outline & Context Quote

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• Sections: metabolism review; fat adaptation; “train low, compete high”; efficacy of low-CHO strategies; glycogen recovery; daily recommendations.

• Prof Louise Burke quote: nutrition trends are cyclical; await robust evidence before adopting fads.

Slide 5 – Energy Systems in Maximal Effort

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• Immediate: ATP-CP (≤10 s).

• Short-term: anaerobic glycolysis → lactate (≈10 s–2 min).

• Long-term: aerobic glycolysis + lipolysis (≥2 min).

• Relative contribution shifts with intensity/duration; CHO central to rapid ATP at ≥75 % VO₂max.

Slide 6 – Fuel Stores in an Average Male

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Slide 7 – Integrated Pathways Map

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• Shows glycolysis, β-oxidation, TCA, trans/de-amination.

• Carbohydrate (glucose → pyruvate → acetyl-CoA) intersects fat (FA → acetyl-CoA) at TCA; proteins feed via keto-acids.

• Liver gluconeogenesis sustains blood glucose as muscle uptake rises.

Slide 8 – Endogenous Storage Schema

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• Glycogen: skeletal muscle (locally used), liver (systemic).

• Fat: adipocytes, intramuscular TG droplets, visceral stores.

• Practical: athletes with low muscle glycogen cannot fully compensate via adipose fat during high-intensity work.

Slide 9 – Fuel Utilisation References Figure

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• Reinforces previous schematic; emphasises shifting contribution with exercise intensity/duration and training status.

Slide 10 – Muscle Glycogen Use Dynamics

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• Glycogenolysis accelerates rapidly at exercise onset; adrenaline activates phosphorylase.

• Rate rises exponentially with intensity; depletes faster when starting concentration is low.

• Muscle prefers its own glycogen; non-working muscle can export glucose, supporting systemic needs.

Slide 11 – Storage Sites Re-emphasised

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• Revisits slide 8 figure; underlines finite glycogen vs ample fat reserves.

Slide 12 – Lipolysis Overview

‡EXSS3071+CHO+fat+and+Sports+Performance+2025+S1.pdf](file-service://file-FZy8HV5AWcieTraTJHWTQW)

• TG → glycerol + 3 FA via hormone-sensitive lipase.

• Glycerol returns to liver for gluconeogenesis; FA transported to muscle for β-oxidation.

• Catecholamines and low insulin favour lipolysis; high insulin suppresses.

Slide 13 – Intramuscular TG (IMTG) Characteristics

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• IMTG droplets nestle near mitochondria; ~300-350 g in active musculature.

• Higher in type I fibres and endurance-trained athletes; influenced by habitual diet.

• Acts as rapid fat source during prolonged moderate exercise.

Slide 14 – FA Transport from Blood to Mitochondria

‡EXSS3071+CHO+fat+and+Sports+Performance+2025+S1.pdf](file-service://file-FZy8HV5AWcieTraTJHWTQW)

• Steps: dissociation from albumin → sarcolemma transporters (FAT/CD36) → cytosolic FABPs → outer membrane → carnitine-dependent CPT-I, translocase, CPT-II → β-oxidation matrix.

• Each step can limit oxidation rate, especially under high insulin.

Slide 15 – Carnitine Shuttle Detail

‡EXSS3071+CHO+fat+and+Sports+Performance+2025+S1.pdf](file-service://file-FZy8HV5AWcieTraTJHWTQW)

• Long-chain FA require CPT complex; malonyl-CoA inhibits CPT-I during fed state.

• Carnitine availability can be limiting; supplementation evidence equivocal.

Slide 16 – Pathways Map (Revisited)

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• Repetition emphasises integration and control points (PDH, CPT, glycogen phosphorylase).

Slide 17 – Factors Inhibiting Fat Oxidation During Endurance Exercise

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• ↑ Insulin or CHO intake decreases LCFA entry to mitochondria.

• High glycolytic flux and rising muscle acidity reduce CPT activity.

• Elevated glycogenolysis shifts substrate preference toward CHO.

Slide 18 – Fat vs Carbohydrate “Score Card”

‡EXSS3071+CHO+fat+and+Sports+Performance+2025+S1.pdf](file-service://file-FZy8HV5AWcieTraTJHWTQW)

Fat advantages: colossal energy store (200–400 MJ); 37 kJ g⁻¹; 147 ATP mol⁻¹; lighter per kJ.

CHO advantages: yields 10 % more ATP per L O₂; less O₂ per ATP; superior when O₂ delivery limited; supports higher power output.

Slide 19 – Historical Milestones in Fuel Research

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• 1842 Von Leibig: wrongly championed protein as exercise fuel.

• 1920 Krogh & Lindhard: low- vs high-CHO diets and performance.

• 1960s Bergström & Hultman: muscle biopsy & glycogen loading.

• 1996–2008 series: fat-adaptation and train-low paradigms.

• 2017-21: ketogenic diet scrutiny (Burke et al.).

Slide 20 – Glycogen Resynthesis After Exercise

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• Quadriceps glycogen rises fastest (≈8 mmol kg⁻¹ ww h⁻¹) in first 2 h post-exercise when CHO provided.

• Previously active leg replenishes quicker due to higher GLUT-4 and insulin sensitivity.

Slide 21 – Scandinavian Innovation (Biopsy Method)

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• Bergström needle enabled repeated intramuscular glycogen sampling, underpinning CHO loading protocols.

Slide 22 – Diet Effect on Muscle Glycogen

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• Graph: exhaustive exercise + low-CHO diet → depletion; subsequent high-CHO diet → super-compensation (>200 % baseline).

• Established classic glycogen-loading model.

Slide 23 – CHO % and Swim Training

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• 80 % vs 43 % CHO diets (935 g vs 502 g d⁻¹) showed no swim-time differences over 3 km; suggests ceiling once absolute grams sufficient; g kg⁻¹ better metric than %.

Slide 24 – Fat Adaptation Phase Concept

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• Athletes can “train okay” on low-CHO due to enzymatic up-regulation of fat oxidation, potentially sparing glycogen for race pace surges.

Slide 25 – Substrate Use After 5 d High-Fat + 1 d CHO Reload

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• During 120 min cycling at 70 % VO₂max: ↑ IMTG and plasma FA contribution; ↓ muscle glycogen oxidation.

• Indicates metabolic re-tooling toward lipid.

Slide 26 – Performance Test After Fat-Adapt

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• 7 kJ kg⁻¹ time-trial showed no group-wide benefit (P = 0.21); two responders skewed mean.

• Subsequent study with sports drink still neutral; evidence weak for performance gain.

Slide 27 – Fat-Adapt Diminishes PDH Activation

‡EXSS3071+CHO+fat+and+Sports+Performance+2025+S1.pdf](file-service://file-FZy8HV5AWcieTraTJHWTQW)

• Reduced active PDH at rest, during 70 % VO₂peak, and during 1-min sprint; implies impaired rapid CHO oxidation capacity needed for surges.

Slide 28 – Pathways Map (Third Viewing)

‡EXSS3071+CHO+fat+and+Sports+Performance+2025+S1.pdf](file-service://file-FZy8HV5AWcieTraTJHWTQW)

• Reinforces concept: PDH acts as gatekeeper; down-regulation in fat-adapt reduces high-intensity power.

Slide 29 – Classic “Train Low, Compete High” One-Leg Study

‡EXSS3071+CHO+fat+and+Sports+Performance+2025+S1.pdf](file-service://file-FZy8HV5AWcieTraTJHWTQW)

• Protocol: one leg trained daily (low glycogen) vs other leg every other day (high glycogen).

• Measurements: biopsies, Pmax, time to exhaustion (Texh).

• Aim: evaluate adaptation to chronic low CHO availability.

Slide 30 – Results: Time to Exhaustion

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• Low-glycogen leg: Texh ↑ from 5.6 → 19.7 min; High leg: 5.0 → 11.9 min.

• Suggests enhanced endurance capacity when some sessions completed with low glycogen.

Slide 31 – Mechanistic Summary of Train-Low

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• ↑ glycogen storage efficiency & citrate synthase activity; greater catecholamine stress; but potential compromise in HIIT capacity; requires careful periodisation.

Slide 32 – Pathways Map (Fourth)

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• Highlights signalling: AMPK/PGC-1α triggered by glycogen depletion promotes mitochondrial biogenesis.

Slide 33 – Yeo et al. Study in Well-Trained Cyclists

‡EXSS3071+CHO+fat+and+Sports+Performance+2025+S1.pdf](file-service://file-FZy8HV5AWcieTraTJHWTQW)

• Low group began HIIT with low glycogen, couldn’t sustain target power despite monetary incentives.

• Adaptations: ↑ glycogen storage & fat oxidation, ↑ mitochondrial proteins; performance gains matched High group (~10 % TT improvement).

Slide 34 – Practical Insight from Yeo et al.

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• Quality of high-intensity work can be jeopardised on low CHO; mixing “low” sessions with “high” fuelled quality sessions recommended.

Slide 35 – Substrate Use vs Exercise Intensity Curve

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• At 25 % VO₂max: FA dominate; at 65 % peak fat oxidation; ≥85 % VO₂max: CHO (muscle glycogen + plasma glucose) predominant.

• Half-marathon pace (~80 % VO₂max) relies heavily on CHO despite trained fat oxidation.

Slide 36 – FATmax & MFO Concepts

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• Maximal fat oxidation (MFO) typically 0.4–0.7 g min⁻¹ at 55–65 % VO₂max; highly individual; influenced by training status, diet, sex.

Slide 37 – Draft Horse vs Race Horse Analogy

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• Phenotype and event demand dictate macronutrient emphasis: power athletes ≈ “draft” (more reliance on phosphagens/CHO); endurance elites ≈ “race horse” (higher oxidative capacity).

Slide 38 – High-Intensity Exercise Limits Fat Use

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• 85 % VO₂max: FA delivery and oxidation insufficient; lactic acidosis inhibits CPT; glycogenolysis spikes; underscores need for ample muscle glycogen in final race phases.

Slide 39 – (Video Reference Slide)

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• Mentions Louise Burke media discussing low-CHO; takeaway: remain evidence-led, not trend-led.

Slide 40 – Burke 2021 Review on Ketogenic Diet

‡EXSS3071+CHO+fat+and+Sports+Performance+2025+S1.pdf](file-service://file-FZy8HV5AWcieTraTJHWTQW)

• Summarises current position: keto boosts fat oxidation but compromises CHO-dependent high-intensity; limited benefit for elite endurance where surges determine outcomes.

Slide 41 – Nutrition Strategies to Elevate Fat Oxidation

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Slide 42 – Periodisation Message

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• “Uni-dimensional” recommendations are flawed; athletes should periodise CHO availability around session goals (e.g., high for quality/competition, low for adaptation).

Slide 43 – Individual Fat Oxidation Curve

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• MFO testing allows personalised strategies; practitioners can tailor pre-race fuelling and training-low frequency based on curve.

Slide 44 – Practical Ways to Reduce CHO Availability

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• Options: overnight fasted training; two-a-day with no CHO between; low-CHO diet blocks; glycogen-depleting PM workout followed by fasted AM session.

Slide 45 – Alternative Explanations for Perceived Fat-Adapt Gains

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• Placebo/novelty, caloric restriction enhanced weight-to-power ratio, water loss, reduced GI distress, or simply better periodisation rather than substrate effect.

Slide 46 – Carbohydrate in Recovery

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• Components: timing, amount, type, and interfering factors; objective is rapid glycogen resynthesis when <8 h between sessions.

Slide 47 – When to Ingest CHO Post-Exercise

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• Early window (0–2 h) critical; immediate provision of 1–1.2 g kg⁻¹ raises synthesis rate; high-GI preferred if next exercise soon.

Slide 48 – Mechanisms Accelerating Glycogen Resynthesis

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• ↑ glycogen synthase activity, membrane permeability, GLUT-4 translocation, insulin sensitivity.

• Synthesis slows after 2 h but continues for 24 h if CHO supplied.

Slide 49 – Amount, Frequency & “Gorging vs Nibbling”

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• Over 24 h, total CHO intake dictates glycogen restoration; meal pattern less critical; protein co-ingestion can enhance insulin yet not replace CHO.

Slide 50 – Daily CHO Needs (IOC 2010)

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Slide 51 – Example: 60 kg Athlete at 10 g kg⁻¹

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• Requires 600 g CHO ≈ 2400 kcal from CHO; must distribute across meals/snacks + specialised sports foods.

Slide 52 – Example: 60 kg Athlete at 5.5 g kg⁻¹

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• 330 g CHO suited to moderate training or weight-control phases; emphasises periodisation.

Slide 53 – Forms of CHO Feeding

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• Liquid (sports drink, smoothies) vs solid (rice, fruit, bread) equally effective.

• Selection influenced by gastric comfort, appetite, logistics, concurrent fluid need.

Slide 54 – Practical Barriers to Post-Exercise Intake

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• “Low appetite” post-intense work, travel, limited food availability, GI upset, weight management goals.

• Solutions: portable high-CHO fluids, pre-packed snacks, team catering.

Slide 55 – Other Factors Modulating Glycogen Restoration

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• Delayed by muscle damage (eccentric/contact), very-low-GI diet, additional high-intensity exercise during recovery.

• Light active recovery does not impair replenishment.

Slide 56 – Glycaemic Index Fundamentals

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• GI ranks blood-glucose response relative to glucose.

• Influenced by starch type, fibre viscosity, fat/protein content, acidity, processing, cooking.

• Low-GI pre-exercise meal may attenuate glycaemia yet sustain oxidation; context dependent.

Slide 57 – Factors Changing GI Ranking (Detail)

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• Structural integrity (whole grains vs flour), amylose:amylopectin ratio, retrogradation, food matrix interactions all modulate digestibility.

Slide 58 – “Putting It All Together” Blank Notes

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• Slide prompts students to integrate training strategy, pre-competition fuelling, in-competition CHO, and recovery plan.

Slide 59 – End / Thank-You Slide

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• Signals conclusion; reiterates gratitude.

Slide 60 – Carbohydrate-Rich Food Examples

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• Lists practical CHO sources: cereals, rice, pasta, breads, fruit, juice, flavoured milk, sport drink/gels.

Slide 61 – Reference Slide 1 (Team-Sport Strategies)

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• Points to literature on sport-specific nutrition; underscores need for contextual application (e.g., intermittent sports).

Slide 62 – Reference Slide 2

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• Continuation of key texts; encourages further reading for applied practice.

Slide 63 – Reference Slide 3

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• Additional seminal sources; illustrates depth of evidence base.

Slide 64 – Topic Objectives (Part 1)

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• List learning outcomes: food sources, glycogen storage/measurement, hormonal control, exercise substrate factors, athlete vs sedentary CHO needs, GI definition/effects.

Slide 65 – Topic Objectives (Part 2)

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• Continues objectives: practical CHO attainment, recovery factors, train-low rationale, fuel storage capacities, RER interpretation, substrate shifts with intensity/duration.