block 8 - metabolic control and regulation Flashcards
Energy Content (Bomb Calorimeter vs Metabolism)
Carb: 4.2 kcal/g → 4 kcal/g (in body)
Fat: 9.4 kcal/g → 9 kcal/g
Protein: 5.65 kcal/g → 4 kcal/g (due to nitrogen loss)
- first values are from calorimeter, second is when they metabolise in the body
Reason for Difference: Not all energy can be utilised — some is lost in digestion/absorption.
-Bomb calorimeter meausres the heat energy produced.
Basal Metabolic Rate (BMR)
how much energy do humans require
Equations:
Men: 66 + (13.7 × weight) + (5 × height) − (6.8 × age)
Women: 655 + (9.6 × weight) + (1.7 × height) − (4.7 × age)
Units: Weight (kg), Height (cm), Age (years)
Accuracy:
Spirometry/expired gas analysis is more precise
Precision more critical for athletes
converting expired gas to energy expenditure
-More accurate than estimations like BMR equations.
-Especially useful in athletic populations to fine-tune energy needs.
Key Variables Needed:
VO₂ (oxygen consumption)
VCO₂ (carbon dioxide production)
-Resting Energy Expenditure (REE) can be calculated using VO₂ and VCO₂:
-These values are collected from expired gas samples during rest.
Weir Equation is commonly used:
REE (kcal/day) = [3.941 × VO₂ (L/min) * 1.106 × VCO₂ (L/min)] × 1.44
energy balance
Importance:
Relevant to public health (obesity, Type 2 diabetes)
Vital for athletes’ nutrition planning to understand their energy requirements
Need for Balance: Accurate measurements of Energy Intake (EI) and Energy Expenditure (EE)
- calories in vs calories burned (BMR + activity)
ATP & Energy Systems
ATP = Adenine + Ribose + 3 Phosphates
- produces 7.3kcal of free energy when broken down
Used in:
Muscle contraction, digestion, nerve conduction, glandular excretion, circulation etc.
Muscle Contraction:
Myosin head attaches to actin, creating a crossbridge -> power stroke releases ADP when head of myosin pivots → ATP binds to myosin head → actin-myosin bond breaks, cross bridge detaches -> ATP broken up and myosin head is now energized again
-ATP is crucial for contraction cycle
ATP Limits:
Stored: body stores 80–100g
Usage: 1.6 kg/hr at rest; up to 0.5 kg/min during exercise
ATP must be resynthesised continuously from ADP to meet body requirements.
Carbohydrate Metabolism
where does energy come from
Forms: Mono-, Di-, and Polysaccharides
Storage:
Glucose → Glycogen (glycogenesis)
Glycogen → Glucose (glycogenolysis)
~400g glycogen stored in muscle at rest, 503g in full body
- other 103g comes from- plasma glucose(3g) and liver glycogen(100g)
-storage form~ liver + muscle
Oxidation Formula: Glucose + 6 O₂ → CO₂ + H₂O + ATP (36)
- high oxygen cost
- carbohydrates broken down into glucose units that are then taken into cells and broken down to release their energy.
Exercise Intensity:
-Higher intensity = faster glycogen usage
-We want glycogen store to be as high as they can be with the correct nutrients to fuel exercise
glycogenesis and glycogenolysis pathways
Glycogenesis (Glucose → Glycogen)
1. Glucose → Glucose-6-phosphate (via hexokinase or glucokinase)
2. Glucose-6-phosphate → Glucose-1-phosphate
3. Glucose-1-phosphate + UTP → UDP-glucose
4. UDP-glucose added to glycogen chain by glycogen synthase
Glycogenolysis (Glycogen → Glucose)
1. Glycogen → Glucose-1-phosphate (via glycogen phosphorylase)
2. Glucose-1-phosphate → Glucose-6-phosphate
3. In liver: Glucose-6-phosphate → Glucose (via glucose-6-phosphatase) → released into blood
Glycolysis- CHO oxidation
- phosphorylation of glucose to glucose-6-phosphate by ATP
2+3. rearrangement followed by a second ATP phosphorylation
4+5. the 6 carbon molcule is spilt into two 3-carbon molecules of G3P (first 4 steps producing ATP) - oxidation folllowed by phosphorylation produces two NADH molecules (NAD to NADH + H+ (X2)
- removal of high-energy phosphate by two ADP, produces two ATP
8+9. removal of water gives two PEP molecules - removal of phosphate by 2ADP gives 2 ATP and 2 pyruvate
phosphofructokinase = rate-limiting enzyme
Pyruvate produced → can become Lactate(anaerobic) or go to Krebs
Net Yield: 2 ATP
NADH: Electron carrier to ETC
Lactate & Exercise Intensity
Lactate Formation:
Pyruvate + NADH → Lactate + NAD⁺ (no oxygen present)
NAD⁺ recycled to keep glycolysis going
- Lactate builds up in muscle in high intensity exercise (burning sensation)
Exercise Levels:
Light: Low ATP demand, lactate removal = production
Moderate: Lactate diffuses into blood from muscle fibers via MCT transporters, removed easily as lactate levels decrease due to good blood flow
Heavy: lactate concentration is high and constant. Uncomfortable for athlete but tolerable
High intensity: Lactate accumulates rapidly in the blood. Exercise at this level can only be tolerated for a few minutes due to muscle function reducing.
Fate of Lactate:
Recycled via Cori Cycle in liver → converted back to glucose to be utilised again
(we don’t want it in the muscle for too long)
- 80% of lactate formred can be used by the muscle as an energy source
Krebs Cycle (Citric Acid Cycle)
Starts with: Acetyl-CoA in mitochondria
Outputs per 2 Acetyl-CoA: 4 CO₂, 16 H⁺
-NADH and FADH₂ generated → go to ETC
Electron Transport Chain (ETC)
Location: Inner mitochondrial membrane
-Electrons are not transferred from food molecules directly to O2
-These electrons require special carriers. These carriers are NAD+ and FAD.
- They accept a hydrogen ion and 2 electrons….forms NADH and FADH2
Carriers: NADH, FADH₂ transfer electrons to 02
Final Electron Acceptor: Oxygen → forms water
Process: Oxidative Phosphorylation
90% of ATP made here
Net ATP gain from full glucose oxidation of one carbohydrate molecule: ~36 ATP
Oxidation of 1 glucose molecule (aerobic respiration)
overview of the steps
- Glycolysis (in cytoplasm)
Glucose → 2 Pyruvate
Net gain: 2 ATP, 2 NADH - Link Reaction (pyruvate → mitochondria)
Pyruvate → Acetyl-CoA
Produces: 2 NADH, 2 CO₂ - Krebs Cycle (in mitochondria)
Acetyl-CoA → CO₂
Produces: 2 ATP, 6 NADH, 2 FADH₂, 4 CO₂ - Electron Transport Chain (ETC)
NADH & FADH₂ donate electrons → ATP made via oxidative phosphorylation
Final electron acceptor: O₂ → forms H₂O
Produces: ~32 ATP
💡 Total ATP yield: ~36-38 ATP
ATP energy summary
where it is generated and lost in the different stages
glycolysis:
- 4 produced in cytosol
- 2 used up to initiate glycolysis
- net gain of 2
electron transport chain and citric acid cycle:
- 4 from NADH in glycolysis
- 24 from NADH in citric acid cycle
- 4 from FADH2 in citric acid cycle
- 2 by GTP during enzyme reactions
36 net gain to cell from complete catabolism of 1 glucose molecule
Immediate Energy Stores
Phosphocreatine (PCr)/ creatine phosphate/ phosphagen system
Phosphocreatine (PCr): A high-energy phosphate compound stored in muscles.
Used immediately to regenerate ATP during short bursts of high-intensity exercise.
Reaction: PCr + ADP + H⁺ → ATP + Creatine.
- ATP must be re-synthesised if muscle contraction is to be sustained
- The PCr rephosphorylates the ADP back to ATP.
Enzyme involved: Creatine Kinase.
Duration of use: About 10-15 seconds (e.g., during sprints like the 100m).
ATP: Stored in small amounts in muscles (~80-100g), depleted rapidly during exercise.
Must be resynthesized quickly for continued high-intensity output.
Muscle Fibre Types and Energy
Type 1 (Slow-twitch): Primarily uses fat store to utilise energy, aerobic metabolism, best for long-duration activities like marathons, low glycolysis
Type IIa ( moderately fast-twitch): high glycolysis, Pcr and glycogen is the energy store utilised, long anaerobic metabolism
Type IIx (Fast-twitch): Primarily short anaerobic metabolism, uses PCr and glycogen energy stores for quick, explosive movements, high glycolysis
slow twich = energy over long time
fast twitch = energy over short time
Can muscle fibre types change?
Studies show fast-to-slow fibre shifts may occur with proper training, but slow-to-fast fibre shifts are not typically supported by evidence.
- reguardless of conflict, several findings imply that with careful manipulation of exercise variables, one may potentially experience fast to slow twitch fiber shift, and vice versa
Genetics also play a role in muscle fibre distribution.
ATP Use in High-Intensity Exercise
ATP levels decrease during intense exercise, starting with Type IIx fibres and then Type IIa and Type I fibres.
ATP resynthesis is critical for maintaining power output. After depletion of ATP stores, phosphocreatine (PCr) plays a key role in quick regeneration.
Phosphocreatine and Energy Provision
PCr as Energy: Used for rapid ATP resynthesis in short-duration, high-intensity activities.
Stored 4 times more than ATP in muscles.
Duration of PCr use: About 10-15 seconds for sprints (~50m in a 100m sprint).
PCr Depletion: After high-intensity exercise (e.g., sprints), PCr levels deplete.
Recovery: PCr stores are replenished during rest. (needed to be able to sprint to full power again)
- oxidative phosphorylation occuring in rest phases
Replenishment time: Full recovery typically takes 3-4 minutes, with partial recovery (50%) in about 30 seconds.
creatine supplementation
Creatine Monohydrate increases muscle PCr content.
* Cr concentrations in the muscle averages 110-120 mmol/kg/dry weight of muscle. Supplementation can increase this to ~130-160 mmol/kg/dry weight of muscle.
typical strategies:
1. Loading phase: 20g/day for 5 days (4 x 5g doses), then 3-5g/day for maintenance.
2. Gradual supplementation: 2-3g/day for 15 days to reach similar muscle Cr content.
effectiveness of creatine supplementation- responders and non-responders
Some athletes respond better to creatine supplementation (especially those with lower initial PCr stores).
- Starting with high levels before supplementation, lower chances of responding
Vegans tend to benefit more due to lower baseline creatine levels.
benefits of supplementing creatine
Improves repeated sprint performance (e.g., team sports, high-intensity interval training).
Increases PCr resynthesis, enabling faster recovery between intense bouts.
Muscle Mass: Increases fat-free mass and lean body mass.
Training Performance: Enhances performance in exercises like squat jumps, where sustained power output is needed.
Resistance Training and Creatine
Creatine enhances performance during resistance training by improving recovery between sets.
This results in higher power output across sets, facilitating muscle adaptations.
creatine summary of performance
- Increases PCr resynthesis during recovery between bouts of high intensity exercise.
2) Enhances performance of repeated maximal sprints (6-30s duration) with 20s-5min recovery in-between.
3) Little evidence to support benefit for single sprint.
4) Poor evidence to support endurance based performance (My MSc research).
5) Acute supplementation: may benefit a single event involving repeated high intensity effort (e.g. Team sports etc.).
6) Chronic supplementation: can enhance performance in training.
anaerobic Metabolism and Energy Provision
switching systems
anaerobic metabolism becomes more prominent in longer events as phosphocreatine depletes.
switching to lactic acid system:
glucose/glycogen -> pyruvate -> lactate
- anaerobic glycolysis is maximal at around 5s into high intensity exercise
- 200-400m (-20s-50s) requires rapid energy transfer that exceeds Pcr supply
In events like middle-distance running (1500m), the athlete will rely on a mix of anaerobic and aerobic energy systems, with PCr used for explosive starts and finishes.
- stores are replenished as the race proceeds
