Quiz 1 Bioenergetics & Metabolic Pathways part 2

VO2 Max provides

quantitative measure of a person's capacity for aerobic ATP resynthesize. Energy substrates (types) at certain points (fat metabolism)

what percent does physical activity account for of human energy expenditure?

10-40%

What are the factors that effect energy expenditure?

Intensity, duration, Type, Muscles involved

Most important factor affecting exercise metabolism

Intensity

How long is the AVG. VO2 maxing test

10-12 minutes. Looking for aerobic capacity

What are the metabolic pathways?

ATP-PCr system and

Creatine,

Aerobic Metabolism

How long does the body's stored ATP alone last during max effort?

About 2-3 seconds - muscle cells only store a very small amount of ATP so it's used up almost immediately at the start of intense effort.

After stored ATP runs out, what extends max-effort energy for other 5-8 seconds?

Phosphocreatine (PCr), stored in muscle. It doesn't power contraction directly - it rapidly rebuilds ATP from ADP, giving ~10 seconds of max-effort energy total (e.g. a 100m sprint)

What enzyme breaks down PCr, and what does it do?

Creatine Kinase.

It breaks PCr into creatine + Pi, then donates the Pi to ADP to regenerate ATP.

What is the rate-limit step of the ATP-PCr system?

Creatine Availability. The Reaction itself is fast and efficient - the limiting factor is how much creatine/ PCr is on hand to keep regenerating ATP.

The ATP-PCr system only provides ~10 seconds of ATP - so how does it support activities lasting up to 30 seconds?

other systems (glycolysis) begin contributing as PCr depletes, so energy systems overlap rather than switching on/off instantly - ATP PCr just dominates the first ~10seconds of an up-to-30 second effort

Where in the cell does the ATP-PCr system occur, and does it need oxygen?

In the cytosol, it is anaerobic and, unlike glycolysis, doesn't meaningfully change muscle pH since it's so short lived.

List 4-5 documented outcomes of Creatine supplementation

Increased work capacity, improved anaerobic performance, increased energy capacities, increased lean muscle mass, and improved recovery

In the creatine-and-menstrual-cycle study (Gorden et al.), what was the main finding about creatine monohydrate loading?

CM improved anaerobic (repeated sprint) performance in women regardless of menstrual cycle phase.

Why does most creatine research raise a research-gap question worth asking?

most creatine research has been done in young, college-aged, athletic men - raising the question of whether the same performance/ health benefits translate to women

For Optimal PCr regeneration between high-intensity bouts, what's the better recovery strategy: complete stop or active recovery?

active recovery - this helps shift the body into a different energy system and regenerate more efficiently. Classic rationale behinds interval training.

What are two categories of carbohydrate sources in the body?

Exogenous (sugars, starches, fiber from fruit, grains, veg, milk, and meat). Endogenous (blood glucose or glycogen already in the body)

Roughly how much carbohydrate energy (as glycogen) is stored in the average body, and where?

about ~2,000kcal, stored in liver and muscle

How many calories of carbs stored in muscle?

~ 400 grams (1600 kcals)

How many calories of carbs stored in the liver?

About 100 grams (400 kcals)

What are typical fasting vs. post-meal blood glucose concentrations?

Fasting ~72-99 mg/dL. Up to 2 hours post meal: ~140 mg, returning to baseline by 2-3 hours post-meal.

How much oral blood glucose is circulating in the ~5L of blood in an average adult? (In grams)

Only about 5g of glucose is circulating in blood at a given time - a small regulated amount could be used for emergencies.

Stored glucose is called

glycogen

During exercise, what does skeletal muscle glycogen fuel vs. what does liver glycogen fuel?

Skeletal muscle glycogen: fuels the working muscles itself (affected in both anaerobic and aerobic exercise).

Liver glycogen: maintains blood glucose and fuels the brain/ RBC's (primarily affected during aerobic exercise)

What is the strength and the limitation of glycolysis as an energy pathway?

Strength: one of the FASTEST ways to generate ATP.

Limitation: it can only generate a finite amount of ATP - not suited for a long-ration effort.

What are the two possible end products of glycolysis, and which pathway does each feed?

Pyruvate (aerobic glycolysis) —> aceyl CoA —> Krebs cycle —> electron transport chain—> ATP.

Lactate (anaerobic glycolysis) —> produces H+ that Can make the muscle cell increasingly acidic.

What is pyruvate

- The end product of glycolysis

-The first step in cellular respiration

- Stands in the junction between anaerobic and aerobic pathways

What is lactate threshold

The exercise intensity at which lactate accumulates faster than it is removed.

If H+ builds up too much, the muscle can no longer contract effectively and exercise must stop.

How does training improve lactate/ H+ buffering capacity?

buffering capacity inc. naturally with exercise adaptation and can also be aided nutritionally (primarily via supplementation), letting the body clear/recycle lactate and H+ more efficiently before fatigue sets in.

How much net ATP does glycolysis yield starting from glucose vs.starting with glycogen and why the difference

Glucose—> 2 net ATP

Glycogen—> 3 net ATP. Glycogen skips the initial ATP-costing phosphorylation step that free glucose requires, effectively storing an extra usable carbon/energy unit

Name three glycolytic enzymes that adapt/improve with training and their roles?

Glycogen phosphorylase (breaks down muscle glycogen to glucose).

Phosphofructokinase PFK (the rate-limiting sep of glycolysis).

lactate dehydrogenase LDK (makes pyruvate into lactate)

Why does weightlifting-driven muscle hypertrophy inc. glycolytic enzymes activity?

More muscle mass means more substrate (glucose) availability plus greater overall enzyme volume and capacity within the larger muscle tissue.

Besides more glycogen and more enzymes, what other training adaptations improves glycolytic performance, and why does it matter?

improved buffering capacity - more buffering agents to manage the rise in H+/ pH change. Maintaining pH preserves force, power, and energy production, and support better recovery with less muscle damage

How man kcal per gram does fat provide, and how much fat energy is stored in the average adult male?

9kcal/g.

Roughly 80,000-100,000 kcal

Total stored fat energy, with about 2,500 2,800 kcal specifically stored as intramuscular triglyceride.

Name several primary physiological roles of fat beyond energy.

Cell membrane strength, satiety, nutrient absorption, inflammation regulation (pro- or anti-), body temp, immune support, cushion/ protect organs, and nerve transmission.

Why is adequate fat intake relevant to hormonal functional and recovery in athletes?

Adequate fat is needed for proper androgen hormone function (Test and estrogen).

Also, It effects cell membranes, inflammation from training damage, and nutrient delivery -all central to recovery.

How much ATP is produced from full aerobic breakdown of glucose vs. glycogen via the Krebs cycle/ ETC?

Glucose—> 32 ATP

Glycogen —> 33 ATP

one extra due to step that's skipped (PFK)

Roughly how much ATP can a 16-carbon fatty acid chain yield through aerobic metabolism?

~106 ATP - fat yields far more ATP per molecule than carbs, though it's released much slower

What stimulates the release of free fatty acids (FFA) from muscle triglycerides during exercise?

Epinephrine stimulates FFA release, inc. serum free fatty acids delivery into muscle for use as fuel.

At low intensity (~25% VO2 max) on a typical moderate-to-high carb diet, roughly what% of energy comes from fat, and from where?

About 80% of energy from fat, with most of that adipose tissue derived from FFA

At moderate intense exercise up to 65% VO2 max, where does most fat-based energy shift to.

Fat-based energy now comes predominantly from muscle triglycerides rather than adipose tissue

What is the "crossover concept"n in exercise metabolism?

The crossover concept is the shift from fat to carbohydrate as the main fuel source as exercise intensity increases. Fat dominates at lower intensities, while carbohydrates dominate at higher intensities

What three factors affect where the crossover point falls?

1.) Intensity, 2.) endurance training status, 3.) body comp

At high intensity (>85% VO2 max), what happens to FFA oxidation vs. carb oxidation

As intensity rises, FFA oxidation decreases while Carb oxidation increases. Muscle glycogen becomes dominant fuel source

What are the key benefits of aerobic metabolism compared to anaerobic pathways?

No acidic buildup in working cell; more total ATP yield per substrate (though slower per second); can use carb, fat, and protein as fuel; and waste products (water, CO2) are easily cleared via urine/ exhalation.

List the five training adaptations that improve substrate use during exercise

1.) inc. mitochondrial enzymes, 2.) inc. capillary number and density 3.) improved blood oxygen transport, 4.) higher cardiac output, 5.) fasted lactate recycling

How does endurance training shift lactate threshold, and why?

Shifts to a higher percentage VO2max. Allowing higher intensity before switching to anaerobic metabolism - due to improved metabolism, more KREBS cycle/ETC enzymes, and greater capillary density

What structural adaptations define "aerobic metabolism a its best" after training?

Increased mitochondrial density & volume, and increased blood supply — via higher cardiac output and more capillaries around muscle fibers (plus increased myoglobin within fibers) to improve oxygen delivery.

How long should a VO2max test typically run to get an accurate result, and what is it capturing?

About 10-12 minutes to accurately capture aerobic capacity and expenditure

How is a VO2max test typically structured, and what determines the endpoint?

Done in intervals. Athlete continues until they tap out.

What is glycogen phosphorylase?

Glycogenolysis = breaks down glycogen to glucose

What is phosphofructokinase?

rate limiting enzyme in glycolysis

What is lactate dehydrogenase?

A serum enzyme that catalyzes the conversion of lactate to pyruvate