KNHES Bioenergetcis & Metabolic pathways part 1

Bioenergetics

The chemical process of converting food into energy; also referred to as metabolism.

Ultimate source of all energy on Earth

The sun.

Primary energy molecule used in human physiology

Adenosine triphosphate (ATP).

Two primary types of energy measurements in the human body

1. Energy for life (basal/resting metabolism) 2. Energy for activity.

Basal metabolism

A direct measurement of how much energy the body needs to sustain life at rest.

Resting metabolism

An indirect measurement (estimation) of how much energy the body needs to sustain life at rest.

Three primary energy systems fueling physical activity

1. Phosphocreatine (PCr, immediate/explosive) 2. Anaerobic metabolism (sprints/short-powerful) 3. Aerobic metabolism (endurance/extended high-intensity).

Three components of Total Energy Expenditure (TEE)

Thermal Effect of Food (5-10%), Basal Metabolic Rate (60-70%), and Physical Activity (10-40%).

Physiological factors affecting the physical activity component of energy expenditure

Intensity, duration, type of movement, and muscle size/activation.

One Calorie (kcal)

Equal to 1,000 gram calories; raises the temperature of $1\,kg$ ($1000\,g$) of water by $1\,^\circ\text{C}$.

Difference between direct and indirect calorimetry

Direct calorimetry measures heat produced (e.g., room calorimeter). Indirect calorimetry measures gas exchange ($\text{O}_2$ and $\text{CO}_2$) as an estimate of energy production.

Two methods for assessing indirect calorimetry in humans

1. Laboratory conditions (measuring $\text{O}_2$ uptake and $\text{CO}_2$ production) 2. Real-life conditions (doubly labeled water technique).

Doubly labeled water technique

Ingestion of stable isotopes of hydrogen and oxygen, followed by blood or urine analysis to measure $\text{CO}_2$ fluctuation.

Average energy expenditure per liter of oxygen consumed

$\sim 5$ calories per liter of $\text{O}_2$.

Effect of age on Resting Energy Expenditure (REE)

REE changes from infancy through adulthood, generally declining with advancing age.

Effect of biological sex on Resting Energy Expenditure (REE)

Females typically have a Resting Energy Expenditure about 10-15% lower than males.

Effect of body composition on Resting Energy Expenditure (REE)

Higher fat-free mass (muscle) relative to fat mass raises REE. Weight loss lowers REE, while maintaining weight while increasing muscle mass may raise REE.

Effect of temperature extremes on Resting Energy Expenditure (REE)

Cold exposure can increase REE via thermogenesis; heat exposure increases REE via sweating and cardiovascular demand.

Effect of altitude, smoking, and caffeine on Resting Energy Expenditure (REE)

Altitude increases REE via increased ventilation; nicotine is a stimulant that increases REE; caffeine can increase REE by up to $\sim 10\%$.

Typical fuel breakdown for aerobic metabolism at rest

$\sim 60\%$ from fat and $\sim 40\%$ from carbohydrates.

Energy yield and metabolic pathway of carbohydrates

$4\,kcal/g$, via both anaerobic and aerobic metabolism.

Energy yield and metabolic pathway of fats

$9\,kcal/g$, via aerobic metabolism only.

Energy yield of protein

$4\,kcal/g$.

Energy yield and metabolic pathway of alcohol

$7\,kcal/g$, via anaerobic metabolism.

Information provided by a $\text{VO}_2\text{max}$ test

Maximum $\text{O}_2$ utilized during endurance exercise, cardiovascular fitness, carbohydrate-to-fat usage ratio at various intensities, and caloric expenditure rates.

Limitations of a $\text{VO}_2\text{max}$ test

Does not measure protein metabolism, does not correlate directly with athletic performance, and does not dictate overall daily caloric needs.

Anabolism vs. Catabolism

Anabolism refers to constructive metabolic processes (building/growth). Catabolism refers to metabolic breakdown processes.

Smallest substrate breakdown products of macronutrients

Carbohydrates break down into glucose, fats into fatty acids, and proteins into amino acids.

Common precursor molecule for macronutrient substrates before the Krebs cycle

Acetyl CoA.

Pathway from Acetyl CoA to ATP generation

Acetyl CoA —> Krebs Cycle —> Electron Transport Chain —> ATP.

Three structural components of ATP

Adenine, ribose, and three phosphate groups.

Chemical reaction for ATP breakdown

$$\text{ATP} + \text{H}_2\text{O} \rightleftharpoons \text{ADP} + \text{P}_i + \text{H}^+ + \text{energy}$$

Thermodynamic nature of ATP breakdown vs. ATP formation

ATP breakdown to ADP is exergonic (releases energy). ATP formation from ADP is endergonic (requires energy).

Cause of increased acidity during ATP breakdown

The release of free hydrogen ions ($\text{H}^+$).

Dominant energy system during the first 30 seconds of high-intensity exercise

ATP-PCr (phosphagen) system.

Dominant energy system from 30 seconds to 3 minutes of exercise

Anaerobic glycolysis (carbohydrate-based).

Dominant energy system after 3 minutes of continuous exercise

Aerobic metabolism (mitochondrial respiration utilizing oxygen).

Five forms of stored energy in the body (smallest to largest reserve)

ATP \rightarrow Phosphocreatine (PCr) \rightarrow Carbohydrates (glycogen) \rightarrow Protein (amino acid pool) \rightarrow Fat (adipose tissue).

Fuel capacity comparison: stored ATP vs. adipose tissue triglycerides

Stored ATP fuels approximately 17.5 yards of running, whereas adipose tissue triglycerides can fuel approximately 800 miles.

Energy system and event parameters for anaerobic power

ATP-PCr (phosphagen) system; distance of 60 to 200 meters (duration of 6 to 20 seconds).

Energy system and event parameters for anaerobic capacity

Anaerobic glycolysis (lactic acid system); distance of 400 to 800 meters (duration of 43 to 103 seconds).

Energy system and event parameters for aerobic power

Aerobic glycolysis; distance of 5,000 to 10,000 meters (duration of 12 to 26 minutes).

Energy system and event parameters for aerobic capacity

Aerobic lipolysis; distance of 42.2 to 100 kilometers (duration of 125 to 360 minutes).