Ch. 13: Physiology of training

Flashcards covering the physiological effects of endurance training on VO2max, performance, muscle structure, and the consequences of detraining.

Acute Responses

Immediate or short-term physiological changes that occur during or immediately after exercise.

Chronic Responses

Long-term training adaptations that occur as a result of accumulating acute responses over time.

Overload

The principle that a physiological system must be exercised at a level beyond which it is normally accustomed to induce adaptation.

Reversibility

The loss of training gains when the overload stimulus is removed, often leading to a plateau or decline in fitness.

Specificity

The concept that training effects are specific to the muscle fibers recruited, the energy systems involved, and the velocity or type of contraction used.

Average Expected Increase in $VO_2max$

An average improvement of $15-20\%$ in maximal oxygen uptake with a proper exercise prescription.

High Initial $VO_2max$ Training Intensity

Individuals with high initial fitness require a training intensity of >70\% \text{ VO}_2\text{max} to see improvements.

Low Initial $VO_2max$ Training Intensity

Individuals with low initial fitness require an intensity of $40-50\% \text{ VO}_2\text{max}$ to induce adaptations.

Genetic Heritability of $VO_2max$

Genetics explain approximately $47\%$ of the training-induced changes in maximal oxygen uptake.

FITT: Frequency (Improving $VO_2max$)

The guideline recommending exercise $3-5\text{ times/week}$ to improve cardiovascular fitness.

FITT: Intensity (Improving $VO_2max$)

The guideline recommending an intensity of $50-85\% \text{ VO}_2\text{max}$.

FITT: Time (Improving $VO_2max$)

The guideline recommending exercise durations of $20-60\text{ min}$.

FITT: Type (Improving $VO_2max$)

Dynamic activities using large muscle groups, such as running, cycling, or High-Intensity Interval Training (HIIT).

Fick Equation

$$\text{VO}<em>2\text{max} = [ \text{HR}</em>{\text{max}} \times \text{SV}<em>{\text{max}} ] \times [ (\text{a-v})\text{O}_2\text{ diff}</em>{\text{max}} ]$$

Maximal Stroke Volume ($SV_{max}$) Factors

The three components contributing to an increase in maximal stroke volume: increased preload, decreased afterload, and increased contractility.

Preload ($EDV$)

The end-diastolic volume, which increases due to higher plasma volume, blood volume, and venous return.

Afterload ($TPR$)

The total peripheral resistance, which decreases following training due to reduced arterial constriction in trained muscles.

Plasma Volume Adaptation

A rapid adaptation occurring within $6\text{ days}$ of training, characterized by an $11\%$ increase in volume.

Maximal Arteriovenous $O_2$ Difference

The peripheral component of the Fick Equation representing the muscles' ability to extract oxygen from the blood.

Angiogenesis

The formation of new blood vessels, leading to increased capillary density in trained skeletal muscles.

VEGF

Vascular Endothelial Growth Factor, which is secreted into muscle fibers to stimulate capillary growth.

Mitochondrial Biogenesis

The biochemical process of increasing the number and volume of mitochondria in skeletal muscle cells.

Fiber Type Shift (Aerobic)

A transition from fast-twitch myosin to slow-twitch myosin, specifically moving from $\text{Type IIa}$ to $\text{Type I}$ or $\text{Type IIx}$ to $\text{Type IIa}$.

Beta-oxidation ($\beta\text{-oxidation}$)

The primary metabolic pathway for using fats as a substrate, which increases reliance on fats following aerobic training.

Glucose Sparing

The reduction in reliance on plasma glucose and muscle glycogen due to increased capillary and mitochondrial density.

Lactate Dehydrogenase $H_4$ (Heart form)

An LDH isoform with a lower affinity for pyruvate, leading to decreased lactic acid formation in trained individuals.

Oxygen Deficit

The delay in oxygen uptake at the start of exercise; it is reduced in trained individuals due to faster transitions to steady state.

Mitochondrial Turnover

The process by which damaged mitochondria are removed and replaced, improving metabolic efficiency.

Primary Messengers

Signals activated by muscle contraction within seconds or minutes of exercise that trigger gene transcription.

Secondary Messengers

Intracellular signals that follow primary messengers to coordinate the synthesis of new muscle proteins.

mRNA Expression Timeline

Messenger RNA typically peaks $4-8\text{ hr}$ post-exercise and returns to baseline within $24\text{ hr}$.

Detraining $VO_2max$ Decline (12 days)

An initial $8\%$ decrease in maximal oxygen uptake primarily caused by a rapid loss of plasma volume and stroke volume.

Detraining $VO_2max$ Decline (84 days)

A cumulative $20\%$ decrease in fitness, where later losses are driven by a reduction in $\text{a-v O}_2\text{ difference}$.

Retraining Mitochondrial Recovery

It takes approximately $3-4\text{ weeks}$ of retraining to regain mitochondrial adaptations lost after $1\text{ week}$ of detraining.

MAP

Mean Arterial Pressure; aerobic training allows for higher muscle blood flow with no change in this value during exercise.

Mitochondrial Training Gain

Mitochondrial volume can increase by $50-100\%$ within the first $6\text{ weeks}$ of training.

Submaximal Heart Rate Adaptation

At a given intensity, training leads to a lower heart rate while maintaining the same cardiac output through a higher stroke volume.

Acid-Base Balance Improvement

Training results in less $H^+$ formation due to reduced carbohydrate utilization and increased NADH shuttling.

NADH Shuttling System

The biochemical mechanism that moves NADH from the cytoplasm to the mitochondria, preventing it from being used for lactic acid formation.

Ventricular Volume

A structural change in the heart that typically takes months to years of training to fully adapt.

Homeostasis Maintenance

Adaptations such as more rapid steady state and improved thermoregulation that allow for prolonged submaximal exercise.

Resting Heart Rate Adaptation

A reduction in resting HR due to a higher resting stroke volume and improved oxygen extraction at the muscles.

Central Component Adaptation Time-course

Increases in stroke volume and cardiac output typically occur early, between $6\text{ days}$ and $4\text{ months}$.

Peripheral Component Adaptation Time-course

Improvements in $\text{a-v O}_2\text{ difference}$ and capillary density typically occur later, occurring at $\geq 28\text{ months}$.

RER (Respiratory Exchange Ratio)

A ratio where values < 1.0 indicate fat utilization and values $\geq 1.0$ indicate carbohydrate utilization.

Daily Exercise Requirement

The need for frequent exercise to maintain adaptations because protein synthesis and mRNA levels return to baseline within $24\text{ hours}$.

Muscle Mitochondria Loss (Detraining)

Training gains in mitochondria decrease by $50\%$ within only $1\text{ week}$ of detraining.

Angiogenesis vs Biogenesis

Angiogenesis refers to structural capillary growth, while biogenesis refers to the biochemical increase in mitochondria.

Static Muscle Fibers

The total number of muscle fibers does not change with exercise training despite shifts in fiber type.

Training Intensity for Maximum Health Benefit

The dose-response relationship showing that health benefits like improved insulin sensitivity and BP occur with incremental minutes of weekly exercise.