Ch 3- Bioenergetics of Exercise and Training

Bioenergetics

the flow of energy in a biological system, concerning primarily conversion of macros into usable forms of energy

catabolism

breakdown of larger molecules into smaller molecules, releases energy

anabolism

building up of larger molecules from smaller molecules, requires energy

Exergonic reactions

energy releasing/generally catabolic

Endergonic reactions

require energy, generally include anabolic processes and contraction of muscle

What is the sum of all catabolic/exergonic and anabolic/endergonic reactions in a biological system?

metabolism

hydrolysis

breakdown of ATP to yield energy, requires one molecule of water

adenosine triphosphatase (ATPase)

enzyme that catalyzes hydrolysis of ATP

Myosin ATPase

catalyzes ATP hydrolysis for crossbridge recycling

calcium ATPase

catalyzes ATP hydrolysis, pumps calcium into SR following muscle contraction

sodium-potassium ATPase

maintains sarcolemmal concentration gradient after depolarization

phosphagen system

high intensity, short duration activities

ADP + CP ←→ ATP + Creatine (RLE Creatine Kinase)

2ADP←→ATP + AMP (RLE is Adenylate Kinase)

glycolytic system

breakdown of carbohydrate as either glycogen stored in the muscle or glucose delivered via blood to remake ATP

If no oxygen- pyruvate is converted into lactate in sarcoplasm anaerobic glycolysis

if yes oxygen- pyruvate is shuttled to mitchondria aerobic glycolysis

What causes fatigue ?

proton accumulation that reduces pH, inhibiting glycolytic reactions, directly interfering with muscle’s excitation contraction coupling

• potentially inhibits calcium binding to troponin or by interfering crossbridge recycling

• decreased pH is metabolic acidosis, which can also be responsible

• increased interstitial K+ concentration and Pi that impairs Ca++ release

Lactate production_______ with exercise intensity?

increases

higher rate of lactate production by type II fibers may reflect what?

a higher activity or [glycolytic enzyme] than in type I fibers

Cori cycle

when lactate is transported in the blood to the liver where it is converted into glucose

what happens to blood glucose levels within 1 hour of activity?

return to pre-exercise levels

peak [blood lactate] occur approximately how long after exercise stoppage?

5 minutes

Process of pyruvate through oxidative pathway

1. if oxygen is present in sufficient quantities, pyruvate is transported there (along with 2 molecules of reduced NADH)

2. pyruvate is then converted to Acetyl-CoA by pyruvate dehydrogenase complex (carbon lost as breathed off CO2)

3. Acetyl-CoA enters krebs cycle for further resynthesis of ATP

4. NADH drops off H+ at ETC to do same

what happens during oxidative phosphorylation?

resynthesis of ATP in the ETC

Substrate level phosphorylation

direct resynthesis of ATP from ADP during single reaction in metabolic pathways

how many net ATP are created starting with glucose?

net 2

how many net ATP are created starting with muscle glycogen?

net 3

Lactate threshold

exercise intensity at which blood lactate begins an abrupt increase above baseline concentration

% maximal oxygen uptake at which LT occurs in untrained individuals

50-60%

% maximal oxygen uptake at which LT occurs in trained individuals

70-80%

Onset of Blood Lactate Accumulation

when [blood lactate] reaches 4 mmol/L

Krebs Cycle

series of reactions that continues oxidation of the substrate from glycolysis and produces 2 ATP indirectly from GTP

• also produced is 6 NADH and 2 FADH2

• 1 NADH→2.5 ATP

• 1 FADH2→1.5 ATP

Free fatty acids enter mitochondria and undergo what?

Beta oxidation, where they are further broken down resulting in Acetyl-CoA and hydrogen protons

Degree to which anaerobic/oxidative systems contribute to energy produced is determined by what?

intensity first

duration second

Fatigue during exercise appears to be at least partially related to decrease in what?

phosphagens (ATP and Pi)

complete ATP resynthesis takes how long?

3-5 minutes

how long does it take for full resynthesis of CP?

8 minutes

Type II fibers have been shown to have elevated _____?

phosphagen concentrations, likely due to selective hypertrophy of type II fibers

What does post exercise carb consumption do for athletes?

repletes muscle glycogen stores during recovery

Other factors that aid in fatigue?

1. Increased intracellular Pi

2. ammonia accumulation

3. increased ADP

4. impaired calcium release from SR

oxygen deficit

the anaerobic contribution of energy at the onset of exercise (catch-up)

EPOC, Oxygen debt, or recovery O2

after exercise ceases, oxygen uptake remains above pre exercise levels for a period of time

interval training

emphasizes bioenergetic adaptations by using predetermined intervals (work:rest) of exercise and rest periods

HIIT

involves brief repeated bouts of high intensity exercise with intermittent recovery periods

what can be manipulated to achieve metabolic specificity

1. intensity/duration of active portion

2. intensity/duration of recovery portion

3. # of work bouts/# of sets

4. rest time between sets

5. recovery intensity between sets

6. mode of exercise

benefits of HIIT

• stimulus for both oxidative muscle fiber adaptation and myocardial hypertrophy

• increase in VO2 max

• proton buffering

• glycogen content

• anaerobic thresholds

• time to exhaustion

• time trial performance

combination training

any training program that includes a mix of different types of activities or exercises

Cross training

incorporating different types of exercise with the same underlying metabolic adaptation profile, not overstressing primary activity muscles with aim of complementing main sport performance

concurrent training

both anaerobic and aerobic training at multiple times within the same period, often in same session or day

what are the mechanisms by which development of strength is hindered while also doing endurance training?

• decreasing rapid voluntary activation

• chronically lower muscle glycogen levels that limit intracellular signaling responses during RT

• fiber type transition to ST fibers

what happens to performance in runners when performing strength training?

it is improved while not hindering metabolic parameters like VO2 max