Chapter 9: High Intensity Exercise

what occurs with exercise as a metabolic stressor?

it stimulates the degradation of stored energy

stored potential energy gets broken down and converted into ATP

how does anaerobic ATP generation occur?

via degradation of glucose or glycogen in the cytoplasm

how does aerobic ATP generation occur?

via a series of energy capturing chemical reactions in the mitochondria

aerobically generated ATP can be quantified by translating the O2 use into kcal expended

what is high intensity exercise?

a maximal bout of activity which lasts for less than a second (as in a kick, jump, punch, or throw) or as long as 1-2 minutes, and in which the major sources of energy are derived from anaerobic processes

what does high intensity exercise demand regarding ATP and muscle fibers?

it demands not just the use of anaerobic energy sources, but also that all appropriate muscle fiber types are recruited → generation of large amounts of ATP at a very rapid rate

the rate at which ATP is generated determines how much force or velocity can be produced and for how long

what is the energy demand of high intensity exercise?

100-fold increase in the rate of ATP use compared to resting

what is the oxygen deficit?

the difference between the amount of oxygen required for the exercise bout and the actual oxygen consumed

where does energy for muscle contraction come from during the oxygen deficit lag phase?

anaerobic sources, compensating for the inability of the cardiovascular system to provide sufficient oxygen immediately to the muscle

once steady state is reached, then oxygen uptake is equivalent to the demand, unless the exercise intensity is above VO2max

what is VO2max?

the maximal rate of oxygen consumption during incremental exercise - the upper limit of aerobic metabolism

beyond this point, aerobic ATP production cannot increase further, even if exercise intensity does

even though aerobic metabolism is maxed out, total energy demand can continue to rise

we can exercise above VO2max for short periods because anaerobic energy systems supplement ATP production

what is the physiological evidence showing that we can work at intensities above VO2max?

during high intensity intervals or “supramaximal” workloads, VO2 may plateau at VO2max while power output continues to rise - driven by anaerobic contributions

blood lactate levels and muscle phosphocreatine depletion confirm heavy reliance on non-oxidative energy systems (anaerobic)

what is the oxygen deficit when exercising at or above VO2max?

it is much greater

it cannot be “paid back” during the exercise bout because 1) the cardiovascular system is incapable of delivering sufficient oxygen to the muscle and 2) the muscles don’t have the ability to fully utilize the oxygen

consequentially, there is an inability to fully sustain the energy required → why we cannot sprint a marathon

where does energy production for high intensity exercise occur?

in the cytoplasm

what processes for anaerobic energy production do allosteric effectors activate?

glycogenolysis, glycolysis, and PCr degradation → this “gets the ball rolling” in energy production terms

increased need for ATP triggers production

what is glycogenolysis?

the fast metabolic process to breakdown stored glycogen into glucose

what is glycogenesis?

the metabolic process to store glucose as glycogen

what is glycolysis?

an anaerobic process occurring in the cytoplasm where this pathway breaks down one molecule of glucose into two molecules of pyruvate, generating a small net amount of energy in the form of ATP and high-energy electron carriers (NADH)

what is gluconeogenesis?

the process for lactic acid to be converted to glucose or glycogen

how does non-hormone allosteric regulation occur?

hormones would take too long!
allosteric regulation is based on concentrations of ATP, ADP, AMP, Ca, H, etc.

quantities of these effectors modulate ATP generating processes by activating/de-activating enzymes for

PCr breakdown, Glycogenolysis, Glycolysis, lactic acid production, adenylate kinase aka “myokinase”

how is myokinase activated and what are its functions?

it is activated by sufficient levels of ADP in the cytoplasm

it converts two molecules of ADP to: 

ATP (used to fuel muscle contraction)

AMP (cleared via the purine-nucleotide cycle) → NH3, which has been shown to increase substantially in plasma at exercise intensities greater than 100% VO2max

ADP + ADP = ATP, AMP

what is the lactate threshold (LT)?

the exercise intensity at which blood lactate accumulates faster than it can be cleared

excess pyruvate → lactate via lactate dehydrogenase 

similar to NH3 threshold

what is the fate of pyruvate in anaerobic conditions?

pyruvate → into other products like lactate via lactate dehydrogenase (LDH)

what are the potential fates of pyruvate in the TCA cycle?

it can be converted into glucose by reversing the process of glycolysis (in the liver, not in muscle)

it can be converted into glycogen by reversing glycolysis (in the liver and muscle)

what is the fate of pyruvate and lactate at low intensity exercise?

oxygen supply meets demand so

pyruvate from glycolysis enters the mitochondria for oxidation

lactate production = lactate clearance (steady-state)

what occurs with pyruvate and lactate at high intensities or as intensity rises?

ATP demand increases faster than oxygen delivery

glycolysis speeds up → more pyruvate made than mitochondria can handle

excess pyruvate is converted to lactate (via lactate dehydrogenase) (buffer H+)

lactate and H+ start accumulating in muscle and blood

once accumulation exceeds removal → you’ve hit lactate threshold

what training adaptations occur from high intensity exercise?

fast twitch fibers have fewer mitochondria, rely more on glycolysis

catecholamines (epinephrine/norepinephrine) rise and accelerate glycolysis

reduced blood flow in some tissues limits lactate clearance

lactate shuttle capacity (moving lactate to oxidative tissues) is maxed out

how is lactate threshold a performance predictor?

a higher LT (as % of VO2max) means you can sustain a faster pace before fatigue

how is lactate threshold a training tool?

endurance and interval training can shift the LT upward

how does lactate threshold provide metabolic insight?

reflects mitochondrial density, capillarization, and enzymatic adaptations

what were the findings of studies using electrical stimulation and muscle biopsy?

over a period of 1.68-5 seconds, PCr is rapidly decreased, and lactic acid is produced within 1.68 seconds

levels of PCr were depleted by nearly two thirds after 30 seconds of intense exercise 

levels of muscle glycogen was depleted by nearly one third