L8: Force, Work, Energetics

Describe the trade off of larger muscles:

Can produce higher peak tension but:

• Consumes more energy, adds weight, decreases mobility

ATP is generated from:

the breakdown/catabolism of glucose, lipids, organic molecules

________ is a form of anaerobic ATP synthesis and occurs within the ________ . It ________ O2.

glycolysis - cytosol - doesn’t -

____________ which involves the _________ and ________ is a form of aerobic ATP synthesis occurs within the ________ and ________ O2.

Aerobic metabolism - Citric acid cycle - electron transport chain - mitochondria - requires

___________ metabolism is faster but ___________ and cannot use __________

Anaerobic - produces 2 ATP/Glucose - fatty acids

___________ metabolism is slower but ___________ and __________

Aerobic - 30+ ATP/Glucose - uses fatty acids

Glycolysis:

____________ → __________+ __________

Glucose → Pyruvate + ATP

Aerobic Metabolism:

__________ + __________ → __________+ __________ + __________

Pyruvate + O2 → ATP + CO2 + H2O

• Besides ATP can react with ________ to produce _______, a higher energy phosphate bond compound.

• This process ______ O2 and is very fast/very slow, but _____________

• Creatine - creatine phosphate

• doesn’t require - very fast - rapidly depletes

Resting muscles use ________ respiration of _________ to build an ATP___________ and create ___________ and ___________ stores.

aerobic - free fatty acids - surplus - glycogen - creatine phosphate

Moderately active muscles use _________ respiration of _______and _______ from _________ stores to build an ATP ____________.

aerobic - free fatty acids - glucose - glycogen - requirement

• Muscles at peak activity use _________ respiration using up __________ and ___________ stores.

• Waste products ___________ and ___________ build up.

• Aerobic + Anaerobic - glycogen - CP

• Lactate - Creatine

Muscle fatigue: Reduced ___________ for the same ___________

contractile tension - stimulus

Muscle fatigue impairs a muscle’s ability to ___________ or ___________ the ___________ because of ___________.

initiate - maintain - contraction cycle - rapid ATP production

Fatigue factors that impact ___________:

• Depletion of ____ vesicles in the ______ neuron axon terminal

• Accumulation of ____ in the ________ due to repeated APs

Excitation

• ACh - motor

• K+ - T-tubules (ECF)

Fatigue factors that impact ______:

• Leakage of _____ into the sarcoplasm

• Microtears in _________

• Build up of _________

contraction

• Ca2+

• myofibrils

• Lactate and H+

Recovery from fatigue requires some coordination with the _________.

liver

For short term recovery from fatigue, how is lactate disposed?

• Used in aerobic metabolism at rest

• Goes through gluconeogenesis at the liver

In the long term, ___________ are rebuilt by ___________ cells which proliferate using ___________ in the blood.

myofibrils - myosatellite cells - amino acids

A muscle twitch is the ___________ response of a muscle fiber to a ___________.

contractile - single action potential

Describe the trade off that occurs at myofibrillar hypertrophy:

• Myofibrillar hypertrophy: more myofibrils within a fiber are produced.

• maximal tension production vs energy efficiency

  • Mitochondria can get squished

  • ATP is not sufficient → rapid fatigue

Muscle fibers can vary by ______ timing and ___________, ___________, and ___________ composition.

twitch - protein - tissue - organelle

Type I fibers are fatigue resistant/prone and fast/slow to recover.

resistant - fast

Type IIB are also known as ___________ fibers.

Type IIA are also known as ___________ fibers.

ast-glycolytic

fast-oxidative

Type II fibers are fatigue resistant/prone and fast/slow to recover.

prone - slow

Which type of fiber has slower, longer twitches? Why?

Type I: slow myosins and pumps

Which type of fiber has a higher maximum tension? Why?

Type II: More myofibrils

Which type of fiber is utilized for aerobic exercises? Why?

Type I: more mitochondria and steady oxygen supply (more capillaries) → higher aerobic capacity

Which type of fiber has higher levels of Creatine Phosphate?

Type II: fewer capillaries per fibre

Type IIA fibers will have the characteristic fast contraction speeds of type II fibers but have intermediate __________, __________, _________ and __________ density, and resistance/recovery from _________.

twitch durations - size/power - mitochondria - capillary - fatigue

Describe a motor unit’s activation pattern:

All or none, but not all motor units within a muscle need to be activated for a contraction.

What makes up a motor unit?

Motor units are a single MN + 1-1000 muscle fibers of the same type

The smallest motor units will have ______ fibers that are all type ____ while the largest will have _____ fibers that are all type _______

few - type I - many - type IIB

Explain the Size Principle for motor neuron activation in the spinal cord:

Weak stimuli in the spinal cord will only recruit the smallest motor units.

Synchronous Recruitment:

As stimulus intensity increases, the spinal cord will recruit more fibers which increase in size as per the intensity.

Describe asynchronous recruitment within a sustained contraction:

Similar-sized motor units take turns activating and resting dow the duration of the contraction.

Muscles enhance their peak tension by _________ through _________ or __________(the only one applicable to humans)

becoming larger - hyperplasia - hypertrophy

Hyperplasia:

More myofibers per fascicle → fascicle larger

Note: not possible in humans

Hypertrophy:

more myofibrils per myofibre → increase fiber diameter, larger fascicle

Why can humans only grow muscle size through hypertrophy?

After embryonic development, fibers can be repaired but not created.

Conversion between type ____ and ____ fibers is harder than type ____ and ____

I & II — IIA & IIB

Aerobic training leads to the hypertrophy of type ___ fibers.

Anaerobic training leads to the hypertrophy of type ____ fibres

type I - type IIb