Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral...

91
Neuromuscular Fatigue Muscle Physiology 420:289

Transcript of Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral...

Page 1: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Neuromuscular Fatigue

Muscle Physiology

420:289

Page 2: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Agenda

Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery

Page 3: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Introduction Fatigue

Common definition:Any reduction in physical or mental

performance Physiological definitions:

The gradual increase in effort needed to maintain a constant outcome

The failure to maintain the required or expected outcome/task

Page 4: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Mechanisms Difficult to Study Many potential sites of fatigue Task specificity Central vs. peripheral factors Environment Depletion vs. accumulation Interactive nature of mechanisms Compartmentalization Training status

Page 5: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Potential Outcomes of Fatigue Muscle force:

Isometric or dynamic Peak force and RFD

reduced

Rate of relaxation: Reduced

Figure 15.6, McIntosh et al., 2005

Adopted from Garland et al. (1988)

Page 6: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Potential Outcomes of Fatigue

Muscle velocity and power: Peak and mean

reduced

McIntosh et al., 2005

Page 7: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Potential Outcomes of Fatigue EMG

Increases with fatigue (submaximal load) as CNS attempts to recruit more motor units

Power frequency spectrum shifts to left FT MUs fatigue resulting in greater stimulation of

ST MUs (lower threshold lower frequency)

Page 8: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Brooks et al., 2000

Page 9: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Brooks et al., 2000

Page 10: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Gandevia, 2001

Page 11: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Potential Outcomes of Fatigue

Ratings of perceived exertion Rate of fatigue

Fatigue index Wingate Time to fatigue

Page 12: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Mechanisms of Fatigue

Fatigue can be classified in many ways:Psychological vs. physiologicalNeuromuscular vs. metabolicCentral vs. peripheral

Page 13: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Agenda

Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery

Page 14: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Central Fatigue - Introduction

Central fatigue: A progressive reduction in voluntary activation of muscle during exercise

Difficult to study however strong indirect evidence

Page 15: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Central Fatigue - Introduction

Central fatigue may manifest itself in several ways:Emotions and other psychological factorsAfferent input (pain, metabolites, ischemia,

muscle pressure/stretching) Intrinsic changes of the neuron

(hyperpolarization of RMP)

Page 16: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Figure 1, Kalmer & Cafarelli, 2004

Bottom line: Central fatigue causes neural inhibition greater voluntary effort to drive any motor unit

Page 17: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Evidence of Central Fatigue

Reduced motor unit firing rate and ½ relaxation time

Suggests less central drive

Page 18: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Figure 12, Gandevia, 2001

Page 19: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Evidence of Central Fatigue Concept of muscle wisdom Decline in MU firing rate does not correlate well

with decline in force As MU firing rate declines ½ relaxation time

increases (prolonged contractile mechanism) Prolongation steady force maintained with

lower MU firing rate Increased efficiency? Eventual fatigue is imminent

Page 20: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Evidence of Central Fatigue

Best evidence: Improvement in performance with severe fatigueSudden encouragementLast “kick” at end of race

Page 21: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

McIntosh et al., 2005

Page 22: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Gandevia, 2001

Page 23: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Gandevia, 2001

Page 24: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Agenda

Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery

Page 25: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Peripheral Fatigue

Potential sites include (but not limited to):

1. Impulse conduction of efferent neurons and terminals

2. Impulse conduction of muscle fibers

3. Excitation contraction coupling

4. Sliding of filaments

Page 26: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Efferent Neurons and Terminals Impulse conduction

may fail at branch points of motor axons

Unusual Branch point diameter < axon diameter

Evidence: Krnjevic & Miledi (1958)

Zhou & Shui, 2001

Page 27: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Krnjevic & Miledi (1958)

Rat diaphragm motor nerve Motor end plates of two fibers within same

motor unit observed Fatigue One fiber did not demonstrate

motor end plate depolarization with stimulation

Conclusion: Branch point failure

Page 28: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Normal branch point propagation

Page 29: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Branch point failure

Page 30: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Efferent Neurons and Terminals

Note: “Dropping out” of muscle fibers in single muscle fiber EMG studies is very rare

More research is needed

Page 31: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Efferent Neurons and Terminals

ACh release from axon terminals? ACh is synthesized and repackaged

quickly even during repetitive activity Safety margin: Very little ACh is required

to stimulate AP along sarcolemmaAt least 100 vescicles released/impulse

Not considered a site of peripheral fatigue

Page 32: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Peripheral Fatigue

Potential sites include (but not limited to):

1. Impulse conduction of efferent neurons and terminals

2. Impulse conduction of muscle fibers

3. Excitation contraction coupling

4. Sliding of filaments

Page 33: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Impulse Conduction Muscle Fibers

The ability of the sarcolemma to propagate APs will eventually fail during repetitive voluntary muscle actions

Attenuation is modest Mechanism: Leaking of K+ from cell

hyperpolarization of RMP

Page 34: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Figure 15.6, McIntosh et al., 2005

Adopted from Garland et al. (1988)

Page 35: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Peripheral Fatigue

Potential sites include (but not limited to):

1. Impulse conduction of efferent neurons and terminals

2. Impulse conduction of muscle fibers

3. Excitation contraction coupling

4. Sliding of filaments

Page 36: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Excitation-Contraction Coupling

Potential sites of fatigue: Tubular system:

T-tubulesSarcoplasmic reticulum

Page 37: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

ECC Fatigue T-Tubules

Mechanism: Inability of AP to be propagated down t-tubule Due to pooling of K+ in t-tubule (interstitial fluid)

Recall: Muscle activation causes:

Increase of intracellular [Na+] Decrease of intracellular [K+]

Na+/K+ pump attempts to restore resting [Na+/K+] Na+/K+ pump is facilitated by:

Increased intracellular [Na+} Catecholamines

Page 38: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

ECC Fatigue T-Tubules

T-tubule membrane surface area is small Less absolute Na+/K+ pumps Pooling of K+ in t-tubules hyperpolarizes t-

tubule RMP Time constant for movement of K+ from t-

tubules = ~ 1s Does 1 s of rest alleviate fatigue?

More mechanisms!

Page 39: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

ECC Fatigue Sarcoplasmic Reticulum Several potential mechanisms:

Impaired SERCA function Reduced uptake of Ca2+ prolonged relaxation?

Impaired RYR channel function Reduced release of Ca2+ less crossbridges?

General rise in intracellular Ca2+ Increased uptake of Ca2+ by mitochondria

reduced mitochondrial efficiency?

Page 40: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Peripheral Fatigue

Potential sites include (but not limited to):

1. Impulse conduction of efferent neurons and terminals

2. Impulse conduction of muscle fibers

3. Excitation contraction coupling

4. Sliding of filaments

Page 41: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Sliding of Filaments

Troponin: Two potential mechanisms of fatigue

1. Decreased responsiveness: Less force at any given [Ca2+]

2. Decreased sensitivity: More [Ca2+] needed for any given force

Page 42: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.
Page 43: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Agenda

Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery

Page 44: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Biochemistry of Fatigue

Metabolic fatigueDepletionAccumulation

Metabolic depletion and accumulation is related to central and peripheral fatigue

Page 45: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Metabolic Depletion

Phosphagens Glycogen Blood glucose

Page 46: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Phosphagen Depletion Phosphagens include:

ATP Creatine phosphate

CP is most immediate source of ATP due to creatine kinase

Rate of ATP: High

Capacity: Low

Page 47: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Phosphagen Depletion

Pattern of CP/ATP depletionCP and ATP deplete rapidlyCP continues to deplete task failureATP levels off and is preserved

Page 48: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Brooks, et al., 2000

Page 49: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Phosphagen Depletion

ATP depleted why task failure?

1. Down regulation of “non essential” ATP utilizing functions in order to maintain “essential” functions

2. Free energy theory

Page 50: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Phosphagen Depletion

Bottom line:CP depletion results in fatigue during high

intensity exerciseCP supplementation delays onset of task

failure

Page 51: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Metabolic Depletion

Phosphagens Glycogen Blood glucose

Page 52: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Glycogen Depletion

Recall: Glycogen is storage mechanism for CHO in muscle

Highly branched polyglucose molecule

Page 53: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Glycogen Depletion Glycogen depletion is associated with fatigue

during prolonged submaximal exercise Glycogen depletion is fiber type specific

depending on intensity of exercise Bottom line:

Glycogen depletion impairs ability to generate ATP at relatively fast rate task failure at moderate intensities

Supercompensation?

Page 54: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Metabolic Depletion

Phosphagens Glycogen Blood glucose

Page 55: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Low Blood Glucose

High intensity exercise increased blood sugar due to liver glycogenolysis

The rate of glycogenolysis does not match the rate of glycolysis lower blood glucose

Bottom line:Duration of exercise depends glycogen storesCHO supplementation?

Page 56: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Brooks, et al., 2000

Page 57: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Biochemistry of Fatigue

Metabolic fatigueDepletionAccumulation

Page 58: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Metabolic Accumulation

Inorganic phosphate Lactate and H+

Page 59: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Pi Accumulation

ATP ADP + Pi (HPO42-)

Effects of intracellular accumulation Inhibition of PFKReduction of ATP free energy

ADP and Pi accumulation

Inhibition of Ca2+ binding with Tn-C

Page 60: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Lactate and H+ Accumulation

Recall

Page 61: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Two possible fates for pyruvate:

1. Lactic acid

2. Mitochondria

Page 62: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Lactate and H+ Accumulation

When LA production > LA clearance Accumulation

At physiological pH LA dissociates a proton (H+)

As [H+] increases, pH decreasespH = -log of [H+]

Page 63: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

www.lorenzsurgical.com/ CF_lactosorbSE_DE.shtml

H+

Lactate C3H5O3

Page 64: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Lactate and H+ Accumulation

Effects of intracellular H+ accumulation Inhibition of PFK Inhibition of Ca2+ binding of Tn-C Pain receptor stimulation afferent inhibition Nausea and disorientation Inhibition of O2-Hg association Inhibition of FFA release Decreased force/crossbridge Reduced Ca2+ sensitivity Inhibition of SERCA function

Page 65: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Lactate and H+ Accumulation

Lactate accumulation is beneficial:Lactate liver glucose via

gluconeogenesis

Page 66: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

http://cwx.prenhall.com/bookbind/pubbooks/mcmurrygob/medialib/media_portfolio/text_images/FG23_10.JPG

Page 67: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Agenda

Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery

Page 68: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Recovery - Intro

Recovery oxygen: Amt of O2 consumed in excess of normal consumption at test EPOC: Excess post-exercise oxygen consumption

Duration of recovery depends on: Intensity of exercise Duration of exercise Training status Mode of exercise

Page 69: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Short Term Recovery Two main

components: Fast component Slow component

Page 70: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

ST Recovery: Fast Component

Time: 2-3 minutes VO2 declines rapidly Related to intensity of exercise Not related to duration of exercise

Page 71: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

ST Recovery: Fast Component

Elevated metabolic rate during fast component has many functions:Resaturation of myoglobinRestore blood O2

Provide O2 for energy cost of ventilation

Provide O2 for energy cost of cardiac activity

Replenishment of ATP-PC stores

Page 72: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.
Page 73: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.
Page 74: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

ATP-PC restoration dependent on blood flow

Page 75: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Short Term Recovery Two main

components: Fast component Slow component

Page 76: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

ST Recovery: Slow Component

Time: ~ 1 hour Attenuated decline in VO2

Related to intensity and duration of exercise

Page 77: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

ST Recovery: Slow Component

Elevated metabolic rate during slow component has many functions:Reduce core temperatureProvide O2 for energy cost of ventilationProvide O2 for energy cost of cardiac activityDecrease catecholamine levelsReplenishment of glycogenRemoval of lactate

Page 78: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Glycogen Repletion

Full repletion of glycogen requires several days

Glycogen depletion is dependent on:

1. Type of exercise (continuous vs. intermittent)

2. Dietary CHO consumed during repletion period

Page 79: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Glycogen Repletion

Glycogen repletion after continuous exercise2 hours: Insignificant repletion5 hours: Significant repletion10 hours: Greatest rate of repletion46 hours required for complete repletion with

high CHO intakeCHO vs. PRO/Fat diet

Page 80: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

High CHO diet

PRO/Fat diet

Page 81: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.
Page 82: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Glycogen Repletion

Glycogen repletion after intermittent exercise30 min: Significant repletion2 hours: Greatest rate of repletion24 hours needed for complete repletion with

normal CHO intake

Page 83: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.
Page 84: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.
Page 85: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Glycogen Repletion

Reasons for differences b/w continuous and intermittent exercise:

1. Total glycogen depleted-Twice as much depleted with continuous-Same amount synthesized in first 24 h

2. Availability of glycogen precursors-Ex: Lactate, pyruvate, glucose-Less precursors with continuous

3. Fiber type activation-Glycogen resynthesis faster in Type II

Page 86: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

Supercompensation

Glycogen repletion levels can be greater than pre-exercise levels with CHO loading

Page 87: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

ST Recovery: Slow Component

Elevated metabolic rate during slow component has many functions:Reduce core temperatureProvide O2 for energy cost of ventilationProvide O2 for energy cost of cardiac activityDecrease catecholamine levelsReplenishment of glycogenRemoval of lactate

Page 88: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.

ST Recovery: Lactate

Lactate is removed during the slow component of short term recovery 30 min - 1 h

Possible fates Urine/sweat excretion (minimal) Lactate glucose Lactate protein Lactate glycogen Lactate pyruvate Kreb’s cycle CO2 + H2O

Page 89: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.
Page 90: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.
Page 91: Neuromuscular Fatigue Muscle Physiology 420:289. Agenda Introduction Central fatigue Peripheral fatigue Biochemistry of fatigue Recovery.