Skeletal Muscle Fatigue And

Cellular Mechanisms

By: Izatty Lim(0308188)

Learning Outcomes:

Definition

Cellular mechanism of muscle fatigue & recovery

Muscle Fatigue

decline in muscle performance associated with muscle activity.

As fatigue sets in, o force in your muscles reduces, o muscle responses to brain stimuli reduceso activity levels decrease.

temporary and reversible condition

 continuous high-frequency stimulation

 repeated tetanicstimulation

Muscle Fatigue

Fatigue mechanisms have been found to be multifactorial.

Key Factors

Fuel depletion Metabolic by-products

Neuromuscular events

•Intramuscular ATP

• Muscle glycogen

• Blood glucose

• Hydrogen ions (H+) in plasma and muscle

• Inorganic phosphate (Pi)

• Adenosine diphosphate(ADP)

• Decreased ‘firing’ of the central nervous system

• Impaired sodium (Na+) and potassium (K+) gradients

Problem: build up of lactic acid

Problem: needs oxygen

Problem: only make 1 ATP at a time

(15-20s of activity)

ATP Formation

MYOSIN Ca2+ ATPase

Mechanism Of Fatigue (ATP Depletion)

Myosin: for cross-bridge cycling

Ca2+ ATPase: o terminate contraction, pump Ca2+ back into sarcoplasmic

reticulum

Mechanism Of Fatigue (ATP Depletion)

Mechanism Of Fatigue (Pi Accumulation)

reduced maximum force-generating capacity reduced myofibrillar Ca2+ sensitivity reduced Ca2+ release

↓ force

Mechanism of Fatigue(Lactic Acid Accumulation)

• ACIDOSIS

• H+ competes with Ca2+ for binding sites on troponin C

•  ↓ maximal Ca2+ activated force and Ca2+ sensitivity (slows the maximal shortening velocity and prolongs relaxation)

• Burning sensation

Fatigue and Recovery

Fatigue and Recovery

Predominantenergy system

Likely causes of fatigue Types of recovery

ATP/PC Fuel Depletion: ATP & PC

Rest recovery

Lactic Acid Accumulation of metabolic by-products:

H+ (hydrogen ions) Pi (inorganic phosphates)

Non-dietaryActive RecoveryMassageHydro/water based therapiese.g. contrasting via hot/cold

baths

Aerobic Fuel Depletion: Glycogen stores, then fats

Elevated body temperature leading to:

Dehydration

Dietary High Glycemic Index foodsRehydration

Non-dietaryActive RecoveryMassageHydro/water based therapies

References

http://www.ncbi.nlm.nih.gov/pubmed/18195089

http://www.mendeley.com/catalog/cellular-mecha

nisms-muscle-fatigue/

http://lib.bioinfo.pl/pmid:7576593

http://www.pc.maricopa.edu/Biology/thoff

man/Common201/MuscularSystem.pdf

THANK YOU