Fatigue Flashcards
How is fatige defineid in exercise science?
A process involving an exercise-induced reduction in the ability to exert muscle force or power
What are the two main categories or fatigue?
Central
Peripheral
What is peripheral fatigue?
Fatigue from changes at or distal to the neuromuscular junction
What is central fatigue?
A reduction in neural drive to the muscles, not due to muscle contractility changes
What are key metabolic causes of peripheral fatigue?
Substrate depletion and accumulation of deleterious metabolites
What activation falure can cause peripheral fatigue?
Impaired actin potential propagation
What are four key outcomes of peripheral fatigue?
Changes in [Ca2+]
Myofibrillar function
Shortening velocity
Relaxation time
What phosphagens are linked to short, high-intensity fatigue?
ATP
Phosphocreatine (PCr)
What happens when PCr is depleted?
ATP regeneration is limited, leading to fatigue
What reaction helps buffer H+ during ATP resynthesis?
ADP + PCr + H+ <–> ATP + Cr
How long can glycogen support moderate exercise?
1.5-2 hours
What happens when glycogen is depleted?
Reliance on protein breakdown and reduced performance
How can glycogen depletion be offset?
Lactate suttle
Liver glucose release
Carbohydrate loading
What role does lactate plat in fatigue?
It allows glycolysis to continue but H+ accumulation can cause issues
What does H+ do in muscle?
Inhibits PFK
Displaces Ca2+ on troponin
Stimulation pain receptors
What effect does inorganic phosphate (Pi) have?
Inhibits cross-bridge formation and reduces calcium sensitivity
What type of fatigue dominates a 100m sprint?
PCr depletion
What type of fatigue dominates repeated sprints?
Metabolite accumulation
What causes fatigue in a matathon?
Glycogen depletion
What causes central fatigue?
Changes in neurotransmitters and afferent feedback reducing motor drive
Why might central fatigue be beneficial?
It’s a protective mechanism - part of a negative feedback loop
How can you test if fatigue is central or peripheral?
Induce muscle contraction via external action potentials without voluntary effort
What is the sewuence from brian to force output?
Brain - Spinal cord - Peripheral nerve - Muscle sarcolemma - T-tubules - Ca2+ - Actin-Myosin - Cross-bridge - Force output
What are common causes of muscle fatigue?
Substrate depletion
Muscle fibre damage
Build-up of metabolic by-products
What is DOMS and when does it occur?
Delayed Onset Muscle Soreness
12-72 hours post-exercise
What determines the ratio of fast glycolytic and slow oxidative muslce fibres?
Genetics
What muscle fibre type is suited for sprinting and weight lifting?
Fast glycolytic (FG)
What type of muscle fibre is ideal for endurance?
Slow oxidative (SO)
How does aerobic training affect muscle fibres?
Converts some FG to fast oxidative glycolytic - increases mitochondrial volume and oxidative enzyme levels
What are key mitochondrial adaptation to endurance training?
Larger mitochondria - increased number
What happens to glycolytic enzymes?
Increases in enzymes like glycogen phosphorylase, phosphofructokinase, and LDH
Which oxidative enzymes increase with training?
Citrate synthase
Cytochrome c oxidase
Do these enzymes becone more efficient?
No - they increase in number, not efficiency
How does endurance trianing affect fat metabolsim?
Increases fat oxidation at rest and during submaximal exercise
How does it affect carbohydrate metabolsim?
Increases CHO oxidation during max exercise - enchances glycogen storage
What other physiological changes occur with endurance training?
Improved ionic balance
Better lactate/H+ regulation
Neural and cardiovascular adaptations
What vascular change improves nutrient delivery?
Increased capillaristion
How does postnatal muscle growth occur?
Via hypertrophy - enlargment of existing fibres
What causes muscle atrophy?
Disease or denervation (nerve damage)
What happens in long-term denervation?
Muscle shrinks to 25% of size and becomes connective tissue (6-24 month)
What is a benefit of muscle hypertrophy?
Greater strength from more corss-bridges
What is a downisde of muscle hypertrophy?
Increased diffusion distance for nutrients and waste
What causes tetnus?
Infection by Clostridium tetani producing the neurotoxin tetanospasmin
How does tetanospasmin affect the body?
Blocks inhibitory neurotransmitter release in the spinal cord –> uncontrolled excitation –> spasms
What is msucle is usually affected first in tetanus?
The jaw
What is Duchenne Muscular Dystrophy (DMD)?
A fatal, X-linked disorder
Affects 1 in 3,500 males
Caused by mutation in dystrophin
What does dystrophin do?
Links actin to the extracellular matrix, stabilises muscle cell membranse during contration
What happens without dystrophin?
Muscle cells break down under contraction stress and are replaced by connective tissue
What is Distal Arthrogryposis?
A congenital condition causing contractures in hands and feet
What causes Distal Arthrogryposis?
Mutation in myosin, tropomyosin, troponin, or myosin-binding protein C
What is contracture?
Immobility from stiffness/constriciton in connective tissue
What structural changes occur from resistance training?
Increases in myofibril, mitochondrial, sarcoplasmic reticulum, and organelles
What causes strength increases with resistance training?
Hypertrophy (more contractile proteins) and neural adaptations
