Acute and Chronic Adaptations - Healthy Ageing Flashcards
Decrease in Muscle force - at what age?
Starts declining around 30 IF you don’t exercise regularly. Otherwise it happens around 60 years old.
Muscle atrophy due to aging
Called sarcopenia.
Defined as loss of muscle mass of 15-20%.
Leads to decline in muscle strength, power and muscle function.
What are the 4 main factors contributing to Sarcopenia?
Physical inactivity
Alterations in the nervous system
Altered hormonal level
Decreased energy and protein
What is Dynapenia?
age-related loss of muscle strength and power.
Muscular and neural adaptation.
Atrophy - Decrease in muscle fiber size in ageing (fast vs slow fibers)(upper vs lower limb)
Type II fibers (fast) decrease 20-50% and are more vulnerable to atrophy than type I fibers (slow) 1-25% decrease.
Decrease greater in the lower body compared to upper body due to plasticity and/or lesser use of lower limbs with ageing.
Hypoplasia
Decrease in muscle fiber nr.
Causes a loss of actin and myosin.
Changes in cross-bridges formation.
Less ability to contract.
Excitation-contraction Coupling
Process that converts the sarcolemmal action potential into muscle action and force generation. Dihydropyridine receptors activate calcium release, binds to troponin with tropomyosin resulting in actin-myosin interaction.
Excitation-contraction coupling - Ageing effect
Reduction in nr. of dihydropyridine receptors, deficit in calcium release.
Less receptors - less calcium passing through - less strong contractions.
Adipocyte Infiltration
Infiltration of adipose tissue that accumulates with age. Can contribute to muscle loss.
The more you exercise the less adipose tissue you accumulate.
Alterations in Muscle Architecture
Decrease in fascicle length (10%) and pennation angle (13%). Suggest a loss of sarcomeres. Not due to less physical activity.
Alterations in Tendon Properties
Increased tendon compliance.
Decreases the rate of force development. Reduced ability to produce rapid force.
Nr. of MUs
Reduced nr of functioning MUs.
Due to the apoptosis phenomena: death of MNs in spinal cord due to neurotoxic factors, denervation of corresponding muscle fiber.
MU remodeling
Surviving MNs develop collaterals that will innervate some of the denervated muscle fibers. Formation of giant MUs.
More fibers per motor unit. Decrease in MU frequency discharge.
MU Remodeling - Fiber type specific changes
MU remodeling explains the fiber type specific changes that result in denervation of type II (fast) fibers with collateral re-innervation of type I muscle fibers.
Alterations in Sensory Pathways
Ageing is associated with a decrease in H-reflex amplitude.
Decrease in Ia fiber efficiency to activate MNs.
Increase in presynaptic inhibition.
Use descending pathways more extensively.
