Adaptation to Physical Stress and Aging Flashcards
What are the components of the SAID principle?
Specific Adaption to Imposed Demands - adaptation imposed by mechanical loading (physical stress) can be observed as structural, functional, local, and systemic changes
What is mechanotransduction?
mechanical loading (physical stress) stimulates cellular responses to make structural and/or functional changes
What are the steps of mechanotrasduction?
mechanocoupling, cell to cell communication, and effector response
Describe the process of mechanocoupling.
mechnical trigger initiates the process of MCTD - the direct or indirect physical perturbation of a cell - transformed into a variety of chemical signals
Describe the process of cell to cell communication.
once tissues have been exposed to the mechanical stimulus, the message of this is distributed to tissues via cell to cell comm.
True/False: A stimulus in one location can lead to a distant cell registering a new signal even though the distant cell did not receive a mechanical stimulus.
true
Describe the effector response.
Rxn to mechanical stimulus to produce and assemble necessary material in the correct alignment for successful adaptation
What are the characteristic tissue responses?
maintenance of physical stress tolerance occurs when physical loading is maintained in typical ranges and results in no apparent tissue change,
increase physical stress tolerance when loading exceeds maintenance range but still within adaptive capacity,
decrease physical stress tolerance when loading falls under maintenance range,
injury occurs when loading exceeds tissue tolerance beyond adaptive capacity of tissue - tissue damage and initiation of healing response,
death occurs when extreme loading levels exceed the adaptive capacity of tissue - complete loss of tissue vitality, function, and recovery ability
What are the factors influencing level of physical stress?
frequency, rate, duration, magnitude, type
What are the general effects of prolonged stress deprivation/immobilization?
loss of glycosaminoglycans, increased quantity collagen cross-links, randomized orientation of newly deposited collagen fibers, fatty fibrous infiltrations of edematous areas, pannus formation inside joints, generalized tissue atrophy
What are the effects of immobilization of a muscle in a shortened position?
decrease in the number of sarcomeres with a compensatory increase in sarcomere length, increase in the amount of periomysium, thickening of endomysium, collagen fibril orientation becomes more circumferential, increase in ratio of CT to muscle fiber tissue, loss of weight and muscle atrophy , adjusts sarcomeres to a length at which muscle is capable of developing maximal tension in immobilized position, displaces the length-tension relationship so that max tension generated corresponds to immobilized position, muscle is able to generate max tension in the shortened position, muscle will not be able to function effectively at joint it crosses immediately after cessation of immobilization
What are the effects of immobilization of a muscle in a lengethened position?
fewer structural and functional changes than if in shortened position, increase in # of sarcomeres resulting in a decreases in sarcomere length at the lengthened position, increased endomyseal and perimyseal CT, muscle hypertrophy that may be followed by atrophy, increase in max tension-generating capacity, displacement of the length-tension curve close to the longer immobilized position
Describe the decreased adaptive ability.
lowered thresholds for subsequent adaptation and injury due to prolonged low physical stress
What are the effects of repeated stress exposure/exercise?
tissues appear to respond favorably to gradual progressive loading/exercise by adapting to meet increased mechanical demands, responses vary among tissues and depends on nature of stimulus, increased quantity of glycosaminoglycans, reduction of collagen cross-links, functional orientation of collagen fibers in the CT align according to tissue stress, generalized tissue hypertrophy, increased load bearing capacity
Describe the increased adaptive ability.
elevated thresholds for subsequent adaptation and injury due to repeated stress exposure
What is the bone response to each physical stress level?
low - decreased mineral density, decreased strength;
high - increased mineral density, increased strength; excessive - fracture
What is the cartilage response to each physical stress level?
low - decreased proteoglycan content, decreased thickness, decreased stiffness;
high - increased proteoglycan content, increased thickness, increased stiffness;
excessive - tear or degeneration
What is the ligament response to each physical stress level?
low- decreased cross sectional area, decreased stiffness, decreased strength;
high - increased cross sectional area, increased stiffness, increased strength;
excessive - sprain
What is the tendon response to each physical stress level?
low - decreased cross-sectional area, decreased stiffness, decreased strength;
high - increased cross-sectional area, increased stiffness, increased strength;
excessive - strain
What is the muscle response to each physical stress level?
low - decreased contractile protein, decreased fiber diameter, decreased peak tension, decreased peak power;
high - increased contractile protein, increased fiber diameter, increased peak tension, increased peak power;
excessive - strain
What is the neuronal response to each physical stress level?
low - decreased maximum discharge rate, increase recruitment threshold, decreased activation with maximum voluntary contraction, loss of neurons;
high - increased maximum discharge rate, decreased recruitment threshold, increased activation with maximum voluntary contraction, increased motor unit synchronization, increased dendritic arborization, increased serotonergic neural activity, neurogenesis;
excessive - axonal demyelination and degeneration
What is the heart response to each physical stress level?
low - decreased cardiac muscle mass, decreased capillary density, decreased stroke volume;
high - increased cardiac muscle mass, decreased capillary density, increased stroke volume, increased metabolic capacity;
excessive - fibrosis, aneurysm, ventricular hypertrophy
What is the BV response to each physical stress level?
low - decreased vascular diameter, decreased arterial compliance;
high - increased vascular diameter, increased arterial compliance;
excessive - fibrosis, aneurysm
What is the skin response to each physical stress level?
low - decreased collagen content, collagen fiber diameter, decreased strength, decreased thickness;
high - increased collagen content, increased collagen fiber diameter, increased strength, increased thickness;
excessive - abrasion or wound
What are the factors influencing tissue tolerance for physical stress?
muscle performance, motor control, postural alignment, physical activity, occupational/leisure/self-care activities, physiological factors: meds/systemic pathology/obesity/age, psychosocial factors: depression/anxiety/PTSD, extrinsic factors: orthotic devices/taping/assisted devices/footwear/ergonomic environment
What are the age-related changes in bone?
progressive loss of bone density, reduction in collagen cross-linking, decrease in overall amount of bone, slight decrease in size, decrease in strength and stiffness, increased brittleness, reduction of bone toughness, increased fragility, water content decreases, decrease in size of hydrodynamic aggrecan, changes in proteoglycan population that could be considered part of accumulated tissue damage, can contribute to vicious cycle of degeneration
What are the age-related changed in ligament and tendon?
number and quality of cross-links increased beyond ideal level, overall decrease in collagen fibril diameter, increased collagen fibril concentration through reduced water content, changes in active differentiated fibrocytes, reduced ability of growth factors to induce fibroblastic activity
What are the age-related changes in muscle?
sarcopenia, alteration of proportion of fiber types with inactivity, changes in motor units
What are the connective tissue changes associated with age?
amount increases maybe due to decreased ROM and increased muscle stiffness
According to “Progressive Resistance Strength Training for Improving Physical Function in Older Adults” what types of measures were improved in older people performing high intensity progressive resistance training 2-3x a week?
muscle strength, balance, gait speed, timed walk, timed up and go, chair rise, stair climbing
