12. Bone adaptation to training and nutrition Flashcards
- what 2 things lead to _______ which increases bone formation?
- describe the cross-sectional image of a thigh of a paralyzed person
- mechanical loading + pulling of muscle (?) –> increase strain –> increase bone formation
- decrease muscle, and bone
- thinner cortical wall
- marbling effect in muscle (fat infiltration)
what are the 4 main goals (associated to age categories ish) to achieve bone health as we age? (think of schéma of bone mass as age increases)
- EARLY AGE: Increasing peak bone mass
- ADULTHOOD: Maintaining bone mass after peak bone mass is attained
- OLDER ADULT (>50 ish, post menopause) Minimizing bone loss with aging
- SENIORS: Preventing falls and fractures
- during growth and periods of loading, WHAT occurs. explain –> increase (2)
- during aging and periods of unloading, WHAT occurs. explain + decrease in what?
- PERIOSTEAL EXPANSION
- bone is added to the periosteal (outer) surface)
- increase bone size = increase bone strength - ENDOSTEAL RESORPTION
- bone is removed from endosteal (inner) surface
- decrease bone mass but does NOT decrease bone size (cause periosteal stays the same (?)) –> minimizing reduction in bone strength (?)
what is Wolff’s Law? what year?
vs what is the other important theory? by who?
Julius Wolff, 1892
Bone undergoes remodeling in response to mechanical stresses placed upon it, leading to changes in the external form and internal architecture of the bone
- mechanostat theory, by Harold Frost (1960s) = refine of Wolff’s Law
what are the 3 key points of the mechanostat theory?
- Bone adapts to forces via modeling and remodeling to keep typical strains within a physiologically safe range
- Bone is altered to satisfy its functional need and to create a structure appropriate for the individual’s daily activities
- Bone mass is regulated according to certain thresholds
explain the mechanostat theory (schéma with colors)
- 4 different zones
- in every day life, activities of daily living put a certain strain on bones, stay in the PHYSIOLOGICAL LOADING ZONE (yellow)
- if you pass the MINIMUM EFFECTIVE STRAIN (ie by doing plyometrics) –> you go in OVERLOAD ZONE (green) where you have modeling
- if you increase strain too much, you can get to the PATHOLOGICAL OVERLOAD ZONE (blue) –> where if you exercise too often, can have traumatic fracture + microdamage in bone
- on the opposite end, if you don’t do enough physical activity (bed rest, space flight…) –> increase bone resorption = TRIVIAL LOADING ZONE
MECHANOSTAT THEORY
- when do you have bone gain?
- vs when you have bone loss?
BONE GAIN: when strain or deformation is larger than normal (ie > minimum effective strain) –> increase bone formation relative to resorption –> bone gain!
BONE LOSS: strain or deformation is reduced relative to normal –> increase bone resorption relative to formation –> bone loss
Wnt/b cathenin signaling:
- osteocytes need _________ to survive
- WHAT down-regulates ___A_____ –> increase or decrease Wnt/b-catenin signaling?
- VS WHAT up-regulates ___A_____ –> increase or decrease Wnt/b-catenin signaling?
- what produces ___A_____? function of ___A_____?
- osteocytes need loading to survive
- mechanical loading down-regulates sclerostin expression (less sclerostin) –> INCREASE Wnt/b-catechin signaling = increase bone formation
- disuse or unloading up-regulates sclerotin expression –> decrease Wnt/b-catenin signaling = blocks bone formation = decrease bone mass
- osteocytes produce sclerostin –> sclerostin = inhibits Wnt/b catenin signaling
*sclerostin binds to osteoprotegrin = inhibit bone resorption
how does loading influence bone physiologically? define + explain 4 steps!
- bone loading communicates within WHAT and signals WHAT of the bone
- MECHANOTRANSDUCTION! transformation of mechanical signal (loading) to cellular/chemical signal (bone formation)
1. loading (mechanical force > threshold) –> deformation of bone = mechanical signal (pressure gradients and fluid movement within canaliculae exert SHEAR stress on cell membranes of osteocytes
2. mechanical signal detected by osteocytes that convert this mechanical signal to cellular signalling to bone lining cells
3. bone lining cells release biochemical compounds that stimulate production of osteoblasts –> signal bone formation
4. leads to increase bone mass and bone geometry –> increase bone strength - Bone loading communicates within the osteocyte-bone-lining cell network and signals site-specific addition of bone
what are modulators of the mechanostat theory?
- age
- hormones
- sex
- genetics, strain stimulus
- pharmacological agents
- nutrition
what can be the impact of disuse on muscle and bone? (study with twins without/with spinal cord injury)
- twin without SCI –> -0.5 T-score
- twin with SCI: -4.9 T-score + 25.9-36.2% of twin’s BMD!!!
bc twin with SCI has lack of loading + no muscles acting on bones
is there a correlation btw aLM and total femur BMD? what about aLM and failure load/bone strength?
- does osteoporosis or osteopenia have lower ALM?
- yes! positive correlation: as aLM increases, better the BMD –> bone strength and ALMI also positive correlation! as ALMI increases, failure load also increases
- osteoporosis has significantly less ALMI than osteopenia
appendicular lean mass index
why is muscle important for bone health?
what has been associated with lower muscle size and strength?
- what is an effective strategy to address sarcopenia? which may in turn help what?
- Appendicular and whole-body lean mass contribute to bone mass, structure, and strength
- Low muscle mass –> poor balance –> increase falls risk
- Osteoporotic fractures have been associated with lower muscle size and strength
- Resistance exercise (esp. in combination with adequate protein) is an effective strategy to address sarcopenia, which in turn may help to prevent falls and fractures
mechanical loading and bone adaptations: animal and human studies suggest (5)
give example of low vs mod vs high intensity for mechanical loading exercises +
- Higher magnitude of loading (>4G)
- Low frequency loading @ fast rate (i.e., 10-20 jumps)
- Dynamic loading > static loading
- Multiple bouts of short-duration loading w/ rest periods (i.e., 3 times/day, 3-4 times/week)
- “Odd” impact, multidirectional > unidirectional loading
LOW: <2x bw (<2G), >15 reps < 65% 1RM
- walking, jogging, cuyling, aquating interventions, bw or light resitance training
MOD: 2-4x bw (2-4G), 8-15 reps, 2-4x bw
- heel drops, rope skipping, aerobics, jumps with soft landing or with knees and hip bent
HIGH:
- >4x bw (>4G), <6 reps, >80% 1RM
- jumps with stiff-legged landing (ie plyometrics, gymnastics, triple jump, weight lifting, basketball))
what are 6 principles for bone adaptation to loading? + explain
- DYNAMIC
- rhythmic/dynamic pattern of loading (running, jogging) rather than static mechanical stimulation leads to increases in bone formation!
- increases both periosteal and endocortical bone formation) - SPECIFICITY
- major impact of activity is at the site of strain or deformation!
- ie weight bearing activity (against gravity, tennis, jogging) > non-weight bearing activity (swimming, cycling) - OVERLOAD
- to change bone mass, exercise load or stimulus > normal load - INITIAL VALUES
- individuals with lowest BMD have the greatest capacity for change - REVERSIBILITY
- positive effect of exercise will be lost if exercise is discontinued (ie detraining, bed rest, space flight) - UNCUSTOMARY
- unusual pattern of loading and deviation from normal pattern of loading (aka odd-impact –> ie soccer, diversion…) induce better adaptations in bone
