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![Page 1: 1 Exercise and Aging Skeletal Muscle Reading - Rogers p 65-97 Brooks - end of Ch 19 Nygard - Musculoskeletal Capacity Outline Body composition changes.](https://reader036.fdocuments.net/reader036/viewer/2022082820/5697bfa51a28abf838c97f5b/html5/thumbnails/1.jpg)
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Exercise and Aging Skeletal Muscle
• Reading - Rogers p 65-97• Brooks - end of Ch 19• Nygard - Musculoskeletal Capacity• Outline• Body composition changes• Changes in muscle function• Morphological changes• Metabolic capacity• Adaptations to training
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Aging• Decline of physiological capacity is
inevitable consequence of aging– physical inactivity may contribute to
this decline - not predominant explanation
• Body composition with aging• inc % body fat / dec lean body mass
– studies illustrate selective decline in sk ms protein vs non muscle protein
– body K+ and Nitrogen levels
• muscle peaks at 25-30 yrs– decline in X sec area, ms density
– inc intra-muscular fat
• Resting Metabolic Rate (RMR)– decline associated with dec ms mass
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Muscle Function• Decline in ms strength
– sig loss of max force production
• Fig 3.1 - Cross-sec study ages 11-70 men
– inc strength to 30, constant to 50, then decline (24-36%)
– similar dec in isometric, dynamic and speed of movement
• women - 20-70 yrs – dec 35% in strength, 33% in Xsec area
– dec 15% / decade after 50 yrs
– dec 30% / decade after 70 yrs
• evidence of selective declines in type II fiber area, no change in type I
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Size and Strength• Decline in strength with aging either• loss of muscle mass, or• alteration in ms capacity to generate
force - motor unit activation / contractile properties
• MVC / CSA (max vol vs X sec area)
– older subject ~70% of young
– other studies - women no change
– men 8.7-7.1 with age ~ 20 % weaker
• values for old men similar to women• difference in young men may be
activity related• Fig 3.2 - cadaver study
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Endurance Capacity• Fitts - no difference in fatigability
– 28 vs 9 month old rats
• Human studies – maintenance of MV isometric and
dynamic strength for 1min similar
– at same % of MVC (70 vs young)
• other studies– greater force loss in 30 sec stimulation
– greater relative force loss and reduced capacity to resist fatigue
• observed slow return to resting function following fatigue test– dec rate of twitch force relaxation and
inc half relaxation time
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Morphology
• Muscle fiber types– divisions based on physiological,
ultrastructural and metabolic characteristics
• Distribution with aging– may be result of inter-conversion or
secondary to preferential loss of specific fiber type
• Lexell - cadaver studies– ~50 % type I in all age groups
– found 25% fewer fibers (30-70)
– accounting for 18% decline in strength
• between 20 and 80 - 39% loss of fibers - all types
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Denervation and Fiber loss• What is cause of fiber loss with age
– damage to ms cells without regeneration
– interruption of m neuron connection
• Fig 19-9 Brooks - 47% decline• EMG studies
– # of active motor units dec with age
– low threshold M units that remain become larger
– elderly - lower # of functioning spinal cord motor neurons
• Aging and fiber size– no sig change in type I fiber size
– sig dec in type II fiber size ~26%
– (age 20-80) accounts for dec strength
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Capillarization and Metabolic Capacity
• Observe 25 % dec in cap density• 20-40 % dec in cap / fiber ratio
– * screened for activity level - truly sedentary - still may be confounded
– inconclusive evidence
• Metabolic Capacity and Aging• Study enzymatic activity
– marker enzyme glycolysis, Krebs, ETC, Beta oxidation, ATP synthesis
• Glycolytic Capacity• considerable evidence glycolytic
enzyme activity and high energy phosphates not adversely affected
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Respiratory Capacity• Scandinavian studies - no change in
mito ox capacity B - HAD, CS
• later studies– ~25% dec in men and women
– 40% less O2 uptake capacity
• contrast - Scandinavian may not be truly sedentary - activity inc mito
• Adaptation to Endurance Training• healthy sedentary - ~10% decline per
decade in VO2 max– aging and physical inactivity contribute
• Cartee - relative inc in VO2 max and ms resp capacity is similar old and young
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Endurance Training• Seals - 6 months low and high
intensity training– 30% mean increase in VO2 max 60-70
– others 9-12 months - ~24 % inc
• Oxidative Capacity• Table 3.1 - Suominen
– 20 min 3-5 X/week - 8 weeks- 56-70yrs
– inc 45% in Resp capacity
– inc 12% in VO2 max
• Orlander - no inc - 12 weeks 70-75• Meredith - 128% inc Ox cap, 20 in
VO2 max -young 27 % inc in ox cap
– ** 45 minutes 3 X / week
• Coggan - fig 3.4A - 10 month program
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Endurance Training• Glycolytic capacity - minimal impact
• Capillarization– Coggan Fig 3.4 B
– cap density inc 20 %
– cap / fiber ratio inc 25%
• Fiber type alterations– Gollnick - 30 yrs old - 5 months
– 23 % inc in size of type I
– no change in type II
– no change in % type I
– type II b to a shift
• Cogan - elderly - similar to above– changes that occur function of intensity
and duration of stimulus
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Prolonged Endurance Training
• Animal studies - prolonged wheel running or swimming training– for significant portion of life span
– inc type I fiber mass, dec type II
– 20-40% inc in SDH, CS and B-HAD
• Human Studies– chronic intense endurance training in
master athletes - reduce or eliminate decline in VO2 max over 10 yrs
• compared to performance matched younger athletes– same max (a-v)O2 difference
– 25-30% higher ox enzyme capacity
– cap / fiber inc, cap / mm same
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Resistance Training• Regular resistance tx over sufficient
time period– muscle hypertrophy, inc strength
– alteration in body comp
• older individuals– table 3.3
• Frontera - 12 weeks - 80 % 1RM– Inc 5 % / day (similar to young)
• Fig 3.6 a inc 100 % ext, 200 % flexors
• Fig 3.6 b - 11 % inc in Xsec area– inc type I and II ~30 % each
– inc CS, Cap density, and VO2 max
• very old - 8 weeks high intensity– inc 174 % strength, 15 % X sec area