Transcript
Adattamenti muscolari all’invecchiamento e ai
fenomeni osteodegenerativi
Marsilio Saccavini
UOC Degenza di Medicina Riabilitativa
TREVISO
Lean body mass• Main sites of loss: muscle, liver, kidneys,
adrenal glands, brain
• General population shows ~constant LBM up to 4th decade and a decline thereafter.
• By 8th decade, men show a 40% loss, women a 20% loss of young adult LBM
• Decline in IGF-1, testosterone, insulin level, and physical activity, are associated with LBM reduction
Loss of Muscle Strength and Power
• At the age of 70-79 yrs, quadriceps force is ~60% of that at 20-29 yrs. Relative force loss is similar for both gender.
• The loss of muscle power seem to be greater than that of force. From 65 to 84 yrs, force is lost at a rate of 1.5%/yr, power at a rate of 3.5%/year (Young & Skelton 1994)
• Leg extension muscle power is correlated with speed or raising from a chair, stair climbing test & speed of walking (Bassey et al. 1992)
Skeletal muscle strength
Decline in motor unit number
Loss of Strength and Power in old age
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20
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60
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180
0 1 2 3 4 5 6
Angular velocity (rad/s)
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20
40
60
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Torque YOUNG
Torque OLD
Power YOUNG
Power OLD
Series5
Series6
Absence of muscle weakness in eccentric contractions
Causes of force loss
• Muscle fibre atrophy, particularly of type II
• Decrease in fibre number– SARCOPENIA
• Decrease in neural drive (voluntary contractions)
• Decrease in the force per cross-sectional area of each muscle fibre
Fibre number and ageing
Sprouting
Muscle twitch
Decreased fusion frequency
Resistance to fatigue
Frailty
• “A state of reduced physiological reserves associated with increased susceptibility to disability” (Buchner and Wagner, Clin. Geriatr. Med.
7, 1992)
• Frailty is characterised by generalised weakness, impaired mobility and balance and poor endurance.
Muscle strength with age
Muscle Strength Kg
60
40
20
8020 40 60
Age (years)
Independence Threshold
Active Person
Sedentary Person Training
Can frailty be prevented by physical activity ?
Effects of:
• Low-intensity, long duration exercise
• High-intensity, short duration exercise
Effects of endurance training on muscle strength of elderly men
PHYSICAL ACTIVITY IN OLD AGE
Strength training has repeatedly been shown to be a safe and effective intervention to mitigate muscle weakness and sarcopenia.
Improves mobility and reduces incidence of falls(Tracy et al. 1994).
Holistic type of training is recommended
Tai Chi shown to be effective falls prevention exercise in over 65’s with poor strength and balance.
Improves postural stability and muscle strength reducing risk of falls.Also proven to be beneficial to:
cardiorespiratory function, flexibility and balance control (Wolf et al. 1993).
Protocol
METHODS
Training Program:
3x wk: 2 supervised, 1 home
based session. Approx. 1hr.
• 10min warm up and stretch
• Aerobics exercise
• Strengthening exercises: 6
machines and therabands
• 10min cool down - Tai Chi.
Adaptations to training
• Structural adaptations
• Contractile adaptations
• Neural adaptations
• Performance adaptations
Structural adaptations
• Muscle hypertrophy
• Fibre hypertrophy
• Fibre distribution
Muscle hypertrophyAge
(yrs)
Muscle Duratn
(wks)
CSA
(%)
Reference
86-96 Knee
ext.
8 9.0 Fiatarone et al.JAMA 13, 1990
85-97 Kneeext.
12 9.8 Harridge et al.Muscle&Nerve 22, 1999
60-72 Kneeext.
12 9.3 Frontera et al.JAP 64, 1998
57-65 Kneeext.
10 8.5 Häkkinen et al.J Gerontol 53A, 1998
Fibre hypertrophy
Muscle fibre distribution
• No significant changes in type I/type II fibre proportion
• Distribution of type I fibre unaffected
• Type II fibre subtypes show changes similar to those of young adults:– Type IIa proportion decreases– Type IIab proportion increases– Type IIb proportion decreases
Fibre transformations
Training-induced fibre transformations in young adults
Contractile adaptations
• Maximum weight lifting ability: increases
• Isometric MVC: increases
• Maximum power: increases
• Twitch characteristics: TPT, unchanged, 1/2RT increases (?)
• Work sustainable: increases
1-RM of knee extensors & flexors
Isokinetic Torque & Power
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0 5 10 15
Angular velocity (rad.s -1 )
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Total work performed during 25 reps at 240º/s
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500
1000
1500
Before After
+41%
From: Roman et al. J Appl Physiol 74, 1993
Neural changes
• Muscle activation capacity
• Maximum EMG activity
• Antagonist muscle co-activation
Muscle Activation Capacity
Maximum EMG activity
Gains in strength and size: elderly and young compared
Population trainingduration
Strengthgain (%)
gain/day(%)
Authors
Elderly(65-81 yrs)
16 wks 21.9 0.19 Narici et al.2000
Elderly(60-72 yrs)
12 wks 16.7 0.20 Frontera et al.1988
Elderly(85-97 yrs)
12 wks 37.0 0.44 Harridge et al.1999
Youngadults
24 wks 26.8 0.16 Hakkinen et al.1985
Youngadults
12 wks 15.0 0.18 Rutherfordet al. 1987
Youngadults
24 wks 29.6 0.18 Narici et al.1996
Strength is correlated with performance
Effect of ageing on myosin molecule
speed
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