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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0 1 2 3 4 5 6

Angular velocity (rad/s)

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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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Angular velocity (rad.s -1 )

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Total work performed during 25 reps at 240º/s

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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