Post by carruthersjam on May 12, 2008 10:16:57 GMT -8
Aging causes a shift from type II to type I (fast twitch to slow
twitch). Below are a few presentation notes from Dr Henning
Wackerhage (Molecular Exercise Physiology Atrophy):
The primary problem in ageing sarcopenia appears to be a loss of a-
motor neurones (Tomlinson & Irving, 1977;Kawamura et al., 1977). As a
result, almost half of the muscle fibres are lost from the age of 20
to the age of 80, at least in the vastus lateralis (Lexell et al.
1988).
Ageing sarcopenia is a very slow process. Lexell et al.'s (1988) data
suggest that » 12 fibres out of half a million are lost daily from
the age of 20 to the age of 80 years. Similarly, a hypothetical loss
of 10 kg of muscle mass over 40 years equates to a daily muscle loss
of ≈ 0.7 g. Thus, the net muscle changes are very hard to detect.
• Type 2 fibres atrophy and the percentage of type 2 fibres decreases
(Lexell et al. 1988).
• Basal protein synthesis and degradation are probably unchanged
(Dorrens & Rennie, 2003). However, the response to resistance
training and nutrition is likely to be different.
• The slow elimination of fibres and myonuclei is likely due to
apoptosis, at least in rats (Dirks & Leeuwenburgh, 2002;Pollack et
al., 2002).
• Aging causes cell death and functional changes in the
neuroendocrine system (Rehman & Masson, 2001) and this affects the
growth environment of the muscle.
• The pulse amplitude of growth hormone secretion (Finkelstein et
al., 1972) and systemic IGF-1 concentrations decrease with aging
(Copeland et al., 1990).
• In addition, old age is often associated with a low-grade
inflammation as demonstrated by higher levels of cytokines such as
TNFa and IL-6 (Bruunsgaard et al., 2001) and an "inflammation theory
of aging" has been proposed (Chung et al., 2001).
* Ageing sarcopenia leads to a change in body composition. The
relative contribution of fat and non-muscle fat free muscle increases
whereas the contribution of muscle decreases (Balagopal et al. 1997).
• Serum myostatin is higher in older men and women than in young
(Yarasheski et al., 2002), although there is a high variation.
*Many other changes could contribute to the net loss of muscle mass:
decreased growth hormone, IGF-1, increased myostatin and pro-
inflammatory cytokines.
===============
What is the cause of the ageing atrophy? Total number, size and
proportion of different fiber types studied in whole vastus lateralis
muscle from 15- to 83-year-old men.
J Neurol Sci. 1988 Apr;84(2-3):275-94.Links
Lexell J, Taylor CC, Sjöström M.
In order to study the effects of increasing age on the human skeletal
muscle, cross-sections (15 micron) of autopsied whole vastus
lateralis muscle from 43 previously physically healthy men between 15
and 83 years of age were prepared and examined. The data obtained on
muscle area, total number, size, proportion and distribution of type
1 (slow-twitch) and type 2 (fast-twitch) fibers were analysed using
multivariate regression. The results show that the ageing atrophy of
this muscle begins around 25 years of age and thereafter accelerates.
This is caused mainly by a loss of fibers, with no predominant effect
on any fiber type, and to a lesser extent by a reduction in fiber
size, mostly of type 2 fibers. The results also suggest the
occurrence of several other age-related adaptive mechanisms which
could influence fiber sizes and fiber number, as well as enzyme
histochemical fiber characteristics.
=========================
Skeletal muscle atrophy in old rats: differential changes in the
three fiber types.
Mech Ageing Dev. 1991 Oct;60(2):199-213.
Holloszy JO, Chen M, Cartee GD, Young JC.
This study was undertaken to reevaluate the effects of ageing on
skeletal muscle mass and on mitochondrial and glycolytic enzyme
levels in the different types of skeletal muscle in rats. It was
found that some muscles atrophy with ageing, while others do not, in
male rats. Atrophy appears to occur in weight-bearing muscles, and is
most marked in those with a high proportion of type IIb fibers. The
muscles that did not atrophy are non-weight-bearing, and include the
epitrochlearis (predominantly type IIb fibers) and the adductor
longus (predominantly type I fibers). The average cross-sectional
area of muscle fibers in the plantaris muscles of 28-30-month-old
rats was approximately 30% smaller than that of 9-10-month-old
animals, providing evidence that the approximately 30% lower weight
of the plantaris in the old group was entirely due to fiber atrophy.
The proportion of type IIa fibers was decreased and the proportion of
type I fibers was increased in the plantaris of the old rats. The
respiratory capacity of the soleus muscle (predominantly type I
fibers), and the glycolytic capacity of the superficial, white (type
IIb) and deep, red (predominantly type IIa) portions of the vastus
lateralis, were reduced in the old rats. Our results provide evidence
that ageing has differential effects on the three types of skeletal
muscle fiber, and on weight-bearing and non-weight-bearing muscles,
in the rat.
twitch). Below are a few presentation notes from Dr Henning
Wackerhage (Molecular Exercise Physiology Atrophy):
The primary problem in ageing sarcopenia appears to be a loss of a-
motor neurones (Tomlinson & Irving, 1977;Kawamura et al., 1977). As a
result, almost half of the muscle fibres are lost from the age of 20
to the age of 80, at least in the vastus lateralis (Lexell et al.
1988).
Ageing sarcopenia is a very slow process. Lexell et al.'s (1988) data
suggest that » 12 fibres out of half a million are lost daily from
the age of 20 to the age of 80 years. Similarly, a hypothetical loss
of 10 kg of muscle mass over 40 years equates to a daily muscle loss
of ≈ 0.7 g. Thus, the net muscle changes are very hard to detect.
• Type 2 fibres atrophy and the percentage of type 2 fibres decreases
(Lexell et al. 1988).
• Basal protein synthesis and degradation are probably unchanged
(Dorrens & Rennie, 2003). However, the response to resistance
training and nutrition is likely to be different.
• The slow elimination of fibres and myonuclei is likely due to
apoptosis, at least in rats (Dirks & Leeuwenburgh, 2002;Pollack et
al., 2002).
• Aging causes cell death and functional changes in the
neuroendocrine system (Rehman & Masson, 2001) and this affects the
growth environment of the muscle.
• The pulse amplitude of growth hormone secretion (Finkelstein et
al., 1972) and systemic IGF-1 concentrations decrease with aging
(Copeland et al., 1990).
• In addition, old age is often associated with a low-grade
inflammation as demonstrated by higher levels of cytokines such as
TNFa and IL-6 (Bruunsgaard et al., 2001) and an "inflammation theory
of aging" has been proposed (Chung et al., 2001).
* Ageing sarcopenia leads to a change in body composition. The
relative contribution of fat and non-muscle fat free muscle increases
whereas the contribution of muscle decreases (Balagopal et al. 1997).
• Serum myostatin is higher in older men and women than in young
(Yarasheski et al., 2002), although there is a high variation.
*Many other changes could contribute to the net loss of muscle mass:
decreased growth hormone, IGF-1, increased myostatin and pro-
inflammatory cytokines.
===============
What is the cause of the ageing atrophy? Total number, size and
proportion of different fiber types studied in whole vastus lateralis
muscle from 15- to 83-year-old men.
J Neurol Sci. 1988 Apr;84(2-3):275-94.Links
Lexell J, Taylor CC, Sjöström M.
In order to study the effects of increasing age on the human skeletal
muscle, cross-sections (15 micron) of autopsied whole vastus
lateralis muscle from 43 previously physically healthy men between 15
and 83 years of age were prepared and examined. The data obtained on
muscle area, total number, size, proportion and distribution of type
1 (slow-twitch) and type 2 (fast-twitch) fibers were analysed using
multivariate regression. The results show that the ageing atrophy of
this muscle begins around 25 years of age and thereafter accelerates.
This is caused mainly by a loss of fibers, with no predominant effect
on any fiber type, and to a lesser extent by a reduction in fiber
size, mostly of type 2 fibers. The results also suggest the
occurrence of several other age-related adaptive mechanisms which
could influence fiber sizes and fiber number, as well as enzyme
histochemical fiber characteristics.
=========================
Skeletal muscle atrophy in old rats: differential changes in the
three fiber types.
Mech Ageing Dev. 1991 Oct;60(2):199-213.
Holloszy JO, Chen M, Cartee GD, Young JC.
This study was undertaken to reevaluate the effects of ageing on
skeletal muscle mass and on mitochondrial and glycolytic enzyme
levels in the different types of skeletal muscle in rats. It was
found that some muscles atrophy with ageing, while others do not, in
male rats. Atrophy appears to occur in weight-bearing muscles, and is
most marked in those with a high proportion of type IIb fibers. The
muscles that did not atrophy are non-weight-bearing, and include the
epitrochlearis (predominantly type IIb fibers) and the adductor
longus (predominantly type I fibers). The average cross-sectional
area of muscle fibers in the plantaris muscles of 28-30-month-old
rats was approximately 30% smaller than that of 9-10-month-old
animals, providing evidence that the approximately 30% lower weight
of the plantaris in the old group was entirely due to fiber atrophy.
The proportion of type IIa fibers was decreased and the proportion of
type I fibers was increased in the plantaris of the old rats. The
respiratory capacity of the soleus muscle (predominantly type I
fibers), and the glycolytic capacity of the superficial, white (type
IIb) and deep, red (predominantly type IIa) portions of the vastus
lateralis, were reduced in the old rats. Our results provide evidence
that ageing has differential effects on the three types of skeletal
muscle fiber, and on weight-bearing and non-weight-bearing muscles,
in the rat.