The benefits of strength training in the elderly

Abstract

Topics - The number of people reaching advanced adult age in many countries of the world has increased dramatically in the last century, The main problem associated with aging is the loss of functional capacity and independence. An important contributor to this problem is the age-related decline in muscle mass (sarcopenia) and strength seen in both men and women. Longitudinal studies show a loss of approximately 1-2% per year in isokinetic strength of the knee. Changes in the elbow flexors and extensors were less dramatic and more significant in men than women. Although muscle atrophy is a significant contributor to the weakness seen in the elderly, single fiber studies have demonstrated a loss of muscle fiber quality (specific force). This may be due to alterations in the myosin molecule. Perspectives - Strength training has been shown to partially reverse age-related losses in muscle function, Progressive resistance training results in dramatic increases in muscle strength, significant hypertrophy (although to a lesser degree), an increase in protein synthesis, an increase in muscle fiber specific force, and changes in functional tests such as walking speed and stair-climbing power. It remains to be seen whether the myosin molecule is altered with strength training. (C) 2002 Editions scientifiques et m6dicales Elsevier SAS.

Full text

Science & Sports 2002 ;17 :109-16
2002 Éditions scientifiques et médicales Elsevier SAS. Tous droits réservés
S0765-1597(02)00135-1/REV Revue générale
The benefits of strength training in the elderly ✩
Walter R. Frontera1∗, Xavier Bigard2,1
1Department of Physical Medicine and Rehabilitation, Harvard Medical School and Spaulding Rehabilitation
Hospital, Boston, MA, USA; 2CRSSA, BP 87, 38702 La Tronche cedex, France
Summary
Topics –
The number of people reaching advanced adult age in many countries of the world has increased
dramatically in the last century. The main problem associated with aging is the loss of functional capacity and
independence. An important contributor to this problem is the age-related decline in muscle mass (sarcopenia)
and strength seen in both men and women. Longitudinal studies show a loss of approximately 1–2% per year
in isokinetic strength of the knee. Changes in the elbow flexors and extensors were less dramatic and more
significant in men than women. Although muscle atrophy is a significant contributor to the weakness seen in the
elderly, single fiber studies have demonstrated a loss of muscle fiber quality (specific force). This may be due to
alterations in the myosin molecule.
Perspectives –
Strength training has been shown to partially reverse age-related losses in muscle function.
Progressive resistance training results in dramatic increases in muscle strength, significant hypertrophy (although
to a lesser degree), an increase in protein synthesis, an increase in muscle fiber specific force, and changes in
functional tests such as walking speed and stair-climbing power. It remains to be seen whether the myosin
molecule is altered with strength training. 2002 Éditions scientifiques et médicales Elsevier SAS
aging / myosin / resistance training / sarcopenia / skeletal muscle
Résumé – Les bénéfices de l’entraînement en force chez les personnes âgées. (Synthèse française du
texte.)
Actualités – Le nombre de personnes atteignant un âge avancé a considérablement augmenté au cours
du siècle dernier. L’une des conséquences majeures liées à ce vieillissement tient à la baisse de la
capacité fonctionnelle et à l’autonomie des personnes âgées. Cette incapacité fonctionnelle progressive est
essentiellement liée à une réduction de la masse musculaire (sarcopénie) et de la force développée. L’attrition
des performances musculaires affecte aussi bien les hommes que les femmes. Des études longitudinales ont
permis d’estimer à 1–2% la perte de force annuelle enregistrée en mode isocinétique. Il semble exister une
spécificité du sexe dans la réponse des performances musculaires au vieillissement puisque la perte de force en
mode isocinétique est plus marquée chez les hommes que chez les femmes. Cependant, les niveaux de force
étant plus élevés chez les hommes à l’âge adulte, les effets du vieillissement ont chez eux des conséquences
fonctionnelles moins marquées. L’amyotrophie est un des facteurs qui permettent de rendre compte de la baisse
de la production de force. Cependant, des études sur fibres isolées ont permis de suggérer que des altérations
biochimiques complexes participent aussi à expliquer la baisse de performance au cours du vieillissement.
Parallèlement à l’amyotrophie, on enregistre une véritable diminution de la capacité qu’ont les fibres à produire
de la force. L’origine de ce dysfonctionnement reste obscure mais pourrait impliquer les propriétés de la molécule
de myosine elle-même dont la synthèse et le taux de renouvellement sont ralentis.
Perspectives – L’entraînement en force annule ou presque, les effets de l’âge sur les performances musculaires.
Ce type d’entraînement se traduit par une augmentation de la masse musculaire résultant principalement d’une
✩Conférence prononcée lors du XXème Congrès International de Médecine du Sport, Paris-Maison de l’UNESCO, 6–8 décembre 2000, France.
∗Correspondence and reprints: Walter R. Frontera, MD, PhD, Department of Physical Medicine and Rehabilitation, Spaulding Rehabilitation Hospital,
125 Nashua Street, Boston, MA, 02114, USA.
E-mail addresses: frontera.walter@mgh.harvard.edu (W.R. Frontera), BigardXavier@compuserve.com (X. Bigard).
1This author has written the abridged French version.

110 W.R. Frontera, X. Bigard
augmentation des synthèses protéiques. Les performances de force sont elles aussi améliorées, au niveau du
muscle entier comme de la fibre elle-même ; les effets de l’entraînement en force chez le sujet âgé se traduisent
par une amélioration de tests fonctionnels simples comme la vitesse de marche ou la montée d’escaliers.
Les réponses spécifiques des isoformes de la myosine à l’entraînement chez le sujet âgé restent cependant
à déterminer.

2002 Éditions scientifiques et médicales Elsevier SAS
entraînement en résistance / muscle squelettique/ myosine/ sarcopénie / vieillissement
1. DEMOGRAPHICS OF AGING
Demographical data suggest that, by the year 2025, the
number of people above age 60 in all the countries in the
world will exceed one billion [27]. Rowe and Kahn have
stated in their book “Successful Aging” that in the forty-
five hundred yearsfrom the Bronze Age to the year 1900,
life expectancy increased twenty-seven years, and that in
the short period from 1900 to 1990 it increased by at least
that much [24]. In fact, it is currently estimated that of all
human beings who have ever lived to be sixty-five years
or older, half are currently alive [24]. These are impressive
changes in the age composition of our society. However,
as stated by Banks and Fossel [2], chronological age per
se does not determine aging.
The main problem associated with advanced adult age
is the dramatic decline in functional capacity and the asso-
ciated loss of independence. Since maximal physiological
capacities are greatly diminished with aging, the ability to
perform physical tasks at the same level of energyexpen-
diture or muscular force becomes limited. In other words,
an activity that represents a submaximal effort in young
adults, such as rising from a chair, could become a maxi-
mal or supramaximal endeavor in the elderly. Research
to understand the basis for this decline in physiological
capacity and functional abilities is urgently needed. Like-
wise, clinical studies to test the efficacy of new preventive
and rehabilitative strategies are necessary.
One important contributor to the functional loss that re-
sults in impairment and disability is the decline in skeletal
muscle strength and mass (sarcopenia) associated with ad-
vancing age. It has been established that skeletal muscle
strength correlates with walking speed, balance, time to
rise from a chair, ability to climb stairs, incidence of falls,
and survival rates [21]. Furthermore, muscle strength has
been demonstrated to be a predictor of physical dysfunc-
tion (Fig. 1) in a large recent 5 year longitudinal study
of strength and disability [3]. Thus, understanding the
mechanism underlying contractile muscle dysfunctionhas
significant functional implications and could help us de-
sign better rehabilitative programs to enhance indepen-
dence in the elderly.
Figure 1. Muscular strength and physical function. Percentage of
subjects with functional problems after 5 years. * P<0.05. Adapted
from Brill et al., 2000.
This brief paper summarizes some of the research on
the loss of skeletal muscle mass and strength with ad-
vanced adult age. It is our objectiveto also emphasize the
effects of strength (heavy resistance) training programs on
skeletal muscle function and structure in older men and
women. Due to the limitations in space, we will not at-
tempt to present a comprehensive analysis of the scientific
literature on the topic. Emphasis will be given to the re-
sults of our cross-sectional and longitudinal studies and,
when appropriate, reference will be made to many excel-
lent studies published in the literature.
2. SKELETAL MUSCLE IN THE ELDERLY
2.1. Muscle strength
A cross-sectional study of muscle strength and mass in
45- to 78-yr-old men and women showed that isokinetic
strength of the elbow and knee extensors and flexors
was lower (range 15.5–26.7%) in the 65- to 78- than in
the 45- to 54-yr-old men and women [6]. Other cross-
sectional studies have reported similar differences in
strength among age groups. More recently, approximately
10 years after the baseline evaluation, we tested again
64% of the volunteers (54 men and 78 women) who
participated in that cross-sectional study [10]. Significant
losses were observed in the isokinetic strength of the knee

The benefits of strength training in theelderly 111
Figure 2. Annualized changes in isokinetic strength of the knee and
elbow extensors and flexors in men and women over a period of ten
years.
and elbow extensors and flexors of both, men and women
(Fig. 2). Men demonstrated a higher absolute strength
than women in all muscle groups and lost absolute
strength at a faster rate than women.
This recent study gave us the opportunity to compare
strength losses using cross-sectional and longitudinal de-
signs in the same cohort of subjects. No sex-related dif-
ferences were seen in the cross-sectional design; thus the
data were combined. However, in men, longitudinallosses
of muscle strength in the knee extensorsand flexors were
significantly higher than cross-sectional losses suggesting
that cross-sectional studies may underestimate the decline
in strength with age. This may be due to the bias intro-
duced by the selection of healthier (i.e., those who have
survived) older groups in cross-sectional studies. On the
other hand, for the elbow extensors and flexors, cross-
sectional and longitudinal analysis revealed similar rates
of changes, except for the elbow flexors in women.
Finally, it is of interest to note that, depending on the
muscle group and sex, between 7 and 32% of the subjects
showed gains in muscle strength. Thus, muscle atrophy
and weakness is not a homogeneous and universal phe-
nomenon. The genetic, physiological, and environmental
factors preventing muscle weakness with advancing age
in some subjects must be understood and deserve serious
study.
2.2. Muscle size and composition
A reduction in muscle size explains, at least partially,
the muscle weakness commonly seen in the elderly. The
relative contribution of muscle atrophy, however, is not
clear. In a subset of subjects (n=9) participating in
our longitudinal study, strength at the time of the first
evaluation and the change in muscle cross-sectional area
determined by computerized tomography over 12 years
accounted for 90% of the variability in strength in the
second evaluation [7]. In that group, a 25% decline in
the strength of the knee extensors was accompanied by
a 16% reduction in muscle cross-sectional area by CT. It
is of interest to note that macroscopic changes in thigh
cross-sectional area may reflect not only muscle atrophy,
but also an increase in the amount of non-contractile
tissues (i.e., fat and connective tissue). For example, Kent-
Braun et al. [13], have recently reported differences in the
relative composition of the thigh between young and older
subjects as determined by magnetic resonance imaging.
In that study, the % of the muscle cross-sectional area
representing contractile tissue was reduced from 94 to 86
andfrom94to84inoldermenandwomen,respectively.
In addition to muscle wasting, a change in muscle
quality could also contribute to muscle weakness in the
elderly. Indeed,a report from the Baltimore Longitudinal
Study show a reduction in the in vivo strength to whole
muscle size ratio [18]. It is of significant scientific interest
to determine if specific age-related cellular alterations
in skeletal muscle contribute to contractile dysfunction
independently of the absolute reduction in the amount of
the contractile proteins such as actin and myosin.
2.3. Studies of single human muscle fibers
Muscle fiber segments obtained using the percutaneous
muscle biopsy needle technique and chemical skinning
can be used to study the possibility of changes in specific
force (strength corrected for size) due to alterations in the
intrinsic ability of muscle fibers to generate force. With
this method, the contractile properties of single fibers
obtained using the biopsy needle, can be studied isolated
from the influences of the nervous system. Also, since
the process of chemical skinning disrupts the sarcolemma
and sarcoplasmic reticulum, and the concentration of
the substances present in the medium can be carefully
controlled, weakness in single fibers can be interpreted as
representing structural and/or functional alterations in the
regulatory and/or contractile proteins.
Recently, we reported an age-related reduction in the
specific force (Fig. 3) of single muscle fiber segments
expressing type I and IIa myosin heavy chain isoforms
(determined by SDS-PAGE) in older men [8]. Fibers from
older men demonstrated significantly lower specific forces
than younger men expressing the same myosin heavy
chain isoform. In young and older men, fibers expressing
type IIa myosin heavy chain had higher specific forces
than type I fibers. Also, our results demonstrated signi-
ficant differences in single fiber maximal force between
older men and women that were dependent on fiber type
and that could not explained by differences in fiber size.
2.4. Myosin molecule alterations
One possible site for the alteration resulting in contrac-
tile dysfunction is the cross-bridge and more specifically

112 W.R. Frontera, X. Bigard
Figure 3. Specific force of single skeletal muscle fibers expressing type I
or IIa myosin heavy chain isoform in young and older men. n=number
of fibers; * =young >old, P<0.001; # =young IIa >young I,
P<0.001; ** =old IIa >old I, P<0.005.
the myosin protein. An age-relateddecline in the synthe-
sis rate of the myosin heavy chain has been observed in
humans [1]. At least three molecular/cellularmechanisms
may contribute to a quantitative or qualitative alteration
in the myosin motor: 1) a reduction in gene transcrip-
tion; 2) a slow protein turnover rate resulting in accumu-
lation of dysfunctional myosinmolecules; and/or 3) post-
translational modifications of the myosin protein such as
glycosylation or oxidation.Alone or in combination,these
changes could alter the basic properties of the molecule
resulting in a reduction in the force generated per cross-
bridge. In fact, recent data from Lowe et al. [16], sup-
port this hypothesis. Alterations in the ATPase site of the
myosin molecule couldalso result in changes in other con-
tractile properties of the muscle fiber such as its shorte-
ning velocity. This is supported by the work of Höök et al.
[9], using an in vitro motility assay to study rat muscle.
3. STRENGTH TRAINING IN THE ELDERLY
Since 1988, at least 50 studies have been published in
the scientific literature on the effects of strength training
in older men and women. Despite some differences in
the magnitude of the effect, the vast majority of the
data demonstrate that strengthening exercises result in
significant improvements in skeletal muscle function.
Muscle hypertrophy, cellular adaptations, and changes
in the performance of functional tasks have also been
reported.
3.1. The exercise prescription
Strength training studies have used various combinations
of frequency,intensity, and duration. The type of exercise
and training devices has include free weights, pulleys, and
isokinetic and variable resistance devices. Most studies
have used 5–15 repetitions per set and 2–6 sets per
training session for each muscle group. The weekly
frequency of training has ranged between 2 and 5 days and
the intensity of the training has varied from 40 to 90% of
the one repetition maximum; in most studies the subjects
trained at the 60–80% range. Short (2 weeks) and long
duration studies (1–2 years) have been reported although
most studies are in the 12–24 week range.
3.2. Adaptations in muscle strength
Static and dynamic (including isokinetic) muscle strength
has been shown to increase significantly with strength
training in the young old, old, and even in the frail
elderly [4, 5, 15, 17, 19]. The relative magnitude of
the strength gains ranges between 10 and 180% of the
baseline. The wide range is probably due to the variety
of exercise prescriptions used in the different studies.
The adaptations in strength are noticeable after a few
days of training and are more significant when the
testing technique is similar to the training method. This
observation is very consistent across studies and suggests
that a significant component of the adaptation is neural
and is independent of the peripheral adaptations that occur
in the muscle itself. Although the nature of the neural
adaptations remains vague there is significant indirect
evidence (angle specificity, velocity specificity, cross-over
effect) supporting this hypothesis [14].
With regard to the changes in strength, two interesting
observations must be highlighted. First, it has been noted
that even after long-term training (1–2 years) strength
improvements do not appear to reach a plateau and further
gains appear to be possible [17, 19]. Second, it is feasible
to interrupt training with a period of deconditioning and
continue to show gains in strength after resumption of
training [15].
3.3. Muscle hypertrophy
The majority of studies measuring muscle cross-sectional
area using ultrasound, computerized tomography, or ma-
gnetic resonance imaging have reported significant skele-
tal muscle hypertrophy (range: 2.0–14.5%). Metabolic
studies have shown significant increases in the urinaryex-
cretion of 3-methylhistidine. Clearly, skeletal muscle is
capable of responding to the stimulus of strengthtraining
with an increase in the synthesis of contractile proteins
[28, 29]. These improvements, however, were not en-
hanced when strength training was combined with growth
hormone. Hypertrophyhas been also demonstrated (5 out
of 7 studies) at the microscopic level using histochemi-
cal techniques to study muscle fiber cross-sectional area
in biopsy specimens. Increases of up to 30% have been
noted in both type I and type II fibers after training. It is

The benefits of strength training in theelderly 113
Figure 4. Percent of muscle fibers exhibiting ultrastructural muscle
damage before and after strength training in men. Significantly different
from values measured before training, * P<0.05. @, 24–48 h after the
last training session. Adapted from Roth et al., 1999.
significant to note the differences in the relative change in
strength and muscle size; again emphasizing the impor-
tance of the neural adaptations.
3.4. Cellular and ultrastructural adaptations
Several recent studies have looked at the cellular and
ultrastructural adaptations with strength training. Trappe
et al. [25], recently reported significant increases in the
maximal force and cross-sectional area of type I and
IIa single muscle fibers after 12 weeks of progressive
resistance training. It is interesting that, the unloaded
maximum shortening velocity and power of single muscle
fibers were also increased. A second report from the
same group of researchers demonstrated an increase in
the expression of the type I myosin heavy chain isoform
and a reduction in the frequency of co-expression of
myosin heavy chain isoforms in the same fiber [26] after
training.
Since strength training usually includes eccentric mus-
cle actions, and such actions could induce muscle damage,
it is of importance to know if the elderly are more sus-
ceptible to muscle damage during strength training. Two
studies from the same group [22, 23] demonstrate the
same degree of focal muscle damage with heavy resis-
tance training occur in young and older men (Fig. 4).
However, older women exhibited higher levels of muscle
damage than young women. The sex-related differences
in the response to strength training deserves furtherinves-
tigation [12].
The effect of strength training on other cellular compo-
nents of muscle fibers has been examined. For example,
Hunter et al. [11] have reported that the reduced calcium
Figure 5. Isokinetic strength (60 deg/s) and cross-sectional area (CSA)
determined by computerized tomography scan of the extensors of the
knee: effects of aging and strength training. Adapted from Frontera et
al., 1998 and 2000.
uptake by the sarcoplasmic reticulum in skeletal muscle
of elderly women was partially reversed with resistance
training. Also, the activity of the sarcoplasmic reticulum
ATPase was enhanced after training. These adaptations
did not translate, however, into changes in the time of
relaxation of whole muscle. More research is needed to
understand the effects of strength training on the various
components of the excitation-contraction coupling me-
chanism, energetic processes, and the mechanical events
leading to force generation at the level of the cross-bridges
in the elderly.
3.5. Functional implications
From a rehabilitation perspective it is important to know
if the physiological adaptations to strength training result
in an enhanced functional capacity. Indeed, after trai-
ning, older men and women show improvements in wal-
king speed and stair climbing power (for review see
[20]). If the age-associated decline in muscle strength is
partially reversed, it may be possible for the elderly to
maintain physical independence and perform, once again
with submaximal efforts, many of the activities of daily
living.
3.6. Aging vs. training
Within the limitations of the studies, it is possible to
compare, for the purposes of our discussion, the effects
of aging and the benefits of strength training as in Fig. 5.
It is important to point out that, although the two studies
involved some of the same subjects, the training study was
done first. Nevertheless, the evidence is consistent with
a partial reversal of the age-related losses with relatively
short-term strength training.

114 W.R. Frontera, X. Bigard
SYNTHÈSE FRANÇAISE
De très nombreuses études démographiques ont permis
de souligner le vieillissement constant de la population.
Ce vieillissement va croisant au cours du temps, et s’est
considérablement amplifié au cours du XXème siècle.
L’un des problèmes majeurs de ce vieillissement de la
population générale est lié à la diminution importante
des capacités fonctionnelles et de l’autonomiedes sujets.
Ainsi, des gestes communs, réalisés sans difficulté par des
adultes bien portants, sont susceptibles de représenter une
charge de travail importante pour des sujets âgés. Dans ce
domaine, des recherches sont engagées pour mieux com-
prendre les mécanismes biologiques du vieillissement et
des altérations fonctionnelles, et pour évaluer l’efficacité
de contre-mesures.
Au cours du vieillissement, la baisse de l’autonomie
est en partie liée à l’amyotrophie et à la baisse des
performances musculaires. L’importance des désordres
fonctionnels enregistrés au cours du vieillissement, est
statistiquement liée à l’altération de la force musculaire
(Fig. 1). La compréhension des mécanismes biologiques
affectant le muscle au cours du vieillissement, est donc
d’une grande importance.
1. CARACTÉRISTIQUES DU MUSCLE CHEZ LE
SUJET ÂGÉ
1.1. Force musculaire
Il est bien connu que les performances musculaires
sont affectées par le vieillissement. C’est ainsi que les
couples musculaires développés en mode isocinétique
sont diminués au cours du temps, à la fois pour les
muscles extenseurs et fléchisseurs du coude et du genou,
chez les hommes, comme chez les femmes (Fig. 2).
Cependant, bien que l’altération des performances soit
plus rapide chez les hommes que chez les femmes, ceux-
ci conservent des valeurs de couple plus élevées pour
une même tranche d’âge. Bien que la force développée
soit fonction de la masse musculaire, et par extension, de
la surface moyenne de section du groupe musculaire, au
cours du vieillissement, la perte de performance est plus
importante que l’amyotrophie.Ainsi, la simple mesure de
l’attrition de la masse musculaire sous-estime la baisse de
performances.
1.2. Le muscle, son volume et sa
composition
Comme nous venons de le préciser, on observe une amyo-
trophie au cours du temps, qui rend compte d’une par-
tie des baisse de performances musculaires. Nous avons
montré, au cours d’une étude longitudinale, que 90% de la
variabilité de la force étaient expliqués par des variations
de la surface de section du muscle, estimée par imagerie
médicale, et que pour 25% de baisse de force dévelop-
pée, les sujets présentent en moyenne16 % de baisse de la
surface moyenne de section des muscles [7]. Cependant,
les variations macroscopiquesde la surface de section des
muscles ont des limites et reflètent non seulement les va-
riations du contenu en protéines contractiles, mais aussi en
graisse et en tissu conjonctif. Parallèlement à l’amyotro-
phie, ce sont aussi les qualités intrinsèques du muscle qui
peuvent être affectées par le vieillissement ; la question du
rôle spécifique joué par des modifications des propriétés
contractiles des fibres elles-mêmes mérite d’être posée.
1.3. Les propriétés des fibres musculaires
chez le sujet âgé
Des études sur fibres isolées ont permis de mettre en
évidence une diminution de la force développée par les
fibres lentes de type I comme par les fibres rapides de type
IIa avec le vieillissement (Fig. 3) [8]. La diminution de
force pourrait être liée soit à :
1. une baisse de la transcription des gènes codant pourles
chaînes lourdes de la myosine ;
2. un ralentissement du taux de renouvellement des pro-
téines contractiles, induisant une accumulation de formes
altérées (ou «vieillissantes ») de ces protéines;
3. une altération du contrôle post-traductionnel de ces
gènes avec des anomalies de glycosylation des protéines
produites, les rendant ainsi moins fonctionnelles. Un
ou plusieurs de ces mécanismes combinés contribuent à
une baisse de la force produite par chaque pont actine-
myosine [16].
2. ENTRAÎNEMENT EN FORCE
De très nombreuses études ont permis de mettre en évi-
dence tout le bénéfice tiré de l’application de protocoles
d’entraînement en force chez le sujet âgé, en particulier
sur la fonction musculaire. Les protocoles proposés va-
rient beaucoup d’une étude à l’autre, par le type d’appareil
utilisé, le nombre de répétitions par séance, la fréquence
hebdomadaire, etc.
2.1. Les effets de l’entraînement sur la force
musculaire
Même si les durées d’application de ces entraînements va-
rient beaucoup, tous sont efficaces sur les performances
musculaires. Les progrès enregistrés dans le développe-
ment de force sont très rapides, ce qui laisse à penser
qu’une adaptation neurale à type de meilleures synchroni-
sations des motoneurones précède les réponses cellulaires
périphériques.

The benefits of strength training in theelderly 115
2.2. Les effets de l’entraînement sur la
masse musculaire
Un gain de masse musculaire est régulièrement observé
en réponse à l’entraînement en force (gain de 2 à 14,5%).
Cette hypertrophie du muscle résulte d’une augmentation
de la taille de chaque élément cellulaire, elle-même
résultant d’une augmentationde la synthèse des protéines
contractiles.
2.3. Réponses cellulaires à l’entraînement
en force
Ce type d’entraînement se traduit par une augmentation
du calibre des fibres lentes comme des fibres rapides,
de la force développée par les fibres isolées, et de
l’expression de la forme lente de la myosine (de type I).
Cependant, l’entraînement en force est associé à une
augmentation des contraintes mécaniques appliquées au
muscle, et la question de la susceptibilité des sujets âgés
aux microlésions musculaires a été posée. L’équipe de
Walter Frontera a clairement montréque les hommes âgés
répondent de la même manière, et pas plus, à l’application
d’un exercice excentrique connu pour être traumatisant
pour les fibres cellulaires (Fig. 4) [22, 23].
2.4. Conséquences fonctionnelles
Ces améliorations des performances musculaires ont des
conséquences fonctionnelles évidentes, et ce sont des aug-
mentations de la vitesse de marche ou des capacités à la
montée des escaliers qui sont rapportées [20].L’améliora-
tion des performances musculaires peut ainsi se traduire,
chez les sujets âgés, par une véritable amélioration de la
qualité de vie.
2.5. Vieillissement versus entraînement
On pourrait comparer, avec cependant une certaine pru-
dence, les effets respectifs du vieillissement et de l’en-
traînement (Fig. 5). En 12 ans, on observe une baisse de
24 % de la force développée par les extenseurs de la jambe
(et de 16 % de la surface de section de ces muscles), alors
qu’en 12 semaines d’entraînement, elle augmente de 16 %
(et de 11% pour la surface de section des muscles).
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