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Muscle strength, power and adaptions to resistance training in older people


Abstract and Figures

Muscle strength and, to a greater extent, power inexorably decline with ageing. Quantitative loss of muscle mass, referred to as "sarcopenia", is the most important factor underlying this phenomenon. However, qualitative changes of muscle fibres and tendons, such as selective atrophy of fast-twitch fibres and reduced tendon stiffness, and neural changes, such as lower activation of the agonist muscles and higher coactivation of the antagonist muscles, also account for the age-related decline in muscle function. The selective atrophy of fast-twitch fibres has been ascribed to the progressive loss of motoneurons in the spinal cord with initial denervation of fast-twitch fibres, which is often accompanied by reinnervation of these fibres by axonal sprouting from adjacent slow-twitch motor units (MUs). In addition, single fibres of older muscles containing myosin heavy chains of both type I and II show lower tension and shortening velocity with respect to the fibres of young muscles. Changes in central activation capacity are still controversial. At the peripheral level, the rate of decline in parameters of the surface-electromyogram power spectrum and in the action-potential conduction velocity has been shown to be lower in older muscle. Therefore, the older muscle seems to be more resistant to isometric fatigue (fatigue-paradox), which can be ascribed to the selective atrophy of fast-twitch fibres, slowing in the contractile properties and lower MU firing rates. Finally, specific training programmes can dramatically improve the muscle strength, power and functional abilities of older individuals, which will be examined in the second part of this review.
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Andrea Macaluso Æ Giuseppe De Vito
Muscle strength, power and adaptations to resistance training
in older people
Accepted: 4 September 2003 / Published online: 25 November 2003
Ó Springer-Verlag 2003
Abstract Muscle strength and, to a greater extent,
power inexorably decline with ageing. Quantitative loss
of muscle mass, referred to as ‘‘sarcopenia’’, is the most
important factor underlying this phenomenon.
However, qualitative changes of muscle fibres and
tendons, such as selective atrophy of fast-twitch fibres
and reduced tendon stiffness, and neural changes, such
as lower activation of the agonist muscles and higher
coactivation of the antagonist muscles, also account for
the age-related decline in muscle function. The selective
atrophy of fast-twitch fibres has been ascribed to the
progressive loss of motoneurons in the spinal cord with
initial denervation of fast-twitch fibres, which is often
accompanied by reinnervation of these fibres by axonal
sprouting from adjacent slow-twitch motor units
(MUs). In addition, single fibres of older muscles
containing myosin heavy chains of both type I and II
show lower tension and shortening velocity with respect
to the fibres of young muscles. Changes in central
activation capacity are still controversial. At the
peripheral level, the rate of decline in parameters of
the surface-electromyogram power spectrum and in the
action-potential conduction velocity has been shown to
be lower in older muscle. Therefore, the older muscle
seems to be more resistant to isometric fatigue (fatigue-
paradox), which can be ascribed to the selective atro-
phy of fast-twitch fibres, slowing in the contractile
properties and lower MU firing rates. Finally, specifi c
training programmes can dram atically improve the
muscle strengt h, power and functional abilities of older
individuals, which will be examined in the second part
of this review.
Keywords Ageing Æ Muscle power Æ Muscle strength Æ
Resistance trainin g
Human muscle strength, which can be defined as the
maximum force generation capacity of an individual,
reaches its peak between the second and third decades,
shows a slow or imperceptible decrease until about
50 years of age and then begins to decline thereafter at
the rate of approximately 12% to 15% per decade, with
more rapid losse s above the age of 65 years (Asmussen
and Heeboll-Nielse n 1962; Larsson et al. 1979; Viitasalo
et al. 1985; Vandervoort and McComas 198 6; Borges
1989; Narici et al. 1991; Metter et al. 1997; Lindle et al.
1997). Since this trend has been measured in studies with
cross-sectional design, it would not be appropriate to use
of words such as ‘‘decrease’’, ‘‘decline’’, ‘‘drop’’, etc.,
which imply that the strength of the older participants in
their younger age was the same as that of the younger
participants. This is a questionable assumption, because
the older people are of a different generation, with a
lifetime of physical activity, health and nutrition that is
probably unlike the habits of their young counterparts.
However, as it is common practice in the literature,
words such as ‘‘decrease’’, ‘‘decline’’, ‘‘drop’’, etc., will
be used throughout this review even if inappropriate.
There are few investigations with a longitudinal design
that have determined how strength changes with ageing
and, to the best of the authors knowledge, the same
individuals were followed for no longer than 12 years
(Aniansson et al. 1986; Kallman et al. 1990; Bassey and
Harries 1993; Greig et al. 1993; Winegard et al. 1996;
Rantanen et al. 1997; Frontera et al. 2000a). Most of the
studies indicate that the decline in strength occurs at a
higher rate than reported in cross-sectional investiga-
tions (Aniansson et al. 1986; Kallman et al. 1990; Bassey
and Harries 1993; Winegard et al. 1996; Frontera et al.
2000a), although no change (Greig at al. 1993) or even a
Eur J Appl Physiol (2004) 91: 450–472
DOI 10.1007/s00421-003-0991-3
A. Macaluso (&) Æ G. De Vito
Applied Physiology Department,
Strathclyde Institute for Biomedical Sciences,
University of Strathclyde, 76 Southbrae Drive,
Glasgow, G13 1PP, UK
Tel.: +44-141-9503718
Fax: +44-141-9503132
slight increase in strength (Rantanen et al. 1997) have
both been measured. Direct comparisons between
groups of young and older individuals have shown that
the quadriceps muscles of older people aged around
70 years have approximately 60% of the force-genera t-
ing ability of young individuals aged 20–30 years
(Young et al. 1984, 1985; Klitgaard et al. 1990; Ha
nen and Ha
kkinen 1991; Overend et al. 1992a; Frontera
et al. 2000b), ranging from a minimum of 56% (Klitg-
aard et al. 1990) to a maximum of 76% (Ha
kkinen and
kkinen 1991; Overend et al. 1992a). It is likely that
this variability of strength differences reflects different
study populations, levels of physical activity, muscle
groups investigated and testing methodologies. More-
over, Short and Nair (1999) pointed out that the decline
of muscle function in the whole population may be even
greater than that reported, because many older indi-
viduals are excluded from research studies for the pres-
ence of disease. Finally, further evidence of this
inevitable process of decay is given by measurements
performed on master athletes, whose performance
inexorably decline as they age, although 70-year-old
athletes can have levels of strength, power and other
functional capacities equivalent to those of 20-year-old
sedentary individuals (Moore 1975; Meltzer 1994;
Pearson et al. 2002).
The loss of strength with ageing is apparently true for
both men and women (Danneskiold-Samsoe 1984;
Vandervoort and McComas 1986; Borges 1989; Fron-
tera et al. 1991; Lindle et al. 1997). The early study of
Asmussen and Heeboll-Nielsen (1962) reported that
women began to decline at an earlier age than men, but
this observation was not confirmed in further studies.
However, it is evident that women are weaker than men
in absolute strength of various muscle groups in all
stages of life (Danneskiold-Samsoe 1984; Vandervoort
and McComas 1986; Borges 1989; Frontera et al. 1991;
Lindle et al. 1997). For example, Frontera et al. (1991)
reported that women had 60% and 59% the strength of
men in the lower extremities when they were tested at
slow and fast isokinetic speeds, respectively (the term
isokinetic indicates that the movemen t of the displaced
body segment is performed at constant angular speed).
Similarly, Borges (1989) found women in different age
groups to have 66% and 53% the isokinetic peak torque
of men in the knee-extension and knee-flexion, respec-
tively. Although males and females ap pear to show
comparable age-related trends when maximal strength is
referred to the unit of muscle cross-sectional area (CSA)
(Vandervoort and McComas 1986; Winegard et al. 1996;
Lindle et al. 1997), in the latter stages of life absolute
values of maximal strength in women can approach the
minimal levels necessary to accomplish daily activities,
thus suggesting that women should be the first target
group in intervention and rehabilitation studies (Skelton
et al. 1994).
Regional anatomical differences in the loss of
strength have also been reported in the literature
(Viitasalo et al. 1985; Frontera et al. 1991; Rantanen
et al. 1997; Lynch et al. 1999). The proximal muscles of
the lower extremities are more affected by strength losses
than those of the upper extremities, which in older
people has been ascribed to a decreasing use of lower
compared with upper limb muscles (Viitasalo et al. 1985;
Frontera et al. 1991; Lynch et al. 1999). This is sup-
ported by the fact that age-related morphologica l
changes are more pronounced in the quadriceps than in
the biceps brachii muscle (Aniansson et al. 1986). By
contrast, longitudinal data of Rantanen et al. (1997)
showed that older men and women slightly increased
their knee extensor strength from 75 to 80 years, as
opposed to a decrease in upper extremity and trunk
strength. The investigators suggested that everyday
activities at low intensity might have provided sufficient
stimulus to the knee extensor musculature. This is in
contrast, however, with the evidence that activities of
daily living require little quadriceps strength, as during
normal walking the quadri ceps is activated only briefly
at the beginning and end of the gait cycle (OToole
1997). Moreover, individuals with weak quadriceps tend
to supplement knee extensor movements with other
muscles, such as arm muscles to get up from a chair, or
alter their behaviour to avoid activities such as climbing
Muscle strength can be tested using three different
modalities: isometric, dynamic or isokinetic (Frontera
and Meredith 1989; Abernet hy et al. 1995). Isometric or
static strength is the maximum force that can be exerted
against an immovable object, which corresponds to the
maximum that can be measured in humans. Dynamic
strength is the heaviest weight that can be lifted, whilst
isokinetic strength is the maximal torque that can be
exerted against a pre-set rate-limiting device. Maximum
strength is measured during isometric contractions, in
which there is no change in muscle length, whilst power
is generated in actions that involve movement and is
calculated as the product of force and speed at which
movement occurs. Fewer studies have been conducted
on muscle power as compared to strength, possibly due
to methodological difficulties, as will be discu ssed later
in this review.
Lower levels of strength and, to a greater extent,
power are associated with functional limitations in daily
living activities (Aniansson et al. 1980; Avlund et al.
1994; Skelton et al. 1994; Foldvari et al. 2000). In
addition, muscle weakness is associated with an
increased risk of falls (Tinetti et al. 1988; Campbell et al.
1989; Wolfson et al. 1995), hip fractures (Aniansson
et al. 1984; Langlois et al. 1998) an d adverse physio-
logical changes such as loss of bone mineral density
(Sinaki et al. 1986), which may predispose to osteopo-
This review begins with a systematic examination of
the main causes of muscle strength loss in old age. This
is then followed by a review of the few studies specifi-
cally investigating musc le power, with power being more
related to daily functional activities than strength per se.
Finally, the focus is on how these age-related changes in
muscle function can be improved through appropriate
training programmes. Some of the studies on strength
training in older people will be critically scrutinized,
followed by the more limited number of investigations
specifically aimed at improving muscle power and the
few works looking at the effects of training on selected
functional abilities.
Causes of muscle strength loss in old age
Muscle size and morphology
Muscle size is reduced with ageing an d this quantitative
loss of muscle, referred to as ‘‘sarcopenia’’ (Evans 1995),
affects the generation of force. Sarcopenia has been
demonstrated using various techniques, which include
measurements of total body potassium (Allen et al.
1960) or creatini ne excretion (Tzankoff and Norris
1977), histoch emical analysis of muscle fibres, in either
biopsy (for example Larsson et al. 1979) or autopsy
(Lexell et al. 1983, 1988) specimens, and imaging
methods such as ultrasonography (Young et al. 1984,
1985; Ha
kkinen and Ha
kkinen 1991), computerized
tomography (CT) (Rice et al. 1989; Klitgaard et al. 1990;
Overend et al. 1992b) and, more recently, magnetic
resonance imaging (MRI) (Jubrias et al. 1997; Kent-
Braun and Ng 1999; Kent-Braun et al. 2000).
In the early study of Allen et al. (1960) muscle mass
was reduced by 23% in individuals from 20 to 80 years,
as estimated from measurements of total body potas-
sium. Similarly, Tzankoff and Norris (1977), at the end of
the 1970s, reported that the active muscle mass, as
revealed by creatinine excretion, was 35% less in 80-year-
old individuals as opposed to those in their twenties.
Grimby and Saltin (1983) later pointed out that the loss
of muscle mass, which had been reported in the studies of
Allen et al. (1960) an d Tzankoff and Norris (1977), was in
the same order of magnitude as the decline of strength
in leg, back and arm muscles, thus relating the weakness
of older people entirely to muscle wasting.
Starting in 1977 with Tomonaga, many investigators
have carried out a quantitative histochemical analysis of
muscle samples, obtained either by biopsy (for example
Larsson et al. 1979) or autopsy (for example Lexell et al.
1983, 1988), and have attributed the loss of muscle mass
in older people, at the microscopic level, to a reduction
in the number and size of muscle fibres. An extensive
review of these studies is beyond the purposes of this
manuscript and therefore the reader is referred to the
work of Lexell (1995). The loss of muscle tissue in older
people has been attributed to reduced numb ers of both
slow-twitch fibres and fast-twitch fibres, plus a reduction
in the CSA of single fibres, especially of type II. Fast-
twitch fibres are intrinsically stronger than slow-twitch
fibres and therefore muscles with the same area, but
occupied by a relatively smaller area of fast-twitch fibres,
will be able to generate less force (Jones and Round
With the introduction of modern radiological imag-
ing techniques, it has been possible to estimate muscle
mass more directly. Sarcopenia has been documented
with ultrasound imaging in the works of Young et al.
(1984, 1985), who measured a 25% and 33% small er
quadriceps CSA in older men an d women, respectively,
(age range 70–81 years) than in young individuals (age
range 20–29 years). Also Ha
kkinen and Ha
(1991) have shown a 27% smaller mid-thigh CSA of the
quadriceps in older women aged between 66 and
75 years, as compared to the young, aged between 26
and 35 years. In these studies, however, muscle CSA
may have been overestimated, particularly in older
people, due to the presence of fat and connective tissue
within the muscle belly, which cannot be detected and
separated in the ultrasound scan. This problem has been
overcome by the use of CT and MRI (Rice et al. 1989;
Overend et al. 1992b; Kent-Braun et al. 2000), which
enabled investigators not only to outline the muscle
compartment area on each scan, at different levels of
section, but also to estimate the muscle contractile
component separately from the intramuscular non-
contractile tissues (i.e. connective and fat tissue). The
correlation coefficient between cadaver sections of
human skeletal muscle and corresponding CT or MRI
scans approached unity, with the relative difference be-
tween cadaver and imaging measurements being 1.3%
for both techniques (Mitsipoulos et al. 1998). The use of
both these advanced imaging techniques has provided
further evidence of the wasting of contractile muscle
occurring in older people with a substantial increase of
fat and connective tissue, both within the muscle and in
the overall body (Rice et al. 1989; Overend et al. 1992b;
Jubrias et al. 1997; Kent-Braun and Ng 1999; Janssen
et al. 2000; Kent-Braun et al. 2000; Macaluso et al.
2002). In particular, the recent data of Janssen et al.
(2000), which present reference values for whole-body
skeletal mass of 468 individuals from 18 to 88 years,
show a decline after the end of the fifth decade of 1.9 and
1.1 kg/decade in men and women, respectively, with a
preferential decrease in the lower body.
Comparing the time course of the decline in muscle
mass with that of the decline in force indicates that the
decline in force with ageing is generally greater and
starts sooner than that of muscle bulk (Bruce et al.
1997). Similarly, Kallman et al. (1990) have shown that
there is no relationship between how quickly subjects
lose muscle mass, as indicated by the slope of creatinine
excretion versus age, and how fast they lose grip
strength, as indicated by the slope of grip strength versus
age. This suggests that there may be other causes con-
tributing to the decline in strength, other than muscle
wasting, which are specific to the remai ning muscle. In
further support of this observation, some investigators
have shown that muscle strength of the knee extensors is
highly correlated with muscle size, but this relationship
is higher in young than older populations (Ha
and Ha
kkinen 1991; Overend et al. 1992a). In most of
the research studies, however, it is the ratio between
muscle strength and CSA, referred to as specifi c
strength, which has been compared between young and
older people, or examined across the life span, in order
to determine whether strength losses could be attributed
entirely to reduced muscle mass or whether other factors
had to be taken into account (Young et al. 1984, 1985;
Klitgaard et al. 1990; Ha
kkinen and Ha
kkinen 1991;
Phillips et al. 1993; Jubrias et al. 1997; Kent-Braun and
Ng 1999; Frontera et al. 2000b). The results of these
studies are still controversial. You ng et al. (1985 ) and
Klitgaard et al. (1990) have reported that the isometric
specific strength of quadriceps muscle was 19% and
27% smaller, respectively, in young than older sedentary
men. Similarly, other studies have observed a drop of
isometric (Phillips et al. 1993) and isokinetic (Jubrias
et al. 1997) specific strength of adductor pollicis and
quadriceps muscles, respectively, in older subjects of
both genders. Conversely, Kent-Braun and Ng (1999)
and Frontera et al. (2000b) have reported no age-related
differences in isometric strength of the ankle dorsiflexors
and isokinetic strength of the knee extensors, respec-
tively, after adjusting for CSA. Young et al. (1984) and
kkinen and Ha
kkinen (1991) have also indicated that
the quadriceps weakness of healthy women in their
seventies can be adequately explained by the similarly
smaller size of the muscle group. All of these investiga-
tors (Young et al. 1984, 1985; Klitgaard et al. 1990;
kkinen and Ha
kkinen 1991; Phillips et al. 1993;
Jubrias et al. 1997; Kent-Braun and Ng 1999; Frontera
et al. 2000b) have used the area of muscle cross-section
at right angles to the long axis of the limb, referred to as
anatomical CSA, to interpret data on muscle strength
relative to muscle size in ageing muscle. However, in
pennate muscles, such as the quadriceps, fibres run ob-
liquely to the force-generating axis and insert into the
tendon with an angle, referred to as ‘‘angle of penna-
tion’’ (Narici et al. 1992). Therefore, the anatomical
CSA cuts a limited number of fibres, whilst it is the sum
of the cross-sectional areas of all the muscle fibres within
the muscle which should be used. This has been referred
to as physiological CSA (PSCA), which can be calcu-
lated by measuring, with a combined use of MRI and
ultrasonography, three parameters: muscle volume, fibre
length and pennation angle. It has been recently found
that pennation angle and fibre length in the human
gastrocnemius were 13% and 8% less in older than
young individuals, respectively (Narici et al. 1999).
Therefore, PCSA is expected to decrease with ageing at a
different rate than anatomical CSA, which may lea d to a
misinterpretation of the ratio between force and CSA
(Narici 1999). Recently, Miyatani et al. (2001) have
suggested that determination of muscle volume is a way
of approximating its physiological CSA. Moreover,
because the muscle volume can be expressed as a pro-
duct of physiological CSA and muscle fibre length,
torque relative to muscle volume may theoretically be
considered as an index with the same dimension as that
of muscle force relative to physiological CSA, i.e. spe-
cific tension (kNÆm
) (Miyatani et al. 2001). In light of
these considerations, Macaluso et al. (2002) have
expressed the specific tension of the knee extensors and
flexors as the ratio between maximum isometric torque
and contractile muscle volume, distinguished from
intramuscular non-contractile tissue, and compared it
between young and older women. Women in their
seventies showed a lower specific tension than women in
their twenties, thus suggesting that the lower level of
muscle strength in older women is not completely
explained by their smaller contractile muscle mass, but
also by other factors, which will be presented in the
following paragraphs of this review.
Muscle excitability and contractility
Narici (1999), in his comprehensive review of studies on
the changes of muscle contractile properties with ageing,
has attributed the loss of strength in older people not
only to reduced muscle mass but, more exhaustively, to
reduced excitable muscle mass. Therefore, it is suggested
to take into account only the amo unt of muscle that is
functionally active, as indicated by the term ‘‘excitable’’.
This is strictly dependent, in turn, on the integrity of
both the muscle fibres and the nerve cells that control
them, namely the motoneurons. Neural and muscular
systems cannot therefore be separated and it is appro-
priate to consider muscle fibres and motoneurons as a
whole. A single motoneuron and its family of innervated
muscle fibres have been defined by Sherrington (1929) as
the motor unit (MU). Fast-twitch MUs are composed by
relatively large motoneurons with fast conduction
velocities, which generally innervate between 300 and
500 muscle fibres (McArdle et al. 1996). On the contrary,
slow-twitch MUs are composed of smaller motoneurons
with slow conduction velocities, which innervate a
smaller number of fibres. There are at least nine elec-
trophysiological techniques of MU estimation in hu-
mans, most of which involve applying electric shocks of
varying intensity to a peripheral nerve and measuring
the evoked responses in the muscle (for review see
McComas 199 8). The number of MUs is obtained by
comparing an average parameter of the single MU,
usually its action potentials, with the corresponding
parameter of the whole muscle. The relative size of MUs
is determined by comparing their mechanical responses
to single or maximal repetitive stimulation, which are
referred to as twitch or tetanic contractions, respectively.
MUs have been shown to be reduced with ageing in both
number and size, thus affecting the capacity of skeletal
muscles to produce force (Brown et al. 1988; Doherty
and Brown 1993; Doherty et al. 1993). This is in agree-
ment with previous evidence of a reduced number of
limb motoneurons, in the human lumbosacral cord, by
approximately 25% from the second to the tenth decade
(Tomlinson and Irving 1977). Consistent wi th this
observation is the reduction in the number and diameter
of motor axons in the ventral roots (Kawamura et al.
1977a, 1977b), which is accompanied by slower axonal
conduction velocity (Metter et al. 1998; Wang et al.
1999). In animal studies, the selective atrophy of fast-
twitch fibres, which has been reported earlier in this re-
view, has been ascribed to the progressiv e loss of
motoneurons in the spinal cord with initial denervation
of fast-twitch fibres and reinnervation of these fibres by
axonal sprouting from adjacent slow-twitch MUs
(Brooks and Faulkner 1994). This phenomenon of
remodelling is supported, at the microscopic level of
muscle analysis in humans, by morphological changes
similar to those occurring in motoneuron diseases and
chronic neuropathies, which include the presence of
larger groups of muscle fibres of the same histochemical
type, referred to as fibre type grouping, small and dark
fibres with a peculiar geometrical shape, referred to as
angulated fibres, and group atrophy (Jennek ens et al.
1971; Lexell and Downham 1991). Recent results of in-
creased coexpression of myosin heavy chain (MHC)
isoforms in the same fibre as measured with electro-
phoretic techniques, which will be presented later in this
review, are further evidence of this process of ongoing
denervation and reinnervation (Andersen et al. 1999).
Results of Galea (1996) suggest that the reduction of
excitable muscle mass in the upper limbs is of neuro-
pathic origin, i.e. denervation of MUs due to loss of
peripheral motoneurons, for distal muscles, but of
myopathic origin, i.e. atrophy of muscle fibres, in
proximal muscles. The neuromuscular excitability has
been evaluated by measuring the muscles electrical re-
sponse evoked by the electrical stimulation of the motor
nerve. An M-wave is the result of the direct depolar-
isation of motoneurons that directly innervate muscle
fibres, with its area and amplitude being a measure of
their excitability. The number of MUs has been esti-
mated by comparing the average area of a sample of
MU action potentials, which are obtained by incre-
mental stimulation of the peripheral nerve, and the area
of the maximum M-wave, which is the compound action
potential of a muscle. The authors studied the number of
MUs and the maximum M-wave of both the thenar
muscle, a distal muscle, and the biceps brachii, a prox-
imal muscle, in individual s in their eighties as com pared
to those in their twenties. In the thenar muscle, older
individuals had maximum M-wave area and amplitude
values that were 22% and 33% lower, respectively, than
the young subjects values, with a 50% lower number of
MUs, thus revealing a loss of MUs with the presence of
collateral reinnervation. In contrast, in the biceps bra-
chii, the area and amplitude of maximum M-waves were
50% and 30% less in the older than in the young sub-
jects, respectively, with no significant differences in the
number of MUs, thus indicating the presence of less
excitable muscle mass entirely due to fibre atrophy.
The older muscle is not only atrophied, but is also
slower (Vandervoort and McComas 1986; Narici et al.
1991; Roos et al. 1999), tetanizes at lower fusion fre-
quencies (Narici et al. 1991; Kamen et al. 1995; Connelly
et al. 1999; Roos et al. 1999), and is more resistant to
isometric fatigue than the young muscle (Narici et al.
1991; Bilodeau et al. 2001a). Slowing in the contract ile
properties has been demonstrated in various muscles of
the lower limbs (Vandervoort and McComas 1986;
Roos et al. 1999), and in the adductor pollicis muscle
(Narici et al. 1991), by measuring the duration of
twitch contraction. Tibialis anterior, tibialis posterior
(Vandervoort and McComas 1986) and vastus medialis
(Roos et al. 1999) are slower in individuals over 73 than
in young people in their twenties, as demonstrated by the
longer time taken not only to reach the peak of tension
but also to relax after the twitch. Similarly, the maximum
relaxation rate has been shown to decline from 20 to
91 years of age in the adductor pollicis muscle (Narici
et al. 1991). The reason for this slower relaxation rate (or
longer twitch contraction duration) is probably related to
the selective atrophy of type II fibres. The muscle relaxes
at a lower rate as a result of the predominance of type I
fibres, which are slo wer. At the microscopic level of
muscle analysis, the slower relaxation rate can be
ascribed to a reduction in sarcoplasmic reticulum activity
(Klitgaard et al. 1989; Delbono et al. 1997; Hunter et al.
1999) and actin sliding speed on myosin (Ho
k et al.
2001). As a result of slowing of relaxation and probably
of type II fibre atrophy, it has been shown that muscles of
older individuals demonstrate tetanic fusion, i.e. a max-
imum maintained contraction in response to repetitive
stimulation, at lower frequencies of stimulation than is
required for young adults, thus enabling the individual
MUs to use lower firing frequencies to achieve a full
contraction (Narici et al. 1991; Kamen et al. 1995;
Connelly et al. 1999; Roos et al. 1999). Slowing of
relaxation and type II atrophy may also explain why
older people demonstrated more resistance to isometric
fatigue that young individuals (Narici et al. 1991), a
process which is referred to as the ‘‘fatigue-paradox’’
(Narici 1999).
Recently, Scaglioni et al. (2002) have shown that the
excitability in the spinal reflex pathway, expressed as the
ratio between the maximum H-reflex and the maximum
M-wave, is functionally impaired in older male individ-
uals. Scaglioni et al. (2002) concluded that the impaired
functionality of the reflex pathway with ageing, in
addition to the lack of changes following resistance
training as will be mentioned later in this review, sug-
gests that the H
ratio may be related to
degenerative phenomena rather than physical decondi-
tioning. At higher levels of the central nervous system,
there are still conflicting results on the possibility of a
reduction in the descending drive from supraspinal
centres to the motoneurons during maximum voluntary
contractions in older individuals, which would be a
further explanation for the loss of muscle streng th with
ageing (Phillips et al. 1992; De Serres and Enoka 1998;
Connelly et al. 1999; Harridge et al. 1999b; Kent-Braun
and Ng 1999; Roos et al. 1999; Yue et al. 1999; Bilodeau
et al. 2001a; Jakobi and Rice 2002; Scaglioni et al. 2002).
Some experimenters showed by a twitch interpolation
technique, a method based on delivering one or a brief
series of electrical stimuli to the motor axons of muscles
during maximum voluntary contraction, that older
adults were not able to maximally activate a muscle or
muscle group (Harridge et al. 1999b; Yue et al. 1999;
Bilodeau et al. 2001a). Other investigators, however,
demonstrated that a superimposed stimulus, in the form
of a single twitch or a short tetanus, added little or
nothing to the volitional force of older people (Phillips
et al. 1992; De Serres and Enoka 1998; Connelly et al.
1999; Kent-Braun and Ng 1999; Roos et al. 1999; Jakobi
and Rice 2002; Scaglioni et al. 2002). It must be noted
that central failure in activation was measured in very
old individuals by Harridge et al. (1999b) and that not
enough practice may have been given to the subjects in
measuring maximum voluntary contraction by Yue et al.
(1999) and Bilodeau et al. (2001a). The possibility of
underestimating the ‘‘real’’ maximum should therefore
be discounted if at least one session of familiarization is
practised (Jakobi and Rice 2002) and if the subjects are
not too old. Narici (2001) pointed out that activation
capacity could be muscle specific, as it appears to be
preserved in distal muscles of both upper and lower
extremities (Vandervoort and McComas 1986; Phillips
et al. 1992), but this issue deserves further investigation
as conclusive results on the activation capacity of a
muscle may largely depend on the stimulation technique
that is adopted. In fact, Behm et al. (2001) have recently
indicated that tetanic stimulation superimposed upon
single maximal or multiple contractions seems to pro-
vide the most valid measure of muscle inactivation.
Finally, the authors of this review suggest that voluntary
strength testing should be preferred, since electrical
stimulation determines a full synchronization of MUs
(Solomonow et al. 1994), which is unlikely to occur in
real life.
Surface electromyography is a non-invasive method
that has been used often to monitor changes due to
ageing in the overall neural activation of both agon ist
and antagonist muscles which, in turn, affects the gen-
eration of force (Merletti et al. 199 2; Esposito et al.
1996; Ha
kkinen et al. 1998a; Izquierdo et al. 1999;
Merletti et al. 2002). Inter-subject com parisons of
sEMG parameters as indicators of muscle function are
limited by the presence of skin, subcutaneous and fat
layers between the muscle and the recording electrodes,
which have a filtering effect on the signal (De Luca
1997). Therefore, although it is evident from the data
reported in various studies (Moritani and de Vries 1980;
kkinen and Ha
kkinen 1995; Ha
kkinen et al. 1998c)
that the absolute values of sEMG amp litude were lower
in groups of older individuals as compared to young or
middle-aged subjects, most of the investigators did not
remark on the physiological meaning of this difference,
with the exception of Esposito et al. (1996) and Merletti
et al. (2002). The authors speculated that the lower RMS
in the biceps brachii of individuals in their seventies, as
compared to those in their twenties, may be due not only
to the different thickness or conductivity of the layers
between the muscle and the recording electrodes, but
also to the different MU firing rates betw een the two
groups. This is supported by the observation of a de-
crease in the maximal MU firi ng rate with ageing in
studies where the intramuscular EMG signal was re-
corded (Kamen et al. 1995; Connelly et al. 1999; Erim
et al. 1999). The lower sEMG amplitude in olde r people
has also been ascribed to the reduced number of MUs
(Esposito et al. 1996), in agreement with the observation
made by others with electrophysiolog ical techniques of
MU estimation (Brown et al. 1988; Doherty and Brown
1993; Doherty et al. 1993), which are reported at the
beginning of this paragraph . In agreement with Esposito
et al. (1996) and Merletti et al. (2002), Macaluso et al.
(2002) have attributed the smaller RMS in older indi-
vidual to either a smaller number of recruited MUs or a
decreased firing rate of the individual MUs. As an
additional factor to explain the smaller RMS, the au-
thors have suggested the possibility of a decreased MU
synchronization. However, the relative roles played by
MU recruitment, MU firing rate and synchronization of
the individual MUs cannot be distinguished with surface
EMG. Some authors (Ha
kkinen et al. 1998a; Izquierdo
et al. 1999) , alternatively, used the sEMG to measure the
coactivation of antagonist muscles, which is referre d to
the maximum EMG activity of the same muscle group
during the agonist action. In this measure the influence
of subcutaneous and skin layers can be discounted, al-
though it may increase the danger of cross-talk from
nearby muscles (Solomonow et al. 1994), thus contam-
inating the signal and misleading its interpretation.
Coactivation, also referred to as cocontraction, may
serve to prot ect and stabilize the joint during forceful
contractions (Baratta et al. 1988). The higher levels of
antagonist coactivation, which have been observed in
70-year-old men and women as opposed to 40- and 20-
year-old individuals (Ha
kkinen et al. 1998a; Izquierdo
et al. 1999; Macaluso et al. 2002), could be an additional
explanation for the age-related decline in force produc-
tion. In other words, the net force exerted about a joint
during a given action, e.g. knee extension, would be
reduced in older people due to the greater simultaneous
activation of the musc les exerting a torque in the
direction which is opposite to that of the movement (i.e.
Comparisons between young and older indivi duals in
the frequency-domain parameters of sEMG have been
performed during sustained isometric contractions of
the biceps brachii (Bilodeau et al. 2001b; Merletti et al.
2002) and tibialis anterior muscles (Merletti et al. 1992).
A decline in median frequency (MDF), mean frequency
(MNF) or other parameters of the power spectrum,
which can be attributed to muscle fatigue, has been
observed in both young and older individuals, with the
rate of decrease of spectral parameters being lower in
the older subjects. This observation further supports the
‘‘fatigue-paradox’’ reported in the previous pages
(Narici et al. 1999), which can be ascribed to selective
atrophy of type II fibres, slowing in the contractile
properties, and lower MU firing rates of the older
muscle. By contrast, Hara et al. (1998) and Bilodeau
et al. (2001a) did not find significant differences between
young and older subjects in the decline of spectral
parameters of the abductor digiti minimum and elbow
flexors, respectively, during sustained contractions. The
interpretation of these results is unclear. Hara et al.
(1998) have explained the occurrence of a similar decline
in spectral parameters of young and older individuals
with ischemia, which is due to a stronger muscle con-
traction in the young and to a smaller capillary bed in
the older subjects. This would result in a similar decrease
in the two groups of the pH of interstitial fluids, as blood
flow determines the rate of metabolites removal, thus
affecting the decline in spectral parameters. Merletti
et al. (2002) attributed the results of Bilodeau et al.
(2001a) to the lack of specific criteria in selecting the best
electrode location.
Tendinous factors
Human tendons are responsible for the transmission of
force from muscles to bones and in vitro studies have
shown that ageing is associated with a decrease in their
stiffness (Vogel 1991). Only in recent times have tendon
mechanical properties been studied in vivo using ultra-
sonography (Maganaris 2001; Kubo et al. 2003; Reeves
et al. 2003a, 2003b). A lower gastrocnemius tendon
stiffness, reported as the ratio between force and tendon
elongation, was measured in a group of six older indi-
viduals in their seventies with respect to a control group
of six healthy young adults in their twenties (Maganaris
2001). The older tendons were more compliant in the
higher regions of the maximal tendon force, thus sug-
gesting that older individuals may operate closer to
muscle optimal length as a compensatory mechanism for
the reduction in force (Maganaris 2001; Reeves et al.
2003b). A functional consequence of the reduced tendon
stiffness in older people is likely to be a decrease in the
rate of force development, affecting for example the time
necessary to decelerate body mass, a factor related to the
prevention of falls (Kubo et al. 2003; Reeves et al.
2003b). Increased tendon compliance would also in-
crease the likelihood of strain injury (Reeves et al.
2003a). The mechanisms contributing to reduced tendon
stiffness are unclear, with decreased diameter and
packing density of collagen fibrils and changes in col-
lagen crimp structure being likely factors (Reeves et al.
Hormonal factors
A decline in the levels of many hormones has been
measured in older people, particularly growth hormone
(GH) (Rudman et al. 1990; Welle et al. 1996a), insulin-
like grow factor 1 (IGF-1) (Butterfield et al. 1997), tes-
tosterone (Tenover 1992; Urban et al. 1995; Baumgart-
ner et al. 1999) and oestrogen (Phillips et al. 1993; Taaffe
et al. 1995; Bassey et al. 1996; Skelton et al. 1999;
Onambele et al. 2001), but how these changes are related
to strength and power is still largely unclear (Short and
Nair 1999).
The action of GH, which is known to promote
growth, protein synthesis and fat mobilization, is med-
iated by IGF-1 (Rooyackers and Nair 1997). The hor-
mone deficiency, which has been measured in older
individuals (Rudman et al. 1990), determines a reduction
in muscle mass and an increase in fat mass. The
administration of recombinant human GF to healthy
older adults for 1 month increased circulating IG F-1
and led to a 50% increase in mixed muscle protein
synthesis, as measured using biopsy samples (Butterfield
et al. 1997). However, 3 months of treatment with
slightly higher doses did not produce any significant
change in protein synthesis of another group of older
subjects, although muscle mass and strength increased
(Welle et al. 1996a). Yarasheski at al. (1992, 1995) have
suggested that, as adding GH to a 12- or 16-week
resistance training programme led to an increase in fat-
free mass and whole body protein synthesis but not in
mixed muscle protein synthesis, the hormone enhanced
protein synthesis in non-muscle tissues. Taaffe et al.
(1994, 1996) gave evidence that administering GH dur-
ing the final 10 weeks of a 24-week resistance training
programme did not produce any further gains in muscle
size and strength. Harridge and Young (1998), in their
notable review on skeletal muscle in older people,
pointed out that a treatment for life with GH may lead
to gains that may be equally achieved with exercise
training, with the latter having no undesirable side-
effects of drug administration, such as fluid retention,
with consequent joint swelling and arthralgias, or
hypertension, atrial fibrillation, gynecomastia, and
hyperglycemia. Undesirable side-effects were also
observed after administration of IGF-I (Butterfield et al.
1997), which was associated wi th an increase in protein
synthesis, but muscle strength and size were not moni-
tored, thus requiring further investigation.
It is known that testosterone has a trophic action on
skeletal muscle, which is mediated by androgen recep-
tors in the myofibrils (Celotti and Negri Cesi 1992).
Iannuzzi-Sucich et al. (2002) recently reported that
bioavailable testosterone is a strong predictor of muscle
mass in men, together with body mass index, strength
and power. As many changes associated with testoster-
one deficiency in young men, such as muscle atrophy
and weakness, are similar to the changes associated with
the declined testosterone levels in older men, it has been
suggested that testosterone supplementation may pre-
vent or reverse the effects of ageing (Gruenewald and
Matsumoto 2003). Serum testosterone increased fol-
lowing hormone replacement to a level comparable to
that of young men, with a significant gain in muscle
mass after 3 months (Tenover 1992). In the study of
Urban et al. (1995), administering testosterone to hor-
mone-deficient men for 4 weeks was accompanied by an
increase in both strength and mixed protein synthesis.
Kraemer et al. (1999) have shown that older men
showed a significant increase in testosterone levels in
response to resistance training. Ha
kkinen and Pakarinen
(1994) suggested that the balance between anabolic and
catabolic hormones in ageing men is associated with
muscle atrophy and decreased voluntary force produc-
tion, as the ratio between circulating levels of serum
testosterone and serum cortisol correlated with muscle
CSA and strength. Izquierdo et al. (2001) have shown
that serum total testosterone and free testostero ne cor-
related with the magnitude of the training-related in-
crease in strength and power output in both groups of
middle-aged and older men. Androgens also appear to
be responsible for the reduced release of neurotrans-
mitters and other neuro trophic agents that, in turn, ef-
fect the partial denervation of muscle fibres and the
consequent sarcopenia (Gutmann and Hanzlı
cited in Narici 1999), as reported earlier in this review. In
a recent cross-sectional study, which involved 121 male
and 170 female volunteers aged 65–97 years (Baum-
gartner et al. 1999), a significant correlation between
muscle mass and serum free-testosterone was found in
men, whilst there was no association between oestrogen
levels and strength in women. However, oestrogen levels
in women , which fall at menopause, may play a role in
the loss of force, but conflicting results have been found
in postmenopausal women who were recei ving hormone
replacement therapy (HRT) (Phillips et al. 1993; Taaffe
et al. 1995; Bassey et al. 1996; Skelton et al. 1999;
Onambele et al. 2001). In the study of Phillips et al.
(1993), 25 postmenopausal women, who had been on
HRT for between 1 and 25 years, showed a 26% higher
specific strength in the adductor pollicis muscle than
those not receiving HRT. Similarly, another group
of postmenopausal women treated with HRT for
6–12 months increased their strength by 12%, as
opposed to a slight decline in the control group, wi th
both groups being accompanied by no significant change
in muscle CSA (Skelton et al. 1999). A follow-up study
after 2–4 years on the same population showed that the
benefit of HRT on the isometric muscle strength of
adductor pollicis was maintained in those women who
continued treatment beyond 1 year, although no further
increase in muscle strength was found (Onambele et al.
2001). However, other studies suggest that oestrogen
status does not have any effect on the maximal
muscle strength of older women (Taaffe et al. 1995;
Bassey et al. 1996).
Levels of physical activity
It has been shown that the amount of physical activity
decreases with ageing but it is unclear whether this is a
cause or an effect of the age-related loss of muscle
function (Harridge and Young 199 8). It seems that the
decrease in strength with ageing cannot be explained only
on the basis of a decreased level of physical activity, since
also highly competitive veteran sportsmen inexorably
decline (Meltzer 1994; Pearson et al. 2002). In addition,
muscle disuse results in a reduction in muscle fibre size
(Ferretti et al. 1997) and not, like ageing, in muscle fibre
number (Larsson et al. 1979; Lexell et al. 1988). As a
limitation of current studies, habitual physical activity
levels have often been reported in descriptive rather than
quantitative terms, making them difficult to interpret
(OToole 1997). For example, individuals were classified
as inactive if they participated in normal activities of
daily living or sedentary leisure-time activities and active
if they participated in moderated physical activity more
than once a week or had physically demanding jobs
(Borges 1989). In another study (Rantanen et al. 1997),
the active category was made by individuals reporting at
least 1 or 2 h a week of moderate activity, but include
also individuals involved in strenuous activities several
times a week. Interestingly, OToole (1997 ) pointed out in
her editorial that it is intui tive to think that higher
activity levels should preserve strength better, but further
studies are required to see whether habitual low to
moderate intensity activity for just a few hours a week
can provide an adequate stimulus to maintain muscle
strength and function. The author reported the results of
Rantanen et al. (1997), who observed similar rates of
changes in strength over a period of 5 years in individuals
classified as active, who maintained their level of physical
activity, and those classified as sedentary and remained
sedentary. However, individuals who were sedentary
initially and became more active were able to slow down
their decline in strength, even though their level of
strength remained lower than that of active individuals.
Those who were active initially but for some reason
became sedentary, without changes in their health status,
incurred in the highest rate of strength decline.
Muscle power in older people
Muscle power, i.e. the rate of performing mechanical
work, is also significantly reduced with advancing age
(see for example Bassey et al. 1992; Ferretti et al. 1994;
De Vito et al. 1998). In this review, muscle power will be
considered as that generated in a single explosive
movement, lasting a fraction of a second, where muscle
metabolism does not limit the performance. This is dif-
ferent from ‘‘sustained power’’, which describes the
ability to maintain a submaximal level of power output
in activit ies of longer duration such as cycling or running
(Sargeant 1994). Skelton et al. (1994) have reported that,
between the ages of 65 and 89 years, its decline occurs at
an even higher rate than isometric strength (3–4% per
annum as compared to 1–2% of the value for a 77-year-
old), thus revealing that power is more vulnerable than
strength to the ageing process. This loss of power has
been demonstrated to have severe functional conse-
quences (Bassey et al. 1992; Krebs et al. 1998; Suzuki
et al. 2001). Bassey et al. (1992) indicated that very old
adults who require the use of aids to perform functional
tasks, such as stair climbing, raising from a chair and
walking, had 42–54% less leg exten sor power than those
who could complete these tasks without assistance. Su-
zuki et al. (2001) have recently demonstrated a positive
association between muscle power of the ankle flexors
and func tional limitations in community-dwelling older
women. Among a group of sedentary, community-
dwelling older women, aged between 70 and 95 years,
leg power was the strongest predi ctor of functional sta-
tus, as compared to other physiological parameters
(Foldvari et al. 2000). Rantanen and Avela (1997) have
suggested that diminished leg extensor power may be a
key predictor for mobility problems. Improved knowl-
edge on the mechanisms of power decline is therefore
crucial with regard to the development of effective pre-
vention and treatme nt programmes for restoring
mobility and independence in older people.
As reported earlier in this review, power is the
product of force and speed at which mov ement occurs.
The amount of force produced during a muscle con-
traction varies with the velocity of shortening, as first
demonstrated by Fenn and Marsh in 1935 and then
further investigated by Hill in 1938, who described a
‘‘characteristic equation’’ for the speed of shortening
under a load in isolated animal muscle. The nature of
the force/velocity relationship dictates that power will
have its own distinct relationships with force and
velocity of movement. Thus, there is an optimum force
and an optimum velocity at which maximum power is
developed. In isolated animal muscle, these correspond
to about 30% of P
and 25–30% of V
, respectively
strand and Rodahl 1986) . However, measurements of
force/velocity and power/velocity relationships in hu-
mans in vivo represent the resultant of relatively com-
plex situations, as human muscles are attached to bones
via tendons that cross over one or two articular joints in
order to produce a moment. Not only must the con-
tractile elements of muscle cells be considered, but also
factors such as neural influences, muscle architecture
and intercellular connective tissue. The optimal values of
force and speed for maximum power production in vivo
may therefore be different from those recorded in iso-
lated muscles or skinned single fibre preparations.
In the literature, investigations looking at muscle
power in older people are not as numerous as those
carried out on muscle strength. According to Earles
et al. (2000), this is because muscle power in single
explosive movements is much more difficult to measur e
than muscle strength. Isokinetic dynamometers allow
power to be assessed in single muscle groups from the
torque measur ed whilst the limb rotates at constant
angular velocity, but do not reflect everyday activity
where older subjects have to work against resistance and
overcome speed (Harridge et al. 1999a). Moreover, the
maximum speed of isokinetic devices (about 300°/s) is
too low with respect to the maximum that can be
achieved during ‘‘unloaded’’ movements of human limbs
(estimated at 832°/s, as reported by Perrine 1986), which
limits the measure of power above these value s of speed.
Explosive power has been traditionally measured in
older people using a simple whole body movement, that
is a vertical jump on a force platform (Grassi et al. 1991;
Ferretti et al. 1994; De Vito et al. 1998). Force platforms
essentially operate like a scale for measuring weight.
Velocity of movement of the individuals centre of
gravity is calculated by integration of the acceleration,
which in turn is calculated by the vertical component of
the ground reaction force (VGRF) according to the
Netwons Second Law of Motion, and power is the
product of force (obtained by subtracting body weight
from VGRF) and velocity of movement (Davies and
Rennie 1968). This method presents tw o limitations: (1)
it may not be safe in very-old frail individuals; (2) older
people have to lift their body weight, which represents a
high percentage of their maximum strength, and there-
fore may be forced to work in a less favourable portion
of the force/velocity curve, thus performing the move-
ment at slower speed that is away from the optimal
speed for maximum power production. The first prob-
lem has been overcome by Bassey and Short (1990), who
developed a piece of apparatus that measures the aver-
age power generated by the lower limb muscles during a
single leg extensor thrust agains t a pedal which, in turn,
accelerates a heavy flywheel of a known inertia. This,
however, does not solve the second issue, in that both
young and older individuals have to overcome the same
fixed inertia, with weak-old individuals being forced to
use a relatively greater proportion of their maximum
force-generating ability. Pearson et al. (2001) have
recently introduced a variable inertial testing system
mounted in the apparatus designed by Bassey and Short
(1990), which has the potential to overcome the limita-
tions due to the use of a single inertia. A safe device for
testing older individuals coul d also be the sledge-
ergometer designed by Antonutto et al. (1999), on which
individuals sitting on a carriage-seat push with both feet
on two force platfor ms. In this device different inert ial
loads can be obtained by positioning the sledge at dif-
ferent angles with respect to the horizontal (Zamparo
et al. 2000). Power can also be tested at different inertial
loads by using instrumented weight-stack machines,
where force is measured by a transducer or derived by
the mass of the stack, and velocity by an electrogoni-
ometer at the individuals joint (Harman 1995). How-
ever, the masses of plates in weight-stack machines have
been found both to be variable and to differ from
labelled values, thus complicating the measurement
technique. All things considered, dynamic force testing,
which is performed by measuring the maximum weight
that can be lifted, is also a test of power, as the indi-
vidual is exerting a given force at a given speed that,
however, is not measured, thus not enabling the calcu-
lation of power. Thomas et al. (1996) have developed a
pneumatic system mounted on a double leg-press ma-
chine that also allows one to use the optimal resistance
for maximum power, expressed as a percentage of
maximum dynamic strength. To the authors knowledge,
there is only one study in which explosive power has
been compared between middle-aged and older men
after optimizing the load (Izquierdo et al. 1999), and
another investigation (Macaluso and De Vito 2003),
which has considered this issue in women. In both
studies, the maximum power of the lower limbs, which
was lower in the older individuals, was measured by
pushing a load corresponding to about 60% of maxi-
mum force. Onl y Macaluso and De Vito (2003), how-
ever, have focused their attention on the two
determinants of power output, i.e. optimal force and
optimal speed, and reported that the inferior ability to
generate power was due to a lesser ability to develop
both force and speed. Moreover, as optimal speed was
measured when optimal force was the same percentage
of maximum voluntary contraction in the two groups
(60%), thus standardizing for differences in optimal
force, the authors concluded that the older women
generated less power because they were slower than the
young even when using the same percentage of their
maximum strength. This finding is in contrast with the
recent results of the same authors, carried out in col-
laboration with some other investigators (Pearson et al.
2002), who compared a population of weightlifter ath-
letes with untrained healthy individuals by using a var-
iable inertial testing system (Pearson et al. 2001)
mounted in apparatus designed for measuring explosive
power in older people (Bassey and Short 1990). In their
study, weaker individuals achieved max imum power
output at lower inertial loads than stronger individuals,
but the speed component was found to be not signifi-
cantly different between the two groups. The discrep-
ancy between the results of these two studies could be
ascribed to the diff erent study population and testing
methodology and deserves further investigation.
As power is the product of force and velocity, any-
thing that will affect force production or speed of
shortening of a muscle will also affect its power output.
Therefore, all of the factors that have been reviewed in
the previous paragraph to explain the loss of muscle
strength in older age can be transferred to power. In
addition, all of the factors that may affect speed of
shortening must be taken into account. The selective
atrophy of type II fibres with advancing age may partly
explain power losses, because the power output of type
II muscle fibres is four times that of type I fibres, as
reported in animal studies (Faulkner et al. 1986). The
speed at which a muscle fibre shortens is determined by
the expression of the different isoforms of the MHC, as
measured with a technique based on identification of
MHC as molecular marker with gel electrophoresis
(Harridge et al. 1996). Type I, IIa and IIb fibres of the
traditional classification, based on ATPase sensitivity to
pH, express mainly MHC-I, MHC-IIA and MHC-IIX
isoforms, respectively. Fast fibres have the potential to
generate higher power output, with greater forces and
higher speed of shortening than slow fibres. The signif-
icant reduction in the size of type II fibres, as described
earlier in this review (Lexell et al. 1988), would result in
a decrease in the proportion of the muscle that is
occupied by fast contracting MHC isoforms (Harridge
and Young 199 8). Moreover, it has been shown, by
using electrophoretic techniques, that fibres in older
muscle co-express more than one MHC isoform (hybrid
fibres) to a greater extent than fibres in young muscle
(Klitgaard et al. 1990; Andersen et al. 199 9). This in-
creased presence of hybrid fibres, which had not been
clearly identified by the earlier technique based on the
ATPase reaction, may indicate a shift towards a slower
older muscle (Harridge and Young 1998) and, as re-
ported earlier in this review, is further evidence of the
process of ongoing denerv ation and reinnervation of the
ageing muscle (Vandervoort 2002). The shift towards a
slower muscle with ageing has been confirmed by studies
on the contractile mechanics of single fibres, in which it
was shown that both MHC-I and MHC-IIA single fibres
have lower specific tension and maximum shortening
velocity if they originate from the muscles of an older
person as opposed to a young person (Larsson et al.
1997; Frontera et al. 2000b). Moreover, Ho
k et al.
(2001) recently reported an age-related slowing in the
actin sliding speed on myosin by studying an in vitro
motility assay, in which myosin is extracted and immo-
bilized from a 2- to 4-mm single muscle fibre segment, in
order to focus on actomyosin interactions without
interference from cytoskeletal or regulatory proteins. As
previously pointed out, measurements taken from skin-
ned single fibre preparations or in vitro motility assays
have the advantage that they allow the researcher to
study directly the contractile elements of muscle cells,
thus ruling out the confounding effects of factors such as
neural influences, muscle architecture, and intercellular
connective tissue (Frontera et al. 2000b). However, these
factors should be taken into account when examining
the speed of shortening of the whole body segments in
vivo and the exact interpretation of these phenomena is
still unknown. Metter et al. (1997) speculated that nor-
mal ageing changes in the basal ganglia, consisting of a
continuing loss of dopaminergic neurons in the sub-
stantia nigra (Morgan et al. 1994), could contribute to
the observed slowing in speed, coord ination and power,
together with peripheral changes such as slowing in
nerve conduction velocities (Norris et al. 1953). Another
potential cause of lower power production could be an
age-related decrease in tendon stiffness, which has been
briefly reviewed in a previous paragraph.
The effect of resistance training on muscle strength,
power and selected functional abilities in older
At the end of the 1980s, Frontera et al. (1988) reported
that a heavy-resistance training programme led to an
increase in strength of the quadriceps muscles of older
men aged between 60 and 72 years, which was accom-
panied by an increase in muscle fibre size. Since then, a
growing number of studies each year continue to docu-
ment the benefits of resistance training in older people,
even in individuals over 90 yea rs of age. Resistance-
training programmes are based on the application of the
overload principle, which states that muscles worked
close to their force-generating capacity will increase in
strength (McArdle et al. 1996). The term exercise session
refers to the block of time devoted to the training. The
number of training sessions completed per week is
termed frequency. The basic unit of a resistance training
session is the repetition which, for a given training
movement, is the completion of a whole cycle from the
starting position, through the end of the movement and
back to the start. When a series of repetitions is com-
pleted this is termed a set. Volume is typically calculated
as the product of repetitions and sets (Fry and Newton
2002). Intensity refers to the relative load or resistance
that the muscle is exercising against, usually expressed as
a percentage of the maximum weight that could be lifted
once, i.e. 1 repetition maximum (1-RM). In the older
population, these programmes have a similar structure
to those undertaken by younger people, for example
they can have a duration of 12 weeks, with a frequency
of 3 times per week, where subjects perform 3–4 sets of 8
repetitions at an intensity equal to 80% of 1-RM. To
elicit gains in muscle strength, the loads must be pro-
gressively increased so that the relative intensity remains
high enough to provide an adequate overload through-
out the whole duration of the training programme. The
results of some of the stud ies that have examined the
effects of heavy-resistance training on muscle strength
and size on the most frequently studied muscle, the
quadriceps group, are summarized in Table 1.
One of the main problems of between-study com-
parisons is the variation in the population of subjects.
Studies have been performed on males, females and
mixed populations. The mean age of the participants has
also varied greatly, with older people ranging from those
in their sixties (Ha
kkinen et al. 1998b) to those in their
nineties (Fiatarone et al. 1990; Harridge et al. 1999b).
The presence of med ical conditions and the baseline
fitness of participants are among other variables that
have to be taken into account (Greig et al. 1994).
Additional factors that make the comparison between
studies problematic are the duration and frequency of
the training programme, the number of sets and repeti-
tions of each session, and finally the intensity at which
these repetitions are performed. Resistance training
programmes in older people varied considerably in
length from just 4 weeks (Sherrington and Lord 1997) to
84 weeks (McCartney et al. 1996). On average, however,
most resistance training studies lasted 8–12 weeks
(Frontera et al. 1988; Fiatarone et al. 1990; Charette
et al. 1991; Gr imby et al. 1992; Lexell et al. 1995;
kkinen et al. 1998b; Harridge et al. 1999b; Hunter
et al. 1999; Tracy et al. 1999; Hortoba
gyi et al. 2001).
Most studies involved subjects performing three training
sessions per week, but the number could be as great as
seven per week (Sherrington and Lord 1997). Recently,
Taaffe et al. (1999) have demonstrated that strength
gains can be obtained even with a training frequency of
once per week. The number of sets was three in most of
the studies, but could vary up to six (Charette et al. 1991;
kkinen et al. 1998b; Ha
kkinen et al. 2001). The
number of repetitions also changed from study to study,
with the most common number of repetitions being
eight, although it ranged between 3 (Ha
kkinen et al.
1998b, 1998c) and 18 (Ha
kkinen et al. 2001). The
intensity of heavy-resi stance training was around 80% in
most studies and there have also been few studies com-
paring low- versus high-intensity resistance training
(Pruitt et al. 1995; Hortoba
gyi et al. 2001; Fielding et al.
2002). Strength changes have been quite variab le across
studies, which is likely a reflection of the key design
factors that ha ve just been reviewed. Moreover, vari-
ability in the results depends on the modalities used to
test strength (isometric vs. 1-RM), which are defined at
the beginning of this review. It is important to remark
that even very old people can benefit from progressive
resistance training (Fiatarone et al. 1990; Harridge et al.
1999b). Lexell (2000) pointed out that the lower the
initial levels of strength, such as those in individuals in
their nineties, the higher the magnitude of the percentage
increase with res pect to the baseline.
Various factors can contribute to strengt h gains fol-
lowing heavy-resistance training in both young and
older subjects. These include, in the first phase of
training (about 1–2 weeks), a rapid improvement in the
ability to perform a training exercise, such as lifting
weights, which is mainly the result of a learning effect.
The learning effect, which is mediated by changes in
motor skill coordination and level of motivation, can be
substantial especially when the test adopted to evaluate
muscle strength req uires high levels of skill (Jones and
Round 1990). In the second phase, which lasts
3–4 weeks, muscle strength gains are obtained without a
matching increase in size of the trained muscles. The
improvement in this phase has been mainly attributed to
neural adaptations (Moritani and de Vries 1980; Sale
1988; Ha
kkinen et al. 2001). The term neural adapta-
tions includes many elements such as an increased acti-
vation of prime mover muscles (number of recruited
MUs or firing rate and synchronization of the individual
MUs), a better coordination of synergistic and antago-
nist muscles, and an increased neural drive from the
highest levels of the central nervous system (Sale 1988).
There are, however, few studies investigating changes in
neural properties following strength training in aged
humans (Rice 2000). Some investigations have shown
significant improvements in agonist sEMG with con-
current reductions in the activity of antagonist muscles
kkinen et al. 1998b, 1998c). An increase in M-wave
potentials following strength training has been measured
in older individuals by Hicks et al. (1992), thus sug-
gesting a training-induced increase of muscle membrane
excitability. However, Scaglioni et al. (2002) have
recently shown that the modulation of neuromuscular
excitability, expressed as the ratio between the maximum
Hoffman reflex and the maximum M-wave, did not
change in older male adults following 16 weeks of
Table 1 Effect of resistance training on muscle strength and size of the quadriceps muscle in older individuals. (CSA Cross-sectional area,CT computerized tomography, F female,
GWBE general weight bearing exercises, Isok isokinetic, KE knee extension, LP leg press, M male, MRI magnetic resonance imaging, MVC maximal voluntary contraction, NS non-
significant, 1RM one repetition of maximum weight that could be lifted, 5RM five repetitions of maximum weight that could be lifted, Ultr ultrasonography, vol volume)
Authors Subjects Training programme % Change
Age Gender N Exercise
per week
Sets Repetitions % of 1RM Strength CSA Fibre size increase
1RM MVC Type I Type II
Frontera et al. 1988 60–72 M 12 KE 12 3 3 8 80 107 17 CT: 9 34 28
Fiatarone et al. 1990 86–96 M/F 10 KE 8 3 3 8 80 174 CT: 11
Charette et al. 1991 64–86 F 13 LP, KE 12 3 6 6 75 28–93 7 NS 20
Grimby et al. 1992 78–84 M 9 KE 8–12 3 3 8 Isok 10 at 30°s
CT: 3 8 NS 5 NS
Pyka et al. 1994 61–78 M/F 25 LP, KE 52 3 3 8 75 53–95 59* 67*
Lexell et al. 1995 70–77 M/F 23 KE 11 3 3 6 85 163 - -4 NS -8 NS
McCartney et al. 1996 60–80 M/F 113 LP 84 2 3 12 80 32 CT: 9
Sherrington and Lord 1997 64–94 M/F 21 GWBE 4 7 22
kkinen et al. 1998b 61 M 10 KE 10 3 3–6 3–15RM 17 MRI: 9 23 27
kkinen et al. 1998c 70 M/F 20 KE 26 2 3–6 3–15 50–80 26 Ultr: 6 (F)
Harridge et al. 1999b 85–97 M/F 11 KE 12 3 3 8 80 134 37 MRI: 10
Taaffe et al. 1999 65–79 M/F 46 LP, KE 24 1 3 8 80 23–71
Tracy et al. 1999 65–75 M//F 23 KE 9 3 3 5–10RM 28 MRI(vol): 12
Hunter et al. 1999 64–79 M/F 11 KE 12 3 3 8RM 39 )4NS )2NS
gyi et al. 2001 66–83 M/F 27 LP 10 3 5 4–12 40–80 35 26
kkinen et al. 2001 71 M/F 21 LP 26 2 3–6 10–18 70–80 26 26 32 (F) 32 (F)
After 30 weeks
resistance training of plantar flexor muscles. A 30%
increase in maximal MU firing rate has been measured
in the tibialis anterior muscle of six older individuals in
their seventies following 2 weeks of train ing (Patten and
Kamen 2000). However, the same authors (Patten et al.
2001) reported a bimodal response of maximal MU
discharge rate of the adductor digiti minimi to 6 weeks
of isometric training an initial increase followed by a
return towards baseline which is surprising and diffi-
cult to explain. The third phase of adaptation to strength
training (>6 weeks) is characterized by an increase in
both the size and strength of the exercised muscles.
Muscle size has been measured before and after training
using various non-invasive techniques, such as ultra so-
nography (Ha
kkinen et al. 1998c), CT (Frontera et al.
1988; Fiatarone et al. 1990; Grimby et al. 1992; Mc-
Cartney et al. 1996) or MRI (Ha
kkinen et al. 1998b;
Harridge et al. 1999b). Notable is the recent study of
Tracy et al. (1999), who measured a 12% increase in
quadriceps muscle volume, by MRI, following 9 weeks
of resistance training in both groups of 65- to 75-year-
old men and women. Both type I and type II fibres retain
their capacity for hypertrophy in response to resistance
training (Frontera et al. 1988; Brown et al. 1990; Cha-
rette et al. 1991; Pyka et al. 1994; Ha
kkinen et al. 1998b,
2001), although some studies demonstrated little or no
change (Grimby et al. 1992; Lexell et al. 1995; Hunter
et al. 1999). Ha
kkinen et al. (1998b) have reported a type
MHC II subtype transformation going from type MHC
IIb to IIab to IIa in older men, similar to previous
training studies in young individuals (Adams et al. 1993;
Harridge et al. 1998). In a further study (Sharman et al.
2001), the same result was also found in a group of 65-
year-old women following 24 weeks of heavy resistance
training. Williamson et al. (2000) have measured a sig-
nificant increase in the expression of MHC I as a result
of 12 weeks of low-intensity resistance training, thus
indicating that higher-threshold MUs may not have
been recruited during the programme. Recent investi-
gations on single fibres indicated that 12 weeks of pro-
gressive resistance training increased muscle cell size,
strength and peak power in both older men (Trappe
et al. 2000) and women (Trappe et al. 2001). Interest-
ingly, in contrast with the older men, no change in fibre
unloaded shortening velocity or peak power normalized
to cell size was observed in older women, thus suggesting
that men and women respond differently, at the cell le-
vel, to the same resistance-training stimulus. The
mechanisms of this phenomenon are still unknown.
Some studies (Yarasheski et al. 1995; Welle et al. 1999)
have also given evidence that resistance training leads to
an increase in protein synthesis, accompanied by sig-
nificant improvements in muscle strength. Less is known
about the long-term effects of resistance training in older
people, as most of the available studies did not continue
after 12–24 weeks. Following a 1-year exercise trial
involving 25 individuals aged between 61 and 78, Pyka
et al. (1994) measured increases in strength ranging from
30 to 97% over the first 3 months, which then
maintained a plateau in the remaining months of the
experiment. Similarly, Morganti et al. (1995) showed that
a 1-year training programme with a frequency of twice a
week resulted in strength gains of various muscle groups,
ranging from 4% to 74% in a population of 39 healthy
postmenopausal women, with the greatest gains seen in
the first 3 months of training. McCartney et al. (1996)
reported instead progressive strength gains and moderate
muscle hypertrophy in an older group that continued to
participate in a resistance-training programme for
2 years. Rapid detraining will result if programmes are
interrupted, but the initial gains can be maintained with a
reduced exercise frequency of even once per week (Lexell
et al. 1995; Taaffe et al. 1999; Trappe et al. 2002).
Although several investigations have shown that the
capacity to impr ove muscle strength is not impaired with
increasing age (see the studies of Table 1), few investi-
gations have made a direct comparison of the magnitude
of the responses in older and young individuals to the
same training programme. Jozsi et al. (1999) have shown
that 60-ye ar-old individuals can improve strength and
power in response to 12 weeks of resistance training,
with the same magnitude as that of individuals in their
twenties. Welle et al. (1996b) found that the increase in
specific tension following 3 months of resistance training
in young (22–31 years) and older (62–72 years) individ-
uals was similar for elbow flexion (about 20%) and knee
extension (about 35%), but was more than double in the
older subjects for the knee flexors. Larsson (1982), on
the contrary, had previously shown that the average
increase in isokinetic strength of the knee extensors
following 15 weeks of training at low resistance and high
repetition tended to be higher in a group of 56- to 65-
year-old males (7.5%) as compared to the 20- 39-year-
old group (2.9%). In contrast, in the study of Macaluso
et al. (2000), after 6 weeks of isometric training the force
gain of the bicep s brachii muscle followed the same
temporal pattern in the two groups of young and older
women, in that after 4 weeks the maximum voluntary
contraction reached a plateau, but the absolute force
increments were different, 22.4% in the young and
13.4% in the older women.
In recent times, greater attention has been focused on
the need to design exercise strategies in order to increase
muscle power (Earles et al. 2000; Evans 2000; Fielding
et al. 2002). ‘‘The preservation of muscle power into late
life can greatly decrease the risk of disability and en-
hance functional independence’’ (Evans 2000). As
pointed out by Earles et al. (2000), it is important to
determine whether high-velocity training is comparable
or superior to low-velocity high-resistance programmes
in order to improve function and quality of life in older
individuals. Table 2 summarizes the results of the
training studies in which, to the authors knowledge,
explosive power has been measured. The subjects age
and gender, training mode and testing methodology are
To date there is only one published study, to the
authors knowledge, which was specifically designed to
increase power in older people (Fielding et al. 2002).
Older women in their seventies with mild functional
limitations were randomized into one of two groups:
high-velocity (HI) and low-velocity (LO), in which
absolute training force and total work performed were
similar between groups, but power output was signifi-
cantly higher in HI, since individuals were asked to
perform each repetition as fast as possible. HI and LO
have improved leg-press power output by 97% and
45%, respectively, over 16 weeks of training. This
training programme was designed starting from the
assumption that muscle-strengthening exercises may not
always produce an optimum increase in power. The
authors pointed out that traditional low-velocity resis-
tance training resulted in a small but significant increase
in muscle power ranging from 18% to 25% (Fiatarone
et al. 1994; Skelton et al. 1995; Jozsi et al. 1999) despite
much larger increases in muscle strength. Fiatarone et al.
(1994) showed that in frail very old nursing-home resi-
dents progressive resistance exercise over a 10-week
period produced 113% and 28% increases in muscle
strength (kne e-extension 1-RM) and power output,
respectively, with power being assess ed during a stair-
climbing test (Bassey et al. 1992). Similarly, in 20 heal-
thy, independent, very old women, Skelton et al. (1995)
observed a 27% increase in knee-extension isometric
strength and an 18% increase in leg-extension power
standardized for body weight, which was measured
using the Nottingham Power Rig (Bassey and Short
1990). Jozsi et al. (1999) found that 12 weeks of
progressive resistance-training in men and women in
their sixties resulted in an increase in the strength of knee
extension and arm pull movements of 30% and 18%,
respectively, versus an increase of 26% and 10% in
power, with power being measured with a pneumatic
resistance machine (Thomas et al. 1996). Also Frontera
et al. (1988), in their notable study that has been cited in
the previous paragraph on the effects of resistance
training on strength, examined the effect of resistance
training on quadriceps power, wi th power being mea-
sured with an isokinetic dynamometer, but did not see
any significant change. It can be speculated that the ef-
fect of training on muscle power may have been seen if
power had been measured with the same dynamometer
used to carry out the training programme. Even a low-
intensity general conditioning programme has been
successful in obtaining a 24% increase in peak pow er
during a vertical jump on a force platform in 20 healthy
older women in their sixties (De Vito et al. 1999), but
higher improvements may ha ve been observed if the
programme had been more specific. Earles et al. (2000)
have therefore pointed out the importance of performing
movements at high velocity during resistance training in
order to increase power output. Forty-three volunteers
over the age of 70 years were randomized into one of
two groups: the power group, in which individuals
participated in high-velocity resistance exercise 3 times a
week, and the walking group, in which individuals per-
formed moderate intensity exercise 30 min daily, 6 days
per week. Leg-press power and maximal knee extensor
strength substantially increased in the first group, but
not in the second. Similarly, Izquierdo et al. (2001) re-
ported that in middle-aged and older men a prolonged
total strength training programme, which included high
Table 2 Effect of resistance training on muscle power of various
muscle groups in older individuals. (AP arm pull, BP bench press,
F female, HE hip extension, HI high velocity, HS half-squat, KE knee
extension, LO low velocity, LP leg press, M male, NS non-significant,
PRM pneumatic resistance machine, 1RM one repetition of maxi-
mum weight that could be lifted, SC stair climbing, VJ vertical jump)
Authors Subjects Training programme Testing
Power gain Measurement
Age Gender N Exercise
per week
Sets Repe-
et al. 1988
60–72 M 12 KE 12 3 3 8 80 KE None Isokinetic
et al. 1994
72–98 M/F 100 KE, HE 10 3 3 8 80 SC 28% Stair-climbing
et al. 1995
76–93 M/F 20 Elastic tubing
or rice bags
12 3 3 4–8 LP 18% (NS) Nottingham Rig
De Vito
et al. 1999
60–70 F 11 Low-intensity
12 3 VJ 24% Force platform
et al. 1999
56–66 M/F 17 KE, AP 12 2 3 8–12 80 KE, AP 10–26% PRM
et al. 2001
64 (2) M 11 KE, HS, BP 16 2 3–4 8–15 50–80 KE, HS,
21–37% Instrumented
et al. 2000
77 (5) M/F 18 LP 12 3 3 10 50–70 LP 22% PRM
et al. 2002
73 (1) F 30 LP 16 3 3 8–10 70 LP HI: 97%
LO: 45%
velocity movements, led to gains in maximal strength
and power of the upper and lower extremity muscles,
with the improvements being limited in magnitude pos-
sibly due to neuromuscular or age-related endocrine
As reported in the paragraph entitled ‘‘muscle power
in older people’’, there is an optimum value of force and
velocity at which maximum power is generated. De Vito
et al. (1999) showed that the training-induced increase in
peak power output, which was measured by performing
a vertical jump on a force platform, was due to an in-
crease in both optimal force (18%) and optimal velocity
(13%) at which maximum power was measured. How-
ever, as argued earlier in this review, explosive power
output on a force platform was assessed using a fixed
inertia, which is the subjects body weight and corre-
sponds to a high percentage of their maximum, thus not
representing the optimal value of force for maximu m
power production. Other authors have overcome this
problem by measuring power output using different
loads before and after training (Jozsi et al. 1999; Earles
et al. 2000; Izquierdo et al. 2001; Fielding et al. 2002),
but do not seem to have focused much of their at tention
on whether the training-induced changes in maximum
power were due to an increase of optimal force, optimal
velocity or both. Most of the investigators (Jozsi et al.
1999; Izquierdo et al. 2001; Fielding et al. 2002) showed
how power output varied as a function of different
loads, expressed as a percentage of 1-RM, thereby
identifying the load at which maximum power was
measured, but they did not discuss the role of velocity of
movement in maximum power generation. In the work
of Earles et al. (2000), both power output and velocity of
movement were plotted in two different graphs against
the resistance used, expressed as a percentage of body
mass. However, also these authors did not discuss the
relative role of both optimal force and velocity, but
simply commented that minimal improvements in power
were measured at low resistance, whilst large improve-
ments occurred at higher resistance, in agreement with
the principle of specificity of training (McCafferty and
Horvath 1977). From a closer analysis of the graphical
results of Earles et al. (2000), it is clear that maximum
power was measured before and after training at 30%
and 50% of body mass, respectively, with the optimal
speed at maximum power being decreased after train ing,
although this was not remarked upon by the authors.
Improvements in power can therefore be interpreted
with the fact that individuals were able to push higher
loads despite a decrease in optimal speed of movement.
Possible mechanisms underlying the improvement in
peak power may include specific increa ses in the CSA of
type II musc le fibres and increases in specific force and
shortening velocity of single muscle fibres, as speculated
by Fielding et al. (2002). Notably, Van Cutsem et al.
(1998) have shown that changes in single MU behaviour
contribute to the increase in contraction speed after
dynamic training in humans, which could justify train-
ing-induced changes in power. These changes in MU
behaviour include earlier MU activation, extra doublets,
i.e. brief (2–5 ms) MU interspike intervals, and en-
hanced maximal firing rate. Also Izquierdo et al. (2001)
have speculated that power increases could be due to
training-induced changes in the neural component,
which they vaguely refer to as ‘‘voluntary or reflex/in-
duced rapid neural activation of MUs’’. Indeed, the
various factors included under the term ‘‘neural adap-
tations’’ that have been presented in the previous para-
graph to explain gains in strength following heavy-
resistance training, i.e. increased activation of the prime
mover muscles, better coordination of synergistic and
antagonist muscles and increased neural drive from the
highest levels of the central nervous system, can also
explain improvements in power. However, studying
these mechanisms during dynamic contractions by
sEMG or other electrophysiological techniques could be
problematic, as various mechanical, physiological, ana-
tomical and electrical modifications occur throughout
the contraction that affect, in substantial ways, the
relationship between signal amplitude and muscle force
(De Luca 1997). Also the slowing in nerve conduction
velocities due to ageing (Norris et al. 1953) may be a
mechanism to be recovered following power training.
However, Scaglioni et al. (2002) have recently shown
that the conduction velocity of the posterior tibial nerve
did not change in older male adults foll owing 16 weeks
of resistance training of plantar flexor muscles, thus
suggesting that decreased nerve conduction velocity may
be due to degenerative phenomena rather than disuse.
Moreover, if decreased tendon stiffness, as recently
shown in vivo on human individuals by Maganaris
(2001), is another potential cause for decreased power
with ageing, an appropriate training intervention may
also affect this mechanism. Re cent results of Reeves
et al. (2003a, 2003b) showed that the pa tella-tendon
stiffness increased by 65% in 74-year-old men following
14 weeks of resistance training, which was accompanied
by a 14–23% increa se in dynamic strength during leg
extension and leg press. In contrast, in a population of
older women, it has been shown that 6 months of low-
load resistance training produced no significant changes
in stiffness of the tendon-aponeurosis structures of the
vastus lateralis muscle, but an increase in elasticity
(Kubo et al. 2003).
Selected functional abilities
Functional ability can been described as an individuals
competence in performing everyday physical tasks, like
rising from a chair, climbing stairs or lifting shopping
bags (Harridge et al. 1999a). Although, as reported in
the previous paragraph on muscle power, it has been
shown that muscle strength and pow er correlate with the
ability to perform functional tasks (Bassey et al. 1992;
Skelton et al. 1994; Rantanen and Avela 1997; Fold vari
et al. 2000; Suzuki et al. 2001), this is an area of research
that remains unclear. Some authors (Skelton et al. 1994;
Buchner et al. 1996; and Levy et al. 1994, cited in Har-
ridge et al. 1999a) have attempted to identify functional
‘‘threshold’’ values of muscle performance below which
older people lose their ability to perform basic daily
tasks. Skelton et al. (1994), who measured the greatest
height of step that could be mo unted without using the
hands in healthy men and women aged from 65 to
89 years, found a significant correlation between step
height and lower limb extensor power, but failed to
identify a universally applicable threshold value, even
after adjusting for limb length. In contrast, Levy et al.
(1994, cited in Harridge et al. 1999a) reported that uni-
lateral power/weight ratios of 1.5 and 2.5 W/kg could be
considered as threshold values for mounting a 30- and
50-cm step, respectivel y. Buchner et al. (1996), who used
a slightly different model based on an inverse transfor-
mation of strength, found a significant correlation be-
tween lower limb strength and self-chosen walking
speed. However, they also concl uded that a ‘‘universal
threshold’’ might not exist due to a compensation for
deficiencies in strength by using reserve capac ity in other
determinants of walking speed. Regardless of the diffi-
culties in identifying a precise value, this ‘‘threshold’’
concept makes it easy to recognize that small changes in
physiological capability can have large effects on the
functional ability of a frail person, but little or no effect
in a more robust person.
There are few studies that have investigated the ef-
fects of training protocols on selected functional abilities
in older people (Table 3). It should be noted that in most
of these studies (Judge et al. 1993; Fiatarone et al. 1994;
Hunter et al. 1995; Skelton et al. 1995; Skelton and
McLaughlin 1996; Rooks et al. 1997; Sherrington and
Lord 1997) the age range of participants is widespread,
with individuals in their nineties and in their sixties or
seventies being included in the same group. As these
investigations, with the exception of Fiatarone et al.
(1994), were carried out on a relatively small number of
individuals, the interpretation of results might have been
limited by pulling together subjects within a wide age
range, since in the very old individuals small changes in
physiological capability are likely to have larger effects
on functional ability than in relatively younger subjects.
Health and functional status also vary considerably be-
tween studies, with the participants ranging from frail-
institutionalized (Fiatarone et al. 1990, 1994) to rela-
tively independent (Judge et al. 1993; Skelton and
McLaughlin 1996) or healthy active (Earles et al. 2000;
kkinen et al. 2000), thus limiting inter-study com-
parisons. Regardless of these limitations, the relation-
ship between resistance training and the ability to
perform functional tasks remains unclear. As reported in
Table 3, the effects of resistance training on selected
functional abilities vary from no change (Earles et al.
2000) to a 48% gain (Fiatarone et al. 1990), with most of
the studies reporting improvements in only some of the
functional abilities investigated (Skelton et al. 1995;
Rooks et al. 1997; Sherrington and Lord 1997; Taaffe
et al. 1999). Skelton and McLaughlin (1996) have
concluded that improvements in functional abilities may
be a carried-over effect of strength and power training,
but are more likely to occur if the functional task is also
practised. More recently, Earles et al. (2000) have also
pointed out that power training per se may not neces-
sarily improve functional task performance. Following a
12-week high-velocity training programme, 34 individ-
uals of both genders in their late seventies increased their
muscle strength and peak powe r of lower limb muscles
by 22%, but did not improve functional task perfor-
mance. Rooks et al. (1997), on the contrary, noted a
20% improvement in stair clim b time after 10 months of
moderate-resistance high-velocity training, but similar
changes were also observed in a group of individuals
performing a walk ing programme.
Three selected functional abilities appear to be the
most frequently used in assessing the effects of inter-
vention programmes: chair raising, stair climbing and
maximum or self-sel ected walking speed. Chair raising is
usually assessed as the time taken by older individuals to
rise from a standard chair (seat height 43 cm) with their
arms folded (Fiatarone et al. 1990; Skelton et al. 1995;
Skelton and McLaughlin 1996; Taaffe et al. 1999; Earles
et al. 2000). Stair climbing normally consists of
ascending and often descending a staircase without
stopping at a comfortable pace, with or without using
the handrail (Fiatarone et al. 1994; Skelton et al. 1995;
Skelton and McLaughlin 1996; Rooks et al. 1997). The
time to complete the task is timed. Maximum walking
speed is measured by asking the subjects to walk as fast
as possible over a distance, which is usually around 6 m,
and recording the time taken to cover that distance
(Hunter et al. 1995; Skelton and McLaughlin 1996).
Other authors have measured the so-called usual or
habitual velocity, by instructing the subjects to walk as
they normally do (Fiatarone et al. 1990, 1994; Judge
et al. 1993; Skelton et al. 1995; Sherrington and Lord
1997). In some cases, subjects were asked to walk placing
the heel of one foot directly in front of the toe of the
other with the shoe touching, which is referred to as
tandem walk (Fiatarone et al. 1990), or walking back-
ward using the same pattern (Taaffe et al. 1999). It is
reasonable to expect that the choi ce of discriminatory
tests of functional abilities in a population of older
individuals who are healthy and active could be more
problematic than in a group of frail indivi duals.
Macaluso et al. (2003) have been the first authors to
adopt cycling as a novel approach to perform three
different regimes of resistance training (one performed at
a light intensity with a high speed of movement, another
performed at a heavy intensity with a slower speed of
movement, a third based on a combination of both) in a
population of healthy older women aged 65 to 74 years.
All of the participants improved their maximum walking
speed and other functional abilities (box-stepping and
vertical jumping), with a parallel increase in muscle
strength and power, regardless of the training regime
adopted (Macaluso et al. 2003). These are the novel
findings which deserve to be remarked upon: (1) even fit
Table 3 Effect of resistance training on selected functional abilities in older individuals. (AD ankle dorsiflexion, BL bag lifting, BP bench press, BS box stepping, BT time of getting in
and out of a bath, CB carrying box, CR chair raise time, EE elbow extension, EF elbow flexion, F female, FR functional reach, FRS floor rising, GWBE general weight bearing exercises,
HA hip abduction, HE hip extension, HF hip flexion, HR heart rate during stair climbing or corridor walk, iEMG integrated electromyogram, KE knee extension, KF knee flexion, KR
kneel rise time, LP leg press, M male, MWV maximum walking velocity, PCE postural control exercises, PF ankle plantarflexion, 1RM one repetition of maximum weight that could be
lifted, S supervised, SC self-paced stair climbing speed, sp self-paced, SR self-paced step rate, SU step-up, SUT sit-up for the trunk flexors, TUG timed up and go, U unsupervised, WR
self-paced walking rate)
Authors Subjects Training programme Functional ability
Gain %
Age Gender N Health and
Practice of
Per wk
Sets Reps % of
et al. 1990
86–96 M/F 10 Frail institutionalized NO KE 8 3 3 8 80 CR, MWV, tandem
gait speed
et al. 1993
71–97 M/F 31 Relatively healthy NO KE, HA, AD, HE,
12 3 3 8–12 75–80 MWV, usual gait
et al. 1994
72–98 M/F 100 Frail institutionalized NO KE, HE 10 3 3 8 80 Habitual gait
et al. 1995
60–77 F 14 Healthy independent NO LP, BP, EF, EE,
16 3 2 12RM MWV, iEMG during
18 §
et al. 1995
76–93 F 20 Healthy independent NO Elastic tubing,
rice bags
12 3 3 4–8 FR, SC, WR, SR, HR,
Only KR,
Skelton and
74–89 F 18 Relatively independent YES Elastic tubing,
tin cans, sponge
8 1S-2U 1–3 4–8 FR, CR, TUG, MWV,
11–22 in
only five
and Lord 1997
64–94 M/F 21 Indep. after hip fracture NO GWBE 4 7 FR, habitual walking
et al. 1997
65–95 M/F 37 Independent community
43 3 3 8–15 sp SC time; pen pick-up
20; -24
et al. 1999
65–79 M/F 46 Healthy NO LP, KE 24 1 3 8 80 CR, backward tandem
et al. 2000
62–77 M/F 10 Healthy active NO LP, KE, BP, KF,
24 2 3–5 8–12 50–80 MWV 13
et al. 2000
77±5 M/F 18 Highly functioning YES
12 3 3 10 50–70 CR; 8-foot walk;
6-min walk
Tandem gait speed only;
usual only;
decreased iEMG in CR and CB by36% and 40%, respectively;
SC only;
CR only; n.r.# habitual walking velocity only; percentage increase not reported
older women still have a margin for improvement in
functional abilities; (2) the training-induced increase in
power output was due to a combined increase in both of
the two determinants of power, optimal force and
optimal velocity; (3) the lack of difference between the
three training regimes seems to suggest that it is not the
intensity nor the speed of movement, but the level of
mechanical work, with this being similar in the three
groups, which represents the training stimulus.
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