Si può desiderare di provare un trattamento naturale disfunzione erettile come un diverso per i problemi di costruzione. Al giorno d oggi ci sono diverse terapie sul mercato, ma un trattamento naturale disfunzione erettile è stato confermato qualche ora e ora di nuovo per dare risultati efficienti e permanenti. Cos è la disfunzione sessuale? L incapacità di sviluppare o sostenere una costruzione abbastanza lungo per fare l amore è chiamato disfunzione erettile, ED https://farmacia-senzaricetta.it/ o (maschio) problemi di erezione. Tutti gli uomini possono avere problemi di costruzione di volta in volta e gli scienziati considerano ED essere presenti se si verificano problemi di costruzione almeno il 25% del tempo. Alcuni fatti duri: ED Può essere dovuto a problemi emotivi. Stress, pressione, giltiness, depressione, bassa autostima e ansia prestazioni può essere la causa dei vostri problemi di costruzione. La ricerca ha confermato che il 90 per cento della disfunzione erettile è fisica in origine, non emotiva. L impotenza colpisce la maggior parte degli uomini durante la loro vita e può essere dovuto a troppo colesterolo, problemi cardiaci, diabete, ipertensione, fumo o alcol. Alcuni rimedi possono essere la ragione. Le questioni legate al movimento sono collegate. Se ti occupi dei tuoi problemi di movimento, hai piu possibilita di risolvere questo problema. Qui ci sono 5 consigli facili su come aumentare la circolazione: 1. Mangia i pasti giusti. Questo ti rendera il flusso sanguigno ovvio. Una grande parte di rimanere sani e anche mantenere il flusso sanguigno ovvio è legato al vostro piano di alimentazione quotidiana e quello che si mangia. Una buona cura per la disfunzione erettile è mangiare un piano a basso contenuto di grassi e grande alimentazione di fibre. Mangiare fibre tutti i giorni e questo viene scoperto in prodotti cerealicoli cereali integrali, frutta e verdura. Evitare il più possibile pasti pronti o pasti non sani. 2. Wonder herbal rimedi. Molti rimedi vegetali per ED eseguire bene come possono migliorare il movimento. Hanno molto meno reazioni avverse rispetto ai farmaci convenzionali e si svolgono in modo efficiente per migliorare hardons e la forza, troppo. Erbe naturali come Ginkgo Biloba sono utilizzati come una strategia per ED. Gli specialisti di erboristeria credono anche che le spezie o le erbe come noce moscata, portano al movimento intorno al corpo, tra cui il pene. 3. Vitamine naturali vitali. Gli scienziati sanitari hanno scoperto che una mancanza di supplemento è tipico tra gli uomini con ED in particolare vitamina A. Se si ha una mancanza del nutriente ossido di zinco, Questo è stato confermato per portare alla disfunzione erettile. Queste inadeguatezze derivano dal fatto che molti valori nutrizionali in quello che mangiamo piano non sono sufficienti. Aggiungere al vostro fabbisogno di nutrienti aumenterà la circolazione del sistema e migliorare questa condizione. Gli integratori alimentari sono completamente naturali, quindi non dovrete preoccuparvi dei rischi di reazioni avverse. Inoltre, queste vitamine naturali sono utili per il vostro benessere over-all. Oltre a questi vantaggi benessere, disfunzione erettile vitamine naturali e integratori costano molto meno di farmaci rimedi. 4. Esercitare. Fai una mossa e non un tablet vibrante. Camminare farà di più per migliorare e sostenere hardons di qualsiasi altra compressa chimica nel lungo periodo. Il fitness fisico manterrà bassi livelli di pressione e mantenere grandi stadi di movimento. Andando per un 20-30 minuti di movimento rapido ogni giorno, può affrontare questo problema e può sostenere la vostra libido senza l uso di qualsiasi farmaco. 5. Sottolineare. Questo è il peggior attaccante per problemi di erezione. Scopri diversi metodi per riposare. Alcuni metodi tipici per riposare includono la lettura di un libro, la meditazione, un bagno rilassante o allenamenti di respirazione. Sto solo imparando alcuni semplici allenamenti di respirazione che possono migliorare significativamente il movimento nel reparto pantaloni. Una naturale disfunzione erettile soluzioni di trattamento stanno diventando sempre più popolare con gli uomini. Questi rimedi a base di erbe sono preferiti perché non hanno reazioni avverse e sono confermati essere efficiente come il farmaco. La maggior parte degli uomini combattere parlano dei loro problemi, in particolare la disfunzione erettile come c è poca discussione sui problemi di erezione. La verita e che ED ha un impatto su piu di dieci milioni di uomini solo negli Stati Uniti. Non siete soli e l aiuto è disponibile.
Cls432.dvi
Clinical Science (2003) 105, 663–669 (Printed in Great Britain)
concentration of bioavailable 17-β oestradiol K. J. ELLIOTT∗, N. T. CABLE†, T. REILLY† and M. J. DIVER‡
∗Department of Sport and Exercise Sciences, University of Brighton, Eastbourne BN20 7SP, U.K., †Research Institute for Sportand Exercise Sciences, Liverpool John Moores University, Liverpool L3 2ET, U.K., and ‡Department of Clinical Chemistry,University of Liverpool, Liverpool L7 8XP, U.K.
To investigate the effect of changes in sex hormone concentration on muscle strength and thebioavailability of 17-β oestradiol (oestradiol) and testosterone, seven eumenorrheic females weretested during two phases of the menstrual cycle. Maximum voluntary isometric strength of the firstdorsal interosseus muscle was measured during the early follicular and mid-luteal phases of themenstrual cycle. These phases were chosen for testing as the concentration of total oestradiolis significantly different in these two phases. Total oestradiol has been repeatedly associated withchanges in muscle strength in females, whereas the effects of bioavailable oestradiol are unknown. The concentrations of total and bioavailable oestradiol and testosterone were measured in additionto the concentration of total progesterone. Concentrations of total progesterone and oestradiolwere significantly different between the early follicular and mid-luteal phases of the menstrualcycle (P < 0.05 and P < 0.001 respectively). The concentration of total testosterone (0.7 +
− 0.1 nmol · l−1 respectively) and the ratio of total oestradiol to progesterone (153.0 +
− 27.8 respectively) did not change significantly between the early follicular and mid-
luteal phases. Bioavailable testosterone (102.2 +
− 60.6 pmol · l−1 respectively) did not differ
significantly between phases. There were no significant differences in muscle strength duringthe menstrual cycle (P = 0.1). Mean maximum voluntary isometric force of the first dorsalinterosseus muscle did not correlate significantly with the mean concentration of any reproductivehormone measured. These results indicate that cyclical variation in endogenous reproductive hor-mones does not affect muscle strength. INTRODUCTION
reproductive hormones on muscle function in femaleshave been widely debated. Various indices of muscle
Research into muscle periodicity as a result of menstrual
strength have been shown to increase, decrease or remain
cycle phase has been ongoing since 1876 when a Harvard
unchanged at different phases of the menstrual cycle [3–
student first noted cyclical changes in muscle strength [1].
8]. These ambiguous results may be due to conflicting
Moore and Barker [2] extended this work by making daily
definitions of ‘reproductive status’ [3,4] and ‘strength’
observations on muscle efficiency in 19 women across 12
[2,9], inaccurate identification of menstrual cycle phase
self-reported monthly cycles. Since then, the effects of
[5,10], different modalities of strength assessment [8,11],
Key words: first dorsal muscle, 17-β oestradiol, maximum voluntary isometric force, menstrual cycle, muscle strength, testosterone. Abbreviations: EF, early follicular; FDI, first dorsal interosseus; ML, mid-luteal; MVIF, maximum voluntary isometric force; SHBG, sex hormone binding globulin. Correspondence: Dr Kirsty Elliott (e-mail [email protected]).
examination of dissimilar muscle groups [6,7] and
early follicular (EF) and mid-luteal (ML) phases of
recruitment of non-homogenous groups of subjects [12].
the menstrual cycle] have the potential to change the
In addition, large inter- and intra-individual variability in
equilibrium between free, albumin- and SHBG-bound
hormone secretion [8] undermines studies using the
oestradiol and testosterone and, consequently, the con-
centration of bioavailable oestradiol and testosterone.
Recently, Janse de Jonge et al. [8] addressed some of
If the concentration of bioavailable oestradiol and
these problems by measuring the concentration of total
testosterone changes significantly during the menstrual
oestrogen, progesterone, luteinizing hormone and follicle
cycle, then this may account for the fluctuations in muscle
stimulating hormone and muscle strength, in conjunction
strength observed previously [4,5]. The mechanisms
with percutaneous electrical stimulation, throughout the
behind any possible effects are unknown as, to date,
menstrual cycle. They found that maximum isometric
no mechanistic work has been performed. Phillips
strength and fatigability of the quadriceps muscles did not
et al. [4] proposed that the effects of oestrogen on muscle
change between the menstrual, late follicular and luteal
strength are mediated by the classical steroid receptor
phases of the menstrual cycle, despite significant changes
for oestrogen, whereas Sarwar et al. [5] suggested that the
membrane receptor model probably controls the action of
Vermeulen et al. [13] suggested that (in plasma) the
oestrogen. Sarwar et al. [5] also proposed that changes in
bioavailable fraction, rather than the total concentration
the activity of myosin ATPase or the re-uptake of calcium
of testosterone, is a more accurate representation of the
by the sarcoplasmic reticulum might be responsible for
clinical situation. Testosterone is bound specifically to
sex hormone binding globulin (SHBG) (66 %) and non-
As previous studies have exclusively reported the con-
specifically to albumin (30 %), such that only 1–3 %
centration of total oestradiol [4,8], the objective of the
circulates freely [14]. As testosterone has a low affinity
present study was to examine the effects of menstrual
with, and is easily dissociated from, albumin, both
cycle phase on the bioavailability of oestradiol and
the albumin-bound and free portion can be considered
testosterone. In addition, this study was designed to
‘bioavailable’ [15]. Further evidence to support this
investigate the possible influence of cyclical changes in
hypothesis is provided by Van den Beld et al. [16],
bioavailable oestradiol and testosterone on maximum
who found that albumin-bound testosterone has access
voluntary isometric force (MVIF) of the first dorsal inter-
to target tissues. As both testosterone and 17-β
osseus (FDI) muscle under more rigorous test conditions
oestradiol (oestradiol) have a hydroxy group bound to
than have been used previously. We hypothesize that, if
position C-17, the same biochemical principles apply
after all of the aforementioned methodological flaws are
overcome, any changes in maximum force production
The bioavailable part of oestradiol and testosterone
that are observed will coincide with changes in the
is not a set proportion of the total concentration. The
concentration of bioavailable oestradiol and testosterone.
amount of steroid carried by a particular binding protein
EF and ML phases of the menstrual cycle were chosen for
depends not only on its affinity for the protein, but also on
testing, because the concentration of total oestradiol is
its concentration. First, testosterone and oestradiol have
low and high respectively, at these times and oestradiol
higher affinities with SHBG than albumin; therefore the
is the hormone most implicated in strength regulation
concentration of free hormone in equilibrium with
[4,5,11,18]. Testosterone was measured in the present
the albumin-bound hormone will always be smaller.
study as (i) few investigators have examined the effects of
Secondly, SHBG becomes saturated with testosterone
cyclical changes in testosterone concentration on muscle
and oestradiol more easily than albumin, such that
strength in females, and (ii) testosterone secretion is
large quantities of testosterone and oestradiol should
indirectly influenced by oestrogen concentration [19].
result in an increase in the amount of bioavailable
The bioavailability of progesterone was not measured as
hormone. However, the concentration of SHBG in
progesterone is also bound to cortisol-binding hormone
humans is not constant. Oestrogen administration and
and, to date, cannot be separated into its bioavailable and
the thyroid hormones increase SHBG levels, whereas
bound portions. Consequently, the concentration of total
androgen administration and growth hormone decrease
progesterone was measured and reported.
the concentration of SHBG. Gower and Nyman [17]found that oestrogen replacement therapy increasedSHBG levels (due to the first-pass effect, the liver is
exposed to supraphysiological concentrations of oes-tradiol) and consequently decreased the amount of
Subjects
bioavailable testosterone in postmenopausal women.
Seven healthy female subjects, with mean ( +
Therefore, in theory, the hormonal changes that occur
during the menstrual cycle [e.g. the concentration
of total oestradiol increases significantly between the
from the local University. All subjects reported normal
Muscle strength and menstrual cycle phase
Intra- and inter-assay reproducibility for each hormone
Values are expressed as a percentage coefficient of variation and are from four samples. Coefficient of variation was calculated by dividing the S.D. of the differencesbetween the two tests by the mean of the two tests and multiplying by 100. hCG, human chorionic gonadotropin.
menstrual cycle function, with mean cycle lengths
the method of Tremblay and Dube [26]. Intra- (30 times
− 1 days. Subjects had not been taking oral
in the same run) and inter- (29 different series) assay
contraceptives or any other hormonal treatments for
reproducibility was determined for each hormone using
at least 6 months prior to testing. Only non-smokers
were included in the study [20]. Subjects with anymuscular, neurological or skeletal disorders capable ofinfluencing performance of the hand were excluded. Assessment of MVIF of the FDI muscle
Approval for the experimental protocol was obtained
The FDI muscle was chosen for testing for two reasons.
from the institutions Human Ethics Committee and
First, the FDI muscle is the only muscle that produces
conformed to the Declaration of Helsinki. All subjects
abduction of the index finger. Other muscles attached to
provided written consent having read and understood
the finger are active during abduction but, due to their
anatomical arrangement, they do not contribute force inthis direction [27]. Rutherford and Jones [28] found very
Experimental design
similar maximum voluntary and stimulated contractionforces for the FDI muscle, therefore demonstrating that
All subjects reported to the laboratory in a ‘normal’
the FDI muscle can be maximally activated and isolated
fed state, having abstained from alcohol and caffeine
from the action of other hand muscles. Secondly, these
consumption and any strenuous physical exercise for
[28] and other [29] authors have found no difference in
24 h, due to known effects on muscle strength and re-
force production between dominant and non-dominant
productive hormone concentration [21–24]. A 10 ml ve-
hands, suggesting that this muscle is not trainable under
nous blood sample was drawn from each subject prior
to any physical testing. All testing was undertaken at
Prior to assessing the MVIF of the FDI muscle, the
the same time of day in order to control for circadian
hand and forearm were heated for 10 min to a skin
temperature of 40 ◦C using a hotpack (Dreamland Electric
Prior to experimentation, subjects were familiarized,
Heat Pad; Dreamland Appliances Ltd, Oldham, Lancs.,
on two occasions, with the experimental environment
U.K.). The muscle was warmed due to known effects of
and procedures. Following familiarization, subjects were
pre-exercise muscle temperature on muscle performance
tested on two occasions, day 2 and 21 of the cycle. Day 2
[30]. A reading lamp (60 W bulb) was positioned at a
(EF phase) was the day after the onset of menses and
standard distance over the muscle throughout the test
day 21 (ML phase) was 7 days after ovulation had
session in order to maintain skin temperature.
occurred. Ovulation was determined using 1 month of
A custom-built finger dynamometer [31] was used to
oral temperature measurement (MC 63B; Omron, Vernon
assess MVIF of the FDI muscle. The test re-test ratio
Hills, IL, U.S.A.) and a urinary luteinizing hormone kit
limits of agreement for assessment of MVIF of the FDI
(Clearplan, Bedford, U.K.). Subjects (and hence phases)
muscle using this equipment is 1.2. Based on a 20 %
were tested in random order. MVIF of the FDI muscle
error, the nomogram of Atkinson et al. [32] indicates
that a sample size of seven is adequate to detect at leasta 10 % change {Phillips et al. [4] found a significant
Hormonal analysis
change (10 %) in MVIF of the adductor pollicis muscle}
Plasma concentrations of total oestradiol, progesterone
in maximum force as a result of changes in reproductive
and testosterone were measured using an automated
quantitative system (Mini Vidas; bioMerieux, Lyon,
The dominant arm was placed in a prone position on
France). All samples were analysed using the enzyme-
the finger dynamometer. The forearm was secured to the
linked fluorescent assay technique, an enzyme im-
diagonal slope of the platform, at the wrist, mid-forearm
munoassay sandwich method with a final fluorescent
and distal portion of the elbow joint, with Velcro straps.
detection. The concentration of bioavailable oestradiol
The lateral side of the distal head of the proximal phalanx
and testosterone was measured using an adaptation of
of the index finger was aligned with the force transducer,
which was attached to a strain gauge (Model UL4000;
Mean MVIF of the FDI muscle correlated with
Maywood Instruments Ltd, Tilehurst, Berks., U.K.). The
the mean concentration of bioavailable oestradiol and
strain gauge was calibrated with known weights prior to
testosterone, total oestradiol, testosterone, progesterone,
testing. The thumb was secured, with a strap around the
and the ratio of oestradiol to progesterone
shaft of the first phalanx, in a fully abducted position.
The remaining fingers were covered in bubble-wrap andrestrained using a Velcro strap. An adjustable clamp,
tightened to the shaft of the second metacarpal, prevented
upward movement of the index finger. Hand position
was standardized for each test session. MVIF of the FDI
muscle was measured while the index finger was fully
abducted. Three sub-maximum isometric contractions
Force and the ratio of oestradiol to progesterone
were carried out prior to maximum force assessment. Following a rest of 3 min, three maximum voluntaryisometric contractions were performed, the best of whichwas taken as definitive. A rest of 1 min separated each
Percutaneous electrical stimulation was used to
Total concentrations
superimpose electrical impulses on to the FDI muscle
during each contraction. Two self-adhesive surface
28.3 nmol · l−1 in EF and ML phases respectively;
electrodes (3S; Healthcare, London, U.K.) delivered
P < 0.05) and oestradiol (110.8 +
1 Hz twitches, at a tolerable current, throughout the
83.5 pmol · l−1 in EF and ML phases respectively;
test. Individual tolerable currents were established prior
P < 0.001) were significantly different between phases.
to assessment of maximum isometric force. The anode
was placed directly proximal to the head of the second
0.1 nmol · l−1 in EF and ML phases respectively) and
metacarpal and the cathode medially to the head of
the ratio of oestradiol to progesterone (153.0 +
the first metacarpal. Electrical impulses were applied,
− 27.8 in EF and ML phases respectively) did
using a computer-driven Digitimer Stimulator (Model
not change between the phases of the menstrual cycle.
DS7; Digitimer Ltd, Welwyn Garden City, Herts.,U.K.), at 150 V with a pulse width of 100 µs duration. Force output was amplified and displayed visually on
Bioavailable concentrations
an Apple Macintosh computer interfaced with a data
There were no significant differences in the con-
acquisition system (MP100WS; Biopac Systems, Goleta,
centration of bioavailable testosterone (102.2 +
CA, U.S.A.). Maximum activation was confirmed when
− 90.2 pmol · l−1 in EF and ML phases
no extra force could be generated by the superimposed
pmol · l−1 in EF and ML phases respectively) between thetwo phases of the menstrual cycle. Statistical analysis Muscle strength
There were no significant differences in MVIF of the
Windows (Version 13; Minitab Inc., State College, PA,
FDI muscle between the EF and ML phases of the men-
U.S.A.) was used for data analysis. Verification that
strual cycle (P = 0.1). Mean strength was 28.2 +
data were normally distributed was provided by the
Anderson–Darling normality test. The level of signific-
phase. Mean MVIF did not significantly correlate with the
ance was taken as P < 0.05. A two-sample-dependent
mean concentration of any of the reproductive hormones
Student’s t test was used to detect significant differences
(either bioavailable or total concentration) measured
in MVIF of the FDI muscle and concentrations of
progesterone (total), oestradiol (total and bioavailable),testosterone (total and bioavailable) and the ratio of totaloestradiol to progesterone between the EF and ML phases
DISCUSSION
of the menstrual cycle. The relationship between MVIF ofthe FDI muscle and reproductive hormone status was
Investigators are not in agreement on either the quanti-
examined using Pearson’s correlation coefficient on
tative or directional effects of menstrual cycle phase on
normally distributed data, and Spearman’s rank cor-
strength [3,33,34]. In the present study, muscle strength
relation on non-parametric data. Prior to correlation, all
was measured under strict test conditions and did not
data were averaged so that time was factored out.
differ across the menstrual cycle, despite significant
Muscle strength and menstrual cycle phase
changes in the concentration of total oestradiol and
of oestradiol did not change significantly throughout
progesterone. In addition, muscle strength was not
the menstrual cycle. This might suggest that cyclical
significantly correlated with any of the reproductive
changes in the total concentration of oestradiol are
hormones measured. Janse de Jonge et al. [8] also found no
(i) not sufficient to saturate the concentration of
influence of menstrual cycle phase on muscle contractile
circulating SHBG and hence increase the concentration
properties using a similar research design, measuring
of free and albumin-bound oestradiol (i.e. bioavailable
MVIF of the quadriceps muscles and the concentration of
oestradiol) or (ii) sufficient to cause an increase in the
reproductive hormones. These results are consistent with
concentration of circulating SHBG, resulting in an in-
earlier work by Higgs and Robertson [10], who failed
crease in the amount of unavailable (or bound)
to detect any significant differences in handgrip strength
oestradiol. Future research may benefit from measuring
the concentration of circulating SHBG. No significant
The present findings do not agree with previous
differences in testosterone status (either total or
studies, which have implicated oestrogen and proges-
bioavailable) were noted between the EF and ML
terone in strength regulation [4,5]. Phillips et al. [4]
phases. Given that muscle strength and the bioavailable
demonstrated a 10 % increase in MVIF of the adductor
concentration of oestradiol and testosterone remained
pollicis muscle during the follicular phase (days 1–14)
unchanged, the possibility that muscle strength could
of the menstrual cycle. This was followed by a similar
indeed be affected by changes in the bioavailability of
drop in strength at the onset of ovulation. Although
oestradiol and testosterone cannot be dismissed. A model
Phillips et al. [4] did not find a significant relationship
that manipulates bioavailability of these hormones might
between strength and oestrogen status, they suggested
be used to examine this question. In particular, a model
that changes in muscle strength across the menstrual cycle
that significantly changes the concentration of both total
were related to, or caused by, fluctuations in oestrogen.
and bioavailable testosterone is warranted, so that the
However, if oestrogen was the hormone responsible
independent effects of testosterone on the maximum
for cyclical changes in muscle strength, then the largest
force-generating capacity of females can be investigated.
strength differences should occur between the ovulatory
Bioavailable oestradiol and testosterone have been
and follicular phases in which the highest and lowest
shown to change as a function of age in men. Van den Beld
concentrations of oestrogen are observed respectively.
et al. [16] measured free, albumin-bound, SHBG-bound
Indeed, Sarwar et al. [5] found that the greatest dif-
and total oestradiol and testosterone levels in elderly men
ferences in strength occurred between the ovulatory
(> 70 years). They found that bioavailable testosterone
(high oestrogen levels) and luteal (high oestrogen and
levels decreased with advancing age, whereas the
progesterone levels) phases. They suggested that pro-
concentration of SHBG-bound testosterone increased.
gesterone might inhibit oestrogen’s inotropic effect or
Conversely, total testosterone did not change as a
act directly on the muscle to weaken it. However,
function of age. Total and bioavailable oestradiol de-
this hypothesis is contradicted by the observation that,
creased and SHBG-bound oestradiol increased with
despite low progesterone levels, post-menopausal skeletal
age. In addition, Van den Beld et al. [16] found that
muscle is weak for its size [35]. Furthermore Greeves
bioavailable testosterone, but not bioavailable oestradiol,
et al. [31] reported that maximum muscle strength and
was positively related to muscle strength in men. The
fatigue did not change when progesterone levels were
concentration of total, but not bioavailable, testosterone
suppressed and the concentration of oestradiol was
has been shown to increase with age in women [36], but
raised from hypo- to hyper-oestrogenic levels. Based
muscle strength was not assessed in this study.
on this evidence, it is unlikely that either oestrogen or
Previous studies that have measured the concentration
progesterone significantly affects muscle function.
of free oestradiol and testosterone during the menstrual
To the best of our knowledge, this is the first
cycle have yielded conflicting results. Wu et al. [37] found
investigation of the effects of menstrual cycle phase on
that free oestradiol remained constant throughout the
the bioavailability of oestradiol and testosterone and
cycle. Conversely, Stahl et al. [38] reported significant
their effect on muscle strength in females. As stated
increases in free testosterone (mid-cycle) and oestradiol
previously, the bioavailable fraction of a hormone is
(two peaks), even though SHBG levels did not change.
not a set proportion of the total concentration. The
Mathor et al. [39] found, using equilibrium dialysis
concentration of bioavailable oestradiol and testosterone
of undiluted plasma, that the concentration of free
largely depends on the amount of circulating SHBG,
testosterone increased from the follicular to the luteal
which is affected by the concentration of thyroid,
phase of the menstrual cycle. In contrast, Schijf et al. [40]
growth, oestrogenic and androgenic hormones and the
showed that the free androgen index decreased during
concentration of total oestradiol and testosterone. In
the luteal phase, due to a significant increase in the
the present study, the total concentration of oestradiol
concentration of SHBG during this phase.
increased significantly between the EF and ML phases
In the present study, a large variation (as reflected
of the menstrual cycle. However, the bioavailability
by the S.D. values) in the concentration of reproductive
hormones was noted. In particular, bioavailable testoster-
11 Wirth, J. C. and Lohman, T. G. (1982) The relationship of
one ranged from 169 to 103 and 195 to 15 pmol · l−1
static muscle function to use of oral contraceptives. Med. Sci. Sports Exercise 14, 16–20
during the EF and ML phases respectively. Although
12 Bassey, E. J., Mockett, S. P. and Fentem, P. H. (1996) Lack
all blood samples were taken at the same time of day,
of variation in muscle strength with menstrual status in
ultradian ( < 24 h) fluctuations in hormone production
healthy women aged 45–54 years: data from a national survey. Eur. J. Appl. Physiol. 73, 382–386
may have masked any potential inotropic effects of
13 Vermeulen, A., Verdonck, L. and Kaufman, J. M. (1999)
reproductive hormones on muscle strength.
A critical evaluation of simple methods for the estimation
In conclusion, when measured under strict test
of free testosterone in serum. J. Clin. Endocrinol. Metab. 84, 3666–3672
conditions, menstrual cycle phase had no effect on
14 Dunn, J. F., Nisula, B. C. and Rodbard, D. (1981)
the bioavailability of oestradiol, testosterone or MVIF
Transport of steroid hormones: binding of 21 endogenoussteroids to both testosterone-binding globulin and
of the FDI muscle. Despite a significant increase in
corticosteroid binding globulin in human plasma. J. Clin.
the concentration of total oestradiol and progesterone
Endocrinol. Metab. 53, 58–68
between the EF and ML phases, no cyclical changes in
15 Pardridge, W. M. (1986) Serum bioavailability of sex
steroid hormones. J. Clin. Endocrinol. Metab. 15,
maximum force-generating capacity were noted. Muscle
strength was not significantly correlated with any of the
16 Van den Beld, A., De Jong, F. H., Grobbee, D. E., Pols,
hormones measured, suggesting that cyclical changes in
H. A. P. and Lamberts, S. W. J. (2000) Measures ofbioavailable serum testosterone and estradiol and their
reproductive hormone concentration do not affect muscle
relationships with muscle strength, bone density and body
function. To reduce the inter-individual variability in
composition in elderly men. J. Clin. Endocrinol. Metab. 85,
hormone concentration caused by the menstrual cycle,
17 Gower, B. A. and Nyman, L. (2000) Associations among
future work should utilize more stringent models of
oral estrogen use, free testosterone concentration, and lean
reproductive functioning to examine the effects of sex
body mass among postmenopausal women. J. Clin. Endocrinol. Metab. 85, 4476–4480
hormones on muscle strength. In addition, the effect of
18 Beltran Niclos, B., Welsh, L., Sarwar, R. and Rutherford,
significant changes in the concentration of bioavailable
O. M. (1995) Gender and age comparisons of the
oestradiol and testosterone on muscle strength could be
contractile properties of human quadriceps muscle. J. Physiol. (Cambridge, U.K.) 483, 131P
explored using other models besides the menstrual cycle,
19 Brooks, R. V. (1984) Androgens: physiology and
pathology. In Biochemistry of Steroid Hormones, 2nd edn(Makin, H. J. L., ed.), pp. 289–312, Blackwell ScientificPublications, Oxford
20 De Valk-de Roo, G. W., Netelenbos, J. C., Peters-Muller,
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Received 13 December 2002/9 May 2003; accepted 9 July 2003Published as Immediate Publication 9 July 2003, DOI 10.1042/CS20020360
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