Effect Of Menstrual Cycle Phase Research Articles

No Effect of Menstrual Cycle Phase and Oral Contraceptive Use on Endurance Performance in Rowers

The aim of this study was to examine whether variables commonly used in aerobic exercise testing are influenced by menstrual cycle phases and use of oral contraceptive (OC) in female rowers. Twenty-four eumenorrheic female rowers distinguished on the basis of both menstrual status and athleticism participated in this study and were divided into competitive cyclic athletes (n = 8), recreationally trained cyclic athletes (n = 7), and recreationally trained athletes taking OC pills (ROC; n = 9). Rowers performed 2 incremental tests to voluntary exhaustion on a rowing ergometer during 2 different phases of the menstrual cycle: the follicular phase (FP) and the luteal phase (LP). The study variables were power output (Pa), heart rate (HR), oxygen consumption (VO2), carbon dioxide production (VCO2), minute ventilation (VE), the mean respiratory exchange ratio, and ventilatory equivalents of O2 (VE/VO2)) and CO2 (VE/VCO2), which were measured at maximal and at the aerobic-anaerobic transition intensities. In addition, maximal blood lactate (La) values after the test were obtained. When comparing Pa, &OV0312;o2, HR, and La values, no significant differences (p > 0.05) between FP and LP at maximal load and at threshold intensity were found in all 3 groups of the rowers studied. However, we observed higher values (p < 0.05) for VE/VCO2 at both intensities in LP compared with FP in the ROC group. In conclusion, sport-specific endurance performance was not influenced by the phase of the normal menstrual cycle and the synthetic menstrual cycle of the OC users in the rowers studied. Therefore, normally menstruating female rowers and female rowers taking OC pills should not be concerned about the timing of their menstrual cycle with regard to optimized sport-specific endurance performance.

Effects of Menstrual Cycle Phase on Ratings of Implicitly Erotic Art

Women's perceptions of and responses to explicitly erotic stimuli have been shown to vary across the menstrual cycle. The present study examined responses to implicit eroticism. A total of 83 women provided reactions to paintings by Georgia O'Keeffe in 6 day intervals over the course of 1 month. Among freely cycling women (n = 37), 31% of their descriptions included sexual themes during the first half of their cycle, dropping to 9% of descriptions in the second half. In women using oral contraceptives (n = 46), there was no significant difference in descriptions across the cycle (13% in the first half vs. 17% in the second half). Results were discussed in terms of evolutionary psychology and social-cognitive perspectives on the relationships between hormonal fluctuations and sexuality.

No effect of menstrual cycle phase on fuel oxidation during exercise in rowers

The aim of this investigation was to examine the effects of menstrual cycle phase on substrate oxidation and lactate concentration during exercise. Eleven eumenorrheic female rowers (18.4 ± 1.9 years; 172.0 ± 4.0 cm; 67.2 ± 8.4 kg; 27.7 ± 4.8% body fat) completed 1 h rowing ergometer exercise at 70% of maximal oxygen consumption (VO(2max)) during two different phases of the menstrual cycle: the follicular phase (FP) and the luteal phase (LP). Resting and exercise measurements of the whole body energy expenditure, oxygen consumption (VO(2)), respiratory exchange ratio (RER), substrate oxidation and lactate blood levels were made. Energy expenditure, VO(2) and heart rate during the 1-h exercise were not significantly different (P > 0.05) among menstrual cycle phases. Resting RER and RER during the entire 1 h exercise period were not significantly different among menstrual cycle phases. There was an increase (P < 0.05) in RER in the transition between rest and exercise and a further increase in RER occurred after the first 30 min of exercise at both menstrual cycle phases. Blood lactate concentrations significantly increased in the transition between rest and exercise and remained relatively constant during the whole 1 h of exercise in both menstrual cycle phases. No menstrual cycle phase effect (P > 0.05) was observed for blood lactate concentrations. In conclusion, our results demonstrated no effect of menstrual cycle phase on substrate oxidation and blood lactate concentration during rowing exercise at 70% of VO(2max) in athletes. Normally menstruating female rowers should not be concerned about their menstrual cycle phase with regard to substrate oxidation in everyday training.

Peripheral oxytocin is associated with reduced symptom severity in schizophrenia

Background Emerging evidence from clinical trials suggests that oral estrogen and intranasal oxytocin might reduce symptom severity in schizophrenia. Whether increases in endogenous hormones are similarly associated with improved symptoms is unknown. We investigated the effects of menstrual cycle phase and related fluctuations in peripheral hormone levels on clinical symptoms in women with chronic schizophrenia. Method Twenty-three women with schizophrenia were administered the Positive and Negative Syndrome Scale (PANSS), a measure of clinical symptom severity, at two menstrual cycle phases: 1) early follicular (Days 2–4; low estrogen/progesterone) and 2) midluteal (Days 20–22; high estrogen/progesterone). Twenty-seven males with schizophrenia and 58 controls (31 female) completed testing at comparable intervals. Men were included to examine whether the relationships between clinical symptoms and hormone levels in women generalize to men. Plasma hormone assays of estrogen, oxytocin, progesterone, and testosterone were obtained. Results Female patients showed less severe symptoms during the midluteal versus early follicular phase ( p's < 0.01). Oxytocin did not fluctuate across phases, but in female patients ( p's < 0.01) higher oxytocin levels were associated with less severe positive symptoms and overall psychopathology. In both sexes, higher oxytocin levels were associated with more prosocial behaviors ( p < 0.05). Conclusion Consistent with previous findings in acutely ill patients, our results suggest that clinical symptoms vary across the menstrual cycle in patients with chronic schizophrenia. Similar to recent findings regarding benefits of intranasal oxytocin, these new findings indicate that high levels of endogenous oxytocin might improve positive symptom severity and general psychopathology in women and social behaviors in both sexes.

Longitudinal Study of Insulin Resistance and Sex Hormones over the Menstrual Cycle: The BioCycle Study

Conflicting findings have been reported regarding the effect of menstrual cycle phase and sex hormones on insulin sensitivity. The aim was to determine the pattern of insulin resistance over the menstrual cycle and whether variations in sex hormones explain these patterns. The BioCycle study is a longitudinal study that measured hormones at different phases of the menstrual cycle. Participants had up to eight visits per cycle; each visit was timed using fertility monitors to capture sensitive windows of hormonal changes. The study was conducted in the general community of the University at Buffalo (Buffalo, NY). A total of 257 healthy, premenopausal women (age, 27±8 yr; body mass index, 24±4 kg/m2) participated in the study. We measured fasting insulin, glucose, and insulin resistance by the homeostasis model of insulin resistance (HOMA-IR). Significant changes in HOMA-IR were observed over the menstrual cycle; from a midfollicular phase level of 1.35, levels rose to 1.59 during the early luteal phase and decreased to 1.55 in the late-luteal phase. HOMA-IR levels primarily reflected changes in insulin and not glucose. After adjustment for age, race, cycle, and other sex hormones, HOMA-IR was positively associated with estradiol (β=0.082; P<0.001) and progesterone (β=0.025; P<0.001), and inversely associated with FSH (adjusted β=-0.040; P<0.001) and SHBG (β=-0.085; P<0.001). LH was not associated with HOMA-IR. Further adjustment for BMI weakened the association with SHBG (β=-0.057; P=0.06) but did not affect other associations. Insulin exhibited minor menstrual cycle variability. Estradiol and progesterone were positively associated with insulin resistance and should be considered in studies of insulin resistance among premenopausal women.

Effect of menstrual cycle phase on sprinting performance

This study examined the effects of menstrual cycle phase (MCP) upon sprinting and recovery as well as upon metabolic responses to such exercise. Eight females performed a repeated 30-s sprint on a non-motorised treadmill interspersed with a 2-min rest in three phases of the MCP, follicular (low 17beta-estradiol and progesterone), just prior to ovulation (midcycle trial, highest 17beta-estradiol concentration and low progesterone) and in the luteal phase (high 17beta-estradiol and high progesterone). MCP was verified later by radioimmunoassay of 17beta-estradiol and progesterone. Peak power output (PPO) and mean power output (MPO) were unaltered (P > 0.05) due to MCP [PPO for sprint 1: 463 (18) W vs. 443 (15) W vs. 449 (18) W; PPO for sprint 2: 395 (17) W vs. 359 (16) W vs. 397 (17) W; MPO for sprint 1: 302 (15) W vs. 298 (13) W vs. 298 (14) W; MPO for sprint 2: 252 (10) W vs. 248 (10) W vs. 259 (12) W for follicular, midcycle and luteal trial, mean (SEM), respectively]. Similarly, percentage recovery of PPO and MPO (the PPO or MPO during sprint 2 expressed as a percentage of the PPO or MPO during sprint 1) was also unchanged (P > 0.05). Blood lactate, blood pH and plasma ammonia after sprinting and estimated plasma volume were also unaltered by MCP (P > 0.05). These findings suggest that hormonal fluctuations due to MCP do not interfere with maximal intensity whole body sprinting and the metabolic responses to such exercise.

Effects of menstrual cycle phase on metabolomic profiles in premenopausal women

Characterization of the normal degree of physiological variation in the metabolomic profiles of healthy humans is a necessary step in the development of metabolomics as both a clinical research and diagnostic tool. This study investigated the effects of the menstrual cycle on (1)H nuclear magnetic resonance (NMR) derived metabolomic profiles of urine and plasma from healthy women. In this study, 34 healthy women were recruited and a first void urine and fasting blood sample were collected from each woman at four different time points during one menstrual cycle. Serum hormone levels were used in combination with the menstrual calendar to classify the urine and plasma samples into five different phases i.e. menstrual, follicular, periovulatory, luteal and premenstrual. The urine and plasma samples were analysed using (1)H NMR spectroscopy and subsequent data were analysed using principal component analysis (PCA) and partial least squares discriminant analysis. PCA of the urine spectra showed no separation of samples based on the phases of the menstrual cycle. Multivariate analysis of the plasma spectra showed a separation of the menstrual phase and the luteal phase samples (R(2) = 0.61, Q(2) = 0.41). Subsequent analysis revealed a significant decrease in levels of glutamine, glycine, alanine, lysine, serine and creatinine and a significant increase in levels of acetoacetate and very low density lipoprotein (VLDL CH(2)) during the luteal phase. These results establish a need to control for metabolic changes that occur in plasma due to the menstrual cycle in the design of future metabolomic studies involving premenopausal women.

Mental stress‐induced haemoconcentration in women: Effects of menstrual cycle phase

In women, variation in the incidence of myocardial infarction (MI) has been reported with phase of the menstrual cycle. Mental stress-induced rheological and haemodynamic perturbations have been implicated in the triggering of MI. This study examined cardiovascular reactions to mental stress across the menstrual cycle, as a factor contributing to the known variation between the menstrual cycle phases in MI incidence. Rheological and haemodynamic activity during rest and a prolonged mental stress task were assessed in 12 women during the follicular and luteal phases of the menstrual cycle. The stress task increased haematocrit, colloid osmotic pressure, blood pressure and heart rate, and decreased heart rate variability and R-wave to pulse interval. However, there were no effects of menstrual phase on rheological or haemodynamic function at rest or in response to mental stress. There were also no moderating menstrual cycle effects for the rheological or haemodynamic reactions over time to this prolonged stress task. Our findings do not support the hypothesis that variations in reactions to mental stress can explain the reported variations in risk for MI across the menstrual cycle.

The Effect of Menstrual-Cycle Phase on Hamstring Extensibility and Muscle Stiffness

Preventing noncontact ACL injuries has been a major focus of athletic trainers and researchers. One factor that may influence female noncontact ACL injury is the fluctuating concentrations of hormones in the body. To determine whether muscle properties change across the menstrual cycle. Repeated measures. Testing was performed within 3 d after the onset of menses and ovulation. Repeated-measures ANOVAs were used to determine changes in variables across the menstrual cycle, and Pearson correlations were used to determine relationships between variables. 8 women with normal menstrual cycles. Active hamstring stiffness and hamstring extensibility. Hamstring extensibility (P = .003) increased at the ovulation testing session but hamstring muscle stiffness (P = .66) did not. The results indicate that hamstring muscle stiffness did not change across the menstrual cycle and hamstring extensibility increased at ovulation, when estrogen concentration increases.

Neural activation in the orbitofrontal cortex in response to male faces increases during the follicular phase

Women's sexual interest changes with hormonal fluctuations across the menstrual cycle. It is unclear how hormones modify women's sexual behavior and desire, but one possibility is that they alter women's positive appraisals of stimuli and thus their sexual interest. Using 3 T fMRI, we measured neural activation in women at two time points in their menstrual cycle (late follicular, luteal) while they evaluated photos of men presented as potential sexual partners. Participants were ten heterosexual women aged 23–28 none of who was using hormonal contraceptives or in a committed relationship. In an event-related design, the women were presented with as series of photos of male faces and asked questions to assess their degree of sexual interest in the men depicted. Results demonstrate an overall effect of menstrual cycle phase on neural activation. During their follicular versus luteal phase, women demonstrated increased activation in the right medial orbitofrontal cortex (OFC), suggesting increased positive appraisal. Activation in the OFC was positively correlated with women's estradiol to progesterone ratios. There were no areas that demonstrated increased activation during the luteal versus follicular phase. The observed increase in activation in the OFC during the follicular phase may reflect a hormonally mediated increase in appetitive motivation and may prime women towards increased sexual interest and behavior around ovulation.

Adolescents’ cortisol responses to awakening and social stress; Effects of gender, menstrual phase and oral contraceptives. The TRAILS study

Studies on the influence of sex hormones on cortisol responses to awakening and stress have mainly been conducted in adults, while reports on adolescents are scarce. We studied the effects of gender, menstrual cycle phase and oral contraceptive (OC) use on cortisol responses in a large sample of adolescents. Data come from TRAILS (TRacking Adolescents' Individual Lives Survey), a prospective population study of Dutch adolescents. This study uses data of 644 adolescents (age 15-17 years, 54.7% boys) who participated in a laboratory session including a performance-related social stress task (public speaking and mental arithmetic). Free cortisol levels were assessed by multiple saliva samples, both after awakening and during the laboratory session. No significant effects of gender and menstrual phase on cortisol responses to awakening were found, while girls using OC displayed a slightly blunted response (F(1, 244)=5.30, p=.02). Cortisol responses to social stress were different for boys and free-cycling girls (F(3, 494)=9.73, p<.001), and OC users and free-cycling girls (F(3, 279)=15.12, p<.001). Unexpectedly, OC users showed no response at all but displayed linearly decreasing levels F(1, 279)=19.03, p<.001) of cortisol during the social stress test. We found no effect of menstrual cycle phase on cortisol responses to social stress (F(3, 157)=0.58, p=.55). The absence of a gender difference in the adolescents' cortisol awakening response found in this study is consistent with previous reports. Our results further suggest that adolescent OC users display slightly blunted cortisol responses after awakening, and that gender differences in cortisol responses to social stress during adolescence are comparable to those described for adult populations, that is, stronger responses in men than in women. Whereas previous work in adults suggested blunted stress responses in OC users compared to men and free-cycling women, adolescent OC users showed no cortisol response. Effects of type of OC could not be studied because of low numbers of OC that were only progestin based.

Effect of the menstrual cycle on intraoperative bleeding in rhinoplasty patients

This study aimed to evaluate the effect of menstrual cycle phase on intraoperative bleeding in rhinoplasty patients. One hundred seven female patients grouped as G1 (perimenstrual) and G2 (periovulatory) according to menstrual cycle were included in this study. Intraoperative blood loss was compared using the t test. Fifty-two of the patients were in G1 and 49 were in G2 group. Operative surgeons, presence of additional interventions, and operation duration did not differ among the groups. Mean intraoperative blood loss was 69.0 ± 24.6 ml in G1 and 80.4 ± 27.7 ml in G2. The blood loss difference between the two groups was statistically significant. This study demonstrated that perioperative blood loss is higher in patients operated on during the periovulatory phase. This increase does not seem to create difficulty during the operation or to have an impact on the outcome. Nevertheless, this might be reflected in more pronounced ecchymosis in the early postoperative phase.

The effect of menstrual cycle on 2000-m rowing ergometry performance

The aim of this study was to examine the effect of menstrual cycle phase on 2000-m rowing ergometry performance. Since high concentrations of oestrogen, indicative of the mid-luteal phase of the menstrual cycle, tend to decrease glycogen utilization and reduce blood lactate concentration, it was predicted that time taken to complete a 2000-m rowing trial would be shorter in the mid-luteal phase. Ten eumenorrhoeic, recreationally trained, female volunteers (mean age 33.0 years, s=7.1) completed 2000-m time trials on a Concept 2 rowing ergometer, in both the mid-follicular and mid-luteal phases of their menstrual cycle. In each phase, a 3-min incremental rowing protocol was used to determine a blood lactate concentration of 4 mmol · l−1 (T lac-4mM) and maximum oxygen consumption (VO2max); a five-stroke maximal test was used to establish maximal power. Order of testing was randomized for menstrual cycle phase. Variables (T lac-4mM, VO2max, maximal power) were correlated with speed in the 2000-m time trials, and the effect of menstrual cycle phase on these variables was examined. A blood lactate concentration of 4 mmol · l−1 occurred at a significantly higher mean exercise intensity (mid-luteal vs. mid-follicular: 169.1 W, s=39.1 vs. 159.0 W, s=38.3; P=0.033), heart rate (179 beats · min−1, s=9 vs. 173 beats · min−1, s=11; P=0.0047), and oxygen consumption (2.64 litres · min−1, s=0.66 vs. 2.42 litres · min−1, s=0.62; P=0.04) in the mid-luteal phase than in the mid-follicular phase. There was no significant difference (P=0.11) in 2000-m time trial speed according to menstrual cycle phase. In conclusion, although T lac-4mM differed due to menstrual cycle phase, 2000-m rowing performance was unaffected. Further research into the effects of menstrual cycle on rowing performance of a longer duration, among a more homogenous group of females, is recommended.

The effects of menstrual cycle phase on clinical measures of concussion in healthy college-aged females

The management of concussion and mild traumatic brain injury is an area of clinical uncertainty for many sports medicine professionals. While recent studies suggest sex differences in neurocognitive function may exist, our understanding of the effects of menstrual cycle phase and oral contraceptive pill (OCP) use in healthy females is limited. The purpose of this study was to investigate whether there were changes in neurocognitive function, postural stability and self-reported symptoms between the early and late stages of the menstrual cycle, and also to identify whether performance across menstrual cycle would differ between females using OCP and eumenorrheic females not using OCP. Healthy college-aged females completed a standard concussion test battery including computerised assessment of neurocognitive function, postural stability and symptom status. Participants completed the counterbalanced testing design during the early and late phases of their menstrual cycle. No significant main effects or interactions for any neurocognitive function or postural stability outcome measure were observed. Eumenorrheic females endorsed a higher number of symptoms and reported an increased symptom severity score compared to females using OCP. Menstrual cycle phase had no effect on the total severity or the number of symptoms endorsed. These results suggest preseason neurocognitive and postural stability baseline tests are stable across the menstrual cycle, regardless of OCP use. Therefore, decreased performance on these measures following a suspected concussion is likely not attributable to menstrual cycle phase or use of OCP.

Dichotic listening asymmetry: Sex differences and menstrual cycle effects

The impact of menstrual cyclicity and sex differences on dichotic listening was studied in 25 women and 20 men (aged 20–25 years). Dichotic listening was administered using consonant-vowel (CV) stimuli and tested across three attention conditions. Women were tested at two points in the menstrual cycle (Day 2–5: low oestrogen and progesterone/Low-EP; Day 18–25: high oestrogen and progesterone/High-EP). Men were tested once. Performance averaged across attention conditions was analysed for menstrual cycle and sex effects. Significant menstrual cycle phase effects were observed in women. At the High-EP phase women showed a greater right ear advantage (REA) compared to the Low-EP phase. Sex differences were found when dichotic listening asymmetry in men was compared to women at the Low-EP, but not the High-EP phase. In contrast to laterality effects, baseline perceptual performance (total right plus left ear response) was similar in men and women at both phases of the menstrual cycle. Results support a role for ovarian hormones in shaping laterality of speech perception in women. This study also emphasises the importance of considering menstrual cycle effects when evaluating sex differences in dichotic listening.

Effects of menstrual cycle phase and oral contraceptive use on verbal memory

Surgical or pharmacological suppression of ovarian hormones leads to declines in verbal memory, and estrogen treatment reverses these deficits. In the current study, we investigated the effects of menstrual cycle phase and oral contraceptives on verbal memory, as measured by the California Verbal Learning Test, in two groups of premenopausal women — 16 naturally cycling women and 20 current users of estrogen-based oral contraceptives (OCs). Naturally cycling women were assessed twice — once during the early follicular phase (Days 2–4) and once during the midluteal phase (Days 20–22) of the menstrual cycle. OC users were tested on the same cycle days, corresponding to inactive and active pill phases, respectively. We predicted that naturally cycling women would show improved verbal memory during the midluteal phase, when estradiol levels are high, compared with the follicular phase, when estradiol levels are low. We also predicted that OC users, who show no change in endogenous estradiol across the cycle, would show no change in verbal memory. Contrary to predictions, naturally cycling women showed no changes in verbal memory across the cycle, whereas OC users showed enhanced memory during the active pill phase ( p < .05). None of the secondary cognitive outcome measures varied with cycle phase or OC use including measures of visuospatial memory, verbal fluency, visuospatial abilities, and attention. Overall, these results suggest that verbal memory performance in premenopausal women varies across the cycle with OC use, but does not vary systematically with changes in endogenous estradiol.

Grip strength and endurance throughout the menstrual cycle in eumenorrheic and women using oral contraceptives

This study examined whether grip strength and endurance fluctuate throughout the menstrual cycle, thereby potentially contributing to upper extremity injury risk. This research had two primary objectives: (1) to quantify any changes in grip strength and endurance that occur throughout the menstrual cycle in eumenorrheic (naturally cycling) women, and (2) to examine the potential impact that monophasic oral contraceptive use may have on grip strength and endurance by comparing contraceptive-users to the eumenorrheic sample. Participants in the study (11 eumenorrheic and 8 contraceptive-using women) were measured during the early-follicular (day 4–6), late-follicular (day 11–13), and luteal (day 20–23) phases of the menstrual cycle. During each phase, each subject completed three experiments: single repetition maximum voluntary contraction, 20-repetition grip test, and a 30-s static (continual) hold. To provide a control, a group of 7 males was measured twice, with a 2-week interval between experiments. Menstrual cycle phase did not have a detectable effect on any measure of strength (absolute force production) in eumenorrheic women or women taking chemical contraceptives. However, static endurance (percent change in force throughout the 30-s hold) was significantly reduced during the late-follicular phase in the eumenorrheic women, when levels of estrogen are expected to be elevated. The women using oral contraceptives did not experience any similar fluctuation in static endurance across the three phases; however the static endurance of the contraceptive group was significantly lower than the eumenorrheic women during both the early-follicular and luteal phases. The implications of these data for assessing injury risk, performance, and future study are discussed. Significance Understanding the potential effects of menstrual cycle phase on musculoskeletal function is critical for developing proactive ergonomic interventions that are tailored specifically to women.

Effects of Menstrual Cycle Phase on Face Preferences

While many studies of face preferences have emphasized high agreement among individuals about the types of faces they consider attractive and unattractive, other studies have demonstrated systematic variation in face preferences. Here, we review the evidence that women's preferences for masculinity, apparent health, and self-resemblance in faces change systematically during the menstrual cycle. Our review focuses on the proximate mechanisms that might underpin these changes (i.e., what changes in hormone levels are important for effects of menstrual cycle phase) and the possible functions of these changes (i.e., to maximize the likelihood that offspring inherit strong immune systems or to increase the likelihood of successful pregnancy by either promoting affiliation with individuals who will provide support and care during pregnancy or by promoting strategies to avoid contagion during social interactions). While evidence that differentiates between these two accounts of the function of cyclic shifts in face preferences is currently equivocal for masculinity preferences, there is compelling evidence that the function of the effects of menstrual cycle phase on preferences for apparent health and self-resemblance in faces is to increase the likelihood of successful pregnancy.

Voice Onset Time in Women as a Function of Oral Contraceptive Use

Previous studies of the effect of hormonal changes across phases of the menstrual cycle on voice onset time (VOT) have not considered the variable of oral contraceptive use. The purpose of this study was to examine both the effects of menstrual cycle phase and that of oral contraceptive use on VOT. It was hypothesized that women taking oral contraceptives would exhibit smaller VOT differences across the phases of their menstrual cycles. The study was a prospective matched-group experimental design. Participants were 10 women who were on oral contraceptives and 10 who were not. The participants were recorded over two menstrual cycles, on the 10th and 20th day to evaluate their speech during the preovulation and premenstrual phases of their menstrual cycle. Participants produced 10 repetitions of the phrase "Speak ___ to me" containing the target syllables /bae/ and /pae/. Repeated measure ANOVAs revealed no significant differences in VOT between the two groups. Statistical results showed significant interactions between the menstrual cycle phase and the 2 recording months. It is possible that month-to-month differences in hormonal levels and other factors that can affect speech may have a greater effect on VOT than either the taking of oral contraceptives or the phase differences within a menstrual cycle.

Carbohydrate Loading and Female Endurance Athletes: Effect of Menstrual-Cycle Phase

This study compared 3 d of carbohydrate loading (CHOL; 8.4 g x kg(-1) x d(-1) carbohydrate) in female eumenorrheic athletes with 3 d of an isoenergetic normal diet (NORM; 5.2 g x kg(-1) x d(-1) carbohydrate) and examined the effect of menstrual-cycle phase on performance, muscle-glycogen concentration [glyc], and substrate utilization. Nine moderately trained eumenorrheic women cycled in an intermittent protocol varying in intensity from 45% to 75% VO2max for 75 min, followed by a 16-km time trial at the midfollicular (MF) and midluteal (ML) phases of the menstrual cycle on NORM and CHOL. Time-trial performance was not affected by diet (CHOL 26.10 +/- 1.04 min, NORM 26.16 +/- 1.35 min; P = 0.494) or menstrual-cycle phase (MF 26.05 +/- 1.10 min, ML 26.23 +/- 1.33 min; P = 0.370). Resting [glyc] was lowest in the MF phase after NORM (575 +/- 145 mmol x kg(-1) x dw(-1)), compared with the MF phase after CHOL (728 mmol x kg(-1) x dw(-1)) and the ML phase after CHOL and NORM (756 and 771 mmol x kg(-1) x dw(-1), respectively). No effect of phase on substrate utilization during exercise was observed. These data support previous observations of greater resting [glyc] in the ML than the MF phase of the menstrual cycle and suggest that lower glycogen storage in the MF phase can be overcome by carbohydrate loading.