The influence of ethnicity on thermosensitivity during cold water immersion

PURPOSE: This investigation evaluated the influence of ethnicity, Caucasian (CAU) vs. African American (AA), on thermosensitivity and metabolic heat production (HP) during cold water immersion (20 degrees C) in 15 CAU (22.7 +/- 2.7 yr) vs. 7 AA (21.7 +/- 2.7 yr) males. METHODS: Following a 20-min baseline period (BASE), subjects were immersed in 20 degrees C water until esophageal temperature (Tes) reached 36.5 degrees C or for a maximum pre-occlusion (Pre-OCC) time of 40 min. Arm and thigh cuffs were then inflated to 180 and 220 mm Hg, respectively, for 10 min (OCC). Following release of the inflated cuffs (Post-OCC), the slope of the relationship between the decrease in Tes and the increase in HP was used to define thermosensitivity (beta). RESULTS: ANOVA revealed no significant difference in thermosensitivity between CAU and AA (CAU = 3.56 +/- 1.54 vs. AA = 2.43 +/- 1.58 W.kg(-1). degrees C(-1)). No significant differences (p > 0.05) were found for Tsk (CAU = 24.2 +/- 1.1 vs. AA = 25.1 +/- 1.1 degrees C) or HP (p > 0.05; CAU = 2.5 +/- 0.8 vs. AA = 36.5 +/- 1.8 W.kg(-1)). However, a significant (p < 0.05) main effect for ethnicity for Tes was observed (CAU = 36.7 +/- 1.8 vs. AA = 36.5 +/- 1.8 degrees C). CONCLUSION: These data suggest, despite a differential response in Tes between AA and CAU groups, the beta of HP during cold water immersion is similar between CAU and AA. Therefore, these data demonstrate that when faced with a cold challenge, there is a similar response in HP between CAU and AA that is accompanied by a differential response in Tes.     

Warming by immersion or exercise affects initial cooling rate during subsequent cold water immersion

INTRODUCTION: We examined the effect of prior heating, by exercise and warm-water immersion, on core cooling rates in individuals rendered mildly hypothermic by immersion in cold water. METHODS: There were seven male subjects who were randomly assigned to one of three groups: 1) seated rest for 15 min (control); 2) cycling ergometry for 15 min at 70% Vo2 peak (active warming); or 3) immersion in a circulated bath at 40 degrees C to an esophageal temperature (Tes) similar to that at the end of exercise (passive warming). Subjects were then immersed in 7 degrees C water to a Tes of 34.5 degrees C. RESULTS: Initial Tes cooling rates (initial approximately 6 min cooling) differed significantly among the treatment conditions (0.074 +/- 0.045, 0.129 +/- 0.076, and 0.348 +/- 0.117 degrees C x min(-1) for control, active, and passive warming conditions, respectively); however, secondary cooling rates (rates following initial approximately 6 min cooling to the end of immersion) were not different between treatments (average of 0.102 +/- 0.085 degrees C x min(-1)). Overall Tes cooling rates during the full immersion period differed significantly and were 0.067 +/- 0.047, 0.085 +/- 0.045, and 0.209 +/- 0.131 degrees C x min(-1) for control, active, and passive warming, respectively. DISCUSSION: These results suggest that prior warming by both active and, to a greater extent, passive warming, may predispose a person to greater heat loss and to experience a larger decline in core temperature when subsequently exposed to cold water. Thus, functional time and possibly survival time could be reduced when cold water immersion is preceded by whole-body passive warming, and to a lesser degree by active warming.     

Effect of exercise during the follicular and luteal phases on indices of oxidative stress in healthy women

PURPOSE: Eleven healthy nonsmoking women (24+/-1.1 yr) exercised for 30 min at 75-80% VO2max during the follicular (F) and luteal (L) phases of their menstrual cycle to determine whether menstrual phase influenced indices of oxidative stress. METHODS: Subjects completed the exercise in a randomized order. Subjects reported between 0800 and 0900 in a postabsorptive state, rested for 15-30 min, and had a venous blood sample obtained by Vacutainer before and after exercise. RESULTS: Resting estradiol was 54.4+/-12.0 pg.mL(-1) for F phase and was significantly higher in L phase (147.2+/-25.5 pg.mL(-1)). Plasma malondialdehyde and thiobarbituric acid substances were no different before and after exercise independent of menstrual cycle phase. No differences in resting blood total glutathione (TGSH), oxidized glutathione (GSSG), and reduced glutathione (GSH) were evident comparing the F and L phases. After exercise, TGSH decreased (P = 0.03) but reached significance only in the F phase = 8.1 %(P = 0.04), L phase = 2.5% (P = 0. 15). Exercise increased GSSG 10.5% in F (P = 0.15) and 27.8% in L phases(P = 0.01). GSH decreased after exercise independent of menstrual phase (F = 17%, L = 16%, P = 0.01). CONCLUSION: These data suggest that 30 min of moderate-intensity exercise in female subjects can result in mild oxidative stress as indicated by blood glutathione status and that menstrual cycle phase has minimal influences on these exercise responses.     

Estrogen variation and resting left ventricular structure and function in young healthy females

PURPOSE: A potential confounding factor in the interpretation of left ventricular (LV) structural and functional data in female subjects could be menstrual phase or contraceptive use upon assessment. To date no study has addressed this issue. METHODS: Seventeen eumenorrheic (EU; mean +/- SD age = 21 +/- 3 yr) and 14 combined-oral contraceptive pill-using (COC: mean +/- SD age = 21 +/- 3 yr) females volunteered to participate. The EU had stable menstrual cycles and the COC had all been using the same pill preparation for a minimum of 6 months. Echocardiographic examinations occurred during the mid-follicular phase and mid-luteal phases in the EU and during mid-consumption and mid-end of withdrawal in the COC. LV structure and function were assessed using M-mode and pulsed-wave Doppler echocardiography. Data were compared via Student t-tests and limits of agreement (LoA) were calculated. RESULTS: Structure and function did not significantly differ between phases of the menstrual cycle or between consumption and withdrawal of oral contraception (P > 0.05). However, there was considerable variance in the LoA between variables. Smaller LoA were reported for those variables directly measured from echocardiograms compared with those from derived data. For example, in a measured variable such as LV internal dimension in diastole, the LoA data represented a variation of +/- 0.4 mm (+/- 1%) between phases. Conversely, data for LV mass, a derived variable, reported LoA values of +/- 15 g (10%) between phases. The LoA were consistent between EU and COC. Variation in both measured and derived variables were within, or close to, accepted limits of measurement or biological error. CONCLUSION: It would seem that in studies assessing LV structure and function in women the influence of menstrual phase or oral contraceptive use is of minor significance.     

The combined effect of time of day and menstrual cycle on lactate threshold

PURPOSE: This study examined the isolated and combined effects of time of day and menstrual cycle phase on the determination of the lactate threshold (Tlac) and blood lactate concentration. METHODS: Eleven endurance-trained female athletes (mean age 32.4+/- 6.9 yr) were tested at 06:00 and 18:00 h and at two phases of the menstrual cycle, the midfollicular phase and the midluteal phase. Capillary blood (25 muL) was obtained from the tip of the toe at rest, and during the last 30 s of a continuous, multistage, 3-min incremental protocol on the Concept II rowing ergometer. To determine Tlac, a curve-fitting procedure (Dmax method), a visual method (Tlac-vis), and the fixed blood lactate concentration of 4.0 mmol.L (Tlac-4 mM) were used. Ventilatory threshold (Tvent) was also determined. RESULTS: In the midluteal phase of the menstrual cycle, Tlac-4 mM occurred at a significantly higher exercise intensity, heart rate, and oxygen consumption than it did in the midfollicular phase. Blood lactate concentration at Tvent and at Tlac using the Dmax method was significantly lower in the midluteal phase. No significant interaction effects (menstrual cycle x time of day) were observed for any of the methods used to determine Tlac or for values of blood lactate concentration at rest and at maximum. CONCLUSION: These findings suggest that, when using fixed values of blood lactate in physiologic assessment, consideration should be given to the menstrual cycle phase in which the test is carried out.     

Effects of menstrual phase and amenorrhea on exercise performance in runners

There are few well controlled studies in terms of subject selection, menstrual classification, and exercise protocol that have examined both maximal and submaximal exercise responses during different phases of the menstrual cycle in eumenorrheic runners and compared these runners to amenorrheic runners. Thus, the purpose of this study was to measure selected physiological and metabolic responses to maximal and submaximal exercise during two phases of the menstrual cycle in eumenorrheic runners and amenorrheic runners. Eight eumenorrheic runners (29.0 +/- 4.2 yr) and eight amenorrheic runners (24.5 +/- 5.7 yr) matched for physical, gynecological, and training characteristics were studied. The eumenorrheic runners performed one maximal and one submaximal (40 min at 80% VO2max) treadmill run during both the early follicular (days 2-4) and midluteal (6-8 d from LH surge) phases. The amenorrheic runners performed one maximal and one submaximal (40 min at 80% VO2max) treadmill run. Cycle phases were documented by urinary luteinizing hormone and progesterone assays and by plasma estradiol and progesterone assays. No differences were observed in oxygen uptake, minute ventilation, heart rate, respiratory exchange ratio, rating of perceived exertion, time to fatigue (maximal), and plasma lactate (following the maximal and submaximal exercise tests) between the follicular and luteal phases in the eumenorrheic runners and the amenorrheic runners. We conclude that neither menstrual phase (follicular vs luteal) nor menstrual status (eumenorrheic vs amenorrheic) alters or limits exercise performance in female athletes.     

The influence of menstrual cycle phase upon postexercise hypotension

PURPOSE: Postexercise hypotension (PEH) has been observed in males and females; however, the impact of menstrual cycle phase upon PEH has not been evaluated. We examined the pattern of PEH in the early follicular (EF), late follicular (LF), and midluteal (ML) phases of the menstrual cycle in eight eumenorrheic women following 30 min of exercise at 80% lactate threshold. METHODS: Supine hemodynamic measurements were assessed at rest and then for 45 min following exercise. Blood pressure was measured with manual sphygmomanometry, calf vascular resistance (CVR) via venous occlusion plethysmography, and central hemodynamics with echocardiography. RESULTS: Cardiovascular parameters did not differ between menstrual phases at rest (P > 0.05). The pattern of PEH was unaffected by menstrual phase, but mean arterial and diastolic (DBP) pressures dropped to significantly lower levels across the recovery period in the EF phase than in the LF and ML phases (mean DBP EF: 69 +/- 4; LF 74 +/- 3; ML 72 +/- 5; P < 0.05). Postexercise cardiac output, stroke volume, ejection fraction, left ventricular dimensions, and heart rate did not differ across menstrual phases (P > 0.05). These parameters, except for left ventricular dimensions in systole and heart rate, varied with recovery time, increasing to a peak between 5 and 10 min postexercise (P < 0.05). CVR displayed a significant interaction between cycle phase and recovery time as resistance increased to greater values in the ML phase compared with the EF and LF phases following 30 min of postexercise recovery (P < 0.05). CONCLUSION: Buffering of PEH appears to be enhanced in the LF and ML phases of the cycle where estrogen concentrations are known to be elevated.     

Finger cold-induced vasodilation during mild hypothermia, hyperthermia and at thermoneutrality

BACKGROUND: Exposure of the fingers to severe cold leads to cold-induced vasodilation (CIVD). The influence of ambient temperature on the CIVD-response is well understood and documented, but the response of CIVD to hyperthermia and mild hypothermia has rarely been investigated. METHODS: To investigate the influence of body thermal status on the CIVD response, eight subjects immersed their right hand in 5 degrees C water for 40 min during mild hypothermia (C), thermoneutrality (N) and hyperthermia (W). The mean skin temperature of the body (Tsk), the esophageal temperature (Tes), the temperature of the volar side of the distal phalanx of each immersed finger (Tfi) and the skin perfusion of the immersed middle finger (Qsk) were continuously measured. RESULTS: During the W condition the body temperatures were higher (Tes: 38.0+/-0.1 degrees C; Tsk: 37.9+/-0.7 degrees C) than during N (Tes: 36.8+/-0.2 degrees C; Tsk: 31.8+/-0.7 degrees C) and during C (Tes: 36.1+/-0.8 degrees C; Tsk: 21.2+/-1.9 degrees C). Tfi and Qsk were higher during the W condition (Tfi: 16.5+/-2.3 degrees C; Qsk: 133+/-53 perfusion units (PU)) than during N (Tfi: 8.1+/-1.7 degrees C; Qsk: 57+/-39 PU) and during C (Tfi: 6.8+/-1.2 degrees C; Qsk: 22+/-14 PU). The onset time of CIVD was significantly prolonged in condition C (13.0+/-3.8 min) as compared with N (7.2+/-2.2 min). CONCLUSION: It was concluded that the CIVD response is significantly affected by body core and skin temperatures.     

Physiological changes of the human uterine myometrium during menstrual cycle: preliminary evaluation using BOLD MR imaging

PURPOSE: To investigate the T2* values within the junctional zone and outer uterine myometrium and their changes during the menstrual cycle, and thus to evaluate their physiologic changes on blood oxygenation level-dependent (BOLD) magnetic resonance (MR) imaging. MATERIALS AND METHODS: Single-shot echo-planar imaging (EPI) was used to acquire T2*-weighted images (TR/TE = 1000 msec/23-150 msec) from 15 healthy females with a 1.5-T magnet. T2* values of both junctional zone and outer uterine myometrium were measured within a single breathhold and during three menstrual cycle phases (menstrual, periovulatory, and luteal phase). Signal intensities of uterine myometrium on T2-weighted images were also evaluated. RESULTS: T2* could successfully be calculated in 13 subjects. T2* values for the junctional zone were significantly lower than those of the outer myometrium at every phase(P < 0.001), and T2* values of both junctional zone (P < 0.05) and outer (P < 0.01). Myometrium in the menstrual phase was significantly lower than those in the other phases. On T2-weighted images, the signal intensity of the junctional zone was significantly lower than outer myometrium in every phase (P < 0.01), but there was no significant difference among menstrual cycle phases in both layers (P > 0.05). CONCLUSION: This preliminary study suggested that menstrual cycle changes of the uterine myometrium were shown by BOLD imaging. BOLD MR imaging may be an potential modality to investigate physiologic changes of the uterine myometrium during the menstrual cycle.     

Substrate oxidation is altered in women during exercise upon acute altitude exposure

PURPOSE: The purpose of this study was to determine whether substrate oxidation during submaximal exercise in women is affected by an acute exposure to 4300-m altitude and menstrual cycle phase. METHODS: Eight female lowlanders (mean +/- SD; 33 +/- 3 yr, 58 +/- 6 kg, 163 +/- 8 cm) completed a peak oxygen uptake (VO2peak) and submaximal exercise to exhaustion (EXH) test at 70% of their altitude-specific VO2peak at sea level (SL) and during an acute altitude (AA) exposure to 4300 m in a hypobaric chamber (446 mm Hg) in their early-follicular and midluteal menstrual cycle phase. The respiratory exchange ratio (RER) was calculated from oxygen uptake and carbon dioxide output measurements made during the EXH tests, and used to estimate the percent contribution of fat and carbohydrate to energy metabolism. Blood samples were taken at rest and every 15 min during the EXH tests. Blood samples were evaluated for glucose, lactate, glycerol, free fatty acids, insulin, growth hormone, cortisol, glucagon, epinephrine, norepinephrine, estradiol, and progesterone concentrations. RESULTS: Despite increased (P < 0.05) estradiol and progesterone levels in the midluteal phase, substrate oxidation, energy substrates, and metabolic hormones were not affected by cycle phase at SL or AA. However, free fatty acids and cortisol were increased (P < 0.05) whereas RER was decreased (P < 0.05) during exercise upon AA exposure compared with SL in both cycle phases. CONCLUSIONS: These data suggest that substrate oxidation is altered in women during exercise at AA compared with SL but is not affected by cycle phase. Whether increased fat or protein oxidation accounts for the lower RER values during the AA exposure cannot be determined from this study but warrants further investigation.     

The effect of prolonged exercise on lipid peroxidation in eumenorrheic female runners.

PURPOSE: Recently a protective role has been demonstrated for estrogens as free radical scavengers. In this study, lipid peroxidation was evaluated in eumenorrheic runners before and after participation in a half-marathon. METHODS: Seven female runners who participated in regular training (average 25 miles x wk(-1) and reported regular menses (12/yr) served as subjects. Subjects were all in a low estrogen phase of their menstrual cycle as confirmed by menstrual record and plasma estradiol level (42.71 +/- 21.65 pg x mL(-1). Low density lipoprotein oxidation (formation of conjugated dienes) was determined 2 h prerace and 5 min after subject's completion of the race. RESULTS: Results showed a significant increase in lag phase time of conjugated dienes after prolonged exercise (28.43 +/- 4.89 min vs postrace 35.21 +/- 4.32 min, P < 0.05). No correlation between mean levels of estradiol and mean lipid peroxidation levels at rest, 5 min after exercise, or difference (prepost) was observed. CONCLUSION: Prolonged endurance exercise does not appear to increase potential for lipid peroxidation in trained eumenorrheic runners during a low estrogen phase of the menstrual cycle.     

Finger and toe temperatures on exposure to cold water and cold air

INTRODUCTION: Subjects with a weak cold-induced vasodilatation response (CIVD) to experimental cold-water immersion of the fingers in a laboratory setting have been shown to have a higher risk for local cold injuries when exposed to cold in real life. Most of the cold injuries in real life, however, occur in the foot in cold air rather than in the hand in cold water. Therefore, an experiment was conducted to investigate the within-subject relation between CIVD in the fingers and toes exposed to cold water and cold air. METHODS: In 4 experimental sessions, 11 healthy male subjects immersed their toes and fingers in 5 degrees C water and exposed the fingers and toes to -18 degrees C cold air for 30 min. The pad temperature of the middle three digits was measured. RESULTS: CIVD in water was more pronounced in the fingers (onset time 5.1 +/- 1.8 min; amplitude 5.0 +/- 2.1 degrees C) than in the toes (onset time 10.6 +/- 6.0 min; amplitude 3.0 +/- 1.0 degrees C). Out of 22 skin temperature responses to cold air, 13 were not identifiable as CIVD. The mean skin temperatures for fingers and toes during the last 20 min of cold exposure were 25.6 +/- 7.1 degrees C and 20.9 +/- 6.8 degrees C, respectively, for air and 9.3 +/- 1.9 degrees C and 7.1 +/- 1.3 degrees C for water immersion. There was a strong relation between the mean temperature of the fingers during cold-water immersion and toes during cold air exposure (r = 0.83, P < 0.01), showing that a weak CIVD response in the hand is related to a weak response in the foot. DISCUSSION: We conclude that the cold-water finger immersion test is related to the temperature response in the toes and may thus continue to serve as a valid indicator for the risk of local cold injuries.     

Anaerobic power performance and the menstrual cycle: eumenorrheic and oral contraceptive users

AIM: The purpose of this project was to compare the impact of the menstrual cycle on short-term, high intensity (power) performance in active females who either had normal menstrual cycles (NOC) or who were using oral contraceptives (OC). METHODS: Subjects (7 NOC, 17 OC) completed a Margaria-Kalamen staircase test and a Wingate cycle test on 3 occasions: one for familiarization and the other two trials (random order) during menses (MEN) or luteal (LUT) phase. Phase was documented by urinary luteinizing hormone for the NOC. RESULTS: There were no significant differences between MEN and LUT in the NOC group on the Wingate test (n=7) for any of the following: peak power (P=0.33), peak power per kg body weight (P=0.37), anaerobic capacity (P=0.37), anaerobic capacity per kg body weight (P=0.42), power decline (P=0.36), power decline per kg body weight (P=0.35). Also there were no significant differences in power (P=0.95) for the Margaria-Kalamen test (n=6). There were no significant differences between MEN and LUT in the OC group for any of the following variables calculated from the subjects' performance on the Wingate test (n=17): peak power (P=0.39), peak power per kg body weight (P=0.36), anaerobic capacity (P=0.42), anaerobic capacity per kg body weight (P=0.36), power decline (P=0.57), power decline per kg body weight (P=0.66). Also there were no significant differences in power (P=0.44) for the Margaria-Kalamen test (n=11). CONCLUSIONS: For a moderately active group of women, anaerobic power performance was not influenced by menstrual cycle phase in either NOC or OC users.     

Variations in performance in simple muscle tests at different phases of the menstrual cycle.

The effect of the menstrual cycle on the performance of women in sporting activities is a very confused subject. In this study, performances in simple muscle tests--the handgrip and standing long jump, were studied at three phases of the menstrual cycle--menstrual (day 1-4), follicular (day 12-14) and luteal (day 19-21). Within subject paired "t" testing showed that in the handgrip test, performance was significantly superior during the menstrual phase than those during both the follicular and luteal phases. In the standing long jump test, performance was again superior during the menstrual phase, although not significantly with respect to the luteal phase. This finding is discussed in terms of the reported effects of the menstrual cycle on sporting performance, the variation in the types of exercise, and the possible role of the female sex hormones.     

Sex differences in knee joint laxity change across the female menstrual cycle

AIM: To elucidate the hormonal influences on sex differences in knee joint behavior, normal-menstruating females were compared to males on serum hormone levels and anterior knee joint laxity (displacement at 46N, 89N and 133N) and stiffness (Linear slope of deltaForce/deltaDisplacement for 46-89N and 89-133N) across the female menstrual cycle. METHODS: Twenty-two females were tested daily across one complete menstrual cycle, and 20 males were tested once per week for 4 weeks. Five days each representing the hormonal milieu for menses, the initial estrogen rise near ovulation, and the early and late luteal phases (total of 20 days) were compared to the average value obtained from males across their 4 test days. RESULTS: Sex differences in knee laxity were menstrual cycle dependent, coinciding with significant elevations in estradiol levels. Females had greater laxity than males on day 5 of menses, days 3-5 near ovulation, days 1-4 of the early luteal phase and days 1, 2, 4 and 5 of the late luteal phases. Within females, knee laxity was greater on day 5 near ovulation compared to day 3 of menses, and days 1-3 of the early luteal phase compared to all days of menses and day 1 near ovulation. On average, differences observed between sexes were greater than those within females across their cycle. There were no differences in anterior knee stiffness between sexes or within females across days of the menstrual cycle.     

Magnetic resonance imaging of the ovaries of healthy women: determination of normal values

PURPOSE: To establish normal values for the volume and maximal diameter of ovaries and ovarian follicles and for the number of ovarian follicles in magnetic resonance imaging (MRI) based on menstrual cycle phase and age. MATERIAL AND METHODS: We performed MRI of the pelvis on 100 healthy women. Volume of the ovaries and largest ovarian follicles and the number of ovarian follicles were determined by menstrual cycle phase and age. RESULTS: The mean volume of the ovaries significantly increased with age and reached its peak between 31 and 40 years, and subsequently decreased. The mean volume of the largest ovarian follicles also significantly increased with age to reach its peak at 41-50 years. The highest mean numbers of ovarian follicles were found at 20-40 years. When the volumes of ovaries and of the largest ovarian follicles, and the number of ovarian follicles were compared between the first and second phase of the menstrual cycle, no significant differences were found. CONCLUSION: The volume and maximal diameter of ovaries and ovarian follicles and the number of ovarian follicles differ significantly with age, but not between the two phases of the menstrual cycle. Knowledge of MRI-related normal values can be expected to aid the early identification of ovarian pathologies.     

The relationship between menstrual cycle phase and anterior cruciate ligament injury: a case-control study of recreational alpine skiers

BACKGROUND: Female athletes suffer a greater incidence of anterior cruciate ligament tears compared with male athletes when participating in common sports; however, very little is known about the factors that explain this disparity. STUDY DESIGN: Case-control study; Level of evidence, 3. METHODS: Female recreational alpine skiers with an anterior cruciate ligament rupture and age-matched control skiers provided a serum sample and self-reported menstrual history data immediately after injury. Both serum concentrations of progesterone and menstrual history were then used to group subjects into either preovulatory or postovulatory phases of the menstrual cycle. RESULTS: Analysis of serum concentrations of progesterone revealed that alpine skiers in the preovulatory phase of the menstrual cycle were significantly more likely to tear their anterior cruciate ligaments than were skiers in the postovulatory phase (odds ratio, 3.22; 95% confidence interval, 1.09-9.52; P = .027). Analysis of menstrual history data found similar results, but the difference was not statistically significant (odds ratio, 2.38; 95% confidence interval, 0.86-6.54; P = .086). CONCLUSION: The likelihood of sustaining an anterior cruciate ligament injury does not remain constant during the menstrual cycle; instead, the risk of suffering an anterior cruciate ligament disruption is significantly greater during the preovulatory phase of the menstrual cycle compared with the postovulatory phase. CLINICAL RELEVANCE: Phase of menstrual cycle may be one of the risk factors that influence knee ligament injury among female alpine skiers. The findings from this study should be considered in subsequent studies designed to identify persons at risk for anterior cruciate ligament injury and to develop intervention strategies.     

Effect of opioid antagonism on esophageal temperature during exercise

The effect of naloxone-induced endogenous opioid antagonism on core temperature control during exercise was studied in 8 competitive cyclists. Volume-matched infusions of placebo or 2 mg of naloxone were administered, in a randomized double-blind crossover fashion, prior to maximal graded cycle ergometer exercise testing. Esophageal (Tes), rectal (Tre) and oral (Tor) temperatures were measured before and after exercise, and Tes was continuously measured during exercise. Cardiorespiratory responses and maximal exercise duration were unaffected by naloxone. Naloxone did not significantly modify the Tes response or the highest Tre and Tor elicited by exercise testing. The rise in Tes (placebo: 2.2 +/- 0.4 degrees C; naloxone: 2.1 +/- 0.4 degrees C) and Tre (placebo: 1.1 +/- 0.2 degree C; naloxone: 0.9 +/- 0.4 degree C) was significant (p less than 0.001) with and without naloxone, whereas the rise in Tor was significant (p less than 0.05) with placebo (0.5 +/- 0.5 degree C) but not with naloxone (0 +/- 0.8 degree C, p greater than 0.5). These data indicate that although 2 mg of naloxone might alter heat exchange in the oral cavity during exercise, it does not modify the actual core temperature response. Therefore, insofar as this dosage of naloxone may be used to examine the functional role of opioid-mediated mechanisms, our findings are not tenable with the hypothesis that endogenous opioids play a role in maintenance of thermal homeostasis during exercise.     

Menstrual cycle stage and oral contraceptive effects on anterior tibial displacement in collegiate female athletes

AIM: The aim of this study was to establish if differences in anterior tibial displacement exists in collegiate female student-athletes at different stages of the menstrual cycle. METHODS: Design and setting: a 2 x 3 factorial design with repeated measures on the second factor guided this study. The first independent variable was group with 2 levels (control and oral contraceptive) and the second independent variable was menstrual cycle phase with 3 levels (follicular, ovulation, luteal). The single dependent variable was anterior tibial displacement. All data were collected in a research laboratory. Subjects: 53 female student athletes (control: n=28; oral contraceptive: n=25) with no previous history of knee injury or anomalies with a normal 28-30 day menstrual cycle participated. Measurements: anterior tibial displacement (mm) measurements were taken on days 1 (follicular phase), 13 (ovulation phase), and 23 (luteal phase) of each subject's menstrual cycle using a KT1000 knee arthrometer. RESULTS: For the entire group, statistically significant increases in anterior tibial laxity were found (F=4.49; df=52.1; P<0.05) between the follicular cycle (0+/-SD =5.14 mm) and ovulation cycle (0+/-SD=5.81 mm); and follicular cycle (0+/-SD=5.14 mm) and luteal cycle (0+/-SD=5.79 mm). A separate analysis of the non-birth control group revealed no significant difference in anterior tibial laxity throughout the stages of the menstrual cycle. CONCLUSION: The results of this study suggest that: 1) the menstrual cycle does have an influence on laxity of the anterior displacement of the knee; 2) significant increases in anterior displacement are shown during the ovulation and luteal phases of the menstrual cycle; and 3) birth control subjects tend to have increased laxity when compared to those subjects who are not on hormone therapy.