Does ovulation affect performance in tennis players?

BACKGROUND: Scientific data on the performance of collegiate female tennis players during the menstrual phases are scarce. TRIAL DESIGN: Double-blind, counter-balanced, crossover trials were conducted to examine whether tennis performance was affected during menstruation, with and without dehydroepiandrosterone sulfate (DHEA-S) supplementation. METHODS: Ten Division 1 collegiate tennis players (aged 18-22 years) were evenly assigned into placebo-supplemented and DHEA-supplemented (25 mg/day) trials. Treatments were exchanged among the participants after a 28-day washout. Tennis serve performance was assessed on the first day of menstrual bleeding (day 0/28) and on days 7, 14 and 21. RESULTS: Mood state was unaltered during the menstrual cycles in both trials. The lowest tennis serve performance score (speed times accuracy) occurred on day 14 (P=0.06 vs day 0; P=0.01 vs day 21) in both placebo and DHEA trials. Decreased performance on day 14 was explained by decreased accuracy (P=0.03 vs day 0/28; P=0.01 vs day 21), but not velocity itself. Isometric hip strength, but not quadriceps strength, was moderately lower on day 14 (P=0.08). Increasing plasma DHEA-S (by ~65%) during the DHEA-supplemented trial had no effects on mood state, sleep quality or tennis serve performance. CONCLUSION: We have shown that menses does not affect serve performance of collegiate tennis players. However, the observed decrement in the accuracy of serve speed near ovulation warrants further investigation.

Non-invasive Measures of Core Temperature versus Ingestible Thermistor during Exercise in the Heat.

The accuracy of core temperature (Tc) thermometry from temporal, tympanic, and oral thermometry devices has been variable during exercise in a hot, humid environment. The purpose of the present study was to cross-validate temporal, two tympanic devices, and oral devices compared to an ingestible thermistor during exercise in a hot, humid environment. Fourteen young, active adults (6 women) completed a graded exercise test until voluntary exhaustion in an environmental chamber (35.5 ± 0.6 °C, 53.9 ± 5.8 % RH). There was no statistical difference in mean temperature between tympanic device 1 and pill-based core temperature (PBTc) measurements across all time points and were positively correlated (0.357; P<0.001). Temperatures of tympanic device 2 were statistically higher than PBTc (37.8 ± 0.7 ºC vs. 37.6 ± 1.0 ºC; respectfully) (P=0.008). At all time points, temperatures for the second tympanic device and PBTc were positively correlated (0.192; P=0.043). Temporal and PBTc values did not differ across time points and were positively correlated (0.262; P=0.005) across all time points. Mean oral temperature was significantly less than mean PBTc across all time points. (37.0 ± 0.4 ºC vs. 37.6 ± 1.0 ºC, respectively) (P<0.001). Across all time points, oral and PBTc were positively correlated (0.262; P=0.010). Tympanic and temporal devices can reflect Tc while exercising in a hot, humid environment. However, care should be taken when selecting the tympanic or temporal measurement device and validation is advised prior to heat illness mitigation in the field.

Effects of Acute Vaporized Nicotine in Non-Tobacco Users at Rest and during Exercise.

Smokers, and even non-smokers, may utilize vaporized nicotine delivered by electronic cigarette (EC) due to the perception that EC are "healthier" than traditional tobacco cigarettes. The effects of vaporized nicotine delivered by EC on resting blood pressure (BP) and resting metabolic rate (RMR), or BP and aerobic power during exercise have not been studied. This investigation tested the effects of acute vaporized nicotine inhalation by EC on resting BP and RMR and cycle exercise BP, metabolic responses, and aerobic power in young, normotensive non-smokers. Using a double-blind design, 20 subjects (10 female) participated in two randomized trials: placebo (0 mg nicotine) or nicotine (18 mg nicotine). Participants inhaled from EC once every 30 s for 10 min (20 inhalations total). RMR was assessed 40 min later by indirect calorimetry followed by an incremental cycle test. RMR was not different between trials (p=0.79). Compared to the placebo, resting diastolic pressure (DBP) was 3 mmHg higher with nicotine (p=0.04). VO2peak was not different between the nicotine trial (2.3±0.8 L•min-1) and placebo (2.3±0.7 L•min-1) trials (p=0.77), and Wmax was also similar between nicotine (201.0±53.8 W) and the placebo (204.8±57.8 W) (p=0.29). During the cycle exercise test, average DBP was higher following nicotine use compared with placebo trial (p=0.05), and exercise DBPpeak after nicotine (79.4±7.6) was significantly higher than placebo (74.9±8.3 mmHg) (p=0.02). Resting systolic blood pressure (SBP) was 3.7 mmHg lower for nicotine trial (p=0.04) but no SBP treatment effect was observed during exercise (p=0.14). Our results show that acute vaporized nicotine inhalation via EC increases resting and exercise DBP but does not affect RMR or cycle aerobic power in young, normotensive non-smokers.

Impact of 12-s Rule on Performance and Muscle Damage of Baseball Pitchers.

INTRODUCTION: A recent US Major League Baseball (MLB) rule change requires baseball pitchers to deliver pitches within 12 s. PURPOSES: To examine the effect of three between-pitch rest intervals on throwing performance during a simulated seven-inning game and muscle damage during postgame recovery. DESIGN: A randomized counterbalanced study. METHODS: Seven intercollegiate pitchers threw 15 pitches per inning for seven innings with rest interval trials of 8, 12, and 20 s between pitches and 5 min between innings. Pitchers threw aimed fastballs at their best effort. Trials were separated by ≥2 wk. RESULTS: Progressive decreases in pitching speed and accuracy below baseline (first inning of 20-s trial) occurred after fourth inning during the 8-s and 12-s trials, but not the 20-s trial. Plasma creatine kinase elevated 48 h later for the 8-s and 12-s trials (+105% and +75%, P < 0.01), but not the 20-s trial (+26%, no significance). A transient interleukin (IL)-6 surges immediately after the game for the 8- and 12-s trials (+265%, +128%, P < 0.01) above baseline. IL-6 reversed below the level of 20-s trial at 48 h after game, whereas IL-10 increased significantly above the level of 20-s trial. CONCLUSIONS: Under the same pitching load, decreasing rest interval from 20 to 12 s or less results in an early-onset performance loss during a game and increases in muscle damage and inflammation for more than 2 d after a game. Our data do not favor the current rule change in concern of keeping musculoskeletal health of pitchers.

Acute inhalation of vaporized nicotine increases arterial pressure in young non-smokers: a pilot study.

PURPOSE: Electronic cigarettes are growing in popularity, but the physiological consequences of vaporized nicotine are unknown. METHODS: Twenty healthy non-smokers inhaled vaporized nicotine and placebo (randomized). RESULTS: Nicotine inhalation was associated with higher arterial pressures in the seated position, and increased arterial pressures in the head-up positions with no other effects on autonomic control. CONCLUSIONS: Our results show that vaporized nicotine inhalation is not innocuous. Longitudinal studies in otherwise healthy non-smokers should be conducted.

Cardiovascular and cerebrovascular responses to progressive central hypovolemia in young smokers: a preliminary study.

The purpose of this study was to describe cardiovascular and cerebrovascular responses of smokers and nonsmokers to progressive central hypovolemia. Twenty subjects participated (equal male and female). We recorded the electrocardiogram, beat-to-beat arterial pressure (Finometer), cerebral blood velocity of the middle cerebral artery (transcranial Doppler), and end-tidal CO2. Lower body negative pressure (LBNP) was applied at 3 mm Hg · min(-1) for 20 minutes to an ending pressure of -60 mm Hg, and data were averaged in 2-minute bins. Arterial pressures were similar between groups at baseline, but heart rates tended to be higher, and stroke volumes and cerebral velocities tended to be lower in smokers at baseline and during LBNP (all p ≥ 0.17). Heart rates increased, and arterial pressures, stroke volumes, and cerebral velocities decreased during LBNP (all p ≤ 0.05), but responses were not different between smokers and nonsmokers. During the final stage of LBNP, systolic pressures and mean middle cerebral artery velocities were substantially lower in smokers than nonsmokers: these preliminary data may suggest clinical relevance of smoking status, but the magnitude of differences between groups were not distinguishable statistically. We therefore conclude that smokers and nonsmokers respond similarly to progressive central hypovolemia.

Salivary biomarkers of physical fatigue as markers of sleep deprivation.

STUDY OBJECTIVE: Determine whether a salivary biomarker of physical fatigue, referred to as the fatigue biomarker index (FBI), can discriminate a control group from a sleep deprived group when saliva is collected under controlled conditions. The study expands on previous work examining changes in the composition of saliva during periods of prolonged exercise. METHODS: Thirty (30) young adults (14 Control [CON]; 16 Sleep Deprived [SDEP]) were monitored for mood state (Profile of Mood States [POMS]), cognitive performance (Stroop Color-Conflict Tests), and salivary biomarkers of physical fatigue over a 48-h period with sampling at 3-h intervals. Trials lasted from 06:00 on day 1 (time = -3 h) to 09:00 on day 3 (time = 48 h). Levels of salivary biomarkers were calculated from liquid chromatography-mass spectrometry (LC-MS) data. Statistical comparisons were made using Wilcoxon rank sum tests with a Bonferroni correction to limit type 1 error. Receiver-operator characteristic (ROC) analysis was used to evaluate the ability of the various parameters to distinguish the SDEP population from the CON population. RESULTS: Longitudinal analysis demonstrated significant between-group differences in all three parameters. ROC analysis demonstrated that cognitive performance tests and salivary biomarkers of physical fatigue distinguish the SDEP population from the CON population. CONCLUSIONS: A previously identified salivary biomarker of physical fatigue may provide an alternative method for discriminating sleep deprived from rested individuals. The salivary biomarker of physical fatigue holds promise as an objective measure of sleep deprivation, perhaps eventually removing the reliance on self-reported sleep diaries and/or repeated polysomnographs for longitudinal tracking of sleep quality and/or diagnosis of sleep disorders.

Linear mixed-effects modeling of the relationship between heart rate variability and fatigue arising from sleep deprivation.

INTRODUCTION: Fatigue degrades cognitive performance, yet there is no universally accepted objective measure of fatigue. We tested whether fatigue arising from sleep deprivation can be quantified objectively using heart rate variability (HRV). METHODS: There were 35 male subjects (mean +/- SD; age = 21.4 +/- 2.6 yr) who were assigned to one of two experimental groups: (1) control (N = 16), or (2) 48-h sleep-deprived (N=19). Using 3-h sampling intervals, we simultaneously tracked fatigue level, cognitive performance, and HRV. Linear mixed-effects (LME) models were used to evaluate linear relationships between fatigue level and cognitive performance, as well as between fatigue level and HRV. RESULTS: Significant negative slopes were observed in LME models of cognitive performance and fatigue level. Of the several HRV parameters examined during standing and supine rest, the ratio of low-frequency to high-frequency R-R interval in the supine position had the clearest significant relationship when modeled against fatigue level. DISCUSSION: In summary, our results suggest that HRV tracks fatigue arising from sleep deprivation. This noninvasive, objective tool can quantify fatigue in real time.

Control of cerebral blood velocity with furosemide-induced hypovolemia and upright tilt.

The purpose of this study was to test the hypothesis that exacerbated reductions of cerebral blood velocity (CBV) during upright tilt with dehydration are associated with impaired cerebrovascular control. Nine healthy men were tilted head-up (HUT) to 70° for 10 min on two occasions separated by 7 days under euhydration (EUH) and dehydration (DEH; 40 mg of furosemide and water restriction) conditions. Beat-by-beat arterial pressures and CBV were measured during a 5-min supine baseline and during the first (T1) and last (T2) 5 min of HUT. Cerebral autoregulation and arterial baroreflex sensitivity were assessed in the frequency domain with cross-spectral techniques. DEH reduced plasma volume by 10% (P = 0.008) and supine mean CBV (CBV(mean)) by 11% (P = 0.002). Mean arterial pressure (MAP), stroke volume, and baroreflex sensitivity decreased during HUT (P ≤ 0.002), but absolute reductions were similar between hydration conditions, with the exception of stroke volume, which was lower at T1 during DEH than EUH (P = 0.04). CBV(mean) during DEH was lower (7 cm/s) over the course of the entire 10 min of HUT (P ≤ 0.004) than during EUH. Low-frequency oscillations (0.07-0.2 Hz) of MAP and CBV(mean) and MAP-CBV(mean) coherence were higher during DEH than EUH at T1 (P ≤ 0.02), but not at T2. Our results suggest that increased coherence between arterial pressure and CBV with the combination of DEH and HUT are indicative of altered cerebrovascular control. Increased CBV oscillations with DEH may reflect acute protective mechanisms to ensure adequate cerebral perfusion under conditions of reduced central blood volume.

Using signage to promote stair use on a university campus in hidden and visible stairwells.

BACKGROUND: This study tested the effectiveness of a stair use promotion strategy in visible and hidden stairwells during intervention and post intervention follow up. METHODS: A quasi-experimental study design was used with a 1 week baseline, a 3 week intervention, and post intervention at 2 and 4 weeks in 4 university buildings in San Antonio, Texas with stairwells varying in visibility. Participants were students, faculty, staff, and visitors to the 4 buildings. A total of 8431 observations were made. The intervention incorporated motivational signs with direction to nearby stairwells placed by elevators to promote stair use. Stair and elevator use was directly observed and recorded. Logistic regression analyses were used to test whether stair versus elevator use varied by intervention phase and stairwell visibility. RESULTS: Stair use increased significantly (12% units) during the intervention period and remained above baseline levels during post intervention follow-up. At baseline, visible stairs were 4 times more likely to be used than hidden stairs; however, the increase in stair use during intervention was similar in both types of stairwells. CONCLUSIONS: Motivational and directional signage can significantly increase stair use on a university campus. Furthermore, stairwell visibility is an important aspect of stair use promotion.

A comparison of cognitive performance decreases during acute, progressive fatigue arising from different concurrent stressors.

Fatigue is known to impair cognitive performance, but it remains unclear whether concurrent common stressors affect cognitive performance similarly. We used the Stroop Color-Word Conflict Test to assess cognitive performance over 24 hours for four groups: control, sleep-deprived (SD), SD + energy deficit, and SD + energy deficit + fluid restricted. Fatigue levels were quantified using the Profile of Mood States (POMS) survey. Linear mixed-effects (LME) models allowed for testing of group-specific differences in cognitive performance while accounting for subject-level variation. Starting fatigue levels were similar among all groups, while 24-hour fatigue levels differed significantly. For each cognitive performance test, results were modeled separately. The simplest LME model contained a significant fixed-effects term for slope and intercept. Moreover, the simplest LME model used a single slope coefficient to fit data from all four groups, suggesting that loss in cognitive performance over a 24-hour duty cycle with respect to fatigue level is similar regardless of the cause.

Hydration status of Air Force military basic trainees after implementation of the back-mounted hydration system.

The Air Force makes an extraordinary effort to prevent heat-related illnesses associated with basic military training (BMT) in south Texas. However, inadequate hydration can still contribute to lost training time and qualified trainees leaving military service without completing BMT. The purpose of the present study was to determine whether equipping BMTs with back-mounted hydration systems (BM) is better than the standard-issue (SI) canteens with respect to hydration status. Male BMTs were randomly assigned to either BM (n = 40) or SI (n = 38) groups. Baseline values were assessed at week 0 before any physical readiness training (PRT). Subsequent data collection took place in the a.m. before PRT and in the p.m. before dinner the first 3 weeks, and during the 5 weeks of training. BMT total body water (TBW) and body composition were assessed by bioelectrical impedance. Saliva osmolality and total protein concentration were also determined. Hydration status increased daily in BM and SI and was well maintained over the duration of BMT. A significant hydration effect (p < 0.05) was observed for average daily increases in TBW and body weight with BM gaining more compared to SI. Average a.m. TBW was 0.3-0.8 L greater in SI versus BM (p < 0.05). Our findings demonstrate that adequate hydration status is maintained during Air Force BMT in a hot environment using either hydration mode and therefore do not support widespread issuance of the BM system on the premise of improved hydration during USAF BMT military training.

Heart rate variability to assess combat readiness.

Chronic fatigue/physical exhaustion (FPE) impacts combat readiness but is difficult to identify. We tested the hypothesis that resting heart rate variability (HRV), including both time- and frequency-domain assessments, would correlate with hydration status and aerobic capacity in military recruit-age men and women with varying fitness levels. Cardiac interbeat intervals were recorded using a heart R-R monitor during 20 minutes of quiet, supine rest with paced breathing (0.25 Hz). HRV metrics included average R-R interval (RRIavg), R-R interval standard deviation (RRISD), the percentage of adjacent R-R intervals varying by > or = 50 ms (pNN50), and integrated areas of R-R interval spectral power at the high (0.15-0.4 Hz) (RRIHF) and low (0.04-0.15 Hz) (RRILF) frequencies. Treadmill maximal oxygen uptake (VO2 max), segmental bioimpedance estimates of total body water (TBW), and urine specific gravity (USG) were also assessed. All dependent variables of interest were within expected ranges, although absolute ranges of individual values were considerable. RRI correlated with VO2 max (r = 0.49; p < 0.001), with TBW (r = 0.38; p < 0.001), and inversely with USG (r = -0.23; p = 0.02). RRISD correlated with VO2 max (r = 0.21; p = 0.03), but not with TBW or USG. pNN50 correlated inversely with USG (r = -0.21; p = 0.03) but not with VO2 max or TBW. R-R interval spectral power at the high and low frequencies did not correlate with VO2 max, TBW, or USG. We have demonstrated that fitness level and hydration status may affect cardiac function via changes in autonomic tone, highlighting the potential of field-based assessment of heart rate variability metrics to identify FPE and other aspects of combat readiness.

Diabetes risk, low fitness, and energy insufficiency levels among children from poor families.

BACKGROUND: Low-income populations have higher rates of type 2 diabetes and it is the hope of the investigators to increase support for the dissemination of evidence-based prevention programs aimed at children from poor families. OBJECTIVE: To determine the prevalence of high blood glucose, obesity, low fitness, and energy insufficiency levels among children from poor families. DESIGN: The cross-sectional study conducted in fall 2001 used fasting capillary glucose, body mass index, body fat, step test, and three 24-hour dietary recalls to assess diabetes risk factor levels. SUBJECTS: Participants were 1,402 fourth-grade students aged 8 to 10 years. The racial/ethnic backgrounds were 80% Mexican American, 10% African American, 5% Asian American, and 5% non-Hispanic white. STATISTICAL ANALYSIS PERFORMED: All data were analyzed for descriptive statistics and frequencies of distribution. Means were computed by sex for all diabetes risk factors and t test conducted to determine differences between sexes. RESULTS: Nearly 75% of participants lived in households with

Effect of exercise duration on postprandial hypertriglyceridemia in men with metabolic syndrome.

We examined the effect of exercise on postprandial hypertriglyceridemia (PHTG) and insulin resistance in individuals with metabolic syndrome. Subjects were 10 hypertriglyceridemic men with insulin resistance [age = 35.0 +/- 1.8 yr, body weight = 90.7 +/- 3.3 kg, fasting triglyceride (TG) = 2.6 +/- 0.4 mmol/l, peak oxygen consumption ((.)Vo(2peak)) = 36.0 +/- 1.3 ml(-1).kg(-1).min(-1), and homeostatic model assessment of insulin resistance (HOMA-IR)= 3.1 +/- 0.3]. Each participant performed a control trial (Ctr; no exercise) and three exercise trials at 60% of their (.)Vo(2peak) for 30 min (30 min-Ex), 45 min (45 min-Ex) and 60 min (60 min-Ex). All subjects had a fat meal in each trial. In the exercise trials, the subject jogged on a treadmill for a designated duration of 12 h before ingestion of a fat meal. Blood samples were taken at 0 h (before the meal) and at 2, 4, 6, and 8 h after the meal. The plasma TG, area score under TG concentration curve over an 8-h period (TG AUC) after the meal, and HOMA-IR were analyzed. The TG AUC scores in both the 45 min-Ex and 60 min-Ex were 31 and 33% lower, respectively, than Ctr (P < 0.02). There were no significant differences in TG AUC scores between the 30 min-Ex and the Ctr (P > 0.05). There were no trial differences in the fasting plasma glucose concentration (P > 0.05). HOMA-IR values in the 30 min-Ex, 45 min-Ex, and 60 min-Ex trials were lower than the Ctr (P < 0.03), but no significant differences were found in HOMA-IR among the exercise trials. The results suggest that for physically inactive individuals with metabolic syndrome, exercising at moderate intensity for 45 min effectively attenuates PHTG while exercise for 30 min is sufficient to improve insulin action.

Effect of glycogen synthase overexpression on insulin-stimulated muscle glucose uptake and storage.

Insulin-stimulated muscle glucose uptake is inversely associated with the muscle glycogen concentration. To investigate whether this association is a cause and effect relationship, we compared insulin-stimulated muscle glucose uptake in noncontracted and postcontracted muscle of GSL3-transgenic and wild-type mice. GSL3-transgenic mice overexpress a constitutively active form of glycogen synthase, which results in an abundant storage of muscle glycogen. Muscle contraction was elicited by in situ electrical stimulation of the sciatic nerve. Right gastrocnemii from GSL3-transgenic and wild-type mice were subjected to 30 min of electrical stimulation followed by hindlimb perfusion of both hindlimbs. Thirty minutes of contraction significantly reduced muscle glycogen concentration in wild-type (49%) and transgenic (27%) mice, although transgenic mice retained 168.8 +/- 20.5 micromol/g glycogen compared with 17.7 +/- 2.6 micromol/g glycogen for wild-type mice. Muscle of transgenic and wild-type mice demonstrated similar pre- (3.6 +/- 0.3 and 3.9 +/- 0.6 micromol.g(-1).h(-1) for transgenic and wild-type, respectively) and postcontraction (7.9 +/- 0.4 and 7.0 +/- 0.4 micromol.g(-1).h(-1) for transgenic and wild-type, respectively) insulin-stimulated glucose uptakes. However, the [14C]glucose incorporated into glycogen was greater in noncontracted (151%) and postcontracted (157%) transgenic muscle vs. muscle of corresponding wild-type mice. These results indicate that glycogen synthase activity is not rate limiting for insulin-stimulated glucose uptake in skeletal muscle and that the inverse relationship between muscle glycogen and insulin-stimulated glucose uptake is an association, not a cause and effect relationship.

Effects of recovery beverages on glycogen restoration and endurance exercise performance.

The restorative capacities of a high carbohydrate-protein (CHO-PRO) beverage containing electrolytes and a traditional 6% carbohydrate-electrolyte sports beverage (SB) were assessed after glycogen-depleting exercise. Postexercise ingestion of the CHO-PRO beverage, in comparison with the SB, resulted in a 55% greater time to exhaustion during a subsequent exercise bout at 85% maximum oxygen consumption (VO(2)max). The greater recovery after the intake of the CHO-PRO beverage could be because of a greater rate of muscle glycogen storage. Therefore, a second study was designed to investigate the effects of after exercise CHO-PRO and SB supplements on muscle glycogen restoration. Eight endurance-trained cyclists (VO(2)max = 62.1 +/- 2.2 ml.kg(-1) body wt.min(-1)) performed 2 trials consisting of a 2-hour glycogen-depletion ride at 65-75% VO(2)max. Carbohydrate-protein (355 ml; approximately 0.8 g carbohydrate (CHO).kg(-1) body wt and approximately 0.2 g protein.kg(-1) body wt) or SB (355 ml; approximately 0.3 g CHO.kg(-1) body wt) was provided immediately and 2 hours after exercise. Trials were randomized and separated by 7-15 days. Ingestion of the CHO-PRO beverage resulted in a 17% greater plasma glucose response, a 92% greater insulin response, and a 128% greater storage of muscle glycogen (159 +/- 18 and 69 +/- 32 micromol.g(-1) dry weight for CHO-PRO and SB, respectively) compared with the SB (p < 0.05). These findings indicate that the rate of recovery is coupled with the rate of muscle glycogen replenishment and suggest that recovery supplements should be consumed to optimize muscle glycogen synthesis as well as fluid replacement.