Acute effects of dynamic versus foam rolling warm-up strategies on physical performance in elite tennis players

To date, there is a lack of information about the optimal conditions of the warm-up to lead to a better performance in elite tennis players. The aim of this study was to compare the effects of two different warm-up protocols (dynamic vs. self-myofascial release with foam rolling) on neuromuscular variables associated with physical determinants of tennis performance. Using a crossover randomised experimental design, eleven professional men tennis players (20.6 ± 3.5 years) performed either a dynamic warm-up (DWU) or a self-myofascial release with foam rolling (SMFR) protocol. DWU consisted of 8 min of dynamic exercises at increasing intensity and SMFR consisted of 8 min of rolling on each lower extremity unilaterally. Just before (baseline) and after completing warm-up protocols, players performed a countermovement jump (CMJ), the 5-0-5 agility test, a 10-m sprint test and the Straight Leg Raise and Thomas tests to assess range of motion. Compared to baseline, the DWU was more effective to reduce the time in the 5-0-5 test than SMFR (-2.23 vs. 0.44%, respectively, p = 0.042, ηp² = 0.19). However, both warm-up protocols similarly affected CMJ (2.32 vs. 0.61%, p = 0.373, ηp² = 0.04) and 10-m sprint time changes (-1.26 vs. 1.03%, p = 0.124, ηp² = 0.11). Changes in range of motion tests were also similar with both protocols (p = 0.448–1.000, ηp² = 0.00–0.02). Overall, both DWU and SMFR were effective to prepare well-trained tennis players for highly demanding neuromuscular actions. However, DWU offered a better preparation for performing change of direction and sprint actions, and hence, in high-performance tennis players, the warm-up should include dynamic exercises.     

Effects of 1 vs. 2 sessions per week of equal-volume sprint training on explosive,high-intensity and endurance-intensive performances in young soccer players

The study aimed to evaluate the effects of 1 vs. 2 sessions per week of equal-volume sprint training on explosive, high-intensity and endurance-intensive performances among young soccer players. Thirty-six young male soccer players were randomly divided into 2 experimental groups that performed either a single weekly sprint training session (ST1, n = 18, age: 17.2 ± 0.8 years) or two weekly sprint training sessions (ST2, n = 18; age: 17.1 ± 0.9 years) of equal weekly and total volume, in addition to their regular soccer training regimen. Linear sprinting (10 m, 20 m, 30 m, and flying 10 m), T-test agility, countermovement jump (CMJ) and maximal oxygen consumption were assessed one week before (T1), in the middle (T2) and immediately after the 10 weeks of training (T3). A large magnitude and statistically significant main effect for time was found in all the assessed variables after both training interventions (all p < 0.001; ES ≥ 0.80). No main effect was observed between the 2 groups at any time in linear sprinting, T-test or CMJ test (p > 0.05; ES < 0.20). A significant interaction effect (F = 4.05; p = 0.04, ES = 0.21) was found for maximal oxygen consumption with ST2 inducing better performance than ST1 (p = 0.001; ES = 1.11). Our findings suggested that the two sprint training frequencies were effective in enhancing explosive, high-intensity and endurance-intensive performances. However, it is recommended for coaches and fitness coaches to use a biweekly sprint training modality as it was found to be more effective in improving endurance-intensive performance.     

Post-activation performance enhancement (PAPE) after a single bout of high-intensity flywheel resistance training

This study investigated the post-activation performance enhancements (PAPE) induced by a high-intensity single set of accentuated eccentric isoinertial resistance exercise on vertical jump performance. Twenty physically active male university students performed, in randomized counterbalanced order, two different conditioning activities (CA) after a general preestablished warm-up: a conditioning set of 6 maximum repetitions at high intensity (i.e., individualized optimal moment of inertia [0.083 ± 0.03 kg·m^-2]) of the flywheel half-squat exercise in the experimental condition, or a set of 6 maximal countermovement jumps (CMJ) instead of the flywheel exercise in the control condition. CMJ height, CMJ concentric peak power and CMJ concentric peak velocity were assessed at baseline (i.e., 3 minutes after the warm-up) and 4, 8, 12, 16 and 20 minutes after the CA in both experimental and control protocols. Only after the experimental protocol were significant gains in vertical jump performance (p < 0.05, ES range 0.10–1.34) at 4, 8, 12, 16 and 20 minutes after the CA observed. In fact, the experimental protocol showed greater (p < 0.05) CMJ height, concentric peak power and concentric peak velocity enhancements compared to the control condition. In conclusion, a single set of high-intensity flywheel training led to PAPE in CMJ performance after 4, 8, 12, 16 and 20 minutes in physically active young men.     

Suboptimal Serum α-Tocopherol Concentrations Observed among Younger Adults and Those Depending Exclusively upon Food Sources,NHANES 2003-20061-3

Vitamin E is an essential nutrient for human health, with an established function as a lipid-soluble antioxidant that protects cell membranes from free radical damage. Low vitamin E status has been linked to multiple health outcomes, including total mortality. With vitamin E being identified as a ‘shortfall nutrient’ because >90% of American adults are not consuming recommended amounts of vitamin E, we aimed to determine the prevalence of both clinical vitamin E deficiency (serum α-tocopherol concentration < 12 μmol/L) and failure to meet a criterion of vitamin E adequacy, serum α-tocopherol concentration of 30 μmol/L, based on the Estimated Average Requirement (EAR) and lowest mortality rate in the Alpha-Tocopherol Beta-Carotene (ATBC) study. The most recent nationally-representative cross-sectional data (2003–2006) among non-institutionalized US citizens with available serum concentrations of α-tocopherol from the National Health and Nutrition Examination Survey (NHANES); Centers for Disease Control and Prevention were analyzed. Serum α-tocopherol distributions were compared between those reporting consumption of food without supplement use (FOOD) and food and supplement use (FOOD+DS) by sex, age, and race/ethnicity. Only 1% of the US population is clinically deficient. FOOD consumers have lower average α-tocopherol levels (24.9± 0.2 μmol/L) than FOOD+DS users (33.7 ± 0.3 μmol/L), even when adjusted for total cholesterol. Using a criterion of adequacy of 30 μmol/L, 87% of persons 20-30y and 43% of those 51+y had inadequate vitamin E status (p<0.01). A significant greater prevalence of FOOD compared to FOOD+DS users did not meet the criterion of adequacy which was based on the EAR and low ATBC mortality rate consistently across age, sex, and race/ethnic groups. The prevalence of inadequate vitamin E levels is significantly higher among non-users of dietary supplements. With declining usage of vitamin E supplements, the population should be monitored for changes in vitamin E status and related health outcomes.     

ACUTE EFFECTS OF A RESISTED DYNAMIC WARM-UP PROTOCOL ON JUMPING PERFORMANCE

This study aimed to investigate the kinematic and kinetic changes when resistance is applied in horizontal and vertical directions, produced by using different percentages of body weight, caused by jumping movements during a dynamic warm-up. The group of subjects consisted of 35 voluntary male athletes (19 basketball and 16 volleyball players; age: 23.4 ± 1.4 years, training experience: 9.6 ± 2.7 years; height: 177.2 ± 5.7 cm, body weight: 69.9 ± 6.9 kg) studying Physical Education, who had a jump training background and who were training for 2 hours, on 4 days in a week. A dynamic warm-up protocol containing seven specific resistance movements with specific resistance corresponding to different percentages of body weight (2%, 4%, 6%, 8%, 10%) was applied randomly on non consecutive days. Effects of different warm-up protocols were assessed by pre-/post- exercise changes in jump height in the countermovement jump (CMJ) and the squat jump (SJ) measured using a force platform and changes in hip and knee joint angles at the end of the eccentric phase measured using a video camera. A significant increase in jump height was observed in the dynamic resistance warm-up conducted with different percentages of body weight (p < 0.05). On the other hand, no significant difference in different percentages of body weight states was observed (p > 0.05). In jump movements before and after the warm-up, while no significant difference between the vertical ground reaction forces applied by athletes was observed (p > 0.05), in some cases of resistance, a significant reduction was observed in hip and knee joint angles (p < 0.05). The dynamic resistance warm-up method was found to cause changes in the kinematics of jumping movements, as well as an increase in jump height values. As a result, dynamic warm-up exercises could be applicable in cases of resistance corresponding to 6-10% of body weight applied in horizontal and vertical directions in order to increase the jump performance acutely.     

The Zinc Transporter Slc30a8/ZnT8 Is Required in a Subpopulation of Pancreatic α-Cells for Hypoglycemia-induced Glucagon Secretion

SLC30A8 encodes a zinc transporter ZnT8 largely restricted to pancreatic islet β- and α-cells, and responsible for zinc accumulation into secretory granules. Although common SLC30A8 variants, believed to reduce ZnT8 activity, increase type 2 diabetes risk in humans, rare inactivating mutations are protective. To investigate the role of Slc30a8 in the control of glucagon secretion, Slc30a8 was inactivated selectively in α-cells by crossing mice with alleles floxed at exon 1 to animals expressing Cre recombinase under the pre-proglucagon promoter. Further crossing to Rosa26:tdRFP mice, and sorting of RFP⁺: glucagon⁺ cells from KO mice, revealed recombination in ∼30% of α-cells, of which ∼50% were ZnT8-negative (14 ± 1.8% of all α-cells). Although glucose and insulin tolerance were normal, female αZnT8KO mice required lower glucose infusion rates during hypoglycemic clamps and displayed enhanced glucagon release (p < 0.001) versus WT mice. Correspondingly, islets isolated from αZnT8KO mice secreted more glucagon at 1 mm glucose, but not 17 mm glucose, than WT controls (n = 5; p = 0.008). Although the expression of other ZnT family members was unchanged, cytoplasmic (n = 4 mice per genotype; p < 0.0001) and granular (n = 3, p < 0.01) free Zn²⁺ levels were significantly lower in KO α-cells versus control cells. In response to low glucose, the amplitude and frequency of intracellular Ca²⁺ increases were unchanged in α-cells of αZnT8KO KO mice. ZnT8 is thus important in a subset of α-cells for normal responses to hypoglycemia and acts via Ca²⁺-independent mechanisms.     

Anthropometric and physiological characteristics of Melanesian futsal players: a first approach to talent identification in Oceania

This study assessed the anthropometric and physiological characteristics of elite Melanesian futsal players in order to determine the best performance predictors. Physiological parameters of performance were measured in 14 Melanesian (MEL-G, 24.4±4.4 yrs) and 8 Caucasian (NMEL-G, 22.9±4.9) elite futsal players, using tests of jump-and-reach (CMJ), agility (T-Test), repeated sprint ability (RSA), RSA with change-of-direction (RSA-COD), sprints with 5 m, 10 m, 15 m, and 30 m lap times, and aerobic fitness with the 30-15 intermittent fitness test (30-15 IFT). The anthropometric data revealed significantly lower height for MEL-G compared with NMEL-G: 1.73±0.05 and 1.80±0.08 m, respectively; P = 0.05. The CMJ was significantly higher for MEL-G than NMEL-G: 50.4±5.9 and 45.2±4.3 cm, respectively; P = 0.05. T-Test times were significantly lower for MEL-G than NMEL-G: 10.47±0.58 and 11.01±0.64 seconds, respectively; P = 0.05. MEL-G height was significantly related to CMJ (r = 0.706, P = 0.01), CMJ_peakP (r = 0.709, P = 0.01) and T-Test (r = 0.589, P = 0.02). No significant between-group differences were observed for sprint tests or 30-15 IFT, including heart rate and estimated VO_2max. Between groups, the percentage decrement (%Dec) in RSA-COD was significantly lower in MEL-G than NMEL-G (P = 0.05), although no significant difference was noted between RSA and RSA-COD. Within groups, no significant difference was observed between %Dec in RSA or RSA-COD; P = 0.697. This study presents specific anthropometric (significantly lower height) and physiological (significantly greater agility) reference values in Melanesians, which, taken together, might help coaches and physical fitness trainers to optimize elite futsal training and talent identification in Oceania.     

Acute effects of static stretching and massage on flexibility and jumping performance

Objective:The purpose of this study was to evaluate the effects of static stretching and the application of massage on flexibility and jump performance.Methods:Thirty-five athletes studying Physical Education at University (mean age 23.6±1.3 years, mean height 177.8±6.3 cm and mean weight 72.2±6.7 kg) performed one of three different warm-up protocols on non-consecutive days. Protocols included static stretching [SS], combined static stretching and massage [SSM], and neither stretching nor massage [CONT]. The athletes performed flexibility, countermovement jump (CMJ) and squat jump (SJ) tests.Results:SS and SSM protocols demonstrated 12% (p<0.05) and 16% (p<0.05) respectively greater flexibility than the CONT protocol. SJ and CMJ performances were significantly decreased 10.4% (p<0.05) and 5.5% (p<0.05) respectively after the SS protocol. There was no significant difference between SSM and CONT protocol in terms of SJ and CMJ performance.Conclusion:This research indicates that whereas static stretching increases the flexibility it decreases the jumping performance of the athletes. On the other hand, the application of massage immediately following static stretching increases flexibility but does not reduce jumping performance. Considering the known negative acute effects of static stretching on performance, the application of massage is thought to be beneficial in alleviating such effects.     

5-Aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR) Effect on Glucose Production,but Not Energy Metabolism,Is Independent of Hepatic AMPK in Vivo

Metabolic stress, as well as several antidiabetic agents, increases hepatic nucleotide monophosphate (NMP) levels, activates AMP-activated protein kinase (AMPK), and suppresses glucose production. We tested the necessity of hepatic AMPK for the in vivo effects of an acute elevation in NMP on metabolism. 5-Aminoimidazole-4-carboxamide 1-β-d-ribofuranoside (AICAR; 8 mg·kg⁻¹·min⁻¹)-euglycemic clamps were performed to elicit an increase in NMP in wild type (α1α2^lox/lox) and liver-specific AMPK knock-out mice (α1α2^lox/lox + Albcre) in the presence of fixed glucose. Glucose kinetics were equivalent in 5-h fasted α1α2^lox/lox and α1α2^lox/lox + Albcre mice. AMPK was not required for AICAR-mediated suppression of glucose production and increased glucose disappearance. These results demonstrate that AMPK is unnecessary for normal 5-h fasting glucose kinetics and AICAR-mediated inhibition of glucose production. Moreover, plasma fatty acids and triglycerides also decreased independently of hepatic AMPK during AICAR administration. Although the glucoregulatory effects of AICAR were shown to be independent of AMPK, these studies provide in vivo support for the AMPK energy sensor paradigm. AICAR reduced hepatic energy charge by ∼20% in α1α2^lox/lox, which was exacerbated by ∼2-fold in α1α2^lox/lox + Albcre. This corresponded to a ∼6-fold rise in AMP/ATP in α1α2^lox/lox + Albcre. Consistent with the effects on adenine nucleotides, maximal mitochondrial respiration was ∼30% lower in α1α2^lox/lox + Albcre than α1α2^lox/lox livers. Mitochondrial oxidative phosphorylation efficiency was reduced by 25%. In summary, these results demonstrate that the NMP capacity to inhibit glucose production in vivo is independent of liver AMPK. In contrast, AMPK promotes mitochondrial function and protects against a more precipitous fall in ATP during AICAR administration.     

Excitation-Contraction Coupling in Zebrafish Ventricular Myocardium Is Regulated by Trans-Sarcolemmal Ca2+ Influx and Sarcoplasmic Reticulum Ca2+ Release

Zebrafish (Danio rerio) have become a popular model in cardiovascular research mainly due to identification of a large number of mutants with structural defects. In recent years, cardiomyopathies and other diseases influencing contractility of the heart have been studied in zebrafish mutants. However, little is known about the regulation of contractility of the zebrafish heart on a tissue level. The aim of the present study was to elucidate the role of trans-sarcolemmal Ca²⁺-flux and sarcoplasmic reticulum Ca²⁺-release in zebrafish myocardium. Using isometric force measurements of fresh heart slices, we characterised the effects of changes of the extracellular Ca²⁺-concentration, trans-sarcolemmal Ca²⁺-flux via L-type Ca²⁺-channels and Na⁺-Ca²⁺-exchanger, and Ca²⁺-release from the sarcoplasmic reticulum as well as beating frequency and β-adrenergic stimulation on contractility of adult zebrafish myocardium. We found an overall negative force-frequency relationship (FFR). Inhibition of L-type Ca²⁺-channels by verapamil (1 μM) decreased force of contraction to 22±7% compared to baseline (n=4, p<0.05). Ni²⁺ was the only substance to prolong relaxation (5 mM, time after peak to 50% relaxation: 73±3 ms vs. 101±8 ms, n=5, p<0.05). Surprisingly though, inhibition of the sarcoplasmic Ca²⁺-release decreased force development to 54±3% in ventricular (n=13, p<0.05) and to 52±8% in atrial myocardium (n=5, p<0.05) suggesting a substantial role of SR Ca²⁺-release in force generation. In line with this finding, we observed significant post pause potentiation after pauses of 5 s (169±7% force compared to baseline, n=8, p<0.05) and 10 s (198±9% force compared to baseline, n=5, p<0.05) and mildly positive lusitropy after β-adrenergic stimulation. In conclusion, force development in adult zebrafish ventricular myocardium requires not only trans-sarcolemmal Ca²⁺-flux, but also intact sarcoplasmic reticulum Ca²⁺-cycling. In contrast to mammals, FFR is strongly negative in the zebrafish heart. These aspects need to be considered when using zebrafish to model human diseases of myocardial contractility.     

Determinants of muscle power and force as assessed by Jumping Mechanography in rural Indian children

Objectives:To: 1. Assess muscle function (MF) of rural Indian children (6-11y, n=232), using Jumping Mechanography (JM) and hand dynamometer, 2. Investigate gender differences, 3. Identify determinants of MF.Methods:Data on anthropometry, muscle mass%, diet, physical activity, sunlight exposure, MF (maximum relative power Pmax/mass, maximum relative force Fmax/BW by JM; relative grip strength (RGS) by hand dynamometer) were collected. Pearson’s correlation and hierarchical linear regression was performed.Results:Pmax/mass, Fmax/BW and RGS of the group were 31.7±5.0W/kg, 3.0±0.3 and 0.4±0.1 (mean±SD), respectively. The Pmax/mass Z-score was –1.1±0.9 and Fmax/BW Z-score was –0.9±1 (mean±SD) which was significantly lower than the machine reference data (p<0.05). Positive association of muscle mass% and protein intake was observed with all MF parameters and moderate+vigorous physical activity with Fmax/BW (p<0.05). Determinants of MF identified through regression for Pmax/mass were age (β=1.83,95% CI=0.973 – 2.686), muscle mass% (β=0.244,95% CI=0.131–0.358) and protein intake (β=3.211,95% CI=1.597–4.825) and for Fmax/BW was protein intake (β=0.130,95% CI=0.023–0.237) (p<0.05). Male gender was a positive predictor of having higher Pmax/mass (β=1.707,95% CI=0.040–3.373) (p<0.05).Conclusion:MF was lower than in western counterparts. To optimize MF of rural Indian children, focus should be on improving muscle mass, ensuring adequate dietary protein, and increasing physical activity, especially in girls.     

Prevalence of α-thalassemia 3.7 kb deletion in the adult population of Rio Grande do Norte,Brazil

α-Thalassemia, arising from a defect in α-globin chain synthesis, is often caused by deletions involving one or both of the α-genes on the same allele. With the aim of investigating the prevalence of α-thalassemia 3.7 kb deletion in the adult population of Rio Grande do Norte, 713 unrelated individuals, between 18 and 59 years-of-age, were analyzed. Red blood cell indices were electronically determined, and A₂ and F hemoglobins evaluated by HPLC. PCR was applied to the molecular investigation of α-thalassemia 3.7 kb deletion. Eighty (11.2%) of the 713 individuals investigated presented α-thalassemia, of which 79 (11.1%) were heterozygous (-α^3.7/αα) deletions and 1 (0.1%) homozygous (-α^3.7/-α^3.7). Ethnically, heterozygous deletions were higher (24.8%) in Afro-Brazilians. Comparison of hematological parameters between individuals with normal genotype and those with heterozygous α⁺-thalassemia showed a statistically significant difference in the number of erythrocytes (p < 0.001), MCV (p < 0.001), MCH (p < 0.001) and Hb A₂ (p = 0.007). This study is one of the first dedicated to investigating α-thalassemia 3.7 kb deletion in the population of the State Rio Grande do Norte state. Results obtained demonstrate the importance of investigating this condition in order to elucidate the causes of microcytosis and hypochromia.     

Acute and long-term effects of two different static stretching training protocols on range of motion and vertical jump in preadolescent athletes

This study examined the acute and long-term effects of two static stretching protocols of equal duration, performed either as a single stretch or multiple shorter duration repetitions on hip hyperextension range of motion (ROM) and single leg countermovement jump height (CMJ). Thirty female gymnasts were randomly assigned to stretching (SG) or control groups (CG). The SG performed two different protocols of static stretching, three times per week for 9 weeks. One leg performed repeated stretching (3 × 30 s with 30 s rest) while the other leg performed a single stretch (90 s). The CG continued regular training. ROM and CMJ were measured pre- and 2 min post-stretching on weeks 0, 3, 6, 9, and 3 weeks into detraining. CMJ height increased over time irrespective of group (main effect time, p = 0.001), with no statistical difference between groups (main effect group, p = 0.272). Three-way ANOVA showed that, CMJ height after stretching was not affected by either stretching protocol at any time point (p = 0.503 to 0.996). Both stretching protocols equally increased ROM on weeks 6 (10.9 ± 13.4%, p < 0.001, d = 0.42), and 9 (21.5 ± 13.4%, p < 0.001, d = 0.78), and this increase was maintained during detraining (17.0 ± 15.0%, p < 0.001, d = 0.68). No increase in ROM was observed in the CG (p > 0.874). Static stretching of long duration applied either as single or multiple bouts of equal duration, results in similar acute and long-term improvements in ROM. Furthermore, both stretching protocols do not acutely affect subsequent CMJ performance, and this effect is not influenced by the large increase in ROM and CMJ overtime.     

The Effects of Comprehensive Warm-Up Programs on Proprioception,Static and Dynamic Balance on Male Soccer Players

Purpose

The study investigated the effects of FIFA 11+ and HarmoKnee, both being popular warm-up programs, on proprioception, and on the static and dynamic balance of professional male soccer players.

Methods

Under 21 year-old soccer players (n = 36) were divided randomly into 11+, HarmoKnee and control groups. The programs were performed for 2 months (24 sessions). Proprioception was measured bilaterally at 30°, 45° and 60° knee flexion using the Biodex Isokinetic Dynamometer. Static and dynamic balances were evaluated using the stork stand test and Star Excursion Balance Test (SEBT), respectively.

Results

The proprioception error of dominant leg significantly decreased from pre- to post-test by 2.8% and 1.7% in the 11+ group at 45° and 60° knee flexion, compared to 3% and 2.1% in the HarmoKnee group. The largest joint positioning error was in the non-dominant leg at 30° knee flexion (mean error value = 5.047), (p<0.05). The static balance with the eyes opened increased in the 11+ by 10.9% and in the HarmoKnee by 6.1% (p<0.05). The static balance with eyes closed significantly increased in the 11+ by 12.4% and in the HarmoKnee by 17.6%. The results indicated that static balance was significantly higher in eyes opened compared to eyes closed (p = 0.000). Significant improvements in SEBT in the 11+ (12.4%) and HarmoKnee (17.6%) groups were also found.

Conclusion

Both the 11+ and HarmoKnee programs were proven to be useful warm-up protocols in improving proprioception at 45° and 60° knee flexion as well as static and dynamic balance in professional male soccer players. Data from this research may be helpful in encouraging coaches or trainers to implement the two warm-up programs in their soccer teams.     

Demonstration of catch bonds between an integrin and its ligand

Binding of integrins to ligands provides anchorage and signals for the cell, making them prime candidates for mechanosensing molecules. How force regulates integrin–ligand dissociation is unclear. We used atomic force microscopy to measure the force-dependent lifetimes of single bonds between a fibronectin fragment and an integrin α₅β₁-Fc fusion protein or membrane α₅β₁. Force prolonged bond lifetimes in the 10–30-pN range, a counterintuitive behavior called catch bonds. Changing cations from Ca²⁺/Mg²⁺ to Mg²⁺/EGTA and to Mn²⁺ caused longer lifetime in the same 10–30-pN catch bond region. A truncated α₅β₁ construct containing the headpiece but not the legs formed longer-lived catch bonds that were not affected by cation changes at forces <30 pN. Binding of monoclonal antibodies that induce the active conformation of the integrin headpiece shifted catch bonds to a lower force range. Thus, catch bond formation appears to involve force-assisted activation of the headpiece but not integrin extension.     

The acute effects of a warm-up including static or dynamic stretching on countermovement jump height, reaction time, and flexibility

The purpose of this research was to compare the effects of a warm-up with static vs. dynamic stretching on countermovement jump (CMJ) height, reaction time, and low-back and hamstring flexibility and to determine whether any observed performance deficits would persist throughout a series of CMJs. Twenty-one recreationally active men (24.4 ± 4.5 years) completed 3 data collection sessions. Each session included a 5-minute treadmill jog followed by 1 of the stretch treatments: no stretching (NS), static stretching (SS), or dynamic stretching (DS). After the jog and stretch treatment, the participant performed a sit-and-reach test. Next, the participant completed a series of 10 maximal-effort CMJs, during which he was asked to jump as quickly as possible after seeing a visual stimulus (light). The CMJ height and reaction time were determined from measured ground reaction forces. A treatment × jump repeated-measures analysis of variance for CMJ height revealed a significant main effect of treatment (p = 0.004). The CMJ height was greater for DS (43.0 cm) than for NS (41.4 cm) and SS (41.9 cm) and was not less for SS than for NS. Analysis also revealed a significant main effect of jump (p = 0.005) on CMJ height: Jump height decreased from the early to the late jumps. The analysis of reaction time showed no significant effect of treatment. Treatment had a main effect (p < 0.001) on flexibility, however. Flexibility was greater after both SS and DS compared to after NS, with no difference in flexibility between SS and DS. Athletes in sports requiring lower-extremity power should use DS techniques in warm-up to enhance flexibility while improving performance.     

In Intact Cone Photoreceptors,a Ca2+-dependent,Diffusible Factor Modulates the cGMP-gated Ion Channels Differently than in Rods

We investigated the modulation of cGMP-gated ion channels in single cone photoreceptors isolated from a fish retina. A new method allowed us to record currents from an intact outer segment while controlling its cytoplasmic composition by superfusion of the electropermeabilized inner segment. The sensitivity of the channels to agonists in the intact outer segment differs from that measured in membrane patches detached from the same cell. This sensitivity, measured as the ligand concentration necessary to activate half-maximal currents, K _1/2, also increases as Ca²⁺ concentration decreases. In electropermeabilized cones, K _1/2 for cGMP is 335.5 ± 64.4 μM in the presence of 20 μM Ca²⁺, and 84.3 ± 12.6 μM in its absence. For 8Br-cGMP, K _1/2 is 72.7 ± 11.3 μM in the presence of 20 μM Ca²⁺ and 15.3 ± 4.5 μM in its absence. The Ca²⁺-dependent change in agonist sensitivity is larger in extent than that measured in rods. In electropermeabilized tiger salamander rods, K _1/2 for 8Br-cGMP is 17.9 ± 3.8 μM in the presence of 20 μM Ca²⁺ and 7.2 ± 1.2 μM in its absence. The Ca²⁺-dependent modulation is reversible in intact cone outer segments, but is progressively lost in the absence of divalent cations, suggesting that it is mediated by a diffusible factor. Comparison of data in intact cells and detached membrane fragments from cones indicates that this factor is not calmodulin. At 40 μM 8Br-cGMP, the Ca²⁺-dependent change in sensitivity in cones is half-maximal at K _Ca = 286 ± 66 nM Ca²⁺. In rods, by contrast, K _Ca is ∼50 nM Ca²⁺. The difference in magnitude and Ca²⁺ dependence of channel modulation between photoreceptor types suggests that this modulation may play a more significant role in the regulation of photocurrent gain in cones than in rods.     

Effect of Static and Dynamic Stretching on the Diurnal Variations of Jump Performance in Soccer Players

Purpose

The present study addressed the lack of data on the effect of different types of stretching on diurnal variations in vertical jump height - i.e., squat-jump (SJ) and countermovement-jump (CMJ). We hypothesized that dynamic stretching could affect the diurnal variations of jump height by producing a greater increase in short-term maximal performance in the morning than the evening through increasing core temperature at this time-of-day.

Methods

Twenty male soccer players (age, 18.6±1.3 yrs; height, 174.6±3.8 cm; body-mass, 71.1±8.6 kg; mean ± SD) completed the SJ and CMJ tests either after static stretching, dynamic stretching or no-stretching protocols at two times of day, 07:00 h and 17:00 h, with a minimum of 48 hours between testing sessions. One minute after warming-up for 5 minutes by light jogging and performing one of the three stretching protocols (i.e., static stretching, dynamic stretching or no-stretching) for 8 minutes, each subject completed the SJ and CMJ tests. Jumping heights were recorded and analyzed using a two-way analysis of variance with repeated measures (3 [stretching]×2 [time-of-day]).

Results

The SJ and CMJ heights were significantly higher at 17:00 than 07:00 h (p<0.01) after the no-stretching protocol. These daily variations disappeared (i.e., the diurnal gain decreased from 4.2±2.81% (p<0.01) to 1.81±4.39% (not-significant) for SJ and from 3.99±3.43% (p<0.01) to 1.51±3.83% (not-significant) for CMJ) after dynamic stretching due to greater increases in SJ and CMJ heights in the morning than the evening (8.4±6.36% vs. 4.4±2.64%, p<0.05 for SJ and 10.61±5.49% vs. 6.03±3.14%, p<0.05 for CMJ). However, no significant effect of static stretching on the diurnal variations of SJ and CMJ heights was observed.

Conclusion

Dynamic stretching affects the typical diurnal variations of SJ and CMJ and helps to counteract the lower morning values in vertical jump height.     

Both Transmembrane Domains of BK β1 Subunits Are Essential to Confer the Normal Phenotype of β1-Containing BK Channels

Voltage/Ca²⁺ _i-gated, large conductance K⁺ (BK) channels result from tetrameric association of α (slo1) subunits. In most tissues, BK protein complexes include regulatory β subunits that contain two transmembrane domains (TM1, TM2), an extracellular loop, and two short intracellular termini. Four BK β types have been identified, each presenting a rather selective tissue-specific expression profile. Thus, BK β modifies current phenotype to suit physiology in a tissue-specific manner. The smooth muscle-abundant BK β1 drastically increases the channel''s apparent Ca²⁺ _i sensitivity. The resulting phenotype is critical for BK channel activity to increase in response to Ca²⁺ levels reached near the channel during depolarization-induced Ca²⁺ influx and myocyte contraction. The eventual BK channel activation generates outward K⁺ currents that drive the membrane potential in the negative direction and eventually counteract depolarization-induced Ca²⁺ influx. The BK β1 regions responsible for the characteristic phenotype of β1-containing BK channels remain to be identified. We used patch-clamp electrophysiology on channels resulting from the combination of smooth muscle slo1 (cbv1) subunits with smooth muscle-abundant β1, neuron-abundant β4, or chimeras constructed by swapping β1 and β4 regions, and determined the contribution of specific β1 regions to the BK phenotype. At Ca²⁺ levels found near the channel during myocyte contraction (10 µM), channel complexes that included chimeras having both TMs from β1 and the remaining regions (“background”) from β4 showed a phenotype (V_half, τ_act, τ_deact) identical to that of complexes containing wt β1. This phenotype could not be evoked by complexes that included chimeras combining either β1 TM1 or β1 TM2 with a β4 background. Likewise, β “halves” (each including β1 TM1 or β1 TM2) resulting from interrupting the continuity of the EC loop failed to render the normal phenotype, indicating that physical connection between β1 TMs via the EC loop is also necessary for proper channel function.