Evaluation of an innovative critical power model in intermittent vertical jump

The aim of this study was to test if the critical power model can be used to determine the critical rest interval (CRI) between vertical jumps. Ten males performed intermittent countermovement jumps on a force platform with different resting periods (4.1 +/- 0.3 s, 5.0 +/- 0.4 s, 5.9 +/- 0.6 s). Jump trials were interrupted when participants could no longer maintain 95% of their maximal jump height. After interruption, number of jumps, total exercise duration and total external work were computed. Time to exhaustion (s) and total external work (J) were used to solve the equation Work = a + b . time. The CRI (corresponding to the shortest resting interval that allowed jump height to be maintained for a long time without fatigue) was determined dividing the average external work needed to jump at a fixed height (J) by b parameter (J/s). in the final session, participants jumped at their calculated CRI. A high coefficient of determination (0.995 +/- 0.007) and the CRI (7.5 +/- 1.6 s) were obtained. In addition, the longer the resting period, the greater the number of jumps (44 13, 71 28, 105 30, 169 53 jumps; p<0.0001), time to exhaustion (179 +/- 50, 351 +/- 120, 610 +/- 141, 1,282 +/- 417 s; p<0.0001) and total external work (28.0 +/- 8.3, 45.0 +/- 16.6, 67.6 +/- 17.8, 111.9 +/- 34.6 kJ; p<0.0001). Therefore, the critical power model may be an alternative approach to determine the CRI during intermittent vertical jumps.

Monitoring stress tolerance and occurrences of upper respiratory illness in basketball players by means of psychometric tools and salivary biomarkers

The aim of the study was to evaluate the possible relationships between stress tolerance, training load, banal infections and salivary parameters during 4 weeks of regular training in fifteen basketball players. The Daily Analysis of Life Demands for Athletes` questionnaire (sources and symptoms of stress) and the Wisconsin Upper Respiratory Symptom Survey were used on a weekly basis. Salivary cortisol and salivary immunoglobulin A (SIgA) were collected at the beginning (before) and after the study, and measured by enzyme-linked immunosorbent assay (ELISA). Ratings of perceived exertion (training load) were also obtained. The results from ANOVA with repeated measures showed greater training loads, number of upper respiratory tract infection episodes and negative sensation to both symptoms and sources of stress, at week 2 (p < 0.05). Significant increases in cortisol levels and decreases in SIgA secretion rate were noted (before to after). Negative sensations to symptoms of stress at week 4 were inversely and significantly correlated with SIgA secretion rate. A positive and significant relationship between sources and symptoms of stress at week 4 and cortisol levels were verified. In summary, an approach incorporating in conjunction psychometric tools and salivary biomarkers could be an efficient means of monitoring reaction to stress in sport. Copyright (C) 2010 John Wiley & Sons, Ltd.

Manipulation of rest period length induces different causes of fatigue in vertical jumping

The aim of this study was to directly compare the causes of fatigue after a short- and a long-rest interval between consecutive stretch-shortening cycle exercises. Eleven healthy males jumped with different resting period lengths (short = 6.1 +/- 1 s, long = 8.6 +/- 0.9 s), performing countermovement jumps at 95% of their maximal jump height until they were unable to sustain the target height. After short- and long-rest, the maximal voluntary isometric contraction knee extension torque decreased (-7%; p = 0.04), comparing to values obtained before exercise protocols. No change was seen from pre- to post-exercise, for either short- or long-rest, in biceps femoris coactivation (-1%; p = 0.95), peak-to-peak amplitude (1%; p = 0.95) and duration (-8%; p = 0.92) of the compound muscle action potential of the vastus lateralis. Evoked peak twitch torque reduced after both exercise protocols (short = -26%, long = -32%; p = 0.003) indicating peripheral fatigue. However, central fatigue occurred only after short-rest evidenced by a reduction in voluntary activation of the quadriceps muscle (-14%; p = 0.013) measured using the interpolated twitch technique. In conclusion, after Stretch-shortening cycle exercise using short rest period length, the cause of fatigue was central and peripheral, while after using long rest period length, the cause of fatigue was peripheral.

Transient effects of stretching exercises on gait parameters of elderly women

This study aimed to analyse the effects of a single stretching exercise session on a number of gait parameters ill elderly participants in all attempt to determine whether these exercises can influence the risk of fall. Fifteen healthy women living in the community Volunteered to participate in the study. A kinematic gait analysis was performed immediately before and after a session of static stretching exercises applied oil hip flexor/extensor muscles. Results showed a significant influence of stretching exercises on a number of gait parameters, which have previously been proposed as fall predictors. Participants showed increased gait velocity, greater step length and reduced double Support time during stance after performing stretching exercises, suggesting improved stability and mobility. Changes around the pelvis (increased anterior-posterior tilt and rotation range of motion) resulting from the stretching exercises were suggested to influence the gait parameters (velocity, step length and double support time). Therefore, stretching exercises were shown to be a promising strategy to facilitate changes in gait parameters related to the risk of fall. Some other gait variables related to the risk of fall remained Unaltered (e.g., toe clearance). The stable pattern of segmental angular velocities was proposed to explain the stability of these unchanged gait variables. The results indicate that stretching exercises, performed oil a regular (daily) basis, result in gait adaptations which can be considered as indicative of reduced fall risk. Other Studies to determine whether regular stretching routines are an effective strategy to reduce the risk of fall are required. (C) 2008 Elsevier Ltd. All rights reserved.

The impact of a 17-day training period for an international championship on mucosal immune parameters in top-level basketball players and staff members

This investigation examined the impact of a 17-d training period (that included basketball-specific training, sprints, intermittent running exercises, and weight training, prior to an international championship competition) on salivary immunoglobulin A (SIgA) levels in 10 subjects (athletes and staff members) from a national basketball team, as a biomarker for mucosal immune defence. Unstimulated saliva samples were collected at rest at the beginning of the preparation for the Pan American Games and 1 d before the first game. The recovery interval from the last bout of exercise was 4 h. The SIgA level was measured using enzyme-linked immunosorbent assay and expressed as absolute concentrations, secretion rate, and SIgA level relative to total protein. The decrease in SIgA levels following training was greater in athletes than in support staff; however, no significant differences between the two groups were detected. A decrease in SIgA level, regardless of the method used to express IgA results, was verified for athletes. Only one episode of upper respiratory tract illness symptoms was reported, and it was not associated with changes in SIgA levels. In summary, a situation of combined stress for an important championship was found to decrease the level of SIgA-mediated immune protection at the mucosal surface in team members, with greater changes observed in the athletes.

Effects of strength training and vascular occlusion

The purpose of our study was to determine if vascular Occlusion produced an additive effect on muscle hypertrophy and strength performance with high strength training loads. Sixteen physically active men were divided into two groups: high-intensity (HI = 6 RM) and moderate-intensity training (MI = 12 RM). An occlusion cuff was attached to the proximal end of the right thigh, so that blood flow was reduced during the exercise. The left leg served as a control, thus was trained without vascular occlusion. Knee extension 1 RM and quadriceps cross-sectional area (MRI) were evaluated pre- and post-8 weeks of training. We only found a main time effect for both strength gains and quadriceps hypertrophy (p < 0.001). Therefore, we conclude that vascular occlusion in combination with high-intensity strength training does not augment muscle strength or hypertrophy when compared to high-intensity strength training alone.

The influence of resting period length on jumping performance

Pereira, G, Almeida, AG, Rodacki, ALF, Ugrinowitsch, C, Fowler, NE, Kokubun, E. The influence of resting period length on jumping performance. J Strength Cond Res 22: 1259-1264, 2008-The purpose of this study was to determine a resting interval between countermovement jumps (i.e., volleyball spikes) that allows the maintenance of maximal jumping performance. Ten male volleyball players (1.85 +/- 0.05 m, 77.2 +/- 10.6 kg, 21.6 +/- 5.3 years) performed 6 experimental jumping sessions. In the first and sixth sessions, maximal countermovement jump height was measured, followed by submaximal countermovement jumps to the point of volitional fatigue. The number of countermovement jumps was used as a reference to test the effect of rest period between volleyball spikes. From the second to fifth experimental sessions, 30 maximal volleyball spikes were performed with different resting periods (i.e., 8, 14, 17, and 20 seconds) followed by countermovement jumps. Between the 15th and 30th spikes, the blood lactate concentration and heart rate were measured. Because the performance on the first and sixth sessions was the same, no training effects were noticed. During the 8-second resting interval set, the lactate concentration increased significantly between the 15th and 30th spikes (i.e., from 3.37 +/- 1.16 mmol to 4.94 +/- 1.49 mmol); the number of countermovement jumps decreased significantly after spikes compared to those performed without a previous effort (i.e., from 23 +/- 7 jumps to 17 +/- 9 jumps); and these variables were significantly correlated (r = -0.7). On the other hand, the lactate concentration and number of countermovement jumps were stable across the other resting intervals, without a heart rate steady state. The results indicate that an adequate resting period between spikes allowed participants to achieve a lactate steady state in which the performance was maintained during the exercise. These findings show that resting intervals between 14 and 17 seconds, typical during volleyball matches, are indicated to use in volleyball spike drills due to their capacity to maintain maximal jumping performance.

The effect of carbohydrate mouth rinse on maximal strength and strength endurance

It has been previously reported that carbohydrate (CHO) mouth rinse can improve exercise performance. The proposed mechanism involves increased activation of brain regions believed to be responsible for reward/motivation and motor control. Since strength-related performance is affected by central drive to the muscles, it seems reasonable to hypothesize that the positive CNS response to oral CHO sensing may counteract the inhibitory input from the muscle afferent pathways minimizing the drop in the central drive. The purpose of the current study was to test if CHO mouth rinse affects maximum strength and strength endurance performance. Twelve recreationally strength-trained healthy males (age 24.08 +/- 2.99 years; height 178.09 +/- 6.70 cm; weight 78.67 +/- 8.17 kg) took part in the study. All of the tests were performed in the morning, after an 8 h overnight fasting. Subjects were submitted to a maximum strength test (1-RM) and a strength endurance test (six sets until failure at 70% of 1-RM), in separate days under three different experimental conditions (CHO mouth rinse, placebo-PLA mouth rinse and control-CON) in a randomized crossover design. The CHO mouth rinse (25 ml) occurred before every attempt in the 1-RM test, and before every set in the endurance strength test. Blood glucose and lactate were measured immediately before and 5 min post-tests. There were no significant differences in 1-RM between experimental conditions (CHO 101 +/- 7.2 kg; PLA 101 +/- 7.4 kg; CON 101 +/- 7.2 kg; p = 0.98). Furthermore, there were no significance between trial differences in the number of repetitions performed in each set (p = 0.99) or the total exercise volume (number of repetitions x load lifted [kg]) (p = 0.98). A main effect for time (p < 0.0001) in blood lactate concentration was observed in both tests (1-RM and strength endurance). Blood glucose concentration did not differ between conditions. In conclusion, CHO mouth rinse does not affect maximum strength or strength endurance performance.

Influence of strength training background on postactivation potentiation response

Batista, MAB, Roschel, H, Barroso, R, Ugrinowitsch, C, and Tricoli, V. Influence of strength training background on postactivation potentiation response. J Strength Cond Res 25(9): 2496-2502, 2011-The aim of this study was to evaluate the influence of the subjects` level of maximal dynamic strength and training background on postactivation potentiation (PAP). A group of 23 subjects, composed of power track-and-field athletes (PT = 8), bodybuilders (BB = 7), and physically active subjects (PA = 8), participated in the study. Maximal dynamic strength (1 repetition maximum test) was assessed in the leg press exercise for subjects` characterization. Their countermovement vertical jump (CMJ) performance was assessed before and after 2 different conditioning activity (CA) protocols (1 or 3 maximum voluntary isometric contractions [MVICs] of 5-second duration in the leg press exercise) or after control (no CA), performed on separate days. No significant differences among groups were found for CMJ height or take-off velocity after any of the CA protocols (p <= 0.05). However, individual analysis showed that some subjects increased performance in response to the CA, despite their previous training history. We concluded that subjects` level of maximal dynamic strength and training background have no influence on PAP manifestation. Our data suggest that coaches should individually identify the athletes that are PAP responders before introducing MVICs as part of their warm-up routines.

Effects of creatine supplementation on renal function: a randomized, double-blind, placebo-controlled clinical trial

Creatine (CR) supplementation is commonly used by athletes. However, its effects on renal function remain controversial. The aim of this study was to evaluate the effects of creatine supplementation on renal function in healthy sedentary males (18-35 years old) submitted to exercise training. A randomized, double-blind, placebo-controlled trial was performed. Subjects (n = 18) were randomly allocated to receive treatment with either creatine (CR) (similar to 10 g day(-1) over 3 months) or placebo (PL) (dextrose). All subjects undertook moderate intensity aerobic training, in three 40-min sessions per week, during 3 months. Serum creatinine, serum and urinary sodium and potassium were determined at baseline and at the end of the study. Cystatin C was assessed prior to training (PRE), after 4 (POST 4) and 12 weeks (POST 12). Cystatin C levels (mg L-1) (PRE CR: 0.82 +/- 0.09; PL: 0.88 +/- 0.07 vs. POST 12 CR: 0.71 +/- 0.06; PL: 0.75 +/- 0.09, P = 0.0001) were decreased over time, suggesting an increase in glomerular filtration rate. Serum creatinine decreased with training in PL but was unchanged with training in CR. No significant differences were observed within or between groups in other parameters investigated. The decrease in cystatin C indicates that high-dose creatine supplementation over 3 months does not provoke any renal dysfunction in healthy males undergoing aerobic training. In addition, the results suggest that moderate aerobic training per se may improve renal function.

Effects of creatine supplementation on glucose tolerance and insulin sensitivity in sedentary healthy males undergoing aerobic training

Recent findings have indicated that creatine supplementation may affect glucose metabolism. This study aimed to examine the effects of creatine supplementation, combined with aerobic training, on glucose tolerance in sedentary healthy male. Subjects (n = 22) were randomly divided in two groups and were allocated to receive treatment with either creatine (CT) (similar to 10g .day over three months) or placebo (PT) (dextrose). Administration of treatments was double blind. Both groups underwent moderate aerobic training. An oral glucose tolerance test (OGTT) was performed and both fasting plasma insulin and the homeostasis model assessment (HOMA) index were assessed at the start, and after four, eight and twelve weeks. CT demonstrated significant decrease in OGTT area under the curve compared to PT (P = 0.034). There were no differences between groups or over time in fasting insulin or HOMA. The results suggest that creatine supplementation, combined with aerobic training, can improve glucose tolerance but does not affect insulin sensitivity, and may warrant further investigation with diabetic subjects.

Microstructural characterization of rapidly solidified and heat-treated Ti(92)B(8) eutectic alloy

In this work, Ti(92)B(8) alloy was processed via rapid solidification (splat-cooling) and then heat-treated at 700 degrees C and 1000 degrees C. A careful microstructural characterization indicated that, after rapid solidification, a very fine two-phase microstructure was produced with no significant saturation of B in alpha/beta Ti. There was no indication of amorphous formation in the rapidly solidified splats. Both alpha Ti and TiB were observed in the microstructures of the splats after heat-treatment at 700 degrees C and 1000 degrees C, confirming the stability of the alpha Ti+TiB two-phase region in this temperature range. (C) 2008 Elsevier Inc. All rights reserved.

Fault current test of a bifilar Bi-2212 bulk coil

A bifilar Bi-2212 bulk coil with parallel shunt resistor was tested under fault current condition using a 3 MVA single-phase transformer in a 220 V-60 Hz line achieving fault current peak of 8 kA. The fault current tests are performed from steady state peak current of 200 A by applying controlled short circuits up to 8 kA varying the time period from one to six cycles. The test results show the function of the shunt resistor providing homogeneous quench behavior of the HTS coil besides its intrinsic stabilizing role. The limiting current ratio achieves a factor 4.2 during 5 cycles without any degradation.

Production, microstructural characterization and mechanical properties of as-cast Ti-10Mo-xNb alloys

Beta titanium (Ti) alloys are one of the most promising groups of Ti alloys for biomedical applications. This work presents the production, microstructural characterization, and mechanical properties of as-cast Ti-10Mo-xNb (x = 0, 3, 6, 9, 20, and 30) alloys. They were produced via arc melting and characterized by scanning electron microscopy and X-ray diffraction. The density of each alloy was measured by the Archimedes method and the mechanical characterization was carried out by using the Vickers microhardness test and Young`s modulus measurements. The results show a near beta microstructure for niobium (Nb) contents lower or equal to 9 wt% while beta single-phase microstructure was obtained for higher Nb additions. The microhardness values decreased with the increase of Nb content in the alloys. The elastic modulus values of Ti-10Mo-3Nb and Ti-10Mo-20Nb alloys were lower than those of cp Ti and Ti-6Al-4V.

Test of a Modular Fault Current Limiter for 220 V Line Using YBCO Coated Conductor Tapes With Shunt Protection

A modular superconducting fault current limiter (SFCL) consisting of 16 elements was constructed and tested in a 220 V line for a fault current between 1 kA to 7.4 kA. The elements are made up of second generation (2G) YBCO-coated conductor tapes with stainless steel reinforcement. For each element four tapes were electrically connected in parallel with effective length of 0.4 m per element, totaling 16 elements connected in series. The evaluation of SFCL performance was carried out under DC and AC tests. The DC test was performed through pulsed current tests and its recovery characteristics under load current were analysed by changing the shunt resistor value. The AC test performed using a 3 MVA/220 V/60 Hz transformer has shown the current limiting ratio achieved a factor higher than 10 during fault of up to five cycles without conductor degradation. The measurement of the voltage for each element during the AC test showed that in this modular SFCL the quench is homogeneous and the transition occurs similarly in all the elements.