Isokinetic Fatigue Characteristics for the Leg Extensors versus Flexors

Maximal isokinetic muscle actions are often used in research studies to examine fatigability and even estimate muscle fiber-type. However, the majority of previous investigations have examined these topics for the leg extensors (i.e., quadriceps), and we are unaware of investigations that have specifically assessed the fatigue characteristics for the flexors (i.e., hamstrings). The purpose of this study was to compare the percent decline values for the leg extensors versus flexors for 50 and 100 repeated, maximal concentric isokinetic muscle actions. Fifteen healthy men (mean ± SD age = 23 ± 3 years; body mass = 94.1 ± 11.9 kg) with previous lower-body strength training experience volunteered to participate in this study. All of the subjects were familiarized with the testing procedures prior to data collection. For data collection, each subject performed 100 repeated, maximal concentric isokinetic muscle actions of the left leg extensors and flexors in a reciprocal manner. Each muscle action was performed at 180 degrees/second through a full 90 degree range of motion. Strong verbal encouragement was provided throughout testing. Percent decline was determined using the mean peak torque values of the initial and final three muscle actions for each muscle group (i.e., extensors versus flexors) and condition (i.e., 50 versus 100 repetitions). A two-way repeated measure analysis of variance was used to examine the data. The mean ± SD percent decline for the leg extensors was 61.8 ± 7.8 and 71.2 ± 6.5% for the 50 and 100 conditions, respectively (Cohen’s d = 1.31). For the leg flexors, these corresponding values were 48.0 ± 12.2 and 54.3 ± 11.7 % (Cohen’s d = 0.53). There was no significant muscle group × condition interaction (p= .114; partial eta squared = .169) There were, however, main effects for both factors. The bonferroni marginal mean pairwise comparisons indicated that when collapsed across condition, the leg extensors fatigued more so than the flexors (66.5 vs. 51.2%). Similarly, when collapsed across muscle group, the percent decline values were greater following 100 (62.8%) versus 50 (54.9%) repetitions. These finding demonstrated greater isokinetic fatigue characteristics for the leg extensors versus flexors. Furthermore, the additional decline in peak torque from repetitions 50-100 was more pronounced for the extensors. We speculate that these findings could be related to differences in muscle fiber-type, lower absolute strength and mass for the posterior aspect of the thigh, and/or unfamiliarity with single-joint testing of the leg flexors

Relationships Between Anthropometric and Performance Variables in Youth: Predictors of Lower-Body Vertical Jump Peak Power

ABSTRACT Anthropometric and physical performance measurements are commonly used for identifying specific physical traits in youth. Laboratory-based tests (e.g., linear velocity transducers), while accurate, provide practical limitations due to high costs and technical necessities. Thus, commonly used field tests may be useful alternatives for assessing fitness/performance characteristics of youth. The purpose of this study was to examine the relationships between anthropometric measures and lower-and upper-body power and strength measures; and to assess the predictive ability of these measures for lower-body vertical jump peak power (PP) output in youth. Thirty-nine pre-adolescent (mean±SD, range: age=7.8±1.7, 5-12 years) children volunteered to participate in this investigation. Subjects were measured for body mass and stature on a calibrated physicians scale. Lower-body PP was assessed using a linear velocity transducer, which was attached to the posterior side of a belt that was securely fastened to the subjects’ waistline. Subjects performed countermovement jumps, starting in a standing position, with hands placed on hips and feet firmly on the ground. Following the descent to the midpoint position and without pause, the subjects exploded upward as hard and fast as possible. Broad jump testing involved subjects performing a countermovement jump in the horizontal direction, on a scaled mat. Maximum isometric hand grip strength of the dominant hand was assessed using a dynamometer. For all testing, 1-2 practice trials were performed, followed by testing consisting of 2-3 trials. The highest trial was used for analyses. Peak power values were normalized to body mass using allometric scaling procedures (PP· body mass-0.67). Pearson correlation (r) and stepwise linear regression analyses were performed to examine the relationships. Results indicated all variables (age, stature, body mass, broad jump and grip strength) were significantly correlated (r=0.38-0.64) to PP. Age was correlated to all variables (r=0.39-0.82) and stature and body mass were correlated to all variables (r=0.37-0.77) except broad jump. Broad jump was correlated only to age (r=0.39) and PP (r=0.38). Linear regression for all variables revealed that stature was the only variable entered into the model (R=0.64; R2=0.41). With the anthropometric variables removed, grip strength was the only variable entered into the model (R=0.57; R2=0.32). These findings suggest that while all the anthropometric and performance variables may be correlated to PP, only stature and grip strength were effective, and thus, necessary to predict PP abilities. Interestingly, broad jump performance was not a good predictor of lower body vertical PP

Linear Progression for Increased External Loads during Strength Training

Improvements in muscular strength require an individual to train with progressively increased external loads over time. While it is well documented that the initial adaptations to strength training occur rapidly, previous researchers have not thoroughly examined the most effective means of inducing these changes. The purpose of this study was to examine the ability to add 2.27 kg to the barbell for 20 consecutive training sessions, and to compare these responses between the sexes. Thirty-four subjects ([mean ± SD age = 23 ± 3 years] men, n = 17; women, n = 17) participated in this study. The subjects were taught how to perform the barbell deadlift exercise, and received individual instruction and verbal feedback regarding their technique throughout the entire investigation. The subjects visited the laboratory twice per week for ten weeks. The external loads corresponded to the maximum weight that each subject could use to perform five sets of five repetitions with correct technique. If five sets of five repetitions were performed, 2.27 kg were added to the barbell for the following training session. The mean external load for each training session was recorded. The data were analyzed with bivariate regression and repeated measures analyses of variance (ANOVAs). The mean ± SD external loads used in this study increased from 66.2 ± 22.3 to 123.1 ± 21.8 kg for the men and 37.8 ± 7.0 to 70.7 ± 12.2 for the women. The results from the repeated measures ANOVAs indicated that men were able to add 2.27 kg to the barbell for 17 consecutive training sessions. For the women, however, the progress stalled at roughly week six. As a result, the coefficient of determination for the external load versus training session number relationship was r2 = .960 for the men and r2 = .881 for the women. These findings demonstrated that adding 2.27 kg to the barbell for each training session was an effective method for progressively increasing the external load over a ten week period. Many of the women had a difficult time with this gradual increase after week six, however, suggesting that smaller absolute changes with fractional plates (e.g., 0.91 kg) may be necessary

Effects of a Ten Week Barbell Deadlift Training Program on Vertical Jump Height in College-Aged Women

The barbell deadlift is a large muscle mass exercise that primarily involves extension at the hip and knee joints. Although it is often incorporated into strength training programs with a variety of other exercises (e.g., back squat), no previous studies have examined the effects of deadlift training on strength or power adaptations. The purpose of this investigation was to examine the effects of a ten week barbell deadlift training program on vertical jump height in previously untrained women. Twenty-eight women (mean ± SD age = 22 ± 2 years) were randomly assigned to either the training group (n = 17) or the control group (n = 11). The training group visited the laboratory for supervised exercise twice per week for ten weeks. Each training session involved five sets of the barbell deadlift, and each set utilized the heaviest external load that allowed for five repetitions with proper exercise technique. If all repetitions were performed with correct technique, additional weight (≤ 2.27 kg) was added to the barbell during the next training session. The control group was asked to refrain from lower-body exercise throughout the course of the study. Vertical jump height was assessed with a Vertec before and after the ten week intervention. An analysis of covariance (ANCOVA) was used to examine the data, and the pretest and posttest values were used as the covariate and dependent variable, respectively. The ANCOVA indicated that the posttest mean for the training group (42.5 cm) was significantly greater than that for the control group (39.0 cm) after adjusting for the pretest vertical jump height scores (p = .012, η² = .229). The effect size for the unadjusted mean increase for the training group (3.6 cm) was considered small-to-moderate (Cohen’s d = .37). These findings demonstrated that a ten week exercise training program using only the barbell deadlift significantly improved vertical jump height in college-aged women

Optical follow-up of the tidal disruption event iPTF16fnl: new insights from X-shooter observations

We present the results from Nordic Optical Telescope and X-shooter follow-up campaigns of the tidal disruption event (TDE) iPTF16fnl, covering the first similar to 100 d after the transient discovery. We followed the source photometrically until the TDE emission was no longer detected above the host galaxy light. The bolometric luminosity evolution of the TDE is consistent with an exponential decay with e-folding constant t(0) = 17.6 +/- 0.2 d. The early-time spectra of the transient are dominated by broad He II lambda 4686, H beta, H alpha, and N III lambda 4100 emission lines. The latter is known to be produced together with the N III lambda 4640 in the Bowen fluorescence mechanism. Due to the medium-resolution X-shooter spectra we have been able to separate the Bowen blend contribution from the broad He II emission line. The detection of the Bowen fluorescence lines in iPTF16fnl place this transient among the N-rich TDE subset. In the late-time X-shooter spectra, narrow emission lines of [O III] and [N II] originating from the host galaxy are detected, suggesting that the host galaxy harbours a weak active galactic nucleus in its core. The properties of all broad emission lines evolve with time. The equivalent widths follow an exponential decay compatible with the bolometric luminosity evolution. The full width at half-maximum of the broad lines decline with time and the line profiles develop a narrow core at later epochs. Overall, the optical emission of iPTF16fnl can be explained by being produced in an optically thick region in which high densities favour the Bowen fluorescence mechanism and where multiple electron scatterings are responsible for the line broadening

Current challenges in software solutions for mass spectrometry-based quantitative proteomics

This work was in part supported by the PRIME-XS project, grant agreement number 262067, funded by the European Union seventh Framework Programme; The Netherlands Proteomics Centre, embedded in The Netherlands Genomics Initiative; The Netherlands Bioinformatics Centre; and the Centre for Biomedical Genetics (to S.C., B.B. and A.J.R.H); by NIH grants NCRR RR001614 and RR019934 (to the UCSF Mass Spectrometry Facility, director: A.L. Burlingame, P.B.); and by grants from the MRC, CR-UK, BBSRC and Barts and the London Charity (to P.C.

Performance and Operation of the CMS Electromagnetic Calorimeter

The operation and general performance of the CMS electromagnetic calorimeter using cosmic-ray muons are described. These muons were recorded after the closure of the CMS detector in late 2008. The calorimeter is made of lead tungstate crystals and the overall status of the 75848 channels corresponding to the barrel and endcap detectors is reported. The stability of crucial operational parameters, such as high voltage, temperature and electronic noise, is summarised and the performance of the light monitoring system is presented

A kilonova as the electromagnetic counterpart to a gravitational-wave source

Gravitational waves were discovered with the detection of binary black-hole mergers1 and they should also be detectable from lower-mass neutron-star mergers. These are predicted to eject material rich in heavy radioactive isotopes that can power an electromagnetic signal. This signal is luminous at optical and infrared wavelengths and is called a kilonova2,3,4,5. The gravitational-wave source GW170817 arose from a binary neutron-star merger in the nearby Universe with a relatively well confined sky position and distance estimate6. Here we report observations and physical modelling of a rapidly fading electromagnetic transient in the galaxy NGC 4993, which is spatially coincident with GW170817 and with a weak, short γ-ray burst7,8. The transient has physical parameters that broadly match the theoretical predictions of blue kilonovae from neutron-star mergers. The emitted electromagnetic radiation can be explained with an ejected mass of 0.04 ± 0.01 solar masses, with an opacity of less than 0.5 square centimetres per gram, at a velocity of 0.2 ± 0.1 times light speed. The power source is constrained to have a power-law slope of −1.2 ± 0.3, consistent with radioactive powering from r-process nuclides. (The r-process is a series of neutron capture reactions that synthesise many of the elements heavier than iron.) We identify line features in the spectra that are consistent with light r-process elements (atomic masses of 90–140). As it fades, the transient rapidly becomes red, and a higher-opacity, lanthanide-rich ejecta component may contribute to the emission. This indicates that neutron-star mergers produce gravitational waves and radioactively powered kilonovae, and are a nucleosynthetic source of the r-process element