Seasonal variation in isokinetic peak torque in youth soccer players

The aim of the study was to investigate the seasonal variation in the strength of the knee flexors and\ud extensors in highly trained youth soccer players. The players (n=16; age 16.7±0.7) were measured at the end\ud of the competitive season, at the beginning of the off-season and during the sixth week of a new competitive\ud season. Isokinetic concentric peak torque was measured at 60°·s-1, 180°·s-1, 360°·s-1 in a sitting position. The\ud testing range of motion was set from 10–90° of knee flexion. Players performed a set of six maximal repetitions\ud for both the dominant and non-dominant limb. Average values of peak torque significantly changed during\ud the observed periods. Significant differences (p<.05) between the three measurement sessions were noted\ud with respect to the knee flexors at all angular velocities. A post-hoc test confirmed a significant increase\ud between the first and the second measurement for flexion in both the dominant (180°·s-1; p=.033) and nondominant\ud legs (360°·s-1; p=.004). A significant increase was also found between the first and the third session\ud for both limbs during the knee flexion at all angular velocities. The results indicate that peak torque values\ud of knee flexors and extensors varied differently in trained youth soccer players depending on muscle group and movement velocity with statistically significant changes in knee flexors only

"Decessit sine prole" - childlessness, celibacy, and survival of the richest in pre-industrial England

In explaining England's early industrial development, previous research has highlighted that wealthy pre-industrial elites had more surviving offspring than their poorer counter- parts. Thus, entrepreneurial traits spread and helped England grow rich. We contest this view, showing that lowerclass reproduction rates were no different from the elites when accounting for singleness and childlessness. Elites married less and were more often childless. Many died without descendants (decessit sine prole). We find that the middle classes had the highest reproduction and argue that this advantage was instrumental to England's economic success because the middle class invested most strongly in human capital

Active Stretching and Eccentric Length-Tension Relationship of Hamstring Muscles

The purpose of this study was to investigate the acute effect of an active lower limb stretching routine with a sports-related training load on the hamstring eccentric length-tension relationship. 49 recreational sportsmen completed three assessment sessions, an initial familiarization session and two experimental sessions (control and stretching in random order). Immediately after the interventions (stretching or control), eccentric isokinetic peak torque, maximum force angle and total work were measured in prone position. If the alteration of the eccentric length-tension relationship could be used as a primary risk factor of hamstring muscle strains, the findings of the present study tentatively suggest that static stretching would not be able to alter the relative risk of hamstring muscles

'Nordic' Hamstrings Exercise - Engagement Characteristics and Training Responses

The present study examined the neuromuscular activation characteristics of the hamstrings during the 'Nordic' hamstrings exercise (NHE) and changes in the eccentric strength of the knee flexors with NHE training. Initially, the normalised root mean square electromyographic (EMG) activity of the hamstrings of both limbs during various phases (90-61 degrees, 60-31 degrees and 30-0 degrees of knee extension) of the NHE were determined in 18 soccer players. Subsequently participants were randomly allocated to either a training (n = 10) or control group. The isokinetic eccentric peak torques of the dominant and non-dominant limbs were recorded at 60, 120 and 240 degrees/s pre- and post-training. The EMG values of both limbs were comparable (P = 0.184) and greater EMG activity was recorded at more extended knee positions of the NHE (P = 0.001). 4 weeks of NHE training significantly improved peak torque by up to 21% in all assessment conditions. Data indicate the hamstrings of both limbs are engaged identically during the NHE and training results in gains in the eccentric peak torque of the hamstrings of both limbs; these gains may augment the force that the hamstrings can withstand when forcefully stretched, attenuating injury risk

Active Stretching and Eccentric Length-Tension Relationship of Hamstring Muscles

The purpose of this study was to investigate the acute effect of an active lower limb stretching routine with a sports-related training load on the hamstring eccentric length-tension relationship. 49 recreational sportsmen completed three assessment sessions, an initial familiarization session and two experimental sessions (control and stretching in random order). Immediately after the interventions (stretching or control), eccentric isokinetic peak torque, maximum force angle and total work were measured in prone position. If the alteration of the eccentric length-tension relationship could be used as a primary risk factor of hamstring muscle strains, the findings of the present study tentatively suggest that static stretching would not be able to alter the relative risk of hamstring muscles

Optimized versus corrected peak power during friction-braked cycle ergometry in males and females

The aim of this study was to compare optimization and correction procedures for the determination of peak power output during friction-loaded cycle ergometry. Ten male and 10 female sports students each performed five 10- s sprints from a stationary start on a Monark 864 basket- loaded ergometer. Resistive loads of 5.0, 6.5, 8.0, 9.5, and 11.0% body weight were administered in a counterbalanced order, with a recovery period of 10 min between sprints. Peak power was greater and occurred earlier, with less work having been done before the attainment of peak power, when the data were corrected to account for the inertial and frictional characteristics of the ergometer. Corrected peak power was independent of resistive load ( P > 0.05), whereas uncorrected peak power varied as a quadratic function of load ( P > 0.001). For males and females, optimized peak power ( 971 +/- 122 and 668 +/- 37 W) was lower ( P < 0.01) than either the highest ( 1074 +/- 111 and 754 +/- 56 W respectively) or the mean ( 1007 +/- 125 and 701 +/- 45 W respectively) of the five values for corrected peak power. Optimized and mean corrected peak power were highly correlated both in males ( r = 0.97, P < 0.001) and females ( r = 0.96, P < 0.001). The difference between optimized and mean corrected peak power was 37+ 30 W in males and 33 +/- 14 W in females, of which approximately 15 W was due to the correction for frictional losses. We conclude that corrected peak power is independent of resistive load in males and females

Heart Rate Variability : Effect of Exercise Intensity on Postexercise Response

The purpose of the present study was to investigate the influence of two exercise intensities (moderate and severe) on heart rate variability (HRV) response in 16 runners 1 hr prior to (-1 hr) and at +1 hr, +24 hr, +48 hr, and +72 hr following each exercise session. Time domain indexes and a high frequency component showed a significant decrease (p < .001) between -1 hr and +1 hr for severe intensity. The low frequency component in normalized units significantly increased (p <.01) for severe intensity at +1 hr. Only severe exercise elicited a change in HRV outcomes postexercise, resulting in a reduction in the parasympathetic influence on the heart at +1 hr; however, values returned to baseline levels by +24 hr

Reproducibility of an isokinetic eccentric muscle endurance task

Despite the widespread use of isokinetic eccentric muscle endurance protocols, no research has examined the absolute and relative reliability of such tests. The aim of this study was to examine the reliability of an isokinetic eccentric knee muscle endurance task. Fifteen healthy untrained males volunteered to take part in the study and written informed consent was obtained. The procedures received approval from the University Research Ethics Committee. Participants visited the laboratory on three separate occasions: 2 weeks before testing to familiarize them with the experimental procedures, and on two separate occasions, 2 weeks apart and at the same time of day. Isokinetic eccentric knee extension and flexion movements of the dominant limb were performed using a calibrated dynamometer (Biodex System 3). Range of motion during testing was set using voluntary maximal full extension (0 rad) to 1.57 rad of knee flexion and testing was conducted at 1.56 rad . s(-1). Participants performed four maximal efforts to determine maximal peak torque. After 2 min rest, participants completed the all-out endurance test of 50 continuous eccentric repetitions. Data were gravity corrected and windowed to only include constant velocity periods. Repeated-measures analyses of variance were used to examine differences in maximal peak extension and flexion torque and the maximal torque measurement recorded during the endurance test. Absolute and relative reliability of the torque fatigue index, work fatigue index, and total work were assessed through calculation of intra-class correlation coefficients, coefficients of variation, and absolute 95% limits of agreement using the methods described by Bland and Altman (1986). Differences between the strength test and the endurance trial for peak torque were found to be non-significant for both quadriceps (323 vs. 323 N . m) and hamstrings (183 vs. 178 N . m). The intra-class correlation coefficients revealed significant (P<0.05) positive moderate to strong correlations (r=0.44-0.94) across repeated trials for all parameters except hamstring torque fatigue (P=0.11) and hamstring work fatigue index (P=0.08). Coefficients of variation ranged from 6% to 48% and were large for the work fatigue index and torque fatigue index but acceptable for total work for both the extensors and flexors. The 95% limits of agreement indicated systematic bias in repeated trials for both the work fatigue index and torque fatigue index for extensors and flexors, ranging from -3% to -10%, with less fatigue evident in the second test. There was also systematic bias for total work, with more work being performed during the second than the first test for both extensors and flexors. The random error was large for all variables and there was greater random error in the hamstrings compared with the quadriceps. Together with moderate to strong intra-class correlation coefficients and large coefficients of variation, the data suggest that there is small systematic bias in repeated eccentric muscle actions for both the quadriceps and hamstrings, although the random error was large despite habituation procedures. Therefore, data from an isokinetic eccentric muscle endurance task should be viewed with some caution even when participants receive considerable habituation before assessment

G-Quadruplex Dynamics Contribute To Regulation Of Mitochondrial Gene Expression

Single-stranded DNA or RNA sequences rich in guanine (G) can adopt non-canonical structures known as G-quadruplexes (G4). Mitochondrial DNA (mtDNA) sequences that are predicted to form G4 are enriched on the heavy-strand and have been associated with formation of deletion breakpoints. Increasing evidence supports the ability of mtDNA to form G4 in cancer cells; however, the functional roles of G4 structures in regulating mitochondrial nucleic acid homeostasis in non-cancerous cells remain unclear. Here, we demonstrate by live cell imaging that the G4-ligand RHPS4 localizes primarily to mitochondria at low doses. We find that low doses of RHPS4 do not induce a nuclear DNA damage response but do cause an acute inhibition of mitochondrial transcript elongation, leading to respiratory complex depletion. We also observe that RHPS4 interferes with mtDNA levels or synthesis both in cells and isolated mitochondria. Importantly, a mtDNA variant that increases G4 stability and anti-parallel G4-forming character shows a stronger respiratory defect in response to RHPS4, supporting the conclusion that mitochondrial sensitivity to RHPS4 is G4-mediated. Taken together, our results indicate a direct role for G4 perturbation in mitochondrial genome replication, transcription processivity, and respiratory function in normal cells