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

'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

Back foot influence on dorsiflexion using three different positions of the weight bearing Lunge test

Objectives To determine whether back foot (BF) position influences dorsiflexion range of motion (DFROM) during three different positions of the weight bearing lunge test (WBLT). Design Randomised, repeated measures design Setting Sports clubs Participants 52 athletes participating in cutting and pivoting sports Main Outcome measures DFROM was obtained using a WBLT in three different BF positions: BF heel in full contact with the floor, BF heel raised off the floor and BF was non weight bearing (NWB). All measurements were obtained using three methods: inclinometer at the tibial tuberosity, toe to wall distance and goniometer angle from the lateral malleolus to the fibula head. Differences between testing positions were determined using a repeated measures one-way ANOVA and reliability analysis was performed using the Intraclass Correlation Coefficient (ICC). Results DFROM was statistically significantly different for all three positions of the WBLT for each measurement technique (P<.001). These results were associated with large effect sizes for all BF positions and measurement techniques. Reliability ICC values were excellent for all measurements (ICC 0.94-0.99). Conclusions Results show that DFROM differs depending upon the position of the BF during the WBLT. Further research is needed to establish the reproducibility of these three BF positions due to the variability observed

Knee Joint Strength Ratios and Effects of Hip Position in Rugby Players

Measures of knee joint function, although useful in predicting injury, can be misleading because hip position in traditional seated isokinetic tests is dissimilar to when injuries occur. This study aimed to determine the differences between seated and supine peak torques and strength ratios and examine the interaction of position with joint velocity. This was a cross-sectional, repeated measures study. Isokinetic knee extensor and flexor concentric and eccentric peak torque was measured seated and supine (10 degrees hip flexion) at 1.04 and 3.14 rad.s(-1) in 11 Rugby players. Repeated measures analysis of variance and paired t-tests were used to analyze peak torques and strength ratios. Bonferroni post hoc, limits of agreement, and Pearson's correlation were applied. Seated peak torque was typically greater than that for supine for muscle actions and velocities. The values ranged from 109 +/- 18 N.m (mean +/- sigma) for supine hamstring concentric peak torque at 1.04 rad.s(-1) to 330 +/- 71 for seated quadriceps eccentric peak torque at 1.04 rad.s(-1). There was a significant position x muscle action interaction; eccentric peak torque was reduced more than concentric in the supine position. Knee joint strength ratios ranged from 0.47 +/- 0.06 to 0.86 +/- 0.23, with a significant difference in means between supine and seated positions for functional ratio at 3.14 rad.s(-1) observed; for seated it was 0.86 +/- 0.23; and for supine, it was 0.68 +/- 0.15 (p < 0.05). Limits of agreement for traditional and functional ratios ranged from 1.09 x/divided by 1.37 to 1.13 x/divided by 1.51. We conclude that hip angle affects isokinetic peak torques and knee joint strength ratios. Therefore, the hip angle should be nearer 10 degrees when measuring knee joint function because this is more ecologically valid. Using similar protocols, sports practitioners can screen for injury and affect training to minimize injury

The cardiorespiratory, anthropometric and performance characteristics of an international/national touring ballet company

The cardiorespiratory, anthropometric, and performance characteristics of an international/national touring ballet company. J. Strength Cond. Res. 21(2):389-393. - This study examined the cardiorespiratory and anthropometric indices of professional classical ballet dancers in relation to company seniority, gender, and supplemental training. Forty-nine participants from an international touring company carried out a peak VO2 test and vertical jump test. Anthropometric measurements and supplemental training activities were also recorded for each participant. Statistical analyses showed significant differences between gender and dancer seniority levels. Gender differences were seen for jump height (M = 52.7 +/- 7.12 cm; F = 37.6 +/- 5.32 cm) and peak VO2 (M = 49.32 +/- 3.72 ml center dot kg(-l)center dot min(-1); F = 43.3 +/- 5.16 ml center dot kg(-1) center dot min(-1)). Differences were also seen between dancer levels for peak VO2 (artist = 46.47 +/- 4.67 ml center dot kg(-1)center dot min(-1); first artist = 42.72 +/- 5.81 ml center dot kg(-1)center dot min(-1); soloist = 43.38 +/- 7.14 ml center dot kg(-1)center dot min(-1); principal = 49.04 +/- 3.63 ml center dot kg(-1)center dot min(-1)) and jump height (artist = 42.0 +/- 9.11 cm; first artist = 50.33 +/- 11.65 cm; soloist = 45.6 +/- 9.78 cm; principal = 44.67 +/- 9.53 cm). Pairwise post hoc comparisons showed that corps and principals had significantly greater relative peak VO2 than first artists and soloists (p < 0.05), while soloists and first artists had significantly greater jump heights compared to principals and corps (p < 0.05). Analysis of covariance modeling indicated that the self-reported mode of supplemental training had no association with relative peak VO2 or the percentage at which ventilatory threshold occurred. The present study has provided further insight into the cardiorespiratory profiles of classical ballet dancers, where soloists have significantly greater power capacities compared to principals and corps, who in turn had significantly greater aerobic power. These data can help guide strength and conditioning intervention strategies that need to take into account the nuances of the different seniority levels within a dance company