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° 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 ± σ) 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 × 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 ×/÷ 1.37 to 1.13 ×/÷ 1.51. We conclude that hip angle affects isokinetic peak torques and knee joint strength ratios. Therefore, the hip angle should be nearer 10° 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.

Age- and sex-associated differences in isokinetic knee muscle endurance between young children and adults.

The purpose of this study was to examine the age- and sex-associated differences of repeated isokinetic knee extension and flexion. Fifty one participants, 30 young children (16 boys and 14 girls; aged 11 and 12 years) and 21 adults (9 males and 12 females; aged 18-35 years), agreed to participate in the study. Isokinetic concentric peak knee extension (PET) and flexion (PFT) torque were measured using a calibrated Biodex System 3. Participants performed 4 concentric extension-flexion cycles with maximum effort; after a 2 min rest, 50 continuous concentric cycles were performed at 1.56 rad.s-1. Total work of the extensors (WKEX) and flexors (WKFL) for the complete 50 repetitions was recorded. Average peak torque and average work for the first and last 3 repetitions were calculated to represent the percentage decline in torque and work. There were no significant differences between groups in the peak torque generated during the pretrial and endurance task, suggesting that participants gave a maximal effort at the start of the endurance task. There was a significant interaction effect in the total work done for both extensors and flexors, with adult males producing the greatest amount of work (6622 and 3444 J, respectively). When total work was divided by body mass, there were no significant sex effects, only main effects for group. The percentage decline for PET (40% vs. 60%), PFT (50% vs. 65%), WKET (43% vs. 61%), and WKFL (60% vs. 69%) demonstrated significant main effects for group, with greater fatigue in adults. We found no significant sex effect for fatigue. This study concludes that females do not resist fatigue from repeated isokinetic muscle actions to a greater extent than males, and that the greater fatigue in adults than in children is probably a product of greater initial torque production and work performed.

[Evaluation of knee peak torque in athletic and sedentary children]. / Atletik ve sedanter çocuklarda diz zirve torkunun degerlendirilmesi.

OBJECTIVES: We examined the influence of sex, level of activity, and pubertal status on knee extension (Ext) and flexion (Fl) peak torque (PT) in children using an allometric modeling approach. METHODS: A total of 140 students (67 males, 73 females) aged 12/13 years were enrolled from a Hong Kong junior high school, whose curricula were based on physical education (n=69) or arts (n=71). Isokinetic concentric Ext and Fl PT of the dominant leg was assessed at 1.04 rad/sec using a Cybex II+ dynamometer and body mass, stature, and pubertal stage were measured. A repeated-measures ANOVA test was performed on absolute PT data with muscle action (Ext and Fl) as a within-subject factor and between-subject factors including sex, group, and pubertal stage. To assess the effects on body size-adjusted PT, linear ANCOVA and log-linear ANCOVA techniques were used with body mass and stature taken as covariates. RESULTS: Peak torque was significantly greater in boys compared to girls, and in the physical education group compared to the arts group. When PT was adjusted for differences in body size, there was a greater difference in PT between girls in the two groups compared to boys, and there was a significant effect of pubertal stage. Allometric analysis showed that PT was influenced more by stature than body mass, and PT increased at a greater rate than body size (both p<0.01). CONCLUSION: There may be a need for a physical activity intervention in sedentary 12/13 year old girls. Peak torque appears to increase disproportionately to body size. This may result from a greater increase in leg muscle mass relative to body mass.

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

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 Vo(2) 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 Vo(2) (M = 49.32 +/- 3.72 ml.kg(-1).min(-1); F = 43.3 +/- 5.16 ml.kg(-1).min(-1)). Differences were also seen between dancer levels for peak Vo(2) (artist = 46.47 +/- 4.67 ml.kg(-1).min(-1); first artist = 42.72 +/- 5.81 ml.kg(-1).min(-1); soloist = 43.38 +/- 7.14 ml.kg(-1).min(-1); principal = 49.04 +/- 3.63 ml.kg(-1).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 Vo(2) 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 Vo(2) 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.