Linear flexural natural frequencies and stability analysis of spinning Rayleigh beams: application to clamped-clamped beams.

In the present paper 3D bending linear free vibrations of spinning Rayleigh beams are investigated. Four linear models, that differ in the linearization process, are studied. A focus on analytical computation of natural frequencies for a broad range of boundary conditions is highlighted. Then, the conditions of occurrence of divergence and flutter instabilities are determined. Finally, a case study consisting of a clamped-clamped Rayleigh beam is studied. It is found that the free vibrations destabilization process depends on the used linearization approach

Linear flexural natural frequencies and stability analysis of spinning Rayleigh beams: application to clamped-clamped beams.

In the present paper 3D bending linear free vibrations of spinning Rayleigh beams are investigated. Four linear models, that differ in the linearization process, are studied. A focus on analytical computation of natural frequencies for a broad range of boundary conditions is highlighted. Then, the conditions of occurrence of divergence and flutter instabilities are determined. Finally, a case study consisting of a clamped-clamped Rayleigh beam is studied. It is found that the free vibrations destabilization process depends on the used linearization approach

Acute Effect of Four Stretching Protocols on Change of Direction in U-17 Male Soccer Players.

International audienceBackground: The ability to rapidly change direction while sprinting is a desirable athletic skill in soccer. Enhancing change of direction (COD) performance depends almost exclusively on specific training, with stretching traditionally considered one such intervention. However, the comparative impact of diverse stretching methods on COD in soccer players remains an area of interest. Therefore, this study aimed to compare the effects of different stretching methods on COD ability in soccer players. Methods: Twelve male soccer players playing in the national championship football division II (age: 16.3 ± 0.3 years, height: 1.81 ± 0.10 m, body mass: 67.7 ± 7.2 kg) were tested for COD performance (i.e., Illinois agility test) after (1) control condition (20 min general warm-up without stretching), (2) static stretching, (3) dynamic stretching, (4) combined static-dynamic stretching, and (5) combined dynamic-static stretching. The duration of stretching intervention was approximately 6 min for static and dynamic stretching and 12 min for both the combined stretching conditions. The experimental sessions were separated by 72 h. Results: COD improved after dynamic stretching when compared to any other condition (p: 0.03–0.002; ηp2: 0.56–0.73), except for the control condition (p = 0.146; ηp2 = 0.18). In contrast, static stretching induced a detrimental effect on COD when compared only to the dynamic stretching condition (p < 0.01; ES = 1.35). Conclusion: Dynamic stretching exercises used by male soccer players in the warm-up improved COD. Other forms of stretching exercises, particularly static stretching, negatively impacted the COD performance. Therefore, coaches can consider integrating dynamic stretching protocols tailored to the athletes’ specific needs. Moreover, extending the investigation to encompass a wider range of athletes, including different age groups and genders, would enhance the applicability and generalization of the findings

Lower limbs micro-loading acutely attenuates repeated change-of-direction performance in male youth during small-sided soccer games

Abstract Background Soccer players often wear light-weighted wearable resistance (WR) attached to different body parts during the warm-up period with the aim to improve measures of physical fitness. However, the effect of WR on physical performance is unknown. This study evaluated the effects of WR with different micro-loadings on repeated change-of-direction (RCoD) performance while executing small-sided soccer games (SSG). Methods Twenty male soccer players aged 16.0 ± 1.5 years (body mass 74.0 ± 7.4 kg, body-height 175.0 ± 10.0 cm) volunteered to participate in this study. Following a within-subject study design, players performed four specific warm-up protocols in randomized order with a rest of 72 h between protocols: (1) WR micro-loadings with 0.1% of body mass (WR0.1); (2) WR micro-loadings with 0.2% of body mass (WR0.2); (3) WR micro-loadings with 0.3% of body mass (WR0.3); (4) no WR (control = CONT). After the warm-up protocols, players performed 2 sets of 20-min SSG. The RCoD was collected at the 8th min of SSG (SSG 1–8 min), the 15th min of SSG1 (SSG1-15 min), and at the 15th min of SSG2 (SSG2-15 min). Outcomes included mean and total RCoD indices (i.e., mean time and total time for each condition). Results Based on the outcomes of a two-way repeated measures analysis of variance (ANOVA), WR0.1 and WR0.2 were more effective than control in dampening the decrease of RCoD’s total time during SSG1-8 min, and SSG2-15 min (small ES: 0.24–0.35; p < 0.05). However, no significant differences were observed between WR0.3 and control. In addition, WR0.1 and WR0.2 significantly affected the decreases in RCoD’s mean best time during SSG1 and SSG2 which was observed in the unloaded condition (CONT) and consequently displayed a lower rate of RCoD performance decrease. Conclusion This study reports that wearing lower extremity WRs with micro-loads of 0.1% or 0.2% of body mass attenuates physical fatigue indicated in attenuated RCoD performance while executing SSG