Mechanics of standing and crouching sprint starts

The aim of this study was to compare the kinetic and kinematic parameters of standing and crouch sprint starts. Parallel starts (PS), false starts (FS), jump starts (JS) and crouch starts (3PS) were compared. Eighteen participants performed each start on a force plate and six infrared cameras captured the three-dimensional coordinates of 36 retro-reflective markers. Performance during a five-metre sprint (T_5m) was analysed. Duration of the start phase (T_start), mean values of horizontal and total ground reaction forces (GRFs) (F_{x_mean} and F_{tot_mean}), ratio of force (RF), maximal power (P_max) and kinetic energy (KE) of each limb were calculated. Significant differences were found for T_5m, T_start, KE, P_max, F_{x_mean}, F_{tot_mean} and RF for the crouch start compared to the other starts (P ≤ 0.05). Significant correlations were found between T_5m and T_start (r = 0.59; P ≤ 0.001), and T_5m and P_max, F_{x_mean} and RF (?0.73 ≤ r ≤ ?0.61; P ≤ 0.001). To conclude, the crouch start resulted in the best performance because T_start was shorter, producing greater P_max, F_{x_mean} with a more forward orientation of the resultant force. Greater KE of the trunk in each start condition demonstrated the role of the trunk in generating forward translation of the centre of mass (CM).     

Upper limb and trunk muscle activity patterns during seated and standing cycling

The objective of this study is to clarify the functional roles of upper limb muscles during standing and seated cycling when power output increases. We investigated the activity of seven upper limb and trunk muscles using surface electromyography (EMG). Power outputs ranged from ~100–700 W with a pedalling frequency of 90 revolution per minute. Three-dimensional handle and pedal forces were simultaneously recorded. Using non-negative matrix factorisation, we extracted muscle synergies and we analysed the integrated EMG and EMG temporal patterns. Most of the muscles showed tonic activity that became more phasic as power output increased. Three muscle synergies were identified, associated with (i) torso stabilisation, (ii) compensation/generation of trunk accelerations and (iii) upper body weight support. Synergies were similar for seated and standing positions (Pearson’s r > 0.7), but synergy #2 (biceps brachii, deltoidus and brachioradialis) was shifted forward during the cycle (~7% of cycle). The activity levels of synergy #1 (latissimus dorsi and erector spinae) and synergy #2 increased markedly above ~500 W (i.e., ~+40–70% and +130–190%) and during periods corresponding to ipsi- and contralateral downstrokes, respectively. Our study results suggest that the upper limb and trunk muscles may play important roles in cycling when high power outputs are required.     

Relationships between cohesion, collective efficacy and performance in professional basketball teams: an examination of mediating effects

The main aim of this study was to examine mediating effects in the relationships between cohesion, collective efficacy and performance in professional basketball teams. A secondary aim was to examine the correlates of collective efficacy in a professional sport. A total of 154 French and foreign professional players completed French or English versions of questionnaires about cohesion and collective efficacy. Two composite measures of individual performance were used (pre- and post-performance). Individual-level analyses were performed. Regression analyses supported two mediating relationships with collective efficacy as a mediator of the pre-performance - Group integration-task relationship, and Group integration-task as a mediator of the pre-performance - collective efficacy relationship. Statistical analyses indicated that neither Group integration-task nor collective efficacy was a better mediator in the relationship between pre-performance and the other group variables. Results also revealed positive relationships between three dimensions of cohesion (i.e. Individual attractions to the group-task, Group integration-task, Group integration-social) and collective efficacy. These findings suggest that in professional basketball teams, staff members should look after athletes who perform at a lower or below their usual level because their performances might lead them into a downward cohesion - collective efficacy spiral. Staff members should also develop a high quality of group functioning, both on and off the basketball court, given its relationship with collective efficacy.     

‘Alternative’ universities revisited: A study of the distinctiveness of universities established in the spirit of 1968

Abstract

In the late 60s and early 70s, several universities were set up in various European countries with the intention of providing an alternative to established institutions of higher education. The new universities were expected, amongst other things, to experiment with new forms of leadership and management internally, give teaching and learning higher priority, and to be regional relevant institutions for the area in which they were located. The paper analyses to what extent three such university establishments: Aalborg University in Denmark, Maastricht University in the Netherlands and Troms?University in Norway have managed to maintain and develop their alternative profile during the last thirty years. The study suggests that even though the universities in some areas have adapted to environmental pressure, they have managed to keep their profile as innovative and alternative.     

The importance of being elastic: Deflection of a badminton racket during a stroke

Abstract

The deflection profiles of a badminton racket during strokes performed by elite and world-class badminton players were recorded by strain gauges and subsequently analysed to determine the role of shaft stiffness in racket performance. Deflection behaviour was consistent in all strokes across all players, suggesting a controlled use of racket elasticity. In addition, all impacts occurred within 100 ms of each other, a duration in which deflection velocity provides an increase in racket velocity, indicating that the players were able to use racket elasticity to their advantage. Since deflection behaviour is a product of the racket–player interaction, further work is required to determine the effects of different racket properties and player techniques on the elastic response of rackets during strokes.     

Electromyographic Patterns During Level and Inclined Treadmill Running and Their Relationship to Step Cycle Measures

Abstract

Eight highly skilled male distance runners were filmed while running on level and inclined treadmills. During the filming sequence, EMG measurements were collected on vastus medialis (VM) and semimembranosus (SM) of the right thigh. The initiation and duration of electrical activity of the two muscles was extracted from the recordings relative to the step cycle events. Analysis of covariance for repeated measures was utilized as a statistical treatment to examine the effect of treadmill grade (– 10%, 0%, and + 10%) upon step cycle and EMG data. Results indicate that treadmill grade had a significant effect on the relative duration of both stance and swing phases of the running step cycle and total step cycle duration. Total step cycle time and relative swing phase duration decreased as the treadmill grade was changed from a negative grade to a zero grade to a positive grade while the duration of the stance phase increased. EMG measures indicated decreases in relative duration of SM activity during the stance phase progressing from negative grade to zero grade to positive grade while an increase in SM activity was noted during the swing phase. VM activity during stance was longest in negative grade running, decreased in level grade running, and increased again in positive grade running.     

Effects of Training on the Estimation of Muscular Moment in Submaximal Exercise

Abstract

The purpose of this study was to observe the effects of a submaximal isometric training program on estimation capacity at 25, 50, and 75% of maximal contraction in isometric action and at two angular velocities. The second purpose was to study the variability of isometric action. To achieve these purposes, participants carried out an isokinetic extension movement of the dominant lower limb during six test sessions and nine training sessions. Following the training program, estimation capacity in the different actions did not improve. However, an improvement in performance was observed with a reduction in the variability of submaximal isometric actions. The proprioceptors activated in isometric action seemed to adapt to the training program itself, which would promote better adaptation by a greater solicitation of internal feedback.     

The Relative Age Effect in Elite Sport

The relative age effect (RAE) is considered a common phenomenon in elite sport. However, it has not been examined systematically in previous research, and the mechanisms likely to generate or to limit such an effect are little understood. This paper investigates the prevalence of the RAE in French professional championship-level players, taking into account the potential influence of gender. Among all investigated sports, no statistically significant RAE was found, except for male ice hockey. For male handball and rugby union a trend was detected, but the RAE did not appear statistically significant. In line with previous studies, no significant RAEs were found in female elite sports. The results are discussed with regard to the potential mechanisms underlying RAE.