HAMSTRINGS COACTIVATION IN TRAINED LONG JUMPERS AND UNTRAINED INDIVIDUALS DURING DROP JUMPING

The purpose of this study was to examine the EMG activity patterns of the hamstrings during drop jumping from different heights in trained longer jumpers and controls. A group of trained long jumpers and a group of untrained subjects performed maximal drop jumps from 20cm, 40cm and 60 cm on a force platform. The surface EMG activity of the hamstrings was recorded using bipolar electrodes. The ground reaction forces (GRF) and 3-D kinematic data were also recorded. Two-way analysis of variance tests indicated non-significant differences in hamstring EMG amplitude between trained and untrained athletes. However, the long jumpers had significantly higher vertical GRF values and some kinematic differences compared to untrained individuals. The absence of higher hamstrings activity in the long jumpers may have been a contributing factor in their higher performance compared to controls. However, the same result indicates that this increased performance may be accompanied by a possible increased risk of knee joint instability

The Effect of Body Mass on the Shoe-Athlete Interaction

Long-distance running is known to induce joint overloading and elevate cytokine levels, which are the hallmarks for a variety of running-related injuries. To address this, footwear systems incorporate cushioning midsoles to mitigate injurious mechanical loading. The aim of this study was to evaluate the effect of athlete body mass on the cushioning capacity of technical footwear. An artificial heel was prototyped to fit the impact pattern of a heel-strike runner and used to measure shock attenuation by an automated drop test. Impact mass and velocity were modulated to simulate runners of various body mass and speeds. The investigation provided refined insight on running-induced impact transmission to the human body. The examined midsole system was optimized around anthropometric data corresponding to an average (normal) body mass. The results suggest that although modern footwear is capable of attenuating the shock waves occurring during foot strike, improper shoe selection could expose an athlete to high levels of peak stress that could provoke an abnormal cartilage response. The selection of a weight-specific cushioning system could provide optimum protection and could thus prolong the duration of physical exercise beneficial to maintaining a simulated immune system

Variable, but not free-weight, resistance back squat exercise potentiates jump performance following a comprehensive task-specific warm-up

Studies examining acute, high-speed movement performance enhancement following intense muscular contractions (frequently called "post-activation potentiation"; PAP) often impose a limited warm-up, compromizing external validity. In the present study, the effects on countermovement vertical jump (CMJ) performance of back squat exercises performed with or without elastic bands during warm-up were compared. After familiarization, fifteen active men visited the laboratory on two occasions under randomized, counterbalanced experimental squat warm-up conditions: (a) free-weight resistance (FWR) and (b) variable resistance (VR). After completing a comprehensive task-specific warm-up, three maximal CMJs were performed followed by three back squat repetitions completed at 85% of 1-RM using either FWR or VR Three CMJs were then performed 30 seconds, 4 minutes, 8 minutes, and 12 minutes later. During CMJ trials, hip, knee, and ankle joint kinematics, ground reaction force data and vastus medialis, vastus lateralis, and gluteus maximus electromyograms (EMG) were recorded simultaneously using 3D motion analysis, force platform, and EMG techniques, respectively. No change in any variable occurred after FWR (P > 0.05). Significant increases (P < 0.05) were detected at all time points following VR in CMJ height (5.3%-6.5%), peak power (4.4%-5.9%), rate of force development (12.9%-19.1%), peak concentric knee angular velocity (3.1%-4.1%), and mean concentric vastus lateralis EMG activity (27.5%-33.4%). The lack of effect of the free-weight conditioning contractions suggests that the comprehensive task-specific warm-up routine mitigated any further performance augmentation. However, the improved CMJ performance following the use of elastic bands is indicative that specific alterations in force-time properties of warm-up exercises may further improve performance

Performance-based index in sprinting

Le ratio travail dynamique lors d'un saut plyométrique sur travail statique lors d'une extension de la jambe de 130-170 degrés constitue un indice utile pour le contrôle de la préparation à des épreuves explosives et particulièrement pour la course de vitesse

An adaptive model of achilles tendon mechanical properties during adolescence: Effect of sex

Background. This longitudinal study aimed to quantify the relative effects of body mass, peak muscle force, maturation and sex on Achilles tendon (AT) mechanical properties and to examine the external factors that trigger mechanical changes, or intrinsic tendon adaptations during adolescence. Methods. We measured AT mechanical properties and dimensions during pre-pubertal and adolescent growth in 41 participants (20 boys and 21 girls). Participants were tested over 18 months; longitudinal changes were examined through linear mixedmodelling. Results. Sex and maturation were found to be the major factors influencing AT mechanical changes. Their effects were largely exerted through increases in muscle force, which imposed greater stress on AT and strongly predicted changes in stiffness and Young’s modulus in boys and girls, while strain was consistent. Conclusions. The more rapid increase in stiffness before the age of peak height velocity in boys was associated with an increase in force at that time, which may have evoked the molecular signaling required for adaptations to internal tendon structure leading a different adaptive response between sexes. The present data are suggestive of an adaptive model in which increases in muscle force production impose greater mechanical loading, on the tendon to trigger increases in stiffness as children mature through adolescence

The four-year functional result after a displaced subcapital hip fracture treated with three different surgical options

According to the literature, hip function after hip fracture is affected by the type of surgery. Our aim was to determine the correlation between surgical treatment of hip fracture and postoperative function in the elderly. Inclusion criteria were displaced hip fracture and age over 70 years. One hundred and twenty-nine participants were randomly divided into three groups according to the type of the surgical operation they underwent (hemi-arthroplasty [Merete, Berlin, Germany], total arthroplasty [Plus; De Puy, Warsaw, IN, USA] and internal fixation [Richards plate screw; Smith & Nephew, Memphis, TN, USA]). The function of the patients was estimated using the following parameters: the Barthel Index and Harris Hip Score, the range of passive hip motion, the gait speed of individuals, after 1 and 4 years of follow-up. The Barthel Index scores after 4 years of follow-up were 85.3, 82.6, 80.1 after total arthroplasty, hemi-arthroplasty and internal fixation respectively. Similarly, the Harris Hip Scores after 4 years of follow-up were 83.7, 79.5 and 73.6. The range of passive hip motion in the three groups of patients did not differ significantly (p > 0.05). Also, patients of the total arthroplasty and hemi-arthroplasty groups walked faster than the patients of the internal fixation group 4 years after discharge (p < 0.05). In conclusion, we believe that total hip arthroplasty is the treatment of choice for displaced subcapital hip fractures in patients over 70 years old

Lower limb mechanical properties : determining factors and implications for performance

Limb stiffness or musculotendinous stiffness (MTS) has previously been examined in relation to performance and characterized using a number of different methods. However, the fact that MTS shows only low to moderate correlations to performances may indicate a lack of understanding of this parameter. In addition to this, variation is seen between studies examining the same factors. To date, our understanding of MTS and its components are not complete and thus it is unclear which characteristic value represents the ideal index of stiffness as it relates to performance. Moreover, it is uncertain how MTS stiffness as a functional measure relates to performance, and also if there is an optimal amount of MTS stiffness for specific functions or tasks. The knowledge of the interplay of MTU stiffness as it relates to performance and injury risk is also poorly understood in that there is likely a disparity between levels of stiffness required to optimize performance and those required to minimize injury risk. The aim of this article is to review the literature as it describes the components of MTS and to discuss these in terms of their relationship to functional performance; consider adaptations of the MTU with training along with associated performance changes; highlight and discuss how stiffness may affect loading of the soft and bony tissues in terms of the MTU components and gender, with respect to risk of injury; discuss the apparent differences in the literature regarding associations of the various forms of stiffness index to function; suggest recommendations for training in light of adaptation of the muscle and tendon and injury risk in context of gender; and, finally, to highlight potential limitations of current methodologies and suggest further work to gain insight into the mechanisms of stiffness. It is hoped that by suggesting future work, a more detailed and comprehensive understanding of MTS will be gained, thus enabling appropriate interventions to optimally modify this parameter for specific requirements