Female recreational athletes demonstrate different knee biomechanics from male counterparts during jumping rope and turning activities

Background

A variety of athletic exercises are performed in sports training or rehabilitation after knee injuries. However, it remains unclear whether males and females exhibit similar joint loading during the various athletic motions. The purpose of this study was to identify gender differences in knee biomechanics during the athletic motions.

Methods

Three-dimensional knee kinematics and kinetics were investigated in 20 recreational athletes (10 males and 10 females) while jumping rope, backward running, side running, side-to-side running, side-to-forward running, inside turning, and outside turning. The strengths of the quadriceps and hamstring muscles, the knee joint force, the knee joint angle, and the knee joint moment were compared between males and females using one-tailed t tests.

Results

Peak knee anterior force was greater in female recreational athletes than in their male counterparts during jumping rope, side-to-forward running, inside turning, and outside turning. Female subjects displayed greater peak knee abduction angles and greater peak knee flexion moments while jumping rope compared to their male counterparts. There were no significant differences between the sexes in knee kinematics and kinetics in the frontal and transverse planes during running and turning motions.

Conclusions

Female recreational athletes exhibited significantly different knee biomechanics compared with male counterparts during jumping rope and turning motions.     

Detraining-Related Changes in Left Ventricular Wall Thickness and Longitudinal Strain in a Young Athlete Likely to Have Hypertrophic Cardiomyopathy

One of the diagnostic criteria in order to differentiate between physiological and pathological left ventricular hypertrophy is the wall thickness reduction after at least 3-month detraining period, which is considered a marker of the athlete’s heart. This report describes detraining-related regression of LV hypertrophy and improvement in myocardial deformation in a junior athlete likely to have hypertrophic cardiomyopathy.

Key points

• Hypertrophic cardiomyopathy in adolescent athletes can be discovered by 12-lead ECG
• Physical training is an important trigger for the clinical presentation of hypertrophic cardiomyopathy
• Reverse LV remodeling (wall thickness reduction) with detraining is a common echocardiographic finding in athletes with physiological hypertrophy
• This report demonstrates that reverse remodeling can also be found in adolescent athletes likely to have hypertrophic cardiomyopathy

Key words: Athlete’s heart, detraining, echocardiography, hypertrophic cardiomyopathy, left ventricular hypertrophy, myocardial function, strain echocardiography.     

The Effect of Gender and Fatigue on the Biomechanics of Bilateral Landings from a Jump: Peak Values

Female athletes are substantially more susceptible than males to suffer acute non-contact anterior cruciate ligament injury. A limited number of studies have identified possible biomechanical risk factors that differ between genders. The effect of fatigue on the biomechanics of landing has also been inadequately investigated. The objective of the study was to examine the effect of gender and fatigue on peak values of biomechanical variables during landing from a jump. Thirty-two recreational athletes performed bilateral drop jump landings from a 40 cm platform. Kinetic, kinematic and electromyographic data were collected before and after a functional fatigue protocol. Females landed with 9° greater peak knee valgus (p = 0.001) and 140% greater maximum vertical ground reaction forces (p = 0.003) normalized to body weight compared to males. Fatigue increased peak foot abduction by 1.7° (p = 0.042), peak rectus femoris activity by 27% (p = 0.018), and peak vertical ground reaction force (p = 0.038) by 20%. The results of the study suggest that landing with increased peak knee valgus and vertical ground reaction force may contribute to increased risk for knee injury in females. Fatigue caused significant but small changes on some biomechanical variables. Anterior cruciate ligament injury prevention programs should focus on implementing strategies to effectively teach females to control knee valgus and ground reaction force.

Key points

• Female athletes landed with increased knee valgus and VGRF which may predispose them to ACL injury.
• Fatigue elicited a similar response in male and female athletes.
• The effectiveness of sports injury prevention programs may improve by focusing on teaching females to land softer and with less knee valgus.

Key words: Anterior cruciate ligament injury, injury prevention, knee injury, sports biomechanics     

Acute Effects of Foot Rotation in Healthy Adults during Running on Knee Moments and Lateral-Medial Shear Force

As runners age, the likelihood of developing osteoarthritis (OA) significantly increases as 10% of people 55+ have symptomatic knee OA while 70% of people 65+ have radiographic signs of knee OA. The lateral-medial shear force (LMF) and knee adduction moment (KAM) during gait have been associated with cartilage loading which can lead to OA. Foot rotation during gait has been shown to alter the LMF and KAM, however it has not been investigated in running. The purpose of this study was to investigate changes in the KAM and LMF with foot rotation during running. Twenty participants volunteered and performed five running trials in three randomized conditions (normal foot position [NORM], external rotation [EXT], and internal rotation [INT]) at a running speed of 3.35m·s^-1 on a 20 meter runway. Kinematic and kinetic data were gathered using a 9-camera motion capture system and a force plate, respectively. Repeated measures ANOVAs determined differences between conditions. The KAM and LMF were lower in both EXT and INT conditions compared to the NORM, but there were no differences between EXT and INT conditions. The decreases in KAM and LMF in the EXT condition were expected and concur with past research in other activities. The reductions in the INT condition were unexpected and contradict the literature. This may indicate that participants are making mechanical compensations at other joints to reduce the KAM and LMF in this abnormal internal foot rotation condition.

Key points

• External rotation of the foot during running reduced the loads on the medial compartment of the knee
• Internal rotation of the foot also reduced the medial loads, but is a more unnatural intervention
• External and internal rotation reduced the shear forces on the knee, which may help slow the degeneration of knee joint cartilage

Key words: Osteoarthritis, cartilage, biomechanics, gait     

A Kinematic Analysis of the Jumping Front-Leg Axe-Kick in Taekwondo

The jumping front-leg axe-kick is a valid attacking and counterattacking technique in Taekwondo competition (Streif, 1993). Yet, the existing literature on this technique is sparse (Kloiber et al., 2009). Therefore, the goal of this study was to determine parameters contributing significantly to maximum linear speed of the foot at impact. Parameters are timing of segment and joint angular velocity characteristics and segment lengths of the kicking leg. Moreover, we were interested in the prevalence of proximal-to-distal-sequencing. Three-dimensional kinematics of the kicks of 22 male Taekwondo-athletes (age: 23.3 ± 5.3 years) were recorded via a motion capturing system (Vicon Motion Systems Limited, Oxford, UK). The participants performed maximum effort kicks onto a rack-held kicking pad. Only the kick with the highest impact velocity was analysed, as it was assumed to represent the individual’s best performance. Significant Pearson correlations to impact velocity were found for pelvis tilt angular displacement (r = 0.468, p < 0.05) and for hip extension angular velocity (r = -0.446, p < 0.05) and for the timing of the minima of pelvis tilt velocity (r = -0.426, p < 0.05) and knee flexion velocity (r = -0.480, p < 0.05). Backward step linear regression analysis suggests a model consisting of three predictor variables: pelvis tilt angular displacement, hip flexion velocity at target contact and timing of pelvic tilt angular velocity minimum (adjusted R² = 0.524). Results of Chi-Squared tests show that neither for the leg-raising period (χ² = 2.909) of the technique, nor for the leg-lowering period a pattern of proximal-to-distal sequencing is prevalent (χ² = 0.727). From the results we conclude that the jumping front-leg axe-kick does not follow a proximal-to-distal pattern. Raising the leg early in the technique and apprehending the upper body to be leant back during the leg-lowering period seems to be beneficial for high impact velocity. Furthermore, striking by extending the hip rather than by flexing the knee could raise impact velocity.

Key points

• Angular velocity characteristics of the pelvis segment and the kicking leg’s hip and knee joint show no proximal-to-distal sequencing, neither for the leg-raising or leg-lowering period in a jumping front-leg axe-kick.
• Anthropometric parameters of taekwondo athlete’s do not influence their impact velocities.
• In order to raise the impact velocity in the jumping front-leg axe-kick an athlete should avoid tilting back with the torso. Instead, an upright position should be maintained.
• In the leg-lowering period, we suggest hitting the target by using hip extension with a rather straight knee, instead of flexing the knee.

Key words: Biomechanics, motion analysis, martial arts, timing, kicking velocity, joint angle     

The Role of Echocardiography in the Differential Diagnosis Between Training Induced Myocardial Hypertrophy Versus Cardiomyopathy

Increased myocardial mass due to regular high-volume intense exercise training (so-called athlete’s heart) is not uncommon. Although directly correlated with the extent of training loads, myocardial hypertrophy is not present exclusively in well-trained or elite athletes. Athlete’s heart is considered a physiological phenomenon with no known harmful consequences. However, extreme forms of myocardial hypertrophy due to endurance training resemble a structural heart disease such as hypertrophic cardiomyopathy, a condition associated with substantially increased risk of cardiac event. Endurance sports such as rowing and road cycling, rather than strength/power training, are most commonly associated with left ventricular (LV) wall thickness compatible with hypertrophic cardiomyopathy. The differentiation between physiological and maladaptive cardiac hypertrophy in athletes is undoubtedly important, since untreated cardiac abnormality often possesses a real threat of premature death due to heart failure during intense physical exertion. Luckily, the distinction from pathological hypertrophy is usually straightforward using transthoracic echocardiography, as endurance athletes, in addition to moderately and proportionally thickened LV walls with normal acoustic density, tend to possess increased LV diameter. In more uncertain cases, a detailed evaluation of myocardial function using (tissue) Doppler and contrast echocardiography is effective. When a doubt still remains, knowledge of an athlete’s working capacity may be useful in evaluating whether the insidious cardiac pathology is absent. In such cases cardiopulmonary exercise testing typically resolves the dilemma: indices of aerobic capacity are markedly higher in healthy endurance athletes compared to patients. Other characteristics such as a decrease of LV mass due to training cessation are also discussed in the article.

Key points

• Transthoracic echocardiography is still the most common relevant differentiation technique applied to distinguish athlete’s heart from the cardiomyopathy.
• Conventional echocardiographic criteria such as left ventricular chamber size and diastolic function parameters are to be regarded first when making differential diagnosis between substantially increased wall thickness in athlete’s heart (i.e. physiological adaptation) versus a disease (usually hypertrophic cardiomyopathy).
• When conventional echocardiographic parameters fail to diagnose the nature of myocardial hypertrophy, other differentiation criteria such as aerobic fitness, cardiac performance in response to physical exertion, and changes in echocardiographic parameters due to detraining, must be taken into consideration.
• Tissue Doppler, contrast and three-dimensional imaging are state-of-the-art echocardiographic techniques which have recently appeared in the differential diagnostics.

Key words: Left ventricle, physical exercises, physiological adaptation     

Effect of Half-Marathon Running on Arterial Stiffness and Blood Biomarkers in High-Level and Recreational Male Athletes

There is no clear understanding about the effect of intensive physical load on arterial stiffness and related biomarkers. The aim of this study was to evaluate the effect of half-marathon running on arterial stiffness and blood biomarkers during post-competitive recovery period in competitive and recreational male athletes. Eleven high-level long-distance runners (27.1 ± 4.8 yrs) and seven recreational athletes (34.3 ± 6.1 yrs), who participated in a half-marathon run were examined. Blood biomarkers and arterial stiffness (SphygmoCor 7.1) were measured at baseline and at 18 to 22 hours after the competition. There were no statistically significant changes between the groups in augmentation index (AIx, )57@xIA or pulse wave velocities at carotid-femoral segment (cfPWV) during recovery period. Between-group comparison did not reveal significant differences in blood pressure and arterial stiffness values at baseline and during recovery period. The change of cfPWV (difference between cfPWV at baseline and cfPWV during post-competitive recovery period) was significantly dependent on race time and sports level of the athlete (high-level or recreational). A significant increase was found in hsCRP, creatine kinase and LDH activity during the post-race period in both groups. No significant changes were found in oxidative stress markers in the groups after the race except for higher diene conjugates level in recreational athletes in comparison with the high-level group during recovery period. Our study results showed that half-marathon competition did not cause any significant changes in arterial stiffness parameters during the recovery period. However, the change in cfPWV was independently associated with half-marathon race time and the athlete’s level of training revealing a mild increase of arterial stiffness in high-level athletes and athletes with a faster race time. Key points

• Half-marathon race did not cause significant changes in blood pressure and arterial stiffness parameters during post-competition recovery period in high-level and recreational athletes.
• The change of arterial stiffness after intensive half-marathon race depends on the training level of the athlete, revealing a mild increase of arterial stiffness in high-level athletes and athletes with a faster race time
• High-sensitivity CRP increased significantly during the recovery period in recreational and high-level athletes.
• Half-marathon running did not influence serum level of oxidative stress biomarkers except for higher diene conjugate concentration in recreational athletes as compared to high-level runners during recovery period.

Key words: Arterial compliance, elite athletes, physical load, oxidative stress, cardiovascular risk     

The Metabolic Demands of Kayaking: A Review

Flat-water kayaking is one of the best-known competitive canoeing disciplines in Australia and across the European countries. From a stationary start, paddlers are required to paddle their kayaks with maximal effort along the length of the competing distance. The ultimate criterion of kayak performance is the time taken to paddle a designated competition distance. In flat-water racing, events are contested over 500 and 1000 metres. To approximate the ultimate criterion over these distances, the velocity of the kayak should be measured. Furthermore, other factors that affect performance, such as force, power, technique and aerobic fitness, would all provide a valuable insight to the success of the kayak paddler. Specific research performed examining the physiological demands on kayak paddlers demonstrate high levels of both aerobic power and anaerobic capacity. It is the purpose if this review to present the published physiological data relating to men’s and women’s kayaking. With a number of recent publications, a need for an updated review is necessary. The present review summarises recent data on anthropometrics, physiological characteristics of successful and unsuccessful kayak athletes and methods of physiological testing. Due to the fact that more data have been reported for male competitors than for their female counterparts, the demands of kayaking on male athletes will be the main focus for this review. The review also suggests areas for future research into flatwater kayaking performance. Understanding the physiological requirements of kayaking can assist coaches and athletes in a number of ways. During competition or training, such information is helpful in the selection of appropriate protocols and metabolic indices to monitor an athlete’s performance improvements and assess an athlete’s suitability for a particular race distance. Furthermore, it may aid the coach in the development of more specific training programs for their athletes.

Key points

• Flat water kayaking is characterised by exceptional demands on upper body performance.
• When examining the oxygen consumption, it is notable that although a high value is attainable, they are not quite as high as other sporting events such as road cycling, rowing or running where lower body is dominant.
• Elite kayakers demonstrate superior aerobic and anaerobic quantities and have reported maximal oxygen consumptions of around 58 ml·kg^-1·min^-1 (4.7 L·min^-1) and lactate values of around 12 mM during laboratory and on water testing.

Key words: Kayak, ergometer, anthropometry, oxygen demand, aerobic power, lactate     

Paths to Expertise in Portuguese National Team Athletes

The purpose of this study was to identify the quantity and type of sporting activities undertaken by expert team sport athletes in the earlier stages of the long- term athlete development. Experts in roller-hockey (n = 19), volleyball (n = 14), soccer (n = 42) and basketball (n = 37) provided detailed information about the sporting activities they undertook throughout their careers. Results showed considerable variation between and within sports; however, generally, athletes began participating in sports between 6 and 10 years of age. The pattern of participation in specific and non-specific (team, individual and combat) sports for each stage of involvement demonstrated an increase in the number of activities participated in until early adolescence. Our results suggest that involvement in multiple sports during early stages of development is an alternative to early specialization and add further evidence of the complexity of skill acquisition in sport.

Key points

• Although most athletes began sport participation between 6 and 10 years of age, there was significant variation across groups suggesting considerable flexibility in the pathways to expertise.
• The path to expertise in volleyball was clearly distinct from the paths of basketball, soccer and roller-hockey.
• There is a considerable involvement in sports other than the athlete’s primary sport, suggesting early specialization is not required for these sports.
• The pattern of participation in specific and non-specific sports for each stage of involvement demonstrated an increase in the number of activities participated in until early adolescence.

Key words: performance, specialization, skill acquisition     

The Kinetics and Stiffness Characteristics of the Lower Extremity in Older Adults During Vertical Jumping

The purpose of this study was to examine the modulating effects of age on lower limb stiffness and net muscle joint activity degeneration when performing a functional activity involving SSC. Seven young males and seven older males were recruited as subjects for this study. A high-speed camera and a force plate were synchronized to collect the biomechanical parameters. The kinetic parameters were calculated with the inverse dynamics process. The stiffness of lower limbs was calculated with the spring-mass model. The Student’s t-test was used to test the differences of two age groups. Statistical significance was set at α = 0.05. The present research showed that the older group produced a smaller peak net muscle joint moment at hip and knee. There were no differences in leg stiffness, hip stiffness, and ankle stiffness between the two age groups. Knee stiffness was smaller in the older group. In elderly adults, reduced muscle strength in the lower limbs, especially in the hip and knee, and reduced stiffness of the knee, influence the basic functions of human life and increase the risk of injury. Differences in lower extremity kinetics and stiffness in elderly adults during SSC movement may have implications for new preventive measures.

Key points

• The present research showed that the older group reduced muscle strength in the lower limbs, especially in the hip and knee, and reduced stiffness of the knee, influence the basic functions of human life and increase the risk of injury.
• There were no differences in leg stiffness, hip stiffness, and ankle stiffness between the two age groups.
• Older subjects maintain hip angular stiffness by decreasing joint angles in order to protect the joint and to increase stability during movement.
• In elderly adults, insufficient angular stiffness of the knee joint may increase the risk of knee injury during a functional activity involving SSC.

Key words: Aging, biomechanics, inverse dynamic, spring-mass model     

Monitoring Athletes Through Self-Report: Factors Influencing Implementation

Monitoring athletic preparation facilitates the evaluation and adjustment of practices to optimize performance outcomes. Self-report measures such as questionnaires and diaries are suggested to be a simple and cost-effective approach to monitoring an athlete’s response to training, however their efficacy is dependent on how they are implemented and used. This study sought to identify the perceived factors influencing the implementation of athlete self-report measures (ASRM) in elite sport settings. Semi-structured interviews were conducted with athletes, coaches and sports science and medicine staff at a national sporting institute (n = 30). Interviewees represented 20 different sports programs and had varying experience with ASRM. Purported factors influencing the implementation of ASRM related to the measure itself (e.g., accessibility, timing of completion), and the social environment (e.g., buy-in, reinforcement). Social environmental factors included individual, inter-personal and organizational levels which is consistent with a social ecological framework. An adaptation of this framework was combined with the factors associated with the measure to illustrate the inter-relations and influence upon compliance, data accuracy and athletic outcomes. To improve implementation of ASRM and ultimately athletic outcomes, a multi-factorial and multi-level approach is needed.

Key points

• Effective implementation of a self-report measure for monitoring athletes requires a multi-factorial and multi-level approach which addresses the particular measure used and the surrounding social environment.
• A well-designed self-report measure should obtain quality data with minimal burden on athletes and staff.
• A supportive social environment involves buy-in and coordination of all parties, at both an individual and organization level.

Key words: Training diary, questionnaire, wellbeing, athletic injury, overtraining     

Number of Successive Cycles Necessary to Achieve Stability of Selected Ground Reaction Force Variables During Continuous Jumping

Because of inherent variability in all human cyclical movements, such as walking, running and jumping, data collected across a single cycle might be atypical and potentially unable to represent an individual’s generalized performance. The study described here was designed to determine the number of successive cycles due to continuous, repetitive countermovement jumping which a test subject should perform in a single experimental session to achieve stability of the mean of the corresponding continuously measured ground reaction force (GRF) variables. Seven vertical GRF variables (period of jumping cycle, duration of contact phase, peak force amplitude and its timing, average rate of force development, average rate of force relaxation and impulse) were extracted on the cycle-by-cycle basis from vertical jumping force time histories generated by twelve participants who were jumping in response to regular electronic metronome beats in the range 2-2.8 Hz. Stability of the selected GRF variables across successive jumping cycles was examined for three jumping rates (2, 2.4 and 2.8 Hz) using two statistical methods: intra-class correlation (ICC) analysis and segmental averaging technique (SAT). Results of the ICC analysis indicated that an average of four successive cycles (mean 4.5 ± 2.7 for 2 Hz; 3.9 ± 2.6 for 2.4 Hz; 3.3 ± 2.7 for 2.8 Hz) were necessary to achieve maximum ICC values. Except for jumping period, maximum ICC values took values from 0.592 to 0.991 and all were significantly (p ≤ 0.05) different from zero. Results of the SAT revealed that an average of ten successive cycles (mean 10.5 ± 3.5 for 2 Hz; 9.2 ± 3.8 for 2.4 Hz; 9.0 ± 3.9 for 2.8 Hz) were necessary to achieve stability of the selected parameters using criteria previously reported in the literature. Using 10 reference trials, the SAT required standard deviation criterion values of 0.49, 0.41 and 0.55 for 2 Hz, 2.4 Hz and 2.8 Hz jumping rates, respectively, in order to approximate the ICC results. The results of the study suggest that the ICC might be a less conservative but more objective method to evaluate stability of the data. Based on these considerations, it can be recommended that a force time history due to continuous, repetitive countermovement jumping should include minimum of four (the average from the ICC analysis) and possibly as many as nine successive jumping cycles (the upper limit of the ICC analysis) to establish stable mean values of the selected GRF data. This information is important for both experimental measurements and analytical studies of GRF signals due to continuous, repetitive countermovement jumping.

Key points

• The number of successive jumping cycles due to continuous, repetitive countermovement jumping obtained from a test subject during in a single testing session influences the stability of the corresponding ground reaction force variables on a cycle-by-cycle basis.
• Researchers have used different criteria and methods for determining stability of ground reaction force data for a variety of activities, making comparisons among studies and activities difficult.
• In the present study, segmental averaging technique indicated that an average of ten successive jumping cycles were necessary to achieve stability of the selected force parameters using criteria previously reported in the literature, while less conservative test-retest intra-class correlation (ICC) analysis showed that an average of four successive jumping cycles were necessary for stability.
• Based on these considerations, it can be recommended that a force time history due to continuous, repetitive countermovement jumping should include minimum of four (the average from the ICC analysis) and possibly as many as nine successive jumping cycles (the upper limit of the ICC analysis) to achieve stability of jumping force data on a cycle-by-cycle basis.
• Knowledge about the stability of jumping force data is an important to maximize reliability of their experimental and analytical characterizations.

Key words: Reliability, stability, variability, jumping, ground reaction forces     

The Effect of Patellar Taping on Some Landing Characteristics During Counter Movement Jumps in Healthy Subjects

The aim of the present study was to determine the effect of patellar taping (PT) on landing characteristics of the vertical ground reaction force (VGRF) and on flight time during a counter movement jump (CMJ). Eleven healthy male subjects (age: 31.1 ± 4.2 years) volunteered for the study. Each subject performed six CMJs under two different jumping conditions: with PT and without PT (WPT). The order of the two conditions was randomized. All of the measured variables had fair-to-good reliability (intra-class correlation coefficient > 0.75). When we compared the PT and WPT groups, we did not find a significant difference in the magnitude of the first (F1) and second (F2) peaks of the VGRF. We also did not find a significant difference in the time to production of these peaks (T1 and T2), and the time to stabilization (TTS) (p < 0. 05). Furthermore, the flight time was similar in the two groups (0.475 ± 0.046 and 0.474 ± 0.056 s, respectively, for PT and WPT). These results suggest that PT does not jeopardize performance during CMJ. Furthermore, it also does not soften the VGRF generated during the landing, indicating that PT may be of limited utility in preventing injuries associated with this type of movement.

Key points

• We investigated whether patellar taping interferes with athletic performance, as has been suggested by previous studies.
• We also explored the effect of patellar taping on the forces generated during the landing phase of counter movement jumps.
• Patellar taping had no effect on the flight time during counter movement jumps.
• Patellar taping also had no effect on the vertical ground reaction force variables measured during the landing phase of counter movement jumps.
• This information may be relevant to athletes and trainers who are concerned about the effects of patellar taping on performance.

Key words: Biomechanics, force platform, vertical ground reaction force, landing phase     

Motor Learning as Young Gymnast’s Talent Indicator

Talent identification plans are designed to select young athletes with the ability to achieve future success in sports. The aim of the study was to verify the predictive value of coordination and precision in skill acquisition during motor learning, as indicators of talent. One hundred gymnasts, both cadets (aged 11.5 ± 0.5 yr.) and juniors (aged 13.3 ± 0.5 years), competing at the national level, were enrolled in the study. The assessment of motor coordination involved three tests of the validated Hirtz’s battery (1985), and motor skill learning involved four technical tests, specific of rhythmic gymnastics. All the tests were correlated with ranking and performance scores reached by each gymnast in the 2011, 2012, and 2013 National Championships. Coordination tests were significantly correlated to 2013 Championships scores (p < 0.01) and ranking (p < 0.05) of elite cadet athletes. Precision, in skill acquisition test results, was positively and significantly associated with scores in 2013 (adj. R² = 0.26, p < 0.01). Gymnasts with the best results in coordination and motor learning tests went on to achieve better competition results in three- year time.

Key points

• In talent identification and selection procedures it is better to include the evaluation of coordination and motor learning ability.
• Motor learning assessment concerns performance improvement and the ability to develop it, rather than evaluating the athlete’s current performance.
• In this manner talent identification processes should be focused on the future performance capabilities of athletes.

Key words: Training, precision, coordination, talent selection, gymnastics, motor skills     

Electromyographic analysis on a windsurfing simulator

Recent technical innovations in windsurfing have been concentrated on the evolution of the sails and the board. It is only recently that manufacturers have become interested in the wishbones which have evolved becoming thinner and lighter than in the past. A group of six experienced windsurfers participated in an experiment on a land based windsurfing simulator. The goal of the study was to analyze the muscular force used for different techniques for holding onto the wishbone. The test consisted in recording the global electromyographic activity of several muscles on the forearm using surface electrodes. There were two different wind force conditions possible with the simulator: medium (15 kg) and strong (25 kg). Three different wishbone diameters were tested (28, 30 and 32 mm). Four different hand positions on the wishbone were analyzed: leading hand and/or following hand in pronation and/or supination. The electrical muscular activity obtained varied significantly (p < 0.05) depending on the type of grip and according to the diameter of the wishbone. The position with the two hands in supination on a wishbone of 28 mm in diameter was the most economical in muscular terms, notably the flexions of the forearm. The confirmation of the results should lead windsurfers to reconsider the positioning of the wishbone and the adapted posture to waste the least amount of energy possible.

Key points

• Female athletes landed with increased knee valgus and VGRF which may predispose them to ACL injury.
• Fatigue elicited a similar response in male and female athletes.
• The effectiveness of sports injury prevention programs may improve by focusing on teaching females to land softer and with less knee valgus.

Key words: Forearm, performance, windsurf.     

The Lower Extremity Biomechanics of Single- and Double-Leg Stop-Jump Tasks

The anterior cruciate ligament (ACL) injury is a common occurrence in sports requiring stop-jump tasks. Single- and double-leg stop-jump techniques are frequently executed in sports. The higher risk of ACL injury in single-leg drop landing task compared to a double-leg drop landing task has been identified. However the injury bias between single- and double-leg landing techniques has not been investigated for stop-jump tasks. The purpose of this study was to determine the differences between single- and double-leg stop-jump tasks in knee kinetics that were influenced by the lower extremity kinematics during the landing phase. Ground reaction force, lower extremity kinematics, and knee kinetics data during the landing phase were obtained from 10 subjects performing single- and double-leg stop-jump tasks, using motion-capture system and force palates. Greater peak posterior and vertical ground reaction forces, and peak proximal tibia anterior and lateral shear forces (p < 0.05) during landing phase were observed of single-leg stop-jump. Single-leg stop-jump exhibited smaller hip and knee flexion angle, and knee flexion angular velocity at initial foot contact with the ground (p < 0.05). We found smaller peak hip and knee flexion angles (p < 0.05) during the landing phase of single-leg stop-jump. These results indicate that single-leg landing may have higher ACL injury risk than double-leg landing in stop-jump tasks that may be influenced by the lower extremity kinematics during the landing phase.

Key points

• Non-contact ACL injuries are more likely to occur during the single-leg stop-jump task than during the double-leg stop-jump task.
• Single-leg stop-jump exhibited greater peak proximal tibia anterior and lateral shear forces, and peak posterior and vertical ground reaction forces during the landing phase than the double-leg stop-jump task.
• Single-leg stop-jump exhibited smaller hip flexion angle, knee flexion angle, and knee flexion angular velocity at initial foot contact with the ground.
• Single-leg stop-jump exhibited greater peak knee extension and valgus moment during the landing phase than the double-leg stop-jump task.
• Single-leg stop-jump extended the hip joint at initial foot contact with the ground.

Key words: Anterior cruciate ligament, kinematics, kinetics, ground reaction force     

Professional Soccer Player Neuromuscular Responses and Perceptions to Acute Whole Body Vibration Differ from Amateur Counterparts

Acute whole body vibration (WBV) is an increasingly popular training technique amongst athletes immediately prior to performance and during scheduled breaks in play. Despite its growing popularity, evidence to demonstrate its effectiveness on acute neuromuscular responses is unclear, and suggestions that athlete ability impacts effectiveness warrant further investigation. The purpose of this study was to compare the neuromuscular effects of acute WBV and perceptions of whether WBV is an effective intervention between amateur and professional soccer players. Participants were 44 male soccer players (22 professional and 22 amateur; age: 23.1 ± 3.7 years, body mass: 75.6 ± 8.8 kg and height: 1.77 ± 0.05 m). Participants in each group were randomly assigned to either an intervention of 3 x 60 s of WBV at 40 Hz (8mm peak-to-peak displacement) or control group. Peak knee isometric force, muscle activation and post activation potentiation (PAP) of the knee extensors along with self-report questionnaire of the perceived benefits of using the intervention were collected. A three-way ANOVA with repeated measures revealed professional players demonstrated a significant 10.6% increase (p < 0.01, Partial Eta² = 0.22) in peak knee isometric force following acute WBV with no significant differences among amateur players. A significant difference (p < 0.01, Partial Eta² = 0.16) in PAP amongst professional players following acute WBVT was also reported. No significant differences amongst amateur players were reported across measurements. Results also indicated professional players reported significantly stronger positive beliefs in the effectiveness of the WBV intervention (p < 0.01, Partial Eta² = 0.27) compared to amateur players. Acute WBV elicited a positive neuromuscular response amongst professional players identified by PAP and improvements in knee isometric peak force as well as perceived benefits of the intervention, benefits not found among amateur players.

Key points

• Acute WBV improves knee extensor peak isometric force output and PAP amongst professional and not amateur soccer players
• Professional players perceived acute WBV as more beneficial to performance than amateur players
• Isometric strength,vibration intensity and duration appear to influence results amongst players of different playing levels

Key words: Potentiation, power, strength, perceptions     

Influence of Increased Posterior Tibial Slope in Total Knee Arthroplasty on Knee Joint Biomechanics: A Computational Simulation Study

Background

The reconstructed posterior tibial slope (PTS) plays a significant role in restoring knee kinematics in cruciate-retaining-total knee arthroplasty (TKA). A few studies have reported the effect of the PTS on biomechanics.

Carbohydrate Intake Considerations for Young Athletes

Good nutritional practices are important for exercise performance and health during all ages. Athletes and especially growing children engaged in heavy training have higher energy and nutrient requirements compared to their non-active counterparts. Scientific understanding of sports nutrition for the young athlete is lacking behind the growing number of young athletes engaged in sports. Most of the sports nutrition recommendations given to athletic children and adolescents are based on adult findings due to the deficiency in age specific information in young athletes. Therefore, this review reflects on child specific sports nutrition, particularly on carbohydrate intake and metabolism that distinguishes the child athlete from the adult athlete. Children are characterised to be in an insulin resistance stage during certain periods of maturation, have different glycolytic/metabolic responses during exercise, have a tendency for higher fat oxidation during exercise and show different heat dissipation mechanisms compared to adults. These features point out that young athletes may need different nutritional advice on carbohydrate for exercise to those from adult athletes. Sport drinks for example may need to be adapted to children specific needs. However, more research in this area is warranted to clarify sports nutrition needs of the young athlete to provide better and healthy nutritional guidance to young athletes.

Key points

• Athletic girls show lower carbohydrate intakes compared to boys.
• Substrate oxidation during exercise appears to be maturity related, fat being the preferred fuel for oxidation in younger athletic children.
• Children appear to have lower endogenous but greater exogenous carbohydrate oxidation rates during exercise.
• Carbohydrate intake during exercise appears to show no additional performance improvement in young athletes. Perhaps fat intake or a combination of both nutrients may be a better approach for nutrient supplementation during exercise.
• Gastric emptying physiology of young athletes is not well known. Adult sport drinks showed a tendency to delay gastric emptying in young athletes during exercise at higher intensities.
• More research is needed in paediatric sports nutrition.

Key Words: Exercise, diet, nutrients, children, sport drinks     

Effects of menarcheal age on the anterior cruciate ligament injury risk factors during single-legged drop landing in female artistic elite gymnasts

Introduction

Although numerous studies have demonstrated the relationship between maturation and lower extremity biomechanics during landing in team sport athletes, we are presently uninformed of any research that examined the single-legged drop landing biomechanics of gymnasts. The purpose of this study is to investigate the effects of the menarcheal age on the lower extremity biomechanics during a single-legged drop landing in female artistic elite gymnasts.

Materials and methods

Twenty-two female artistic elite gymnasts, between 9 and 36 years of age, participated in this study. The participants were divided into two groups pre- (n = 11) and post- (n = 11) menarche and asked to perform a single-legged drop landing on top of a 30 cm platform and land on a force plate. The statistical analysis consisted of the multivariate analysis with the level of significance set at p < 0.05.

Results

The post-menarche group showed a decrease in their maximum knee flexion angle and increase in their maximum knee abduction angle, maximum internal tibial rotation angle, maximum knee abduction moment, and hamstring-quadriceps muscle activity ratio compared with the pre-menarche group during the single-legged drop landing.

Conclusions

The post-menarche group showed an increased noncontact anterior cruciate ligament injury risk, due to their greater knee loads, compared with the pre-menarche group.