Cross-Education of Skill: Assessment of Overhand Throwing Using Product- and Process-Oriented Assessment.

Purpose: The aims of the present study were to: (1) investigate the magnitude and direction of the cross-education effect in a unilateral sport skill (overhand throw) and (2) to establish which practice condition (dominant hand only or alternating hands) would yield the best results. Methods: The study involved three experimental groups of 11-year-old children (n = 59). The first group (n = 20) used only the dominant hand to throw the ball. The second group (n = 19) used the nondominant hand only, while the third (n = 20) alternated hands for each throw. A pre- and post-testing of both hands preceded and followed the intervention period. Results: The results of our study revealed no asymmetry in cross-education effect between the limbs for children's overhand ball throwing. It was also shown that training both hands is superior to training the dominant hand alone. Conclusion: Our findings would be of particular interest to physical education teachers and coaches of unilateral sports who are advised to review their unilateral skill teaching methods as bilateral training offers a superior approach to augmenting the process of motor learning and performance.

Jumping demands during classical ballet class.

Ballet class represents a considerable portion of professional ballet training, yet the external training load demands associated with class-and particularly the jumping demands-have not been investigated. The purpose of this study was to measure the jumping demands of ballet class by sex and rank. Eleven female and eight male elite professional ballet dancers participated in 109 ballet classes taught by 12 different teachers. Jump counts and jump heights were measured during each class. A Poisson generalized linear mixed effects model was used to examine the differences in jump counts between sexes and ranks. Greater jump counts were observed during class in men than in women (153, 95% confidence intervals [CI] [137, 170] vs. 119, 95% CI [109, 131], p = 0.004) and in junior ranking dancers compared with senior ranking dancers (151, 95% CI [138, 165] vs. 121, 95% CI [108, 135], p = 0.006). Female junior and senior ranking dancers jumped at rates of 9.2 ± 2.6 and 8.6 ± 4.7 jumps·min-1 , respectively, while male junior and senior ranking dancers jumped at rates of 9.1 ± 2.6 and 8.7 ± 2.6 jumps·min-1 , respectively. Across all classes, 73% of jumps observed were below 50% of maximum double-legged countermovement jump height. Unlike rehearsals and performances, class offers dancers an opportunity to self-regulate load, and as such, are a useful session to manage jump load, and facilitate gradual return-to-dance pathways. Communication between health care and artistic staff is essential to facilitate load management during class.

Femoroacetabular Impingement in Ice Hockey Athletes.

ABSTRACT: Femoroacetabular impingement (FAI) in ice hockey is a concern for many athletes. The biomechanics of skating and the injury mechanism, prevalence, identification, and treatment protocols currently available for FAI in ice hockey athletes are important for all coaches and practitioners to understand. This article discusses the underlying anatomical issues and biomechanical considerations surrounding FAI. Furthermore, this article describes the interventions that can be used when encountering FAI and well-established protocols to aid in the return to play. Finally, prevention strategies that can aid in injury prevention are discussed.

Patellofemoral pain syndrome assessed by Lysholm score, radiological and biorheometric measurements.

INTRODUCTION: The aim of In this study was to verify the relationship among clinical indicators of patellofemoral pain syndrome (PFPS) and the results of modifying radiological investigation. Previous research suggests that there is a poor association between them. Therefore we have employed a technique for the functional evaluation of PFPS based on measuring the stiffness of the knee joint during passive flexion (biorheometry). METHOD: The correlation between clinical examination and a standardized Lysholm score, radiological and biorheometric measures was investigated in the 28 knee joints of 14 subjects exhibiting clinical features of PFPS. A modified axial radiological projection of the patellofemoral articulation in 90° of flexion provided the parameters quantifying the anatomical - morphological arrangement of the patellofemoral joint. The biorheometric properties of the knee were evaluated using a custom made measuring apparatus during passive flexion and extension of the knee. RESULTS: Our results confirm that the link between the clinical findings and the X-ray imaging examinations was not evident. On the contrary, the biorheometric examination proved to correlate well with the clinical symptoms of PFPS. Parameters were identified which can characterize the biorheograms of people suffering PFPS. CONCLUSIONS: Analysis of the relationship among the clinical, radiological and biorheometric examinations leads to the recommendation that biorheometric examination is an effective method for the objective assessment of PFPS.

Principal Component Analysis can Be Used to Discriminate Between Elite and Sub-Elite Kicking Performance.

Contemporary descriptions of motor control suggest that variability in movement can be indicative of skilled or unskilled performance. Here we used principal component analysis to study the kicking performance of elite and sub-elite soldiers who were highly familiar with the skill in order to compare the variability in the first and second principal components. The subjects kicked a force plate under a range of loaded conditions, and their movement was recorded using optical motion capture. The first principal component explained >92% of the variability across all kinematic variables when analyzed separately for each condition, and both groups and explained more of the variation in the movement of the elite group. There was more variation in the loading coefficient of the first principal component for the sub-elite group. In contrast, for the second principal component, there was more variation in the loading coefficient for the elite group, and the relative magnitude of the variation was greater than for the first principal component for both groups. These results suggest that the first principal component represented the most fundamental movement pattern, and there was less variation in this mode for the elite group. In addition, more of the variability was explained by the hip than the knee angle entered when both variables were entered into the same PCA, which suggests that the movement is driven by the hip.

Stronger Subjects Select a Movement Pattern That May Reduce Anterior Cruciate Ligament Loading During Cutting.

ABSTRACT: Davies, WT, Ryu, JH, Graham-Smith, P, Goodwin, JE, and Cleather, DJ. Stronger subjects select a movement pattern that may reduce anterior cruciate ligament loading during cutting. J Strength Cond Res 36(7): 1853-1859, 2022-Increased strength has been suggested to reduce the incidence of anterior cruciate ligament (ACL) injury as part of wider neuromuscular training programs; however, the mechanism of this is not clear. Cutting is a high-risk maneuver for ACL injury, but limited research exists as to how strength affects sagittal plane biomechanics during this movement. Sixteen subjects were split into a stronger and weaker group based on their relative peak isometric strength in a unilateral squat (stronger: 29.0 ± 3.4 N·kg-1 and weaker: 18.3 ± 4.1 N·kg-1). Subjects performed 45° cuts with maximal intent 3 times, at 3 different approach velocities (2, 4, and 6 m·s-1). Kinematics and ground reaction forces were collected using optical motion capture and a force platform. The stronger group had lower knee extensor moments, larger hip extensor moments, and a greater peak knee flexion angle than the weaker group (p < 0.05). There was a trend for greater knee flexion at initial contact in the stronger group. There were no differences in resultant ground reaction forces between groups. The stronger group relied more on the hip than the knee during cutting and reached greater knee flexion angles. This could decrease ACL loading by reducing the extensor moment required at the knee during weight acceptance. Similarly, the greater knee flexion angle during weight acceptance is likely to be protective of the ACL.

Differences in Motor Control Strategies of Jumping Tasks, as Revealed by Group and Individual Analysis.

The aim of this study was to investigate the motor control strategies adopted when performing two jumping tasks with different task demands when analysed at an individual and group level. Twenty-two healthy individuals performed two jumping tasks: jumping without the use of an arm swing (CMJnas) and jumping starting in a plantar flexed position with the use of an arm swing (PF). Principal component analysis (PCA) was performed using hip, knee and ankle joint moment data on individual (PCAi) and group data (PCAc). The results demonstrate that a greater number of PCs are required to explain the majority of variance within the dataset in the PF condition at both an individual and group level, compared to CMJnas condition. Although common control strategies were observed between the two jumping conditions, differences in the organisation of the movement (PC loading coefficients) were observed. Results from the group analysis did not completely reflect the individual strategies used to perform each jumping task and highlight the value in performing individual analysis to determine emergent control strategies.

Task Demand Changes Motor Control Strategies in Vertical Jumping.

The purpose of this study was to examine the motor control strategies employed to control the degrees of freedom when performing a lower limb task with constraints applied at the hip, knee, and ankle. Thirty-five individuals performed vertical jumping tasks: hip flexed, no knee bend, and plantar flexed. Joint moment data from the hip, knee, and ankle were analyzed using principal component analysis (PCA). In all PCA performed, a minimum of two and maximum of six principal components (PC) were required to describe the movements. Similar reductions in dimensionality were observed in the hip flexed and no knee bend conditions (3PCs), compared to the plantar flexed condition (5PCs). A proximal to distal reduction in variability was observed for the hip flexed and no knee bend conditions but not for the plantar flexed condition. Collectively, the results suggest a reduction in the dimensionality of the movement occurs despite the constraints imposed within each condition and would suggest that dimensionality reduction and motor control strategies are a function of the task demands.

The Effects of a 9-Week Hip Focused Weight Training Program on Hip and Knee Kinematics and Kinetics in Experienced Female Dancers.

Increased involvement of the hip musculature during some movements is associated with enhanced performance and reduced injury risk. However, the impact of hip dominant weight training methods on movement strategy has seen limited attention within the literature. The aim of this study was to evaluate if a 9-week hip dominant weight training intervention promotes a more hip dominant movement strategy leading to an improvement in countermovement jump performance. Twenty-two experienced female dancers were recruited and separated into an intervention (age 24.4 ± 6.3 years, body height 165.5 ± 5.8 cm, body mass 65.9 ± 5.6 kg) and a control (age 22.9 ± 5.6 years, body height 163.3 ± 5.4 cm, body mass 57.4 ± 6.8 kg) group. The intervention group participated in a 9-week hip dominant training intervention, which consisted of a wide stance back squat, Romanian deadlift, hip thrusters, and a bent over row. Hip and knee kinematics and kinetics, and countermovement jump performance were assessed pre and post training. Significant interaction effects were found for peak hip joint moment (p = 0.030, η2 = 0.214) and countermovement jump performance (p = 0.003, η2 = 0.356), indicating an increase in peak hip joint moment and countermovement jump performance for the intervention group. Specifically, the intervention group showed a mean increase in jump height of 11.5%. The data show that the use of a hip dominant weight training strategy can improve hip contribution in the propulsion phase of the countermovement jump. Strength and conditioning specialists should incorporate hip dominant weight training exercises to increase hip strength and improve performance.

Knee Forces During Landing in Men and Women.

Sex differences in biomechanics may provide one explanation for the greater incidence of knee injuries in women, but few studies have compared internal forces. In this study, a musculoskeletal model was used to compare male and female, bilateral and unilateral landings based on motion capture and force plate data. Participants were classified as landing medially or laterally loaded based upon the mediolateral load share at the knee (bilateral: p < 0.001, η2=0.452; unilateral: p < 0.001, η2 = 0.444). Knee kinematics and ground reaction forces were not different between the two groups (p > 0.05, η2 = 0.001 - 0.059), but there were differences in muscular recruitment. Landing strategy did not appear to be dependent on sex. However, for both medially and laterally loaded bilateral landings men had greater gluteal (p = 0.017, η2 = 0.085) and hamstrings forces (p < 0.001, η2 = 0.183), whereas women had greater quadriceps forces (p = 0.004, η2 = 0.116). This study demonstrates an association between muscular recruitment and medially loaded landings. Landing strategy seems to be a function of skill not sex; however, within a particular landing strategy there may be sex differences in muscular activation that contribute to the difference in injury rates.

Principal Component Analysis Reveals the Proximal to Distal Pattern in Vertical Jumping Is Governed by Two Functional Degrees of Freedom.

The successful completion of motor tasks requires effective control of multiple degrees of freedom (DOF), with adaptations occurring as a function of varying performance constraints. In this study we sought to compare the emergent coordination strategies employed in vertical jumping under different task constraints [countermovement jump (CMJ) with arm swing-CMJas and no arm swing-CMJnas]. In order to achieve this, principal component analysis (PCA) was conducted on joint moment waveform data from the hip, knee and ankle. This statistical approach has the advantage of analyzing the whole movement within a time series and reduces multidimensional datasets to lower dimensions for analysis. Both individual and group analyses were conducted. For individual analysis, PCA was conducted on combined hip, knee, and ankle joint moment data for each individual across both CMJnas (thirty-eight participants), and CMJas (twenty-two participants) conditions. PCA was also performed comparing all data from each individual across CMJnas and CMJas conditions. The results revealed a maximum of three principal components (PC) explained over 90% of the variance in the data sets for both conditions and within individual and group analyses. For individual analysis, no more than 2PCs were required for both conditions. For group analysis, CMJas required 3PCs to explain over 90% of the variance within the dataset and CMJnas only required 2PCs. Reconstruction of the original NJM waveforms from the PCA output demonstrates a greater loading of hip and knee joint moments to PC1, with PC2 showing a greater loading to ankle joint moment. The reduction in dimensions of the original data shows the proximal to distal extension pattern in the sagittal plane, typical of vertical jumping tasks, is governed by only 2 functional DOF, at both a group, and individual level, rather than the typically reported 3 mechanical DOF in some forms of jumping.

The Magical Horizontal Force Muscle? A Preliminary Study Examining the "Force-Vector" Theory.

The force-vector theory contends that horizontal exercises are more specific to horizontal sports skills. In this context, the focus is on horizontal force production relative to the global coordinate frame. However, according to the principle of dynamic correspondence, the direction of force relative to the athlete is more important, and thus the basis for the force-vector theory is flawed. The purpose of this study was therefore to test the force-vector theory. According to the force-vector theory, hip thrust is a horizontally loaded exercise, and so hip thrust training would be expected to create greater improvements in horizontal jump performance than vertical jump performance. Eleven collegiate female athletes aged 18⁻24 years completed a 14-week hip thrust training programme. Pre and post testing was used to measure the following: vertical squat jump, vertical countermovement jump, horizontal squat jump, horizontal countermovement jump and hip thrust 3 repetition maximum (3RM). Subjects improved their 3 repetition maximum hip thrust performance by 33.0% (d = 1.399, p < 0.001, η² = 0.784) and their vertical and horizontal jump performance (improvements ranged from 5.4⁻7.7%; d = 0.371⁻0.477, p = 0.004, η² = 0.585). However, there were no differences in the magnitude of the improvement between horizontal and vertical jumping (p = 0.561, η² = 0.035). The results of this study are contrary to the predictions of the force-vector theory. Furthermore, this paper concludes with an analysis of the force-vector theory, presenting the mechanical inconsistencies in the theory. Coaches should use the well established principle of dynamic correspondence in order to assess the mechanical similarity of exercises to sports skills.

An important role of the biarticular hamstrings is to exert internal/external rotation moments on the tibia during vertical jumping.

Most research considering biarticular muscle function has tended to focus on the sagittal plane. Instead, the purpose of this study was to evaluate the internal/external rotation moment arms of the biarticular muscles of the knee, and then to explore their function. The FreeBody musculoskeletal model of the lower limb was used to calculate the moment arms and moments that each of the muscles of the knee exerted on the proximal tibia of 12 athletic males during vertical jumping. Biceps femoris and tensor fascia latae were external rotators of the tibia, whereas semimembranosus, semitendinosus, sartorius, gracilis, popliteus and the patellar tendon were internal rotators. The magnitudes of the internal/external rotation and flexion moments exerted on the tibia by the biarticular hamstrings were similar, suggesting that the creation of internal/external rotation is a key aspect of their role. One potential reason is to stabilise the tibia during femoral extension (and it is argued that it may be helpful to characterise the creation of active joint stability as the stabilisation of one segment during the rotation of an adjacent segment). A second explanation may be to mechanically couple hip abduction when the hip is flexed with internal rotation of the tibia.

Effects of an 8-week strength training intervention on tibiofemoral joint loading during landing: a cohort study.

OBJECTIVES: To use a musculoskeletal model of the lower limb to evaluate the effect of a strength training intervention on the muscle and joint contact forces experienced by untrained women during landing. METHODS: Sixteen untrained women between 18 and 28 years participated in this cohort study, split equally between intervention and control groups. The intervention group trained for 8 weeks targeting improvements in posterior leg strength. The mechanics of bilateral and unilateral drop landings from a 30 cm platform were recorded preintervention and postintervention, as was the isometric strength of the lower limb during a hip extension test. The internal muscle and joint contact forces were calculated using FreeBody, a musculoskeletal model. RESULTS: The strength of the intervention group increased by an average of 35% (P<0.05; pre: 133±36 n, post: 180±39 n), whereas the control group showed no change (pre: 152±36 n, post: 157±46 n). There were only small changes from pre-test to post-test in the kinematics and ground reaction forces during landing that were not statistically significant. Both groups exhibited a post-test increase in gluteal muscle force during landing and a lateral to medial shift in tibiofemoral joint loading in both landings. However, the magnitude of the increase in gluteal force and lateral to medial shift was significantly greater in the intervention group. CONCLUSION: Strength training can promote a lateral to medial shift in tibiofemoral force (mediated by an increase in gluteal force) that is consistent with a reduction in valgus loading. This in turn could help prevent injuries that are due to abnormal knee loading such as anterior cruciate ligament ruptures, patellar dislocation and patellofemoral pain.

Reliability and Minimal Detectable Change Values for Predictions of Knee Forces during Gait and Stair Ascent Derived from the FreeBody Musculoskeletal Model of the Lower Limb.

FreeBody is a musculoskeletal model of the lower limb used to calculate predictions of muscle and joint contact forces. The validation of FreeBody has been described in a number of publications; however, its reliability has yet to be established. The purpose of this study was, therefore, to establish the test-retest reliability of FreeBody in a population of healthy adults in order to add support to previous and future research using FreeBody that demonstrates differences between cohorts after an intervention. We hypothesized that test-retest estimations of knee contact forces from FreeBody would demonstrate a high intra-class correlation. Kinematic and kinetic data from nine older participants (4 men: mean age = 63 ± 11 years; 5 women: mean age = 49 ± 4 years) performing level walking and stair ascent was collected on consecutive days and then analyzed using FreeBody. There was a good level of intra-session agreement between the waveforms for the individual trials of each activity during testing session 1 (R = 0.79-0.97). Similarly, overall there was a good inter-session agreement within subjects (R = 0.69-0.97) although some subjects showed better agreement than others. There was a high level of agreement between the group mean waveforms of the two sessions for all variables (R = 0.882-0.997). The intra-class correlation coefficients (ICC) were very high for peak tibiofemoral joint contact forces (TFJ) and hamstring forces during gait, for peak patellofemoral joint contact forces and quadriceps forces during stair ascent and for peak lateral TFJ and the proportion of TFJ accounted for by the medial compartment during both tasks (ICC = 0.86-0.96). Minimal detectable change (MDC) of the peak knee forces during gait ranged between 0.43 and 1.53 × body weight (18-170% of the mean peak values). The smallest MDCs were found for medial TFJ share (4.1 and 5.8% for walking and stair ascent, respectively, or 4.8 and 6.7% of the mean peak values). In conclusion, the results of this study support the use of FreeBody to investigate the effect of interventions on muscle and joint contact forces at the cohort level, but care should be taken if using FreeBody at the subject level.

Effect of a gluteal activation warm-up on explosive exercise performance.

OBJECTIVES: To evaluate the effect of a gluteal activation warm-up on the performance of an explosive exercise (the high hang pull (HHP)). METHODS: Seventeen professional rugby union players performed one set of three HHPs (with 80% of their one repetition maximum load) following both a control and activation warm-up. Peak electrical activity of the gluteus maximus and medius was quantified using electromyography (EMG). In addition, the kinematics and kinetics of nine players was also recorded using force plate and motion capture technology. These data were analysed using a previously described musculoskeletal model of the right lower limb in order to provide estimates of the muscular force expressed during the movement. RESULTS: The mean peak EMG activity of the gluteus maximus was significantly lower following the activation warm-up as compared with the control (p<0.05, effect size d=0.30). There were no significant differences in the mean peak estimated forces in gluteus maximus and medius, the quadriceps or hamstrings (p=0.053), although there was a trend towards increased force in gluteus maximus and hamstrings following the activation warm-up. There were no differences between the ground reaction forces following the two warm-ups. CONCLUSION: This study suggests that a gluteal activation warm-up may facilitate recruitment of the gluteal musculature by potentiating the glutes in such a way that a smaller neural drive evokes the same or greater force production during movement. This could in turn potentially improve movement quality.

The effect of weightlifting shoes on the kinetics and kinematics of the back squat.

Weightlifting shoes (WS) are often used by athletes to facilitate their squat technique; however, the nature of these benefits is not well understood. In this study, the effects of footwear and load on the mechanics of squatting were assessed for 32 participants (age: 25.4 ± 4.4 years; mass 72.87 ± 11.35 kg) grouped by sex and experience. Participants completed loaded and unloaded back squats wearing both WS and athletic shoes (AS). Data were collected utilising a 3D motion capture system synchronised with a force platform and used to calculate kinematic and kinetic descriptors of squatting. For both load conditions, WS gave significantly (P < 0.05) reduced ankle flexion and increased knee flexion than AS, as well as a more upright trunk and greater knee moment for the unloaded condition. In addition, the experienced group experienced a significantly greater increase in knee and hip flexion with WS than the novices when unloaded. These results are consistent with the idea that WS permit a more knee flexed, upright posture during squatting, and provide preliminary evidence that experienced squatters are more able to exploit this effect. Decisions about footwear should recognise the effect of footwear on movement and reflect an athlete's movement capabilities and training objectives.

In Vivo Knee Contact Force Prediction Using Patient-Specific Musculoskeletal Geometry in a Segment-Based Computational Model.

Segment-based musculoskeletal models allow the prediction of muscle, ligament, and joint forces without making assumptions regarding joint degrees-of-freedom (DOF). The dataset published for the "Grand Challenge Competition to Predict in vivo Knee Loads" provides directly measured tibiofemoral contact forces for activities of daily living (ADL). For the Sixth Grand Challenge Competition to Predict in vivo Knee Loads, blinded results for "smooth" and "bouncy" gait trials were predicted using a customized patient-specific musculoskeletal model. For an unblinded comparison, the following modifications were made to improve the predictions: further customizations, including modifications to the knee center of rotation; reductions to the maximum allowable muscle forces to represent known loss of strength in knee arthroplasty patients; and a kinematic constraint to the hip joint to address the sensitivity of the segment-based approach to motion tracking artifact. For validation, the improved model was applied to normal gait, squat, and sit-to-stand for three subjects. Comparisons of the predictions with measured contact forces showed that segment-based musculoskeletal models using patient-specific input data can estimate tibiofemoral contact forces with root mean square errors (RMSEs) of 0.48-0.65 times body weight (BW) for normal gait trials. Comparisons between measured and predicted tibiofemoral contact forces yielded an average coefficient of determination of 0.81 and RMSEs of 0.46-1.01 times BW for squatting and 0.70-0.99 times BW for sit-to-stand tasks. This is comparable to the best validations in the literature using alternative models.