Inertial measurement units (IMUs) allow for measurements of kinematic movements outside the laboratory, persevering the athlete-environment relationship. To use IMUs in a sport-specific setting, it is necessary to validate sport-specific movements. The aim of this study was to assess the concurrent validity of the Xsens IMU system by comparing it to the Vicon optoelectronic motion system for lower-limb joint angle measurements during jump-landing and change-of-direction tasks. Ten recreational athletes performed four tasks; single-leg hop and landing, running double-leg vertical jump landing, single-leg deceleration and push off, and sidestep cut, while kinematics were recorded by 17 IMUs (Xsens Technologies B.V.) and eight motion capture cameras (Vicon Motion Systems, Ltd). Validity of lower-body joint kinematics was assessed using measures of agreement (cross-correlation: XCORR) and error (root mean square deviation and amplitude difference). Excellent agreement was found in the sagittal plane for all joints and tasks (XCORR > 0.92). Highly variable agreement was found for knee and ankle in transverse and frontal plane. Relatively high error rates were found in all joints. In conclusion, this study shows that the Xsens IMU system provides highly comparable waveforms of sagittal lower-body joint kinematics in sport-specific movements. Caution is advised interpreting frontal and transverse plane kinematics as between-system agreement highly varied.
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Wearable inertial sensors (WIS) facilitate the preservation of the athlete-environment relationship by allowing measurement outside the laboratory. WIS systems should be validated for team sports movements before they are used in sports performance and injury prevention research. The aim of the present study was to investigate the concurrent validity of a wearable inertial sensor system in quantifying joint kinematics during team sport movements. Ten recreationally active participants performed change-of-direction (single-leg deceleration and sidestep cut) and jump-landing (single-leg hop, single-leg crossover hop, and double-leg vertical jump) tasks while motion was recorded by nine inertial sensors (Noraxon MyoMotion, Noraxon USA Inc.) and eight motion capture cameras (Vicon Motion Systems Ltd). Validity of lower-extremity joint kinematics was assessed using measures of agreement (cross-correlation: XCORR) and error (root mean square deviation; and amplitude difference). Excellent agreement (XCORR >0.88) was found for sagittal plane kinematics in all joints and tasks. Highly variable agreement was found for frontal and transverse plane kinematics at the hip and ankle. Errors were relatively high in all planes. In conclusion, the WIS system provides valid estimates of sagittal plane joint kinematics in team sport movements. However, researchers should correct for offsets when comparing absolute joint angles between systems.
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External focus instructions have been shown to result in superior motor performance compared to internal focus instructions. Using an EF may help to optimize current anterior cruciate ligament (ACL) injury prevention programs. The purpose of the current study was to investigate the effects of instructions on landing technique and performance by comparing an external focus (EF), internal focus (IF), video (VI) and control (CTRL) group. Subjects (age 22.50 ± 1.62 years, height 179.70 ± 10.43 cm, mass 73.98 ± 12.68 kg) were randomlyassigned to IF (n = 10), EF (n = 10), VI (n = 10) or CTRL group (n = 10). Landing was assessed from a drop vertical jump (DVJ) in five sessions: pretest, two training blocks (TR1 and TR2) and directly after the training sessions (post test) and retention test 1 week later. Group specific instructions were offered in TR1 and TR2. Landing technique was assessed with the Landing Error Scoring System (LESS) and jump height was taken as performance measure.The results show that males in the VI group and females both in the VI and EF groups significantly improved jump-landing technique. Retention was achieved and jump height was maintained for males in the VI group and females both in the VI and EF groups. It is therefore concluded that EF and VI instructions have great potential in ACL injury prevention.
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The aim of this study is to investigate the predictivevalue of landing stability and technique togain insight into risk factors for ankle and kneeinjuries in indoor team sport players. Seventyfivemale and female basketball, volleyball orkorfball players were screened by measuringlanding stability after a single-leg jump landingand landing technique during a repeated countermovement jump by detailed 3-dimensional kinematicsand kinetics. During the season 11 acuteankle injuries were reported along with 6 acuteand 7 overuse knee injuries by the teams’ physicaltherapist. Logistic regression analysis showedless landing stability in the forward and diagonaljump direction (OR 1.01–1.10, p ≤ 0.05) in playerswho sustained an acute ankle injury. Furthermorelanding technique with a greater ankle dorsiflexionmoment increased the risk for acuteankle injury (OR 2.16, p ≤ 0.05). A smaller kneeflexion moment and greater vertical groundreaction force increased the risk of an overuseknee injury (OR 0.29 and 1.13 respectively,p ≤ 0.05). Less one-legged landing stability andsuboptimal landing technique were shown inplayers sustaining an acute ankle and overuseknee injury compared to healthy players. Determiningboth landing stability and technique mayfurther guide injury prevention programs.
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Video feedback may be a powerful tool to change biomechanical landing patterns associated with anterior cruciate ligament (ACL) injury risk. This study investigated the effect of video feedback on drop vertical jump (DVJ) landing strategies in team sport athletes. 59 athletes were assigned to a video feedback (VI) or control (CTRL) group. A pretest, 2 training sessions and a posttest were conducted. In both training sessions, video feedback, consisting of a video of the athlete's contour superimposed onto an expert's contour performing the DVJ landing task, was provided to the VI group; the CTRL group did not receive feedback. Outcomes included: kinematics and kinetics at peak knee valgus/varus moment during pre- and posttest and percentage overlap of expert and athlete during the training sessions. At posttest, males in the VI group showed greater hip flexion angles (p=0.001) and range of motion (p<0.001), smaller vertical ground reaction force, and smaller ankle dorsiflexion moment (p<0.001) compared to pretest. At posttest, males in the VI group demonstrated smaller vertical ground reaction force (p=0.031) and ankle dorsiflexion moment (p=0.001) compared to males in the CTRL group. The VI group increased percentage overlap with the expert during training sessions and from start of the first to the end of the second training session (p<0.001). Overall, video feedback was effective to modify landing strategies favorably in males. While females imitated the expert model, their landing strategy did not change significantly. While Females may need additional (verbal) feedback to benefit from video feedback.
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Implicit (IF) and explicit (EF) feedback are two motor learning strategies that have been demonstrated to alter biomechanical movement patterns. While both strategies have been utilized for injury prevention, it remains unclear which strategy may be more effective. PURPOSE: To examine the effects of reduced relative IF and EF feedback on lower extremity landing mechanics. METHODS: Seventeen participants (23.5±0.9 years, 1.72±0.1m, 67.7±11.5kg) were randomly assigned to three groups: IF (n=6), EF (n=5), and Control (CG) (n=6). A box-drop jump task was performed three times a week for six weeks. Testing occurred before and after 6 weeks of intervention. IF and EF were provided by ? video feedback with instructions, while CG received no feedback. IF were instructed to focus their attention outside their body, while EF were instructed to focus their attention to their lower extremities. Intervention sessions were partitioned into 100% feedback, 33% feedback, and 16.6% feedback frequency phases. Participants viewed video recordings of their task to analyze their jump-landing mechanics from both a sagittal and frontal plane cameras. Participants viewed 2 video recordings per camera, once in real-time and once in slow motion. Multivariate analysis of variance was conducted to compare differences between groups and time for hip abduction angle (HA), knee abduction moment (KAM), and knee flexion angle (KF). RESULTS: No statistically significant difference (p>0.05) was found for: HA (CG:pre=-9.85±5.3, post=-7.36±8.65; IF:pre=-4.17±2.67, post=-7.52±5.27; EF:pre=-5.68±6.12, post=-5.98±5.43), KAM (CG:pre=-0.5±0.3, post=-0.34±0.13; IF:pre=-0.5±0.21, post=-0.48±0.13; EF:pre=-0.48±0.12, post=-0.46±0.26), and KF (CG:pre=-92.26±9.12, post=-100.33±15.2; IF:pre=-106.37±16.34, post=-103.45±19.97; EF:pre=-100.32±11.4, post=-112.4±18.22). CONCLUSION: We did not find statistically significant differences for any dependent measures between groups from pre to post-test. It should be noted that IF HA slightly decreased from pre to post-test whereas it increased for CG. For KAM, CG was lower on post-test comparing to IF and EF. EF and CG trended to decrease from pre to post-test, while IF slightly increased KF. Our preliminary findings partially support that implicit and explicit feedback alters lower body mechanics while jumping.
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Background: In team handball an anterior cruciate ligament (ACL) injury often occurs during landing after a jump shot. Many intervention programs try to reduce the injury rate by instructing the athletes to land safer. Video feedback is an effective way to provide feedback although little is known about its influence on landing technique in sport-specific situations. Objective: To test the effectiveness of a video overlay feedback method on landing technique in elite handball players. Method: Sixteen elite female handball players were assigned to a Control or Video Group. Both groups performed jump shots in a pre-test, two training sessions (TR1 & TR2) and a post-test. The Video Group received video feedback of an expert model with an overlay of their own jump shots in TR1 and TR2 whilst the Control Group did not. Main outcome measures were sagittal ankle, knee and hip angles during initial contact (IC), maximum (MAX) and range of motion (ROM), in addition to the Landing Error Scoring System (LESS) score. One 2x4 repeated measures ANOVA was conducted to analyze group, time and interaction effects of all kinematic outcome measures and the LESS score. Results: The Video Group displayed significant improvement in knee and hip flexion at IC, MAX and ROM. In addition, MAX ankle flexion and their LESS score improved an average of 8.1 in the pre-test to 4.0 in the post-test. When considering performance variables, no differences between Control Group and Video Group were found in shot accuracy or vertical jump height, whilst horizontal jump distance in the Video Group became greater over time. Conclusion: Overlay visual feedback is an effective method to improve landing kinematics during a sport-specific jump shot. Further research is now warranted to determine the long-term effects and transfer to training and game situations.
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It is unknown how movement patterns that are learned carry over to the field. The objective was to deter- mine whether training during a jump-landing task would transfer to lower extremity kinematics and kinetics during sidestep cutting.Methods Forty healthy athletes were assigned to the ver- bal internal focus (IF, n = 10), verbal external focus (EF, n = 10), video (VI, n = 10) or control (CTRL, n = 10) group. A jump-landing task was performed as baseline followed by training blocks (TR1 and TR2) and a post-test. Group-spe- cific instructions were given in TR1 and TR2. In addition, participants in the IF, EF and VI groups were free to ask for feedback after every jump during TR1 and TR2. Retention was tested after 1 week. Transfer of learned skill was deter- mined by having participants perform a 45° unanticipated sidestep cutting task. 3D hip, knee and ankle kinematics and kinetics were the main outcome measures.Results During sidestep cutting, the VI group showed greater hip flexion ROM compared to the EF and IF groups (p < 0.001). The EF (p < 0.036) and VI (p < 0.004) groups had greater knee flexion ROM compared to the IF group. Conclusions Improved jump-landing technique car- ried over to sidestep cutting when stimulating an external attentional focus combined with self-controlled feedback. Transfer to more sport-specific skills may demonstrate potential to reduce injuries on the field. Clinicians and practitioners are encouraged to apply instructions that stimulate an external focus of attention, of which visual instructions seem to be very powerful.
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PURPOSE: It has been reported that there is no correlation between anterior tibia translation (ATT) in passive and dynamic situations. Passive ATT (ATTp) may be different to dynamic ATT (ATTd) due to muscle activation patterns. This study aimed to investigate whether muscle activation during jumping can control ATT in healthy participants.METHODS: ATTp of twenty-one healthy participants was measured using a KT-1000 arthrometer. All participants performed single leg hops for distance during which ATTd, knee flexion angles and knee flexion moments were measured using a 3D motion capture system. During both tests, sEMG signals were recorded.RESULTS: A negative correlation was found between ATTp and the maximal ATTd (r = - 0.47, p = 0.028). An N-Way ANOVA showed that larger semitendinosus activity was seen when ATTd was larger, while less biceps femoris activity and rectus femoris activity were seen. Moreover, larger knee extension moment, knee flexion angle and ground reaction force in the anterior-posterior direction were seen when ATTd was larger.CONCLUSION: Participants with more ATTp showed smaller ATTd during jump landing. Muscle activation did not contribute to reduce ATTd during impact of a jump-landing at the observed knee angles. However, subjects with large ATTp landed with less knee flexion and consequently showed less ATTd. The results of this study give information on how healthy people control knee laxity during jump-landing.LEVEL OF EVIDENCE: III.
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Anterior cruciate ligament (ACL) injury prevention programs have been successful in the short term. Motor learning strategies with an internal focus (IF) to body movements have traditionally been utilized, but may be less suitable than an external focus (EF) for the acquisition and control of complex motor skills required for sport. To investigate the available literature and provide an overview of the effect of IF and EF instructions on jump landing technique. Systematic searches were conducted in PubMed (1966 to May 2014), CINAHL (1981 to May 2014) and PsycInfo (1989 to May 2014). A priori defined inclusion criteria were: (i) full text; (ii) published in English, German or Dutch; (iii) healthy adult subjects (mean age !18 years); (iv) jump and landing performance tested and (v) study used comparison between an EF and IF. Performance (jump height and distance) and technique (kinematics and kinetics) were the pri- mary outcome variables of interest. Nine papers were included. Significant better motor performance and movement technique was found with an EF compared to an IF. Considering the beneficial results in the included studies when utilizing an EF, it is suggested to implement these strategies into ACL injury prevention programs.
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