Spatiotemporal lower-limb asymmetries during stair descent in athletes following anterior cruciate ligament reconstruction.

PURPOSE: This study evaluated motor control recovery at different times following anterior cruciate ligament reconstruction (ACLR) by investigating lower-limb spatiotemporal symmetry during stair descent performances. METHODS: We used a cross-sectional design to compare asymptomatic athletes (Controls, n = 18) with a group of people with ACLR (n = 49) divided into three time-from-ACLR subgroups (Early: <6 months, n = 17; Mid: 6-18 months, n = 16; Late: ≥18 months, n = 16). We evaluated: "temporal symmetry" during the stance subphases (single-support, first and second double-support) and "spatial symmetry" for hip-knee-ankle intra-joint angular displacements during the stance phase using a dissimilarity index applied on superimposed 3D phase plots. RESULTS: We found significant between-group differences in temporal variables (p ≤ 0.001). Compared to Controls, both Early and Mid (p ≤ 0.05) showed asymmetry in the first double-support time (longer for their injured vs. non-injured leg), while Early generally also showed longer durations in all other phases, regardless of stepping leg. No statistically significant differences were found for spatial intra-joint symmetry between groups. CONCLUSION: Temporal but not spatial asymmetry in stair descent is often present early after ACLR; it may remain for up to 18 months and may underlie subtle intra- and inter-joint compensations. Spatial asymmetry may need further exploration.

Asymmetric loading strategies during squats following anterior cruciate ligament reconstruction: A longitudinal investigation with curve analyses throughout and after rehabilitation.

Investigations of kinetic asymmetries during bilateral squats following anterior cruciate ligament reconstruction (ACLR) are limited to mainly cross-sectional studies and discrete value data extracted at specific knee angles. We assessed loading asymmetries during squats longitudinally throughout rehabilitation using curve analysis and compared patient-reported outcome measures (PROMs) between those with and without asymmetry. Bodyweight squats were performed by 24 individuals (13 females) post-ACLR on three occasions: (1) Early 2.9 (1.1) months; (2) Mid 8.8 (3.1) months; (3) at Return to Sport (RTS) 13.1 (3.6) months; and 29 asymptomatic controls (22 females) once. Time-normalized between-leg asymmetry curves of sagittal plane hip, knee, and ankle moments and vertical ground reaction forces were compared using functional data analysis methods. Individual asymmetrical loading for ACLR was classified when exceeding the 95% confidence interval of controls during ≥50% of the squat. At Early, ACLR had greater asymmetry than controls for knee (15%-100% eccentric phase; 0%-100% concentric) and ankle flexion moments (56%-65% concentric). At Mid, ACLR had greater asymmetry for knee (41%-72% eccentric) and ankle flexion moments (56%-69% concentric). No between-group differences were found at RTS. From Early to RTS, ACLR reduced asymmetry for hip (21%-46% eccentric), knee (27%-58% concentric), and ankle flexion moments (21%-57% eccentric). At Early, 11/24 underloaded their ACLR knee and 1 overloaded compared with controls. At RTS, 4 underloaded and 6 overloaded. No differences in PROMs were found based on loading asymmetry. Beyond the early phase of rehabilitation from ACLR, individual-level analyses are required to reveal differing loading strategies during bilateral squats.

A Longitudinal Case-Control Study of a Female Athlete Preinjury and After ACL Reconstruction: Hop Performance, Knee Muscle Strength, and Knee Landing Mechanics.

Athletes with an anterior cruciate ligament (ACL) injury followed by ACL reconstruction (ACLR) often perform various testing to guide return to sport, but preinjury data are rarely available for comparison. This longitudinal case-control study reports absolute value and between-leg symmetry data on maximal performances for single-leg hop height and distance, muscle strength, and side hop landing mechanics of an 18-year-old female soccer athlete collected 5 months before sustaining an ACL injury and again at 10, 13, and 29 months post-ACLR. Her data were compared across test sessions and to cross-sectional data of 15 asymptomatic female athletes.

Side-hops challenge knee control in the frontal and transversal plane more than hops for distance or height among ACL-reconstructed individuals.

We compared knee landing mechanics with presumed relation to risk of anterior cruciate ligament (ACL) injury among three single-leg hop tests and between legs in individuals with unilateral ACL reconstruction. Thirty-four participants (>10 months' post-surgery, 23 females) performed the standardised rebound side hop (SRSH), maximal hop for distance (OLHD) and maximal vertical hop (OLVH). We calculated the following knee outcomes from motion capture and force plate data: finite helical axis inclination angles (approximates knee robustness), frontal and transversal plane angles at initial contact, peak angles of abduction and internal rotation during landing, and peak external moments of flexion, abduction and internal rotation during landing. Repeated-measures MANOVA analysis ('sex' as covariate) confirmed that SRSH induced greater angles and moments, particularly in the frontal plane, compared to OLHD and OLVH. There was between-leg asymmetry for peak knee flexion moment for males during OLHD and OLVH, and for females during SRSH. Our results advocate the SRSH over OLHD and OLVH for assessment of knee landing control to screen for movement patterns potentially related to ACL injury risk. However, clear differences in both knee kinematics and kinetics between OLHD and SRSH motivate the use of both tests to evaluate different aspects of landing control.

A Minority of Athletes Pass Symmetry Criteria in a Series of Hop and Strength Tests Irrespective of Having an ACL Reconstructed Knee or Being Noninjured.

BACKGROUND: Between-leg symmetry in 1-leg hop and knee strength performances is considered important after anterior cruciate ligament reconstruction (ACLR) to facilitate a safer return to sport. While few athletes with ACLR demonstrate symmetry in test batteries, reference data for noninjured athletes are lacking, thus questioning how ACLR-specific poor symmetry is. HYPOTHESIS: Athletes with ACLR (hamstring autograft) show lower symmetry and have a lower proportion of symmetric individuals than noninjured athletes for knee flexion strength but not for hop for distance, vertical hop, and knee extension strength. STUDY DESIGN: Cross-sectional. LEVEL OF EVIDENCE: Level 3. METHODS: A total of 47 athletes with ACLR (median 13.0 months post-ACLR) who had returned to their sport, and 46 noninjured athletes participated. Symmetry was calculated between the worse and better legs for each test and combinations of them using the limb symmetry index (LSIWORSE-BETTER, ranging from 0% to 100%). The 2 groups were compared for these values and the proportions of individuals classified as symmetric (LSIWORSE-BETTER ≥90%) using independent t-tests and Fisher's exact tests, respectively. RESULTS: Athletes with ACLR were less symmetric than noninjured athletes for knee flexion strength with a lower LSIWORSE-BETTER (83% vs 91%, P < 0.01) and a lower proportion of symmetric individuals (39% vs 63%, P = 0.04). No differences between groups were revealed for the hop tests, knee extension strength, or combinations of tests (P > 0.05). Only 17% of the athletes with ACLR and 24% of the noninjured athletes demonstrated symmetric performances for all 4 tests. CONCLUSION: Athletes with ACLR (hamstring autograft) showed poorer symmetry in knee flexion strength than noninjured athletes, although both groups had few individuals who passed the test battery's symmetry criteria. CLINICAL RELEVANCE: Symmetry is uncommon among athletes irrespective of ACLR and should be considered regarding expected rehabilitation outcomes and return-to-sport decisions post-ACLR.

Atypical Lower Limb Mechanics During Weight Acceptance of Stair Descent at Different Time Frames After Anterior Cruciate Ligament Reconstruction.

BACKGROUND: An anterior cruciate ligament (ACL) rupture may result in poor sensorimotor knee control and, consequentially, adapted movement strategies to help maintain knee stability. Whether patients display atypical lower limb mechanics during weight acceptance of stair descent at different time frames after ACL reconstruction (ACLR) is unknown. PURPOSE: To compare the presence of atypical lower limb mechanics during the weight acceptance phase of stair descent among athletes at early, middle, and late time frames after unilateral ACLR. STUDY DESIGN: Controlled laboratory study. METHODS: A total of 49 athletes with ACLR were classified into 3 groups according to time after ACLR-early (<6 months; n = 17), middle (6-18 months; n = 16), and late (>18 months; n = 16)-and compared with asymptomatic athletes (control; n = 18). Sagittal plane hip, knee, and ankle angles; angular velocities; moments; and powers were compared between the ACLR groups' injured and noninjured legs and the control group as well as between legs within groups using functional data analysis methods. RESULTS: All 3 ACLR groups showed greater knee flexion angles and moments than the control group for injured and noninjured legs. For the other outcomes, the early group had, compared with the control group, less hip power absorption, more knee power absorption, lower ankle plantarflexion angle, lower ankle dorsiflexion moment, and less ankle power absorption for the injured leg and more knee power absorption and higher vertical ground reaction force for the noninjured leg. In addition, the late group showed differences from the control group for the injured leg revealing more knee power absorption and lower ankle plantarflexion angle. Only the early group took a longer time than the control group to complete weight acceptance and demonstrated asymmetry for multiple outcomes. CONCLUSION: Athletes with different time frames after ACLR revealed atypically large knee angles and moments during weight acceptance of stair descent for both the injured and the noninjured legs. These findings may express a chronically adapted strategy to increase knee control. In contrast, atypical hip and ankle mechanics seem restricted to an early time frame after ACLR. CLINICAL RELEVANCE: Rehabilitation after ACLR should include early training in controlling weight acceptance. Including a control group is essential when evaluating movement patterns after ACLR because both legs may be affected.

Fear of Reinjury Following Anterior Cruciate Ligament Reconstruction Is Manifested in Muscle Activation Patterns of Single-Leg Side-Hop Landings.

OBJECTIVE: The purpose of this study was to determine whether fear of re-injury is manifested in joint kinematics and muscle activation patterns during landings of a standardized rebound side-hop (SRSH), or in patient-reported outcome measures (PROMs), among individuals with anterior cruciate ligament reconstruction (ACLR). METHODS: In this cross-sectional observational study, 38 individuals within 2 years post-ACLR were grouped into HIGH-FEAR (n = 21, median 11.2 months post-surgery) or LOW-FEAR (n = 17, median 10.1 months post-surgery) based on a discriminating question (Q9; Tampa Scale of Kinesiophobia-17). These individuals and 39 asymptomatic controls performed the SRSH. Three-dimensional motion recordings were used to calculate trunk, hip, and knee joint angles at initial contact and range of respective joint motion during landing. Surface electromyography registered mean amplitudes and co-contraction indexes for thigh muscles during pre-activation (50 ms) and landing phases. PROMs of knee function, knee health, and physical activity were also analyzed. RESULTS: The HIGH-FEAR and LOW-FEAR classification was corroborated by distinct Tampa Scale of Kinesiophobia-17 total and subscale scores and revealed distinguishable muscle activation patterns. HIGH-FEAR demonstrated higher biceps femoris electromyography amplitude and higher anterior-posterior co-contraction index during landing than both LOW-FEAR and controls. However, there were no fear-related differences for kinematics or PROMs. Instead, both ACLR subgroups showed different kinematics at initial contact to controls; HIGH-FEAR with more trunk, hip, and knee flexion, and LOW-FEAR with more hip and knee flexion. CONCLUSION: Individuals with ACLR who had high fear of re-injury seem to have adopted a protective strategy with higher muscular activation patterns, presumably to stabilize the knee joint, compared with individuals with low fear of re-injury and controls. SRSH landing kinematics or knee-related PROMs may not be as sensitive to fear of re-injury. IMPACT: Fear of reinjury following anterior cruciate ligament injury should be evaluated as an independent psychological outcome throughout rehabilitation after ACLR for improved return to sport transition. LAY SUMMARY: If you have an anterior cruciate ligament injury treated with reconstructive surgery, you might have a high fear of reinjury, and that can change how you activate the muscles around your knee. Your physical therapist can do a simple screening test in addition to functional tests to help reduce your fear and improve your treatment outcomes.

Test-retest reliability measures for curve data: an overview with recommendations and supplementary code.

The purpose of this paper is to provide an overview of available methods for reliability investigations when the outcome of interest is a curve. Curve data, or functional data, is commonly collected in biomechanical research in order to better understand different aspects of human movement. Using recent statistical developments, curve data can be analysed in its most detailed form, as functions. However, an overview of appropriate statistical methods for assessing reliability of curve data is lacking. A review of contemporary literature of reliability measures for curve data within the fields of biomechanics and statistics identified the following methods: coefficient of multiple correlation, functional limits of agreement, measures of distance and similarity, and integrated pointwise indices (an extension of univariate reliability measures to curve data, inclusive of Pearson correlation, intraclass correlation, and standard error of measurement). These methods are briefly presented, implemented (R-code available as supplementary material) and evaluated on simulated data to highlight advantages and disadvantages of the methods. Among the identified methods, the integrated intraclass correlation and standard error of measurement are recommended. These methods are straightforward to implement, enable results over the domain, and consider variation between individuals, which the other methods partly neglect.

Test-retest reliability of entire time-series data from hip, knee and ankle kinematics and kinetics during one-leg hops for distance: Analyses using integrated pointwise indices.

Motion capture systems enable in-depth interpretations of human movements based on data from three-dimensional joint angles and moments. Such analyses carry important bearings for evaluation of movement control during for instance hop landings among sports-active individuals from a performance perspective but also in rehabilitation. Recent statistical development allows analysis of entire time-series of angle and moment during hops using functional data analysis, but the reliability of such multifaceted data is not established. We used integrated pointwise indices (intra-class correlation, ICC; standard error of measurement, SEM) to establish the test-retest reliability of three-dimensional hip, knee and ankle angle and moment curves during landings of one-leg hop for distance (OLHD) in 23 asymptomatic individuals aged 18-28. We contrasted these findings to reliability of discrete variables extracted at specific events (initial contact, peak value). We extended the calculations of ICC and SEM to handle unbalanced situations (varying number of repetitions) to include all available data. Hip and knee angle curves proved reliable with stable ICC curves throughout the landing, with integrated ICCs ≥ 0.71 for all planes except for knee internal/external rotation (ICC = 0.57). Hip and knee moment curves and ankle angle and moments were less reliable and less stable, particularly in the first ~ 10-25% of the landing (integrated ICCs 0.44-0.57). Curve data were generally not in agreement with the results for discrete event data, thus advocating analysis of curve data which contains more information. To conclude, hip and knee angle curve data during OLHD landings can reliably be evaluated, while moment curves necessitate careful consideration.

A novel standardised side hop test reliably evaluates landing mechanics for anterior cruciate ligament reconstructed persons and controls.

We propose a novel one-leg standardised rebound side-hop test (SRSH) specifically designed for detailed analysis of landing mechanics. Anterior cruciate ligament reconstructed persons (ACLR, n = 30) and healthy-knee controls (CTRL, n = 30) were tested for within-session and test-retest (CTRL only, n = 25) reliability and agreement. Trunk, hip and knee angles and moments in sagittal, frontal, and transversal planes during landing, including time to stabilisation (TTS), were evaluated using intra-class correlations (ICCs), average within-person standard deviations (SW) and minimal differences. Excellent within-session reliability were found for angles in both groups (most ICCs > 0.90, SW ≤ 5°), and excellent to good for moments (most ICCs > 0.80, SW ≤ 0.34 Nm/kg). Only knee internal rotation moment showed poor reliability (ICC < 0.4). Test-retest results were excellent to fair for all angles and moments (ICCs 0.47-0.91, SW < 5° and ≤ 0.25 Nm/kg), except for peak trunk lateral bending angle and knee internal rotation moment. TTS showed excellent to fair within-session reliability but poor test-retest results. These results, with a few exceptions, suggest promising potential of evaluating landing mechanics during the SRSH for ACLR and CTRL, and emphasise the importance of joint-specific movement control variables in standardised tasks.

Individuals With an Anterior Cruciate Ligament-Reconstructed Knee Display Atypical Whole Body Movement Strategies but Normal Knee Robustness During Side-Hop Landings: A Finite Helical Axis Analysis.

BACKGROUND: Atypical knee joint biomechanics after anterior cruciate ligament reconstruction (ACLR) are common. It is, however, unclear whether knee robustness (ability to tolerate perturbation and maintain joint configuration) and whole body movement strategies are compromised after ACLR. PURPOSE: To investigate landing control after ACLR with regard to dynamic knee robustness and whole body movement strategies during sports-mimicking side hops, and to evaluate functional performance of hop tests and knee strength. STUDY DESIGN: Controlled laboratory study. METHODS: An 8-camera motion capture system and 2 synchronized force plates were used to calculate joint angles and moments during standardized rebound side-hop landings performed by 32 individuals with an ACL-reconstructed knee (ACLR group; median, 16.0 months after reconstruction with hamstring tendon graft [interquartile range, 35.2 months]) and 32 matched asymptomatic controls (CTRL). Dynamic knee robustness was quantified using a finite helical axis approach, providing discrete values quantifying divergence of knee joint movements from flexion-extension (higher relative frontal and/or transverse plane motion equaled lower robustness) during momentary helical rotation intervals of 10°. Multivariate analyses of movement strategies included trunk, hip, and knee angles at initial contact and during landing and hip and knee peak moments during landing, comparing ACLR and CTRL, as well as legs within groups. RESULTS: Knee robustness was lower for the first 10° motion interval after initial contact and then successively stabilized for both groups and legs. When landing with the injured leg, the ACLR group, as compared with the contralateral leg and/or CTRL, demonstrated significantly greater flexion of the trunk, hip, and knee; greater hip flexion moment; less knee flexion moment; and smaller angle but greater moment of knee internal rotation. The ACLR group also had lower but acceptable hop and strength performances (ratios to noninjured leg >90%) except for knee flexion strength (12% deficit). CONCLUSION: Knee robustness was not affected by ACLR during side-hop landings, but alterations in movement strategies were seen for the trunk, hip, and knee, as well as long-term deficits in knee flexion strength. CLINICAL RELEVANCE: Knee robustness is lowest immediately after landing for both the ACLR group and the CTRL and should be targeted in training to reduce knee injury risk. Assessment of movement strategies during side-hop landings after ACLR should consider a whole body approach.

A novel test reliably captures hip and knee kinematics and kinetics during unanticipated/anticipated diagonal hops in individuals with anterior cruciate ligament reconstruction.

Unanticipated land-and-cut maneuvers might emulate lower limb mechanics associated with anterior cruciate ligament (ACL) injury. Reliability studies on landing mechanics of such maneuvers are however lacking. This study investigated feasibility and within-session reliability of landing mechanics of a novel one-leg double-hop test, mimicking a land-and-cut maneuver, in individuals with ACL reconstruction (ACLR). Our test comprised a forward hop followed by a diagonal hop in either of two directions (medial/lateral) under anticipated and unanticipated conditions. Twenty individuals with a unilateral ACLR (aged 24.2 ±â€¯4.2 years, 0.7-10.8 years post-surgery) performed three successful hops/direction per leg. We determined reliability (intraclass correlation coefficient [ICC]) and agreement (standard error of measurement [SEM]) of 3-dimensional hip and knee angles and moments during the deceleration phase of the land-and-cut maneuver (vulnerable for non-contact ACL injuries). Mean success rate for unanticipated hops was 71-77% and for anticipated hops 91-95%. Both limbs demonstrated moderate-excellent reliability (ICC 95% confidence intervals: 0.50-0.99) for almost all hip and knee peak angles and moments in all planes and conditions, with a few exceptions: poor-good reliability for hip and knee frontal and/or transverse plane variables, especially for lateral diagonal hops. The SEMs were ≤5° and ≤0.23 N·m/kg·m for most peak angles and moments, respectively. Our test seems feasible and showed satisfactory reliability for most hip and knee angles and moments; however, low knee abduction and internal rotation angles and moments, and moderate reliability of these moments deserve consideration. The test appears to challenge dynamic knee control and may prove valuable in evaluation during knee rehabilitation.

Dynamic knee control and movement strategies in athletes and non-athletes in side hops: Implications for knee injury.

Athletes exposed to rapid maneuvers need a high level of dynamic knee stability and robustness, while also controlling whole body movement, to decrease the risk of non-contact knee injury. The effects of high-level athletic training on such measures of movement control have not, however, been thoroughly evaluated. This study investigated whether elite athletes (who regularly perform knee-specific neuromuscular training) show greater dynamic knee robustness and/or different movement strategies than non-athletic controls, in relation to overall knee function. Thirty-nine women (19 athletes, 20 controls) performed standardized rebound side hops (SRSH) while a motion capture system synchronized with two force plates registered three-dimensional trunk, hip, and knee joint angles and moments. Dynamic knee robustness was evaluated using finite helical axis (FHA) inclination angles extracted from knee rotation intervals of 10°, analyzed with independent t tests. Angle and moment curves were analyzed with inferential methods for functional data. Athletes had superior knee function (less laxity, greater hop performances, and strength) but presented similar FHA inclination angles to controls. Movement strategies during the landing phase differed; athletes presented larger (a) hip flexion angles (during 9%-29% of the phase), (b) hip adduction moments (59%-99%), (c) hip internal rotation moments (83%-89%), and (d) knee flexion moments (79%-93%). Thus, elite athletes may have a greater ability than non-athletes to keep the knee robust while performing SRSH more efficiently through increased engagement of the hip. However, dynamic knee robustness associated with lower FHA inclination angles still show room for improvement, thus possibly decreasing knee injury risk.

Introducing a novel test with unanticipated medial/lateral diagonal hops that reliably captures hip and knee kinematics in healthy women.

Despite a vast literature on one-leg hops and cutting maneuvers assessing knee control pre/post-injury of the anterior cruciate ligament (ACL), comprehensive and reliable tests performed under unpredictable conditions are lacking. This study aimed to: (1) assess the feasibility of an innovative, knee-challenging, one-leg double-hop test consisting of a forward hop followed by a diagonal hop (45°) performed medially (UMDH) or laterally (ULDH) in an unanticipated manner; and (2) determine within- and between-session reliability for 3-dimensional hip and knee kinematics and kinetics of these tests. Twenty-two healthy women (22.3 ±â€¯3.3 years) performed three successful UMDH and ULDH, twice 1-4 weeks apart. Hop success rate was 69-84%. Peak hip and knee angles demonstrated moderate to excellent within-session reliability (intraclass correlation coefficient [ICC] 95% confidence interval [CI]: 0.67-0.99, standard error of measurement [SEM] ≤ â€¯3°) and poor to excellent between-session reliability (ICC CI: 0.22-0.94, SEM ≤ 3°) for UMDH and ULDH. The smallest real difference (SRD) was low (≤ 5°) for nearly all peak angles. Peak hip and knee moments demonstrated poor to excellent reliability (ICC CI: 0-0.97) and, in general, moments were more reliable within-session (SEM ≤ 0.14 N.m/kg.m, both directions) than between-session (SRD ≤ 0.43 N.m/kg.m). Our novel test was feasible and, in most but not all cases, provided reliable angle estimates (within-session > between-session, both directions) albeit less reliable moments (within-session > between-session, both directions). The relatively large hip and knee movements in the frontal and transverse planes during the unanticipated hops suggest substantial challenge of dynamic knee control. Thus, the test seems appropriate for evaluating knee function during ACL injury rehabilitation.

ACL-reconstructed and ACL-deficient individuals show differentiated trunk, hip, and knee kinematics during vertical hops more than 20 years post-injury.

PURPOSE: Little is known regarding movement strategies in the long term following injury of the anterior cruciate ligament (ACL), and even less about comparisons of reconstructed and deficient knees in relation to healthy controls. The present purpose was to compare trunk, hip, and knee kinematics during a one-leg vertical hop (VH) ~20 years post-ACL injury between persons treated with surgery and physiotherapy (ACLR), solely physiotherapy (ACLPT), and controls (CTRL). Between-leg kinematic differences within groups were also investigated. METHODS: Sixty-six persons who suffered unilateral ACL injury on average 23 ± 2 years ago (32 ACLR, 34 ACLPT) and 33 controls performed the VH. Peak trunk, hip, and knee angles during Take-off and Landing phases recorded with a 3D motion capture system were analysed with multivariate statistics. RESULTS: Significant group effects during both Take-off and Landing were found, with ACLPT differing from CTRL in Take-off with a combination of less knee flexion and knee internal rotation, and from both ACLR and CTRL in Landing with less hip and knee flexion, knee internal rotation, and greater hip adduction. ACLR also presented different kinematics to ACLPT and CTRL in Take-off with a combination of greater trunk flexion, hip flexion, hip internal rotation, and less knee abduction, and in Landing with greater trunk flexion and hip internal rotation. Further, different kinematics and hop height were found between legs within groups in both Take-off and Landing for both ACL groups, but not for CTRL. CONCLUSION: Different kinematics for the injured leg for both ACL groups compared to CTRL and between treatment groups, as well as between legs within treatment groups, indicate long-term consequences of injury. Compensatory mechanisms for knee protection seem to prevail over time irrespective of initial treatment, possibly increasing the risk of re-injury and triggering the development of osteoarthritis. Detailed investigation of movement strategies during the VH provides important information and a more comprehensive evaluation of knee function than merely hop height. More attention should also be given to the trunk and hip in clinics when evaluating movement strategies after ACL injury. LEVEL OF EVIDENCE: Prospective cohort study, Level II.

Countermovement jump peak force relative to body weight and jump height as predictors for sprint running performances: (in)homogeneity of track and field athletes?

The purpose of this study was to investigate: (a) If variables from 1-leg drop jump (DJ), DJ, squat jump (SJ), and countermovement jump (CMJ) tests can predict sprint performances for sprinters. (b) If sprinters and jumpers can be distinguished based on variables from 1-leg DJ, DJ, SJ, and CMJ tests, also if sprinters and throwers can be distinguished based on variables from stiff leg jump (SLJ), SJ, and CMJ tests. A single linear regression and multiple linear regression analysis approach with models including 2 or 3 variables were used when predicting sprint performances. Five elite sprinters (1 woman) participated in the first subexamination and 5 sprinters (1 woman) vs. 5 jumpers and 6 sprinters vs. 6 throwers (4 women) participated in the second. The force variable CMJ peak force (PF) relative to body weight significantly predicted the sprint performances maximal running velocity through 10-m (V[Combining Dot Above]O2max10m) and 60-m time. The Vmax10m was also predicted by CMJ height. Jump heights from SJ and DJ did not predict sprint performances. The between-group analysis of the athletes showed a nonsignificant group difference with respect to the jump variables. However, planned comparisons between sprinters and throwers showed significant differences in a number of SLJ variables. When constructing training programs for sprinters, the aim should be to improve CMJ PF and CMJ height because of the prediction of Vmax10-m and 60-m time, presumably because of velocity specificity components.