Males and females have different muscle activity patterns during gait after ACL injury and reconstruction.

Kinematic and kinetic changes following anterior cruciate ligament (ACL) rupture and reconstruction (ACLR) have been fundamental to the understanding of mechanical disrupted load as it contributes to the development of posttraumatic osteoarthritis. These analyses overlook the potential contribution of muscle activity as it relates to the joint loading environment. Males and females classified as non-copers present with unique knee kinematics and kinetics after ACL injury. The purpose of this study was to perform sex-specific analyses in these individuals to explore muscle activity timing during gait after ACL rupture. Thirty-nine participants (12 females, 27 males) were enrolled. Muscle activity during gait was evaluated before and after pre-operative physical therapy, and six months after ACLR. Surface electromyography data were evaluated to determine timing (e.g., the time the muscle activity begins ('On') and ends ('Off')) for seven muscles: vastus lateralis and medialis (VL, VM), lateral and medial hamstrings (LH, MH), lateral and medial gastrocnemius (LG, MG), and soleus (SOL). General linear models with generalized estimating equations detected the effects of limb and time for muscle activity timing. Males presented with more limb asymmetries before and after pre-operative PT in the VL On (p < 0.001) and Off (p = 0.007), VM On and Off (p < 0.001), and MH off (p < 0.001), but all limb differences resolved by six months post ACLR. Changes in muscle activity in males were pervasive over time in both limbs. Females presented with no interlimb differences pre-operatively, and only involved limb VL off (p = 0.027) and VM off (p = 0.003) and the LH off in both limbs (p < 0.038) changed over time. Our data indicate that inter-limb differences in muscle activity across time points and changes in muscle activity timing over the course of physical therapy were sex specific. Males presented with more inter-limb differences in muscle activity across time points, and females presented with fewer asymmetries before and after pre-operative physical therapy. These data support that sex-specific adaptations should be taken into consideration when assessing biomechanical changes after ACLR.

Self-assessment during Jump Shot Drills Translates to Decreased Vertical Ground Reaction Forces during Single Limb Drop Jump Landing.

BACKGROUND: Prevention programs reduce hard and stiff landings associated with risk of anterior cruciate ligament (ACL) injury, yet cost and time are barriers to implementation. Providing feedback about landing mechanics during shooting drills at practices using minimal resources and time may improve adherence to educating athletes how to avoid risky mechanics associated with ACL injury when landing. Implementing video, auditory, written, and pictorial feedback into basketball practices to cue athletes on landing mechanics after taking a jump shot may soften the landing. PURPOSE: The purpose of this study was to test whether implementing video, auditory, written, and pictorial feedback into a basketball practice jump shot drill (i.e., double limb drop jump landing task) will result in lesser vertical ground reaction force (vGRF) during a single limb drop jump landing without decreasing maximal jump height. STUDY DESIGN: Observational, Case-control Study. METHODS: During a summer league, 16 female high school basketball players were assigned to an intervention (Int) or control (Con) group. The Int group (n=8) utilized delayed video feedback and task cards (written and pictorial cues) at six practices while the Con group (n=8) received typical coaching only. Cost and compliance with the intervention were measured. Pre- and post-season data collections included five single limb drop jumps from a 31 cm high box onto force plates. The vGRF impulses over the first 10% of landing were calculated for each limb. Data did not differ between limbs, thus data for both limbs were pooled. Two mixed model ANOVAs were used to compare groups over time (p<0.05) for vGRF and maximum jump height, respectively. RESULTS: Compliance with the intervention was 100% and did not increase the time of drills. The implementation cost was less than $10. A time*group interaction (p=0.04; Int significantly decreased vGRF over time), main effect of time (p=0.004), and no main effect of group (p=0.412) were found for vGRF during single limb drop jump landings. A time*group interaction (p=0.03; Int significantly decreased max jump height over time), no main effect of time (p=0.10) and no main effect of group (p=0.32) were found for max jump height. CONCLUSION: Athletes landed more softly and jumped less high during a single limb drop jump landing task after receiving feedback during jump shot drills. High team compliance may occur since the intervention required minimal resources and addressed different learning styles. LEVEL OF EVIDENCE: Level 3b.

Relationships Between Knee Extension Moments During Weighted and Unweighted Gait and Strength Measures That Predict Knee Moments After ACL Reconstruction.

BACKGROUND: Weighted gait increases internal knee extension moment impulses (KEMI) in the anterior cruciate ligament-reconstructed (ACLR) limb; however, limb differences persist. HYPOTHESES: (1) KEMI during normal gait will influence KEMI during weighted gait and (2) peak knee extension (PKE) torque and time to reach PKE torque will predict KEMI during gait tasks. STUDY DESIGN: Descriptive laboratory study. METHODS: Twenty-four women and 14 men completed 3 gait tasks (unweighted, vest, sled) and strength testing after discharge from rehabilitation and clearance to return to sports. KEMI were calculated during the first 25% of stance. PKE torque and time to reach PKE torque were obtained using a dynamometer. Data on the ACLR limb and symmetry indices (SIs) were analyzed for each sex. RESULTS: Women presented with asymmetrical PKE torques and KEMI across tasks. There were three correlations noted for KEMI: between the walk and vest, walk and sled, and vest and sled tasks. Slower time to PKE torque predicted limb asymmetries across tasks and KEMI in the ACLR limb during the sled task. Men presented with asymmetrical PKE torques and KEMI during the sled task. There was a correlation noted for KEMI between walk and vest tasks only. During the sled task, ACLR limb time to PKE torque predicted KEMI in the ACLR limb and PKE torque SI predicted KEMI SI. CONCLUSION: Women use asymmetrical KEMI profiles during all gait tasks, and those with worse KEMI during walking have worse KEMI during weighted gait. Men have asymmetrical KEMI when sled towing, and these KEMIs do not correlate with KEMI during walking or vest tasks. CLINICAL RELEVANCE: PKE torque deficits persist when attempting to return to sports. Only men use gains in PKE torque to improve KEMI profiles. Although quicker PKE torque generation will increase KEMI in women, normalization of KEMI profiles will not occur by increasing rate of force development only. Gait retraining is recommended to correct asymmetrical KEMI profiles used across gait tasks in women.

Muscle Activation Differs between Three Different Knee Joint-Angle Positions during a Maximal Isometric Back Squat Exercise.

The purpose of this study was to compare muscle activation of the lower limb muscles when performing a maximal isometric back squat exercise over three different positions. Fifteen young, healthy, resistance-trained men performed an isometric back squat at three knee joint angles (20°, 90°, and 140°) in a randomized, counterbalanced fashion. Surface electromyography was used to measure muscle activation of the vastus lateralis (VL), vastus medialis (VM), rectus femoris (RF), biceps femoris (BF), semitendinosus (ST), and gluteus maximus (GM). In general, muscle activity was the highest at 90° for the three quadriceps muscles, yet differences in muscle activation between knee angles were muscle specific. Activity of the GM was significantly greater at 20° and 90° compared to 140°. The BF and ST displayed similar activation at all joint angles. In conclusion, knee position alters muscles activation of the quadriceps and gluteus maximus muscles. An isometric back squat at 90° generates the highest overall muscle activation, yet an isometric back squat at 140° generates the lowest overall muscle activation of the VL and GM only.

Biomechanical Profiles When Towing a Sled and Wearing a Weighted Vest Once Cleared for Sports Post-ACL Reconstruction.

BACKGROUND: Though rehabilitation attempts to correct "stiff knee gait" and control for dynamic limb valgus after anterior cruciate ligament reconstruction (ACLR), impaired biomechanics often persist when an individual is cleared to return to sport (RTS). Reduced knee extension moments (KEMs) and knee flexion angles (KFAs) often continue. While at the hip, increased hip adduction angles (HADDAs) and hip internal rotation angles (HIRAs) often persist in spite of dynamic hip stabilization exercises. Sled towing and weighted vest tasks increase KEM and hip extension moments (HEMs) in healthy individuals, yet biomechanical profiles during these tasks after ACLR are unknown. HYPOTHESIS: Weighted gait will increase KEM, HEM, hip abduction moments (HABDMs), and hip external rotation moments (HERMs) and will not increase unwanted biomechanics (limb asymmetries, HIRA, HADDA) compared with normal gait. STUDY DESIGN: Controlled laboratory study. LEVEL OF EVIDENCE: Level 4. METHODS: Fourteen men and 24 women who were 5 to 12 months after ACLR, had no concomitant ligament injuries, and were cleared to RTS were recruited. Sexes were evaluated independently given the sex-specific incidence to ACL injury, reinjury, and gait responses to certain interventions. Joint moment impulses and peak angles over the first 25% of stance were compared between limbs and across tasks (eg, unweighted gait, sled 50% body weight [BW], and vest 50% BW). RESULTS: Men showed that weighted gait increased KEM, HEM, HERM, HADBM (vest only), HADDA, HIRA (sled only), and KFA. Asymmetrical KEM and KFA existed across tasks. Women showed that weighted gait increased KEM, HEM, HERM, HADBM (vest only), HFA (sled only), HADDA, and KFA. Asymmetrical KEM, HEM, HIRA, and KFA (sled only) existed across tasks. CONCLUSION: Weighted gait generally increased joint moments. Unwanted biomechanics were unique for each weighted gait task. CLINICAL RELEVANCE: Though joint moments increased, both tasks created unwanted biomechanics after ACLR. Persistent hip (women only) and KEM asymmetries across tasks when cleared to RTS are concerning given the relationship among these biomechanics and decreased functional performance.

Immediate Effect of Active Abdominal Contraction on Inter-recti Distance.

STUDY DESIGN: Controlled laboratory study. BACKGROUND: Inter-recti distance (IRD) is the measurement of the linear distance between the medial aspects of the rectus abdominis muscle. Inter-recti distance has been reported to decrease in postpartum women during a curl-up maneuver. OBJECTIVE: To determine if IRD decreases with active abdominal contraction in men and in nulliparous and parous women. METHODS: Fifty-six subjects (male, 11; nulliparous female, 22; parous female, 23) participated. Inter-recti distance was measured with the abdominal muscles at rest and during active contraction (curl-up), at 2 locations (above and below the umbilicus), using ultrasound imaging. A mixed-model, repeated-measures analysis of covariance was used for each of the 2 locations, to determine whether IRD differed between contraction states among the 3 groups, with age and umbilicus circumference as covariates. When significant differences were found, planned t test comparisons were made. RESULTS: The parous group's IRD significantly decreased from rest to contraction at both locations, whereas the nulliparous and male groups' IRD did not significantly change from rest to contraction. The nulliparous group's IRD was significantly narrower than the other groups at rest at both locations, and narrower than the parous group during active contraction. CONCLUSION: Parous women had a narrower IRD in the curl-up condition than at rest, as hypothesized. However, an unexpected finding of a lack of significant within-group change in IRD in nulliparous women and men occurred. Findings suggest that the IRD in men may only differ from that of nulliparous women.

Sex-specific gait adaptations prior to and up to 6 months after anterior cruciate ligament reconstruction.

STUDY DESIGN: Controlled longitudinal laboratory study. OBJECTIVES: To compare sagittal plane gait mechanics of men and women before and up to 6 months after anterior cruciate ligament reconstruction (ACLR). BACKGROUND: Aberrant gait patterns are ubiquitous after anterior cruciate ligament (ACL) rupture and persist after ACLR despite skilled physical therapy. Sex influences postoperative function and second-ACL injury risk, but its influence on gait adaptations after injury has not been investigated. METHODS: Sagittal plane knee and hip joint excursions during midstance and internal knee and hip extension moments at peak knee flexion were collected in 12 women and 27 men using 3-D gait analysis before (screening) and after preoperative physical therapy (presurgery), and 6 months after ACLR (6 months postsurgery). Repeated-measures analysis-of-variance models were used to determine whether limb asymmetries changed differently over time in men and women. RESULTS: Significant time-by-limb-by-sex interactions were identified for hip and knee excursions and internal knee extension moments (P ≤.007). Both sexes demonstrated smaller knee excursions on the involved limb compared to the uninvolved limb at each time point (P ≤.007), but only women demonstrated a decrease in the involved knee excursion from presurgery to 6 months postsurgery (P = .03). Women also demonstrated smaller hip excursions (P<.001) and internal knee extension moments (P = .005) on the involved limb compared to the uninvolved limb at 6 months postsurgery. Men demonstrated smaller hip excursions and knee moments on the involved limb compared to the uninvolved limb (P<.001) regardless of time. CONCLUSION: The persistence of limb asymmetries in men and women 6 months after ACLR indicates that current postoperative rehabilitation efforts are inadequate for some individuals following ACLR.

The acute effects of unilateral ankle plantar flexors static- stretching on postural sway and gastrocnemius muscle activity during single-leg balance tasks.

The aim of this study was to investigate the acute effects of unilateral ankle plantar flexors static- stretching on surface electromyography (sEMG) and the center of pressure (COP) during a single-leg balance task in both lower limbs. Fourteen young healthy, non-athletic individuals performed unipodal quiet standing for 30s before and after (stretched limb: immediately post-stretch, 10 and 20 minutes and non-stretched limb: immediately post-stretch) a unilateral ankle plantar flexor static- stretching protocol [6 sets of 45s/15s, 70-90% point of discomfort (POD)]. Postural sway was described using the COP area, COP speed (antero-posterior and medio-lateral directions) and COP frequency (antero-posterior and medio-lateral directions). Surface EMG (EMG integral [IEMG] and Median frequency[FM]) was used to describe the muscular activity of gastrocnemius lateralis. Ankle dorsiflexion passive range of motion increased in the stretched limb before and after the static-stretching protocol (mean ± SD: 15.0° ± 6.0 and 21.5° ± 7.0 [p < 0.001]). COP area and IEMG increased in the stretch limb between pre-stretching and immediately post-stretching (p = 0.015 and p = 0.036, respectively). In conclusion, our static- stretching protocol effectively increased passive ankle ROM. The increased ROM appears to increase postural sway and muscle activity; however these finding were only a temporary or transient effect. Key PointsThe postural control can be affected by static- stretching protocol.The lateral gastrocnemius muscle action was increased after the static- stretching protocol.The static- stretching effects remain for less than 10 minutes.

Relationship of the functional movement screen in-line lunge to power, speed, and balance measures.

BACKGROUND: The in-line lunge of the Functional Movement Screen (FMS) evaluates lateral stability, balance, and movement asymmetries. Athletes who score poorly on the in-line lunge should avoid activities requiring power or speed until scores are improved, yet relationships between the in-line lunge scores and other measures of balance, power, and speed are unknown. HYPOTHESIS: (1) Lunge scores will correlate with center of pressure (COP), maximum jump height (MJH), and 36.6-meter sprint time and (2) there will be no differences between limbs on lunge scores, MJH, or COP. STUDY DESIGN: Descriptive laboratory study. LEVEL OF EVIDENCE: Level 3. METHODS: Thirty-seven healthy, active participants completed the first 3 tasks of the FMS (eg, deep squat, hurdle step, in-line lunge), unilateral drop jumps, and 36.6-meter sprints. A 3-dimensional motion analysis system captured MJH. Force platforms measured COP excursion. A laser timing system measured 36.6-m sprint time. Statistical analyses were used to determine whether a relationship existed between lunge scores and COP, MJH, and 36.6-m speed (Spearman rho tests) and whether differences existed between limbs in lunge scores (Wilcoxon signed-rank test), MJH, and COP (paired t tests). RESULTS: Lunge scores were not significantly correlated with COP, MJH, or 36.6-m sprint time. Lunge scores, COP excursion, and MJH were not statistically different between limbs. CONCLUSION: Performance on the FMS in-line lunge was not related to balance, power, or speed. Healthy participants were symmetrical in lunging measures and MJH. CLINICAL RELEVANCE: Scores on the FMS in-line lunge should not be attributed to power, speed, or balance performance without further examination. However, assessing limb symmetry appears to be clinically relevant.

Kinesiophobia after anterior cruciate ligament rupture and reconstruction: noncopers versus potential copers.

STUDY DESIGN: Secondary-analysis, longitudinal cohort study. OBJECTIVES: To compare kinesiophobia levels in noncopers and potential copers at time points spanning pre- and post-anterior cruciate ligament (ACL) reconstruction and to examine the association between changes in kinesiophobia levels and clinical measures. BACKGROUND: After ACL injury, a screening examination may be used to classify patients as potential copers or noncopers based on dynamic knee stability. Quadriceps strength, single-leg hop performance, and self-reported knee function are worse in noncopers. High kinesiophobia levels after ACL reconstruction are associated with poorer self-reported knee function and lower return-to-sport rates. Kinesiophobia levels have not been examined before ACL reconstruction, across the transition from presurgery to postsurgery, or based on potential coper and noncoper classification. METHODS: Quadriceps strength indexes, single-leg hop score indexes, self-reported knee function (Knee Outcome Survey activities of daily living subscale, global rating scale), and kinesiophobia (Tampa Scale of Kinesiophobia [TSK-11]) scores were compiled for potential copers (n = 50) and noncopers (n = 61) from 2 clinical trial databases. A repeated-measures analysis of variance was used to compare TSK-11 scores between groups and across 4 time points (before preoperative treatment, after preoperative treatment, 6 months post-ACL reconstruction, and 12 months post-ACL reconstruction). Correlations determined the association of kinesiophobia levels with other clinical measures. RESULTS: Presurgery TSK-11 scores were significantly higher in noncopers than in potential copers. Postsurgery, no group differences existed. TSK-11 scores in both groups decreased across all time points; however, TSK-11 scores decreased more in noncopers in the interval between presurgery and postsurgery. In noncopers, the decreases in TSK-11 scores from presurgery to postsurgery and after surgery were related to improvements in the Knee Outcome Survey activities of daily living subscale, whereas the association was only present in potential copers after surgery. CONCLUSION: Kinesiophobia levels were high in both noncopers and potential copers preoperatively. Restoration of mechanical knee stability with surgery might have contributed to decreased kinesiophobia levels in noncopers. Kinesiophobia is related to knee function after surgery, regardless of preoperative classification as a potential coper or noncoper.

Lower limb moments differ when towing a weighted sled with different attachment points.

Sprinting while towing a sled improves sprinting parameters, however, only kinematic and temporal-spatial variables have been reported. The purpose of this study was to determine how lower extremity joint moment impulses alter when towing a sled compared to normal walking. Twelve participants walked normally, walked while towing a sled with a 50% body weight load attached at the waist, and with a 50% body weight load attached at the shoulders. Joint moment impulses were calculated for the hip, knee, and ankle. A mixed-model ANOVA with a between-subject factor of limb and repeated measures of condition was used to compare differences between limbs and towing conditions for each joint. Towing a sled increased joint moment impulses at the hip, knee, and non-dominant ankle. When compared with normal walking waist attachment increased hip extension moment impulse by 214.5% (-3.31 vs. -10.41Nms/kg), and shoulder attachment increased knee extension moment impulse by 166.9% (4.62 vs. 12.33Nms/kg). The dominant limb produced greater knee extension moment impulse (p < 0.001), while the non-dominant limb produced greater hip extension (p < 0.001) and ankle plantarflexion moment impulse (p < 0.001) across all conditions. Results suggest that walking while towing may increase hip and knee extension strength.

Unilateral stance strategies of athletes with ACL deficiency.

Aberrant movement strategies are characteristic of ACL-deficient athletes with recurrent knee instability (noncopers), and may instigate premature or accelerate joint degradation. Biomechanical evaluation of kinematic changes over time may elucidate noncopers' responses to neuromuscular intervention and ACL reconstruction (ACLR). Forty noncopers were randomized into a perturbation group or a strength training only group. We evaluated the effects of perturbation training, and then gender on knee angle and tibial position during a unilateral standing task before and after ACLR. No statistically significant interactions were found. Before surgery, the strength training only group demonstrated knee angle asymmetry, but 6 months after ACLR, both groups presented with similar knee flexion between limbs. Aberrant and asymmetrical tibial position was found only in females following injury and ACLR. Neither treatment group showed distinct unilateral standing strategies following intervention; however, males and female noncopers appear to respond uniquely to physical therapy and surgery.

Preoperative predictors for noncopers to pass return to sports criteria after ACL reconstruction.

Less than 50% of athletes pass criteria to return to sports (RTS) 6 months after ACL reconstruction (ACLR). Using data on 38 noncopers, we hypothesized that preoperative age, quadriceps strength index (QI), and knee flexion moments (KFM) during gait would predict the ability to pass/fail RTS criteria and that preoperative quadriceps strength gains would be predictive of passing RTS criteria. Gait analysis and strength data were collected before and after a preoperative intervention and 6 months after ACLR. Age, QI, and KFM each contributed to the predictability to pass or fail RTS criteria 6 months after ACLR. Collectively, the variables predict 69% who would pass and 82% who would fail RTS criteria 6 months after ACLR. Younger athletes who have symmetrical quadriceps strength and greater KFM were more likely to pass RTS criteria. Further, 63% of those who increased preoperative quadriceps strength passed RTS criteria, whereas 73% who did not failed. Increasing quadriceps strength in noncopers before ACLR seems warranted.

Time line for noncopers to pass return-to-sports criteria after anterior cruciate ligament reconstruction.

STUDY DESIGN: Randomized clinical trial. OBJECTIVES: Determine effective interventions for improving readiness to return to sports postoperatively in patients with complete, unilateral, anterior cruciate ligament (ACL) rupture who do not compensate well after the injury (noncopers). Specifically, we compared the effects of 2 preoperative interventions on quadriceps strength and functional outcomes. BACKGROUND: The percentage of athletes who return to sports after ACL reconstruction varies considerably, possibly due to differential responses after acute ACL rupture and different management. Prognostic data for noncopers following ACL reconstruction is absent in the literature. METHODS: Forty noncopers were randomly assigned to receive either progressive quadriceps strength-training exercises (STR group) or perturbation training in conjunction with strength-training exercises (PERT group) for 10 preoperative rehabilitation sessions. Postoperative rehabilitation was similar between groups. Data on quadriceps strength indices [(involved limb/uninvolved limb force) x 100], 4 hop score indices, and 2 self-report questionnaires were collected preoperatively and 3, 6, and 12 months postoperatively. Mann-Whitney U tests were used to compare functional differences between the groups. Chi-square tests were used to compare frequencies of passing functional criteria and reasons for differences in performance between groups postoperatively. RESULTS: Functional outcomes were not different between groups, except a greater number of patients in the PERT group achieved global rating scores (current knee function expressed as a percentage of overall knee function prior to injury) necessary to pass return-to-sports criteria 6 and 12 months after surgery. Mean scores for each functional outcome met return-to-sports criteria 6 and 12 months postoperatively. Frequency counts of individual data, however, indicated that 5% of noncopers passed RTS criteria at 3, 48% at 6, and 78% at 12 months after surgery. CONCLUSION: Functional outcomes suggest that a subgroup of noncopers require additional supervised rehabilitation to pass stringent criteria to return to sports. LEVEL OF EVIDENCE: Therapy, level 2b.Note: If watching the first video, we recommend downloading and referring to the accompanying PowerPoint slides for any text that is not readable.

Perturbation training prior to ACL reconstruction improves gait asymmetries in non-copers.

We investigated whether preoperative perturbation training would help anterior cruciate ligament (ACL) deficient individuals who complain of knee instability ("non-copers") regain quadriceps strength and walk normally after ACL reconstruction. Nineteen non-copers with acute ACL injury were randomly assigned into a perturbation group (PERT) or a strengthening group (STR). The PERT group received specialized neuromuscular training and progressive quadriceps strength training, whereas the STR group received progressive quadriceps strength training only. We compared quadriceps strength indexes and knee excursions during the mid-stance phase of gait preoperatively to data collected 6 months after ACL reconstruction. Analyses of Variance with repeated measures (time/limb) were conducted to compare quadriceps strength index values over time (time x group) and differences in knee excursions in limbs between groups over time (limb x time x group). If significance was found, post hoc analyses were performed using paired and independent t-tests. Quadriceps strength indexes before intervention (Pert: 87.2%; Str: 75.8%) improved 6 months after ACL reconstruction in both groups (Pert: 97.1%; Str: 94.4%). Non-copers who received perturbation training preoperatively had no differences in knee excursions between their limbs 6 months after ACL reconstruction (p = 0.14), whereas those who received just strength training continued to have smaller knee excursions during the mid-stance phase of gait (p = 0.007). Non-copers strength and knee excursions were more symmetrical 6 months postoperatively in the group that received perturbation training and progressive quadriceps strength training than the group who received strength training alone.