Timothy E. Hewett

Core stability training, operationally defined as training focused to improve trunk and hip control, is an integral part of athletic development, yet little is known about its direct relation to athletic performance. This systematic review focuses on identification of the association between core stability and sports-related performance measures. A secondary objective was to identify difficulties encountered when trying to train core stability with the goal of improving athletic performance. A systematic search was employed to capture all articles related to athletic performance and core stability training that were identified using the electronic databases MEDLINE, CINAHL and SPORTDiscus™ (1982–June2011). A systematic approach was used to evaluate 179 articles identified for initial review. Studies that performed an intervention targeted toward the core and measured an outcome related to athletic or sport performances were included, while studies with a participant population aged 65 years or older were excluded. Twenty-four in total met the inclusionary criteria for review. Studies were evaluated using the Physical Therapy Evidence Database (PEDro) scale. The 24 articles were separated into three groups, general performance (n=8), lower extremity (n=10) and upper extremity (n = 6), for ease of discussion. In the majority of studies, core stability training was utilized in conjunction with more comprehensive exercise programmes. As such, many studies saw improvements in skills of general strengths such as maximum squat load and vertical leap. Surprisingly, not all studies reported measurable increases in specific core strength and stability measures following training. Additionally, investigations that targeted the core as the primary goal for improved outcome of training had mixed results. Core stability is rarely the sole component of an athletic development programme, making it difficult to directly isolate its affect on athletic performance. The population biases of some studies of athletic performance also confound the results. Targeted core stability training provides marginal benefits to athletic performance. Conflicting findings and the lack of a standardization for measurement of outcomes and training focused to improve core strength and stability pose difficulties. Because of this, further research targeted to determine this relationship is necessary to better understand how core strength and stability affect athletic performance.

Although intrinsic and extrinsic risk factors for anterior cruciate ligament (ACL) injury have been explored extensively, the factors surrounding the inciting event and the biomechanical mechanisms...

Orthopedics | Neuromuscular training has a significant effect on reducing relative ACL injury risk in female athletes in high-risk landing and cutting sports like soccer, basketball, volleyball, and team handball. As many as 1 in 20 collegiate-level and 1 in 50 to 100 high school-level female athletes sustain an anterior cruciate ligament (ACL) injury during any given year of varsity sports.1,2 The answer to

Patellofemoral pain (PFP) is a common disorder in female athletes with an undefined etiology. PFP symptoms can affect up to 30% of adolescents (13-19 years). Of these, PFP may cause 74% to limit or stop their sport participation. Purpose: The purpose of this study was to evaluate measures of lower extremity strength, motion and load prospectively to examine their relationship with PFP development. Our hypothesis was that increased dynamic knee abduction and decreased hip abduction strength would be associated with PFP in female athletes relative to teammates without PFP. Methods: Two hundred forty middle and high school aged female athletes were evaluated by a physician for active PFP (APFP) prior to the start of their basketball season. In addition, laboratory analyses of each athlete's hip isokinetic strength and hip, knee and ankle biomechanics during landing were conducted. The athletes were monitored on a weekly basis for athletic exposures (AEs) and the onset of any new PFP (NPFP). The athletes were also subsequently re-evaluated for any new PFP by the same physician at the conclusion of the basketball season. Results: The point prevalence of APFP at the beginning of the season was 14.2 per 100 athletes. The cumulative incidence risk and rate for the development of NPFP during the season was 9.7 per 100 athletes and 1.09 per 1000 AEs, respectively. All new cases of PFP occurred in the middle school-aged athletes. Biomechanical analyses indicated a significant interaction (p = 0.04) of increased knee abduction moment at initial contact in APFP and NPFP involved limbs relative to CTRL and their uninvolved limbs (Figure 1). The post hoc analysis of involved limbs showed that external knee abduction moment at initial contact was increased (95%CI: 0.49 to 4.40 Nm) in the APFP relative to CTRL. Hip strength or static knee abduction angle did not discriminate between study groups (p > 0.05). Conclusions: The current study results did not directly support the hypothesis that decreased hip abduction strength was related to PFP development. The increased knee abduction in APFP, and the interaction of increased knee abduction in APFP and NPFP involved limbs relative to CTRL and their uninvolved limbs, indicate that increased knee abduction loads at landing may contribute to increased risk of PFP. Future prospective and longitudinal study designs of these potential neuromuscular correlates underlying PFP in middle school aged female basketball players are warranted. Interestingly all new PFP occurred in the middle school aged female basketball players. The data suggest that neuromuscular training focused to reduce initial contact knee abduction implemented at a young age (10-12 years) level should be assessed to determine its effectiveness to minimize lower extremity pathomechanics to PFP and reduce the occurrence of PFP during sports participation in middle school or higher school levels.

Objective Impaired biomechanics and neuromuscular control have been suggested as probable links to female sex bias in the onset of patellofemoral pain syndrome. There are limited objective, clinical measures for assessment of impaired biomechanics and neuromuscular control. The primary objective of this investigation was to examine sex differences in vertical ground reaction force (vGRF) and force loading rate in young athletes performing maximum, repeated vertical single-leg hops (RVSHs). The authors hypothesised that females would demonstrate greater vGRF and force loading rate than males and show interlimb differences in force attenuation. Design Cross-sectional study. Setting Paediatric sports medicine clinic. Participants 109 Healthy high school, soccer and basketball athletes. Assessment of risk factors Participants performed RVSHs for 15 seconds on a portable force plate with a sampling rate of 400 Hz (Accupower; AMTI, Watertown, Massachusetts, USA). Main outcome measurements Raw vGRF was filtered with a generalised cross-validation spline using a 50-Hz cutoff frequency and then normalised to potential energy. Force loading rate was calculated by dividing normalised vGRF by time-to-peak force. Group means were compared using analysis of variance. Results The females demonstrated significantly greater normalised vGRF (pConclusions The female athletes may have altered force attenuation capability during RVSHs as identified by increased vGRF and force loading rate compared with the male athletes. Portable force plates may be potential tools to identify altered force attenuation in clinical settings.

A high school forward rebounds the basketball, as she has thousands of times before. She lands with a flat foot, extended knee, and torso leaning awkwardly sideways, as her knee buckles inward. An audible pop is heard and felt as the anterior cruciate ligament (ACL) in her knee tears and ends her season, compromising her hopes of a college scholarship and perhaps even her expectation of a long, active, and healthy life. My M.D./Ph.D. student Carmen, who began working in my laboratory after both she and her identical twin sister suffered devastating noncontact ACL injuries while playing high school sports, recently gave me the gift of an irreverent treatise titled The Black Swan: The Impact of the Highly Improbable. Written by self-assured and self-described "empirical skeptic" Nassim Nicolas Taleb, the running theme of the book is a zealous critique of our ability to predict unexpected events, which he refers to as "black swans." Taleb's definition of a black swan is an event that is rare, has a major impact, and to which we teleologically ascribe the obvious reasons for its happening, but only after it has already occurred. My student gave me the book because "it reminded her of me"! As an empirical skeptic of sorts myself, I was only a page or two into the prologue when I realized that a noncontact ACL injury is, by Taleb's definition, a black swan. The underlying mechanisms of noncontact ACL injuries have yet to be defined precisely; however, we now have a relatively good understanding of the mechanisms and interventions to prevent these injuries. Although I agree with Taleb that chaotic events are difficult, if not impossible, to predict, most of the available evidence indicates that prophylactic interventions that target underlying mechanisms of ACL injuries can decrease risk. Theories for the underlying mechanisms of these injuries may be divided into intrinsic and extrinsic mechanisms. Extrinsic factors include variables such as playing surface, shoe type, and number of risk exposures. Intrinsic mechanisms include anatomical, hormonal, and most importantly, neuromuscular factors. Neuromuscular mechanisms should be emphasized because they are the intrinsic factors that appear to have the greatest effect and the only ones we can readily alter. Anatomic variables include increased quadriceps (Q)-angles or decreased notch width, which may strain or impinge the ACL. Hormonal theories propose that estrogen increases ligamentous laxity of the ACL, predisposing it to injury. Systematic review of the literature shows that there is a slight increase in ACL laxity during the postovulatory phase of the menstrual cycle, but the injury events show significant clumping during the preovulatory phase of the cycle. Hence, these "predictive" factors are as chaotic (and contradictory) as the injury occurrences themselves! It is too much to expect of naïve scientists to discover the contributions of such complex hormonal feedback and feed-forward systems on such an acute injury event. Finally, a multitude of studies show neuromuscular control differences between women and men. However, a major caveat to these studies is that if a measurable variable is observed to be different between the sexes, we cannot conclude that this difference must underlie the injury risk disparity between the sexes. We need to remember that men experience many ACL injuries, too. Despite intensive study of ACL injuries during the past three decades, previous reports on actual ACL injuries were based on interviews with the athletes or descriptive analyses of videotapes.

Background: Anterior cruciate ligament (ACL) injury is a devastating injury that puts an athlete at high risk of future osteoarthritis. Identification of risk factors and development of ACL prevention programmes likely decrease injury risk. Although studies indicate that sagittal plane biomechanical factors contribute to ACL loading mechanisms, it is unlikely that non-contact ACL injuries occur solely in a sagittal plane. Some authors attempt to ascribe the solely sagittal plane injury mechanism to both female and male ACL injuries and rebuff the concept that knee “valgus” is associated with isolated ACL injury. Prospective studies that utilise coupled biomechanical and epidemiological approaches demonstrated that frontal knee motions and torques are strong predictors of future non-contact ACL injury risk in female athletes. Video analysis studies also indicate a frontal plane “valgus collapse” mechanism of injury in women. As load sharing between knee ligaments is complex, frontal as well as sagittal and transverse plane loading mechanisms likely contribute to non-contact ACL injury. The purpose of this review is to summarise existing evidence regarding ACL injury mechanisms and to propose that sex-specific mechanisms of ACL injury may occur, with women sustaining injuries by a predominantly “valgus collapse” mechanism. Conclusion: Prevention programmes and interventions that only target high-risk sagittal plane landing mechanics, especially in the female athlete, are likely to be less effective in ameliorating important frontal and transverse plane contributions to ACL injury mechanisms and could seriously hamper ACL injury prevention efforts. Programmes that target the reduction of high-risk valgus and sagittal plane movements will probably prove to be superior for ACL injury prevention.

Background: The combined positioning of the trunk and knee in the coronal and sagittal planes during non-contact anterior cruciate ligament (ACL) injury has not been previously reported. Hypothesis: During ACL injury female athletes demonstrate greater lateral trunk and knee abduction angles than ACL-injured male athletes and uninjured female athletes. Design: Cross-section control-cohort design. Methods: Analyses of still captures from 23 coronal (10 female and 7 male ACL-injured players and 6 female controls) or 28 sagittal plane videos performing similar landing and cutting tasks. Significance was set at p⩽0.05. Results: Lateral trunk and knee abduction angles were higher in female compared to male athletes during ACL injury (p⩽0.05) and trended toward being greater than female controls (p = 0.16, 0.13, respectively). Female ACL-injured athletes showed less forward trunk lean than female controls (mean (SD) initial contact (IC): 1.6 (9.3)° vs 14.0 (7.3)°, p⩽0.01). Conclusion: Female athletes landed with greater lateral trunk motion and knee abduction during ACL injury than did male athletes or control females during similar landing and cutting tasks. Clinical relevance: Lateral trunk and knee abduction motion are important components of the ACL injury mechanism in female athletes as observed from video evidence of ACL injury.

Objective A multifactorial combination of predictors may increase anterior cruciate ligament (ACL) injury risk in athletes. The objective of this twin study was to examine these risk factors to identify commonalities in risk factors that predisposed female fraternal twins to ACL injury. Methods Female twins in high-risk sports were prospectively measured prior to an injury for neuromuscular control using three-dimensional motion analysis during landing, hamstrings and quadriceps muscular strength on a dynamometer and joint laxity using a modified Beighton–Horan index and a Compu-KT arthrometer. Intraoperative measures of femoral intercondylar notch width were recorded during ACL reconstruction. Results Abduction angles were increased at one knee in both of the twin sister athletes relative to uninjured controls at initial contact and at maximum displacement during landing. The twin female athletes that went on to ACL injury also demonstrated decreased peak knee flexion motion at both knees than uninjured females during landing. The twin athletes also had increased joint laxity and decreased hamstrings to quadriceps (H/Q) torque ratios compared to controls. Femoral intercondylar notch widths were also below the control mean in the twin siblings. Conclusions Prescreened mature female twins that subsequently experienced ACL injury demonstrated multiple potential risk factors including: increased knee abduction angles, decreased knee flexion angles, increased general joint laxity, decreased H/Q ratios and femoral intercondylar notch width.