Randy J. Schmitz

Triple-Hop Distance as a Valid Predictor of Lower Limb Strength and Power

CONTEXT Hop tests are functional tests that reportedly require strength, power, and postural stability to perform. The extent to which a triple-hop distance (THD) test measures each of these characteristics is relatively unknown. OBJECTIVE To determine the extent to which the THD predicts performance on clinical measures of power, strength, and balance in athletic individuals. DESIGN Within-subjects correlational study. SETTING Station-based, preseason screening of athletes. PATIENTS OR OTHER PARTICIPANTS Forty National Collegiate Athletic Association Division I-AA mens and womens soccer student-athletes (20 women, 20 men; age = 20.0 +/- 1.4 years, height = 172.8 +/- 9.2 cm, mass = 71.9 +/- 8.9 kg). INTERVENTION(S) As part of a comprehensive preseason screening of athletes, participants completed the Balance Error Scoring System (BESS) test, 3 trials each of the THD and vertical jump, and 5 repetitions each of concentric isokinetic quadriceps and hamstrings strength testing at 60 degrees /s and 180 degrees /s. Bivariate correlations and linear regression analyses determined the extent to which THD (cm) predicted each of the strength, power, and balance measures. MAIN OUTCOME MEASURE(S) Maximal vertical jump height (cm), total BESS error scores, and quadriceps (Quad(60), Quad(180)) and hamstrings (Ham(60), Ham(180)) isokinetic maximum peak torque (Nm) at 60 degrees /s and 180 degrees /s, respectively. RESULTS Triple-hop distance was a strong predictor of vertical jump height, explaining 69.5% of the variance (P < .01). THD also predicted 56.7% of the variance in Ham(60) (P < .01), 55.5% of the variance in Ham(180) (P < .01), 49.0% of the variance in Quad(60) (P < .01), and 58.8% of the variance in Quad(180) (P < .01). No relationships between THD and BESS scores were noted. CONCLUSIONS Triple-hop distance is a useful clinical test to predict an athletes lower extremity strength and power. Although THD was not a predictor of static balance, further research is needed to examine its relationship with more dynamic balance tests.

Activation of the VMO and VL during dynamic mini-squat exercises with and without isometric hip adduction

OBJECTIVE the purpose of this study was to compare vastus medialis obliquus (VMO) and vastus lateralis (VL) activity while performing a mini-squat with and without isometric hip adduction. DESIGN AND SETTING a repeated measures within subjects design was used. Subjects performed two sets of three repetitions of a traditional mini-squat and a mini-squat with concurrent hip adduction (squeeze). SUBJECTS 20 recreationally active subjects (10 men, 10 women age=28.10+/-5.91 years, height=170.94+/-11.03 cm, mass=72.32+/-16.66 kg) with no history of patellofemoral pain (PFP), quadriceps injury, or other knee injury participated in the study. MEASUREMENTS the EMG signal of the VMO and VL was recorded bilaterally during both exercises. EMG data were normalized to the maximal voluntary isometric contraction (MVIC) of the quadriceps produced during seated, isometric knee extension. RESULTS results of repeated measures ANOVAs revealed that the squeeze squat produced significantly greater VMO and VL activity than the traditional squat (p=0.02). For both the traditional and squeeze squats, intrasession reliability from the first to the second set was calculated using intraclass correlation coefficient (ICC) formula (3:1) bilaterally for both the VMO and the VL. All ICC values were greater than 0.9. CONCLUSION combining isometric hip adduction with a mini-squat exercise significantly increases the activity of the quadriceps. Performing mini-squats with isometric hip adduction will be beneficial to patellofemoral patients as they increase quadriceps activity, however, based on our data we cannot conclude that this exercise preferentially recruits the VMO. Further research is needed to determine the exact mechanism by which quadriceps function is altered.

ACL Research Retreat V: An Update on ACL Injury Risk and Prevention, March 25–27, 2010, Greensboro, NC

It has been well recognized that multiple factors, whether individually or in combination, contribute to noncontact anterior cruciate ligament (ACL) injury. The ongoing mission of the ACL Research Retreat is to bring clinicians and researchers together to present and discuss the most recent advances in ACL injury epidemiology, risk factor identification, and injury-risk screening and prevention strategies and to identify future research directives. The sixth retreat held March 22–24, 2012, in Greensboro, North Carolina, was attended by more than 70 clinicians and researchers, including representatives from Canada, Iceland, Japan, The Netherlands, Norway, and South Africa. The meeting featured keynote presentations and discussion forums by expert scientists in ACL injury risk and prevention and 34 podium and poster presentations by attendees. Keynotes delivered by Ajit Chaudhari, PhD (The Ohio State University), Malcolm Collins, PhD (Medical Research Council and University of Cape Town, South Africa), and Tron Krosshaug, PhD (Oslo Sports Trauma Research Center, Norway) described their ongoing work related to proximal trunk control and lower extremity biomechanics, genetic risk factors associated with ACL injury, and methodologic approaches to understanding ACL loading mechanisms, respectively. Discussion forums led by Jennifer Hootman, PhD, ATC, FNATA, FACSM (Centers for Disease Control and Prevention) and Scott McLean, PhD (University of Michigan), focused on strategies for implementing injury-prevention programs in community settings and took a critical look at the strengths and limitations of motion-capture systems and how we might continue to refine our research approaches to increase the relevance and influence of our biomechanical research, respectively. Podium and poster presentations were organized into thematic sessions of anatomical, genetic, and hormone risk factors; the role of body position in ACL injury risk; pubertal and sex differences in lower extremity biomechanics; injury-risk screening and prevention; and methodologic considerations in risk factor research. Substantial time was provided for group discussion throughout the conference. From these discussions, the 2010 consensus statement1 was updated to reflect recent advances in the field and to chart new directions for future research. Following is the updated consensus statement. The presentation abstracts organized by topic and presentation order appear online at http://nata.publisher.ingentaconnect.com/content/nata/jat.

ACL Research Retreat VI: An Update on ACL Injury Risk and Prevention

It has been well recognized that multiple factors, whether individually or in combination, contribute to noncontact anterior cruciate ligament (ACL) injury. The ongoing mission of the ACL Research Retreat is to bring clinicians and researchers together to present and discuss the most recent advances in ACL injury epidemiology, risk factor identification, and injury-risk screening and prevention strategies and to identify future research directives. The sixth retreat held March 22–24, 2012, in Greensboro, North Carolina, was attended by more than 70 clinicians and researchers, including representatives from Canada, Iceland, Japan, The Netherlands, Norway, and South Africa. The meeting featured keynote presentations and discussion forums by expert scientists in ACL injury risk and prevention and 34 podium and poster presentations by attendees. Keynotes delivered by Ajit Chaudhari, PhD (The Ohio State University), Malcolm Collins, PhD (Medical Research Council and University of Cape Town, South Africa), and Tron Krosshaug, PhD (Oslo Sports Trauma Research Center, Norway) described their ongoing work related to proximal trunk control and lower extremity biomechanics, genetic risk factors associated with ACL injury, and methodologic approaches to understanding ACL loading mechanisms, respectively. Discussion forums led by Jennifer Hootman, PhD, ATC, FNATA, FACSM (Centers for Disease Control and Prevention) and Scott McLean, PhD (University of Michigan), focused on strategies for implementing injury-prevention programs in community settings and took a critical look at the strengths and limitations of motion-capture systems and how we might continue to refine our research approaches to increase the relevance and influence of our biomechanical research, respectively. Podium and poster presentations were organized into thematic sessions of anatomical, genetic, and hormone risk factors; the role of body position in ACL injury risk; pubertal and sex differences in lower extremity biomechanics; injury-risk screening and prevention; and methodologic considerations in risk factor research. Substantial time was provided for group discussion throughout the conference. From these discussions, the 2010 consensus statement1 was updated to reflect recent advances in the field and to chart new directions for future research. Following is the updated consensus statement. doi: 10.4085/1062-6050-47.5.13. PMID: 23068597

Thigh Strength and Activation as Predictors of Knee Biomechanics during a Drop Jump Task

PURPOSE To examine whether normalized quadriceps and hamstring strength would predict quadriceps and hamstring muscle activation amplitudes and whether these neuromuscular factors would predict knee kinematics and kinetics during a drop jump task. METHODS Thirty-nine females and 39 males were measured for isometric quadriceps and hamstring strength and were instrumented to obtain surface electromyography, kinematic, and kinetic measures during the initial landing of a drop jump. Multiple linear regressions first examined the relationship between thigh strength and activation then examined whether these neuromuscular variables were predictive of hip and knee flexion excursions, knee extensor moments (KEM), and anterior knee shear forces during the deceleration phase of the drop jump. RESULTS Females versus males produced lower normalized thigh strength and demonstrated greater quadriceps and hamstring activation amplitudes during the drop jump. Lower thigh muscle strength was a weak (males) to moderate (females) predictor of greater quadriceps activation amplitudes. However, thigh strength and activation were poor predictors of hip and knee joint excursions and KEM. Regardless of sex and thigh strength, anterior shear forces were greater in individuals who demonstrated less hip flexion and greater knee flexion excursions and greater peak quadriceps activation and internal KEM during the landing. CONCLUSIONS Although thigh muscle strength explained some of the variance in quadriceps and hamstring activation levels as measured with surface electromyography, we failed to support the hypothesis that these neuromuscular factors are strong predictors of sagittal plane hip and knee flexion excursions or KEM. Although greater quadriceps activation amplitude was a significant predictor of greater anterior tibial shear forces, its contribution was relatively small compared with kinematic and kinetic variables.

Effects of Transverse and Frontal Plane Knee Laxity on Hip and Knee Neuromechanics During Drop Landings

Background Varus-valgus (LAXVV) and internal-external (LAXIER) rotational knee laxity have received attention as potential contributing factors in anterior cruciate ligament injury. This study compared persons with above- and below-average LAXVV and LAXIER values on hip and knee neuromechanics during drop jump landings. Hypothesis People with greater LAXVV and LAXIER values will have greater challenges controlling frontal and transverse plane knee motions, as evidenced by greater joint excursions, joint moments, and muscle activation levels during the landing phase. Study Design Descriptive laboratory study. Methods Recreationally active participants (52 women and 44 men) between 18 and 30 years old were measured for LAXVV and LAXIER and for their muscle activation and transverse and frontal plane hip and knee kinetics and kinematics during the initial landing phase of a drop jump. The mean value was obtained for each sex, and those with above-average values on LAXVV and LAXIER (LAXHIGH = 17 women, 16 men) were compared with those with below-average values (LAXLOW = 18 women, 17 men). Results Women with LAXHIGH verus LAXLOW were initially positioned in greater hip adduction and knee valgus and also produced more prolonged internal hip adduction and knee varus moments as they moved toward greater hip adduction and internal rotation as the landing progressed. These patterns in LAX HIGH women were accompanied by greater prelanding and postlanding muscle activation amplitudes. Men with LAXHIGH versus LAXLOW also demonstrated greater hip adduction motion and produced greater internal hip internal rotation and knee varus and internal rotation moments. Conclusion Participants with greater LAXVV and LAXIER landed with greater hip and knee transverse and frontal plane hip and knee motions. Clinical Relevance People (especially, women) with increased frontal and transverse plane knee laxity demonstrate motions associated with noncontact anterior cruciate ligament injury mechanisms.

Varus/Valgus and Internal/External Torsional Knee Joint Stiffness Differs between Sexes

Background Torsional joint stiffness is thought to play a role in the observed sex bias in noncontact anterior cruciate ligament injury rates. Hypothesis Women will exhibit lower torsional stiffness values of the knee in response to varus/valgus and internal/external rotations than will men. Study Design Controlled laboratory study. Methods Knee kinematics of 20 university students (10 men, 27.3 ± 3.4 years, 177.3 ± 6.8 cm, 81.1 ± 7.0 kg; 10 women, 22.9 ± 1.5 years, 169.0 ± 7.1 cm, 66.1 ±11.4 kg) were measured while 0 to 10 Nm of varus and valgus torques were applied with the subject nonweightbearing and while 0 to 5 N.m of internal and external torques were applied with the subject nonweightbearing and weightbearing with the use of a custom joint testing device. Joint stiffness values were calculated at 1-N.m increments. Results When low magnitudes of torque were applied to the knee, women had significantly lower stiffness values than did men-With the exception of applied external torque with the joint weightbearing and varus torque with the joint nonweightbearing, women demonstrated an increase in joint stiffness as the magnitude of torque increased from lower to higher magnitudes. In contrast, for the men, joint stiffness values remained unchanged as the magnitude of applied torque increased. Conclusion Women exhibited lower knee stiffness in response to low magnitudes of applied torque compared to men and demonstrated an increase of joint stiffness as the magnitude of applied torque increased. Clinical Relevance The decreased stiffness behavior of the knee in response to low torques that was observed for women may have a role in detrimentally affecting knee biomechanics and resulting neuromuscular function, particularly when an individual transitions from nonweightbearing to weightbearing.

The Relationships Among Sagittal-Plane Lower Extremity Moments: Implications for Landing Strategy in Anterior Cruciate Ligament Injury Prevention

CONTEXT Excessive quadriceps contraction with insufficient hamstrings muscle cocontraction has been shown to be a possible contributing factor for noncontact anterior cruciate ligament (ACL) injuries. Assessing the relationships among lower extremity internal moments may provide some insight into avoiding muscle contraction patterns that increase ACL injury risk. OBJECTIVE To examine the relationships of knee-extensor moment with ankle plantar-flexor and hip-extensor moments and to examine the relationship between knee moment and center of pressure as a measure of neuromuscular response to center-of-mass position. DESIGN Cross-sectional study. SETTING Applied Neuromechanics Research Laboratory. PATIENTS OR OTHER PARTICIPANTS Eighteen healthy, recreationally active women (age = 22.3 +/- 2.8 years, height = 162.5 +/- 8.1 cm, mass = 57.8 +/- 9.3 kg). INTERVENTION(S) Participants performed a single-leg landing from a 45-cm box onto a force plate. Kinetic and kinematic data were collected. MAIN OUTCOME MEASURE(S) Pearson product moment correlation coefficients were calculated among the net peak knee-extensor moment (KEMpk), sagittal-plane ankle (AM) and hip (HM) net internal moments, and anterior-posterior center of pressure relative to foot center of mass at KEMpk (COP). RESULTS Lower KEMpk related to both greater AM (r = -0.942, P < .001) and HM (r = -0.657, P = .003). We also found that more anterior displacement of COP was related to greater AM (r = -0.750, P < .001) and lower KEMpk (r = 0.618, P = .006). CONCLUSIONS Our results suggest that participants who lean the whole body forward during landing may produce more plantar-flexor moment and less knee-extensor moment, possibly increasing hip-extensor moment and decreasing knee-extensor moment production. These results suggest that leaning forward may be a technique to decrease quadriceps contraction demand while increasing hamstrings cocontraction demand during a single-leg landing.

Dynamic Valgus Alignment and Functional Strength in Males and Females During Maturation

CONTEXT Sex differences in dynamic measures have been established in physically mature populations. Gaining information on maturations effect on dynamic performance measures implicated in injury risk may enable us to better design injury prevention programs. OBJECTIVE To examine sex differences in dynamic valgus alignment and triple-hop distance measures across maturational stages in males and females. A secondary purpose was to determine if a field test of strength and power predicts dynamic valgus alignment. DESIGN Cross-sectional study. SETTING Laboratory. PATIENTS OR OTHER PARTICIPANTS 157 young athletes (78 females, 79 males) aged 9 to 18 years. INTERVENTION(S) Subjects performed drop-jump landings and single-leg triple-hop tests as part of a broader injury screening. MAIN OUTCOME MEASURE(S) Maturational status was ascertained from self-report questionnaires and grouped according to Tanner stages 1 and 2 (MatGrp1), 3 and 4 (MatGrp2), and 5 (MatGrp3). Frontal-plane knee valgus displacement, which served as a measure of dynamic valgus alignment, and single-leg triple-hop distance were assessed. RESULTS Males demonstrated less dynamic valgus alignment during drop jumps in the latter maturational stages (MatGrp1 = 13.1 degrees +/- 8.7 degrees , MatGrp2 = 9.0 degrees +/- 6.2 degrees , MatGrp3 = 9.2 degrees +/- 9.4 degrees ), whereas females increased dynamic valgus alignment throughout maturation (MatGrp1 = 11.5 degrees +/- 6.9 degrees , MatGrp2 = 12.8 degrees +/- 8.8 degrees , MatGrp3 = 15.5 degrees +/- 8.7 degrees ). Thus, in the more mature groups, males had less dynamic valgus alignment than females. Both males (MatGrp1 = 393.5 +/- 63.7 cm, MatGrp2 = 491.8 +/- 95.1 cm, MatGrp3 = 559.3 +/- 76.3 cm) and females (MatGrp1 = 360.3 +/- 37.1 cm, MatGrp2 = 380.1 +/- 44.3 cm, MatGrp3 = 440.0 +/- 66.2 cm) increased triple-hop distance, but males increased more. Within each subgroup of MatGrp and sex, triple-hop distance had no predictive ability for dynamic malalignment. CONCLUSIONS When dynamic valgus alignment and strength were assessed, sex and maturational status displayed an interaction. However, functional strength did not predict degree of dynamic valgus alignment.

Joint laxity is related to lower extremity energetics during a drop jump landing.

PURPOSE To examine the relationships between anterior knee laxity (AKL), genu recurvatum (GR), and general joint laxity (GJL) with sagittal plane energetics in males and females during a drop jump task. METHODS A total of 68 females and 50 males were measured for AKL, GR, and GJL and were instrumented to obtain neuromuscular and biomechanical data on their dominant limb during the initial landing phase of a 45-cm drop jump. Multiple linear regressions determined the extent to which the three joint laxity variables combined to predict hip, knee, and ankle work absorption and stiffness. Associations between joint laxity and joint kinematics, joint kinetics, and muscle activation amplitudes were also investigated to further interpret significant relationships. RESULTS Higher AKL and GJL and lower GR combined to predict greater knee work absorption (R2 = 0.210, P = 0.002) and stiffness (R2 = 0.127, P = 0.033) and lower ankle stiffness (R2 = 0.115, P = 0.048) in females. These associations were modulated through greater peak knee extensor moments and flexion angles, lower hamstring activation, and lower ankle extensor moments. In males, joint laxity had little impact on knee energetics, but a significant association was observed between greater GJL and decreased ankle stiffness (R2 = 0.209, P = 0.012), a product of both greater peak ankle flexion and decreased ankle extensor moment. CONCLUSIONS Females with greater AKL and GJL and lower GR demonstrated a landing strategy that increased work absorption and stiffness about the knee, whereas females with greater GR demonstrated a landing style that reduced knee work absorption and stiffness. The findings suggest that AKL, GR, and GJL may represent distinct risk factors and support the need to consider more comprehensive laxity profiles as they relate to knee joint function and anterior cruciate ligament injury risk.