Thomas W. Kernozek

Gender Differences in Lower Extremity Landing Mechanics Caused by Neuromuscular Fatigue

Background Neuromuscular fatigue has been suggested as an extrinsic factor in the mechanism of noncontact anterior cruciate ligament injury in both genders. Purpose To determine and describe the lower extremity kinematic and kinetic differences caused by neuromuscular fatigue during drop landings and compare changes between age- and skill-matched male and female athletes. Methods Inverse dynamic solutions estimated lower extremity flexion-extension and varus-valgus kinematics and kinetics for 14 female and 16 male athletes performing a single-legged 50-cm drop landing. Subjects performed landings prefatigue and postfatigue with fatigue induced via a parallel squat exercise (60% of 1 repetition maximum) until failure. A mixed-model, repeated-measures analysis of variance (fatigue * gender) was performed on select kinematic and kinetic variables. Results Neuromuscular fatigue caused men and women to land with more hip flexion (main effect fatigue, P = .012; main effect gender, P = .001). Men exhibited greater peak knee flexion angles postfatigue; women did not alter knee flexion (fatigue * gender, P =.028). Men exhibited larger peak knee varus angles irrespective of fatigue (main effect gender, P = .039; main effect fatigue, P = .127; fatigue * gender, P = .153); women demonstrated larger peak valgus angles overall (main effects gender, P = .009). There were no changes with fatigue (main effect fatigue, P = .127) or a different response due to fatigue with gender (fatigue * gender, P = .091). Women exhibited greater knee anterior shear force postfatigue (fatigue * gender, P = .010). Men and women exhibited lower knee extension moments (main effect fatigue, P = .000; main effect gender, P = .927; fatigue * gender, P = .309) and abduction moments (main effect fatigue, P = .014; main effect gender, P = .670; fatigue * gender, P = .191). Conclusion Neuromuscular fatigue caused significant alterations in women that may be indicative of the noncontact anterior cruciate ligament injury mechanisms. Clinical Relevance Current noncontact anterior cruciate ligament prevention programs should incorporate a fatigue component to help minimize the deleterious effects of neuromuscular fatigue on landing mechanics.

Effects of walking poles on lower extremity gait mechanics.

PURPOSE The purpose of this study was to determine whether walking with poles reduces loading to the lower extremity during level over ground walking. METHODS Three-dimensional gait analysis was conducted on 13 healthy adults who completed 10 walking trials using three different poling conditions (selected poles, poles back, and poles front) and without the use of poles (no poles). The inverse dynamics approach was used to calculate kinetic data via anthropometric, kinematic, and kinetic data. RESULTS All walking with poles conditions increased walking speed (P = 0.0001-0.0004), stride length (P < 0.0001), and stance time (P < 0.0001) compared with the no poles condition. There also was a decrease in anterior-posterior GRF braking impulse (P = 0.0001), a decrease in average vertical GRF walking with poles (P < 0.0001-0.0023), and a decrease in vertical (compressive) knee joint reaction force (P < 0.0001-0.0041) compared with the no poles condition. At the knee, extensor impulse decreased a 7.3% between the no poles and selected poles conditions (P = 0.0083-0.0287) and 10.4% between the no poles and poles back conditions (P < 0.0001). The support moment was reduced between the no poles and poles back (P = 0.0197) and poles front (P = 0.0002) conditions. Ankle plantarflexor work (A2) was reduced in the poles-front condition (P = 0.0334), but no differences were detected in all other ankle, knee or hip power and work variables (P > 0.05). CONCLUSION There were differences in kinetic variables between walking with and without poles. The use of walking poles enabled subjects to walk at a faster speed with reduced vertical ground reaction forces, vertical knee joint reaction forces, and reduction in the knee extensor angular impulse and support moment, depending on the poling condition used.

Influences of hip external rotation strength on knee mechanics during single-leg drop landings in females

BACKGROUND To determine the influence of hip external rotation strength on kinematic and kinetic variables during single-leg drop landings. METHODS Females were divided into strong and weak groups based on isometric hip external rotation strength and lower extremity flexion-extension and varus-valgus kinematics and kinetics were evaluated during single-legged 40 cm drop landings. FINDINGS Hip external rotation strength had no effect on sagittal or frontal plane angular motion throughout the landing cycle at the hip and knee. The strong group generated a statistically significant decrease in the peak vertical ground reaction force and external knee flexor moment. The weak group produced a greater external knee adduction moment, net knee anterior shear joint reaction force, and a greater hip external adduction moment. INTERPRETATION Subjects with greater hip and quadriceps/hamstring strength exhibited a significant decrease in the vertical ground reaction force and external knee adduction and flexor moments. Hip and knee strength appear to relate to differences in high risk landing strategies.

Plantar loading and cadence alterations with fatigue.

PURPOSE The purpose of this investigation was to identify changes in loading characteristics of the foot associated with fatigue during running. METHODS Nineteen healthy subjects ranging from 20 to 30 yr (mean = 22.3, SD = 2.4) were equipped with the Pedar in-shoe measurement system (Novel GmbH) for the assessment of plantar loading. After acclimation to the treadmill, subjects were progressed through the Ohio State protocol for exercise testing until fatigue was reported using Borgs RPE scale. Six right footsteps were recorded at 150 Hz for each subjects comfortable running pace under normal and fatigued conditions. A series of repeated measures multiple analysis of variance was performed for all dependent variables analyzed in this study including peak force (PF), force-time integral (FTI), peak pressure (PP), and pressure-time integral (PTI) for all regions of the plantar surface. RESULTS Decreased step time, significantly smaller values under the heel for PP, PF, FTI, CT, and PTI, and trends toward increased medial forefoot loading were identified while subjects were running under fatigued conditions (alpha < 0.05). CONCLUSION These results suggest that subjects change running technique and plantar surface loading characteristics in response to fatigued conditions through increased cadence, decreased loading of the heel, and increased medial forefoot loading.

Gluteal muscle activation during running in females with and without patellofemoral pain syndrome

BACKGROUND Hip and knee joint motion in the transverse and frontal plane during running may increase patellofemoral joint stress and contribute to the etiology of patellofemoral joint pain. We evaluated the association between these kinematics and the magnitude and timing of gluteus medius and maximus activity during running in females with patellofemoral pain. We also compared the magnitude and timing of gluteal muscle activity during running between females with and without patellofemoral pain. METHODS Twenty females with patellofemoral pain and twenty females without knee pain participated in this study. Three-dimensional running kinematics, gluteus medius and gluteus maximus onset time, activation duration, mean activation level, and peak activation level were recorded simultaneously. Gluteal muscle timing and activation level were compared between groups using independent t-tests. The association of gluteal muscle activation parameters running kinematics in females with patellofemoral pain was quantified using Pearson correlation coefficients. FINDINGS Females with patellofemoral pain demonstrated delayed (P=0.028, effect size=0.76) and shorter (P=0.01, effect size=0.88) gluteus medius activation than females without knee pain during running. The magnitude and timing of gluteus maximus activation was not different between groups. Greater hip adduction and internal rotation excursion was correlated with later gluteus medius and gluteus maximus onset, respectively. INTERPRETATION Neuromuscular control differences of the gluteal muscles appear to exist among females with patellofemoral pain during running. Interventions to facilitate earlier activation of these muscles may be warranted among females with patellofemoral pain who demonstrate altered running kinematics.

Estimation of anterior cruciate ligament tension from inverse dynamics data and electromyography in females during drop landing

BACKGROUND Recent human performance studies have shown that various kinematic and kinetic parameters may be implicated in non-contact anterior cruciate ligament (ACL) injury during landing and cutting. In this paper, a phenomenological sagittal plane model was used to estimate the ACL tension during drop landing from the net knee moments and forces, obtained from inverse dynamics and electromyography. METHODS Model parameters were determined with data from anatomical and ACL loading studies of cadaveric specimens. The model was used to process averaged data from 60 cm drop landing trials of sixteen healthy females. FINDINGS ACL loading during drop landing occurred during the between toe and heel impact with a peak tension of 0.15 body weight. The factors that contributed to ACL tension were the patellar tendon force and the tibial slope in combination with the joint axial loads. Factors responsible for reducing ACL tension were hamstring and ground reaction forces. INTERPRETATION Sagittal plane results largely confirmed a previous forward dynamics study of landing. The knee appeared to be largely stabilized against abduction moments due to the large axial loads present during drop landing for typical landing trials. Rotational moments were small in drop landing and contributed little to ACL tension. Estimates from this model can be used in human performance studies to determine the relative amount of ACL tension produced in different landing scenarios.

Chevron (Austin) distal metatarsal osteotomy for hallux valgus: Comparison of pre- and post-surgical characteristics

The purpose of the study was to compare the range of motion, perceived pain and plantar loading characteristics of the Chevron (Austin) corrective procedures in treating hallux valgus (HV) 12 months postsurgically. Twenty-five female participants with the diagnosis of mild to moderate HV deformity were studied. All participants had a distal metatarsal osteotomy (Chevron (Austin)) to correct their deformity. First metatarsophalangeal and talocrural joint range of motion (ROM) and a 10-point analog pain scale were measured presurgically and 12 months post-surgically on each participant. Radiographic measures of hallux valgus and intermetatarsal (IM) angles were taken preoperatively and six weeks postoperatively for comparison. Five pressure distribution measurements were recorded of barefoot walking using the EMED-SF presurgically and 12 months postsurgically. Statistical analyses revealed that plantar loading is still altered 12 months postsurgically despite a decrease in perceived pain and adequate first metatarsophalangeal joint ROM. Greater loading occurred in the central forefoot (CFF) region with decreases in some of the loading parameters in the medial toe (MT) region postsurgically. Loading parameters in the lateral forefoot (LFF), heel (HL), midfoot (MF), and lateral toe (LT) were unchanged 12 months postsurgery compared to presurgery.

Clinical and Biomechanical Risk Factors of Patients Diagnosed with Hallux Valgus

The purpose of this study was to identify the clinical and plantar loading variables related to hallux valgus. Fifty-one healthy control subjects and 40 subjects with a diagnosis of moderate hallux valgus deformity of similar age and body weight were recruited for this study. Clinical measurements of pain, first metatarsophalangeal joint range of motion, and single-leg resting calcaneal stance position were obtained. Biomechanical measurements were obtained using a capacitive pressure platform. Plantar loading variables were calculated for seven regions of the plantar surface. A univariate analysis followed by a stepwise logistic regression was used to analyze the data. The results indicated that high values for pain, single-leg resting calcaneal stance position, hallux region peak pressure and force-time integral, and central forefoot region force-time integral increased the likelihood of hallux valgus.

Electromyographic activity and applied load during seated quadriceps exercises

PURPOSE The aim of this study was to quantify and compare mean quadriceps muscle activity and applied load for eight seated quadriceps exercises using four types of resistance. METHODS Using surface electromyography (EMG), the right rectus femoris (RF), vastus lateralis (VL), and vastus medialis oblique (VMO) muscles of 52 university students aged 23.5 +/- 3.4 yr (35 female and 17 male subjects) were examined during the exercises. Resistance devices included an ankle weight (78 N), blue Thera-Band tubing, a Cybex 340 isokinetic dynamometer, and an Inertial Exercise Trainer (IET). Electrogoniometer data were collected to determine the range of motion (ROM), angular velocity, and phase (concentric/eccentric) of exercise. Load cell data were analyzed to determine tubing and IET applied loads during exercise. A within-subjects criterion was used to improve intrasubject EMG reliability. All EMG values were normalized to a 100% maximum voluntary isometric contraction. Repeated measures ANOVAs with Bonferroni comparisons were used for statistical analysis. RESULTS Within-subject effects of muscle and exercise were significant (P < 0.05) for both the concentric and eccentric muscle activity. The interaction effect of mean average EMG amplitude across exercises for the concentric phases of knee extension was significant (P = 0.001). No significant interactions were found for the eccentric phases of all seated quadriceps exercises. None of the exercises selectively isolated the VMO over the VL; however, the VMO/VL ratio was less (P < 0.05) during the concentric phases of the free weight and elastic tubing exercise when compared with the others. Eccentric phase VMO/VL ratios revealed that inertial resistance elicited greater muscle activity than other forms of resistance exercise. CONCLUSION These findings suggest clinicians should consider biomechanical and resistance data when developing a strengthening program for the quadriceps muscle. Some seated quadriceps exercises may be more appropriate for certain rehabilitation goals than others.

Hip-Abductor Fatigue and Single-Leg Landing Mechanics in Women Athletes

CONTEXT Reduced hip-abductor strength and muscle activation may be associated with altered lower extremity mechanics, which are thought to increase the risk for anterior cruciate ligament injury. However, experimental evidence supporting this relationship is limited. OBJECTIVE To examine the changes in single-leg landing mechanics and gluteus medius recruitment that occur after a hip-abductor fatigue protocol. DESIGN Descriptive laboratory study. PATIENTS OR OTHER PARTICIPANTS Twenty physically active women (age  =  21.0 ± 1.3 years). INTERVENTION(S) Participants were tested before (prefatigue) and after (postfatigue) a hip-abductor fatigue protocol consisting of repetitive side-lying hip abduction. MAIN OUTCOME MEASURE(S) Outcome measures included sagittal-plane and frontal-plane hip and knee kinematics at initial contact and at 60 milliseconds after initial contact during 5 single-leg landings from a height of 40 cm. Peak hip and knee sagittal-plane and frontal-plane joint moments during this time interval were also analyzed. Measures of gluteus medius activation, including latency, peak amplitude, and integrated signal, were recorded. RESULTS A small (<1°) increase in hip-abduction angle at initial contact and a small (<1°) decrease in knee-abduction (valgus) angle at 60 milliseconds after contact were observed in the postfatigue landing condition. No other kinematic changes were noted for the knee or hip at initial contact or at 60 milliseconds after initial contact. Peak external knee-adduction moment decreased 27% and peak hip adduction moment decreased 24% during the postfatigue landing condition. Gluteus medius activation was delayed after the protocol, but no difference in peak or integrated signal was seen during the landing trials. CONCLUSIONS Changes observed during single-leg landings after hip-abductor fatigue were not generally considered unfavorable to the integrity of the anterior cruciate ligament. Further work may be justified to study the role of hip-abductor activation in protecting the knee during landing.