Liang-Ching Tsai

Effects of Fatigue and Recovery on Knee Mechanics during Side-Step Cutting

INTRODUCTION Changes in knee mechanics immediately after a fatiguing bout of exercise are thought to place an individual at a greater risk for anterior cruciate ligament (ACL) injury. However, the recovery time required to restore normal knee kinetics and kinematics after fatigue has not been established. PURPOSE The purpose of this study was to examine knee mechanics during side-step cutting immediately after a fatigue protocol and after 20 and 40 min of rest. METHODS Knee kinematics (eight-camera system Vicon 612; Oxford Metrics, Oxford, United Kingdom) and kinetics (AMTI force platform; AMTI, Newton, MA) of 15 female recreational athletes were recorded during a side-step cutting task. Data were obtained at four different time points: 1) before a fatigue protocol, 2) immediately after the fatigue protocol, 3) 20 min after the fatigue protocol, and 4) 40 min after the fatigue protocol. Peak knee joint angles and knee joint moments in the sagittal, frontal, and transverse planes were identified during the deceleration phase of the cutting task. One-way ANOVA with repeated measures were used to compare variables among the four time points. RESULTS Peak internal knee adductor moments (external knee valgus moments) and peak knee internal rotation angles were significantly greater after fatigue and remained elevated at 20 and 40 min after fatigue. Peak knee abduction (valgus) angles immediately after the fatigue protocol were significantly greater but returned to prefatigue levels after 20 min of rest. The fatigue protocol had no influence on any other of the variables examined. CONCLUSIONS Fatigue resulted in changes in knee mechanics that are thought to be associated with ACL injury. Forty minutes of recovery was not sufficient in restoring knee mechanics to prefatigue levels.

Increased Hip and Knee Flexion During Landing Decreases Tibiofemoral Compressive Forces in Women Who Have Undergone Anterior Cruciate Ligament Reconstruction

Background: Those who have undergone anterior cruciate ligament reconstruction (ACLR) have been shown to exhibit increased muscle co-contraction, decreased knee flexion, and elevated tibiofemoral compressive forces. Elevated tibiofemoral compressive forces may be associated with the high risk of developing knee osteoarthritis in this population. Purpose: To examine whether muscle co-contraction and tibiofemoral compressive forces in women after undergoing ACLR can be reduced through the use of a landing strategy that emphasizes greater hip and knee flexion. Study Design: Controlled laboratory study. Methods: Ten female recreational athletes who had previously undergone ACLR participated in this study. Participants performed a single-legged drop-land task before and after a training session that encouraged them to use greater hip and knee flexion during landing. Peak tibiofemoral compressive forces before and after training were estimated using an electromyography (EMG)–driven knee model that incorporated joint kinematics, EMG, and subject-specific muscle volumes and patellar tendon orientation estimated from magnetic resonance imaging. A co-contraction index (CCI) was calculated to quantify the level of co-contraction between knee flexor and extensor muscles. Results: After training, peak hip and knee flexion as well as hip and knee flexion excursions increased significantly. Additionally, participants demonstrated a significant decrease after training in the areas of muscle co-contraction (CCI [mean ± SD], 0.28 ± 0.10 vs 0.18 ± 0.05; P < .001) and peak tibiofemoral compressive force (97.3 ± 8.0 vs 91.3 ± 10.2 N·kg−1; P = .044). Conclusion: Increased muscle co-contraction as well as elevated tibiofemoral compressive loads observed in individuals following ACLR can be reduced by using a landing strategy that encourages greater hip and knee flexion. Clinical Relevance: The findings of the current study provide useful information for the growth of rehabilitation and/or intervention programs aimed to decrease knee joint loading to prevent or delay the development of knee osteoarthritis in those who have undergone ACLR.

Magnetic resonance imaging-measured muscle parameters improved knee moment prediction of an EMG-driven model.

INTRODUCTION Acquisition of muscle anatomic parameters is essential for the development of a musculoskeletal model to estimate muscle forces and joint kinetics and can be derived in three ways: 1) use of a generic anatomic model, 2) scaling of a generic model based on anthropometric measures, and 3) direct in vivo measurements using various imaging techniques. PURPOSE The purpose of this study was to investigate how incorporating direct measurements of muscle anatomic parameters using magnetic resonance imaging (muscle volumes and moment arms) influences knee moment predictions when compared with generic and scaled models. METHODS Joint moment predictions of the three modeling approaches were examined by comparing the net knee moments calculated by each model with standard net joint moment measurements (inverse dynamics calculations and dynamometry) obtained while seven subjects (three females, four males) performed a drop landing and isokinetic knee extension task. The coefficient of multiple correlation and mean absolute difference were calculated to examine the prediction error and agreement of each model with standard net knee moment measurements. RESULTS For both tasks, the model incorporating direct measurements of muscle volumes and moment arms had a higher coefficient of multiple correlation and smaller mean absolute difference than the generic and scaled models (effect size range = 0.99-1.37). The scaled model had a lower coefficient of multiple correlation and greater mean absolute difference than the generic model (effect size = 1.36). CONCLUSIONS Our findings demonstrate that knee moment predictions from an EMG-driven model can be improved with direct measurements of muscle anatomic parameters. Knee moment predictions did not improve when scaling a generic anatomic model. Musculoskeletal models that incorporate direct measures of muscle anatomic parameters may provide more accurate assessments of joint kinetics when compared with generic and scaled models.

Influence of maturation on instep kick biomechanics in female soccer athletes.

PURPOSE The purpose of this study was to compare kicking biomechanics between young female soccer players at two different stages of physical maturation and to identify biomechanical predictors of peak foot velocity. METHODS Swing and stance limb kinematics and kinetics were recorded from 20 female soccer players (10 prepubertal, 10 postpubertal) while kicking a soccer ball using an angled two-step approach. Peak foot velocity as well as hip and knee kinematics and kinetics were compared between groups using independent-samples t-tests. Pearson correlation coefficients and stepwise multiple regression were used to identify predictors of peak foot velocity. RESULTS Peak foot velocity and the peak swing limb net hip flexor moment was significantly greater in the postpubertal group when compared with the prepubertal group (13.4 vs 11.6 m·s(-1), P = 0.003; 1.22 vs 1.07 N·m·kg(-1)·m(-1), P = 0.03). Peak stance limb hip and knee extensor moments were not different between groups. Although the peak swing limb hip and knee flexion angles were similar between groups, the postpubertal group demonstrated significantly less peak stance limb hip and knee flexion angles when compared with the prepubertal group (P < 0.001 and P = 0.045). Using a linear regression model, swing limb peak hip flexor moment and peak swing limb hip extension range of motion combined to explain 65% of the variance in peak foot velocity. CONCLUSIONS Despite a difference in stance limb kinematics, similar swing limb kinematics between groups indicates that the prepubertal female athletes kicked with a mature swing limb kick pattern. The ability to generate a large hip flexor moment of the swing limb seems to be an important factor for improving kicking performance in young female soccer players.