Kinetic and Electromyographic Subphase Characteristics With Relation to Countermovement Vertical Jump Performance.

This study sought to identify kinetic and electromyographic subphase characteristics distinguishing good from poor jumpers during countermovement vertical jumps (CMVJs), as defined by the reactive strength index (RSI, CMVJ displacement divided by jump time; cutoff = 0.46 m·s-1). A total of 15 men (1.8 [0.6] m, 84.5 [8.5] kg, 24 [2] y) were stratified by RSI into good (n = 6; RSI = 0.57 [0.07] m·s-1) and poor (n = 9; RSI = 0.39 [0.06] m·s-1) performance groups. The following variables were compared between groups using independent t tests (α = .05) and Cohen's d effect sizes (d ≥ 0.8, large): jump height, propulsive impulse, eccentric rate of force development, and jump time, unloading, eccentric, and concentric subphase times, and average electromyographic amplitudes of 8 lower extremity muscles. Compared with the poor RSI group, the good RSI group exhibited a greater, though not statistically different CMVJ displacement (d = 1.07, P = .06). In addition, the good RSI group exhibited a significantly greater propulsive impulse (P = .04, d = 1.27) and a significantly more rapid unloading subphase (P = .04, d = 1.08). No other significant or noteworthy differences were detected. Enhanced RSI appears related to a quicker unloading phase, allowing a greater portion of the total jumping phase to be utilized generating positive net force. Poor jumpers should aim to use unloading strategies that emphasize quickness to enhance RSI during CMVJ.

Classifying performer strategies in drop landing activities.

Our purpose was to use group and single-case methods to examine inter-individual variability in the context of factors related to landing injuries. We tested the load accommodation strategies model (An exploration of load accommodation strategies during walking with extremity-carried weights. Human Movement Science, 35, 17-29) using landing impulse, revealing pre-landing strategies following height and external load manipulations. Ten healthy volunteers (8 male, 2 female, 24.0 ± 1.4 years, 1.72 ± 0.06 m, 73.5 ± 8.7 kg) were analysed across 12 trials in each of three load conditions (100% body weight [BW], 110% BW, 120% BW) from two landing heights (30 cm, 60 cm). Landing impulse (BW ∙ s) was computed for each participant-condition-trial, using impulse ratios (unit-less; BW ∙ s/BW ∙ s) to evaluate load accommodation strategies between adjacent load conditions (110%/100%, 120%/110%) at each landing height. Load accommodation strategy classifications were based on 95% confidence intervals (CIs) containing mechanically predicted impulse ratios (1.10 and 1.09 for 110/100% BW and 120/110% BW, respectively; α = 0.05). Mean group impulse ratios matched and exceeded predicted impulse ratios. Single-case analyses revealed a range of individual landing strategies that might be overlooked during group analyses, possibly uncovering individuals at greater risk of injury during landing activities.

Effects of Volitional Spine Stabilization and Lower-Extremity Fatigue on the Knee and Ankle During Landing Performance in a Population With Recurrent Low Back Pain.

INTRODUCTION: Recurrent lower back pain (rLBP) and neuromuscular fatigue are independently thought to increase the risk of lower extremity (LE) injury. Volitional preemptive abdominal contraction (VPAC) is thought to improve lumbar spine and pelvis control in individuals with rLBP. The effects of VPAC on fatigued landing performance in individuals with rLBP are unknown. OBJECTIVES: To determine the effects of VPAC and LE fatigue on landing performance in a rLBP population. DESIGN: Cross-sectional pretest-posttest cohort control design. SETTING: A clinical biomechanics laboratory. SUBJECTS: 32 rLBP (age 21.2 ± 2.7 y) but without current symptoms and 33 healthy (age 20.9 ± 2.3 y) subjects. INTERVENTION(S): (i) Volitional preemptive abdominal contraction using abdominal bracing and (ii) fatigue using submaximal free-weight squat protocol with 15% body weight until task failure was achieved. MAIN OUTCOME MEASURE(S): Knee and ankle angles, moments, electromyographic measurements from semitendinosus and vastus medialis muscles, and ground reaction force (GRF) were collected during 0.30 m drop-jump landings. RESULTS: The VPAC resulted in significantly earlier muscle onsets across all muscles with and without fatigue in both groups (mean ± SD, 0.063 ± 0.016 s earlier; P ≤ .001). Fatigue significantly delayed semitendinosus muscle onsets (0.033 ± 0.024 s later; P ≤ .001), decreased GRF (P ≤ .001), and altered landing kinematics in a variety of ways. The rLBP group exhibited delayed semitendinosus and vastus medialis muscle onsets (0.031 ± 0.028 s later; P ≤ .001) and 1.8° less knee flexion at initial contact (P ≤ .008). CONCLUSION: The VPAC decreases some of the detrimental effects of fatigue on landing biomechanics and thus may reduce LE injury risk in a rLBP population.

Effects of lower limb neurodynamic mobilization on intraneural fluid dispersion of the fourth lumbar nerve root: an unembalmed cadaveric investigation.

OBJECTIVES: Manual and physical therapists incorporate neurodynamic mobilisation (NDM) to improve function and decrease pain. Little is known about the mechanisms by which these interventions affect neural tissue. The objective of this research was to assess the effects of repetitive straight leg raise (SLR) NDM on the fluid dynamics within the fourth lumbar nerve root in unembalmed cadavers. METHODS: A biomimetic solution (Toluidine Blue Stock 1% and Plasma) was injected intraneurally, deep to the epineurium, into the L4 nerve roots of seven unembalmed cadavers. The initial dye spread was allowed to stabilise and measured with a digital calliper. Once the initial longitudinal dye spread stabilised, an intervention strategy (repetitive SLR) was applied incorporating NDMs (stretch/relax cycles) at a rate of 30 repetitions per minute for 5 minutes. Post-intervention calliper measurements of the longitudinal dye spread were measured. RESULTS: The mean experimental posttest longitudinal dye spread measurement (1.1 ± 0.9 mm) was significantly greater (P = 0.02) than the initial stabilised pretest longitudinal dye spread measurement. Increases ranged from 0.0 to 2.6 mm and represented an average of 7.9% and up to an 18.1% increase in longitudinal dye spread. DISCUSSION: Passive NDM in the form of repetitive SLR induced a significant increase in longitudinal fluid dispersion in the L4 nerve root of human cadaveric specimen. Lower limb NDM may be beneficial in promoting nerve function by limiting or altering intraneural fluid accumulation within the nerve root, thus preventing the adverse effects of intraneural oedema.

The Effect of Exercise-Induced Central Fatigue on Cervical Spine Joint Position Error, Strength, and Endurance.

Background: Fatigue is common in sports, impairing performance and increasing injury risk, yet little is known regarding fatigue and concussion. Impaired neck neuromuscular function may contribute to concussion at baseline, where central fatigue may further impair neck function resulting in increased concussion risk. These effects may be magnified in athletes with a history of concussion. Purpose: To determine the effect of exercise induced central fatigue on neck joint position error, strength, and endurance in healthy subjects and those with a history of concussion. The investigators hypothesized that EICF would have a negative effect on all variables. Study Design: Healthy subjects were examined using a single factor, within-subjects repeated measures design. Concussion history subjects were examined using a single-subject design. Methods: Nineteen healthy subjects and five subjects with a history of concussion were recruited for the study. Cervical joint position error, muscle strength, and neck flexor endurance were tested before and after exercise induced fatigue. Results: There was a significant increase in constant (p = 0.0027) and absolute joint position error (JPE) (p < 0.001); decrease in neck flexor endurance (p < 0.001); and decrease neck strength into cervical flexion (p = 0.01) in healthy subjects following fatigue. Among concussion history subjects, five demonstrated a significant increase in absolute and constant JPE (p < 0.05); four demonstrated a significant decrease in neck flexor endurance (p < 0.05); one in neck flexion muscle strength (p < 0.05); and three in neck extension and rotation muscle strength (p < 0.05) following fatigue. Conclusions: Cervical neuromuscular function deteriorated following fatigue in healthy subjects. Resulting impairments may affect force alterations in cervical control, potentially increasing concussion risk. Concussion history subjects descriptively demonstrated similar results, however further research should examine formal comparisons involving subjects with and without concussion history. Level of Evidence: 3b.

Adaptation in motor strategies for postural control associated with sensory reweighting.

The purpose of this study was to identify and differentiate the motor strategies associated with sensory reweighting adapted during specific sensory integration tasks by healthy young adults. Thirty-six subjects (age range: 21-33 years) performed standing computerized dynamic posturography balance tasks across progressively increasing amplitudes of visual (VIS), somatosensory (SOM) and both (VIS+SOM) systems perturbation conditions. Adaptation in the motor strategy was measured as changes in electromyographic (EMG) activities and joint angles. The contribution of the perturbed sensory input in maintaining postural stability was calculated to determine the sensory reweighting. A multivariate design was used to model a linear combination of motor adaptation variables that discriminates specific sensory integration tasks. Results showed a significant progressive decrease in postural sway per unit amplitude of sensory perturbation in each condition, indicating dynamic sensory reweighting. Linear discriminant function analysis indicated that the adaptation in motor strategy during the VIS condition was associated with increased activity of EMG and joint angles in the upper body compared to the lower body. Conversely, during the SOM and VIS+SOM conditions, the adaptation in motor strategy was associated with decreased activity of EMG and joint angles in the lower body compared to the upper body. Therefore, the adaptation in motor strategies associated with sensory reweighting were different for different sensory integration tasks.

Exploration of arm weight effects on hemiparetic stroke participants' gait performance.

BACKGROUND: This study explores the potential benefits of an arm weight intervention for improving gait performance in stroke survivors. Consistent with an interlimb neural coupling mechanism, the investigators hypothesized that arm weight would improve gait performance. METHODS: Nine stroke and nine healthy participants (1 female; age: 58.0 ± 6.8 years) participated. Participants walked over-ground at their preferred speed in four conditions: no weight (C1), non-hemiparetic (healthy: dominant) side weights (C2), hemiparetic (non-dominant) side weights (C3), and bilateral weights (C4). Statistical analyses included repeated analysis of variance (ANOVA) and paired t-test planned comparisons to explore the effects of added weight on gait speed, step width, step length, cadence, and arm swing amplitude. Single-subject analyses used randomization tests to delineate further the weight's effect on gait speed. FINDINGS: The stroke group walked significantly faster with arm weight (p = 0.048), exhibiting large ANOVA (η2p = 0.28) and C1 vs. C4 planned comparison (p = 0.021; dD = 0.95) effect sizes. Four of nine stroke participants significantly increased gait speed in at least one condition, and seven of nine exhibited large effect size increases (d = 0.85-4.71). The stroke group's hemiparetic-side step length and cadence significantly (p = 0.008) increased in C4 compared to C1, exhibiting large effect size increases (rb = 0.96). Four of nine healthy participants significantly increased gait speed in at least one condition, with five of nine exhibiting large effect size increases (d = 0.80-6.63). INTERPRETATION: This study's exploratory results demonstrate arm weight's potential for improving higher-functioning stroke survivors' gait performance. Arm weight addition merits further investigation as a possible rehabilitation intervention in the stroke population.

Biomechanical comparison of lag screw versus self-drilling screw fixation of oblique metatarsal osteotomy.

BACKGROUND: Several fixation methods for a Weil metatarsal osteotomy have been proposed. Lag screw fixation has been described as the preferred fixation technique. The self-drilling screw has been introduced and can be used for fixation of the Weil osteotomy. The current study compared self-drilling screws with lag screw fixation. MATERIALS AND METHODS: A Weil metatarsal osteotomy was performed on the second, third, and fourth metatarsals of five matched pairs of fresh frozen cadaver feet. The feet of each pair were randomly assigned ical to fixation with either a 2.0-mm cortical lag screw or a 2.0-mm self-drilling screw. The second metatarsals were stressed using cantilever bending. The third and fourth metatarsals were stressed under a shear force. Yield load, deformation at yield load, structural stiffness, and energy stored at yield load were recorded. RESULTS: There were no statistically significant differences (p < 0.05) noted. However, there was a trend toward greater biomechanical stability with the lag screw. CONCLUSION: There were no significant differences in the stability of fixation of the self-drilling screw and lag screw. There was a trend toward the lag screw fixation being more stable. CLINICAL RELEVANCE: The clinical significance of this trend is uncertain but suggests there is not a large difference between the two methods of fixation.

Gross Motor Skills and Gait Performance in Two- and Three-year-old Children With Developmental Delay Participating in Hippotherapy.

This study examined the effects of 15 sessions of hippotherapy (HPOT) on gross motor skills in children (aged 2-3 years) with gross motor developmental delay (DD) (n = 11) in comparison with age-based controls without DD (n = 6). Gross motor skills in both groups were assessed with the Battelle Developmental Inventory 2nd Edition, and gait parameters were measured using a computerized gait analysis system prestudy and poststudy. The DD group took part in 15 sessions of HPOT, and the control (CON) group did not participate in any equine activities. The statistical analysis examined preintervention and postintervention data in the DD group and compared testing data at the same intervals in controls. Functional motor skills significantly improved after HPOT intervention. Mean percent motor delay score decreased by 24.1 points from pretest to post-test in the DD group, indicating significantly (P < .001) less delay after HPOT. In contrast, mean Battelle Developmental Inventory 2nd Edition motor scores of the CON group were unchanged pre-study to post-study. The two groups' scores were significantly (P < .001) different indicating more improvement in the DD HPOT group when compared with the control group. Gait performance measures did not change significantly (P > .05) from pre-test to post-est in the DD group after HPOT; however, improvement trends were seen in step width and step length after HPOT. The results suggest that HPOT intervention in young children with DD can improve gross motor skills. These data provide important quantitative information concerning the efficacy of early HPOT intervention for children with DD during this critical stage of child development.

Immediate Improvements in Patellofemoral Pain Are Associated With Sagittal Plane Movement Training to Improve Use of Gluteus Maximus Muscle During Single Limb Landing.

OBJECTIVE: The authors sought to examine the immediate effects of movement training aimed at improving use of gluteus maximus (GMAX) in the sagittal plane on hip internal rotation and self-reported patellofemoral pain (PFP) during single-limb landing. METHODS: Seventeen females with PFP participated. Lower extremity kinematics and kinetics, GMAX activation, and self-reported PFP were obtained before and after a single-session movement training program aimed at increasing the use of GMAX. Dependent variables of interest included self-reported PFP, average GMAX activation, average hip extensor moment, and peak hip internal rotation. Post-training changes were evaluated using paired t tests and Wilcoxon signed rank tests. RESULTS: Following movement training, self-reported PFP decreased significantly (mean [standard deviation]) (3.9 [1.1] vs 0.8 [1.3] on a 0-10 scale). Additionally, significant increases were observed for the average hip extensor moment (0.6 [0.3] vs 1.8 [0.4] Nm/kg) and average GMAX activation (41.0% [18.3] vs 51.6% [25.7] maximum voluntary isometric contraction), whereas peak hip internal rotation decreased significantly (8.5 degrees [5.8] vs 6.0 degrees [5.3]). CONCLUSION: Movement training aimed at improving the use of GMAX in the sagittal plane resulted in clinically relevant changes in self-reported pain, GMAX activation, and hip kinetics and kinematics. Improving the use of GMAX during movement merits consideration when designing rehabilitation programs for females with PFP. IMPACT: The current study highlights the clinical utility of movement training for persons with PFP and provides a biomechanical rationale for its use as a potential intervention in this population.

Upper limb neurodynamic testing with radial and ulnar nerve biases: An analysis of cervical spinal nerve mechanics.

BACKGROUND: Clinical research supports a combination of upper limb neurodynamic testing (ULNT) strategies to rule out upper limb and cervical neurogenic pathology; however, knowledge of the biomechanical response of spinal nerves during ULNT is lacking for radial and ulnar nerve biases. OBJECTIVE: To assess whether radial and ulnar nerve biased strategies of ULNT elicit significant displacement and strain of cervical spinal nerves. STUDY DESIGN: Cross-sectional. METHODS: Radiolucent markers were implanted into spinal nerves C5-C8 proximal and distal to the intervertebral foramen in nine unembalmed cadavers (six male; three female) age 80.1 ± 13.2 years. Fluoroscopic images were captured during ULNT with radial and ulnar nerve biases. Images at rest and maximum tension were digitized and displacement and strain were measured. All data were analyzed using one sample t-tests and a generalized linear mixed models approach. RESULTS: Upper limb neurodynamic testing with radial nerve bias resulted in displacement (2.44-3.04 mm) and strain (7.99-11.98%) and ULNT with ulnar nerve bias resulted in displacement (2.16-4.41 mm) and strain (7.12 and 12.95%). Significant extraforaminal displacement occurred during radial and ulnar nerve biases for all spinal nerves (all P < 0.05) whereas significant strain occurred during ulnar nerve biases for all spinal nerves but only in C6-C8 during radial nerve bias. CONCLUSION: Upper limb neurodynamic testing using both radial and ulnar nerve biases resulted in cervical spinal nerve displacement and strain. Such techniques could be used to tension load or mobilize or cervical spinal nerves to evaluate for pathology.

Effects of tai chi exercise on posturography, gait, physical function and quality of life in postmenopausal women with osteopaenia: a randomized clinical study.

OBJECTIVE: to evaluate the effects of tai chi exercise on risk factors for falls in postmenopausal women with osteopaenia through measurements of balance, gait, physical function and quality of life. DESIGN: a randomized, controlled, single-blinded, 24-week trial with stratification by age and bone mass. SETTING: general community. PARTICIPANTS: Sixty-one independently living elderly females aged 65 years and older with low bone mass. INTERVENTIONS: subjects were recruited and randomly assigned to 24 weeks of tai chi (60 minutes/session, three sessions/week, n = 30) or a control group (n = 31). OUTCOME MEASURES: computerized dynamic posturography, gait, 'timed up and go', five-chair sit-to-stand and quality of life assessed at baseline, 12 and 24 weeks. RESULTS: after 24 weeks, subjects in the tai chi group demonstrated an increase in stride width (P = 0.05) and improvement in general health (P = 0.008), vitality (P = 0.02) and bodily pain (P = 0.03) compared with those in the control group. There was no significant difference in balance parameters, 'timed up and go', five-chair sit-to-stand and other domains of quality of life. CONCLUSION: tai chi exercise may reduce risk factors for falls by increasing the stride width, and may improve quality of life in terms of general health, vitality and bodily pain in postmenopausal women with osteopaenia.

The relationship between measures of foot mobility and subtalar joint stiffness using vibration energy with color Doppler imaging-A clinical proof-of-concept validation study.

INTRODUCTION: Subtalar joint (STJ) dysfunction can contribute to movement disturbances. Vibration energy with color Doppler imaging (VECDI) may be useful for detecting STJ stiffness changes. OBJECTIVES: (1) Support proof-of-concept that VECDI could detect STJ stiffness differences; (2) Establish STJ stiffness range in asymptomatic volunteers; (3) Examine relationships between STJ stiffness and foot mobility; and (4) Assess VECDI precision and reliability for examining STJ stiffness. METHODS: After establishing cadaveric testing model proof-of-concept, STJ stiffness (threshold units, ΔTU), ankle complex passive range-of-motion (PROM) and midfoot-width-difference (MFWDiff) data were collected in 28 asymptomatic subjects in vivo. Three reliability measurements were collected per variable; Rater-1 collected on all subjects and rater-2 on the first ten subjects. Subjects were classified into three STJ stiffness groups. RESULTS: Cadaveric VECDI measurement intra-rater reliability was 0.80. A significantly lower STJ ΔTU (p = .002) and ankle complex PROM (p < .001) was observed during the screw fixation versus normal condition. A fair correlation (r = 0.660) was observed between cadaveric ΔTU and ankle complex PROM. In vivo VECDI measurements demonstrated good intra-rater (0.76-0.84) versus poor inter-rater (-3.11) reliability. Significant positive correlations were found between STJ stiffness and both dorsum (r = .440) and posterior (r = .390) PROM. MFWDiff exhibited poor relationships with stiffness (r = .103) and either dorsum (r = .256) or posterior (r = .301) PROM. STJ stiffness ranged from 2.33 to 7.50 ΔTUs, categorizing subjects' STJ stiffness as increased (n = 6), normal (n = 15), or decreased (n = 7). Significant ANOVA main effects for classification were found based on ΔTU (p< .001), dorsum PROM (p = .017), and posterior PROM (p = .036). Post-hoc tests revealed significant: (1) ΔTU differences between all stiffness groups (p < .001); (2) dorsum PROM differences between the increased versus normal (p = .044) and decreased (p = .017) stiffness groups; and (3) posterior PROM differences between the increased versus decreased stiffness groups (p = .044). A good relationship was found between STJ stiffness and dorsum PROM in the increased stiffness group (r = .853) versus poor, nonsignificant relationships in the normal (r = -.042) or decreased stiffness (r = -.014) groups. CONCLUSION: PROM may not clinically explain all aspects of joint mobility. Joint VECDI stiffness assessment should be considered as a complimentary measurement technique.

The effect of stretching on muscle responses and postural sway responses during computerized dynamic posturography in women and men.

OBJECTIVE: To evaluate the effect of stretching on the parameters of postural sway and on the kinematic variables associated with balance control in women and men. DESIGN: Mixed repeated measures design with 2 levels. SETTING: Research laboratory. PARTICIPANTS: Fifteen women and fifteen men (mean age 23.4+/-2.2). INTERVENTION: Two separate sessions of (1) lower extremity stretching and (2) no-stretching, immediately prior to balance testing with simultaneous surface electromyographic (EMG) recordings of muscle responses. MAIN OUTCOME MEASURES: EMG latencies and average amplitudes for 4 lower extremity muscles for the preferred stance limb during computerized dynamic posturography (CDP) tests, specifically the Postural Evoked Response Test, Adaptation Test, Motor Control Test, Sensory Organization Test, and Unilateral Stance Test. RESULTS: Analyses of variance indicated no significant main effect for stretching and 2 significant main effects for gender for the Motor Control Test (P=.021) and latency of tibialis anterior (P=.009). Analyses of covariance with covariants of height and active knee extension revealed no significant main effect of stretching or of gender on muscles responses or CDP performance. CONCLUSIONS: In both women and men, lower extremity stretching did not significantly affect muscle responses or performance during CDP.

Changes in spinal height following sustained lumbar flexion and extension postures: a clinical measure of intervertebral disc hydration using stadiometry.

BACKGROUND: Decreased intervertebral disc height can result in diminished load carrying capacity of the spinal segment. Clinical means of assessing postures able to rehydrate the discs were investigated. OBJECTIVE: The purposes of this study were 3-fold: (1) to determine if our test protocol using a commercially available stadiometer demonstrated findings consistent with prior laboratory-based protocols; (2) to determine if hyperextension in the prone position and trunk flexion in the supine position caused increased spine height after sustained loading; and (3) to compare the effects of hyperextension in the prone position and trunk flexion in the supine position on spine height changes after a period of sustained loading. METHODS: This study used a pretest, posttest crossover design. Ten women and 11 men (mean age, 24 +/- 2.6 years) participated. Subjects held either 10 minutes of hyperextension in the prone position or 10 minutes of trunk flexion in the supine position in the recovery phase. Spine height was measured using a commercially available stadiometer. Spinal height change was determined from measurements taken after loaded sitting and measurements taken after hyperextension in the prone position and trunk flexion in the supine position. RESULTS: A 1-sample t test indicated no significant difference existed between our mean height change after 5 minutes of sitting and previously published validated findings. A paired t test indicated significant increase in height after both supine flexion and prone extension lying (P< .0001). The mean height gain was 3.11 mm using prone extension and 3.19 mm using the supine flexion protocol. A paired t test indicated no significant difference between these 2 recovery positions (P = .927). CONCLUSION: The stadiometer measurement protocol demonstrated that hyperextension in the prone position and trunk flexion in the supine position were easily effective positions for the temporary recovery of spine height after sustained loading. These findings lay the foundation for future research into the viscoelastic creep properties of the intervertebral disk under loading and therapeutic conditions.

Effects of fatigue on frontal plane knee motion, muscle activity, and ground reaction forces in men and women during landing.

Women tear their Anterior Cruciate Ligament (ACL) 2-8 times more frequently than men. Frontal plane knee motion can produce a pathological load in the ACL. During a state of fatigue the muscles surrounding the knee joint may lose the ability to protect the joint during sudden deceleration while landing. The purpose of this study was to investigate the effects of fatigue and gender on frontal plane knee motion, EMG amplitudes, and GRF magnitudes during drop- jump landing. Pretest-posttest comparison group design was used. Twenty-six volunteers (14 women; 12 Men; Mean ± standard deviation age = 24.5 ± 2.7 yrs; height = 1.73 ± 0.09 m; mass = 74.3 ± 11.8 kg) participated in the study. Knee frontal plane ranges of motion and positions, ground reaction force peak magnitudes, and surface EMG RMS amplitudes from five lower extremity muscles (vastus medialis, vastus lateralis, medial hamstring, lateral hamstring, and lateral gastrocnemius) were obtained during the landing phase of a drop-jump. MANOVA and ANOVA indicated that peak GRF significantly (p < 0.05; 2.50 ± 0.75 BW vs. 2.06 ± 0.93 BW) decreased during fatigued landings. No other variables exhibited a fatigue main effect, although there was a significant (p < 0.05) fatigue by gender interaction for the frontal plane range of motion from initial contact to max knee flexion variable. Follow-up analyses failed to reveal significant gender differences at the different levels of fatigue for this variable. Additionally, no variables exhibited a significant gender main effect. Single subject analysis indicated that fatigue significantly altered frontal plane knee motion, peak GRF, and EMG in some subjects and the direction of differences varied by individual. Fatigue altered some aspects of landing performance in both men and women, but there were no gender differences. Additionally, both group and single subject analyses provided valuable but different information about factors representing neuromuscular control during drop-jump landing. Key pointsFatigue reduces ground reaction forces in both men and women during drop-jump landings.There was no significant difference in frontal plane knee kinematics between men and women when they were fatigued.Men and women did show differences in frontal plane knee kinematics in the fatigued state compared to the pre-fatigued state and the increased motion was in the valgus direction and varus direction.Single subject analysis shows that both women and men exhibit characteristics that may predispose them to ACL injury.

Weighted vest effects on impact forces and joint work during vertical jump landings in men and women.

Weighted vest (WV) use during vertical jump landings (VJL) does not appear to alter peak vertical ground reaction forces (GRF) or peak joint torques. However, WV effects on joint work and sex differences during VJL are not well understood. This study assessed WV effects on vertical GRF and sagittal joint work during VJL in men and women. Twelve men and 12 women performed VJL wearing a WV with zero added mass (unloaded) and with 10% body mass (loaded) while GRF and kinematic data were obtained. Mixed-model analyses of variance (α = 0.05) and effect sizes (ES) were used to assess differences between sexes and/or load conditions. Regardless of sex, greater landing height (p < 0.001; ES = 0.37) and peak vertical GRF (p = 0.001; ES 0.51) occurred when unloaded, while greater landing time (p = 0.001; ES = 0.46) and negative lower extremity work (p < 0.001; ES = 0.41) occurred when loaded through greater negative work about the hip (p = 0.001; ES = 0.27) and ankle (p = 0.020; ES = 0.27). No differences in hip (p = 0.753; ES = 0.03), knee (p = 0.588; ES = 0.07), or ankle (p = 0.580; ES = 0.09) joint displacement were detected between loaded and unloaded conditions. Men exhibited greater landing heights (p < 0.001; ES = 2.49) and greater peak vertical GRF than women (p = 0.007; ES = 1.18), though women exhibited greater negative lower extremity work (p < 0.001; ES = 1.98) than men through greater negative knee (p < 0.001; ES = 1.98) and ankle (p = 0.032; ES = 0.94) work. No sex differences were detected for joint angular displacement about the hip (p = 0.475; ES = 0.30), knee (p = 0.666; ES = 0.18), or ankle (p = 0.084; ES = 0.71). These data revealed a unique load accommodation strategy during VJL with a WV characterized by greater lower extremity joint work performed via increased joint torque despite lesser landing height and peak vertical GRF. Women appear to perform greater lower extremity joint work than men during VJL despite lesser landing height and peak vertical GRF. Current and prospective WV users should be aware of their load accommodation strategy during VJL with an external load. Women may consider developing more refined load accommodation strategies for VJL regardless of whether external loading is applied to avoid performing excessive amounts of lower extremity work.

THE EFFECTS OF POSTERIOR TIBIAL MOBILIZATION ON MENISCAL MOVEMENT: AN IN-SITU INVESTIGATION.

BACKGROUND: Anterior knee pain during knee extension may be related to a meniscal movement restriction and increased meniscal load during function. One method of treatment involves the use of manual posterior mobilization of the tibia to specifically target the meniscotibial interface of the knee joint. PURPOSE: The purpose of this study was to measure motion at a cadaveric medial meniscus anterior horn during a posterior tibial mobilization. STUDY DESIGN: Prospective, multifactorial, repeated-measures laboratory study. METHODS: Eight unembalmed cadaveric knee specimens were mounted in a custom apparatus and markers were placed in the medial meniscus, tibia and femur. The tibia was posteriorly mobilized in two randomized knee positions (0 degrees and 25 degrees) using three randomly assigned loads (44.48N, 88.96N, and 177.93N). Markers were photographed and digitally measured and analyzed. RESULTS: All load x position conditions produced anterior displacement of the meniscus on the tibia, where the displacement was significant [t (7) = -3.299; p = 0.013] at 0 degrees loaded with 177.93N (mean 0.41 ± 0.35 mm). The results of 2(position) x 3(load) repeated measures ANOVA for meniscotibial displacement produced no significant main effects for load [F (2,14) = 2.542; p = 0.114) or position [F (1,7) = 0.324, p = 0.587]. All load x position conditions produced significant posterior tibial and meniscal displacement on the femur. The 2(position) x 3(load) repeated measures ANOVA revealed a significant main effect for load for both femoral marker displacement relative to the tibial axis [F (2,14) = 77.994; p < 0.001] and meniscal marker displacement relative to the femoral marker [F (2,14) = 83.620; p < 0.001]. CONCLUSION: Use of a mobilization technique to target the meniscotibial interface appears to move the meniscus anteriorly on the tibia. It appears that this technique may be most effective at the end range position. LEVEL OF EVIDENCE: 2 (laboratory study).

Effects of Tai Chi on gait kinematics, physical function, and pain in elderly with knee osteoarthritis--a pilot study.

Our previous study has demonstrated that 6 weeks of Tai Chi exercise significantly improves knee pain and stiffness in elderly with knee osteoarthritis. This study also examine the effects of Tai Chi exercise on gait kinematics, physical function, pain, and pain self-efficacy in elderly with knee osteoarthritis. In this prospective, pretest-posttest clinical trial, 40 men and women (64.4+/-8.3 years) diagnosed with knee osteoarthritis participated in 6 weeks of instructed Tai Chi training, 1 hour/session, 2 sessions/week. The following measures were taken at baseline and the conclusion of the intervention: (a) gait kinematics including stride length, stride frequency, and gait speed quantified using video analysis, (b) physical function, (c) knee pain, and (d) pain self-efficacy. Data were analyzed using repeated MANCOVA, MANOVA, ANOVA and Wilcoxon tests. After 6 weeks of Tai Chi exercise, stride length (p=0.023; 1.17+/-0.17 vs. 1.20+/-0.14 m), stride frequency (p=0.014; 0.91+/-0.08 vs. 0.93+/-0.08 strides/s), and consequently gait speed (p<0.025; 1.06+/-0.19 vs. 1.12+/-0.15 m/s) increased in the participants. Physical function was significantly improved (p<0.001) and knee pain was significantly decreased (p=0.002), while no change was observed in pain self-efficacy. In conclusion, these findings support that Tai Chi is beneficial for gait kinematics in elderly with knee osteoarthritis, and a longer term application is needed to substantiate the effect of Tai Chi as an alternative exercise in management of knee osteoarthritis.

Volitional Preemptive Abdominal Contraction and Upper Extremity Muscle Latencies During D1 Flexion and Scaption Shoulder Exercises.

CONTEXT: The abdominal-bracing maneuver, a volitional preemptive abdominal contraction (VPAC) strategy, is commonly used during resisted shoulder exercises. How VPAC affects shoulder-muscle function during resisted shoulder exercise is unknown. OBJECTIVE: To identify the effects of VPAC on selected parascapular and glenohumeral muscles during specific shoulder exercises with or without resistance. DESIGN: Cross-sectional study. SETTING: Clinical biomechanics research laboratory. PATIENTS OR OTHER PARTICIPANTS: Twenty-two asymptomatic volunteers between 18 and 40 years of age. INTERVENTION(S): Participants performed arm elevation in scaption and D1 shoulder-flexion (D1F) patterns with and without resistance and VPAC. MAIN OUTCOME MEASURE(S): Electromyography was used to test the muscle-contraction amplitudes and onset timing of the anterior deltoid, posterior deltoid, upper trapezius, lower trapezius, and serratus anterior. Muscle-response amplitudes were quantified using root mean square electromyography. Shoulder-muscle relative-onset timing was quantified in reference to kinematic elbow-movement initiation. RESULTS: The VPAC increased serratus anterior amplitude during D1F ( P < .001) and scaption ( P < .001) and upper trapezius amplitude ( P < .001) in scaption. All muscle amplitudes increased with resistance. The VPAC decreased muscle-onset latencies for the anterior deltoid ( P < .001), posterior deltoid ( P = .008), upper trapezius ( P = .001), lower trapezius ( P = .006), and serratus anterior ( P = .001) during D1F. In addition, the VPAC decreased muscle-onset latencies for the anterior deltoid ( P < .001), posterior deltoid ( P = .007), upper trapezius ( P < .001), lower trapezius ( P < .001), and serratus anterior ( P < .001) during scaption. CONCLUSIONS: The VPAC affected only the parascapular muscles that had the greatest scapular-stabilizing roles during the specific open chain movement we tested. It decreased latencies in all muscles. These neuromuscular changes may enhance the stability of the shoulder during D1F and scaption exercises.