The Effect of Tactical Tasks and Gear on Muscle Activation of SWAT Officers.

ABSTRACT: Keeler, JM, Pohl, MB, Bergstrom, HC, Thomas, JM, and Abel, MG. The effect of tactical tasks and gear on muscle activation of SWAT officers. J Strength Cond Res 36(1): 238-244, 2022-Special Weapons and Tactics (SWAT) officers perform a variety of tactical operations while wearing tactical gear. Load carriage has been shown to alter muscle activation in the torso and is also associated with lower back pain, which is a prevalent musculoskeletal injury suffered by SWAT Officers. The purpose of this study was to quantify the effect of tactical gear on muscle activation of torso musculature while performing occupational tasks. Twenty male SWAT Officers (age: 34.7 ± 4.5 years; height: 1.79 ± 0.1 m; body mass: 91.5 ± 17.3 kg) performed 4 tasks (standing, rifle walk, sitting, and shield walk) with and without gear (mass of gear: 13.8 ± 1.9 kg). Mean electromyographic amplitude was evaluated bilaterally for the erector spinae, rectus abdominis, and external oblique muscles during the trials and expressed relative to maximal voluntary isometric contraction (MVIC). Addition of gear significantly increased erector spinae mean muscle activation during the rifle walk task (mean delta: +0.16%). However, no differences in muscle activation were identified for any other muscles between gear conditions (effect size ≤ 0.15). The shield walk produced the highest mean activation for each muscle during different tasks. The dynamic tasks yielded (0.24-4.18% MVIC) greater muscle activation levels than sitting and standing tasks. Despite minimal increases in muscle activation levels with the addition of gear, load carriage is known to increase the risk of acute and chronic injury. Collectively, these findings indicate that SWAT Officers should perform most skills without gear during tactical training to simulate task-specific movement patterns but reduce the risk of musculoskeletal injury.

Effects of a Hip Flexor Stretching Program on Running Kinematics in Individuals With Limited Passive Hip Extension.

Mettler, JH, Shapiro, R, and Pohl, MB. Effects of a hip flexor stretching program on running kinematics in individuals with limited passive hip extension. J Strength Cond Res 33(12): 3338-3344, 2019-Tightness of the hip flexor muscle group may theoretically contribute to altered kinematics of the lumbo-pelvic-hip (LPH) complex during dynamic movements. Therefore, the purpose of this study was to analyze the effects of a 3-week home-based stretching program on passive hip extension and sagittal plane kinematics of the LPH complex when running. Twenty healthy subjects with limited passive hip extension underwent a 3D gait analysis both before (PRE) and after (POST) a hip flexor stretching program. After the stretching program, passive hip extension increased significantly (p < 0.001), whereas no improvements during running were reported for active hip extension, anterior pelvic tilt, or lumbar spine extension (p ≥ 0.05). In addition, no relationship was found between the change in passive hip extension with either the change in active hip extension, anterior pelvic tilt, or lumbar spine extension. A 3-week static stretching program of the hip flexor muscle group resulted in an increase in passive hip extension, but the sagittal plane kinematics of the LPH complex during running remained unchanged. The results suggest that passive hip joint flexibility may be of limited importance in determining the kinematics of the LPH complex during submaximal running. However, it is possible that an increase in the range of motion at the hip may be beneficial when running at or near maximal speeds.

Effect of Load Carriage on Tactical Performance in Special Weapons and Tactics Operators.

Thomas, JM, Pohl, MB, Shapiro, R, Keeler, J, and Abel, MG. Effect of load carriage on tactical performance in special weapons and tactics operators. J Strength Cond Res 32(2): 554-564, 2018-Special weapons and tactics (SWAT) operators are specially trained personnel that are required to carry equipment to perform high-risk tasks. Given the need to carry this equipment, it is important to understand the potentially deleterious effect that the additional load may have on tactical performance. Furthermore, it is important to identify physical fitness characteristics that are associated with the potential decrement in performance. Therefore, the purpose of this study was to evaluate the effect of load carriage on tactical physical ability and marksmanship and to identify fitness characteristics associated with any decrement in performance. Twelve male SWAT operators were timed while performing a simulated tactical test (STT) on a live firing range with (loaded condition) and without equipment (unloaded condition). A battery of physical fitness assessments were used to assess anaerobic and aerobic power, muscular endurance, strength, agility, and flexibility. Paired-samples t-tests were used to identify differences between STT conditions, and bivariate correlations were used to determine relationships between STT and fitness outcomes. Time to complete the STT in the loaded condition increased by 7.8% compared with the unloaded condition (p < 0.001). Nine of the 13 STT tasks were performed significantly slower in the loaded condition. Fatigue index (r = 0.64) and V[Combining Dot Above]O2peak (r = -0.62) were associated with the decrement in the overall STT time. Marksmanship was not different between load carriage conditions (p = 0.816). These findings indicate that resistance to anaerobic fatigue and aerobic power are related to the decrement in tactical performance produced by load carriage.

Between-limb kinematic asymmetry during gait in unilateral and bilateral mild to moderate knee osteoarthritis.

OBJECTIVE: To compare lower-limb kinematic asymmetries during gait in individuals with unilateral and bilateral symptomatic osteoarthritis and controls. DESIGN: Cross-sectional. SETTING: Laboratory. PARTICIPANTS: Participants (N=54) had symptomatic unilateral (n=18) or bilateral (n=18) knee osteoarthritis. Healthy controls were sex- and age-matched and similar in height and weight to osteoarthritis groups (n=18). INTERVENTION: Three-dimensional motion analysis was conducted while participants walked on a treadmill at 1.1m/s. MAIN OUTCOME MEASURES: Maximum joint angles and velocities of the knee and hip during stance, knee flexion, knee adduction, and hip adduction at initial contact, pelvic drop, stride length, and average toe out. RESULTS: There was a significant limb effect for knee flexion at initial contact (P=.01). The bilateral osteoarthritis group demonstrated the largest between-limb asymmetry (2.83°; 95% confidence interval, .88-4.78; effect size [ES]=.67). The bilateral osteoarthritis group also displayed tendencies toward between-limb asymmetry in hip adduction at initial contact and peak knee adduction during stance; ESs were small (ES=.33 and .48). Lower-limb kinematics was symmetrical in the control and unilateral knee osteoarthritis groups. CONCLUSIONS: Between-limb asymmetries are present even at mild to moderate stages of knee osteoarthritis. During this stage, between-limb asymmetry appears to be more prevalent in patients with bilateral symptomatic disease, suggesting that patients with unilateral disease maintain kinematic symmetry for longer in the knee osteoarthritis process. Further, early treatment strategies should target the restoration of gait symmetry and involve kinematics changes in both lower limbs. Future research is needed to determine the efficacy of such strategies with respect to kinematic asymmetry, pain, and disease progression.

Steps toward the validation of the Trendelenburg test: the effect of experimentally reduced hip abductor muscle function on frontal plane mechanics.

OBJECTIVE: To investigate the validity of the Trendelenburg test (TT) using an ultrasound-guided nerve block (UNB) of the superior gluteal nerve and determine whether the reduction in hip abductor muscle (HABD) strength would result in the theorized mechanical compensatory strategies measured during the TT. DESIGN: Quasi-experimental. SETTING: Hospital. PARTICIPANTS: Convenience sample of 9 healthy men. Only participants with no current or previous injury to the lumbar spine, pelvis, or lower extremities, and no previous surgeries were included. INTERVENTIONS: Ultrasound-guided nerve block. MAIN OUTCOME MEASURES: Hip abductor muscle strength (percent body weight [%BW]), contralateral pelvic drop (cPD), change in contralateral pelvic drop (ΔcPD), ipsilateral hip adduction, and ipsilateral trunk sway (TRUNK) measured in degrees. RESULTS: The median age and weight of the participants were 31 years (interquartile range [IQR], 22-32 years) and 73 kg (IQR, 67-81 kg), respectively. An average 52% reduction of HABD strength (z = 2.36, P = 0.02) resulted after the UNB. No differences were found in cPD or ΔcPD (z = 0.01, P = 0.99, z = -0.67, P = 0.49, respectively). Individual changes in biomechanics showed no consistency between participants and nonsystematic changes across the group. One participant demonstrated the mechanical compensations described by Trendelenburg. CONCLUSIONS: The TT should not be used as a screening measure for HABD strength in populations demonstrating strength greater than 30%BW but should be reserved for use with populations with marked HABD weakness. CLINICAL RELEVANCE: This study presents data regarding a critical level of HABD strength required to support the pelvis during the TT.

Lower extremity kinematics during running and hip abductor strength in iliotibial band syndrome: A systematic review and meta-analysis.

BACKGROUND: Iliotibial band syndrome is a common overuse injury that is twice as likely to affect female runners compared to male runners. It is unclear if there is a consistent running pattern and strength profile exhibited by female and male runners with iliotibial band syndrome. RESEARCH QUESTION: The purpose of this systematic review and meta-analysis was to determine if any differences existed in lower-extremity kinematics and hip strength between runners who retrospectively, currently, or prospectively had iliotibial band syndrome. METHODS: Papers included must have reported three-dimensional kinematic running data and/or hip strength data that were statistically analyzed between runners that never developed iliotibial band syndrome and runners with iliotibial band syndrome. Meta-analysis was performed for each kinematic or strength variable reported in at least three studies. Female and male runners were analyzed separately and grouped into three cohorts (retrospective, current, prospective). RESULTS: Seventeen articles were included in this systematic review. Data from 10 cross-sectional studies were included for meta-analysis. Female runners with current iliotibial band syndrome exhibited smaller peak hip internal rotation angles and lower isometric hip abductor strength compared to controls. SIGNIFICANCE: Although limited biomechanical evidence exists, risk factors for ITBS are different between female and male runners and may vary according to injury status. Specifically, transverse plane hip motion and hip abductor strength weakness may be biomechanical risk factors in female runners with current iliotibial band syndrome only.

Biomechanical and anatomic factors associated with a history of plantar fasciitis in female runners.

OBJECTIVE: To compare selected structural and biomechanical factors between female runners with a history of plantar fasciitis and healthy control subjects. DESIGN: Cross-sectional. SETTING: University of Delaware Motion Analysis Laboratory, Newark, Delaware; and University of Massachusetts Biomechanics Laboratory, Amherst, Massachusetts. PARTICIPANTS: Twenty-five female runners with a history of plantar fasciitis were recruited for this study. A group of 25 age- and mileage-matched runners with no history of plantar fasciitis served as control subjects. INTERVENTIONS: The independent variable was whether or not subjects had a history of plantar fasciitis. MAIN OUTCOME MEASURES: Subjects ran overground while kinematic and kinetic data were recorded using a motion capture system and force plate. Rearfoot kinematic variables of interest included peak dorsiflexion, peak eversion, time to peak eversion along with eversion excursion. Vertical ground reaction force variables included impact peak and the maximum instantaneous load rate. Structural measures were taken for calcaneal valgus and arch index during standing and passive ankle dorsiflexion range of motion. RESULTS: A significantly greater maximum instantaneous load rate was found in the plantar fasciitis group along with an increased ankle dorsiflexion range of motion compared with the control group. The plantar fasciitis group had a lower arch index compared with control subjects, but calcaneal valgus was similar between groups. No differences in rearfoot kinematics were found between groups. CONCLUSION: These data indicate that a history of plantar fasciitis in runners may be associated with greater vertical ground reaction force load rates and a lower medial longitudinal arch of the foot.

Biomechanical predictors of retrospective tibial stress fractures in runners.

Both kinematics and kinetics of the lower limb have been shown separately to be related with a history of tibial stress fractures (TSFs) in female runners. However, it is likely that these factors interact together to increase the risk of a TSF. This study was conducted to determine which combination of kinematic and kinetic factors are the best predictors of retrospective TSF in female distance runners. Total 30 female runners who had previously sustained a TSF were recruited, along with an age and mileage matched control group (n=30). Subjects ran overground at 3.7m/s while kinematic and kinetic data were recorded. Five trials from each subject were used for data analysis and ensemble means were calculated for both groups. The kinematic variables of peak hip adduction (HADD), peak knee internal rotation (KIR) and knee adduction (KADD), peak rearfoot eversion (RFEV) were entered into a binary logistic regression along with the kinetic variables of vertical instantaneous load rate (VILR) and absolute free moment (FM). The variables HADD, FM and RFEV were able to correctly predict a history of TSF in 83% of cases. Increases in HADD, FM and RFEV (odds ratios of 1.29, 1.37 and 1.18) were associated with an elevated risk of having a history of TSF. The addition of VILR, KIR and KADD did not improve the ability to predict previous injury. Based on these results, HADD, FM and RFEV appear to be the most important of the variables of interest in terms of predicting retrospective TSF in female runners.

Changes in foot and shank coupling due to alterations in foot strike pattern during running.

BACKGROUND: Determining if and how the kinematic relationship between adjacent body segments changes when an individual's gait pattern is experimentally manipulated can yield insight into the robustness of the kinematic coupling across the associated joint(s). The aim of this study was to assess the effects on the kinematic coupling between the forefoot, rearfoot and shank during ground contact of running with alteration in foot strike pattern. METHODS: Twelve subjects ran over-ground using three different foot strike patterns (heel strike, forefoot strike, toe running). Kinematic data were collected of the forefoot, rearfoot and shank, which were modelled as rigid segments. Coupling at the ankle-complex and midfoot joints was assessed using cross-correlation and vector coding techniques. FINDINGS: In general good coupling was found between rearfoot frontal plane motion and transverse plane shank rotation regardless of foot strike pattern. Forefoot motion was also strongly coupled with rearfoot frontal plane motion. Subtle differences were noted in the amount of rearfoot eversion transferred into shank internal rotation in the first 10-15% of stance during heel strike running compared to forefoot and toe running, and this was accompanied by small alterations in forefoot kinematics. INTERPRETATION: These findings indicate that during ground contact in running there is strong coupling between the rearfoot and shank via the action of the joints in the ankle-complex. In addition, there was good coupling of both sagittal and transverse plane forefoot with rearfoot frontal plane motion via the action of the midfoot joints.

Midtarsal locking, the windlass mechanism, and running strike pattern: A kinematic and kinetic assessment.

Changes in running strike pattern affect ankle and knee mechanics, but little is known about the influence of strike pattern on the joints distal to the ankle. The purpose of this study was to explore the effects of forefoot strike (FFS) and rearfoot strike (RFS) running patterns on foot kinematics and kinetics, from the perspectives of the midtarsal locking theory and the windlass mechanism. Per the midtarsal locking theory, we hypothesized that the ankle would be more inverted in early stance when using a FFS, resulting in decreased midtarsal joint excursions and increased dynamic stiffness. Associated with a more engaged windlass mechanism, we hypothesized that a FFS would elicit increased metatarsophalangeal joint excursions and negative work in late stance. Eighteen healthy female runners ran overground with both FFS and RFS patterns. Instrumented motion capture and a validated multi-segment foot model were used to analyze midtarsal and metatarsophalangeal joint kinematics and kinetics. During early stance in FFS the ankle was more inverted, with concurrently decreased midtarsal eversion (p < 0.001) and abduction excursions (p = 0.003) but increased dorsiflexion excursion (p = 0.005). Dynamic midtarsal stiffness did not differ (p = 0.761). During late stance in FFS, metatarsophalangeal extension was increased (p = 0.009), with concurrently increased negative work (p < 0.001). In addition, there was simultaneously increased midtarsal positive work (p < 0.001), suggesting enhanced power transfer in FFS. Clear evidence for the presence of midtarsal locking was not observed in either strike pattern during running. However, the windlass mechanism appeared to be engaged to a greater extent during FFS.

MODIFYING STANCE ALTERS THE PEAK KNEE ADDUCTION MOMENT DURING A GOLF SWING.

BACKGROUND: The knee joint is one of the most frequently injured regions in the game of golf, and the loads experienced by the knee during the golf swing are typically greater than during other activities of daily living. Altering movement patterns is a common strategy that can be used to reduce loading on the knee joint but has received little attention during studies of the golf swing. The primary aim of this study was to examine the effect altering golf stance has on the lead limb peak external knee adduction moment. STUDY DESIGN: Laboratory based, quasi-experimental. METHODS: Twenty healthy participants were recruited for a 3-dimensional biomechanical analysis wherein participants hit three golf shots with a driver using the following stance conditions: self-selected, bilateral 0 º foot angle, bilateral 30 º foot angle, wide stance width, and narrow stance width. RESULTS: Both the 30 º foot angle (0.80 ± 0.51 Nm) and wide stance width (0.89 ± 0.49 Nm) conditions significantly decreased (p < 0.001) the lead limb peak external knee adduction moment compared to the self-selected (1.15 ± 0.58 Nm) golf stance. No significant differences (p = 0.109) in swing speed were found between any of the stance conditions. CONCLUSION: The externally rotated foot position and wider stance width decreased the lead limb peak external knee adduction moment without hindering swing speed. Modifying stance could be a viable option for golfers who wish to continue playing the sport at a high level, while reducing potentially detrimental loads at the knee joint.Levels of Evidence: 2b-Individual cohort study.

Reducing Impact Loading in Runners: A One-Year Follow-up.

Increased vertical impact loading during running has been associated with a variety of running related injuries including stress fractures, patellofemoral pain, and plantar fasciitis. PURPOSE: The purpose of this study was to examine the acute and long-term effect of a gait retraining program aimed at teaching runners with high impact loading to run softer. METHODS: Nineteen runners with high tibial shock (TS) first underwent a control period of eight sessions of treadmill running over 2 wk, progressing from 15 to 30 min. This was followed by eight sessions of gait retraining over 2 wk using the identical treadmill protocol. Real-time feedback of TS was provided as the participant ran. Feedback was gradually removed during the last four sessions. Variables of interest included peak TS, vertical impact peak and vertical average loading rate, and vertical instantaneous loading rate. These variables were assessed at intervals following the retraining and at a 1-yr follow-up. RESULTS: All variables of interest were significantly reduced post-retraining (P < 0.001). TS was reduced by 32%, vertical impact peak by 21%, vertical instantaneous loading rate by 27%, and vertical average loading rate by 25%. All variables continued to be significantly reduced at a 1-yr follow-up. CONCLUSIONS: Impact loading can be reduced through gait retraining and the results persist at least 1 yr. As impact loading is associated with injury, this simple intervention may provide a powerful method of reducing musculoskeletal injury risk in runners.

Forefoot, rearfoot and shank coupling: effect of variations in speed and mode of gait.

BACKGROUND: Although there is a wealth of research into the kinematic coupling between the foot and shank, it remains unclear whether the relationship is stable across speed and mode of gait. The aim of this study was to determine whether the coupling relationship between the forefoot, rearfoot and shank differed between walking and running, and across different running speeds. METHODS: Twelve subjects walked/ran barefoot over-ground at one walking and three running speeds. The shank, rearfoot and forefoot were modelled as rigid segments and three-dimensional joint kinematics were determined using a seven camera ProReflex system. Coupling between the forefoot, rearfoot and shank was assessed using cross-correlation and vector coding techniques. FINDINGS: Cross-correlation of rearfoot eversion/inversion with shank internal/external rotation was lower in walking (r=0.49) compared to running (r>0.95). This was also the case between rearfoot frontal plane and forefoot sagittal plane motion (walking, r=-0.80; running, r=-0.96). Rearfoot frontal plane and forefoot transverse plane cross-correlation was high in both running and walking (r>0.90), but there was little evidence of any coupling between rearfoot frontal plane and forefoot frontal plane motion in any condition. No differences in cross-correlations were found between the three running speeds. INTERPRETATION: Kinematic coupling between the forefoot, rearfoot and shank was weak during walking relative to running. In particular, the low cross-correlation between rearfoot eversion/inversion and shank internal/external rotation during walking implies the two motions are not rigidly linked, as has been assumed in previous injury models.

External loading alters trunk kinematics and lower extremity muscle activity in a distribution-specific manner during sitting and rising from a chair.

BACKGROUND: Excess body mass alters gait biomechanics in a distribution-specific manner. The effects of adding mass centrally or peripherally on biomechanics during sitting and rising from a chair are unknown. METHODS: Motion analysis and lower extremity EMG were measured for fifteen healthy, normal weight subjects during sit-to-stand (SitTS) and stand-to-sit (StandTS) from a chair under unloaded (UN), centrally loaded (CL), and peripherally loaded (PL) conditions. RESULTS: Compared to UN, PL significantly increased support width (SitTS and StandTS), increased peak trunk flexion velocity (SitTS), and trended to increase peak trunk flexion angle (SitTS). During StandTS, CL significantly reduced peak trunk flexion compared to UN and PL. EMG activity of the semitendinosus, vastus lateralis and/or medialis was significantly increased in CL compared to UN during SitTS and StandTS. CONCLUSIONS: Adding mass centrally or peripherally induces contrasting biomechanical strategies to successfully sit or rise from a chair. CL limits trunk flexion and increases knee extensor muscle activity whereas; PL increases support width and trunk flexion, thus preventing increased EMG activity.

Changes in foot and lower limb coupling due to systematic variations in step width.

BACKGROUND: Motion at the midfoot joints can contribute significantly to overall foot motion during gait. However, there is little information regarding the kinematic coupling relationship at the midfoot. The purpose of the present study was to determine whether the coupling relationship at the midfoot and subtalar joints was affected when step width was manipulated during running. METHODS: Twelve subjects ran over-ground at self-selected speeds using three different step widths (normal, wide, cross-over). Coupling at the midfoot (forefoot relative to rearfoot) and subtalar (rearfoot relative to shank) joints was assessed using cross-correlation techniques. FINDINGS: Rearfoot kinematics were significantly different from normal running in cross-over running (P<0.05) but not in wide running. However, coupling between rearfoot eversion/inversion and shank rotation was consistently high (r>0.917), regardless of step width. This was also the case for coupling between rearfoot frontal plane motion and forefoot sagittal plane (r<-0.852) and forefoot transverse plane (r>0.946) motion. There was little evidence of coupling between rearfoot frontal plane motion and forefoot frontal plane motion in any of the conditions. INTERPRETATION: Forefoot frontal plane motion appeared to have little effect on rearfoot frontal plane motion and thus, had no effect on motion at the subtalar joint. The strong coupling of forefoot sagittal and transverse plane motions with rearfoot frontal plane motion suggests that forefoot motion exerts an important influence on subtalar joint kinematics.

Frontal plane kinematics of the hip during running: Are they related to hip anatomy and strength?

Excessive hip adduction has been associated with a number of lower extremity overuse running injuries. The excessive motion has been suggested to be the result of reduced strength of the hip abductor musculature. Hip anatomical alignment has been postulated to influence hip abduction (HABD) strength and thus may impact hip adduction during running. The purpose of this study was to investigate the relationship between hip anatomy, HABD strength, and frontal plane kinematics during running. Peak isometric HABD strength, 3D lower extremity kinematics during running, femoral neck-shaft angle (NSA), and pelvis width-femur length (PW-FL) ratio were recorded for 25 female subjects. Pearson correlations (p<0.05) were performed between variables. A fair relationship was observed between femoral NSA and HABD strength (r=-0.47, p=0.02) where an increased NSA was associated with reduced HABD strength. No relationship was observed between HABD strength and hip adduction during running. None of the anatomical measurements, NSA or PW-FL, were associated with hip adduction during running. Deviations in the femoral NSA have a limited ability to influence peak isometric hip abduction strength or frontal plane hip kinematics during running. Hip abduction strength does also not appear to be linked with changes in hip kinematics. These findings in healthy individuals question whether excessive hip adduction typically seen in female runners with overuse injuries is caused by deviations in hip abduction strength or anatomical structure.

Experimentally reduced hip-abductor muscle strength and frontal-plane biomechanics during walking.

CONTEXT: Researchers have postulated that reduced hip-abductor muscle strength may have a role in the progression of knee osteoarthritis by increasing the external knee-adduction moment. However, the relationship between hip-abductor strength and frontal-plane biomechanics remains unclear. OBJECTIVE: To experimentally reduce hip-abduction strength and observe the subsequent changes in frontal-plane biomechanics. DESIGN: Descriptive laboratory study. SETTING: Research laboratory. PATIENTS OR OTHER PARTICIPANTS: Eight healthy, recreationally active men (age = 27 ± 6 years, height = 1.75 ± 0.11 m, mass = 76.1 ± 10.0 kg). INTERVENTION(S): All participants underwent a superior gluteal nerve block injection to reduce the force output of the hip-abductor muscle group. MAIN OUTCOME MEASURE(S): Maximal isometric hip-abduction strength and gait biomechanical data were collected before and after the injections. Gait biomechanical variables collected during walking consisted of knee- and hip-adduction moments and impulses and the peak angles of contralateral pelvic drop, hip adduction, and ipsilateral trunk lean. RESULTS: Hip-abduction strength was reduced after the injection (P = .001) and remained lower than baseline values at the completion of the postinjection gait data collection (P = .02). No alterations in hip- or knee-adduction moments (hip: P = .11; knee: P = .52) or impulses (hip: P = .16; knee: P = .41) were found after the nerve block. Similarly, no changes in angular kinematics were observed for contralateral pelvic drop (P = .53), ipsilateral trunk lean (P = .78), or hip adduction (P = .48). CONCLUSIONS: A short-term reduction in hip-abductor strength was not associated with alterations in the frontal-plane gait biomechanics of young, healthy men. Further research is needed to determine whether a similar relationship is true in older adults with knee osteoarthritis.

Does tester experience influence the reliability with which 3D gait kinematics are collected in healthy adults?

OBJECTIVES: To determine whether tester experience influences the reliability of three-dimensional gait collections. DESIGN: Reliability study. PARTICIPANTS: Ten healthy subjects visited a university gait laboratory on two separate days and underwent a walking gait analysis. During each visit, kinematic data were collected by a biomechanist with 8 years of 3D gait analysis experience (EXP) and a physical therapist with no previous 3D gait analysis experience (NOV). MAIN OUTCOME MEASURES: Joint kinematic angles were calculated using either a functional or predictive joint identification method. Within-tester and between-tester measures of reliability were determined by calculating the root mean square error (RMS) and coefficient of multiple correlations (CMC). RESULTS: Within-tester RMS and CMC values were not significantly different (P > 0.05) between the EXP and NOV testers using either a functional or predictive joint approach. Within-tester CMC values exceeded 0.90 for both testers across all kinematic variables. Between-tester CMC reliability values were greater than 0.85 for all variables measured. CONCLUSIONS: Following basic training, a physiotherapy clinician with no previous 3D gait experience is as reliable as an experienced gait biomechanist with respect to marker placement accuracy. In addition, reliability comparisons between an experienced and novice tester appear independent of the joint identification method chosen.

Variables during swing associated with decreased impact peak and loading rate in running.

When the foot impacts the ground in running, large forces and loading rates can arise that may contribute to the development of overuse injuries. Investigating which biomechanical factors contribute to these impact loads and loading rates in running could assist clinicians in developing strategies to reduce these loads. Therefore, the goals of our work were to determine variables that predict the magnitude of the impact peak and loading rate during running, as well as to investigate how modulation of knee and hip muscle activity affects these variables. Instrumented gait analysis was conducted on 48 healthy subjects running at 3.3m/s on a treadmill. The top four predictors of loading rate and impact peak were determined using a stepwise multiple linear regression model. Forward dynamics was performed using a whole body musculoskeletal model to determine how increased muscle activity of the knee flexors, knee extensors, hip flexors, and hip extensors during swing altered the predictors of loading rate and impact peak. A smaller impact peak was associated with a larger downward acceleration of the foot, a higher positioned foot, and a decreased downward velocity of the shank at mid-swing while a lower loading rate was associated with a higher positioned thigh at mid-swing. Our results suggest that an alternative to forefoot striking may be increased hip flexor activity during swing to alter these mid-swing kinematics and ultimately decrease the leg's velocity at landing. The decreased velocity would decrease the downward momentum of the leg and hence require a smaller force at impact.

Gait biomechanics and hip muscular strength in patients with patellofemoral osteoarthritis.

A significant number of patients with patellofemoral osteoarthritis (PFOA) have described a history of patellofemoral pain syndrome (PFPS). This leads to speculation that the underpinning mechanical causes of PFPS and PFOA may be similar. Although alterations in gait biomechanics and hip strength have been reported in PFPS, this relationship has not yet been explored in PFOA. Therefore the purpose of this study was compare gait biomechanics and hip muscular strength between PFOA patients and a healthy control group. Fifteen patients with symptomatic, radiographic PFOA and 15 controls participated. All patients underwent a walking gait analysis and maximal hip strength testing. Biomechanical variables of interest included the peak angular values of contra-lateral pelvic drop, hip adduction and hip internal rotation during the stance phase. Hip abduction and external rotation strength were assessed using maximal voluntary isometric contractions. The PFOA group demonstrated significantly lower hip abduction strength compared to controls but no difference in hip external rotation strength. There were no statistical differences between the PFOA and control groups for contra-lateral pelvic drop, hip adduction and hip internal rotation angles during walking. Despite patients with PFOA exhibiting weaker hip abductor muscle strength compared to their healthy counterparts they did not demonstrate alterations in pelvis or hip biomechanics during gait. These preliminary data suggests that weaker hip abductor strength does not result in biomechanical alterations during gait in this population.