Influence of Anticipation and Motor-Motor Task Performance on Cutting Biomechanics in Healthy Men.

CONTEXT: Biomechanical analyses of cutting tasks have demonstrated kinematic differences associated with the noncontact knee-injury risk when the movement direction is unanticipated. Motor-motor dual tasks occur within dynamic environments and change the demand for attentional resources needed to complete athletic maneuvers, which may contribute to injury risk. OBJECTIVE: To investigate the influence of anticipation and motor-motor task performance on cutting biomechanics. DESIGN: Cross-sectional study. SETTING: Laboratory. PATIENTS OR OTHER PARTICIPANTS: A total of 32 healthy, recreationally active men (age = 23.1 ± 3.6 years, height = 180.0 ± 7.0 cm, mass = 81.3 ± 17.3 kg) who self-reported regular participation in cutting sports. INTERVENTION(S): Participants performed a 45° side-step cut on the dominant limb in a random order of conditions: anticipation (anticipated, unanticipated) and task (no ball throw, ball fake, ball throw). MAIN OUTCOME MEASURE(S): Triplanar trunk, hip, and knee angles were assessed throughout the stance phase using 3-dimensional motion capture. Data were analyzed using a time series of means calculated from initial contact to toe-off (0%-100%) with 90% confidence intervals. Mean differences between conditions were identified as regions of nonoverlapping confidence intervals, and those that occurred during the region of peak vertical ground reaction force (0%-25%) are presented. RESULTS: Regardless of anticipation, attending to a ball (ball throw) resulted in more trunk extension (range = 2.9°-3.7°) and less lateral trunk flexion toward the cutting direction (range = 5.2°-5.9°). Planning to attend to a ball (ball fake) resulted in less lateral trunk flexion toward the cutting direction (4.7°). During unanticipated cutting, more trunk rotation away from the cutting direction was observed when attending to a ball (range = 5.3°-7.1°). The interaction of anticipation and task had a similar influence on sagittal- and frontal-plane trunk position. CONCLUSIONS: Motor-motor task performance and its interaction with anticipation induced an upright, neutral trunk position during side-step cutting, which has been associated with the risk for noncontact knee injury. Promoting task complexity during rehabilitation and injury-prevention programs may better prepare individuals to succeed when performing high-risk athletic maneuvers.

Surface electromyography of the forearm musculature during an overhead throwing rehabilitation progression program.

OBJECTIVE: The flexor carpi ulnaris (FCU) and flexor digitorum superficialis (FDS) provide dynamic stabilization to the medial elbow. It remains unclear how these muscles function during progressive throwing exercises. Our objective was to compare FCU and FDS surface electromyography (sEMG) during a throwing progression. DESIGN: Crossover. SETTING: Laboratory. PARTICIPANTS: Sixteen healthy males. MAIN OUTCOME MEASURES: Participants completed a plyometric throw (PLYO), long-toss 50% (LT50), long-toss 75% (LT75), and pitch (PITCH). sEMG was synchronized with three-dimensional kinematics to assess the acceleration phase of each exercise. Peak sEMG amplitude (%MVIC) and percentage change between progressive exercises was measured. Continuous sEMG data were assessed to determine when peak activation occurred during acceleration. RESULTS: FCU activity was greater during PITCH than LT50, and during LT75 than LT50. Percentage change was greater from LT50-to-LT75 than PLYO-to-LT50 for both muscles. PLYO and PITCH increased most during late acceleration, whereas LT50 and LT75 increased most during mid-acceleration. CONCLUSIONS: FCU activity did not increase in a stepwise manner, and FDS remained unchanged. Each muscle demonstrated a disproportionate increase in activation during the second exercise progression (LT50-to-LT75) compared to the first (PLYO-to-LT50), suggesting that additional exercises may be required to achieve a stepwise progression relative to forearm muscle activation.

The associations between quadriceps muscle strength, power, and knee joint mechanics in knee osteoarthritis: A cross-sectional study.

BACKGROUND: Abnormal knee joint mechanics have been implicated in the pathogenesis and progression of knee osteoarthritis. Deficits in muscle function (i.e., strength and power) may contribute to abnormal knee joint loading. The associations between quadriceps strength, power and knee joint mechanics remain unclear in knee osteoarthritis. METHODS: Three-dimensional motion analysis was used to collect peak knee joint angles and moments during the first 50% of stance phase of gait in 33 participants with knee osteoarthritis. Quadriceps strength and power were assessed using a knee extension machine. Strength was quantified as the one repetition maximum. Power was quantified as the peak power produced at 40-90% of the one repetition maximum. FINDINGS: Quadriceps strength accounted for 15% of the variance in peak knee flexion angle (P=0.016). Quadriceps power accounted for 20-29% of the variance in peak knee flexion angle (P<0.05). Quadriceps power at 90% of one repetition maximum accounted for 9% of the variance in peak knee adduction moment (P=0.05). INTERPRETATION: These data suggest that quadriceps power explains more variance in knee flexion angle and knee adduction moment during gait in knee osteoarthritis than quadriceps strength. Additionally, quadriceps power at multiple loads is associated with knee joint mechanics and therefore should be assessed at a variety of loads. Taken together, these results indicate that quadriceps power may be a potential target for interventions aimed at changing knee joint mechanics in knee osteoarthritis.

Real-time feedback during drop landing training improves subsequent frontal and sagittal plane knee kinematics.

BACKGROUND: Although neuromuscular training featuring visual feedback may benefit modification of anterior cruciate ligament injury-risk linked knee kinematics, wide-spread clinical intervention has been limited to date. This study evaluated the effects of a Microsoft Kinect-based feedback system for modification of drop vertical jump knee kinematics traditionally consistent with predisposition to non-contact anterior cruciate ligament injury in female athletes. We hypothesized that a four-week feedback training protocol would increase peak knee flexion angle and frontal plane valgus-correlated knee separation distance during drop jump landing performance. METHODS: Twenty-four female athletes were randomly divided equally into control or Kinect-based feedback groups. Subjects were pre-screened for peak knee flexion angle and minimum knee separation distance during drop landing and later performed twenty 31cm drop landings three days per week for four weeks. The feedback group received Kinect-based visual feedback, while controls did not. Kinematics were re-assessed immediately following the end of the training period. FINDINGS: The feedback group increased peak knee flexion and experienced a greater improvement in peak knee flexion. The feedback group improved normalized knee separation distance with greater improvement in post-training peak knee separation distance as compared with controls. INTERPRETATION: Kinect-based feedback training significantly improved drop vertical jump knee kinematics associated with non-contact anterior cruciate ligament injury. The Kinect-based feedback approach demonstrates promise for mitigating non-contact anterior cruciate ligament injury predisposing knee biomechanics in female athletes within the clinical environment.

Patellofemoral pain syndrome alters neuromuscular control and kinetics during stair ambulation.

The aim of the study was to investigate differences in frontal plane knee kinetics, onset timing and duration of the gluteus medius (GMed), adductor longus (AL), and vastus medialis oblique (VMO) during stair ambulation between those with and without patellofemoral pain syndrome (PFPS). Twenty PFPS patients and twenty healthy participants completed stair ambulation while surface electromyography (EMG), video, and ground reaction forces were collected. PFPS patients had a higher peak internal knee abduction moment during stair ascent, and a higher internal knee abduction impulse for both ascent and descent. During stair ascent, PFPS patients displayed earlier onset of the AL and later onset of GMed, compared to the healthy individuals. Also, PFPS patients had longer activation duration of the AL and shorter activation durations of the VMO and GMed during stair ascent. During stair descent, PFPS patients displayed delayed GMed onset and shorter activation duration of GMed and VMO. The results of the study suggest that altered neuromuscular control of the medial thigh musculature may be an important contributor to PFPS.

Emergency face-mask removal effectiveness: a comparison of traditional and nontraditional football helmet face-mask attachment systems.

CONTEXT: Football helmet face-mask attachment design changes might affect the effectiveness of face-mask removal. OBJECTIVE: To compare the efficiency of face-mask removal between newly designed and traditional football helmets. DESIGN: Controlled laboratory study. SETTING: Applied biomechanics laboratory. PARTICIPANTS: Twenty-five certified athletic trainers. INTERVENTION(S): The independent variable was face-mask attachment system on 5 levels: (1) Revolution IQ with Quick Release (QR), (2) Revolution IQ with Quick Release hardware altered (QRAlt), (3) traditional (Trad), (4) traditional with hardware altered (TradAlt), and (5) ION 4D (ION). Participants removed face masks using a cordless screwdriver with a back-up cutting tool or only the cutting tool for the ION. Investigators altered face-mask hardware to unexpectedly challenge participants during removal for traditional and Revolution IQ helmets. Participants completed each condition twice in random order and were blinded to hardware alteration. MAIN OUTCOME MEASURE(S): Removal success, removal time, helmet motion, and rating of perceived exertion (RPE). Time and 3-dimensional helmet motion were recorded. If the face mask remained attached at 3 minutes, the trial was categorized as unsuccessful. Participants rated each trial for level of difficulty (RPE). We used repeated-measures analyses of variance (α  =  .05) with follow-up comparisons to test for differences. RESULTS: Removal success was 100% (48 of 48) for QR, Trad, and ION; 97.9% (47 of 48) for TradAlt; and 72.9% (35 of 48) for QRAlt. Differences in time for face-mask removal were detected (F(4,20)  =  48.87, P  =  .001), with times ranging from 33.96 ± 14.14 seconds for QR to 99.22 ± 20.53 seconds for QRAlt. Differences were found in range of motion during face-mask removal (F(4,20)  =  16.25, P  =  .001), with range of motion from 10.10° ± 3.07° for QR to 16.91° ± 5.36° for TradAlt. Differences also were detected in RPE during face-mask removal (F(4,20)  =  43.20, P  =  .001), with participants reporting average perceived difficulty ranging from 1.44 ± 1.19 for QR to 3.68 ± 1.70 for TradAlt. CONCLUSIONS: The QR and Trad trials resulted in superior results. When trials required cutting loop straps, results deteriorated.

Scapular muscle activity in overhead athletes with symptoms of secondary shoulder impingement during closed chain exercises.

OBJECTIVE: To determine the amount of muscle activation in 4 scapular muscles in overhead athletes with and without a history of secondary shoulder impingement, during 3 upper extremity closed chain exercises. DESIGN: One-between (group), one-within (exercise) repeated measures. SETTING: Controlled laboratory study. PARTICIPANTS: Overhead athletes (n=15; mean age +/- SD, 21.0+/-2.5 y; mean height +/- SD, 176.0+/-7.8 cm; mean weight +/- SD, 76.1+/-13.4 kg) demonstrating with symptoms of shoulder impingement and overhead athletes (n=15; mean age +/- SD, 20.4+/-3.8 y; mean height +/- SD, 174.1+/-9.7 cm; mean weight +/- SD, 73.3+/-11.7 kg) with no shoulder pathologies. INTERVENTIONS: Subjects completed 5 individual trials of a standard push-up, a push-up on an unstable surface, and a revolution on a shoulder rehabilitation device while electromyography (EMG) recorded muscle activity of the serratus anterior, upper trapezius, middle trapezius, and lower trapezius. MAIN OUTCOME MEASURES: The mean EMG data for the 4 muscles from the standard push-up, push-up on an unstable surface, and shoulder rehabilitation device trials were normalized as a percentage of a maximum voluntary isometric contraction for each muscle. RESULTS: There was a statistically significant interaction for the middle trapezius (F(2,56)=3.856; P=.027). The shoulder impingement push-up on an unstable surface (33.76%+/-26.45%) had significantly greater activation compared with the shoulder impingement standard push-up (25.88%+/-13.76%), the shoulder impingement shoulder rehabilitation device (9.40%+/-5.86%), and the nonpathology push-up on an unstable surface (19.49%+/-7.73%). The shoulder impingement standard push-up had significantly greater activation compared with the shoulder impingement shoulder rehabilitation device and nonpathology standard push-up (17.99%+/-7.31%). The nonpathology standard push-up and nonpathology push-up on an unstable surface had significantly greater activation compared with the nonpathology shoulder rehabilitation device (7.95%+/-4.30%). CONCLUSIONS: These results suggest that the muscle activation of the middle trapezius differs in overhead athletes with a history of secondary shoulder impingement compared with those who lack this history during closed chain exercise, as well as within the 3 closed chain exercises. The levels of muscle activation of the serratus anterior and upper trapezius during these closed chain exercises were similar between the 2 groups. These results support the use of closed chain exercises in the rehabilitation process of overhead athletes with secondary shoulder impingement. However, clinicians should consider the muscle(s) of interest when selecting an exercise.

Electromyography of 3 scapular muscles: a comparative analysis of the cuff link device and a standard push-up.

CONTEXT: The Cuff Link is a closed kinetic chain rehabilitation apparatus for the upper extremity. Limited research has established its effectiveness to elicit muscle activation of the scapular muscles. OBJECTIVE: To determine if scapular muscle activation differs in response to 2 upper extremity closed kinetic chain exercises: Cuff Link and standard push-up. DESIGN: A single-group, repeated-measures design. SETTING: Controlled laboratory. PATIENTS OR OTHER PARTICIPANTS: Twenty-eight healthy individuals (13 women: age = 19.69 +/- 1.55 years, height = 167.44 +/- 9.52 cm, mass = 61.00 +/- 8.79 kg; 15 men: age = 22.00 +/- 3.91 years, height = 181.44 +/- 6.60 cm, mass = 82.36 +/- 13.23 kg) with no history of shoulder or low back injury volunteered to participate in this study. INTERVENTION(S): Participants performed 10 trials of complete revolutions on the Cuff Link and 10 full-weight-bearing push-ups. We controlled trial velocity and randomized order. Trunk and shoulder positions were normalized to the participant's height. Using surface electromyography, we recorded muscle activity of the serratus anterior, middle trapezius, and lower trapezius. Rectified and smoothed electromyography data for the serratus anterior, middle trapezius, and lower trapezius were normalized as a percentage of the maximal voluntary isometric contractions (%MVIC). MAIN OUTCOME MEASURE(S): Mean muscle activity of the serratus anterior, middle trapezius, and lower trapezius. We used paired-samples t tests to analyze the mean data for each condition. The alpha level was adjusted to .016 to avoid a type I error. RESULTS: Middle trapezius %MVIC was greater during push-ups (27.01 +/- 20.40%) than during use of the Cuff Link (11.49 +/- 9.46%) (P = .001). Lower trapezius %MVIC was greater during push-ups (36.07 +/- 18.99%) than during use of the Cuff Link (16.29 +/- 8.64%) (P = .001). There was no difference in %MVIC for the serratus anterior between conditions. CONCLUSIONS: The push-up demonstrated greater middle trapezius and lower trapezius activation levels compared with the Cuff Link. However, the push-up had a high participant failure rate. Because serratus anterior activation levels were similar, the Cuff Link may be an appropriate alternative for individuals lacking the upper body strength to perform a push-up.

Cortisol concentrations in human skeletal muscle tissue after phonophoresis with 10% hydrocortisone gel.

CONTEXT: The delivery of hydrocortisone through phonophoresis is a widely prescribed technique for the treatment of various musculoskeletal inflammatory conditions. However, limited scientific evidence exists to support the efficacy of phonophoresis in delivering hydrocortisone to skeletal muscle tissue in humans. OBJECTIVE: To determine hydrocortisone (cortisol) concentrations in human skeletal muscle tissue after a phonophoresis treatment using 10% hydrocortisone gel. DESIGN: Randomized design in which 12 subjects were randomly assigned to either an ultrasound (sham) treatment or a 10% hydrocortisone phonophoresis treatment. SETTING: Laboratory. PATIENTS OR OTHER PARTICIPANTS: Twelve healthy subjects (8 women, 4 men: age = 22.3 +/- 2.64 years, height = 168.28 +/- 8.19 cm, mass = 69.58 +/- 9.05 kg) with no history of musculoskeletal disease, preexisting inflammatory conditions, or recent orthopaedic injuries. INTERVENTION(S): Ultrasound at 1.0 MHz, 1.0 W/cm (2), at a continuous setting for 7 minutes was applied to a standardized area of the vastus lateralis muscle in both groups. The contralateral limb served as the control (no treatment) for both the sham and the phonophoresis groups. MAIN OUTCOME MEASURE(S): Vastus lateralis muscle biopsies were taken from both legs immediately after treatment, and cortisol concentrations were analyzed using an enzyme-linked immunosorbent assay. RESULTS: We observed no significant difference in muscle cortisol concentration between the contralateral control limb and the treatment limb in either the sham or the phonophoresis group ( P > .05). No significant difference was noted when the treatment limbs in the sham and phonophoresis groups were compared ( P > .05). CONCLUSIONS: Our data suggest that a 10% hydrocortisone-based phonophoresis treatment did not increase cortisol concentrations in human skeletal muscle tissue.

Relationship between hip and knee strength and knee valgus during a single leg squat.

The purpose of this study was to determine the relationship between hip and knee strength, and valgus knee motion during a single leg squat. Thirty healthy adults (15 men, 15 women) stood on their preferred foot, squatted to approximately 60 deg of knee flexion, and returned to the standing position. Frontal plane knee motion was evaluated using 3-D motion analysis. During Session 2, isokinetic (60 deg/sec) concentric and eccentric hip (abduction/adduction, flexion/extension, and internal/external rotation) and knee (flexion/extension) strength was evaluated. The results demonstrated that hip abduction (r2=0.13), knee flexion (r2=0.18), and knee extension (r2=0.14) peak torque were significant predictors of frontal plane knee motion. Significant negative correlations showed that individuals with greater hip abduction (r=-0.37), knee flexion (r=-0.43), and knee extension (r=-0.37) peak torque exhibited less motion toward the valgus direction. Men exhibited significantly greater absolute peak torque for all motions, excluding eccentric internal rotation. When normalized to body mass, men demonstrated significantly greater strength than women for concentric hip adduction and flexion, knee flexion and extension, and eccentric hip extension. The major findings demonstrate a significant role of hip muscle strength in the control of frontal plane knee motion.

Face-Mask Removal: Movement and Time Associated With Cutting of the Loop Straps.

OBJECTIVE: To quantify the amount of helmet movement, time for task completion, tool satisfaction, and overall efficiency for various face-mask removal tools during football helmet face-mask removal. DESIGN AND SETTING: Each subject performed one trial with the anvil pruner (AP), Face Mask Extractor (FME), PVC pipe cutter (PVC), and Trainer's Angel (TA). Each subject cut through 4 loop straps and removed the face mask while kneeling behind the athlete's head. SUBJECTS: Twenty-nine certified athletic trainers (age = 29.5 +/- 6.2 years, athletic training experience = 6.3 +/- 5.0 years). MEASUREMENTS: Time to complete the task was recorded. Total range of motion and total movement of the helmet were assessed using a 6-camera, 3-dimensional motion-capture system. Satisfaction scores were measured for each subject for each tool. Efficiency scores were calculated using time and total helmet-movement data. RESULTS: When using the FME, subjects were significantly faster than with all other tools (P <.05), and when using the AP and TA, they were significantly faster than with the PVC. No differences were noted between tools in either movement variable. Significant differences were noted for satisfaction (P <.05) for all comparisons except TA versus AP. Efficiency scores were FME, 11.6; AP, 14.3; TA, 14.5; and PVC, 22.9, with lower scores identifying increased efficiency. CONCLUSIONS: In general, subjects using the FME were superior in all variables except the movement variables. Future researchers should assess the removal task using specific protocols to determine whether the tools truly differ in terms of the movement created.

A 3-Dimensional Analysis of Face-Mask Removal Tools in Inducing Helmet Movement.

OBJECTIVE: To evaluate the performance of specific face-mask removal tools during football helmet face-mask retraction using 3-dimensional (3-D) video. DESIGN AND SETTING: Four different tools were used: the anvil pruner (AP), polyvinyl chloride pipe cutters (PVC), Face Mask (FM) Extractor (FME), and Trainer's Angel (TA). Subjects retracted a face mask once with each tool. SUBJECTS: Eleven certified athletic trainers served as subjects and were recruited from among local sports medicine professionals. MEASUREMENTS: We analyzed a sample of movement by 3-D techniques during the retraction process. Movement of the head in 3 planes and time to retract the face mask were also assessed. All results were analyzed with a simple repeated-measures one-way multivariate analysis of variance. An overall efficiency score was calculated for each tool. RESULTS: The AP allowed subjects to perform the face-mask removal task the fastest. Face mask removal with the AP was significantly faster than with the PVC and TA and significantly faster with the TA than the PVC. The PVC and AP created significantly more movement than the FME and TA when planes were combined. No significant differences were noted among tools for flexion-extension, rotation, or lateral flexion. The AP had an efficiency score of 14; FME, 15; TA, 18; and PVC, 35. CONCLUSIONS: The subjects performed the face-mask removal task in the least amount of time with the AP. They completed the task with the least amount of combined movement using the FME. The AP and FME had nearly identical overall efficiency scores for movement and time.