Scapulothoracic latent muscle reaction timing comparison between trained overhead throwers and untrained control subjects.

AIM: This study evaluated select scapulothoracic muscles for training-induced latent muscle reaction timing (LMRT) changes. Comparisons were also made between the dominant and non-dominant upper extremities and between individual muscles. MATERIALS AND METHODS: Fifteen male trained overhead throwers (college baseball pitchers) and 15 male untrained, age-matched control subjects participated in this study. Scapulothoracic muscle activation data were collected as subjects attempted to stop a variably timed, sudden glenohumeral joint internal rotation perturbation. RESULTS: Training group differences were not evident for LMRT (P=0.56), however upper extremity dominance (P=0.003) and test muscle (P=0.0002) displayed significant differences. Dominant upper extremity upper trapezius muscle LMRT (72.5+/-26 ms) occurred later than non-dominant upper trapezius muscle LMRT (60.0+/-14.1 ms, P=0.001). Dominant upper extremity middle trapezius-rhomboid muscle LMRT (60.0+/-16.2 ms) occurred later than non-dominant middle trapezius-rhomboid muscle LMRT (50.2+/-12.6 ms, P=0.004). Dominant upper extremity upper trapezius muscle LMRT also occurred later than serratus anterior (55.7+/-16.0 ms, P=0.001) and middle trapezius-rhomboid LMRT (60.2+/-16 ms, P=0.003). Mean overall dominant upper extremity LMRT (62.7+/-19.4 ms) was delayed compared with mean overall non-dominant upper extremity LMRT (53.9+/-12.4 ms, P=0.003). CLINICAL CONSEQUENCES: Although training was not found to influence scapulothoracic LMRT, differences were observed between the dominant and non-dominant upper extremities. Consistent LMRT delays at the dominant upper extremity suggest possible neuromuscular timing differences to enable prolonged glenohumeral joint and scapulothoracic articulation acceleration before deceleration through eccentric muscle activation. Both trained and untrained overhead throwers displayed this response. Variable perturbation test velocities, and in-season testing of larger subject groups may be needed to better elucidate the more subtle differences associated with training.

Physiological coxa varus-genu valgus influences internal knee and ankle joint moments in females during crossover cutting.

This study evaluated the ankle and knee electromyographic, kinematic, and kinetic differences of 20 nonimpaired females with either neutral (group 1) or coxa varus-genu valgus (group 2) alignment during crossover cutting stance phase. Two-way mixed model ANOVA (group, session) assessed mean differences ( p<0.05) and correlation analysis further delineated relationships. During impact absorption, group 2 displayed earlier peak horizontal braking (anterior-posterior) ground reaction force timing, decreased and earlier peak internal knee extension moments (eccentric function), and earlier peak internal ankle dorsiflexion moment timing (eccentric function). During the pivot phase, group 2 displayed later and eccentrically-biased peak ankle plantar flexion moments, increased peak internal knee flexion moments (eccentric function), and later peak knee internal rotation timing. Correlation analysis revealed that during impact absorption, subjects with coxa varus-genu valgus alignment (group 2) displayed a stronger relationship between knee internal rotation velocity and peak internal ankle dorsiflexion moment onset timing ( r= -0.64 vs r = -0.26) and between peak horizontal braking ground reaction forces and peak internal ankle dorsiflexion moment onset timing ( r= 0.61 vs r= 0.24). During the pivot phase these subjects displayed a stronger relationship between peak horizontal braking ground reaction forces and peak internal ankle plantar flexion moment onset timing ( r= -0.63 vs r= -0.09) and between peak horizontal braking forces and peak internal ankle plantar flexion moments ( r= -0.72 vs r= -0.26). Group differences suggest that subjects with coxa varus-genu valgus frontal-plane alignment have an increased dependence on both ankle dorsiflexor and plantar flexor muscle group function during crossover cutting. Greater dependence on ankle muscle group function during the performance of a task that requires considerable 3D dynamic knee joint control suggests a greater need for frontal and transverse plane weight bearing tasks that facilitate eccentric ankle muscle group function to optimize injury prevention conditioning and post-surgical rehabilitation programs.

Medial patellar taping changes the peak plantar force location and timing of female basketball players.

Subtle changes in patellofemoral joint biomechanics may influence lower extremity function. The McConnell method of patellar taping has become an increasingly popular method of managing patients with various patellofemoral joint disorders. The purpose of this order effect controlled study was to assess medial patellar taping (McConnell Method) for changes in peak plantar force location and timing while running and dribbling a basketball prior to the performance of a basketball lay-up. Sixteen non-impaired, right hand dominant members of a female junior varsity basketball team (age=14.6 +/- 2 years) participated in this study. Subject bodyweight and height were 607.8 +/- 99 N and 1.67 +/- 0.10 m, respectively. All data were collected from the preferred stance limb. A series of two way analysis of variance (ANOVA) (condition, trial) were used to determine statistical significance (P < or = 0.05). During medial patellar taping, subjects displayed a more forefoot directed peak plantar force location 89.9 +/- 18 versus 81.3 +/- 21 mm and delayed peak plantar force onset 141 +/ - 23 versus 130 +/- 29 ms following initial ground contact. Medial-lateral peak plantar force location and peak plantar force magnitude did not differ between conditions, however, medial-lateral peak plantar force location displayed significant trial sequence influences with the latter trials displaying more lateral center of plantar force locations (30.4 +/- 2 vs. 32.5 +/- 3 mm). The results of this study suggest that medial patellar taping influences distal lower extremity function by shifting peak plantar force location toward the forefoot, and delaying its onset. These changes with consideration for known synergistic ankle plantar flexor-subtalar joint invertor and knee extensor function during weight bearing suggest the presence of increased muscular stiffness acting through a more rigid foot to improve the impact force attenuating capability of the lower extremity.

Posterior cruciate ligament reconstruction (double bundle) using anterior tibialis tendon allograft.

Posterior cruciate ligament (PCL) reconstruction using a double-bundle technique has been described. However, reconstruction with a cryopreserved anterior tibialis tendon allograft and bioabsorbable fixation has not been described. The purpose of this article is to present this surgical technique with discussion and rationale for its indication and use in patients with PCL-deficient knees.

Crossover cutting during hamstring fatigue produces transverse plane knee control deficits.

OBJECTIVE: To assess the effects of eccentric work-induced hamstring fatigue on sagittal and transverse plane (axial) knee and ankle biodynamics and kinetics during a running crossover cut directional change (functional pivot shift). DESIGN AND SETTING: A pretest-posttest, single-group intervention experimental design was employed. All data were collected in a biodynamics laboratory. SUBJECTS: Twenty healthy athletic females were trained for 3 weeks in crossover cutting before testing. MEASUREMENTS: Data were sampled during 3 unfatigued and 3 fatigued (20% eccentric isokinetic knee-flexor torque reduction) crossover cut trials. Three-dimensional kinematic and ground reaction-force data were sampled at 200 Hz and 1000 Hz, respectively, and joint moment estimates were calculated. Data were standardized to initial force-plate heelstrike for comparisons of mean differences between conditions using paired t tests with Bonferroni adjustments. Pearson product-moment correlations compared kinematic and eccentric hamstring-torque relationships. RESULTS: During internal rotation phase 1, between heelstrike and impact absorption, mean internal rotation velocity increased by 21.2 degrees /s +/- 114 degrees /s. During internal rotation phase II, mean peak transverse plane knee rotation during propulsion decreased by 3.1 degrees +/- 9 degrees . During internal rotation phase II, mean peak ankle plantar flexor moment onsets occurred 12.7 +/- 53 milliseconds earlier, and this activation demonstrated a moderately positive relationship with the onset of mean peak knee internal rotation during propulsion and a weak negative relationship with mean peak hamstring torque/lean body weight. CONCLUSIONS: The increased knee internal rotation velocity during phase I indicates transverse plane dynamic knee-control deficits during hamstring fatigue. Earlier peak ankle plantar-flexor moments and decreased internal rotation during phase II in the presence of hamstring fatigue may represent compensatory attempts at dynamic knee stabilization from the posterior lower leg musculature during the pivot shift portion of the crossover cut. The weak relationship between decreased hamstring torque/lean body weight and delayed knee internal rotation during propulsion further supports greater dependence on ankle plantar flexors for dynamic knee stabilization compensation.

The human glenohumeral joint. A proprioceptive and stability alliance.

The glenohumeral joint, because of its relatively poor osseous and capsuloligamentous stability, depends upon the proprioceptive and stabilizing capabilities of musculotendinous structures more than any other joint in the human body. The purpose of this review is to compare the morphology, histology, and sensorimotor functional relationships of the human glenohumeral joint with the more abundant animal research data. From a synthesis of this information, a proprioceptive and stability alliance is proposed for the human glenohumeral joint which is initiated by mechanoreceptor activation from capsuloligamentous and musculotendinous structures, resulting in reflex-mediated protective muscular responses that are ultimately under the bias and sensitivity control of upper levels of the central nervous system hierarchy. The clinical impact of these findings as they relate to rehabilitation and conditioning strategies, surgical intervention, aging, and injury are discussed in addition to future research directions.

Results of the Kentucky high school football knee injury survey.

The study attempted to: 1) determine knee injury and reinjury incidence of Kentucky high school football players; 2) relate results to initial care provider, treatment following initial physician exam, time lost from injury, injury type, player position, and team size; and 3) assess coaches opinions and practices about lateral prophylactic knee brace (LPKB) usage and effectiveness. A post season, mail-in coaches' survey (50.2% return, 101/201) collected these data. Returned surveys represented 4690 players with average team size (x +/- SD) of 43 +/- 13. Two hundred fifty seven reported knee injuries yielded .055 knee injuries/player with .04 knee injuries/player being "new" and .015 knee injuries/player recurring (27% of reported knee injuries) during the season. Games accounted for 56.4% (56/101) of reported knee injuries. Coaches generally believed that LPKB usage prevented knee injuries (56.4%, 56/101) and allowed LPKB usage (92.1%, 93/101), however only 8.3% (8/101) required their wear (interior linemen 50%, linebackers 25%, entire team (25%). Interior linemen had the greatest number of knee injuries, followed by offensive backs and linebackers. Most knee injuries (81%, 208/257) were out 3-6 weeks or less, 64% (164/257) involved sprains or contusions, 38% (97/257) were treated surgically (alone or with rehabilitation) and 36% (92/257) were treated solely with rehabilitation. Total knee injury and reinjury incidence were under-estimated compared to existing reports. Improved injury recording methods, and post-symposia coaches evaluation are recommended.

The effect of quadriceps femoris, hamstring, and placebo eccentric fatigue on knee and ankle dynamics during crossover cutting.

This study attempted to determine the effect of eccentric quadriceps femoris, hamstring, and placebo fatigue on stance limb dynamics during the plant-and-cut phase of a crossover cut. Twenty female college students (task trained) were tested. Hamstring fatigue resulted in decreased peak impact knee flexion moments (p < or = .01), increased internal tibial rotation at peak knee flexion (p < or = .05), and decreased peak ankle dorisflexion (p < or = .05). Quadriceps fatigue resulted in increased peak ankle dorsiflexion moments (p < .01), decreased peak posterior braking forces (p < or .01), decreased peak knee extension moments (p < or = .01), delayed peak knee flexion (p < or = .01), delayed peak propulsive forces (p < .01), and delayed subtalar peak inversion moments (p < or = .05). Fatigue of either muscle group produced earlier peak ankle plantar flexion moments (p < = .05) and decreased peak propulsive knee flexion moments (p < or = .05). Variables requiring further study (p < or = .1) provide discussion data. Soleus, gastrocnemius, tibialis anterior, and deep posterior compartment calf muscles serve as dynamic impact force attenuators, compensating for fatigued proximal muscles.

Fatigue after eccentric quadriceps femoris work produces earlier gastrocnemius and delayed quadriceps femoris activation during crossover cutting among normal athletic women.

Athletic women are at greater risk of anterior cruciate ligament (ACL) injury than men. Twenty, healthy, athletic women were evaluated for the effect of preferred stance limb isokinetic quadriceps femoris and hamstring fatigue from eccentric work compared with controls on the activation onset of vastus medialis, rectus femoris, vastus lateralis, the medial hamstrings, biceps femoris, and gastrocnemius muscles. Following 3 weeks of crossover cut training, subjects were tested for fatigue effects (5 subjects/week, 3 conditions, 1 condition/day, order effect controlled) on muscle activation onsets prior to crossover cut landing heelstrike (mixed model, ANOVA, P < 0.05). Fatigue from eccentric quadriceps femoris work produced delayed vastus medialis (P = 0.03), rectus femoris (P = 0.007), and vastus lateralis (P = 0.03) activation onsets compared with control, but did not differ compared to hamstring fatigue. Neither hamstring nor quadriceps femoris fatigue produced differences (P > 0.05) in medial hamstring or biceps femoris activation onsets compared to control. Quadriceps femoris fatigue from eccentric work produced earlier gastrocnemius activation onsets (P = 0.048) than control, but did not differ for hamstring fatigue. The gastrocnemius appears to provide synergistic and compensatory dynamic knee stabilization in closed kinetic chain function during quadriceps femoris fatigue. This finding in a normal group at high risk of ACL injury while performing a maneuver with a high ACL injury risk supports gastrocnemius inclusion in knee rehabilitation and conditioning programs and suggests the need for comparative evaluations of knee injured/reconstructed subjects.

Relationship of fatigued run and rapid stop to ground reaction forces, lower extremity kinematics, and muscle activation.

Fatigue may be related to lower extremity injury. The effect of lower extremity fatigue on ground reaction force production, lower extremity kinematics, and muscle activation during the landing phase of a run and rapid stop was investigated. Subjects were 19 female, Division 1 collegiate basketball and volleyball players (mean age = 20.8 +/- 1.8 years, mean weight = 71.7 +/- 6.9 kg, mean height = 174 +/- 5 cm). Dominant leg ground reaction and muscle activation data were sampled at 2,000 Hz. Lower extremity kinematic data were sampled at 200 Hz, and three-dimensional analysis was performed. Knee extensor/flexor muscle activation tended to be delayed during fatigue (p < or = .08). Maximum knee flexion tended to occur earlier during fatigue (p < or = .09). Step-wise multiple regression suggested that the knee may be the primary site of force attenuation following fatigue. During fatigue, biodynamical compensations in the mechanical properties of the knee extensor musculature, as evidenced by differences in knee kinematics and muscle activation times, may occur to enhance knee stability.

Biomechanics of the elbow.

This article examines the basic structure and function of the elbow from a biomechanical perspective. Kinematics, including types and ranges of motion are described. Anatomical and functional parameters related to joint stability and loading patterns are discussed in relation to joint kinetics. A final section summarizes pertinent EMG findings related to elbow function.