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Context: Greater anterior knee laxity (AKL) is associated with impaired sensory input and decreased functional knee stability. As functional magnetic resonance imaging (MRI) is the gold standard for understanding brain function, methods to load the anterior cruciate ligament in the MRI environment could further our understanding of the ligament’s sensory role in knee joint stability. Objective: To design and validate an MRI-compatible anterior knee joint loading device. Design: Descriptive laboratory study. Setting: University laboratory study. Participants: Sixteen healthy and physically active females participated (age = 23.4 [3.7] y; mass = 64.4 [8.4] kg). Interventions: The AKL was assessed by a commercially available arthrometer. The AKL was also assessed with a custom-made, MRI-compatible device that produced anterior knee joint loading in a manner similar to the commercial arthrometer while obtaining dynamic structural MRI data. Main Outcome Measurements: The AKL (in millimeters) at 133 N of loading was assessed with the commercial knee arthrometer. Anterior displacement of the tibia relative to the femur obtained at 133 N of loading was measured from dynamic MRI data obtained during usage of the custom device. Pearson correlations were used to examine relationships between the 2 measures. The 95% limits of agreement compared the absolute differences between the 2 devices. Results: There was a 3.2-mm systematic difference between AKL (6.3 [1.6] mm) and anterior tibial translation (3.2 [1.0] mm) measures. There was a significant positive correlation between values obtained from the commercial arthrometer and the MRI-compatible device values (r = .553, P = .026). Conclusions: While systematic differences were observed, the MRI-compatible anterior knee joint loading device anteriorly translated the tibia relative to the femur in a similar manner to a commercial arthrometer design to stress the anterior cruciate ligament. Such a device may be beneficial in future functional magnetic resonance imaging study of anterior cruciate ligament mechanoreception.

Context: Although the beneficial effects of using an external focus of attention are well documented in attainment and performance of movement execution, neural mechanisms underlying external focus’ benefits are mostly unknown. Objective: To assess brain function during a lower-extremity gross motor movement while manipulating an internal and external focus of attention. Design: Cross-over study. Setting: Neuroimaging center Participants: A total of 10 healthy subjects (5 males and 5 females) Intervention: Participants completed external and internal focus of attention unilateral left 45° knee extension/flexion movements at a rate of 1.2 Hz laying supine in a magnetic resonance imaging scanner for 4 blocks of 30 seconds interspersed with 30-second rest blocks. During the internal condition, participants were instructed to “squeeze their quadriceps.” During the external condition, participants were instructed to “focus on a target” positioned above their tibia. Main Outcome Measures: T1 brain structural imaging was performed for registration of the functional data. For each condition, 3T functional magnetic resonance imaging blood oxygenation level dependent data representing 90 whole-brain volumes were acquired. Results: During the external relative to internal condition, increased activation was detected in the right occipital pole, cuneal cortex, anterior portion of the lingual gyrus, and intracalcarine cortex (Zmax = 4.5–6.2, P Zmax = 3.4–3.5, P Conclusions: Current results suggest that an external focus directed toward a visual target produces more brain activity in regions associated with vision and ventral streaming pathways, whereas an internal focus manipulated through instruction increases activation in brain regions that are responsible for motor control. Results from this study serve as baseline information for future prevention and rehabilitation investigations of how manipulating focus of attention can constructively affect neuroplasticity during training and rehabilitation.

Context:Potential biomechanical compensations allowing for maintenance of maximal explosive performance during prolonged intermittent exercise, with respect to the corresponding rise in injury rates during the later stages of exercise or competition, are relatively unknown.Objective:To identify lower-extremity countermovement-jump (CMJ) biomechanical factors using a principal-components approach and then examine how these factors changed during a 90-min intermittent-exercise protocol (IEP) while maintaining maximal jump height.Design:Mixed-model design.Setting:Laboratory.Participants:Fifty-nine intermittent-sport athletes (30 male, 29 female) participated in experimental and control conditions.Interventions:Before and after a dynamic warm-up and every 15 min during the 1st and 2nd halves of an individually prescribed 90-min IEP, participants were assessed on rating of perceived exertion, sprint/cut speed, and 3-dimensional CMJ biomechanics (experimental). On a separate day, the same measures were obtained every 15 min during 90 min of quiet rest (control).Main Outcome Measures:Univariate piecewise growth models analyzed progressive changes in CMJ performance and biomechanical factors extracted from a principal-components analysis of the individual biomechanical dependent variables.Results:While CMJ height was maintained during the 1st and 2nd halves, the body descended less and knee kinetic and energetic magnitudes decreased as the IEP progressed.Conclusions:The results indicate that vertical-jump performance is maintained along with progressive biomechanical changes commonly associated with decreased performance. A better understanding of lower-extremity biomechanics during explosive actions in response to IEP allows us to further develop and individualize performance training programs.

Context:Functional implications of clinically relevant abdominal postures have been sparsely examined.Objectives:To evaluate the reliability of sustaining abdominal postures during single-leg landings and the effects of abdominal postures on lower extremity kinetics and energetics.Design:One-way ANOVA tested effects of leg-spring stiffness and lower extremity energetics across groups (control, abdominal hollowing [AH], and pelvic tilting [PT]).Participants:12 male (24.0 ± 3.4 years) and 12 female (21.9 ± 2.3 years) healthy, recreationally active subjects.Main Outcome Measures:Leg-spring stiffness and relative joint-energy absorption from control, AH, and PT groups.Results:AH and PT ICCs2,k and standard error of measurements (AH = 0.53 ± 0.4 cm, PT = 0.9° ± 0.8°) were moderate to high. Relative knee-energy-absorption effect sizes comparing the control and treatment groups revealed moderate treatment effects (AH = 0.66%, PT = 0.41%).Conclusions:Abdominal postures can be reliably performed during a single-leg-landing task. Energy-absorption effect sizes suggest a link between the trunk and lower extremity.

Objective:To determine whether gluteus medius (GM) activity increases in response to isometric closed-chain external hip rotation.Design:Subjects performed single-leg stances in 3 different conditions: 0° knee flexion, 0° hip flexion (C1); 0° knee flexion, 20° hip flexion (C2); and knee flexed 20–30°, 20° hip flexion (C3). Posteriorly directed forces of 8.9 N (F1), 17.8 N (F2), and 26.7 N (F3) were applied at the lateral pelvis of the nonstance side during each condition.Subjects:20 college students.Measurements:Surface EMG RMS amplitude from the GM and kinematic data from the trunk, hip, and knee.Results:Statistical analyses revealed a significant Condition 3 Force interaction and significant increases of EMG activity from C1F1 and C1F2 to C1F3 and from C3F1 to C3F2 and C3F3. F2 and F3 of C2 were significantly less than F2 and F3 of both C1 and C3.Conclusions:GM activity increases in response to isometric, closed-chain, external hip-rotation forces, and forward movement of the upper body with respect to the base of support decreases GM activity.

The purpose of this study was to assess the effect of interferential current (IFC) on perceived pain and serum Cortisol levels in subjects with delayed onset muscle soreness (DOMS). DOMS was induced in 10 subjects through repeated eccentric contractions of the elbow flexors. Forty-eight hours later subjects were evaluated. Starting at t = 0:00, blood samples were withdrawn from a superficial vein every 5 min for 65 min. At t = 0:05, subjects received IFC of 10 bps or IFC of 100 bps. Perceived pain levels were evaluated prior to catheter insertion and at t = 0:35, 0:50, and 0:65. Two mixed-model analyses of variance revealed a significant decrease in perceived pain scores across time for both treatment groups but no significant difference in serum Cortisol for the two groups. It was concluded that IFC of high and low beat frequency is effective in controlling the pain of DOMS but does not elicit a generalized stress response as indexed by increasing serum Cortisol levels.