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The Impact of Previous Knee Injury on Force Plate and Field-Based Measures of Balance

research Mar 18, 2019

Individuals with post-traumatic osteoarthritis demonstrate increased sway during quiet stance. The prospective association between balance and disease onset is unknown. Improved understanding of balance in the period between joint injury and disease onset could inform secondary prevention strategies to prevent or delay the disease. 

Participants included 50 individuals (ages 15–26 years) with a sport-related intra-articular knee injury sustained 3–10 years previously and 50 uninjured age-, sex- and sport-matched controls. Force-plate measures during single-limb stance (center-of-pressure 95% ellipse-area, path length, excursion, entropic half-life) and field-based balance scores (triple single-leg hop, star-excursion, unipedal dynamic balance) were collected.

On average the injured participants adjusted their position less frequently and demonstrated a larger magnitude of movement during single-limb stance compared to controls. These findings support the...

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Comparison of Ground Reaction Force During Different Angle of Squatting

research Mar 17, 2019

Squatting is a form of closed kinetic chain movement which commonly being employed in exercise training. However, little is known regarding the amount of force being imposed on the knee at different angles of squat. Thus, the purpose of this study was to compare the vertical ground reaction force (VGRF) at different angles of squatting among the military personnel. Thirty-seven subjects (age=27.1±2.77 years old) participated in this cross-sectional comparative study. The peak of VGRF was identified during squatting at 40°, 70°, and 110 ° of knee flexion, which was measured using a force platform. The data were analysed using the one way repeated measure ANOVA and Pairwise Comparisons via Bonferroni adjustment. The VGRF were shown significantly different between the three angles of squatting (p<0.05). Since the Mauchly Test of Sphericity was significant (p>0 .05), the result was corrected using Greenhouse-Geiser Epsilon and continued to show a significant...

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Relationship of Isometric Mid-Thigh Pull Variables to Weightlifting Performance

research Mar 16, 2019

Twelve weightlifters, ranging from novice to advanced, performed the IMTP 10 days after a competition. Correlations were used to evaluate relationships between variables of the IMTP and absolute and scaled competition results.

Unscaled competition results correlated strongly with IRFD (0-200ms: r=0.567-0.645, 0-250ms: r=0.722-0.781) while results correlated weakly with Peak IRFD (5ms window, r=0.360-0.426). Absolute peak force values correlated very strongly with absolute values for the competition performance (r=0.830-0.838). Force at 100ms, 150ms, 200ms and 250ms also correlated strongly with competition results (r=0.643-0.647, r=0.605-0.636, r=0.714-0.732, r=0.801-0.804). Similar findings were noted for allometrically scaled values.

Measures of average IRFD probably represent a more relevant variable to dynamic performance than does Peak IRFD (5ms). Maximum isometric strength also is likely to have a strong role in weightlifting performance.

 

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Forward Lunge as a Functional Performance Test in ACL Deficient Subjects: Test–Retest Reliability

research Mar 15, 2019

The forward lunge movement may be used as a functional performance test of anterior cruciate ligament (ACL) deficient and reconstructed subjects. The purposes were 1) to determine the test–retest reliability of a forward lunge in healthy subjects and 2) to determine the required numbers of repetitions necessary to yield satisfactory reliability. Nineteen healthy subjects performed four trials of a forward lunge on two different days. The movement time, impulses of the ground reaction forces (IFz, IFy), knee joint kinematics and dynamics during the forward lunge were calculated. The relative reliability was determined by calculation of Intraclass Correlation Coefficients (ICC). The IFz, IFy and the positive work of the knee extensors showed excellent reliability (ICC > 0.75). All other variables demonstrated acceptable reliability (0.4 > ICC < 0.75). The relative reliability increased when more than a single forward lunge was used. In...

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Effects of Gender and Foot-Landing Techniques on Lower Extremity Kinematics during Drop-Jump Landings

research Mar 14, 2019

 3-D kinematics were collected on 50 (25 male and 25 female) college-age recreational athletes selected from a sample of convenience. Separate repeated-measures ANOVAs were used to analyze each variable at three time instants (initial contact, peak vertical ground reaction force, and maximum knee flexion angle). There were no significant differences found between genders at the three instants for each variable. At initial contact, the forefoot technique (35.79° ± 11.78°) resulted in significantly (p = .001) less hip flexion than did the self-preferred (41.25° ± 12.89°) and rear foot (43.15° ± 11.77°) techniques. At peak vertical ground reaction force, the rear foot technique (26.77° ± 9.49°) presented significantly lower (p = .001) knee flexion angles as compared with forefoot (58.77° ± 20.00°) and self-preferred (54.21° ± 23.78°) techniques. A significant difference for knee...

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Fatigue Alters Lower Extremity Kinematics During a Single-Leg Stop-Jump Task

research Mar 13, 2019

Thirty healthy, physically active subjects (15 males and 15 females) Knee and hip joint kinematics were calculated utilizing three-dimensional video analysis. Each subject performed five single-leg stop-jumps before and after an exercise-to-fatigue bout. All subjects underwent a fatigue protocol using the modified Astrand protocol. Fatigue was verified using the Rating of Perceived Exertion along with the subject’s heart rate. All data were analyzed using two factor (test × gender) repeated measures ANOVA (< 0.05). Both males and females demonstrated significantly less maximal knee valgus (P = 0.038) and decreased knee flexion at initial contact (= 0.009) post-fatigue. No significant differences were identified in hip joint angles between sessions or between sexes.

The results show that fatigue developed from exhaustive running alters lower extremity kinematics during a single-leg stop-jump task. The more neutral position in...

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Augmented Feedback Reduces Jump Landing Forces

research Mar 11, 2019

Nonimpaired college students (N = 63) were randomly assigned to 1 of 4 feedback groups. Subjects were instructed to perform maximal vertical jumps onto a force plate for 3 testing sessions (baseline, 2-minute post-test, and 1-week post-test). Three feedback groups (augmented, sensory, and control I) were tested during all 3 testing sessions, while a fourth feedback group (control II) was evaluated at only 2 sessions (baseline and 1-week post-test). Subjects in the augmented feedback condition were provided information via video and verbal analysis of how to land softer. Subjects in the sensory feedback condition were asked to use the experience of their baseline jumps to document how they could land softer. Subjects in each of the control groups were not provided any extraneous feedback. Peak vertical ground reaction force data were collected for analysis.

The subjects in the augmented feedback group significantly reduced their peak vertical ground reaction force in both...

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Normative Data of Vertical Ground Reaction Forces During Landing From a Jump

research Mar 11, 2019

Subjects were 234 adolescents (mean age: 16 years) who were categorised by gender, activity level and type of sport played. Subjects jumped from a box 0.3 metres high to land on a force plate. Results showed that there were no significant differences (p>0.05) across gender, activity levels, and type of sport played. Across all subjects, the mean peak vertical GRF was 4.5 bodyweights (SD: 1.7). In regard to gender, mean peak vertical GRFs were 4.6 (SD:1.7) and 4.2 (SD:1.4) for males and females respectively. The mean peak vertical GRF for subjects involved in recreational sport 1–3 times per week was 4.4 bodyweights (SD:1.7), while the mean for those playing competitive sport 4–7 times per week was 4.5 bodyweights (SD: 1.7). The mean peak vertical GRF for subjects participating in sports involving jumping and landing activities was 4.6 bodyweights (SD: 1.8) as compared to 4.4 bodyweights (SD: 1.5) for subjects in sports that did not involve jumping activities.

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Effects of Load on Ground Reaction Force and Lower Limb Kinematics During Concentric Squats

research Mar 10, 2019

The purpose of this study was to examine the effects of external load on vertical ground reaction force, and linear and angular kinematics, during squats. Eight males aged 22.1±0.8 years performed maximal concentric squats using loads ranging from 7 to 70% of one-repetition maximum on a force plate while linear barbell velocity and the angular kinematics of the hip, knee and ankle were recorded. Maximum, average and angle-specific values were recorded. The ground reaction force ranged from 1.67±0.20 to 3.21±0.29 times body weight and increased significantly as external load increased (P<0.05). Bar linear velocity ranged from 0.54±0.11 to 2.50±0.50 m·s−1 and decreased significantly with increasing external load (P<0.05). Hip, knee and ankle angles at maximum ground reaction force were affected by external load (P<0.05). The force–barbell velocity curves were fitted using linear models with coefficients (r...

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The Relationship Between Maximal Jump-Squat Power and Sprint Acceleration in Athletes

research Mar 09, 2019

Thirty male athletes [height: 183.8 (6.8) cm, and mass: 90.6 (9.3) kg; mean (SD)] each completed six 10-m sprints from a standing start. Sprint times were recorded using a tethered running system and the force-time characteristics of the first ground contact were recorded using a recessed force plate. Three to six days later subjects completed three concentric jump squats, using a traditional and split technique, at a range of external loads from 30–70% of one repetition maximum (1RM)

Average power was maximal at all loads between 30% and 60% of 1RM for both squats. Split squat peak power was also maximal between 30% and 60% of 1RM; however, traditional squat peak power was maximal between 50% and 70% of 1RM. Concentric force development is critical to sprint start performance and accordingly maximal concentric jump power is related to sprint acceleration.

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