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David Hawkins and Mark Smeulders

The purpose of this study was to determine if the characteristic Hill model, used to describe me force–velocity relationship for isolated tetanically stimulated muscle, could be modified and used to describe me torque–velocity behavior of me hip for maximally and submaximally stimulated hip extensor muscles. Fourteen subjects performed hip extension movements at effort levels of 100%, 70%, and 40% of a maximum isometric effort. A solenoid provided isometric resistance to hip extension. Once the desired effort level was achieved, as indicated by me isometric force, the solenoid released and me hip moved against an opposing elastic resistance equal to 75%, 50%, 25%, and 0% of the specified effort level. An electrogoniometer quantified hip angle. Hip velocity was determined by numerically differentiating the angle data. Torque-velocity-activation (or effort level) data were determined for each trial. Model parameters were determined to give me best fit to the data for each subject. Average parameter values were determined for each gender and for the entire group. The modified Hill-type model, T m = (T max · AK 1 · ω)/(K2 · ω + 1), accurately describes me relationship between joint torque (T m), maximum isometric joint torque (T max), joint velocity (ω), and muscle activation level (A) for subject-specific parameters (K 1 and K 2), but not for parameters averaged across genders or the entire group. Values for T max, K 1, and K 2 ranged from 90 to 385 Nm, 6.1 to 47.9 Nms, and 0.030 to 0.716 s, respectively.

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John LaFree, Amy Mozingo and Teddy Worrell

The purposes of this study were to determine the relationship of isokinetic quadriceps and hip extensor peak torque to isokinetic leg press peak torque and to determine the influence of hip position (seated vs. supine) on leg press peak torque. Forty subjects (20 males and 20 females) were tested bilaterally on the isokinetic dynamometer. Subjects were tested during knee extension, hip extension, seated leg press, and supine leg press. Intraclass correlation coefficient and standard error of measurement values revealed acceptable reliability for all tests. An analysis of variance revealed significant dominant versus nondominant differences in all tests except hip extension. A repeated measures analysis of variance revealed no significant difference between seated and supine leg press peak torque. Finally, stepwise regression revealed a significant relationship between knee extension and leg press peak torques, with hip extension adding only minimally to the explained variance. These data suggest that knee extension and leg press peak torque assess similar muscle performance characteristics. Further research involving electromyographic analysis is recommended to determine the influence of other muscles on leg press force performance.

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In-cheol Jeon, Oh-yun Kwon, Jong-hyuck Weon, Ui-jae Hwang and Sung-hoon Jung

Context:

Prone hip extension has been recommended for strengthening the back and hip muscles. Previous studies have investigated prone hip extension conducted with subjects on the floor in the prone position. However, no study has compared 3 different table hip-extension (THE) positions in terms of the activities of the back- and hip-joint muscles with lumbopelvic motion.

Objective:

To identify more effective exercises for strengthening the gluteus maximus (GM) by comparing 3 different exercises (THE alone, THE with the abdominal drawing-in maneuver [THEA], and THEA with chair support under the knee [THEAC]) based on electromyographic muscle activity and pelvic compensation.

Design:

Repeated-measure within-subject intervention.

Setting:

University research laboratory.

Participants:

16 healthy men.

Main Outcome Measures:

Surface electromyography (EMG) was used to obtain data on the GM, erector spinae (ES), multifidus, biceps femoris (BF), and semitendinosus (ST). Pelvic compensation was monitored using an electromagnetic motion-tracking device. Exertion during each exercise was recorded. Any significant difference in electromyographic muscle activity and pelvic motion among the 3 conditions (THE vs THEA vs THEAC) was assessed using a 1-way repeated-measures analysis of variance (ANOVA) with Bonferroni post hoc test.

Results:

The muscle activities recorded by EMG differed significantly among the 3 exercises (P < .01). GM activity was increased significantly during THEAC (P < .01). There was a significant difference in lumbopelvic kinematics in terms of anterior tilting (F = 19.49, P < .01) and rotation (F= 27.38, P < .01) among the 3 exercises.

Conclusions:

The THEAC exercise was the most effective for strengthening the GM without overactivity of the ES, BF, and ST muscles and lumbopelvic compensation compared with THE and THEA.

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Thomas M. Lundin, Dennis W. Jahnigen and Mark D. Grabiner

When rising from a chair, older adults have been reported to use a strategy in which the trunk is flexed to a greater extent than young adults, a strategy attributed by some to concerns with the postural stability demands of the task. This study determined the extent to which maximum trunk flexion angle during a self-paced sit-to-stand from a standardized initial position was influenced by the maximum isometric strength of the knee and trunk/hip extensor muscles in older adults. The hypothesis was that the larger maximum trunk flexion angle attained by older adults when rising from a chair is related to the maximum isometric strength of the knee and trunk-hip extensor muscles. To test this hypothesis, maximum voluntary isometric strength of the trunk extensor and knee extensor muscles of 28 older men and women were measured. Trunk motion during the sit-to-stand by these adults was men assessed using motion analysis. Multiple regression was used to characterize the relationship between the maximum trunk flexion angle and maximum isometric knee extensor and trunk extensor muscle strength. The derived relationship was neither statistically significant nor biomechanically meaningful. This result suggests that the trunk flexion angle attained by healthy older adults when rising from a chair from a standardized initial position is not influenced by knee extension and trunk-hip extension strength as measured in the present study.

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Warren Young, Peter Clothier, Leonie Otago, Lyndell Bruce and David Liddell

Context:

Flexibility tests are sometimes thought to be related to range of motion in dynamic activities, but such a relationship remains to be determined.

Objective:

To determine the correlation between flexibility and hip and knee angles in Australian football kicking.

Design:

Correlation.

Setting:

Biomechanics laboratory.

Participants:

16 Australian Rules football players.

Main Outcome Measures:

Hip and knee angles of the preferred kicking leg in a relaxed position were determined with a modified Thomas test. Maximum hip extension, the knee-flexion angle in this position, the maximum knee-flexion angle, and the hip angle at this position during the swing phase of maximum-effort drop-punt kicks were determined.

Results:

Significant correlations were found between hip flexibility and maximum hip extension (r = .65, P < .01) and hip angle at the maximum knee-flexion angle (r = .70, P < .01).

Conclusions:

The data indicate a moderate association between hip flexibility and hip angles during kicking.

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Curtis Kindel and John Challis

insights into the etiology of patellofemoral syndrome. In addition when assessing the hip extension strength curve, the role of the biarticular muscles which contribute to this moment can be assessed by systematically changing the knee joint angle. 9 However, efficient movement requires more than simply

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Bret Contreras, Andrew D. Vigotsky, Brad J. Schoenfeld, Chris Beardsley and John Cronin

Bridging exercise variations are well researched and commonly employed for both rehabilitation and sport performance. However, resisted bridge exercise variations have not yet been compared in a controlled experimental study. Therefore, the purpose of this study was to compare the differences in upper and lower gluteus maximus, biceps femoris, and vastus lateralis electromyography (EMG) amplitude for the barbell, band, and American hip thrust variations. Thirteen healthy female subjects (age = 28.9 y; height = 164.3 cm; body mass = 58.2 kg) familiar with the hip thrust performed 10 repetitions of their 10-repetition maximum of each variation in a counterbalanced and randomized order. The barbell hip thrust variation elicited statistically greater mean gluteus maximus EMG amplitude than the American and band hip thrusts, and statistically greater peak gluteus maximus EMG amplitude than the band hip thrust (P ≤ .05), but no other statistical differences were observed. It is recommended that resisted bridging exercise be prescribed according to the individual’s preferences and desired outcomes.

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Mary Hellen Morcelli, Dain Patrick LaRoche, Luciano Fernandes Crozara, Nise Ribeiro Marques, Camilla Zamfolini Hallal, Mauro Gonçalves and Marcelo Tavella Navega

( F  = 5.45, degrees of freedom = 29, P  = .001). Peak torque was significantly lower in the slow speed group than functional speed group during hip extension (28%), knee flexion (15%), knee extension (14%), and ankle plantar flexion (16%) (all P s < .05; Table  2 ). Table 2 Differences in Peak

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Gakuto Kitamura, Hiroshige Tateuchi and Noriaki Ichihashi

that the tightness of the hip-flexor muscle can reduce hip extension that create a lumbar hyperextension and pelvic anterior tilt in various movements in water. 6 Pelvic anterior tilting can make the pelvis at a lower position than normal in water. 6 A study examined the swimmers experiencing LBP and

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John H. Hollman, Tyler A. Berling, Ellen O. Crum, Kelsie M. Miller, Brent T. Simmons and James W. Youdas

leading to anterior hip pain. 6 – 8 Sahrmann 9 proposed that when gluteus maximus strength is impaired, or when hamstring muscle recruitment is dominant during hip extension, anterior femoracetabular forces increase because the proximal femur translates anteriorly rather than maintaining a centralized