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Martin G.C. Lewis, Mark A. King, Maurice R. Yeadon and Filipe Conceição

This study determines whether maximal voluntary ankle plantar flexor torque could be more accurately represented using a torque generator that is a function of both knee and ankle kinematics. Isovelocity and isometric ankle plantar flexor torques were measured on a single participant for knee joint angles of 111° to 169° (approximately full extension) using a Contrex MJ dynamometer. Maximal voluntary torque was represented by a 19-parameter two-joint function of ankle and knee joint angles and angular velocities with the parameters determined by minimizing a weighted root mean square difference between measured torques and the two-joint function. The weighted root mean square difference between the two-joint function and the measured torques was 10 N-m or 3% of maximum torque. The two-joint function was a more accurate representation of maximal voluntary ankle plantar flexor torques than an existing single-joint function where differences of 19% of maximum torque were found. It is concluded that when the knee is flexed by more than 40°, a two-joint representation is necessary.

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Karen Roemer, Tibor Hortobagyi, Chris Richter, Yolanda Munoz-Maldonado and Stephanie Hamilton

Although an authoritative panel recommended the use of ergometer rowing as a non-weight-bearing form of exercise for obese adults, the biomechanical characterization of ergometer rowing is strikingly absent. We examined the interaction between body mass index (BMI) relative to the lower extremity biomechanics during rowing in 10 normal weight (BMI 18–25), 10 overweight (BMI 25–30 kg·m−2), and 10 obese (BMI > 30 kg·m−2) participants. The results showed that BMI affects joint kinematics and primarily knee joint kinetics. The data revealed that high BMI leads to unfavorable knee joint torques, implying increased loads of the medial compartment in the knee joint that could be avoided by allowing more variable foot positioning on future designs of rowing ergometers.

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Jack R. Engsberg, Kenneth S. Olree, Sandy A. Ross and Tae S. Park

This investigation quantified maximum active resultant joint torques in children with spastic diplegia cerebral palsy and nondisabled children. An isokinetic dynamometer rotated the limb (10°/s) while the resultant knee joint torques (both assistive and resistive) during knee extension and flexion in 6 nondisabled children and 26 children with cerebral palsy were recorded. Torque-angle data were processed to calculate maximum values during extension and flexion and work done during the movements. An independent t test determined if significant differences existed between groups (p < .05). Maximum extensor and maximum flexor torques and work during extension and flexion were significantly less for the children with cerebral palsy. Results supported previously published research indicating that children with spastic diplegia were weaker than nondisabled children. Additional information regarding the weakness of the children with spastic diplegia near the end range of extension motion is presented.

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Andrea Biscarini, Fabio M. Botti and Vito E. Pettorossi

We developed a biomechanical model to determine the joint torques and loadings during squatting with a backward/forward-inclined Smith machine. The Smith squat allows a large variety of body positioning (trunk tilt, foot placement, combinations of joint angles) and easy control of weight distribution between forefoot and heel. These distinctive aspects of the exercise can be managed concurrently with the equipment inclination selected to unload specific joint structures while activating specific muscle groups. A backward (forward) equipment inclination decreases (increases) knee torque, and compressive tibiofemoral and patellofemoral forces, while enhances (depresses) hip and lumbosacral torques. For small knee flexion angles, the strain-force on the posterior cruciate ligament increases (decreases) with a backward (forward) equipment inclination, whereas for large knee flexion angles, this behavior is reversed. In the 0 to 60 degree range of knee flexion angles, loads on both cruciate ligaments may be simultaneously suppressed by a 30 degree backward equipment inclination and selecting, for each value of the knee angle, specific pairs of ankle and hip angles. The anterior cruciate ligament is safely maintained unloaded by squatting with backward equipment inclination and uniform/forward foot weight distribution. The conditions for the development of anterior cruciate ligament strain forces are clearly explained.

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Rodrigo R. Bini, Tiago C. Jacques and Marco A. Vaz

Context:

Unassisted single-leg cycling should be replaced by assisted single-leg cycling, given that this last approach has potential to mimic joint kinetics and kinematics from double-leg cycling. However, there is need to test if assisting devices during pedaling effectively replicate joint forces and torque from double-leg cycling.

Objectives:

To compare double-leg, single-leg assisted, and unassisted cycling in terms of lower-limb kinetics and kinematics.

Design:

Cross-sectional crossover.

Setting:

Laboratory.

Participants:

14 healthy nonathletes.

Interventions:

Two double-leg cycling trials (240 ± 23 W) and 2 single-leg trials (120 ± 11 W) at 90 rpm were performed for 2 min using a bicycle attached to a cycle trainer. Measurements of pedal force and joint kinematics of participants’ right lower limb were performed during double- and single-leg trials. For the single-leg assisted trial, a custom-made adaptor was used to attach 10 kg of weight to the contralateral crank.

Main Outcome Measures:

Peak hip, knee, and ankle torques (flexors and extensors) along with knee-flexion angle and peak patellofemoral compressive force.

Results:

Reduced peak hip-extensor torque (10%) and increased peak knee-flexor torque (157%) were observed at the single-leg assisted cycling compared with the double-leg cycling. No differences were found for peak patellofemoral compressive force or knee-flexion angle comparing double-leg with single-leg assisted cycling. However, single-leg unassisted cycling resulted in larger peak patellofemoral compressive force (28%) and lower knee-flexion angle (3%) than double-leg cycling.

Conclusions:

These results suggest that although single-leg assisted cycling differs for joint torques, it replicates knee loads from double-leg cycling.

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Kentaro Chino, Naotoshi Mitsukawa, Kai Kobayashi, Yusuke Miyoshi, Toshiaki Oda, Hiroaki Kanehisa, Tetsuo Fukunaga, Senshi Fukashiro and Yasuo Kawakami

To investigate the relationship between fascicle behavior and joint torque, the fascicle behavior of the triceps surae during isometric and eccentric (30 and 60 deg/s) plantar flexion by maximal voluntary and submaximal electrical activation (MVA and SEA) was measured by real-time ultrasonography. Eccentric torque at 30 and 60 deg/s was significantly higher than isometric torque under SEA, but not under MVA. However, fascicle length did not significantly differ between isometric and eccentric trials under either condition. Therefore, the difference in developed torque by MVA and SEA cannot be explained by fascicle behavior. Under both MVA and SEA conditions, eccentric torque at 30 and 60 deg/s was equivalent. Similarly, fascicle lengthening velocities at 30 and 60deg/s did not show any significant difference. Such fascicle behavior can be attributed to the influence of tendinous tissue and pennation angle, and lead to a lack of increase in eccentric torque with increasing angular velocity.

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Bill Stodart, Maria Cup and Curtis Kindel

electrical activity of a muscle as it contracts. Although it seems appropriate that EMG would be useful in determining a muscle’s capacity to produce force, and therefore joint torque, conflicting evidence has been brought forth to support this assumption. 9 , 10 There are many factors that impact the force

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John H. Lawrence III and T. Richard Nichols

Muscle actions are often defined within a single anatomical reference plane. Yet animals must control posture and movement within a three-dimensional (3-D) environment, responding to a 3-D array of perturbing forces. Based on information gained regarding the 3-D muscle mechanics at the cat ankle joint complex (companion paper), we decided to study how alterations in the 3-D AJC orientation might affect ankle joint postural control. We used a 6 degree-of-freedom force-moment sensor to assess the affect of ankle joint orientation on the 3-D isometric joint torques evoked by electrical stimulation of muscles crossing the ankle joint complex (AJC) in the deeply anesthetized cat. An orthogonal axis system was established at the designated ankle rotation center, such that pitch (flexion-extension), yaw (abduction-adduction), and roll (inversion-eversion) axis torques were calculated. Experimental results suggest that both the magnitude and sign of extra-sagittal torques from the gastrocnemius muscles are joint angle dependent. Also, the hind limb levering system stabilizes the AJC against large yaw and roll rotations away from the control position.

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Hirofumi Ida, Seiji Kusubori and Motonobu Ishii

The purposes of this study were to (a) describe the racket-arm kinematics and kinetics of the soft-tennis smash during match rallies, and (b) assess the characteristics of this smash vs. the laboratory-simulated smash of our previous study. In the current study we recorded soft-tennis smash motions during match play of the 3rd East Asian Games. Racket-arm anatomical joint angular velocity and anatomical joint torque were calculated from 3-D coordinate data of 13 collected motions obtained using the direct linear transformation procedure. The results showed that most of the maximum values of the anatomical joint torques were qualitatively smaller than those of the tennis serve. Peak elbow extension, shoulder internal rotation, and elbow varus torques in match play were significantly greater than values reported for laboratory-simulated conditions. The greater forward swing torques did not result in significantly different racket head velocity, possibly because there was a significantly shorter forward swing phase in match conditions. In particular, a clear peak of the elbow extension torque during the forward swing phase was the most characteristic pattern in the smashes under match conditions, for it was 160% greater than laboratory-simulated conditions. These results supported our hypothesis that racket-arm kinematic and kinetic characteristics of the smash under match conditions differ from those under laboratory-simulated conditions. Possible explanations include the time-pressure conditions of the competitive situation in a match, and the Hawthorne effect (Hudson et al., 1986), both of which alter performance between match conditions and laboratory-simulated conditions.

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Doris I. Miller and Eric J. Sprigings

Major factors influencing the ability of divers to perform nontwisting springboard dives of increasing degree of difficulty were investigated. The analysis was based upon 49 dives (42 in pike and 7 in tuck) executed by male and female medalists in the 1996 Olympics. Videotapes were digitized to determine competitors’ vertical velocities and angular momenta at the beginning of dive flight. Centripetal force and resultant joint torque models were used to estimate the effort needed to perform multiple somersaulting dives. Increasing degree of difficulty by spinning in a pike rather than a tuck position for the same number of somersaults was associated with decreased vertical velocity at the start of dive flight, decreased angular velocity while somersaulting in a quasi-rigid position, and little change in centripetal force or related muscular effort. Increasing degree of difficulty by adding a somersault while rotating in a tuck rather than a pike position involved increases in vertical and angular velocities, a smaller increase in angular momentum, and notable increases in resultant joint torque and centripetal force. Sufficient muscular torque to maintain a compact spinning position was considered to be the major additional challenge facing divers making the transition from a 21/2 pike to a 31/2 tuck.