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Paul DeVita and Tibor Hortobagyi

Functional knee braces used during rehabilitation from injury and surgery to the anterior cruciate ligament (ACL) have been reported to provide a strain-shielding effect on the ACL in healthy people while standing, reduce quadriceps electromyoraphy in ACL-deficient individuals, and alter joint torque patterns in people with ACL reconstruction during walking. These results led to the hypothesis that functional knee braces protect a reconstructed ACL during dynamic activity by reducing the anterior shear load applied to the knee. This hypothesis was tested by investigating the effects of a functional knee brace on lower extremity muscle forces and the anteroposterior shear force at the knee joint during the stance phase of walking in people with ACL reconstruction. Ground reactions and sagittal plane video were recorded from 9 ACL-reconstructed individuals as they walked with and without a functional knee brace, and from 10 healthy people without the functional knee brace. Inverse dynamics were used to calculate the net joint torques in the lower extremity during the stance phase. Hamstrings, quadriceps, and gastrocnemius muscle and knee anteroposterior shear force were then predicted with a sagittal-plane mathematical model. Compared to healthy individuals, those with ACL reconstruction walked with 78% more hamstrings impulse and 19% less quadriceps impulse (both p < .05). The functional knee brace produced an additional 43% increase in hamstrings impulse and an additional 13% decrease in quadriceps impulse in the ACL group. Peak anterior knee shear force and anterior impulse were 41% lower and 16% lower in ACL vs. healthy individuals, respectively. The functional knee brace further reduced the peak knee shear force and impulse 28% and 19%, respectively, in the ACL group. It was concluded that a functional knee brace protects a reconstructed ACL during walking by altering muscle forces and reducing the anterior shear force applied to the knee joint.

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Ya-Ting Yang, Yasuyuki Yoshida, Tibor Hortobágyi, and Shuji Suzuki

We determined the angular range of motion and the relative timing of displacement in the thorax, lumbar spine, and pelvis in the transverse plane during treadmill walking at three velocities. Nine healthy young females walked on a treadmill for three minutes at 0.40, 0.93, and 1.47 m/s. The position of seven reflective markers and three rigs placed on the thorax, lumbar spine, and pelvis were recorded at 200 Hz by an eight-camera motion capture system. As gait velocity increased, stride length increased, cycle time decreased, and angular displacement in the thorax and L1 decreased but increased at the pelvis and L5 (all P < .05). The time of maximal angular rotation occurred in the following sequence: pelvis, L5, L3, L1, and thorax (P < .001). The thorax and L1 and L3 were in-phase for shorter duration as gait velocity increased, and this reduction was especially large, approx. 32% (P < .05), between thorax and pelvis. As gait velocity increased, the pelvis rotated earlier, causing the shortening of in-phase duration between thorax and pelvis. These data suggest that, as gait velocity increases, pelvis rotation dictates trunk rotation in the transverse plane during gait in healthy young females.

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Tibor Hortobágyi, Kevin Scott, Jean Lambert, George Hamilton, and James Tracy

Cross-education enhances the performance of muscles not directly involved in the chronic conditioning of the muscles in a remote limb. Substantial cross-education occurs after training with eccentric contractions or with contractions evoked by electromyostimulation (EMS). Since during EMS and eccentric contractions, skin and muscle afferents are activated that have excitatory effects on contralateral homologous muscles, it was hypothesized that exercise training with stimulated vs. voluntary eccentric contractions would lead to greater cross-education. Thirty-two women were randomly assigned to a voluntary (Vol), an EMS, or a remote EMS (rEMS) exercise group and performed 840 voluntary or stimulated eccentric contractions over 6 weeks. All subjects, including nonexercising controls (Con), were tested pre- and posttraining for maximal voluntary and stimulated isometric and eccentric quadriceps strength. Ipsilateral voluntary and stimulated forces increased in all groups. Changes in EMG activity paralleled those in voluntary force in each limb. No changes occurred in grip strength. The greater contra- and ipsilateral strength gains after EMS training were most likely related to an additive effect of EMS and muscle lengthening.

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Tibor Hortobágyi, Jeff Money, Donghai Zheng, Ronald Dudek, David Fraser, and Lynis Dohm

This study compared muscle adaptations after 7 days of exercise with eccentric-overload (EO) or standard (ST) resistive training in young (20 years) and older (69 years) adults. Young EO and ST gained 103 and 30 N, respectively, and older EO and ST gained 63 and 25 N of strength, respectively (all p < .05). Types I and IIa MHC mRNA levels were not altered, but Type IIx levels decreased 31% and 63% after the first and seventh exercise bouts, respectively, in young and decreased 30% after the seventh bout in older participants (all p < 05), independent of loading type. Type 11a fiber increased. Type IIx decreased, and Type IIa increased in both age groups independent of loading type (all p < 05). Electron microscopy revealed no myofibrillar disruption in young or older muscle. These data suggest that short-term EO produces larger strength gains than does ST without muscle-cell disruption or loading-type-specific changes in MHC mRNA isoforms in young and older skeletal muscle.

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János Négyesi, Menno P. Veldman, Kelly M.M. Berghuis, Marie Javet, József Tihanyi, and Tibor Hortobágyi

Sensory input can modify motor function and magnify interlimb transfer. We examined the effects of low-intensity somatosensory electrical stimulation (SES) on motor practice-induced skill acquisition and intermanual transfer. Participants practiced a visuomotor skill for 25 min and received SES to the practice or the transfer arm. Responses to single- and double-pulse transcranial magnetic stimulation were measured in both extensor carpi radialis. SES did not further increase skill acquisition (motor practice with right hand [RMP]: 30.8% and motor practice with right hand + somatosensory electrical stimulation to the right arm [RMP + RSES]: 27.8%) and intermanual transfer (RMP: 13.6% and RMP + RSES: 9.8%) when delivered to the left arm (motor practice with right hand + somatosensory electrical stimulation to the left arm [RMP + LSES]: 44.8% and 18.6%, respectively). Furthermore, transcranial magnetic stimulation measures revealed no changes in either hand. Future studies should systematically manipulate SES parameters to better understand the mechanisms of how SES affords motor learning benefits documented but not studied in patients.

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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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Tibor Hortobágyi, Richard G. Israel, Joseph A. Houmard, Kevin F. O'Brien, Robert A. Johns, and Jennifer M. Wells

Four methods of assessing body composition were compared in 55 black and 35 white, Division 1, American football players. Percent body fat (%BF) was estimated with hydrostatic weighing at residual volume, corrected for race; seven-site skinfolds (7 SF), corrected for race; bioelectrical impedance analysis (BIA); and near-infrared spectrophotometry (NIR). Percent body fat with HW in blacks (mean = 14.7%) and whites (19.7%) did not differ (P > .05) from %>BF with 7 SF (blacks, 14.7%; whites, 19.0%). In relation to HW, BIA significantly (P < .05) overpredicted (blacks: 20.1%, SEE = 3.2%; whites; 22.3%, SEE = 4.3%) and NiR underpredicted %BF (blacks; 12.6%, SEE = 3.9%; whites; 17.7%, SEE = 3.6%). The contribution of BIA variables (resistance, phase angle, conductance) and NIR optical density to predict %BF was trivial compared to body mass index. It appears that race may not substantially influence %BF prediction by NIR and BIA. It was concluded that when considering the cost and expertise required with NIR and BIA, SF measurements appear to be a superior alternative for rapid and accurate body composition assessment of athletes, independent of race.