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Sara L. Arena, Kelsey McLaughlin, Anh-Dung Nguyen, James M. Smoliga and Kevin R. Ford

Athletic individuals may differ in body segment inertial parameter (BSIP) estimates due to differences in body composition, and this may influence calculation of joint kinetics. The purposes of this study were to (1) compare BSIPs predicted by the method introduced by de Leva1 with DXA-derived BSIPs in collegiate female soccer players, and (2) examine the effects of these BSIP estimation methods on joint moment and power calculations during a drop vertical jump (DVJ). Twenty female NCAA Division I soccer players were recruited. BSIPs of the shank and thigh (mass, COM location, and radius of gyration) were determined using de Leva’s method and analysis of whole-body DXA scans. These estimates were used to determine peak knee joint moments and power during the DVJ. Compared with DXA, de Leva’s method located the COM more distally in the shank (P = .008) and more proximally in the thigh (P < .001), and the radius of gyration of the thigh to be further from the thigh COM (P < .001). All knee joint moment and power measures were similar between methods. These findings suggest that BSIP estimation may vary between methods, but the impact on joint moment calculations during a dynamic task is negligible.

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Curtis Kindel and John Challis

action can be held, of the hip musculature? In this study the production of isometric moments at different muscle lengths were examined as a first step to identifying the nature of the hip musculature deficits in subjects with symptoms of patellofemoral syndrome. Joint moment-angle relationships, or

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Tetsuro Muraoka, Tadashi Muramatsu, Daisuke Takeshita, Hiroaki Kanehisa and Tetsuo Fukunaga

This study estimated the passive ankle joint moment during standing and walking initiation and its contribution to total ankle joint moment during that time. The decrement of passive joint moment due to muscle fascicle shortening upon contraction was taken into account. Muscle fascicle length in the medial gastrocnemius, which was assumed to represent muscle fascicle length in plantarflexors, was measured using ultrasonography during standing, walking initiation, and cyclical slow passive ankle joint motion. Total ankle joint moment during standing and walking initiation was calculated from ground reaction forces and joint kinematics. Passive ankle joint moment during the cyclical ankle joint motion was measured via a dynamometer. Passive ankle joint moment during standing and at the time (Tp) when the MG muscle-tendon complex length was longest in the stance phase during walking initiation were 2.3 and 5.4 Nm, respectively. The muscle fascicle shortened by 2.9 mm during standing compared with the length at rest, which decreased the contribution of passive joint moment from 19.9% to 17.4%. The muscle fascicle shortened by 4.3 mm at Tp compared with the length at rest, which decreased the contribution of passive joint moment from 8.0% to 5.8%. These findings suggest that (a) passive ankle joint moment plays an important role during standing and walking initiation even in view of the decrement of passive joint moment due to muscle fascicle shortening upon muscle contraction, and (b) muscle fascicle shortening upon muscle contraction must be taken into account when estimating passive joint moment during movements.

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Gregory Neil Hodges and Dean Johannes Kriellaars

Despite the common use of elastic resistance in training, only the static loading characteristics have been studied, whereas the dynamic components remain undetermined. The purpose was to determine the effect of two movement strategies on the shoulder resultant joint moment (RJM) during internal/external rotation exercise with elastic load. Ten healthy subjects performed sweep and step movement strategies over a constant range of motion and cadence (1:1). Shoulder RJM was determined using a Newtonian model with elastic force measured by force transducer, joint angle by electrogoniometer, and limb acceleration by accelerometer. Relative to the sweep strategy, the step strategy revealed a 49% increase in angle-specific RJM during the initial phase, RJM was reduced to 67–69% during midrange, and increased to over 110% at the end of the repetition. These RJM differences were wholly attributable to strategy-dependent changes in limb acceleration. Shoulder RJM in the sweep strategy was almost entirely explained by moment of elastic force. Movement strategy can substantially alter shoulder loading despite constant range of motion and cadence, impacting the magnitude and nature of the stimulus for neuromuscular adaptation. These acceleration-dependent changes in shoulder RJM may be important to consider for exercise efficacy and safety.

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Goeran Fiedler, Brooke Slavens, Roger O. Smith, Douglas Briggs and Brian J. Hafner

Prosthesis-integrated sensors are appealing for use in clinical settings where gait analysis equipment is unavailable, but accurate knowledge of patients’ performance is desired. Data obtained from load cells (inferring joint moments) may aid clinicians in the prescription, alignment, and gait rehabilitation of persons with limb loss. The purpose of this study was to assess the accuracy of prosthesis-integrated load cells for routine use in clinical practice. Level ground walking of persons with transtibial amputation was concurrently measured with a commercially available prosthesis-integrated load cell, a 10-camera motion analysis system, and piezoelectric force plates. Ankle and knee flexion/extension moments were derived and measurement methods were compared via correlation analysis. Pearson correlation coefficients ranged from 0.661 for ankle pronation/supination moments to 0.915 for ankle flexion/extension moments (P < .001). Root mean squared errors between measurement methods were in the magnitude of 10% of the measured range and were explainable. Differences in results depicted differences between systems in definition and computation of measurement variables. They may not limit clinical use of the load cell, but should be considered when data are compared directly to conventional gait analysis data. Construct validity of the load cell (ie, ability to measure joint moments in-situ) is supported by the study results.

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Wing-Kai Lam, Winson Chiu-Chun Lee, Wei Min Lee, Christina Zong-Hao Ma and Pui Wah Kong

respective volumes, modeling each as simple geometric solids with uniform densities. 21 Positive work or energy generation (negative work or energy absorption) occurs when the resultant joint moment is in the same (opposite) direction as the joint angular velocity. Statistical Analyses Maximum jump height

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Andrew R. Fauth, Andrew J. Hamel and Neil A. Sharkey

This study involved a biomechanical examination of the first and second tar-sometatarsal (TMT) joints. In the in vitro testing protocol, physiologic joint moments were applied to the first and second TMT joints of 10 cadaver specimens, which had been dissected to yield only the midfoot components comprising the tarsals, metatarsals, and associated ligaments. The isolated joints were placed in a 37 °C water bath and were independently cycled into and out of dorsiflexion, while angular displacement and resultant joint moments were collected. The specimens were sequentially cycled between zero and peak moment levels of 2.5, 5.0, 7.5, and 10 Nm, after which mean moment-angle curves were plotted for each TMT joint at each loading condition. Least-squares curve-fitting procedures, employing a root mean square error threshold of 0.005 Nm, were used to describe the average overall moment vs. angle relationship of each joint. Curves for the first and second TMT joints exhibited similar behavior. The joints displayed reasonably constant stiffness at low angles of dorsiflexion, followed by rapidly increasing stiffness at higher angles of dorsiflexion. These data provide new insight into the behavior of the TMT joints under load and are valuable for use in numerical models of the foot, as well as in the understanding and treatment of certain foot pathologies.

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George J. Salem, Man-Ying Wang, Stanley P. Azen, Jean T. Young and Gail A. Greendale

The purpose of this investigation was to determine the effects of two doses of a weighted vest on acute lower-extremity gait kinetics in older adults. Peak ankle, knee, and hip net joint moments were quantified in 56 men and women volunteers (73.8 ± 6.9 years old) enrolled in a 6-month physical activity study. At the initial study visit, participants underwent 6 walking trials (3 with vest, 3 without vest) at their normal pace. During the vest-wearing trials, participants wore a vest loaded with either 0% of body weight (BW) (n = 19), 3% of BW (n = 16), or 5% of BW (n = 21). With acute application of the vests, maximum peak plantarflexion moments increased by 5.7% in the 5% BW group compared to the 0% BW group, p < 0.01. Compared to the 0% vest-weight group, knee extension moments increased by 13.8% when 5% BW was applied, p < 0.01; a marginally significant treatment effect was evident in the 3% BW group, p = 0.04. Despite these acute alterations, knee strength and physical performance did not improve when subjects wore the vests 2 hours a day, 4 days a week for 27 weeks, without additional exercise prescription. These findings suggest that: (a) the acute changes in vest-mediated lower-extremity kinetics are not systemic but joint specific and load dependent, and (b) weighted vest prescription should be greater than 5% BW without prescribed exercise, or should include prescribed exercises, to invoke long-term strength and physical performance gains in older adults.

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Rositsa T. Raikova

This commentary emphasizes three points of discussion. (a) The terminology: The terms multifunctional, synergisic, antagonistic muscles, and synergistic and antagonistic coactivations are discussed and the conclusion is drawn that they could not be used without mentioning the particular joint motion. (b) The importance of the external joint moments for activation of the muscles is confirmed on the basis of logical and mechanical considerations. Not all experimental results, however, could be explained by this means. (c) The optimization criterion: Prilutsky's conclusion concerning the predicted muscle force proportionality to the muscle moment arm and PCSA is confirmed using a simple analytical solution of the optimization problem. It is shown, however, that the proportionality to the PCSA is a consequence of the chosen optimization criterion.

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Yoichi Iino and Takeji Kojima

This study investigated the validity of the top-down approach of inverse dynamics analysis in fast and large rotational movements of the trunk about three orthogonal axes of the pelvis for nine male collegiate students. The maximum angles of the upper trunk relative to the pelvis were approximately 47°, 49°, 32°, and 55° for lateral bending, flexion, extension, and axial rotation, respectively, with maximum angular velocities of 209°/s, 201°/s, 145°/s, and 288°/s, respectively. The pelvic moments about the axes during the movements were determined using the top-down and bottom-up approaches of inverse dynamics and compared between the two approaches. Three body segment inertial parameter sets were estimated using anthropometric data sets (Ae et al., Biomechanism 11, 1992; De Leva, J Biomech, 1996; Dumas et al., J Biomech, 2007). The root-mean-square errors of the moments and the absolute errors of the peaks of the moments were generally smaller than 10 N·m. The results suggest that the pelvic moment in motions involving fast and large trunk movements can be determined with a certain level of validity using the top-down approach in which the trunk is modeled as two or three rigid-link segments.