In numerous motor tasks, muscles around a joint act coactively to generate opposite torques. A va... more In numerous motor tasks, muscles around a joint act coactively to generate opposite torques. A variety of indexes based on electromyography signals have been presented in the literature to quantify muscle coactivation. However, it is not known how to estimate it reliably using such indexes. The goal of this study was to test the reliability of the estimation of muscle coactivation using electromyography. Isometric coactivation was obtained at various muscle activation levels. For this task, any coactivation measurement/index should present the maximal score (100% of coactivation). Two coactivation indexes were applied. In the first, the antagonistic muscle activity (the lower electromyographic signal between two muscles that generate opposite joint torques) is divided by the mean between the agonistic and antagonistic muscle activations. In the second, the ratio between antagonistic and agonistic muscle activation is calculated. Moreover, we computed these indexes considering different electromyographic amplitude normalization procedures. It was found that the first algorithm, with all signals normalized by their respective maximal voluntary coactivation, generates the index closest to the true value (100%), reaching 92 ± 6%. In contrast, the coactivation index value was 82 ± 12% when the second algorithm was applied and the electromyographic signal was not normalized (P < 0.04). The new finding of the present study is that muscle coactivation is more reliably estimated if the EMG signals are normalized by their respective maximal voluntary contraction obtained during maximal coactivation prior to dividing the antagonistic muscle activity by the mean between the agonistic and antagonistic muscle activations.
Background More than 2 years after undergoing anterior cruciate ligament (ACL) reconstruction, wo... more Background More than 2 years after undergoing anterior cruciate ligament (ACL) reconstruction, women still present bilateral asymmetries during multijoint movement tasks. Given the well-known ACL-injury gender bias, the goal of this study was to investigate whether males also present such asymmetries more than 2 years after undergoing ACL reconstruction. Methods This study involved 12 participants submitted to ACL reconstruction in the ACL group and 17 healthy participants in the control group. The mean postoperative period was 37 months. The participants executed bilateral countermovement jumps and load squat tasks. The kinematics and ground reaction forces on each lower limb and pelvis were recorded, and used to compute bilateral peak vertical ground reaction forces, peak knee and hip joint powers in the sagittal plane, and the ratio between these powers. Results For the jump task, the groups had the same performance in the jump height, but for the ACL group the peak knee joint power on the operated side was 13% lower than on the non-operated side (p = 0.02). For the squat task, the hip-knee joint power ratio on the operated side of the ACL group was 31% greater than on the non-operated side (p = 0.02).
Med. (Serv. do Prof. José Laredo Filho). 1. Doutor em Ortop.; Resp. pelo Setor de Artrosc. do Gru... more Med. (Serv. do Prof. José Laredo Filho). 1. Doutor em Ortop.; Resp. pelo Setor de Artrosc. do Grupo de Joelho do Departamento. 2. Prof. Adjunto-Doutor; Chefe do Grupo de Joelho do Departamento. 3. Méd. do Setor de Traumatol. Esport. do Departamento. 4. Resid. do 4º ano do Grupo de Joelho do Departamento. Endereço para correspondência: Mário Carneiro Filho, Rua Afonso Brás, 817, Vila Nova Conceição -04511-011 -São Paulo, SP. Tel. 822-8333.
It is unclear whether athletes change their postural control over the course of a full sport seas... more It is unclear whether athletes change their postural control over the course of a full sport season, or become more asymmetrical with respect to their neuromuscular performance over the same period. The aim of this study was to investigate the effects of a full sport season on the postural control of team handball elite athletes. Ten healthy, elite male team handball players performed bipodal standing (BP) and right and left unipodal standing (UP) during 30s. We used the RMS and speed of the center of pressure to describe postural sway. For the BP task, the sway was lower at the end of the season (p<0.005). For the UP tasks, the sway was lower at the end of the season only for the non-dominant limb (p<0.001). Differences between limbs were observed only at the end of the season (p<0.03). In conclusion, a full team handball season did not lead to deterioration of the athletes' postural control, but by the end of the season, the athletes were more asymmetrical.
The aim of this study was to investigate the effects of unilateral and bilateral fatigue on both ... more The aim of this study was to investigate the effects of unilateral and bilateral fatigue on both postural and power bipedal tasks. Ten healthy subjects performed two tasks: bipedal quiet standing and a maximal bipedal countermovement jumping before and after unilateral (with either the dominant or nondominant lower limb) and bilateral (with both lower limbs) fatigue. We employed two force plates (one under each lower limb) to measure the ground reaction forces and center of pressure produced by subjects during the tasks. To quantify the postural sway during quiet standing, we calculated the resultant center of pressure (COP) speed and COP area of sway, as well as the mean weight distribution between lower limbs. To quantify the performance during the countermovement jumping, we calculated the jump height and the peak force of each lower limb. We observed that both unilateral and bilateral fatigue affected the performance of maximal voluntary jumping and standing tasks and that the e...
Six subjects performed a planar reaching arm movement to a target while unpredictable perturbatio... more Six subjects performed a planar reaching arm movement to a target while unpredictable perturbations were applied to the endpoint; the perturbations consisted of pulling springs having dierent stiness. Two conditions were applied; in the ®rst, subjects had to reach for the target despite the perturbation, in the second condition, the subjects were asked to not correct the motion as a perturbation was applied. We analyzed the kinematics pro®les of the three arm segments and, by means of inverse dynamics, calculated the joint torques. The framework of the equilibrium-point (EP) hypothesis, the k model, allowed the reconstruction of the control variables, the``equilibrium trajectories'', in thè`d o not correct'' condition for the wrist and the elbow joints as well as for the end point ®nal position, while for the other condition, the reconstruction was less reliable. The ®ndings support and extend to a multiple-joint planar movement, the paradigm of the EP hypothesis along with the``do not correct'' instruction.
The aim of this study was to characterize prolonged standing and its effect on postural control i... more The aim of this study was to characterize prolonged standing and its effect on postural control in elderly individuals in comparison to adults. It is unknown how elderly individuals behave during prolonged standing and how demanding such a task is for them. We recorded the center of pressure (COP) position of 14 elderly subjects and 14 adults while they performed prolonged standing (30 min) and quiet stance tasks (60 s) on a force plate. The number and amplitude of the COP patterns, the root mean square (RMS), speed, and frequency of the COP sway were analyzed. The elderly subjects were able to stand for prolonged periods but they produced postural changes of lesser amplitude and a decreased sway during the prolonged standing task. Both the adults and the elderly subjects were influenced by the prolonged standing task, as demonstrated by their increased COP RMS and COP speed in the quiet standing trial after the prolonged standing task, in comparison to the trial before. We suggest that the lack of mobility in elderly subjects may be responsible for the observed sub-optimal postural changes in this group. The inability of elderly individuals to generate similar responses to adults during prolonged standing may contribute to the increased risk of falls in the older population. #
Prolonged (>30 min) unconstrained standing (PUS) was studied in 10 young healthy subjects. The us... more Prolonged (>30 min) unconstrained standing (PUS) was studied in 10 young healthy subjects. The usual methods of stabilographic analysis assume a random center of pressure (COP) migration. This study was based on the opposite idea and showed that during PUS, specific and consistent patterns of the COP migration can be recognized by a computer algorithm. Three COP migration patterns were found: (a) shifting, a fast displacement of the average position of COP from one region to another; (b) fidgeting, a fast and large displacement and returning of COP to approximately the same position; and (c) drifting, a slow continuous displacement of the average position of COP. A software code was written and default parameter values were chosen for recognizing COP migration patterns. For 30-min PUS the following patterns were identified: Shifting was generally observed every 316 f 292 sec in the anterior-posterior (a-p) direction with an average shift amplitude of 17 f 15 mm, and every 199 f 148 sec in the medial-lateral (m-1) direction with an average shift amplitude of 22 +-38 mm. Corresponding time intervals for fidgeting were 59 +-15 sec in the a-p direction and 49+16 sec in the m-1 direction. The average drift-to-drift interval was 3 19 f 173 sec in the a-p direction and 529 +-333 sec in the m-1 direction. Prolonged Unconstrained Standing
In numerous motor tasks, muscles around a joint act coactively to generate opposite torques. A va... more In numerous motor tasks, muscles around a joint act coactively to generate opposite torques. A variety of indexes based on electromyography signals have been presented in the literature to quantify muscle coactivation. However, it is not known how to estimate it reliably using such indexes. The goal of this study was to test the reliability of the estimation of muscle coactivation using electromyography. Isometric coactivation was obtained at various muscle activation levels. For this task, any coactivation measurement/index should present the maximal score (100% of coactivation). Two coactivation indexes were applied. In the first, the antagonistic muscle activity (the lower electromyographic signal between two muscles that generate opposite joint torques) is divided by the mean between the agonistic and antagonistic muscle activations. In the second, the ratio between antagonistic and agonistic muscle activation is calculated. Moreover, we computed these indexes considering different electromyographic amplitude normalization procedures. It was found that the first algorithm, with all signals normalized by their respective maximal voluntary coactivation, generates the index closest to the true value (100%), reaching 92 ± 6%. In contrast, the coactivation index value was 82 ± 12% when the second algorithm was applied and the electromyographic signal was not normalized (P < 0.04). The new finding of the present study is that muscle coactivation is more reliably estimated if the EMG signals are normalized by their respective maximal voluntary contraction obtained during maximal coactivation prior to dividing the antagonistic muscle activity by the mean between the agonistic and antagonistic muscle activations.
Background More than 2 years after undergoing anterior cruciate ligament (ACL) reconstruction, wo... more Background More than 2 years after undergoing anterior cruciate ligament (ACL) reconstruction, women still present bilateral asymmetries during multijoint movement tasks. Given the well-known ACL-injury gender bias, the goal of this study was to investigate whether males also present such asymmetries more than 2 years after undergoing ACL reconstruction. Methods This study involved 12 participants submitted to ACL reconstruction in the ACL group and 17 healthy participants in the control group. The mean postoperative period was 37 months. The participants executed bilateral countermovement jumps and load squat tasks. The kinematics and ground reaction forces on each lower limb and pelvis were recorded, and used to compute bilateral peak vertical ground reaction forces, peak knee and hip joint powers in the sagittal plane, and the ratio between these powers. Results For the jump task, the groups had the same performance in the jump height, but for the ACL group the peak knee joint power on the operated side was 13% lower than on the non-operated side (p = 0.02). For the squat task, the hip-knee joint power ratio on the operated side of the ACL group was 31% greater than on the non-operated side (p = 0.02).
Med. (Serv. do Prof. José Laredo Filho). 1. Doutor em Ortop.; Resp. pelo Setor de Artrosc. do Gru... more Med. (Serv. do Prof. José Laredo Filho). 1. Doutor em Ortop.; Resp. pelo Setor de Artrosc. do Grupo de Joelho do Departamento. 2. Prof. Adjunto-Doutor; Chefe do Grupo de Joelho do Departamento. 3. Méd. do Setor de Traumatol. Esport. do Departamento. 4. Resid. do 4º ano do Grupo de Joelho do Departamento. Endereço para correspondência: Mário Carneiro Filho, Rua Afonso Brás, 817, Vila Nova Conceição -04511-011 -São Paulo, SP. Tel. 822-8333.
It is unclear whether athletes change their postural control over the course of a full sport seas... more It is unclear whether athletes change their postural control over the course of a full sport season, or become more asymmetrical with respect to their neuromuscular performance over the same period. The aim of this study was to investigate the effects of a full sport season on the postural control of team handball elite athletes. Ten healthy, elite male team handball players performed bipodal standing (BP) and right and left unipodal standing (UP) during 30s. We used the RMS and speed of the center of pressure to describe postural sway. For the BP task, the sway was lower at the end of the season (p<0.005). For the UP tasks, the sway was lower at the end of the season only for the non-dominant limb (p<0.001). Differences between limbs were observed only at the end of the season (p<0.03). In conclusion, a full team handball season did not lead to deterioration of the athletes' postural control, but by the end of the season, the athletes were more asymmetrical.
The aim of this study was to investigate the effects of unilateral and bilateral fatigue on both ... more The aim of this study was to investigate the effects of unilateral and bilateral fatigue on both postural and power bipedal tasks. Ten healthy subjects performed two tasks: bipedal quiet standing and a maximal bipedal countermovement jumping before and after unilateral (with either the dominant or nondominant lower limb) and bilateral (with both lower limbs) fatigue. We employed two force plates (one under each lower limb) to measure the ground reaction forces and center of pressure produced by subjects during the tasks. To quantify the postural sway during quiet standing, we calculated the resultant center of pressure (COP) speed and COP area of sway, as well as the mean weight distribution between lower limbs. To quantify the performance during the countermovement jumping, we calculated the jump height and the peak force of each lower limb. We observed that both unilateral and bilateral fatigue affected the performance of maximal voluntary jumping and standing tasks and that the e...
Six subjects performed a planar reaching arm movement to a target while unpredictable perturbatio... more Six subjects performed a planar reaching arm movement to a target while unpredictable perturbations were applied to the endpoint; the perturbations consisted of pulling springs having dierent stiness. Two conditions were applied; in the ®rst, subjects had to reach for the target despite the perturbation, in the second condition, the subjects were asked to not correct the motion as a perturbation was applied. We analyzed the kinematics pro®les of the three arm segments and, by means of inverse dynamics, calculated the joint torques. The framework of the equilibrium-point (EP) hypothesis, the k model, allowed the reconstruction of the control variables, the``equilibrium trajectories'', in thè`d o not correct'' condition for the wrist and the elbow joints as well as for the end point ®nal position, while for the other condition, the reconstruction was less reliable. The ®ndings support and extend to a multiple-joint planar movement, the paradigm of the EP hypothesis along with the``do not correct'' instruction.
The aim of this study was to characterize prolonged standing and its effect on postural control i... more The aim of this study was to characterize prolonged standing and its effect on postural control in elderly individuals in comparison to adults. It is unknown how elderly individuals behave during prolonged standing and how demanding such a task is for them. We recorded the center of pressure (COP) position of 14 elderly subjects and 14 adults while they performed prolonged standing (30 min) and quiet stance tasks (60 s) on a force plate. The number and amplitude of the COP patterns, the root mean square (RMS), speed, and frequency of the COP sway were analyzed. The elderly subjects were able to stand for prolonged periods but they produced postural changes of lesser amplitude and a decreased sway during the prolonged standing task. Both the adults and the elderly subjects were influenced by the prolonged standing task, as demonstrated by their increased COP RMS and COP speed in the quiet standing trial after the prolonged standing task, in comparison to the trial before. We suggest that the lack of mobility in elderly subjects may be responsible for the observed sub-optimal postural changes in this group. The inability of elderly individuals to generate similar responses to adults during prolonged standing may contribute to the increased risk of falls in the older population. #
Prolonged (>30 min) unconstrained standing (PUS) was studied in 10 young healthy subjects. The us... more Prolonged (>30 min) unconstrained standing (PUS) was studied in 10 young healthy subjects. The usual methods of stabilographic analysis assume a random center of pressure (COP) migration. This study was based on the opposite idea and showed that during PUS, specific and consistent patterns of the COP migration can be recognized by a computer algorithm. Three COP migration patterns were found: (a) shifting, a fast displacement of the average position of COP from one region to another; (b) fidgeting, a fast and large displacement and returning of COP to approximately the same position; and (c) drifting, a slow continuous displacement of the average position of COP. A software code was written and default parameter values were chosen for recognizing COP migration patterns. For 30-min PUS the following patterns were identified: Shifting was generally observed every 316 f 292 sec in the anterior-posterior (a-p) direction with an average shift amplitude of 17 f 15 mm, and every 199 f 148 sec in the medial-lateral (m-1) direction with an average shift amplitude of 22 +-38 mm. Corresponding time intervals for fidgeting were 59 +-15 sec in the a-p direction and 49+16 sec in the m-1 direction. The average drift-to-drift interval was 3 19 f 173 sec in the a-p direction and 529 +-333 sec in the m-1 direction. Prolonged Unconstrained Standing
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