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The purposes of this study were to determine whether performing dynamic conditioning activities (CAs) contributes to postactivation potentiation (PAP); to examine the potential confounding effects of CAs with different velocity, total contraction duration, and total work characteristics; and to gain a greater understanding of potential peripheral and central mechanisms underlying PAP. Voluntary (isokinetic knee extensions at 180°·s(-1)) and electrically evoked torques and electromyogram (EMG) data were captured before and 1, 4, 7, 10, and 13 min after 5 different dynamic CAs (4 knee extensions at 60°·s(-1), 4 and 12 at 180°·s(-1), and 4 and 20 at 300°·s(-1)), after the participants had completed a full warm-up including extensive task-specific practice to the point where maximal voluntary contractile capacity was achieved. Even after maximal voluntary contractile capacity had been achieved, the imposition of CAs of longer total contraction duration (6 s) and a minimum total work of ∼750-900 J elicited significant increases in both voluntary (for 7 min; up to 5.9%) and twitch (for 4 min; up to 13.5%) torques (i.e., PAP), regardless of the velocity of the CA. No changes in EMG:M-wave were detected after any CA. A dynamic voluntary CA can contribute to improved voluntary and electrically evoked torques even when maximal voluntary contractile capacity has previously been achieved. Furthermore, a minimum CA contraction duration and minimum total work appear important to increase torque production, although movement velocity appears unimportant. Changes in peripheral function but not central drive may have contributed to the observed PAP under the present conditions.

Background: Glenohumeral displacements assessment would help to design shoulder prostheses with physiological arthrokinematics and to establish more biofidelic musculoskeletal models. Though displacements were documented during static tasks, there is little information on their 3D coupling with glenohumeral angle during dynamic tasks. Our objective was to characterize the 3D glenohumeral displacement-rotation couplings during dynamic arm elevations and rotations., Methods: Glenohumeral displacements were measured from trajectories of reflective markers fitted on intracortical pins inserted into the scapula and humerus. Bone geometry was recorded using CT-scan. Only four participants were recruited to the experiment due to its invasiveness. Participants performed dynamic arm abduction, flexion and axial rotations. Linear regressions were performed between glenohumeral displacements and rotations. The pin of the scapula of one participant moved, his data were removed from analysis, and results are based on three participants., Findings: The measurement error of glenohumeral kinematics was less than 0.15mm and 0.2°. Maximum glenohumeral displacements were measured along the longitudinal direction and reached up to +12.4mm for one participant. Significant couplings were reported especially between longitudinal displacement and rotation in abduction (adjusted R(2) up to 0.94)., Interpretation: The proposed method provides the potential to investigate glenohumeral kinematics during all kinds of movements. A linear increase of upward displacement during dynamic arm elevation was measured, which contrasts with results based on a series of static poses. The systematic investigation of glenohumeral displacements under dynamic condition may help to provide relevant recommendation for the design of shoulder prosthetic components and musculoskeletal models., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Electroencephalographic (EEG) studies have well established that motor cortex (M1) activity ~20 Hz decreases during muscular contraction and increases as soon as contraction stops, which are known as event-related desynchronization (ERD) and event-related synchronization (ERS), respectively. ERD is supposed to reflect M1 activation, sending information to recruited muscles, while the process underlying ERS is interpreted either as active cortical inhibition or as processing of sensory inputs. Investigation of the process behind ERD/ERS in people with spinal cord injury (SCI) would be particularly relevant since their M1 remains effective despite decreased sensorimotor abilities. In this study, we recorded net joint torque and EEG in 6 participants with cervical SCI and 8 healthy participants who performed isometric elbow flexion at 3 force levels. Multifaceted EEG analysis was introduced to assess ERD/ERS according to their amplitude, frequency range and duration. The results revealed that net joint torque increased with the required force level for all participants and time to contraction inhibition was longer in the SCI group. At the cortical level, ERD/ERS frequency ranges increased with the required force level in all participants, indicating that the modulation of cortical activity with force level is preserved after SCI. However, ERS amplitude decreased only in SCI participants, which may be linked to delayed contraction inhibition. All in all, cortical modulation of frequency range and amplitude could reflect two different kinds of neural communication., (© 2013 Elsevier B.V. All rights reserved.)

Background: Several studies have described the biomechanical effects of foot orthotics, as well as their effects at the level of muscular recruitment. Although the latter effect is unlikely to be limited to muscular intensity, the temporal pattern of activity of the muscles involved in walking with orthoses is still unclear., Methods: Twelve adults with everted static rearfoot posture higher than 5° of valgus participated in the study. For all participants, the kinematic data and the muscular temporal activity of the tibialis anterior, the soleus, the gastrocnemius medialis, the gastrocnemius lateralis and the peroneus longus were measured under two experimental conditions, walking with and without custom-made orthoses. Data were recorded and analyzed using a motion analysis and a surface EMG system., Findings: The results showed that, when walking with insoles, the activity of the tibialis anterior, the soleus, the gastrocnemius medialis, the gastrocnemius lateralis and the peroneus longus is shorter than walking without orthoses. Furthermore, when walking with orthoses, the activity of the soleus and the gastrocnemius medialis is delayed., Interpretation: Our study corroborates that the realignment of the calcaneus with the talus decreases the range of eversion and inversion of midfoot. Moreover, it reports noticeable modifications on the start time and the duration of the muscular activity of the tibialis anterior, soleus, gastrocnemii and peroneus longus while using foot orthoses., (© 2013. Published by Elsevier Ltd on behalf of American Society of Biomechanics. All rights reserved.)

Objective: This study investigated the effects of a cervical spinal cord injury (SCI) on the modulation of cortical desynchronization (ERD) during isometric contractions at different force levels., Methods: For 8 able-bodied (AB) and 6 cervical SCI participants, the net joint moment and electroencephalographic activities were recorded during isometric contractions of the right elbow in flexion and in extension at 3 force levels, that is, during intact and altered muscle contractions for SCI participants. The mean net moment and ∼20 Hz ERD from C3 electroencephalographic electrode were compared between AB and SCI participants., Results: In flexion, that is, during intact contractions for all participants, the mean net moment and the ERD increased with the required force level. In extension, that is, during altered contractions, the mean net moment increased for 3 SCI participants while it was almost zero for 3 other SCI participants. The associated ERD increased with the required force level for all participants., Conclusion: The cortical desynchronization was modulated by the intent to modulate the force level rather than the actual modulation of the force production., Significance: These results provide a better understanding of the modulation of the cortical desynchronization following SCI. Potential applications could include the control of neuroprostheses., (Copyright © 2012 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.)

During human contraction, net joint torque production involves the contribution of the antagonist muscles. Their activation protects the articulations and facilitates movement accuracy, but despite these fundamental roles, little is known about the brain mechanisms underlying their control. In view of previous studies that showed lesser antagonist muscles activation in participants engaged in regular strength training (ST) than in participants actively engaged in endurance disciplines (ED), we used this between-group comparison to investigate the possible role of motor cortex activity on the control of antagonist muscles. Electroencephalographic (EEG) and electromyographic (EMG) activity as well as the net joint torque were recorded, while ten ST and eleven ED participants performed isometric knee muscles exertions at different force levels. EEG data showed a linear increase in the suppression of cortical oscillations in the 21-31 Hz frequency band with increasing force level in ST but not in ED participants. This effect was associated with lesser EMG activation of the antagonist muscles in ST than in ED participants, the difference between groups also increasing with the force level. Both effects were found specifically during flexion exertions, indicating that ST participants developed sharp central adaptations to control the antagonist muscles involved as prime movers in their usual training task. This result suggests that the cortical adaptations induced by regular strength training could exert a specific encoding of the antagonist muscles, leading to the minimization of their activation and improved energetic efficiency of the muscle contraction.

The study of the correlations that may exist between neurophysiological signals is at the heart of modern techniques for data analysis in neuroscience. Wavelet coherence is a popular method to construct a time-frequency map that can be used to analyze the time-frequency correlations between two time series. Coherence is a normalized measure of dependence, for which it is possible to construct confidence intervals, and that is commonly considered as being more interpretable than the wavelet cross-spectrum (WCS). In this paper, we provide empirical and theoretical arguments to show that a significant level of wavelet coherence does not necessarily correspond to a significant level of dependence between random signals, especially when the number of trials is small. In such cases, we demonstrate that the WCS is a much better measure of statistical dependence, and a new statistical test to detect significant values of the cross-spectrum is proposed. This test clearly outperforms the limitations of coherence analysis while still allowing a consistent estimation of the time-frequency correlations between two non-stationary stochastic processes. Simulated data are used to investigate the advantages of this new approach over coherence analysis. The method is also applied to experimental data sets to analyze the time-frequency correlations that may exist between electroencephalogram (EEG) and surface electromyogram (EMG)., (Copyright © 2010 Elsevier Inc. All rights reserved.)

Background: Lower and upper body exercise are mandatory constituents of a rehabilitation programme for patients with COPD. However, it is not known how much these exercises may induce pulmonary dynamic hyperinflation (DH)., Objective: To evaluate the DH in patients with COPD exercising the upper and lower parts of the body at the same metabolic demand., Methods: Sixteen patients aged 63 +/- 13 years and with a FEV1 of 1.5 +/- 0.7 L (41 +/- 11% pred) were studied. Patients initially performed a maximal exercise test with the arms using the diagonal movement technique. The lower limbs were exercised on a treadmill at the same metabolic demand., Results: Inspiratory capacity decreased 222 +/- 158 ml (9.8%) after the upper body exercise (p < 0.0001) and 148 +/- 161 ml (7%) after exercise with the lower body (p = 0.0028) and a difference between the two groups was found (p < 0.05). There was no difference between resting IC before upper and lower limbs exercises (p = 0.8); increase in minute ventilation and in pulmonary ventilation in percentage of maximum voluntary ventilation and reduction of expiratory time were larger in the upper limbs exercise (p < 0.05). Dyspnea as measured by the Borg Scale was higher in the upper body (3.9 +/- 2.2) than in the lower body (2.3 +/- 1.3) at the end of the exercise (p = 0.033). Pulmonary ventilation and inspiratory capacity were correlated (p = 0.0001; r = 0.82)., Conclusion: Exercise with the upper part of the body causes more DH and dyspnea than exercise with the lower part of the body at the same metabolic demand.