Percorrer por autor "Pezarat-Correia, Pedro"
A mostrar 1 - 10 de 10
Resultados por página
Opções de ordenação
- Bench-press performed with a velocity- and tempo-based approach : are there differences in volume load, time under tension, and metabolic demands?Publication . Fitas, Afonso; Miras-Moreno, Sérgio; Oliveira, João Henriques; Cidrais, Margarida; Pezarat-Correia, Pedro; Schoenfeld, Brad J.; Mendonça, Gonçalo V.Background: Velocity-based training (VBT) is a resistance training approach that uses lifting velocity to determine training load and track strength progress. This study determined the impact of a VBT versus a tempo-based training (TBT) approach on volume load and time under tension during a single set of submaximal bench press performed to failure. Hypothesis: VBT would result in larger volume load and similar time under tension as TBT. Study Design: Randomized-crossover design. Level of Evidence: Level 3. Methods: A total of 14 healthy men (24.1 ± 5.8 years) performed free-weight bench-press exercise at low intensities (12%, 16%, 20%, and 24% of 1-repetition maximum [1RM]) with oxygen uptake (V.O2) measurements. V.O2 was then extrapolated to a set performed at 70% 1RM to failure and the accumulated O2 deficit was calculated together with the relative energy contribution of aerobic and anaerobic metabolism. Mechanical data were collected with a linear encoder. Results: Despite the lack of differences between conditions for total time under tension (P > 0.05), VBT achieved a higher volume load at set failure (P < 0.05). Moreover, the VBT condition resulted in a larger total V.O2 from set initiation to termination (P < 0.01). Conversely, the accumulated O2 deficit did not differ between conditions (P > 0.05). Compared with TBT, VBT elicited a higher relative contribution of aerobic energy (VBT, ~41%; TBT, 33%) and a lower relative contribution of anaerobic energy (VBT, ~59; TBT, 67%) during exercise (P < 0.01). Conclusion: VBT is an effective strategy to enhance volume load during bench-press performed to failure at 70% 1RM. This effect occurs without compromising time under tension. These findings are associated with a higher contribution of aerobic energy supply to exercise. Clinical Relevance: VBT may be beneficial for athletes aiming to maximize volume load in response to resistance exercise.
- Changes in torque complexity with fatigue are related to motor unit behaviourPublication . Gomes, João Sá; Oliveira, João Henriques; Bauer, Philipp; Pezarat-Correia, Pedro; Vaz, João R.Physiological complexity is believed to reflect a system’s adaptability to environmental challenges having been proposed as an indirect indicator of the functional capacity of the neuromuscular system. This study aimed to investigate the association between torque complexity’s changes with neuromuscular fatigue and motor unit parameters. Twenty-one healthy and young adults visited the laboratory on one occasion. Knee extension maximum voluntary isometric contractions and isometric contractions at 30% of maximum were collected at baseline and immediately after a fatiguing knee extension protocol, which consisted of a series of concentric and eccentric knee extensions at 90°/s until exhaustion. Torque signals were sampled continuously, and torque complexity was assessed through an entropy measure. Motor unit-related parameters were extracted from the submaximal trials and further analysed. Our findings demonstrate that torque complexity’s alteration pre-to-post neuromuscular fatigue is highly correlated with vastus lateralis and medialis average firing rate (r = − 0.618 and r = − 0.659, respectively) and peak motor unit action potential amplitude (rs = − 0.801 and rs = − 0.703, respectively) pre-fatigue. Moreover, alterations in torque complexity were observed, indicating a loss of adaptability within the neuromuscular system with neuromuscular fatigue. Overall, our findings supported our hypothesis by demonstrating alterations in torque complexity with neuromuscular fatigue, rendering the system less adaptable. Moreover, our results added to the current knowledge by highlighting the association between torque complexity’s changes with neuromuscular fatigue and motor unit parameters.
- Effects of attentional focus on the regulation of torque complexityPublication . Bauer, Philipp; Gomes, João S.; Oliveira, João H.; Santos, Paulo; Pezarat-Correia, Pedro; Vaz, João R.Recent scientific evidence suggests that an external focus of attention (vs. an internal focus of attention) promotes a greater number of motor solutions, rendering the system more adaptable and complex. Therefore, the present study investigated the effect of the attentional focus (external vs. internal) on torque complexity and variability as well as its associated intermuscular coordination processes. Fourteen participants performed maximal and submaximal isometric knee extension tasks in three conditions (control, external focus, internal focus) to assess immediate effects of the focus of attention in a within-subjects comparison. Peak torque was extracted from maximal trials. Regarding submaximal trials, torque complexity and the magnitude of variability were assessed through Sample Entropy (SampEn), i.e., a measure of regularity in the temporal structure of torque output and coefficient of variation (CV), respectively. The intermuscular coordination was assessed through co-contraction index. An external focus led to an increase in SampEn (i.e., decreased regularity) when compared to an internal focus (p = 0.032) and a control condition (p = 0.036). Conversely, no differences were found for CV and peak torque. The external focus promoted a decrease in muscular activity of vastus medialis in comparison with the internal focus (p = 0.040) and an increase in muscular activity when compared to the control condition (p < 0.001). Furthermore, an external focus led to decreased muscular activity of semitendinosus as well as a decrease in the co-contraction indices involving semitendinosus in comparison with the internal focus and the control condition (all p < 0.05). The present findings suggest that an external focus leads to an enhanced flexibility of motor control. Moreover, the general decrease in co-contraction and in muscular activity without affecting maximal force parameters that we observed with an external focus suggest a higher efficiency of the motor system caused by intermuscular coordination processes.
- Force fluctuations regulation and the role of neurophysiological mechanisms throughout different isometric contraction intensitiesPublication . Oliveira, João H.; Gomes, João S.; Bauer, Philipp; Pezarat-Correia, Pedro; Vaz, João R.Force complexity is a key indicator of the neuromuscular system’s adaptability and motor control. Although an inverted U-shaped relationship between force complexity and contraction intensity is established, its underlying mechanisms remain unclear. To investigate whether changes in motor unit behaviour (recruitment and firing rate) would accompany and explain this relationship, 25 young male adults performed a 30-second knee extensors’ hold-isometric task at 50%, 75%, 100%, 150% and 175% of their End-Test Torque (ETT), at individual’s optimal angle. Force complexity and motor unit behaviour were assessed through Sample Entropy (SampEn) and high-density surface electromyography, respectively. We demonstrated a trend for an inverted U-shaped relationship between force complexity and contraction intensity, with SampEn at ETT and 150%ETT being significantly higher than at 50%ETT and 75%ETT (all p < 0.05). This pattern was accompanied by an increase in motor unit actions potentials and firing rate as the intensity increased up to 150%ETT (all p < 0.05). A multiple linear regression analysis showed that force complexity was explained in 18% by the vastus lateralis’ motor unit behaviour. The findings suggest that changes in force complexity depend on contraction intensity and are partly explained by alterations in motor unit behaviour, influencing the neuromuscular system’s adaptability to meet task demands.
- Impact of the optimal minimum velocity threshold on the accuracy of one repetition maximum estimation-based on a mixed modelPublication . Fitas, Afonso; Gomes, Miguel; Santos, Paulo; Vila-Chã, Carolina; Pezarat-Correia, Pedro; Mendonça, Gonçalo V.Purpose: This study aimed at developing two mixed methods approaches for 1RM prediction (generalized equations together with the individual load–velocity relationship—LVR). The validity of such equations was explored and compared with the validity of individual LVRs. Methods: The submaximal LVRs of seventy-six males was obtained for the free-weight back squat. Theoretical load at zero velocity (LD0), the slope of the individual LVR, and the individual (ModelIND) and optimal minimum velocity thresholds (MVT) (ModelOPT) were selected to develop the equations. Prediction accuracy was determined through mean differences, absolute percent errors and Bland–Altman plots. Results: ModelIND was predictive of 1RM (p < 0.0001), explaining 89.7% of its variance. ModelOPT increased the prediction power of 1RM to 98.7% (p < 0.0001). No significant differences in the absolute percent errors were found (4.7 and 3.9%, for ModelIND and ModelOPT, respectively). The mean difference between actual and estimated 1RM was nearly zero for both models, while individual LVRs relying on the individual MVT displayed the contrary. The limits of agreement were 15.1 and 11.4 kg for ModelIND and ModelOPT, respectively. Conclusion: The individual and optimal MVTs add predictive value to LD0 and the slope of the individual LVR for 1RM estimation on a group level and avoid error trends over the entire muscular strength spectrum. However, only ModelIND increased the accuracy of estimations when compared with the more direct approach. From a practical standpoint, practitioners are encouraged to rely on the individual LVR instead of ModelOPT, when using the optimal MVT for estimation purposes.
- Muscle activation and intermuscular coordination adaptations to early strength training during maximal force productionPublication . Santos, Paulo D. G.; Vaz, João R.; Gomes, Miguel; Infante, Jorge; Pezarat-Correia, PedroPreviously untrained individuals tend to increase maximal and rapid strength during the initial resistance training stages. Muscle activation and coordination are neural mechanisms contributing to the increased mechanical output. However, how the force production characteristics are accompanied by changes in activation of agonist muscles as well as coordination of muscles with different functional roles is not fully understood. This study investigated the time course of adaptations following 6 weeks of resistance training, evaluating every two weeks a leg-press isometric maximum voluntary contraction. Peak force (PF), rate of force development (RFD), rate of EMG rise (RER) of the agonist muscles and intermuscular coherence between synergist or antagonist pairs of muscles were evaluated. In result of a dynamic squat program, the maximal and rapid leg-press isometric force increased after the 6-week period (p = 0.011 and p = 0.015, respectively), although improvements at specific intervals of RFD at specific time points were observed. Regarding knee extensor activation, generally decreased RER was observed only for rectus femoris and not for the monoarticular portions of quadriceps. Additionally, intermuscular coherence analysis revealed increased coupling between rectus femoris and the monoarticular portions of quadriceps after training, and adaptations between agonist muscles acting in different joints as well as between agonist and antagonist muscle at specific time points were observed concerning specific bands. This is the first study to characterize the time course of intermuscular coordination adaptations during the early phase of strength training in previously untrained individuals, bringing new insights into the neural mechanisms of muscle recruitment following resistance training in what concerns to coordinative strategies in the control of muscles with different functional roles.
- Muscle activity variability patterns and stride to stride fluctuations of older adults are positively correlated during walkingPublication . Jordão, Sofia; Stergiou, Nick; Brandão, Rita; Pezarat-Correia, Pedro; Oliveira, Raúl; Cortes, Nelson; Vaz, João R.It has been found that fractal-like patterns are present in the temporal structure of the variability of healthy biological rhythms, while pathology and disease lead to their deterioration. Interestingly, it has recently been suggested that these patterns in biological rhythms are related with each other, reflecting overall health or lack of it, due to their interaction. However, the underlying neurophysiological mechanisms responsible for such dependency remain unknown. In addition, this relationship between different elements needs to be first verified before we even pursue understanding their interaction. This study aimed to investigate the relationship between two elements of the neuromuscular system, gait and muscle activity variability patterns in older adults. Twenty-one older adults walked at their preferred walking speed on a treadmill. Inter-stride intervals were obtained through an accelerometer placed on the lateral malleoli to assess the temporal structure of variability of stride-to-stride fluctuations. Inter muscle peak intervals were obtained through the electromyographic signal of the gastrocnemius to assess the temporal structure of the variability of the simultaneous muscle activity. The temporal structure of variability from both signals was evaluated through the detrended fluctuation analysis, while their magnitude of variability was evaluated using the coefficient of variation. The Pearson’s Correlation coefficient was used to identify the relationship between the two dependent variables. A significant strong positive correlation was found between the temporal structure of gait and muscle activity patterns. This result suggests that there is an interdependency between biological rhythms that compose the human neuromuscular system.
- Sleep deprivation increases the regularity of isometric torque fluctuationsPublication . Oliveira, João H.; Santos, Paulo; Pezarat-Correia, Pedro; Vaz, João R.The regularity of the fluctuations present in torque signals represent the adaptability of the motor control. While previous research showed how it is affected by neuromuscular fatigue and ageing, the underlying mechanisms remain unclear. It is currently under debate whether these changes are explained by central or peripheral neuromuscular mechanisms. Here, we experimentally manipulated the sleep of thirteen young adults through a supervised 24 h-sleep deprivation protocol. This study aimed to investigate the effect of sleep deprivation on the regularity of torque fluctuations, and other standard torque-related outcomes (Peak Torque – PT – and Rate of Torque Development – RTD). The participants were asked to perform knee extension maximal voluntary contractions (MVC) and submaximal knee extensions at 40% of MVC for 30 s. PT and RTD were calculated from the MVC and the regularity of the torque fluctuations was determined on the submaximal task through Sample Entropy (SampEn). In addition, rate of perceived effort (RPE) was collected. We found no significant changes in PT and RTD. The regularity of torque fluctuations significantly increased (i.e., a decrease in SampEn) after 24 h-sleep deprivation (PRE = 1.76 ± 0.268, POS24 = 1.71 ± 0.306; p = 0.044). Importantly, we found a negative correlation between RPE and SampEn relative changes after sleep deprivation. This study brings new insights towards the understanding of the underlying mechanisms that explain changes in torque fluctuations, demonstrating that these changes are not limited to neuromuscular processes but are also likely to be affected by other domains, such as psychological profile, which can indirectly affect the neural drive to the muscles.
- Torque regularity is not affected by the nature of visual feedback during hold type of isometric contractions in adultsPublication . Oliveira, João Henriques; Gomes, João Sá; Bauer, Philipp; Pezarat-Correia, Pedro; Vaz, João RochaThe literature that investigated the influence of visual feedback properties on the magnitude and temporal structure of variability suggests that increases in the precision of visual information of the torque output (through manipulation of visual gain and its intermittency) lead the neuromuscular system to produce torque in a more steady and complex manner. However, less is known about the influence of the nature of visual feedback on torque variability. The present study aimed to investigate the effect of two different feedback natures, one from the angular position and the other from the torque produced, on the magnitude and temporal structure of torque variability during submaximal hold isometric tasks. Twenty healthy and young participants performed a knee extension isometric task, consisting in sustaining an applied resistance equivalent to 40% of their Maximal Voluntary Isometric Contraction for 30 s with visual feedback from angular position (Hangle) and with visual feedback from torque (Htorque). The magnitude of torque variability was calculated through the coefficient of variation. Sample Entropy was used to analyze the temporal structure of torque fluctuations, i.e., torque complexity. We observed no significant differences between conditions (Hangle vs Htorque) in both magnitude (p = 0.117) and the temporal structure of torque fluctuations (p = 0.940). Our results demonstrated that torque regulation seems not to be affected by the nature of the visual feedback during hold submaximal isometric tasks, suggesting a participation of sensorimotor system due to the nature of the task. Researchers should take this into account to take methodological decisions when using hold submaximal isometric tasks to investigate possible changes in motor control.
- Torque regulation is influenced by the nature of the isometric contractionPublication . Bauer, Philipp; Gomes, João Sá; Oliveira, João; Santos, Paulo; Pezarat-Correia, Pedro; Vaz, João R.The present study aimed to investigate the effects of a continuous visual feedback and the isometric contraction nature on the complexity and variability of force. Thirteen healthy and young male adults performed three MVCs followed by three submaximal isometric force tasks at a target force of 40% of their MVC for 30 s, as follows: (i) push isometric task with visual feedback (Pvisual); (ii) hold isometric task with visual feedback (Hvisual); (iii) hold isometric task without visual feedback (Hnon-visual). Force complexity was evaluated through sample entropy (SampEn) of the force output. Force variability was analyzed through the coefficient of variation (CV). Results showed that differences were task-related, with Pvisual showing higher complexity (i.e., higher SampEn) and decreased variability (i.e., lower CV) when compared with the remaining tasks. Additionally, no significant differences were found between the two hold isometric force tasks (i.e., no influence of visual feedback). Our results are promising as we showed these two isometric tasks to induce different motor control strategies. Furthermore, we demonstrated that visual feedback’s influence is also dependent on the type of isometric task. These findings should motivate researchers and physiologists to shift training paradigms and incorporate different force control evaluation tasks.