Browsing by Author "Velhote, Miguel C."
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- Acute effects of the use of a biofeedback system for the technical training in breaststroke swimmingPublication . Lima, António B.; Capitão, Fátima; Morouço, Pedro; Gonçalves, Pedro; Fernandes, Ricardo J.; Barbosa, Tiago M.; Velhote, Miguel C.; Tani, G.; Vilas-Boas, João PauloThe purpose of this research was to develop, validate, and evaluate a biofeedback system for the technical training in breaststroke swimming. The system lied on the assessment of speed fluctuation curves of an anatomical landmark of the swimmer(hip).
- Adjustments in motor unit properties during fatiguing contractions after trainingPublication . Vila-Chã, Carolina; Falla, Deborah; Velhote, Miguel C.; Farina, DarioThe objective of the study was to investigate the effect of strength and endurance training on muscle fiber membrane properties and discharge rates of low-threshold motor units of the vasti muscles during fatiguing contractions. Methods: Twenty-five sedentary healthy men (age (mean T SD) = 26.3 T 3.9 yr) were randomly assigned to one of three groups: strength training, endurance training, or a control group. Conventional endurance and strength training was performed 3 dIwkj1, during a period of 6 wk. Motor unit conduction velocity and EMG amplitude of the vastus medialis obliquus and lateralis muscles and biceps femoris were measured during sustained isometric knee extensions at 10% and 30% of the maximum voluntary contraction before and immediately after training. Results: After 6 wk of training, the reduction in motor unit conduction velocity during the sustained contractions at 30% of the maximum voluntary force occurred at slower rates compared with baseline (P G 0.05). However, the rate of decrease was lower after endurance training compared with strength training (P G 0.01). For all groups, motor unit discharge rates declined during the sustained contraction (P G 0.001), and their trend was not altered by training. In addition, the biceps femoris–vasti coactivation ratio declined after the endurance training. Conclusions: Short-term strength and endurance training induces alterations of the electrophysiological membrane properties of the muscle fiber. In particular, endurance training lowers the rate of decline of motor unit conduction velocity during sustained contractions more than strength training
- Changes in H reflex and V wave following short-term endurance and strength trainingPublication . Vila-Chã, Carolina; Falla, Deborah; Velhote, Miguel C.; Farina, DarioThis study examined the effects of 3 wk of either endurance or strength training on plasticity of the neural mechanisms involved in the soleus H reflex and V wave. Twenty-five sedentary healthy subjects were randomized into an endurance group (n 13) or strength group (n 12). Evoked V-wave, H-reflex, and M-wave recruitment curves, maximal voluntary contraction (MVC), and time-to-task-failure (isometric contraction at 40% MVC) of the plantar flexors were recorded before and after training. Following strength training, MVC of the plantar flexors increased by 14.4 5.2% in the strength group (P 0.001), whereas time-to-task-failure was prolonged in the endurance group (22.7 17.1%; P 0.05). The V wave-to-maximal M wave (V/Mmax) ratio increased significantly (55.1 28.3%; P 0.001) following strength training, but the maximal H wave-to-maximal M wave (Hmax/Mmax) ratio remained unchanged. Conversely, in the endurance group the V/Mmax ratio was not altered, whereas the Hmax/Mmax ratio increased by 30.8 21.7% (P 0.05). The endurance training group also displayed a reduction in the H-reflex excitability threshold while the H-reflex amplitude on the ascending limb of the recruitment curve increased. Strength training only elicited a significant decrease in H-reflex excitability threshold, while H-reflex amplitudes over the ascending limb remained unchanged. These observations indicate that the H-reflex pathway is strongly involved in the enhanced endurance resistance that occurs following endurance training. On the contrary, the improvements in MVC following strength training are likely attributed to increased descending drive and/or modulation in afferents other than Ia afferents.
- Contributos da biomecânica para o estudo do rendimento desportivo em nataçãoPublication . Vilas-Boas, João Paulo; Oliveira, Sara; Silva, Diana; Sousa, Ana Francisca; Ribeiro, João; Jesus, Kelly de; Costa, Lígia; Figueiredo, Pedro; Pereira, Suzana Matheus; Lima, António B.; Marinho, D.A.; Morouço, Pedro; Barbosa, Tiago M.; Silva, A.J.; Vaz, Mário; Velhote, Miguel C.; Soares, Susana; Sousa, Filipa; Machado, Leandro; Fernandes, Ricardo J.Na actualidade, o progresso do rendimento desportivo ao mais alto nível só é susceptível de ser conseguido através de uma combinação (que diríamos necessariamente feliz) de um vasto conjunto de factores: é necessário desde logo um pouco de sorte (como em tudo na vida – mesmo que seja para cozinhar a sopa de pedra requerida), mas sobretudo um praticante talentoso e motivado, condições de treino adequadas, um envolvimento global propício, uma equipa directiva competente e motivada e uma equipa técnica pluridisciplinar devidamente habilitada e coordenada. No quadro das habilitações desta deve-se destacar a sua sensibilidade e vocação para a contínua avaliação do seu próprio desempenho e do desempenho do seu nadador, para a consideração, ponderação e experimentação de novas opções, para a inovação tecnológica e científica. Apesar de no universo desportivo a inércia científica (e tecnológica) ser ainda superior à verificada noutros domínios da sociedade contemporânea (às vezes por estrito exercício de um carácter “bota de elástico”), são já muitos (e de há muito) os exemplos frutuosos da sua incorporação no quotidiano, seja como background cultural apenas, seja como prática efectiva. No futuro serão cada vez mais; e serão cada vez menos os espaços para o “por acaso”, para o “surpreendente”, para a geração espontânea do campeão apesar de quem o treina. No futuro – e num futuro que se já vem fazendo presente – não haverá nadadores ou treinadores de sucesso que não apelem, mais ou menos exuberantemente, a auxiliares científicos e tecnológicos para o treino.
- Differences in motor unit behavior following endurance and strength trainingPublication . Vila-Chã, Carolina; Falla, Deborah; Velhote, Miguel C.; Farina, DarioAim: Strength and endurance training are two common forms of motor training which induce distinct adaptive neuromuscular responses. There is a considerable debate on the neural adaptations which accompany strength training and little is known about the effects of endurance training. This study investigated changes in motor output and motor unit behavior following 6 weeks of either strength or endurance training. Methods: Twenty-eight sedentary healthy men (age, mean ± SD, 26.1 ± 3.9 yr) were randomly assigned to one of 3 groups: strength training (ST); endurance training (ET) and; control (C; no exercise intervention). The training was performed three days per week, over a period of 6 weeks. Maximum voluntary force (MVC), time-to-task failure at 30% MVC, and rate of force development (RDF) of the knee extensors were measured before and post training (week 7). Additionally, motor unit behavior and muscle activity were studied with intramuscular and surface EMG recordings from the vastus medialis obliquus (VMO) and vastus lateralis (VL) muscles during sustained isometric knee extensions at 10% and 30% MVC. The surface EMG was recorded also during MVC and explosive isometric contractions. Results: In the ST group, the percent change post-training in MVC and RFD was significantly greater (13.8 ± 3.6% and 19.8 ± 5.9%, respectively) compared to the ET (P < 0.05) and C group (P < 0.05). In contrast, the time-to-task failure increased significantly only in the ET group (percent increase: 19.8 ± 5.9%; P < 0.05). For the isometric submaximal contractions (30% MVC), the average rectified value of the surface EMG of VL and VMO increased post training for both ET and ST groups (P < 0.05). For the same contractions, strength training but not endurance training resulted in a significant increase in the mean motor unit discharge rates for the VMO (1.22 pps; P = 0.002) and VL (1.59 pps; P = 0.001). On the contrary, mean discharge rates were reduced following training for the ET group (VMO - 1.12 pps; P = 0.03 and VL - 1.09 pps; P = 0.04) despite an increase in surface EMG amplitude. Only the ST group showed an increase in the ARV of the VL and VMO (P < 0.05) during the maximal and explosive isometric conditions. No change was observed for the C group in any of the conditions. Conclusion: Endurance and strength training induce distinct adaptations in the neural control of the vasti muscles. Strength training was shown to increase the discharge rate of vasti motor units during isometric knee extension contractions whereas endurance training resulted in a reduction in motor unit discharge rates.
- A kinematical, imagiological and acoustical biofeedback system for the technical training in breaststroke swimmingPublication . Lima, António B.; Semblano, P.; Fernandes, Daniel; Gonçalves, Pedro; Morouço, Pedro; Sousa, Filipa; Fernandes, Ricardo J.; Barbosa, Tiago M.; Velhote, Miguel C.; Tani, G.; Vilas-Boas, João PauloA system for real time velocimetric feedback, and for immediate disposal of kinematica data, and model, synchronized with dual-media video images, will be presented.
- The effect of short-term endurance and strength training on motor unit conduction velocityPublication . Vila-Chã, Carolina; Falla, Deborah; Velhote, Miguel C.; Farina, DarioAIM: The aim of this study was to investigate the effect of strength and endurance training on the conduction velocity of vastus medialis obliquus and lateralis single motor units during voluntary sustained knee extensions. METHODS: Seventeen sedentary healthy men (age, mean ± SD, 26.3 ± 3.9 yr) were randomly assigned to one of 2 groups: strength training (ST, n= 8) or endurance training (ET, n= 9). Conventional endurance and strength training was performed three days per week, over a period of 6 weeks. Motor unit conduction velocity (MUCV), maximum voluntary force (MVC) and time-to-task failure at 30% MVC of the knee extensors were measured before and immediately following training. To assess MUCV, multi-channel surface and intramuscular EMG signals were concurrently recorded from the vastus medialis obliquus (VMO) and vastus lateralis (VL) muscles during 60-s isometric knee extensions at 10% and 30% of MVC. RESULTS: After 6 weeks of training, MVC increased in the ST group (16.7 ± 7.4 %; P < 0.05) whereas time to task failure was prolonged in the ET group (33.3 ± 14.2 %; P < 0.05). Both training programs induced an increase in motor unit conduction velocity at both 10% and 30% MVC (P < 0.01). Furthermore after both training programs, the reduction in MUCV over time during the sustained contractions occurred at slower rates compared to baseline (P < 0.01). CONCLUSION: These results indicate that short-term endurance and strength training induce similar alterations of the electrophysiological membrane properties of the muscle fiber and in their changes during sustained contractions
- Validation of a cable speedometer for butterfly evaluationPublication . Morouço, Pedro; Lima, António B.; Semblano, P.; Fernandes, Daniel; Gonçalves, Pedro; Sousa, Filipa; Fernandes, Ricardo J.; Barbosa, Tiago M.; Velhote, Miguel C.; Vilas-Boas, João PauloGetting fast results from the evaluation of swimmers is one of the most important goals to achieve with technological development in the field. The purpose of this study was to validate a real-time velocimetric device (speedometer) through the comparison of their results with computer assisted videogrametry. The sample included 7 international level swimmers (3 females and 4 males). Each swimmer performed four 25m trials, two at 200m race pace and two at 50m race pace. For each trial, two stroke cycles were studied, resulting on a total of 28 cycles SWIMMING EVALUATION, ADVICE AND BIOFEEDBACK Rev Port Cien Desp 6(Supl.2) 201–282 237 analysed. Hip v(t) curves obtained from speedometer and videogrametry were compared, as well as the speedometer hip curve with the one of the centre of mass (CM). The higher mean correlation obtained was between vhip1 and vhip2 (0.955±0.028), followed by vhip1 with vCM (0.920±0.049). The lower correlation was vhip2 vs. vCM (0.878±0.053). It was concluded that the speedometer is a reliable, fast and interactive tool for training advice.
- Validation of a cable speedometer for butterfly strokePublication . Morouço, Pedro; Lima, António B.; Semblano, P.; Fernandes, Daniel; Gonçalves, Pedro; Sousa, Filipa; Fernandes, Ricardo J.; Barbosa, Tiago M.; Velhote, Miguel C.; Vilas-Boas, João PauloMost of the approaches available for technical evaluation of swimmers are very expensive and time consuming. Thus, one of the most important goals to achieve in swimming research should be to get fast and interactive results from the evaluation process. The purpose of this research was to compare me real-time velocimetric results obtained from a cable velocimeter with those extracted from computerised videogrametry.