1,721,286 research outputs found
Optimization of sEMG electrode positioning in vastus lateralis muscle during neuromuscular electrical stimulation
No full textPurpose: The aim of the study was to estimate spatial activation of vastus lateralis (VL) muscle during electrical stimulation applied to the entire muscle in absence of fatigue and properly eliminating the influence of stimulation artifact.
Methods: Ten healthy men were enrolled in this study. The current was delivered to VL by two electrodes placed proximally and distally, for 5 s at the higher intensity that subjects can tolerate. Superficial electromyography (sEMG) signals were acquired using a bidimensional array of 63 electrodes positioned between the two stimulating electrodes along muscle fibers. For each subjects average rectified value (ARV) was estimated on normalized sEMG signals dividing bidimensional array in two areas, then the barycenter of the more active area was estimated. Finally, average barycenter coordinates were calculated among subjects since Kruskal–Wallis and Dunn-Sidak post hoc test confirmed no statistical differences among subjects in the more active area.
Results: ARV analysis showed that the VL more active area was located laterally and distally with respect to the center of the bidimensional array. Mean and standard deviation among subjects revealed that barycenter of more active zone in medio-lateral direction was between electrodes 1 and 2 and in proximal–distal direction was between electrodes 10 and 11. This location corresponds to a well-defined area in the framework of anatomical landmarks defined in the text.
Conclusions: It was possible to assess that VL during electrical stimulation was activated differently throughout its volume. In particular, distal-lateral portion of the muscle was more active with respect to the other
Relationship among explosive power, body fat, fat free mass and pubertal development in youth soccer players: a preliminary study
No full textPurpose: Changes in body size and functional capacities are highly individual during puberty, and the performance of a soccer player is often closely related to their maturity status. The aim of the study was to evaluate the relationships among explosive power, body fat, fat free mass and pubertal development in young soccer players. Methods: Explosive power (countermovement jump-CMJ), body mass index (BMI), percentage of body fat (¿), fat free mass (FFM) and a Self-Administered Rating Scale for pubertal development (PDS) values of 11 "Giovanissimi" (age 13 year), 13 "Allievi" (age 15 year) and 10 "Juniores" (age >17 year) male soccer players were compared. The statistical analysis was performed using an analysis of variance among categories with Fisher's post hoc as appropriate. Furthermore, Pearson correlations among variables were calculated considering all subjects and also within categories. Results: Statistical differences emerged among categories in CMJ (F (2,30) = 28.3, p < 0.01), body fat weight (F (2,31) = 29.2, p < 0.01) and PDS (F (2,29) = 18.5, p < 0.01), while ¿ values showed statistical differences only for "Giovanissimi" and "Juniores" (F (2,31) = 3.4, p = 0.01). CMJ showed significant correlations with FFM (r = 0.68) and PDS (r = 0.63), PDS with FFM (r = 0.66) and BMI with ¿ (r = 0.71) and FFM (r = 0.71). A high correlation was found within categories. Conclusion: Since we found differences between categories and no correlation between chronological age and pubertal status, this study highlights the importance of assessing of puberty in youth soccer team
Relationship among performance value, body fat, fat free mass and pubertal development in youth soccer players
No full textThe Application of sEMG in Aging: A Mini Review
No full textThe aim of this mini-review is to describe the potential application of surface electromyography (sEMG) techniques in aging studies. Aging is characterized by multiple changes of the musculoskeletal system physiology and function. This paper will examine some of the innovative methods used to monitor age-related alterations of the neuromuscular system from sEMG signals. A description of critical assumptions which underlie some of these approaches is emphasized. The first part focuses on the evolution of the recording techniques and describes some methodological issues. The second part focuses on how to use the following techniques to characterize aging: amplitude and spectral sEMG signal analysis, muscle fiber conduction velocity estimation, and myoelectric fatigue assessment. The last part describes a number of advanced sEMG approaches which seem promising in the geriatric population to estimate motor unit number, size, recruitment thresholds, and firing rate
Relative age effect in males, but not females, undergraduate students of sport science
No full textPurpose: Relative age effect (RAE) is a bias usually observed in young athletes and in academia, where participation is higher among those born early in the year. We aimed to determine RAE in undergraduate students of sport science. Methods: The birth dates of a sample of undergraduate students (N = 11,280) at the University of Torino (Italy) were collected. Students belonged to sport science (N = 5229) and other faculties (N = 6051; law, arts, and economics). All students were divided into four groups depending on their birth date, and the distribution of the birth dates was compared with the general population by means of Chi square test. Results: The observed distribution was different from that expected for male undergraduate students of sport science (P = 0.009), where most students were born in the first few months of the year. Differently, in female students of sport science and students belonging to other faculties, the birth dates were more normally distributed (P > 0.05). Conclusion: In conclusion, we observed a skewed distribution of the birth dates in male, but not in female, undergraduate students of sport science. Probably, the physical advantages of the young males born at the year beginning may have oriented the choice of sport science degree, an academic field where physical capacities provide some advantages. © 2017, Springer-Verlag Italia
Sex differences in the rate of torque development and torque–velocity relationship are due to maximal strength only
Full text linkPurpose: This study aimed to analyse the sex differences in the rate of torque development (RTD) and torque-velocity parameters with and without normalisation for maximal voluntary torque (MVT). Methods: Right-leg knee extensors were tested in 64 healthy and active participants (31 F and 33 M). MVT and RTD were obtained under isometric conditions. Individual torque-velocity relationships were obtained using a curvilinear model on averaged torque and velocity over 80°-to-140° knee angle. Dynamic data were acquired through an incremental protocol on a leg extension machine, going from the lightest to the unmovable load despite maximal effort. Results: Independent samples t test revealed (p < 0.001) that males possess greater RTD measured at 50 ms (d = -1.2), 100ms (d = -2.1) and 150ms (d = -2.3), peak RTD (d = -1.3) and MVT (d = 2.1). When normalised by MVT, the sex differences in RTD disappeared. Curvilinear hyperbolic TV relationship well-fitted (R2 = 0.99). In FV parameters, maximal theoretical torque (d = -1.7), maximal power (Pmax) (d = -2.0), and torque at Pmax (d = -1.7) were greater in males (p < .05), while maximal theoretical velocity (V0) and velocity at Pmax did not differ. Conclusions: The sex differences in explosiveness (i.e., rapid isometric and dynamic force production) were mainly due to greater maximal strength in males than in females. These findings suggest that, in non-sedentary people, males do not present higher contraction velocity capacities, i.e. higher maximal velocity until which muscles can produce force, than females in knee extension
Italian student-athletes only need a more effective daily schedule to support their dual career
Full text linkPurpose: The present study aimed to investigate dual-career issues of Italian student-athletes according to gender, age, type of sport, competition level, university path, and year of attendance variables to highlight their main problems and solutions. Methods: An ad hoc 24-item questionnaire was administered to 711 academic Italian student-athletes (Mean age = 23; SD = 4 years). A multivariate analysis was applied for data related to the first 21 (section A), whereas answers from the last 3 items (section B) were only described.Results: For section A items, two factors (factor 2: items 5, 7, 8, 14; Cronbach alpha = 0.728; factor 5: items 10, 11; Cronbach alpha = 0.78) related to sport participation and education for future job emerged. For both factors, effects emerged between “year of attendance” subcategories (i.e., lower values for “out of course” subgroup), whereas only for factor 5, differences emerged in terms of age (i.e., higher values for younger than older subgroup). For section B, most student-athletes declared to wish schedules of lessons and exams (e.g., higher number of sessions; oral online interrogations) for better combining sport and academic requirements.Conclusion: The present study represents a further step to better understand the Italian student-athletes’ daily and weekly limitations and wished solutions related to the combination of sport and academic tasks. Institutional bodies should consider the present findings in case of future policies in supporting dual career
Both Isometric and Dynamic Testing Are Essential for a Comprehensive Assessment of the Knee Extensors
No full textThe improvements of measurement tools and data analysis enhanced our possibilities to assess neuromuscular performance, but also created confusion regarding significance and practical applications of this available information. To simplify the strength assessment understanding, our purpose was to group force, velocity, and power metrics that could provide similar outcomes. We measured single-leg knee extensor strength under isometric and dynamic conditions on 64 young adults (33 men and 31 women). Subjects performed maximal and burst-like contractions under isometric conditions to assess maximal torque (MVT) and rate of torque development (RTD). Under dynamic conditions, a torque-velocity relationship was obtained from an incremental load test. Principal component analysis (PCA) was used to reduce the dimensionality of the data set and group variables. Principal component analysis identified 4 components: (a) "Maximal force" (composed by MVT, T0, RTD100, RTD150, Topt, Pmax), (b) "Explosiveness" (composed by RTD50, RTDpeak, RTD50N, RTD100N, RTD150N, RTDpeakN, time to peak torque, time to RTDpeak), (c) "Force at high velocity" (composed by V0 and Vopt), and (d) "Curvature" (C). When data were normalized by sex differences, "Explosiveness" resulted as the first component and Pmax was included in the "Force at high velocity" component. The present findings remark the importance of testing the explosiveness (i.e., early RTD and normalized RTD metrics) together with torque-velocity profiling, to have a more comprehensive assessment of neuromuscular qualities
Neural and contractile determinants of burst-like explosive isometric contractions of the knee extensors
Full text linkWalking and running are based on rapid burst-like muscle contractions. Burst-like contractions generate a Gaussian-shaped force profile, in which neuromuscular determinants have never been assessed. We investigated the neural and contractile determinants of the rate of force development (RFD) in burst-like isometric knee extensions. Together with maximal voluntary force (MVF), voluntary and electrically evoked (8 stimuli at 300 Hz, octets) forces were measured in the first 50, 100 and 150 ms of burst-like quadriceps contractions in 24 adults. High-density surface electromyography (HDsEMG) was adopted to measure the root mean square (RMS) and muscle fiber conduction velocity (MFCV) from the vastus lateralis and medialis. The determinants of voluntary force at 50, 100 and 150 ms were assessd by stepwise multiple regression analysis. Force at 50 ms was explained by RMS (R2 = 0.361); force at 100 ms was explained by octet (R2 = 0.646); force at 150 ms was explained by MVF (R2 = 0.711) and octet (R2 = 0.061). Peak RFD (which occurred at 60 ± 10 ms from contraction onset) was explained by MVF (R2 = 0.518) and by RMS50 (R2 = 0.074). MFCV did not emerge as a determinant of RFD. Muscle excitation was the sole determinant of early RFD (50 ms), while contractile characteristics were more relevant for late RFD (≥100 ms). As peak RFD is mostly determined by MVF, it may not be more informative than MVF itself. Therefore, a time-locked analysis of RFD provides more insights into the neuromuscular characteristics of explosive contractions
Prevalence of ultrasound signs of Achilles tendinopathy in asymptomatic youth soccer players
No full text- …
