SEX AND STANDARD LEVELS DIFFERENCES IN ANTHROPOMETRIC AND PHYSICAL FITNESS CHARACTERISTICS IN YOUTH HANDBALL PLAYERS

This study analyzed the relationships between throwing velocity and anthropometric and fitness parameters at different ages in young female and male handball players. A total of 159 players participated: female under-16 (FU16, n=44), under-14 (FU14, n=21); male under-16 (MU16, n=54), under-14 (MU14, n=40). The follow measurements were completed: height, arm-span and body mass, total finger-span, hand-length, maximal isometric hand-grip force, handball throwing velocity, 20-m sprints, countermovement jump and change of direction. The MU16 group showed significantly (P&lt;0.05) greater values for anthropometric characteristics than FU16 and MU14. No significant differences were observed between FU14 and MU14 for any of the anthropometric variables analyzed, or between the two female groups (FU16 vs. FU14). MU16 showed significantly (P&lt;0.05) greater performance in all parameters analyzed than FU16 and MU14. No significant differences were observed between FU14 vs. MU14 or between FU16 vs. FU14. Throwing performance correlated (P&lt;0.05) with almost all anthropometric and fitness parameters evaluated within each group. Male handball players showed greater anthropometric and fitness characteristics in the U16 compared to the U14, whereas no substantial differences were observed in female handball players from U14 to U16. Handball throwing velocity is associated with body and hand dimensions and other physical performance parameters. &nbsp;</p

La velocidad de ejecución como factor determinante de las adaptaciones producidas por el entrenamiento de fuerza

Programa de Doctorado en Actividad Física, Rendimiento Deportivo y SaludThis thesis encompassed three consecutive studies that built upon each other's findings and were aimed at investigating the role played by movement velocity as a critical variable determining the adaptations to resistance training (RT). In the first study, we analyzed the effect of performing load displacement at the maximum intended velocity compared to 50% of that velocity to the same relative loads and the same number of sets and repetitions per set during RT. In addition, in the second study, we analyzed the acute and short-term response of different level of effort during the set, which induce different velocity losses. Finally, in the third study, we compared the effects of two RT programs that only differed in the magnitude of repetition velocity loss allowed in each set (20% vs. 40%) on structural and functional adaptations. Neuromuscular system adapts specifically to the stimulus to which it is subjected, resulting in increases in muscle strength (Coffey & Hawley, 2007). These stimuli are determined by a number of variables such as volume, intensity, exercise type and order, rest duration (Spiering et al., 2008), and movement velocity (Gonzalez-Badillo & Sanchez-Medina, 2010). It has been considered that movement velocity, dependent both the loading as the magnitude of effort employed to move that load, is a relevant variable especially when the goal is to improve athletics and physical performance (Crewther, Cronin, & Keogh, 2005). Several studies have compared the effects of high-velocity training respect to low-velocity training with the same load (Fielding et al., 2002; Ingebrigtsen, Holtermann, & Roeleveld, 2009; Jones, Hunter, Fleisig, Escamilla, & Lemak, 1999; Keeler, Finkelstein, Miller, & Fernhall, 2001; Kim, Dear, Ferguson, Seo, & Bemben, 2011; Morrissey, Harman, Frykman, & Han, 1998; Munn, Herbert, Hancock, & Gandevia, 2005; Pereira & Gomes, 2002; Westcott et al., 2001; Young & Bilby, 1993), but there are few works that have equaled volume and intensity in different training groups (Fielding, et al., 2002; Ingebrigtsen, et al., 2009; Jones, et al., 1999; Morrissey, et al., 1998; Munn, et al., 2005; Pereira & Gomes, 2002; Young & Bilby, 1993). Likewise, few studies have compared the effects of performing each repetition at maximal or submaximal velocity (Fielding, et al., 2002; Ingebrigtsen, et al., 2009; Jones, et al., 1999; Young & Bilby, 1993). Furthermore, in these works performed efforts next or to muscular failure, so that differences in the movement velocity in the last repetitions were reduced and tended to disappear (Jones, et al., 1999), because, regardless of the subject¿s will, velocity always ends up being equivalent to that achieved in the 1RM of this exercise (Sanchez-Medina & Gonzalez-Badillo, 2011). Despite the relevance that seems to have the movement velocity on adaptations produced in skeletal muscle in response to strength training, we have not found any work that has analyzed the mechanical and metabolic response to short and medium term caused by the application of stimuli equivalent in all variables (load, reps, sets and recovery time) except in lifting velocity. In addition none of the studies reviewed that used execution velocity as independent variable to observe the effects of this variable on physical performance has measured directly the execution velocity for all repetitions in the training protocol. Therefore, the effect of performing load displacement at the maximum intended velocity compared to 50% of that velocity to the same relative loads and the same number of sets and repetitions per set was investigated in Study I of the present Thesis. Some researchers have compared the effect of failure vs. non-failure training approaches on muscle strength gains (Drinkwater et al., 2005; Folland, Irish, Roberts, Tarr, & Jones, 2002; Izquierdo, Ibanez et al., 2006; Willardson, Emmett, Oliver, & Bressel, 2008). However, little is known about the time of course of recovery following RT protocols leading or not leading to failure (i.e. inability to complete a repetition in a full range of motion, because of fatigue). RT to failure induces a decrease in intramuscular adenosine triphosphate (ATP) and phosphocreatine (PCr) concentrations (Gorostiaga et al., 2012), as well as increases in blood ammonia that could indicate an accelerated purine nucleotide degradation (Gorostiaga, et al., 2012; Sanchez-Medina & Gonzalez-Badillo, 2011), suggesting that the recovery course is increased as the repetition number approaches failure. In addition, it is known that the recovery rate differs between different body systems (Hakkinen & Pakarinen, 1993; Schumann et al., 2013). The endocrine system and the autonomic nervous system both play an important role for physical performance, as wells as for recovery and adaptation (Halson & Jeukendrup, 2004). A more detailed knowledge of the time needed to achieve full recovery in the neuromuscular, neuroendocrine and autonomic cardiovascular systems for the most widely used RT intensities leading to failure or not to failure will enable strength and conditioning coaches as well as sport scientists to establish training designs that ensure optimal adaptation effects. Traditionally, it has been hypothesized that training to failure elicits higher levels of fatigue, which might result in greater hypertrophic adaptations due to greater activation of motor units and secretion of growth-promoting hormones (Willardson, et al., 2008). However, to our best knowledge, only a single previous study has examined the effect of RT leading to failure or not on muscle hypertrophy (Sampson & Groeller, 2015). These authors observed similar changes in muscle hypertrophy between groups, concluding that repetition failure is not critical to elicit significant structural changes in human skeletal muscle at least in previously untrained individuals (Sampson & Groeller, 2015). It is suggested that acute hormonal elevations increase the likelihood of interaction with receptors (Crewther, Keogh, Cronin, & Cook, 2006), which is likely to have relevance for tissue growth and remodeling (Kraemer & Ratamess, 2005). The greater mechanical and metabolic stress induced when RT is performed to failure (Sanchez-Medina & Gonzalez-Badillo, 2011) might evoke elevated secretion of growth-promoting hormones (testosterone, growth hormone (GH), and insulin-like growth factor (IGF-1)), and catabolic hormones (cortisol). However, few data exist on the hormonal response to different repetition schemes leading to muscular failure versus not leading to contraction failure. This knowledge along with the assessment of selected indicators of muscle damage (CK) might explain the different magnitudes of hypertrophic adaptation observed in response to different RT schedules.A perspective approach to the analysis of physiological control system reactions to physical activity is the assessment of heart rate variability (HRV). Given the heart rate dynamics also exhibit complex fluctuations acutely following a stressor stimulus, application of nonlinear dynamic analysis parameters can provide additional information about systems involved in the control of cardiovascular function, which are undetectable by conventional linear HRV analysis (Kuusela, Jartti, Tahvanainen, & Kaila, 2002). Hear rate complexity (HRC) can be measured quantitatively by assessment of the uncertainty of patterns reoccurring within a time event series (Kuusela, et al., 2002). HRC has been proposed as an indicator of integrated cardiac regulation; the higher the complexity of the system the greater its functionality (Costa, Ghiran, Peng, Nicholson-Weller, & Goldberger, 2008). Likewise, there is a growing body of literature showing an acute depression in HRV (Iglesias-Soler et al., 2014; Kingsley & Figueroa, 2014; Kingsley, McMillan, & Figueroa, 2010; Lima et al., 2011) and HRC following RT (Iglesias-Soler, et al., 2014; Kingsley & Figueroa, 2014). It might be speculated that reducing the number of repetitions in the set against the same load might reduce loss of mechanical performance and attenuate the reduction in HRV and HRC. However, the effect of RT leading to failure or not on HRV and HRC has not previously been addressed in detail. When performing resistance exercise, and assuming every repetition is performed with maximal voluntary effort, the instantaneous force, velocity, and power production inevitably declines as fatigue increases (Izquierdo, Gonzalez-Badillo et al., 2006; Sanchez-Medina & Gonzalez-Badillo, 2011). Reaching a certain level of muscular fatigue during the exercise generally is considered a prerequisite for achieving long-term muscular adaptations. However, there is a lack of knowledge about whether less or more fatigue is optimal for these adaptations to take place. The complexity of fatigue assessment often results in the application of models that are dissociated from the fatigue experienced during the task (Cairns, Knicker, Thompson, & Sjogaard, 2005). The appearance of new technologies (linear position transducers, rotary encoders, accelerometers, etc.), which provide feedback in real time on repetition velocity, force and power provides the chance of using new training approaches in which movement velocity can be used to monitor training intensity (Gonzalez-Badillo & Sanchez-Medina, 2010) and to also quantify the magnitude of performance impairment experienced during the RT (Sanchez-Medina & Gonzalez-Badillo, 2011). It has been shown that the measurement of repetition velocity is a practical and non-invasive way to reasonably estimate the magnitude of acute metabolic stress (blood lactate and ammonia) and acute mechanical fatigue induced by RT (Sanchez-Medina & Gonzalez-Badillo, 2011). Additionally, since adaptations to RT are mediated by the interaction between mechanical, hormonal, and metabolic stimuli (Spiering, et al., 2008), it seems highly relevant to analyze the relationship between the velocity loss during successive RT sets and the behavior of the different systems responsible of ensuring skeletal muscle homeostasis, for supporting the validity of using the velocity loss to objectively quantify the degree of acute neuromuscular fatigue during RT. Therefore, the mechanical, hormonal and HRV responses to different loading schemes leading to muscle failure versus non-failure and the potential relationships between the mechanical, biochemical and cardiovascular autonomic responses elicited by resistance exercise performed to failure vs. non-failure were analyzed in Study II of this Thesis. Although some studies (Ahtiainen, Pakarinen, Kraemer, & Hakkinen, 2003; Drinkwater, et al., 2005; Rooney, Herbert, & Balnave, 1994) suggest that performing repetitions to failure may be necessary to maximize muscle mass and strength, others seem to indicate that similar, if not greater, strength gains and improvements in athletic performance can be obtained without reaching muscle failure (Folland, et al., 2002; Izquierdo-Gabarren et al., 2010; Izquierdo, Ibanez, et al., 2006). It has been hypothesized that RT eliciting high levels of fatigue, as it occurs in typical body-building routines, may induce greater strength adaptations due to an enhanced activation of motor units and secretion of growth-promoting hormones (Schoenfeld, 2010; Schott, McCully, & Rutherford, 1995). However, definitive evidence is lacking and the controversial results found in the literature clearly emphasize the need to conduct further research on this topic. Experiments with isolated human muscle fibers (Mogensen, Bagger, Pedersen, Fernstrom, & Sahlin, 2006), as well as in vivo human studies (Aagaard & Andersen, 1998; Sanchis-Moysi et al., 2010) have shown that a high proportion of type II muscle fibers or myosin heavy chain (MHC) II isoforms is associated with high levels of force production during fast muscle contractions. Interestingly, most studies have shown that the percentage of type IIX fibers is reduced following a RT program based on repetitions to failure (J. L. Andersen & Aagaard, 2000; L. L. Andersen et al., 2005; Campos et al., 2002; Staron et al., 1991). Nevertheless, a study by Harridge et al. (1998) showed that maximal isometric strength (voluntary and electrically evoked) can be significantly increased without a reduction in the MHC-IIX fiber pool following a 6-wk training program based on 4 sessions per wk of high-intensity, low-duration, cycling exercise (three 3 s sprints with 30 s recoveries), aimed to avoid a decline in performance during the training session. During RT muscle fatigue increases with the accumulation of repetitions, and if the exercise is not stopped, task failure eventually occurs. However, prior to task failure, other signs of muscle fatigue are detectable, such as reduced maximal force application, slower shortening velocity and decreased power output (Allen, Lannergren, & Westerblad, 1995; Gorostiaga, et al., 2012; Sanchez-Medina & Gonzalez-Badillo, 2011). The complexity of fatigue assessment has led to the utilization of procedures that lack specificity. It has been shown that neuromuscular fatigue induced by RT protocols can be monitored by assessing the repetition velocity loss within a set (Sanchez-Medina & Gonzalez-Badillo, 2011). A novel, velocity-based approach to RT has been proposed in which, rather than prescribing a fixed number of repetitions to perform with a given load, training is configured using two variables: 1) first repetition¿s mean velocity, which is intrinsically related to relative loading magnitude (Gonzalez-Badillo & Sanchez-Medina, 2010); and 2) the velocity loss to be allowed, expressed as a percent loss in mean velocity from the fastest (usually first) repetition of each exercise set (Sanchez-Medina & Gonzalez-Badillo, 2011). Thus, when the prescribed percent velocity loss limit is exceeded, the set is terminated. The effects of two RT programs that only differed in the magnitude of repetition velocity loss allowed in each set (20% vs. 40%) on structural and functional adaptations were investigated in Study III of this Thesis.STUDY I Purpose: The aim of this study was to compare the effect of performing each repetition at maximum voluntary velocity or 50% of that velocity on strength gains in squat (SQ) and bench press (BP), vertical jump (CMJ) and acceleration performance. Methods: Twenty-one subjects were randomly assigned to one of two groups: maximum voluntary velocity (V100, n = 10) or 50% of maximum velocity (V50, n = 11). Ten of them undertook 6 sessions at V100 vs. V50 in SQ-exercise. Blood lactate, ammonia and uric acid concentrations, velocity against the 1 m¿s-1 load (V1-load), and CMJ height pre-post exercise were recorded. Subjects trained during 6 wk for a total of 18 sessions following a periodized resistance training program using BP and SQ exercises. The two groups trained at the same relative intensity and volume but differed in the velocity reached in each repetition (V100 vs. V50). Results: For BP, both groups improved strength performance from pre- to post-training, but V100 resulted in significantly greater gains than V50 in all variables analyzed: one-repetition maximum (1RM) strength (18.2 vs. 9.7%), velocity developed against all (20.8 vs. 10.0%), light (11.5 vs. 4.5%) and heavy (36.2 vs. 17.3%) loads common to pre- and post-tests. For SQ, both groups attained significantly (P < 0.001 - 0.05) higher 1RM (18.6 vs. 10.3%), velocity developed against all (15.9 vs. 7.5%), light (11.2 vs. 5.0%) and heavy (18.9 vs. 12.7%) loads common to pre- and post-tests, in V100 vs. V50 compared with pre-training. Furthermore, V100 improved the performance in CMJ height and acceleration capacity (P < 0.01). However, V50 only showed increased in CMJ (P < 0.05). Moreover, V100 had significantly higher gains (P < 0.01) than V50 for CMJ. V1-load was not significant in any of effort performed. CMJ height loss, blood lactate and ammonia tended to be higher for V100 compared to V50. However blood uric acid levels remained unaltered in both protocols. Conclusions: Movement velocity can be considered a fundamental component of RT intensity since, for a given %1RM, the velocity at which loads are lifted largely determines the resulting training effect. Strength gains and performance improvements can be maximised when repetitions are performed at maximal intended velocity. STUDY II Purpose: to analyze the time course of recovery following ten resistance exercise protocols (REP) differing in the number of repetitions (R) performed in each set with respect to the maximum predicted number (P). Methods: Nine males performed 10 REP [R(P): 6(12),12(12),5(10),10(10),4(8),8(8), 3(6),6(6),2(4), and 4(4)]. Three sets with 5 min inter-set rests were performed in each REP in the BP and SQ exercises. Mechanical muscle function (CMJ; velocity against the 1 m¿s-1 load, V1-load), biochemical plasma profile (testosterone, cortisol, GH, prolactin, IGF-1, CK), and HRV/HRC were assessed at several time-points from 24 h pre- to 48 h post-exercise. Results: REPs to failure, especially those in which the number of repetitions performed was high [12(12), 10(10), 8(8) and 6(6)] resulted in larger reductions in repetition velocity, velocity against V1-load and jump height, remaining reduced up to 48 h post-exercise. Along with these changes greater increments were observed in plasma cortisol, GH, prolactin and CK concentrations. REPs to failure also showed greater reductions in HRV and HRC during exercise and post-exercise. Furthermore, relationships were observed (r = 0.67 - 0.95, P < 0.05) between the repetition velocity and hormonal/cardiovascular responses. Conclusion: REPs to failure resulted in greater fatigue accumulation and an attenuated rate of recovery, accompanied by greater hormonal, muscle damage and HRV/HRC responses, respectively, especially when the maximal number of repetitions was high. The strong associations observed between repetition velocity loss versus hormonal responses and HRV/HRC responses support the validity of using velocity loss to objectively quantify fatigue accumulation during resistance training. STUDY III Purpose: To compare the effects of two RT programs only differing in the level of effort achieved in each set, objectively quantified by repetition velocity loss allowed in each set (20% (VL20) vs. 40% (VL40)) on structural and functional neuromuscular adaptations. Methods: Twenty-two young males were randomly assigned to a VL20 (n=12) or VL40 (n=10) training group. Subjects followed an 8-wk velocity-based RT program using the full squat exercise with execution velocity recorded in all repetitions. Quadriceps muscle volume (magnetic resonance imaging), vastus lateralis fiber-type distribution and cross-sectional areas (CSA), 1RM strength, full load-velocity SQ profile, CMJ height, and 20 m sprint time were determined pre- and post-training. Results: Both groups increased mean fiber CSA (9.8 vs. 11.0%) and whole quadriceps muscle volume (4.6 vs. 7.7%) for VL20 vs. VL40 respectively. VL20 resulted in moderate hypertrophic adaptations but greater improvement in CMJ (9.5 vs. 3.5%, P < 0.05) and squat performance (1RM strength and velocity developed against all loads, from light to heavy) in SQ exercise, despite 58% lower repetitions than VL40. VL40 training resulted in higher muscle hypertrophy and IIX to IIA fiber-type shift in muscle phenotype, whereas the IIX muscle fibers were preserved in VL20. Conclusion: A higher loss of repetition velocity during training (VL40) seems suitable to maximize the hypertrophic response, but tends to induce a fast-to-slow shift in muscle phenotype. Despite moderate hypertrophic adaptations, VL20 training resulted in superior gains in 1RM squat strength, velocity developed against any given load (from light to heavy), and vertical jump performance.Universidad Pablo de Olavide. Departamento de Deporte e Informátic

Determinant factors of pull up performance in trainedathletes

Aim: to investigate the relationship among pull up and lat pull exercises and differentanthropometric dimensions in trained athletes. Methods: twenty-five males were evaluated for maximum number of pull ups, one-repetitionmaximum lat pull (1RM Lat Pull), lat pull repetitions at 80% 1RM (Lat Pull at 80% 1RM), latpull repetitions at a load equivalent to body mass (Lat Pull at BM-load), and differentanthropometric variables. Furthermore, the subjects were divided in higher (HPG, n = 12) andlower pull up performance (LPG, n = 13) to compare the differences in the variables analyzedbetween both levels. Results: pull ups were significantly correlated with Lat Pull at BM-load (r = .62, P < .01) butneither with 1RM Lat Pull (r = .09) nor with Lat Pull at 80% 1RM (r = -.15). Pull ups showed asignificant (P < .05) negative relationship with body mass (BM, r = -.55), lean body mass(LBM, r = -.51), and fat mass (FM, r = -.52), while BM and LBM were significantly correlatedwith 1RM Lat Pull (r = .55, P < .05). HPG showed significantly (P < .05) lower BM (0/3/97%),FM (1/3/97%) and LBM (1/4/95%) than LPG. Furthermore, HPG attained significantly (P < .05– .001) greater performance in Lat Pull at BM-load (100/0/0%) and 1RM Lat Pull•BM-1(96/3/2%) than LPG. Conclusion: these findings suggest that pull up and lat pull exercises have common elements.Moreover, the anthropometric dimensions seem to influence differently on both exercises,depending on the strength indicator evaluated

Performance and reference data in the jump squat at different relative loads in elite sprinters, rugby players, and soccer players

The aims of this study were to compare the outcomes and provide reference data for a set of barbell mechanical parameters collected via a linear velocity transducer in 126 male sprinters (n = 62), rugby players (n = 32), and soccer players (n = 32). Bar-velocity, bar-force, and bar-power outputs were assessed in the jump-squat exercise with jump-squat height determined from bar-peak velocity. The test started at a load of 40% of the athletes\u27 body mass (BM), and a load of 10% of BM was gradually added until a clear decrement in the bar power was observed. Comparisons of bar variables among the three sports were performed using a one-way analysis of variance. Relative measures of bar velocity, force, and power, and jump-squat height were significantly higher in sprinters than in rugby (difference ranging between 5 and 35%) and soccer (difference ranging between 5 and 60%) players across all loads (40-110% of BM). Rugby players exhibited higher absolute bar-power (mean difference = 22%) and bar-force (mean difference = 16%) values than soccer players, but these differences no longer existed when the data were adjusted for BM (mean difference = 2.5%). Sprinters optimized their bar-power production at significantly greater relative loads (%BM) than rugby (mean difference = 22%) and soccer players (mean difference = 25%); nonetheless, all groups generated their maximum bar-power outputs at similar bar velocities. For the first time, we provided reference values for the jump-squat exercise for three different bar-velocity measures (i.e., mean, mean propulsive, and peak velocity) for sprinters, rugby players, and soccer players, over a wide range of relative loads. Practitioners can use these reference values to monitor their athletes and compare them with top-level sprinters and team-sport players

Are cluster sets an effective method to induce muscular hypertrophy in response to resistance training?

[EN] There are a plethora of studies that have analyzed the effects of different resistance training methods on muscle hypertrophy. Recent studies have pointed out some potential advantage of training using cluster sets (CS) compared with traditional sets. It is still unclear whether CS are an effective method. The objective of this review was to investigate and discuss the current knowledge about the effect of CS on muscle hypertrophy. Four studies investigating the effect of CS on muscle hypertrophy were found. These studies demonstrated that CS induced similar or lower muscle hypertrophy than traditional sets. Thus, CS may lead to muscle hypertrophy, but did not provide a superior stimulus when compared to traditional sets of equated load.[PT] Um conjunto de estudos que tem analisado o efeito de diferentes métodos de treinamento resistido na hipertrofia muscular. Estudos têm pontuado várias potenciais vantagens do treinamento usando séries em conglomerados (SC) quando comparado com séries tradicionais. Ainda não está claro se as SC é um método efetivo. O objetivo desta revisão foi investigar e discutir o conhecimento recente sobre o efeito das SC na hipertrofia muscular. Quatro estudos investigando o efeito das SC na hipertrofia muscular foram encontrados. Esses estudos demonstraram que as SC induziram similar ou menor hipertrofia muscular do que séries tradicionais. Portanto, as SC podem induzir hipertrofia, porém não fornecem um estímulo superior quando comparado às séries tradicionais com carga equiparada

Load that maximizes power output in countermovement jump

Introduction: One of the main problems faced by strength and conditioning coaches is the issue of how to objectively quantify and monitor the actual training load undertaken by athletes in order to maximize performance. It is well known that performance of explosive sports activities is largely determined by mechanical power. Objective: This study analysed the height at which maximal power output is generated and the corresponding load with which is achieved in a group of male-trained track and field athletes in the test of countermovement jump (CMJ) with extra loads (CMJEL). Methods: Fifty national level male athletes in sprinting and jumping performed a CMJ test with increasing loads up to a height of 16 cm. The relative load that maximized the mechanical power output (Pmax) was determined using a force platform and lineal encoder synchronization and estimating the power by peak power, average power and flight time in CMJ. Results: The load at which the power output no longer existed was at a height of 19.9 ± 2.35, referring to a 99.1 ± 1% of the maximum power output. The load that maximizes power output in all cases has been the load with which an athlete jump a height of approximately 20 cm. Conclusion: These results highlight the importance of considering the height achieved in CMJ with extra load instead of power because maximum power is always attained with the same height. We advise for the preferential use of the height achieved in CMJEL test, since it seems to be a valid indicative of an individual's actual neuromuscular potential providing a valid information for coaches and trainers when assessing the performance status of our athletes and to quantify and monitor training loads, measuring only the height of the jump in the exercise of CMJEL.Actividad Física y Deport

Mechanomyographic measures of muscle contractile properties are influenced by electrode size and stimulation pulse duration

The aim was to determine the effects of changing pulse duration and electrode size on muscle contractile properties. Thirty-six healthy young male participated in the study (age 24.8 ± 5.8 years; height 178.2 ± 0.6 cm; body mass 71.8 ± 7.3 kg; self-reported weekly moderate intensity activity 3.5 ± 1.2 h·week−1). Tensiomyography was used to assess rectus femoris (RF) and vastus medialis (VM) muscles neuromuscular properties of the dominant leg according to the electrode size (3.2–5 cm) and the stimulus length (0.2, 0.5, and 1 ms). Maximal radial displacement (Dm); Contraction time (Tc); Delay time (Td); Sustained time (Ts) and Half relaxation time (Tr) were measured. Relative and absolute reliability was quantified. To analyze the effects of the electrode and the stimulus length, a repeated-measures analysis of variance was used. Dm and Tc parameters showed for both muscles an excellent relative (0.95–0.99) and absolute reliability (1.6–4.2%). However, Ts and Tr showed low values of absolute reliability (4.4–40.9%). The duration of the stimulus length applied to the RF and VM and electrode size significantly influences muscle’s contractile properties (p < 0.05; η2p = 0.09–0.60). The Dm increases substantially as the duration of the stimulus increases and with the use of the larger electrode in both muscles. However, Tc and Td are less affected by both conditions and not entirely clear. Practically, our study suggests that a stimulus pulse duration of 1 ms together with a 5 × 5 cm electrode is necessary to reach a reliable and reproducible assessment of both RF and VM muscles contractile properti

Mechanomyographic Measures of Muscle Contractile Properties are Infuenced by Electrode Size and Stimulation Pulse Duration

The aim was to determine the efects of changing pulse duration and electrode size on muscle contractile properties. Thirty-six healthy young male participated in the study (age 24.8±5.8 years; height 178.2±0.6cm; body mass 71.8±7.3kg; self-reported weekly moderate intensity activity 3.5±1.2h·week−1). Tensiomyography was used to assess rectus femoris (RF) and vastus medialis (VM) muscles neuromuscular properties of the dominant leg according to the electrode size (3.2–5cm) and the stimulus length (0.2, 0.5, and 1ms). Maximal radial displacement (Dm); Contraction time (Tc); Delay time (Td); Sustained time (Ts) and Half relaxation time (Tr) were measured. Relative and absolute reliability was quantifed. To analyze the efects of the electrode and the stimulus length, a repeated-measures analysis of variance was used. Dm and Tc parameters showed for both muscles an excellent relative (0.95–0.99) and absolute reliability (1.6–4.2%). However, Ts and Tr showed low values of absolute reliability (4.4–40.9%). The duration of the stimulus length applied to the RF and VM and electrode size signifcantly infuences muscle’s contractile properties (p<0.05; η2 p=0.09–0.60). The Dm increases substantially as the duration of the stimulus increases and with the use of the larger electrode in both muscles. However, Tc and Td are less afected by both conditions and not entirely clear. Practically, our study suggests that a stimulus pulse duration of 1ms together with a 5 × 5cm electrode is necessary to reach a reliable and reproducible assessment of both RF and VM muscles contractile properties.Ciencias de la Actividad Física y del Deport

Squat and countermovement jump performance across a range of loads: A comparison between Smith machine and free weight execution modes in elite sprinters

The aims of this study were to: 1) provide and compare the height achieved during Smith machine (SM) and free weight (FW) loaded jumps executed over a wide spectrum of loads (40–120 % of body mass [BM]); and 2) test the difference between loaded and unloaded squat jump (SJ) and countermovement jump (CMJ) attempts in ten highly trained male sprinters. On the first visit, athletes performed unloaded SJ and CMJ, loaded SJ with loads corresponding to 40, 60, 80, 100, and 120 % BM, and loaded CMJ at 100% BM using an Olympic barbell (FW). On the second visit, they performed loaded SJ and CMJ tests under the same loading conditions on the SM device and, subsequently, a half-squat one-repetition maximum (1RM) assessment. The relative strength (RS = 1RM/BM) of the athletes was 2.54 ± 0.15. Loaded SJ performance was similar between SM and FW, and across all loading conditions. Differences in favour of CMJ (higher jump heights compared with SJ) were superior in the unloaded condition but decreased progressively as a function of loading. In summary, sprinters achieved similar SJ heights across a comprehensive range of loads, regardless of the execution mode (FW or SM). The positive effect of the countermovement on jump performance is progressively reduced with increasing load

El sistema ferroviario argentino: análisis de los procesos de privatización y estatización

El presente trabajo pretende identificar las políticas de los gobiernos que gestaron períodos de estatización y privatización del sistema ferroviario argentino y analizar los resultados de las mismas en los servicios que establecieron para los usuarios de los trenes de pasajeros y en el transporte de carga. Considerando a la red ferroviaria un recurso estratégico para la logística y comercialización de los productos comerciales y una de las herramientas principales para el abaratamiento del traslado de mercaderías fundamentalmente por la vasta extensión de nuestro territorio y la interconexión de las zonas agroganaderas hacia los puertos. Por otro lado, el sistema ferroviario de pasajeros constituye uno de los medios de transporte de mayor demanda debido a la rapidez en recorrer distancias y un costo menor del pasaje, comparado con la oferta de otros medios de transportes como colectivos, autos y taxis. En esta investigación se abordará un tipo de investigación explicativa de los procesos de estatización y privatización y para ello se efectuará un barrido bibliográfico exhaustivo, donde se pueda analizar las políticas de gestión y económicas y el contexto coyuntural que le dio surgimiento a cada cambio de proceso de estatización y/o privatización para evidenciar sus resultados. En este período de avance del trabajo, se comenzó con el contexto se encontraba la Argentina y el mundo cuando el primer Ferrocarril del Oeste se creó. Se ha descripto los proceso de creación de las distintas vías férreas instaladas a fines del siglo XIX, la estatización en el gobierno de Perón, su la política y teorías económicas que justificaron este cambio, así como el Plan Larkin que llevó al racionamiento de los trenes en la década del 60, hasta llegar a las nuevas corrientes de ideas neoliberales y Planes internacionales que llevaron a las privatizaciones de la década de los 90.Fil: Silva, Raúl Alberto. Universidad Nacional de La Matanza; Argentina.Fil: Ibarra, José Ángel. Universidad Nacional de La Matanza; Argentina.Fil: Almaraz, Lorena Paola. Universidad Nacional de La Matanza; Argentina.Fil: González, Rosana Diana. Universidad Nacional de La Matanza; Argentina.Fil: Merino, Romina. Universidad Nacional de La Matanza; Argentina.Fil: Pace, María Evangelina. Universidad Nacional de La Matanza; Argentina.Fil: Panetta, Romina Noemí. Universidad Nacional de La Matanza; Argentina.Fil: Pareja, Daniel Fernando. Universidad Nacional de La Matanza; Argentina.Fil: Silva, María Gabriela. Universidad Nacional de La Matanza; Argentina.Fil: Blanco, Patricia. Universidad Nacional de La Matanza; Argentina.Fil: Costantini, Dario Fernando. Universidad Nacional de La Matanza; Argentina.Fil: Enriquez, Gisela Soledad. Universidad Nacional de La Matanza; Argentina