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

Resumen

SUMMARY This 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. 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