Carlos Gomes de Oliveira

Electromyographic Analysis of Three Different Types of Lat Pull-Down

Sperandei, S, Barros, MAP, Silveira-Júnior, PCS, and Oliveira, CG. Electromyographic analysis of three different types of lat pull-down. J Strength Cond Res 23(7): 2033-2038, 2009-The purpose of this work was to evaluate the activity of the primary motor muscles during the performance of 3 lat pull-down techniques through surface electromyography (EMG). Twenty-four trained adult men performed 5 repetitions of behind-the-neck (BNL), front-of-the-neck (FNL), and V-bar exercises at 80% of 1 repetition maximum. For each technique, the root mean square from the EMG signal was registered from the pectoralis major (PM), latissimus dorsi (LD), posterior deltoid (PD), and biceps brachii (BB) and further normalized in respect to that which presented the highest value of all the techniques. A series of two-way repeated measures analysis of variance was used to compare the results, with Tukey-Kramer as the post hoc test and α = 0.05. During the concentric phase, PM value showed the FNL to be significantly higher than V-bar/BNL and V-bar higher than BNL. During the eccentric phase, FNL/V-bar was higher than BNL. For LD, there was no difference between techniques. PD presented BNL higher than FNL/V-bar and FNL higher than V-bar in the concentric phase and BNL higher than V-bar in the eccentric phase. BB exhibited BNL higher than V-bar/FNL and V-bar higher than FNL in both concentric and eccentric phases. Considering the main objectives of lat pull-down, we concluded that FNL is the better choice, whereas BNL is not a good lat pull-down technique and should be avoided. V-bar could be used as an alternative.

Muscle fatigue and metabolic responses following three different antagonist pre-load resistance exercises

PURPOSE Preload of antagonist muscles can be achieved by reciprocal actions (RAs) or by opposing muscle actions. However, evidence concerning neuromuscular and fatigue responses are scarce. OBJECTIVE To compare the effects of different knee flexor (KF) preload methods on knee extension (KE) vastus medialis muscle fatigue, based on EMG-spectral index (FI), load range (LR), total work (TW), blood lactate (LAC) and biceps femoris co-activation (BFc) during resistance exercise. METHODS Twenty-four healthy men (23.5±3.6yrs) performed three antagonist pre-load isokinetic exercises (4 sets, 10 repetitions, 60°s(-1), 1min rest between sets): RA (KF contraction immediately followed by KE); Superset (SS; one KF set immediately followed by one KE set); Multiple Set (MS; four KF sets followed by four KE sets). RESULTS Total work was significantly greater in RA. There was no significant decrease in LR between sets in RA. The BFc did not differ between protocols (p=0.063). However, RA presented greater biceps femoriscoactivation. The FI was greater during SS compared to RA and MS (p<0.05). The SS had greater LAC when compared to MS and RA (p=0.005 and p=0.007, respectively). CONCLUSION It is suggested that the RA protocol is more neuromuscular and metabolic efficient during the performance of knee extension resistance exercise.

Influência da distância intereletrodos e da cadência de movimento no domínio da frequência do sinal de EMG de superfície

Surface electromyography (SEMG), despite being widely used in biomechanical investigations, still presents massive questioning about the influence of the distance of the inter-electrodes (DIE) in the signal morphology, especially in isotonic contractions. Thus, much of the research developed is still limited to the laboratory, where it is possible to establish better control over the recording and analysis protocols, which is not commonly observed in the clinical-sportive practice. Therefore, the aim of this study was to examine the effects of two electrodes placement protocols and the performance of isotonic contractions in the SEMG sign frequency domain. Fifteen right-handed male subjects (aged 22.8 ± 3.5 years) performed dynamic contractions of the right brachial biceps with load estimated in 20% of the maximum voluntary contraction in three different cadences (30, 45 and 60 bpm). The SEMG signals were registered by two channels with DIEs of 4.2 and 13 cm, respectively. The SEMG signals assessment was based on the median frequency of the potential spectrum of the signal, calculated via fast Fourier transform. DIE and cadence were defined as factors (two-way ANOVA; α = 0.05). No statistical differences or any interaction between both factors were observed in the three cadences (P> 0.05). Regardless of the distance used between electrodes, an investigation in the SEMG signal frequency domain in dynamic tasks should be avoided, even from reduced DIEs, as suggested in the literature, since variations in the torque and muscular length may disrupt the signal and hence its interpretation.

Reprodutibilidade no teste de uma repetição máxima no exercício de puxada pela frente para homens

OBJECTIVE: To verify the test-retest 1RM reproducibility in the lat pulldown exercise. METHODS: Twenty-six healthy and physically actives men (25 ± 3 years, 76.8 ± 9.86 kg, 177 ± 5.3 cm, 12.5 ± 4.25 % body fat) signed an informed consent before participate in this study. The data was collected in two visits, 48-72 hours apart. During the first visit, anthropometric data was measured and progressive 1RM test was performed. For each attempt progressive loads of 5 kg were added until the fail, when the load was reduced in 3 kg and a last attempt was performed. A five-minute rest was allowed before each attempt. During the second visit, the 1RM test was repeated following the same protocol. The Maximum loads of each day were compared by paired t-test to systematic error and limits of agreement technique to random error was employed. RESULTS: The mean error found was 2.9 ± 2.48 kg, being significantly different between days (p<0.00001). The error 95% limit of agreement was between -1.9 and 7.8 kg. CONCLUSION: This study showed a tendency to an increase in the second-day load, which when planning and analyzing strength training studies using 1RM test.

Effects of peak torque angle on the bilateral deficit of knee extensors and flexors at two velocities of contraction

PurposeTo examine effects of the peak torque angle (PTA) on the bilateral deficit (BD) index at two low velocities of contraction.MethodsTwenty young men performed right and left knee concentric extension–flexion (1 set, 5 repetitions) unilaterally and bilaterally in an isokinetic dynamometer at 30°/s and 60°/s. The peak torque (PT) from right, left and bilateral tests and their respective PTA were registered. Two BD indexes were determined as the bilateral PT divided by the summation of right and left PT (BDI1) and by the summation of left and right torque values found at the bilateral PTA (BDI2). Additionally, the mean of the absolute differences (MAD) between bilateral and unilateral PTAs was calculated as the mean of the modulus of the difference between bilateral minus right and bilateral minus left values divided.ResultsThe knee extensors showed difference between bilateral and unilateral PTA (p < 0.01) and effect of velocity on bilateral PTA (p < 0.05). MAD was not influenced by the direction of movement (p = 0.673), whereas on knee flexors it depended on velocity (p = 0.01). Knee extensors and flexors presented higher BDI1 than BDI2 at both velocities (p < 0.001). The difference between BDI1 and BDI2 was strongly correlated with MAD (p < 0.01).ConclusionThe BD is generally attributed to neural mechanisms, whereas the BD index was influenced by the PTA. Hence, it is suggested that the angle–torque relationship plays a role on the BD reported because it may enhance the BD index.

Variation in isometric force after active shortening and lengthening and their mechanisms: a review

Introduction The isometric force history dependence of skeletal muscle has been studied along the last one hundred years. Several theories have been formulated to explain and establish the causes of the phenomenon, but not successfully, as they have not been fully accepted and demonstrated, and much controversy on such a subject still remains. Objective To present a systematic literature review on the dynamics of the mechanisms of force depression and force enhancement after active shortening and lengthening, respectively, identifying the key variables involved in the phenomenon, and to date to present the main theories and hypothesis developed trying to explaining it. Method The procedure of literature searching complied the major databases, including articles either, those which directly investigated the phenomena of force depression and force enhancement or those which presented possible causes and mechanisms associated with their respective events, from the earliest studies published until the year of 2010. Results 97 references were found according to the criteria used. Conclusion Based on this review, it is suggested that the theory of stress inhibition of actin-myosin cross-bridges is that better explain the phenomenon of force depression. Whereas regarding the force enhancement phenomenon, one theory have been well accepted, the increased number of actin-myosin cross-bridges in strong binding state influenced by the recruitment of passive elastic components, which hole is attributed to the titin filament.