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INTRODUCTION: Effects on strength performance and muscle activation in the contralateral limb have been observed after training with the ipsilateral limb (IL). Cross fatigue effects in the contralateral limb (CL) can occur at intervals of up to 48 h after a training session performed with the ipsilateral limb. The objective of this study was to verify the effect of a training session in the ipsilateral limb, on the strength and activation of the muscles in the contralateral limb also submitted to the training protocol. METHODS: 10 untrained men (mean ± SD: age = 23.7 ± 4.9 years) performed unilateral knee extension with both limbs in equated protocols, in two conditions with different intervals between limbs - 20 min and 24 h. RESULTS: There were no differences in the comparison of the force produced between the pre x post interventions with the CL limb, as well as in the activation of the quadriceps during its performance. These results were similar for the two different intervals between the protocols. CONCLUSION: It was concluded that when the CL member performs the protocol after the IL, the responses in the CL depend mainly on the requirement imposed on the protocol performed by this member, without influence of the training protocol performed previously with the IL member.

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This study is aimed at evaluating the profile of inflammatory markers and components of redox regulation in untrained women after 10 weeks of resistance training using equalized protocols but different muscle action duration (MAD). Twenty-two women underwent progressive resistance training exercising the knee extensor muscles for 10 weeks-3x/week, with 3-5 sets of 6 repetitions at 50% of the 1 repetition maximum strength test (1RM), with a rest of 180 s between the series, following the training protocol (i) 5 s of concentric muscle action for 1 s of eccentric muscle action (5C-1E) and (ii) 1 s of concentric muscle action for 5 s of eccentric muscle action (1C-5E). Quadriceps muscle hypertrophy maximum strength (1RM) and redox regulation/muscle damage/inflammatory markers (CAT, SOD, TBARS, FRAP, CH, LDH, CXCL8, and CCL2) were evaluated. Plasma markers were evaluated before and 30 minutes after the first and last training sessions. A similar gain in hypertrophy and maximum strength was observed in both groups. However, in the 5C-1E, a significant major effect was observed for SOD (F 1.19 = 10.480, p = 0.004) and a significant major time effect, with a reduction in the last training session, was observed for CXCL8 (F 1.37 = 27.440, p < 0.001). In conclusion, similar protocols of resistance training, with different MAD, produced similar inflammatory and adaptive responses to strength training. As the training load is progressive, the maintenance of this inflammatory and redox regulation profile suggests an adaptive response to the proposed strength training.

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ABSTRACT: Diniz, RCR, Tourino, FD, Lacerda, LT, Martins-Costa, HC, Lanza, MB, Lima, FV, and Chagas, MH. Does the muscle action duration induce different regional muscle hypertrophy in matched resistance training protocols? J Strength Cond Res 36(9): 2371-2380, 2022-The manipulation of the muscle action duration (MAD) can influence the instantaneous torque along the range of motion, which can lead to adaptations of regional muscle hypertrophy. The aim of this study was to compare the effects of matched resistance training (RT) on the knee extension machine with different MAD in the cross-sectional area (CSA) responses within the quadriceps femoris (QF) and its muscles. Forty-four subjects were allocated into a control and 3 experimental groups. For a period of 10 weeks, subjects in the experimental groups performed the training protocols that were different only by the MAD: group 5c1e (5s concentric action [CON] and 1s eccentric action [ECC]; group 3c3e (3s CON and 3s ECC) and group 1c5e (1s CON and 5s ECC). Magnetic resonance imaging was performed (before and after the intervention) to determine the relative change (%) in CSA of the QF muscles along proximal (30%), middle (50%), and distal regions (70% distal of the femur). The change in CSA of the rectus femoris at the middle region are greater in 5c1e (6.8 ± 6.5%) and 1c5e (7.4 ± 6.0%) groups than 3c3e (3.4 ± 6.6%) and control groups (0.2 ± 1.8%). In addition, vastus lateralis at the distal region (5c1e = 15.9 ± 11.8%; 1c5e = 14.4 ± 10.0%) presenting greater increases in change of CSA than the others vastus only 5c1e (vastus lateralis [VI] = 5.0 ± 4.7%; vastus medialis [VM] = 4.2 ± 3.2%) and 1c5e groups (VI = 4.7 ± 3.6%; VM = 3.4 ± 3.1%). In conclusion, this study showed that matched RT protocols with different MAD resulted in different region-specific muscle hypertrophic across the individual muscles of QF.

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The present study investigated the effect of 10-week matched (range of motion, volume, intensity, rest, and repetition duration) training protocols with varying muscle action duration (MAD) on maximal voluntary isometric contraction (MVIC) test at eight different knee angles and one-repetition maximum (1RM) test after in seated knee extensor machine. Forty women were allocated into one control and three training groups with varying MAD: 5C1E (5s concentric action [CON] and 1s eccentric action [ECC]), 3C3E (3s CON and 3s ECC), and 1C5E (1s CON and 5s ECC). All training groups (5C1E, 3C3E, and 1C5E) showed a greater relative response in 1RM performance than the control group (0.1 ± 3.5%, p ≤ 0.05). The 1C5E group presented greater relative increases in the 1RM performance (22.1 ± 11.6%) compared to 5C1E (13.6 ± 9.2%; p ≤ 0.05) and 3C3E (14.1 ± 5.5%, p ≤ 0.05) groups. The training groups increased the MVIC performance more than the control group (p ≤ 0.05), although there were no significant differences between the training groups. This study demonstrated that isoinertial resistance training protocols with shorter CON MAD showed greater maximum dynamic strength performance response than matched training protocols with other MAD configurations. However, the configuration of MAD did not induce angle-specificity to increase the maximum isometric strength.

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BACKGROUND: This study investigated the effects of two 14-week resistance training protocols with different repetition duration (RD) performed to muscle failure (MF) on gains in strength and muscle hypertrophy as well as on normalized electromyographic (EMG) amplitude and force-angle relationships. METHODS: The left and right legs of ten untrained males were assigned to either one of the two protocols (2-s or 6-s RD) incorporating unilateral knee extension exercise. Both protocols were performed with 3-4 sets, 50-60% of the one-repetition maximum (1RM), and 3 min rest. Rectus femoris and vastus lateralis cross-sectional areas (CSA), maximal voluntary isometric contraction (MVIC) at 30o and 90o of knee flexion and 1RM performance were assessed before and after the training period. In addition, normalized EMG amplitude-angle and force-angle relationships were assessed in the 6th and 39th experimental sessions. RESULTS: The 6-s RD protocol induced larger gains in MVIC at 30o of knee angle measurement than the 2-s RD protocol. Increases in MVIC at 90o of knee angle, 1RM, rectus femoris and vastus lateralis CSA were not significant between the 2-s and 6-s RD protocols. Moreover, different normalized EMG amplitude-angle and force-angle values were detected between protocols over most of the angles analyzed. CONCLUSION: Performing longer RD could be a more appropriate strategy to provide greater gains in isometric maximal muscle strength at shortened knee positions. However, similar maximum dynamic strength and muscle hypertrophy gains would be provided by protocols with different RD.

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OBJECTIVES: Despite advancements in resistance training (RT) methods, the acute metabolic and neuromuscular responses to time under tension (TUT) and load remains poorly understood. The aim of the present study was to investigate how TUT or resistance load impact muscular activation and blood lactate during an RT session. DESIGN: A randomized cross-over design. METHODS: Participants performed a squat exercise in three different conditions: baseline protocol (BPRO; three sets of eight repetitions with four second repetitions at 60% of 1RM) long duration protocol (LDPRO: six second repetitions) and high load protocol (HLPRO: 70% 1RM). RESULTS: Muscular activation of the vastus lateralis and biceps femoris, and blood lactate were assessed. Blood lactate was ∼19% and ∼26% higher after set one and three in LDPRO compared to BPRO (P≤0.011) and ∼17% higher for LDPRO compared to HLPRO (P=0.002). Additionally, blood lactate was ∼17% higher for HLPRO compared to BPRO after the third set of exercise (P=0.003). Vastus lateralis activation was ∼10% higher for HLPRO compared to BPRO and LDPRO for sets one and two. Biceps femoris activation was ∼17% higher for HLPRO compared to BPRO for set one (P= 0.023) while for set two HLPRO was greater than BPRO and LDPRO (∼19% and ∼14%, respectively; P≤0.007). CONCLUSIONS: Squatting with higher TUT caused a greater impact on the metabolic responses than lower TUT or higher loads, whereas an increase in training load resulted in greater muscle activation than higher TUT or lower training load.

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This study determined the time-course of recovery after resistance training (RT) sessions and the association between changes in performance with changes in biomechanical, physiological and perceptual parameters. After a 4-week familiarization period, 14 resistance-trained males performed 3 experimental conditions, each one including 2 sessions with a recovery interval of 24, 48 h or 72 h, in a randomized order. RT sessions consisted of 5 sets of 8-10RM on squat and leg press exercises. The resistance was equal for the 2 sessions of each condition and repetitions were performed until concentric failure. Volume load (VL) and first set volume load (FSVL) were compared between sessions. Tests before each session included countermovement jump (CMJ), maximal voluntary isometric contraction (MVIC), creatine kinase (CK) and delayed onset muscle soreness (DOMS). (2 × 3) ANOVA with effect sizes (ES) assessed the time-course of recovery and Kendall test the correlation between variables (α = 0.05). Significant interaction was observed for all variables, except for CK, where a condition main effect occurred. Comparisons between post and pre-intervals showed VL (p = 0.011;ES = -0.90) decreased for 24 h condition, while FSVL remained decreased for 48 h (p = 0.031;ES = -0.63) and DOMS increased (p = 0.001;ES = 3.52). CMJ (p = 0.025;ES = 0.25) and MVIC (p = 0.031;ES = 0.14) performance increased at 72 h. FSVL (r = 0.424), CMJ (r = 0.439), MVIC (r = 0.389) and DOMS (r = -0.327) were significantly correlated with VL (p < 0.05). Time-course of VL showed the necessity of at least 48 h for the reestablishment of performance, though better perceptual responses were evident at 72h. Thus, both recovery intervals may be beneficial after lower-limbs RT until concentric failure, though chronic effects still need to be investigated.

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ABSTRACT Resistance training protocols performed to muscle failure (MF) have been employed in an attempt to maximize activation and neuromuscular fatigue. Therefore, the aim of this study was to compare the surface electromyography amplitude (EMGRMS) and frequency (EMGFREQ) of the pectoralis major between protocols performed to MF and non muscle failure (NMF). Seven trained men performed three sets at 60% of a repetition maximum, with a 3 min rest period and a 6s repetition duration. MF protocol was performing with maximum number of repetitions in all sets, while in NMF protocol subjects performed 6 repetitions in 3 sets. For data analysis two two-way repeated measures ANOVAs (Protocol x Repetition) were used and when necessary, Bonferroni post hoc was performed. The EMGRMS was higher in the protocol MF compare to NMF, but there was no difference in EMGFREQ between protocols. Although there were no significant differences in the frequency domain between protocols, perform repetitions to MF was a determining factor to generate higher amplitude of the electromyography signal. Thus, perform repetitions to MF could be considered an effective strategy to increase muscle activation in trained individuals, however, with similar neuromuscular fatigue.

RESUMO Protocolos de treinamento realizados até a falha muscular (FM) têm sido realizados na tentativa de maximizar a ativação e a fadiga neuromuscular. Portanto, o objetivo deste estudo foi comparar a amplitude do sinal eletromiografico (EMGRMS) e a frequência (EMGFREQ) do peitoral maior entre os protocolos realizados até a FM e sem falha muscular (SFM). Sete homens treinados realizaram três séries com 60% de uma repetição máxima, com um período de descanso de 3 min e uma duração da repetição de 6s. O protocolo FM foi realizado com o número máximo de repetições em todas as séries, enquanto no protocolo SFM os indivíduos realizaram 6 repetições em 3 séries. Para análise dos dados, foram utilizadas duas ANOVAs two-way com medidas repetidas (Protocolo x Repetição) e, quando necessário, foi realizado o post hoc de Bonferroni. Como resultado, a EMGRMS foi maior no protocolo FM comparado ao SFM, mas não houve diferença na EMGFREQ entre os protocolos. Embora não houvesse diferenças significativas no domínio da frequência entre os protocolos, a realização de repetições até a FM foi um fator determinante para gerar maior amplitude do sinal eletromiográfico. Assim, a realização de repetições até a FM pode ser considerada uma estratégia eficaz para aumentar a ativação muscular em indivíduos treinados, porém com fadiga neuromuscular semelhante.

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This study compared the electromyographic response, the blood lactate concentration (BLC), and the maximum number of repetitions (MNR) between protocols of different concentric/eccentric duration taken to muscle failure. This comparison may help to understand how different concentric/eccentric duration may influence performance and the central and metabolic responses in trained men. Seventeen strength-trained men performed two protocols in a counterbalanced design. Three sets of the Smith bench press exercise were performed to failure at 60% of the one-repetition maximum (1RM) using each protocol (4-s concentric/2-s eccentric [4 s: 2 s]; and 2-s concentric/4-s eccentric [2 s: 4 s]). The normalized root mean square (EMGRMS) and the mean frequency (EMGMF) of the electromyographic signals for the pectoralis major and the triceps brachii were compared in the first, middle, and last repetitions. The BLC was assessed at rest, during and after the test sessions. To compare the EMG and BLC, a 3-way ANOVA with repeated measures with a post hoc Tukey's test was used. To compare the MNR performed across the sets, an ANOVA-type rank test with the Dunn's post hoc test was used. The ANOVA indicated a greater EMGRMS for Protocol 4 s: 2 s in the pectoralis major and a lower EMGMF for Protocol 4 s: 2 s in the triceps brachii at the middle and last repetitions. Both protocols increased the EMGRMS and decreased the EMGMF across repetitions. Despite the results show different levels of activation and neuromuscular fatigue between protocols, the BLC and the MNR were similar.

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Abstract This study investigate the effect of 10-week strenght training on the amplitude of the electromyographic (EMG) signal of vastus medialis, vastus lateralis and rectus Femoris. Twenty three untrained volunteers performed 3-5 sets (3 sets - weeks 1 and 2; 4 series - weeks 3 and 4; 5 series weeks 5 to 10) with 6 repetitions, intensity of 50% of 1 repetition maximum (1RM), 3 min rest between sets and 6 s repetition duration at the knee extensor exercise. One group (5:1) performed concentric action of 5 s and eccentric of 1 s and the other (3:3) performed concentric of 3 s and eccentric of 3 s. The VM, VL and RF EMG (RMS) activities were recorded in each repetition of the three series at the first training session and the first three series at the last session. The protocol 5:1 led to EMG reduction in all portions, with a greater number of repetitions presenting differences at the VL and RF. VM and RF presented similar results at Group 3:3. It was verified that all the differences occurred in the second half of the series. It was also verified differences in EMG ratios just in group 3:3 and only in VM/VL and VM/RF. These results suggest that the coordination was not affected when equivalent repetitions of series were compared. It was also suggested that these results were influenced by the reduced degrees of freedom of the exercise and the training load progression adopted.

Resumo Este estudo investigou o efeito de 10 semanas de treinamento de força na resposta eletromiográfica (EMG) do vasto medial, vasto lateral e reto femoral. 23 voluntárias executaram 3 a 5 séries de 6 repetições, intensidade de 50% de 1 repetição máxima (RM), 3 minutos de pausa entre as séries e duração da repetição de 6 s no exercício extensor de joelhos. Um grupo (5:1) realizou a duração da ação concêntrica em 5 s e excêntrica em 1s e outro grupo (3:3) realizou a concêntrica em 3s e a excêntrica em 3s. A atividades EMG (RMS) destas três porções do quadríceps foram registradas em cada repetição das 3 séries da primeira sessão de treinamento e nas três primeiras séries da última sessão. Os resultados mostraram diferenças na metade final das séries, sendo que no grupo 5:1 houve redução na EMG em todas as porções e o VL e o RF mostraram redução em um número maior de repetições. No grupo 3:3 o VM e o RF apresentaram redução. Para as relações de ativação entre as porções, diferenças foram identificadas apenas no grupo 3:3 nas relações VM/VL e VM/RF em um número reduzido de repetições. Estes resultados apontam que a coordenação entre as porções sofreu poucas alterações quando comparadas as repetições equivalentes de cada série. Sugere-se que os reduzidos graus de liberdade do movimento utilizado e a progressão da carga de treinamento tenham sido os fatores que conduziram a este resultado