Does rest interval between unilateral exercise protocols influences on contralateral neuromuscular responses in untrained individuals?

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.

Training in the Initial Range of Motion Promotes Greater Muscle Adaptations Than at Final in the Arm Curl.

OBJECTIVE: The effects of ROM manipulation on muscle strength and hypertrophy response remain understudied in long-term interventions. Thus, we compared the changes in strength and regional muscle hypertrophy after training in protocols with different ranges of motion (ROM) in the seated dumbbell preacher curl exercise using a within-participant experimental design. DESIGN AND METHODS: Nineteen young women had one arm randomly assigned to train in the initial ROM (INITIALROM: 0°-68°; 0° = extended elbow) while the contralateral arm trained in the final ROM (FINALROM: 68°-135°), three times per week over an eight-week study period. Pre- and post-training assessments included one repetition maximum (1RM) testing in the full ROM (0°-135°), and measurement of biceps brachii cross-sectional area (CSA) at 50% and 70% of humerus length. Paired t-tests were used to compare regional CSA changes between groups, the sum of CSA changes at 50% and 70% (CSAsummed), and the strength response between the training protocols. RESULTS: The INITIALROM protocol displayed a greater CSA increase than FINALROM protocol at 70% of biceps length (p = 0.001). Alternatively, we observed similar increases between the protocols for CSA at 50% (p = 0.311) and for CSAsummed (p = 0.111). Moreover, the INITIALROM protocol displayed a greater 1RM increase than FINALROM (p < 0.001). CONCLUSIONS: We conclude that training in the initial angles of elbow flexion exercise promotes greater distal hypertrophy of the biceps brachii muscle in untrained young women. Moreover, the INITIALROM condition promotes a greater dynamic strength increase when tested at a full ROM compared to the FINALROM.

Muscle volume vs. anatomical cross-sectional area: Different muscle assessment does not affect the muscle size-strength relationship.

Muscle volume (MV) and anatomical cross-sectional area (CSA) are used as measures of muscle-size, but determining these from magnetic resonance imaging (MRI) is a very time-consuming process. Additionally, it is unclear if the use of different muscle size assessments (all vs. reduced number of slices images) would impact the muscle size-strength relationship. Thus, this study aimed to investigate if muscle size calculation by using a reduced or all slices images from pectoralis major (PM) would maintain a similar muscle size-strength relationship with bilateral maximal dynamic and isometric contractions on a bench press exercise. Twenty-four healthy males underwent an MRI examination to measure PM muscle size, and maximal isometric and dynamic contractions (by one repetition maximum, 1RM) were performed. Correlations between maximal isometric voluntary force (MVF) and dynamic strength (1RM) with muscle size variables [three images from the largest part of PM (CSA3MAX), three images accounting for the shape -first image, middle image, final image- of the PM (CSA3), and MV] were performed. The correlation between 1RM with MV, CSA3, and CSA3MAX were 0.84, 0.832, and 0.727 (p < 0.001), respectively. The correlation between MVF with MV, CSA3, and CSA3MAX were 0.738, 0.733, and 0.604 (p < 0.001), respectively. Overall, PM MV and CSA3 exhibit a stronger and similar muscle size-strength relationship during maximal dynamic and isometric tests than CSA3MAX. Therefore, a reduced number of slices (CSA3) could be used as an alternative to considerably reduce the time of analysis without compromise muscle size-strength relationship.

Equalization of Training Protocols by Time Under Tension Determines the Magnitude of Changes in Strength and Muscular Hypertrophy.

ABSTRACT: Martins-Costa, HC, Lacerda, LT, Diniz, RCR, Lima, FV, Andrade, AGP, Peixoto, GH, Gomes, MC, Lanza, MB, Bemben, MG, and Chagas, MH. Equalization of training protocols by time under tension determines the magnitude of changes in strength and muscular hypertrophy. J Strength Cond Res 36(7): 1770-1780, 2022-The aim of this study was to investigate the effects of 2 training protocols equalized by tension (TUT) on maximal strength (1 repetition maximum [RM]), regional cross-sectional areas (proximal, middle, and distal), and total cross-sectional areas (sum of the regional cross-sectional areas) of the pectoralis major and triceps brachii muscles. Thirty-eight men untrained in resistance training participated in the study and were allocated under 3 conditions: Protocol 3s (n = 11; 12 repetitions; 3s repetition duration), Protocol 6s (n = 11; 6 repetitions; 6s repetition duration), and Control (n = 11; no training). Training protocols (10 weeks; bench press exercise) were equated for TUT (36 seconds per set), number of sets (3-4), intensity (50-55% of 1RM), and rest between sets (3 minutes). Analysis of variance was used to examine a percentage change in variables of interest across the 3 groups with an alpha level of 0.05 used to establish statistical significance. Protocols 3s and 6s showed no differences in the increase of total and regional muscle cross-sectional areas. There were no differences in regional hypertrophy of the pectoralis major muscle. In the triceps brachii muscle, the increase in distal cross-sectional area was greater when compared with the middle and proximal regions. Both experimental groups had similar increases in the 1RM test. In conclusion, training protocols with the same TUT promote similar strength gains and muscle hypertrophy. Moreover, considering that the protocols used different numbers of repetitions, the results indicate that training volumes cannot be considered separately from TUT when evaluating neuromuscular adaptations.

Does the Muscle Action Duration Induce Different Regional Muscle Hypertrophy in Matched Resistance Training Protocols?

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.

The effect of different resistance training protocols equalized by time under tension on the force-position relationship after 10 weeks of training period.

This study investigated the impact of performing two equalized resistance training (RT) protocols for 10 weeks that differ only by repetition duration and number in the force-position and EMG-position relationship. Participants performed an equalized (36 s of time under tension; 3-4 sets; 3 min between sets; 50-55% of one-repetition maximum; 3× week) RT intervention on the bench press and the only different change between protocols was repetition number (RN; 12 vs.6) or duration (RD; 3 s vs. 6 s). Two experimental groups (RN12RD3, n = 12; and RN6RD6, n = 12) performed the RT, while one group was the control (Control, n = 11). Maximal isometric contractions at 10%, 50% and 90% of total bench press range of motion were performed pre- and post-RT, while electromyography was recorded. It demonstrated an increase in isometric force (+14% to 24%, P < 0.001) shifting up the force-position relationship of the training groups after RT, although no difference was between training groups compared to the Control. Neuromuscular activation from pectoralis major presented an increase after training for both RT groups (+44%; P < 0.001) compared to the Control. However, although not significantly different, triceps brachii also presented an increase depending on the protocol (+25%). In conclusion, 10 weeks of an equalized RT with longer RN and shorter RD (or opposite) similarly increases the ability to produce maximal isometric force during the bench exercise across different angles, while neuromuscular activation of the pectoralis major partially explained the shift-up of the force-position relationship after training.

Partial range of motion training elicits favorable improvements in muscular adaptations when carried out at long muscle lengths.

The study compared changes in strength and regional muscle hypertrophy between different ranges of motion (ROM) in the knee extension exercise. Forty-five untrained women were randomized to either a control group or to perform the exercise in one of the following 4 groups (0°=extended knee): Full ROM (FULLROM: 100°-30° of knee flexion); Initial Partial ROM (INITIALROM: 100°-65°); Final Partial ROM (FINALROM: 65°-30°); Varied ROM (VARROM: daily alternation between the ROM of INITIALROM and FINALROM). Pre- and post-training assessments included one repetition maximum (1RM) testing in the ROM corresponding to the initial, final and full ROM, and measurement of cross-sectional areas of the rectus femoris and vastus lateralis muscles at 40%, 50%, 60% and 70% of femur length in regard to regional muscle hypertrophy. Results showed that the INITIALROM group presented a greater relative increase than all groups at 70%, and at 50% and 60% the increases were greater than FINALROM, FULLROM, and non-training control (CON) groups. Moreover, FINALROM group presented similar changes compared to the CON group at 60% and 70%. In regard to 1RM, FINALROM and INITIALROM groups presented greater relative increases at the ROM trained, and no group showed greater increases than VARROM or INITIALROM, regardless the ROM tested. In conclusion, partial ROM training in the initial phase of the knee extension exercise promoted greater relative hypertrophy in certain muscle regions than training in other ROM configurations, and no group promoted a greater 1RM increase than VARROM group, which showed similar 1RM increases in the different ROMs tested.

Acute physiological responses with varying load or time under tension during a squat exercise: A randomized cross-over design.

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.

Is Performing Repetitions to Failure Less Important Than Volume for Muscle Hypertrophy and Strength?

Lacerda, LT, Marra-Lopes, RO, Diniz, RCR, Lima, FV, Rodrigues, SA, Martins-Costa, HC, Bemben, MG, and Chagas, MH. Is performing repetitions to failure less important than volume for muscle hypertrophy and strength? J Strength Cond Res 34(5): 1237-1248, 2020-The aim of this study was to investigate the effects of muscle failure (MF) or not to MF (NMF) training on strength and muscle hypertrophy relative gains (average and individual data). Ten men untrained in resistance training participated in the study. Each leg was allocated in 1 of 2 unilateral training protocols (MF or NMF with equal volume) on knee extension exercise. Both protocols were performed with 3-4 sets, 3 minutes' rest, and 55-60% of one repetition maximum (1RM). Rectus femoris and vastus lateralis muscles cross-sectional area (CSA), maximal muscle strength (1RM and maximal voluntary isometric contraction), and muscular endurance (maximum number of repetition) were assessed before and after 14 weeks. In addition, neuromuscular activation by normalized root mean square of the electromyographic signal (EMGRMS) was measured in 2nd and 35th training sessions. The average results showed that both training protocols were similarly effective in inducing increases in strength and muscle hypertrophy gains. However, individual analysis data suggest that NMF protocol with equal volume may promote similar or even greater muscle hypertrophy (vastus lateralis) and muscular endurance performance when compared with MF protocol. Also, normalized EMGRMS responses analyzed during 2nd and 35th sessions were similar in MF and NMF protocols for rectus femoris and vastus lateralis muscles. In conclusion, MF and NMF protocol conducted with the same total repetition numbers produced similar maximal muscle strength performance and neuromuscular activation. Nevertheless, NMF training could be a more appropriate strategy to increase muscle hypertrophy (vastus lateralis) and muscular endurance performance in untrained individuals when compared with MF.

Longer Concentric Action Increases Muscle Activation and Neuromuscular Fatigue Responses in Protocols Equalized by Repetition Duration.

Lacerda, LT, Costa, CG, Lima, FV, Martins-Costa, HC, Diniz, RCR, Andrade, AGP, Peixoto, GHC, Bemben, MG, and Chagas, MH. Longer concentric action increases muscle activation and neuromuscular fatigue responses in protocols equalized by repetition duration. J Strength Cond Res 33(6): 1629-1639, 2019-The aim of this study was to investigate the impact of protocols equalized by the repetition duration but composed of different concentric (CON) and eccentric (ECC) durations on muscle activation and neuromuscular fatigue. Seventeen males with previous experience in resistance training performed 3 training protocols (A - 2 second CON: 4 second ECC; B - 3 second CON: 3 second ECC; and C - 4 second CON: 2 second ECC) with the Smith machine bench press exercise, all with 3 sets, 6 repetitions, 3 minutes' rest, and 60% of 1RM. The normalized root mean square of the electromyographic signal (EMGRMS) and mean frequency electromyography (EMGMF) for pectoralis major and triceps brachii muscles were calculated for second and fifth repetitions in each set. The results showed an EMGMF decrease across the repetitions accompanied by a progressive increase of the EMGRMS across the repetitions for all protocols and muscles. The EMGRMS was higher in protocol C when compared with protocol A and B for pectoralis major. The EMGMF was lower in protocols B and C than in protocol A for pectoralis major throughout the sets and repetitions. A higher EMGRMS and a lower EMGMF were observed in protocols B and C compared with protocol A for triceps brachii, solely in the fifth repetition. In conclusion, training protocols conducted with the same repetition duration, but with different concentric and eccentric durations, produce distinct muscle activation and neuromuscular fatigue responses, in which performing longer concentric durations could be the more appropriate strategy to increase muscle activation and neuromuscular fatigue.

Variations in Repetition Duration and Repetition Numbers Influence Muscular Activation and Blood Lactate Response in Protocols Equalized by Time Under Tension.

The aim of this study was to investigate the impact of protocols equalized by the time under tension (TUT) but composed of different repetition durations and repetitions numbers on muscle activation and blood lactate concentration. Twenty-two males with previous experience in resistance training performed 2 training protocols (A and B) with the Smith machine bench press exercise, both with 3 sets, 3 minutes' rest, and 60% of 1 repetition maximum (1RM). Protocol A consisted of 6 repetitions with a 6-second repetition duration for each repetition, whereas in Protocol B the subjects performed 12 repetitions with a 3-second repetition duration for each repetition. Muscular activation was measured in the anterior deltoid, pectoralis major, and triceps brachii muscles while performing the 2 protocols, and the normalized root mean square of the electromyographic signal (EMGRMS) was calculated for each set. Blood lactate concentrations were measured during and until 12 minutes after the completion of each protocol. The results showed that the EMGRMS of all muscles increased during the sets and was higher in Protocol B when compared with Protocol A. Likewise, blood lactate concentrations also increased throughout the sets and were higher in Protocol B both during and after the completion of each training session. The data obtained in this study show that training protocols conducted with the same TUT, but with different configurations, produce distinct neuromuscular and metabolic responses so that performing higher repetition numbers with shorter repetition durations might be a more appropriate strategy to increase muscle activation and blood lactate concentration.

Repetition duration influences ratings of perceived exertion.

This study investigated the effect of different repetition durations on ratings of perceived exertion (RPE) in active muscles (RPE-AM) and the overall body (RPE-O). 19 male volunteers (M age = 25.4 yr., SD = 3.5) performed strength training protocols with multiple sets matched by the number of sets and repetitions, intensity and rest interval but different repetition durations: 4 sec., 6 sec., or self-paced. Participants were asked to estimate their RPE-AM and RPE-O after each set. Training protocols with a 6-sec. repetition duration produced distinct responses on RPE during and after performance compared to 4-sec. and self-paced durations. However, there were no significant differences between 4-sec. and self-paced durations.