Mind-muscle connection training principle: influence of muscle strength and training experience during a pushing movement

The Disconnect Between Soccer Players' Perceived and Actual Electromyographic-Measured Muscle Activation

Understanding muscle activation during exercises is crucial for devising effective training programs. We examined correlations between self-reported and electromyographic (EMG) muscle activity during upper-body exercises performed at loads corresponding to 4-6 repetition maximums (RMs). Thirteen male sub-elite soccer players who had previously engaged in resistance training participated in two testing sessions. In the initial session, the loads corresponding to 4-6 repetitions were determined for six exercises: Lat Pull Down (LPD), Barbell Bent Over Row (BBOR), Dumbbell Row (DR), Barbell Pull Over (BPO), Dumbbell Reverse Fly (DRF), and Dumbbell Concentration Curl (DCC). At post-exercise, participants rated their perceived muscle activation for three targeted muscles in each exercise on a 1-10 point Likert scale (LS). In the subsequent session, we used EMG to measure the activity of eight agonist and synergist muscles during these exercises. We found that one of two synergist muscles consistently demonstrated higher activity levels. Interestingly, we observed no difference in activity between primary and secondary (or synergist) muscles across all exercises. Most importantly, we found no significant correlation between the perceived muscle activation rate and the EMG measured activation level for any exercise. In conclusion, our findings suggest that, despite differential muscle activity during specific exercises, self-reported muscle activation may not accurately correspond to actual muscle activation, as measured via EMG, due to the participants' poor interoceptive awareness of muscles. These data highlight the potential limitations of relying on perceived muscle activation as a sole gauge of training intensity.

The associations of physical parameters with the Closed Kinetic Chain Upper Extremity Stability Test, the Upper Quarter Y Balance Test, and the Upper Limb Rotation Test in professional overhead athletes

OBJECTIVE

To investigate the associations of glenohumeral internal (IR) and external rotation (ER), horizontal adduction (HA), and thoracic spine rotation ranges of motion (ROM), isometric muscle strength of the shoulder rotators, and trunk muscle endurance with the Closed Kinetic Chain Upper Extremity Stability Test (CKCUEST), the Upper Quarter Y Balance Test (YBT-UQ), and the Upper Limb Rotation Test (ULRT) in overhead athletes.

DESIGN

Cross-sectional study.

SETTINGS

Laboratory.

PARTICIPANTS

One hundred twenty-one athletes were enrolled.

MAIN OUTCOME MEASURES

Independent variables were: IR, ER, HA, and thoracic spine rotation ROMs, isometric muscle strength of glenohumeral IR and ER muscles, and trunk muscle endurance. Dependent variables were: CKCUEST, YBT-UQ, ULRT.

RESULTS

IR ROM of the nondominant side was associated with the CKCUEST, the YBT-UQ, and the ULRT. IR muscle strength of the dominant side was associated with the CKCUEST and the ULRT. Trunk flexor and lateral endurance of the dominant side were associated with the CKCUEST and the YBT-UQ, respectively.

CONCLUSIONS

Many of the physical parameters influencing scores on the CKCUEST and the YBT-UQ are different. Common parameters influence the CKCUEST and ULRT scores, yet more parameters influence the CKCUEST score. We suggest the combined use of the CKCUEST and the YBT-UQ in overhead athletes.

Appropriate Reporting of Exercise Variables in Resistance Training Protocols: Much more than Load and Number of Repetitions

Manipulating resistance training variables is crucial to plan the induced stimuli correctly. When reporting the exercise variables in resistance training protocols, sports scientists and practitioners often refer to the load lifted and the total number of repetitions. The present conceptual review explores all within-exercise variables that may influence the strength and hypertrophic gains, and the changes in muscle architecture. Together with the (1) load and (2) the number of repetitions, (3) performing repetitions to failure or not to failure, (4) the displacement of the load or the range of movement (full or partial), (5) the portion of the partial movement to identify the muscle length at which the exercise is performed, (6) the total time under tension, the duration of each phase and the position of the two isometric phases, (7) whether the concentric, eccentric or concentric-eccentric phase is performed, (8) the use of internal or external focus and (9) the inter-set rest may all have repercussions on the adaptations induced by each resistance exercise. Manipulating one or more variable allows to increase, equalize or decrease the stimuli related to each exercise. Sports scientists and practitioners are invited to list all aforementioned variables for each exercise when reporting resistance training protocols.

The Effects of Verbal Instructions on Lower Limb Muscles' Excitation in Back-Squat

The present study investigated whether or not verbal instruction affects the electromyographic (EMG) amplitude of back-squat prime movers. Fifteen resistance-trained men performed back-squat at 50%1-RM and 80%1-RM and received external (EF) or internal focus (IF) on lower-limb posterior muscles. EMG amplitude of gluteus maximus, biceps femoris, gastrocnemius medialis, vastus lateralis, and tibialis anterior was recorded during both concentric and eccentric phases. During the concentric phase, the gluteus maximus and biceps femoris EMG amplitude was greater in IF vs EF at 50% [effect size (ES): 0.63 (95%CI 0.09/1.17) and 0.49 (0.10/0.78), respectively] and 80% [ES: 1.30 (0.29/2.21) and 0.59 (0.08/1.10)]. The gastrocnemius medialis EMG amplitude was greater in IF vs EF during the eccentric phase at 50% [ES: 0.73 (0.13/1.33)] and at 80% [ES: 0.72 (0.10/1.34)]. Concomitantly, vastus lateralis EMG amplitude was lower at 50% [ES: -0.71 (-1.38/-0.04)] and 80% [ES: -0.68 (-1.33/-0.03)]. During the eccentric phase, the tibialis anterior EMG amplitude was greater in IF vs EF at 50% [ES: 0.90 (0.12 to 1.68)] and 80% [ES: 0.74 (0.13/1.45)]. Irrespective of the load, in the thigh muscles the internal focus promoted a different motor pattern, increasing the hip extensors and reducing the knee extensor excitation during the concentric phase. Concomitantly, both ankle muscles were more excited during the eccentric phase, possibly to increase the anterior-posterior balance control. The internal focus in back-squat seems to have phase-dependent effects, and it is visible at both moderate and high loads.

Differences in the Electromyographic Activity of Lower-Body Muscles in Hip Thrust Variations

Collazo García, CL, Rueda, J, Suárez Luginick, B, Navarro, E. Differences in the electromyographic activity of lower-body muscles in hip thrust variations. J Strength Cond Res 34(9): 2449-2455, 2020-Coaches often use variations of an exercise to train a specific muscle. The purpose of this study was to analyze motor patterns in 4 variations of one of the most popular strength training exercises for the lower body: the barbell hip thrust. Seven experienced personal trainers performed a series of 8 repetitions of each variation with a load of 40% one repetition maximum. Subjects rested 3' between series. Electromyographic (EMG) muscle activity was measured in the rectus femoris, vastus medialis; vastus lateralis; gluteus maximus; gluteus medius; biceps femoris; and semitendinosus. Variations of the hip thrust exercise were performed by changing the position of the feet (feet were moving away from the body) and the direction of force exerted by subjects (intentional force aimed at hip's external rotation and knee's flexion). Repeated-measures analysis of variance revealed significant differences in EMG in all muscles except for the gluteus medius, where no differences were observed among variations. The results obtained suggest that hip thrust variations have different motor patterns, which can be exploited to adapt an exercise to the individual needs of each athlete.

An Electromyographic Analysis of Lateral Raise Variations and Frontal Raise in Competitive Bodybuilders

The present study examined the muscle activation in lateral raise with humerus rotated externally (LR-external), neutrally (LR-neutral), internally (LR-internal), with flexed elbow (LR-flexed) and frontal raise during both the concentric and eccentric phase. Ten competitive bodybuilders performed the exercises. Normalized surface electromyographic root mean square (sEMG RMS) was obtained from anterior, medial, and posterior deltoid, pectoralis major, upper trapezius, and triceps brachii. During the concentric phase, anterior deltoid and posterior deltoid showed greater sEMG RMS in frontal raise (effect size (ES)-range: 1.78/9.25)) and LR-internal (ES-range: 10.79/21.34), respectively, vs. all other exercises. Medial deltoid showed greater sEMG RMS in LR-neutral than LR-external (ES: 1.47 (95% confidence-interval—CI: 0.43/2.38)), frontal raise (ES: 10.28(95% CI: 6.67/13.01)), and LR-flexed (ES: 6.41(95% CI: 4.04/8.23)). Pectoralis major showed greater sEMG RMS in frontal raise vs. all other exercises (ES-range: 17.2/29.5), while upper trapezius (ES-range: 2.66/7.18) and triceps brachii (ES-range: 0.41/3.31) showed greater sEMG RMS in LR-internal vs. all other exercises. Similar recruitment patterns were found during the eccentric phase. When humerus rotates internally, greater activation of posterior deltoid, triceps brachii, and upper trapezius occurs. Humerus external rotation increases the activation of anterior and medial deltoid. Frontal raise mainly activates anterior deltoid and pectoralis major. LR variations and frontal raise activate specifically shoulders muscles and should be proposed accordingly.

Evaluation of the Lower Limb Muscles' Electromyographic Activity during the Leg Press Exercise and Its Variants: A Systematic Review

The aim of this study was to analyze the literature on muscle activation measured by surface electromyography (sEMG) of the muscles recruited when performing the leg press exercise and its variants. The Preferred Reporting Items of Systematic Reviews and Meta-Analyses (PRISMA) guidelines were followed to report this review. The search was carried out using the PubMed, Scopus, and Web of Science electronic databases. The articles selected met the following inclusion criteria: (a) a cross-sectional or longitudinal study design; (b) neuromuscular activation assessed during the leg press exercise, or its variants; (c) muscle activation data collected using sEMG; and (d) study samples comprising healthy and trained participants. The main findings indicate that the leg press exercise elicited the greatest sEMG activity from the quadriceps muscle complex, which was shown to be greater as the knee flexion angle increased. In conclusion, (1) the vastus lateralis and vastus medialis elicited the greatest muscle activation during the leg press exercise, followed closely by the rectus femoris; (2) the biceps femoris and the gastrocnemius medialis showed greater muscular activity as the knee reached full extension, whereas the vastus lateralis and medialis, the rectus femoris, and the tibialis anterior showed a decreasing muscular activity pattern as the knee reached full extension; (3) evidence on the influence of kinematics modifications over sEMG during leg press variants is still not compelling as very few studies match their findings.

Mind-Muscle Connection: Limited Effect of Verbal Instructions on Muscle Activity in a Seated Row Exercise

Verbal instruction increases electromyographic (EMG) activity in the first three repetitions of an exercise, but its effect on an entire exercise set until failure is unknown. Once there are changes in motor unit recruitment due to fatigue, the effect of verbal instructions can change during different intervals of a set. This study analyzed whether verbal instruction emphasized the contraction of back muscles (i.e., myoelectric activity) during initial, intermediate, and final exercise repetitions performed until failure. Twenty participants with little or no experience in strength training performed a seated row exercise with and without verbal instruction. Surface electrodes were fixed over the latissimus dorsi, teres major, biceps brachii, and posterior deltoid (PD) muscles. Myoelectric activity was computed by mean amplitude and by the median frequency. We analyzed data with repeated measures multivariate analysis of variance and found that, with verbal instruction, there was increased EMG mean amplitude in the latissimus dorsi (15.21%, p = .030) and reduced EMG mean amplitude in the PD (14.39%, p = .018) on initial repetitions. Other muscle EMG amplitudes did not change. On intermediate repetitions, there was reduced signal amplitude only in the PD (15.03%, p = .022). The verbal instruction did not interfere with signal amplitude on final repetitions nor in the median frequency throughout the series. Verbal instruction seems to have little effect on increasing myoelectric activity of these targeted muscles in an entire set of a resistance training.

Electromyographic Effect of Using Different Attentional Foci During the Front Plank Exercise

OBJECTIVE

The aim of this cross-sectional study was to examine whether an internal focus on different core muscles during the isometric prone plank exercise increased muscle activity.

DESIGN

Twenty university students performed the following five different conditions: regular prone plank (external focus) and prone plank with an internal focus on different muscles. Surface electromyography signals were recorded for the upper rectus abdominis, lower rectus abdominis, external oblique, and lumbar erector spinae.

RESULTS

For the upper rectus abdominis, an internal focus on using any muscle increased activity. For the lower rectus abdominis, internal focus on any muscle except the lumbar erector spinae increased activity. No changes were found for external oblique and lumbar erector spinae activity.

CONCLUSIONS

Upper rectus abdominis and lower rectus abdominis activities increased during an internal focus on the abdominal muscles. external oblique and lumbar erector spinae activities were nonaffected by an internal focus on any muscle.

Attentional Focus and Grip Width Influences on Bench Press Resistance Training

This study evaluated the influence of different attentional foci for varied grip widths in the bench press. Eighteen resistance-trained men were familiarized with the procedure and performed a one-repetition maximum (1RM) test during Session 1. In Session 2, they used three different standardized grip widths (100%, 150%, and 200% of biacromial width distance) in random order at 50% of 1RM while also engaged in three different attention focus conditions (external focus on the bench press, internal focus on pectoralis major muscles, and internal focus on triceps brachii muscles). Surface electromyography (EMG) signals were recorded from the triceps brachii and pectoralis major, and peak EMG of the filtered signals were normalized to maximum EMG of each muscle. Both grip width and focus influenced the muscle activity level, but there were no significant interactions between these variables. Exploratory analyses suggested that an internal focus may slightly (4%-6%) increase pectoralis major activity at wider grip widths and triceps brachii activity at narrower grip widths, but this should be confirmed or rejected in a study with a larger sample size or through a meta-analysis of research to date.