Neuromuscular efficiency of the rectus abdominis differs with gender and sport practice

Effect of Lactobacillus plantarum PS128 on neuromuscular efficiency after a half-marathon

Introduction: Lactobacillus plantarum PS128 (PS128) could be considered an antioxidant supplement to reduce muscle fatigue and improve exercise capacity recovery after vigorous exercise. Purpose: The purpose of this study is to investigate the effect of PS128 on muscle fatigue and electromyography (EMG) activity after a half-marathon (HM). Methods: The experimental design used a repeated-measures design with a double-blind approach. The participants either took two capsules of PS128 for 4 weeks as the PS128 group (PSG, n = 8) or took two capsules of a placebo for 4 weeks as the placebo group (PLG, n = 8) to ensure counterbalancing. The time points of the maximal voluntary isometric contraction (MVIC) and EMG activity test were set before probiotics were taken (baseline), 48 h before HM (Pre), and immediately at 0 h, 3 h, 24 h, 48 h, 72 h, and 96 h after HM. Results: EMG activity included median power frequency (MDF), integrated EMG (iEMG), and neuromuscular efficiency (peak torque/iEMG). The MVICs of knee extensors, analyzed by using an isokinetic dynamometer, showed a decrease from the Pre to 0 h (p = 0.0001), 3 h (p < 0.0001), 24 h (p < 0.0001), 48 h (p < 0.0001), 72 h (p = 0.0002), and 96 h (p = 0.0408) time points in the PLG. Sidak's multiple comparisons tests showed that the PLG was significantly lower than the PSG at 0 h (p = 0.0173), 3 h (p < 0.0001), 24 h (p < 0.0001), 48 h (p < 0.0001), 72 h (p < 0.0001), and 96 h (p = 0.0004) time points. The MDF of vastus medialis oblique (VMO) in the PLG was significantly decreased 24 h after HM and significantly lower than that in the PSG at all times points after HM. The iEMG of VMO in the PLG was significantly decreased 48 h after HM and significantly lower than that in the PSG at 0 h, 3 h, 24 h, 48 h, and 72 h after HM. Conclusion: The PS128 supplementation may prevent the decrease in MDF, iEMG, and peak torque after vigorous exercise. Recreational runners may consider implementing a probiotic supplementation regimen as a potential strategy to mitigate muscle fatigue following HM.

Long-Term Neurophysiological Adaptations to Strength Training: A Systematic Review With Cross-Sectional Studies

ABSTRACT

Santos, PDG, Vaz, JR, Correia, J, Neto, T, and Pezarat-Correia, P. Long-term neurophysiological adaptations to strength training: a systematic review with cross-sectional studies. J Strength Cond Res 37(10): 2091-2105, 2023-Neuromuscular adaptations to strength training are an extensively studied topic in sports sciences. However, there is scarce information about how neural mechanisms during force production differ between trained and untrained individuals. The purpose of this systematic review is to better understand the differences between highly trained and untrained individuals to establish the long-term neural adaptations to strength training. Three databases were used for the article search (PubMed, Web of Science, and Scopus). Studies were included if they compared groups of resistance-trained with untrained people, aged 18-40 year, and acquired electromyography (EMG) signals during strength tasks. Twenty articles met the eligibility criteria. Generally, strength-trained individuals produced greater maximal voluntary activation, while reducing muscle activity in submaximal tasks, which may affect the acute response to strength training. These individuals also presented lower co-contraction of the antagonist muscles, although it depends on the specific training background. Global intermuscular coordination may be another important mechanism of adaptation in response to long-term strength training; however, further research is necessary to understand how it develops over time. Although these results should be carefully interpreted because of the great disparity of analyzed variables and methods of EMG processing, chronic neural adaptations seem to be decisive to greater force production. It is crucial to know the timings at which these adaptations stagnate and need to be stimulated with advanced training methods. Thus, training programs should be adapted to training status because the same stimulus in different training stages will lead to different responses.

Validity of Gymnastics-Specific Assessment of Neuromuscular Function of Shoulder Flexor and Extensor Muscles to Predict Performance in Gymnastics Skills

ABSTRACT

Milosis, DC. Validity of gymnastics-specific assessment of neuromuscular function of shoulder flexor and extensor muscles to predict performance in gymnastics skills. J Strength Cond Res 37(3): 652-660, 2023-This study examined the relationships between gymnastics-specific laboratory measurements of neuromuscular function of the shoulder flexor and extensor muscles and performance in specific gymnastics skills. Fifteen highly competitive male gymnasts and 18 male students (age 20.41 ± 2.51 years, body mass 69.7 ± 7.07 kg; mean ± SD ) participated voluntarily. The electromyogram (EMG) was used to assess muscle activation of 3 flexor and 3 extensor shoulder muscles during isometric (45, 90, and 135°) and isokinetic (concentric and eccentric 60, 180, and 300°/s) flexion-extension of the shoulder. Peak torque (PT), neuromuscular efficiency (NME: torque to EMG ratio), and antagonist coactivation index (CI) were evaluated. Furthermore, performance in specific gymnastics skills was evaluated. The results supported the ecological validity of the measurements. Specifically, significant correlations emerged between the shoulders' neuromuscular function parameters and the performance in the gymnastics skills (PT: r = 0.798, p < 0.001, NME: r = 0.576, p < 0.001, CI: r = -0.351, p < 0.05). In addition, according to the results of the regression analysis, neuromuscular function of the shoulder flexor and extensor muscles predicted gymnastics performance. Specifically, the model that was produced significantly predicted the dependent variable (performance in specific gymnastics skills) in all steps and explained a total variance of 64.4% ( p < 0.001). Based on beta coefficients, PT had the higher contribution to the prediction of performance. The insight gained on these relationships could help coaches to plan the training of their gymnasts and to monitor the longitudinal changes in neuromuscular function of shoulder muscles induced by training more effectively.

Resistance Training Improves Muscle Strength and Function, Regardless of Protein Supplementation, in the Mid- to Long-Term Period after Gastric Bypass

Inadequate protein intake and low levels of physical activity are common long-term sequelae after bariatric surgery and can negatively affect muscle strength (MS) and physical function (PF). The study investigated the effects of resistance training with or without protein supplementation on MS and PF. The study, which involved a 12-week controlled trial (n = 61) of individuals 2-7 years post-Roux-en-Y gastric bypass (RYGB), comprised four groups: whey protein supplementation (PRO; n = 18), maltodextrin placebo (control [CON]; n = 17), resistance training combined with placebo (RTP; n = 11), and resistance training combined with whey protein supplementation (RTP+PRO; n = 15). An isokinetic dynamometer was used to measure MS (peak torque at 60°/s and 180°/s). PF was measured with the 30-s sit-to-stand (30-STS), 6-min walk (6-MWT), and timed up-and-go (TUG) tests. There were improvements in the absolute and relative-to-bodyweight peak torque at 60°/s and 180°/s, TUG, 6-MWT and 30-STS in the RTP and RTP+PRO groups, but not in the CON and PRO groups. Changes in MS were significantly correlated with changes in PF between the pre- and post-intervention periods. A supervised resistance training program, regardless of protein supplementation, improved MS and PF in the mid-to-long-term period after RYGB and can lead to clinical benefits and improved quality of life.

Acute effects of different rest intervals between agonist-antagonist paired-sets in the neuromuscular system performance of young adults

INTRODUCTION

The agonist-antagonist paired-sets (APS) is a resistance training that involves alternating between exercises for agonist/antagonist muscles of a joint, with little or no rest between then. There is evidence that APS is more strenuous than traditional methods, but evidence on the optimal RI between agonist-antagonist actions is unknown.

OBJECTIVE

The aim of this study was to compare different rest intervals between agonist-antagonist actions during APS in young adults.

METHOD

Fifty healthy men (mean age 23.2 ± 2.8 years; 1.76 ± 0.1m height, 78.03 ± 8.1 kg) were included and performed three different agonist-antagonist paired-sets protocols separated by 72h, consisting of 4 sets of 10 repetitions. The protocols differed in terms of the rest interval between the knee flexion and extension movements: 0s (no rest); 60s and 120s. The rest intervals between exercise sets were standardized at 60s. Total work, peak torque, neuromuscular efficiency, surface EMG amplitude (sEMG, root mean square) and fatigue index obtained by processing of sEMG signal, were compared between rest intervals and exercise sets within each protocol.

RESULTS

There were no significant differences between rest intervals for total work, peak torque and neuromuscular efficiency (P > 0.05), but significant differences were found for sEMG and fatigue (P < 0.01), in which the protocol with 60s interval resulted in greater fatigue.

CONCLUSION

We showed that peak torque, total work and neuromuscular efficiency were not different between RI. The 60s RI showed a lower sEMG and a greater muscle fatigue. Although there were no significant differences, the NME was higher in the 60s interval.

Neuromuscular efficiency of men with high and low spinal cord injury levels compared with non-disabled participants

BACKGROUND: The neuromuscular efficiency index (NME) is defined as the individual ability to generate force in relation to the muscle activation level and might be useful to the assessment of individuals with spinal cord injury (SCI) and might elucidate the modifications in strength after an SCI compared to non-disabled subjects (CG). OBJECTIVE: Verify if the NME of fully and partially preserved muscles discriminate men with low and high levels of SCI and a matched non-disabled CG. METHODS: Fifty-four men with SCI were stratified into the high (HP), and low (LP) paraplegia groups and twenty-seven non-disabled individuals were selected (CG). All subjects performed maximum strength tests in the isokinetic dynamometer for shoulder abduction/adduction (isokinetic) and trunk flexion/extension (isometric). Surface electromyography was measured to calculate the NME, and discriminant analysis was carried out to identify which NME variables would be able to discriminate HP, LP, and CG. RESULTS: There were no NME significant differences between groups for the primary muscles of the shoulder abduction/adduction. All NME data failed at discriminant tolerance test to compare HP from LP. The latissimus dorsi NME during trunk extension discriminated CG from HP and LP. CONCLUSIONS: The latissimus dorsi NME during trunk extension might be used as an assessment tool to compare SCI individuals and the non-disabled-matched controls. The authors recommend using the NME index for the analysis or comparisons between the same SCI levels.

Effect of a 6-week strength-training program on neuromuscular efficiency in type 2 diabetes mellitus patients

Background

The neuromuscular system generates human movement. The functional capacity of the neuromuscular system in patients with type 2 diabetes mellitus (T2DM) is decreased and this affects the generation of muscle force. Exercise is recommended as an effective treatment in such cases. Short-duration strength training causes neural adaptations in healthy participants, but the effects of strength training on T2DM are unclear. The present study aimed to evaluate the effect of strength training on neuromuscular efficiency of lower limb muscles in T2DM.

Methods

Surface electromyograms (SEMG) of the knee flexors and extensors were recorded during isometric contractions. The ratio of peak torque to SEMG amplitude was calculated as neuromuscular efficiency. Measurements were taken before the intervention after 6 weeks of non-training, and after 6 weeks of strength training.

Results

SEMG amplitudes did not differ among the subsequent measurement sessions. Flexor and extensor peak torque increased after the strength-training program. The neuromuscular efficiency of all muscles increased after the 6 weeks of strength training.

Conclusion

A 6-week strength-training program increased the neuromuscular efficiency and peak torque in patients with T2DM; however, the electrical properties of the muscles did not change. These results may be related to increased neural adaptations and motor learning in the early stages of strength training.

Muscle excitation, force response, and efficiency during explosive force production after diacutaneous fibrolysis on lateral gastrocnemius of recreational athletes

OBJECTIVE

Fibrous adhesions impair normal muscle mechanics. The present study aimed to assess lateral gastrocnemius muscle excitation, isometric force response, and neuromuscular efficiency during explosive force in plantarflexion before and after diacutaneous fibrolysis.

METHODS

Thirty-five recreational athletes were allocated in the intervention group (n = 20) treated with diacutaneous fibrolysis, while the sham group (n = 15) was treated with placebo diacutaneous fibrolysis. Force response synchronized with surface electromyography during a plantarflexion task was collected.

RESULTS

Differences between Pre- and Post-diacutaneous fibrolysis were observed for all variables, except for the placebo group.

CONCLUSIONS

Diacutaneous fibrolysis was effective to increase force, muscle excitation, and neuromuscular efficiency on lateral gastrocnemius.

Construct validity of gymnastics-specific assessment on the neuromuscular function of shoulder flexor and extensor muscles

The present study examined the construct validity of gymnastics-specific measurements of the shoulder flexor and extensor neuromuscular function. Fifteen male gymnasts and 18 male physical education (PE) students participated voluntarily. The electromyogram (EMG) of 3 flexor and 3 extensor shoulder muscles was assessed during isometric (45, 90, and 135º) and isokinetic (concentric and eccentric 60, 180, and 300º/s) shoulder flexion/extension. Peak torque (PT) and neuromuscular function in terms of neuromuscular efficiency (NME, i.e. torque to EMG ratio) and antagonist/agonist coactivation index were evaluated. The construct validity of the measurements was supported by the ability to discriminate between gymnasts and physical education (PE) students, taking into consideration the shoulders' neuromuscular function parameters (37%-57% of the variability explained). After accounting for the limitations of the study, these findings may assist gymnastics coaches and researchers to develop and evaluate more effective training methods for athletes related to shoulder joint physiological characteristics and level of expertise.

Does sEMG normalization change results on sex differences in the activation of the shoulder girdle muscles during a simulated work task?

The aim was to investigate if the method of normalizing surface electromyography (sEMG) can change results on sex differences in the muscular activation of the shoulder girdle muscles during a simulated work task. sEMG was recorded in 36 asymptomatic participants (17 females, 19 males) from four parts of trapezius and from serratus anterior muscles during a simulated work task. Four normalization methods, one involving maximal voluntary contractions (MVCs) and three involving submaximal voluntary contractions were applied. Sex differences in absolute and normalized amplitude of sEMG were analyzed. The normalization method had a significant influence on the observed sex differences. Females only showed higher sEMG amplitude than males when the sEMGs were normalized to MVC and to a submaximal contraction based on 20% of MVC for the upper trapezius (acromial fibers). Researchers and practitioners should be aware of the impact of the sEMG normalization method in sex differences investigation.

Neuromuscular efficiency of the multifidus muscle in pilates practitioners and non-practitioners

BACKGROUND

Pilates exercises help stabilize the vertebral segments by recruiting the abdominal and spinal muscles. Pilates training may increase joint stability and improve neuromuscular efficiency (NME).

OBJECTIVE

This study aimed to evaluate NME of the multifidus (MU) muscle through electromyography (EMG) analysis and torque test, applied to practitioners and non-practitioners of Pilates.

METHODS

Participants included thirty women: Pilates practitioners (n = 15) and non-practitioners (n = 15). They were tested for trunk extension. Their right and left MU muscles were submitted to EMG to estimate NME. Results concerning torque, EMG, and NME from all participants were compared.

RESULTS

Statistical analysis concerning isometric torque peak (p = 0.0275) and NME (p = 0.0062) showed significant difference (Student t test; p < 0.05) between practitioners and control. No significant difference (p = 0.3387) in EMG was observed.

CONCLUSION

Our results suggest Pilates exercises is effective in training spinal muscles to improve NME in women.

Postural- and respiratory-related activities of abdominal muscles during post-exercise hyperventilation

The present study focuses on the role of superficial abdominal muscles revealed by electromyographic recordings during the maintenance of a bipedal stance perturbed by post-exercise hyperventilation. Twelve healthy subjects performed six 30-s postural tests: one pre-exercise test while breathing quietly, then one test every minute for the 5 min immediately following a maximum-intensity, incremental cycling exercise test. Displacement of the centre of pressure in the sagittal plane was monitored over time. Myoelectric activities of the obliquus externus (OE), obliquus internus (OI) and rectus abdominis (RA) muscles were recorded by surface electromyography (EMG). Metabolic parameters were measured with a portable telemetric device. The change in ventilatory drive induced by exercise was accompanied by a significant increase in both postural sway parameters and EMG activities. For OE and OI, the increased EMG activities were prominent during expiration, whereas OI was silent during inspiration. OE and RA were activated during both expiration and inspiration. It is concluded that the compensation of respiratory disturbances of the erect posture appears to be less effective when minute ventilation increases. The patterns of muscle activity suggest that abdominal muscles are controlled differentially and that their functional coordination is dependent on the respiratory demand.

Large asymmetric hypertrophy of rectus abdominis muscle in professional tennis players

PURPOSE

To determine the volume and degree of asymmetry of the musculus rectus abdominis (RA) in professional tennis players.

METHODS

The volume of the RA was determined using magnetic resonance imaging (MRI) in 8 professional male tennis players and 6 non-active male control subjects.

RESULTS

Tennis players had 58% greater RA volume than controls (P = 0.01), due to hypertrophy of both the dominant (34% greater volume, P = 0.02) and non-dominant (82% greater volume, P = 0.01) sides, after accounting for age, the length of the RA muscle and body mass index (BMI) as covariates. In tennis players, there was a marked asymmetry in the development of the RA, which volume was 35% greater in the non-dominant compared to the dominant side (P<0.001). In contrast, no side-to-side difference in RA volume was observed in the controls (P = 0.75). The degree of side-to-side asymmetry increased linearly from the first lumbar disc to the pubic symphysis (r = 0.97, P<0.001).

CONCLUSIONS

Professional tennis is associated with marked hypertrophy of the musculus rectus abdominis, which achieves a volume that is 58% greater than in non-active controls. Rectus abdominis hypertrophy is more marked in the non-dominant than in the dominant side, particularly in the more distal regions. Our study supports the concept that humans can differentially recruit both rectus abdominis but also the upper and lower regions of each muscle. It remains to be determined if this disequilibrium raises the risk of injury.