The Effect of Resistance Training on Motor Unit Firing Properties: A Systematic Review and Meta-Analysis

A Randomized Controlled Trial to Determine the Impact of Resistance Training versus Aerobic Training on the Management of FGF-21 and Related Physiological Variables in Obese Men with Type 2 Diabetes Mellitus

Fibroblast growth factor 21 (FGF-21) has been suggested as a potential therapeutic target for insulin resistance in health-related metabolic disorders such as type 2 diabetes. Despite the metabolic effects of resistance (RT) and aerobic training (AT) on diabetes symptoms, uncertainty exists regarding the superiority of effects manifested through these training approaches on FGF-21 and biochemical and physiological variables associated with metabolic disorders in men diagnosed with type 2 diabetes. This study aimed to investigate the impact of a 12-week RT and AT on FGF-21 levels and symptoms associated with metabolic disorders in male individuals diagnosed with type 2 diabetes. Thirty-six sedentary obese diabetic men (40 to 45 years old) were matched based on the level of FGF-1. They and were randomly divided into two training groups (RT, n = 12 and AT, n = 12) performing three days per week of moderate-intensity RT or AT for 12 weeks and an inactive control group (n = 12). Both training interventions significantly improved FGF-21, glucose metabolism, lipid profile, hormonal changes, strength, and aerobic capacity. Subgroup analysis revealed that RT had greater adaptive responses (p < 0.01) in fasting blood sugar (ES = -0.52), HOMA-IR (ES = -0.87), testosterone (ES = 0.52), cortisol (ES = -0.82), FGF-21 (ES = 0.61), and maximal strength (ES = 1.19) compared to AT. Conversely, AT showed greater changes (p < 0.01) in cholesterol (ES = -0.28), triglyceride (ES = -0.64), HDL (ES = 0.46), LDL (ES = -0.73), and aerobic capacity (ES = 1.18) compared to RT. Overall, both RT and AT interventions yielded significant moderate to large ES in FGF-21 levels and enhanced the management of biochemical variables. RT is an effective method for controlling FGF-21 levels and glucose balance, as well as for inducing hormonal changes. On the other hand, AT is more suitable for improving lipid profiles in overweight men with type 2 diabetes mellitus.

The effects of a two-week neuromuscular intervention on biopsychosocial variables in people with patellofemoral pain: an observational study

Introduction

Patellofemoral pain (PFP) is common and predominately affects active populations. Altered biomechanics and psychosocial variables have been reported in people with PFP, but the effects of neuromuscular exercise on these variables is unknown. We aimed to investigate changes in biopsychosocial measures following a two-week neuromuscular intervention in people with PFP.

Materials and Methods

We measured pain (visual analogue scale), function (Kujala), activity level (Tegner), psychological well-being (Orebro), lower-limb isometric strength (handheld dynamometry), three-dimensional (3D) lower limb kinematics, and surface electromyography (sEMG), in people with PFP. 3D lower-limb kinematics and sEMG were synchronously sampled during step-up, step-down, and overground running. All measures were repeated after participants had completed a two-week neuromuscular intervention consisting of three exercises completed once per day, five days per week.

Results

18 participants completed pre/post testing (60% females, mean age 30.6 years ±7.0, height 173.4cm ±10.4, mass 70.2kg ±12.4, symptom duration 39.0 months ±58.8), with three of 21 participants lost to follow-up. Across all clinical measures (muscle onsets, muscle activation and kinematics), the 95% bootstrapped confidence intervals (CI) of the mean difference contained the null hypothesis following the two-week neuromuscular intervention, indicating no significant differences.

Conclusion

A two-week neuromuscular intervention did not change biomechanical or psychosocial measures in people with PFP. Interventions with a longer duration or greater load magnitude are required to fully evaluate the biopsychosocial mechanisms of effect for exercise in people with PFP.

Motor Unit Discharge Characteristics and Conduction Velocity of the Vastii Muscles in Long-Term Resistance-Trained Men

PURPOSE

Adjustments in motor unit (MU) discharge properties have been shown after short-term resistance training; however, MU adaptations in long-term resistance-trained (RT) individuals are less clear. Here, we concurrently assessed MU discharge characteristics and MU conduction velocity in long-term RT and untrained (UT) men.

METHODS

Motor unit discharge characteristics (discharge rate, recruitment, and derecruitment threshold) and MU conduction velocity were assessed after the decomposition of high-density electromyograms recorded from vastus lateralis (VL) and vastus medialis (VM) of RT (>3 yr; n = 14) and UT ( n = 13) during submaximal and maximal isometric knee extension.

RESULTS

Resistance-trained men were on average 42% stronger (maximal voluntary force [MVF], 976.7 ± 85.4 N vs 685.5 ± 123.1 N; P < 0.0001), but exhibited similar relative MU recruitment (VL, 21.3% ± 4.3% vs 21.0% ± 2.3% MVF; VM, 24.5% ± 4.2% vs 22.7% ± 5.3% MVF) and derecruitment thresholds (VL, 20.3% ± 4.3% vs 19.8% ± 2.9% MVF; VM, 24.2% ± 4.8% vs 22.9% ± 3.7% MVF; P ≥ 0.4543). There were also no differences between groups in MU discharge rate at recruitment and derecruitment or at the plateau phase of submaximal contractions (VL, 10.6 ± 1.2 pps vs 10.3 ± 1.5 pps; VM, 10.7 ± 1.6 pps vs 10.8 ± 1.7 pps; P ≥ 0.3028). During maximal contractions of a subsample population (10 RT, 9 UT), MU discharge rate was also similar in RT compared with UT (VL, 21.1 ± 4.1 pps vs 14.0 ± 4.5 pps; VM, 19.5 ± 5.0 pps vs 17.0 ± 6.3 pps; P = 0.7173). Motor unit conduction velocity was greater in RT compared with UT individuals in both VL (4.9 ± 0.5 m·s -1 vs 4.5 ± 0.3 m·s -1 ; P < 0.0013) and VM (4.8 ± 0.5 m·s -1 vs 4.4 ± 0.3 m·s -1 ; P < 0.0073).

CONCLUSIONS

Resistance-trained and UT men display similar MU discharge characteristics in the knee extensor muscles during maximal and submaximal contractions. The between-group strength difference is likely explained by superior muscle morphology of RT as suggested by greater MU conduction velocity.

An Integrated Approach to Skeletal Muscle Health in Aging

A decline in muscle mass and function represents one of the most problematic changes associated with aging, and has dramatic effects on autonomy and quality of life. Several factors contribute to the inexorable process of sarcopenia, such as mitochondrial and autophagy dysfunction, and the lack of regeneration capacity of satellite cells. The physiologic decline in muscle mass and in motoneuron functionality associated with aging is exacerbated by the sedentary lifestyle that accompanies elderly people. Regular physical activity is beneficial to most people, but the elderly need well-designed and carefully administered training programs that improve muscle mass and, consequently, both functional ability and quality of life. Aging also causes alteration in the gut microbiota composition associated with sarcopenia, and some advances in research have elucidated that interventions via the gut microbiota-muscle axis have the potential to ameliorate the sarcopenic phenotype. Several mechanisms are involved in vitamin D muscle atrophy protection, as demonstrated by the decreased muscular function related to vitamin D deficiency. Malnutrition, chronic inflammation, vitamin deficiencies, and an imbalance in the muscle-gut axis are just a few of the factors that can lead to sarcopenia. Supplementing the diet with antioxidants, polyunsaturated fatty acids, vitamins, probiotics, prebiotics, proteins, kefir, and short-chain fatty acids could be potential nutritional therapies against sarcopenia. Finally, a personalized integrated strategy to counteract sarcopenia and maintain the health of skeletal muscles is suggested in this review.

Motor point heatmap guide for neuromuscular electrical stimulation of the quadriceps muscle

PURPOSE

To create an anatomical chart that indicates the probability of finding a motor point (MP) in different areas of the quadriceps muscle.

METHODS

On 31 healthy adults, the individual anatomy of the vastus medialis (VM), rectus femoris (RF) and vastus lateralis (VL) was determined using ultrasound. Thereafter, a 3 Hz neuromuscular electrical stimulation (NMES) MP-search with a MP-pen was performed. The thigh anatomy was normalized and divided into 112 (8x14) 3x3cm areas, and the probability of finding a MP in the different areas was calculated to create a MP heat-map.

RESULTS

The heat-map displayed the two best 3x3cm areas, over VL and VM respectively, each with a probability greater than 50% of finding a MP and a higher probability compared to all other areas (p <.05). RF exhibited two areas with a 29% probability of finding a MP. A higher number of MPs on the quadriceps, mean (±SD) 9.4 ± 1, was in regression analysis found to be significantly associated with two independent factors higher physical activity level and lower body fat (R² = 0.42, p=<.0001).

CONCLUSION

Large inter-individual variations in location, and number of MPs were found, but the heat-map displayed areas with higher probability of finding a MP and can be used to facilitate NMES-application.

Additional Active Movements Are Not Required for Strength Gains in the Untrained during Short-Term Whole-Body Electromyostimulation Training

Recommendations for conventional strength training are well described, and the volume of research on whole-body electromyostimulation training (WB-EMS) is growing. The aim of the present study was to investigate whether active exercise movements during stimulation have a positive effect on strength gains. A total of 30 inactive subjects (28 completed the study) were randomly allocated into two training groups, the upper body group (UBG) and the lower body group (LBG). In the UBG (n = 15; age: 32 (25-36); body mass: 78.3 kg (53.1-114.3 kg)), WB-EMS was accompanied by exercise movements of the upper body and in the LBG (n = 13; age: 26 (20-35); body mass: 67.2 kg (47.4-100.3 kg)) by exercise movements of the lower body. Therefore, UBG served as a control when lower body strength was considered, and LBG served as a control when upper body strength was considered. Trunk exercises were performed under the same conditions in both groups. During the 20-min sessions, 12 repetitions were performed per exercise. In both groups, stimulation was performed with 350 μs wide square pulses at 85 Hz in biphasic mode, and stimulation intensity was 6-8 (scale 1-10). Isometric maximum strength was measured before and after the training (6 weeks set; one session/week) on 6 exercises for the upper body and 4 for the lower body. Isometric maximum strength was significantly higher after the EMS training in both groups in most test positions (UBG p < 0.001-0.031, r = 0.88-0.56; LBG p = 0.001-0.039, r = 0.88-0.57). Only for the left leg extension in the UBG (p = 0.100, r = 0.43) and for the biceps curl in the LBG (p = 0.221, r = 0.34) no changes were observed. Both groups showed similar absolute strength changes after EMS training. Body mass adjusted strength for the left arm pull increased more in the LBG group (p = 0.040, r = 0.39). Based on our results we conclude that concurring exercise movements during a short-term WB-EMS training period have no substantial influence on strength gains. People with health restrictions, beginners with no experience in strength training and people returning to training might be particularly suitable target groups, due to the low training effort. Supposedly, exercise movements become more relevant when initial adaptations to training are exhausted.

Consensus for experimental design in electromyography (CEDE) project: Single motor unit matrix

The analysis of single motor unit (SMU) activity provides the foundation from which information about the neural strategies underlying the control of muscle force can be identified, due to the one-to-one association between the action potentials generated by an alpha motor neuron and those received by the innervated muscle fibers. Such a powerful assessment has been conventionally performed with invasive electrodes (i.e., intramuscular electromyography (EMG)), however, recent advances in signal processing techniques have enabled the identification of single motor unit (SMU) activity in high-density surface electromyography (HDsEMG) recordings. This matrix, developed by the Consensus for Experimental Design in Electromyography (CEDE) project, provides recommendations for the recording and analysis of SMU activity with both invasive (needle and fine-wire EMG) and non-invasive (HDsEMG) SMU identification methods, summarizing their advantages and disadvantages when used during different testing conditions. Recommendations for the analysis and reporting of discharge rate and peripheral (i.e., muscle fiber conduction velocity) SMU properties are also provided. The results of the Delphi process to reach consensus are contained in an appendix. This matrix is intended to help researchers to collect, report, and interpret SMU data in the context of both research and clinical applications.

Effect of resistance circuit training on health-related physical fitness, plasma lipid, and adiponectin in obese college students

The purpose of this study is to investigate the effects of resistance circuit training on health-related physical fitness, plasma lipid and adiponectin in obese college students. Twenty male college students participated in this study and they were randomly divided into the sedentary group (SG, n=10) and the resistance circuit training group (RCG, n=10). The exercise group underwent the resistance circuit training program for 60 min 3 times a week for 12 weeks, while the sedentary group continued activities of daily living as usual. The levels of health-related fitness, blood lipid, and adiponectin were measured twice before and after the experiment. To analyze the statistically significance of collected data, Two-way repeated measure analysis of variance was used to determine the changes in the groups over the training period. A paired t-test was used to verify the difference within each group, and an independent t-test was used to verify the difference between the groups. In this study, the body composition including body fat mass, percent body fat and body mass index were significantly decreased in RCG compared to those in SG, and the health-related fitness showed a significant difference between RCG and SG. In addition, RCG positively modulated blood concentration of total cholesterol, triglycerides, high-density and low-density lipoprotein cholesterol. However, plasma adiponectin concentration did not show any significant differences between the two groups. Therefore, the present data suggested that resistance circuit training might be regulator to improve health-related physical fitness and decrease the level of plasma lipid in obese male college students.

Effects of plyometric training on skill and physical performance in healthy tennis players: A systematic review and meta-analysis

Background: Plyometric training (PT) has been researched extensively in athletic populations. However, the effects of PT on tennis players are less clear. Methods: We aim to consolidate the existing research on the effects of PT on healthy tennis players' skill and physical performance. On 30th May 2022, a comprehensive search of SCOPUS, PubMed, Web of Science, and SPORTDiscus (via EBSCOhost) databases was performed. PICOS was employed to define the inclusion criteria: 1) healthy tennis players; 2) a PT program; 3) compared a plyometric intervention to a control group or another exercise group, and single-group trials; 4) tested at least one measures of tennis skill or physical performance; and 5) non-randomized study trials and randomized control designs. Individual studies' methodological quality was evaluated by using the Cochrane RoB-2 and ROBINS-I instruments. Using Grading of Recommendations Assessment, Development, and Evaluation (GRADE), the certainty of the body of evidence for each outcome was assessed, and Comprehensive Meta-Analysis software was employed for the meta-analysis. Results: Twelve studies comprising 443 tennis players aged 12.5-25 years were eligible for inclusion. The PT lasted from 3 to 9 weeks. Eight studies provided data to allow for the pooling of results in a meta-analysis. A moderate positive effect was detected for PT programs on maximal serve velocity (ES = 0.75; p < 0.0001). In terms of measures of physical performance, small to moderate (ES = 0.43-0.88; p = 0.046 to < 0.001) effects were noted for sprint speed, lower extremity muscle power, and agility. While no significant and small effect was noted for lower extremity muscle strength (ES = 0.30; p = 0.115). We found no definitive evidence that PT changed other parameters (i.e., serve accuracy, upper extremity power and strength, reaction time, and aerobic endurance). Based on GRADE, the certainty of evidence across the included studies varied from very low to moderate. Conclusion: PT may improve maximal serve velocity and physical performance components (sprint speed, lower extremity muscular power, and agility) for healthy tennis players; however, more high-quality evidence about the effects of PT on the skill and physical performance of tennis players merits further investigation. Systematic Review Registration: [https://inplasy.com/], identifier [INPLASY202250146].

Training induced improvements in knee extensor force accuracy are associated with reduced vastus lateralis motor unit firing variability

NEW FINDINGS

What is the central question of this study? We aimed to determine levels of bilateral knee extensor force accuracy and any subsequent alterations to central and/or peripheral motor unit features, following 4 weeks of unilateral force accuracy training. What is the main finding and its importance? In the trained limb only, knee extensor force tracking accuracy improved with reduced motor unit firing rate variability in the vastus lateralis, and no change to neuromuscular junction transmission instability. Interventional strategies to improve force accuracy may be directed to older/clinical populations where such improvements may aid performance of daily living activities.

ABSTRACT

Background Muscle force output during sustained submaximal isometric contractions fluctuates around an average value and is partly influenced by variation in motor unit (MU) firing rates. MU firing rate (FR) variability seemingly reduces following exercise training interventions, however, much less is known with respect to peripheral MU properties. We therefore investigated whether targeted force accuracy training could lead to improved muscle functional capacity and control, in addition to determining any alterations of individual MU features. Methods Ten healthy participants (7 females, 3 males, 27±6 years, 170±8 cm, 69±16kg) underwent a 4-week supervised, unilateral knee extensor force accuracy training intervention. The coefficient of variation for force (FORCE^CoV ) and sinusoidal wave force tracking accuracy (FORCE^Sinu ) were determined at 25% maximal voluntary contraction (MVC) pre- and post-training. Intramuscular electromyography was utilised to record individual MU potentials from the vastus lateralis (VL) muscles at 25% MVC during sustained contractions, pre- and post-training. Results Knee extensor muscle strength remained unchanged following training, with no improvements in unilateral leg-balance. FORCE^CoV and FORCE^Sinu significantly improved in only the trained knee extensors by ∼13% (p = 0.01) and ∼30% (p<0.0001) respectively. MU FR variability significantly reduced in the trained VL by ∼16% (n = 8; p = 0.001), with no further alterations to MU FR or neuromuscular junction transmission instability. Conclusion Our results suggest muscle force control and tracking accuracy is a trainable characteristic in the knee extensors, which is likely explained by the reduction in MU FR variability which was apparent in the trained limb only. This article is protected by copyright. All rights reserved.