Assessment of Skeletal Muscle Contractile Properties by Radial Displacement: The Case for Tensiomyography

Muscle contraction time after caffeine intake is faster after 30 minutes than after 60 minutes

BACKGROUND

This study aimed to determine the optimal time point, either 30 or 60 minutes, at which muscle reactivity to caffeine administration is highest. Unlike previous studies that focused on the nervous system response, we employed tensiomyography (TMG) to directly assess the effects of caffeine on muscle fibers.

METHODS

TMG measurements were performed on the gastrocnemius medialis muscle of 42 male athletes who regularly consumed caffeine. Participants received a dose of 6 mg/kg body weight and TMG measurements were taken prior to caffeine intake, as well as 30 and 60 minutes afterward.

RESULTS

Analysis of TMG parameters including time to contraction (Tc), time delay (Td), and maximal displacement (Dm) revealed that muscles exhibited faster contractions and greater stiffness at the 30-minute mark compared to both pre-caffeine intake and the 60-minute time point. Time exerted a significant main effect on Tc (F(2, 246) = 12.09, p < .001, ή2p = 0.09), Td (F(2, 246) = 3.39, p = .035, ή2p = 0.03), and Dm (F(2, 246) = 6.83, p = .001, ή2p = 0.05), while no significant effect of body side was observed.

CONCLUSIONS

The findings indicate that muscle contraction time (Tc) and delay time (Td) are influenced by the time elapsed since caffeine ingestion, with the fastest responses occurring after 30 minutes. Additionally, a systemic effect of caffeine was observed, as there were no discernible differences in measurements between the two sides of the body. TMG proves to be an effective noninvasive method for assessing muscle responses following caffeine administration.

Innovations in the Assessment of Skeletal Muscle Health: A Glimpse into the Future

Skeletal muscle is the largest organ system in the human body and plays critical roles in athletic performance, mobility, and disease pathogenesis. Despite growing recognition of its importance by major health organizations, significant knowledge gaps remain regarding skeletal muscle health and its crosstalk with nearly every physiological system. Relevant public health challenges like pain, injury, obesity, and sarcopenia underscore the need to accurately assess skeletal muscle health and function. Feasible, non-invasive techniques that reliably evaluate metrics including muscle pain, dynamic structure, contractility, circulatory function, body composition, and emerging biomarkers are imperative to unraveling the complexities of skeletal muscle. Our concise review highlights innovative or overlooked approaches for comprehensively assessing skeletal muscle in vivo. We summarize recent advances in leveraging dynamic ultrasound imaging, muscle echogenicity, tensiomyography, blood flow restriction protocols, molecular techniques, body composition, and pain assessments to gain novel insight into muscle physiology from cellular to whole-body perspectives. Continued development of precise, non-invasive tools to investigate skeletal muscle are critical in informing impactful discoveries in exercise and rehabilitation science.

Shoulder Tensiomyography and Isometric Strength in Swimmers Before and After a Fatiguing Protocol

CONTEXT

Shoulder muscles are active during front-crawl swimming to provide propulsion and stabilize the glenohumeral and scapulothoracic joints. Researchers have proposed that fatigue might contribute to altered activation of these muscles and represent a risk factor for injuries. Tensiomyography (TMG) might function as a noninvasive tool to detect changes in contractile measures of the skeletal muscles due to exercise-induced neuromuscular fatigue, though it has not yet been used in the shoulder muscles of swimmers.

OBJECTIVE

To assess the effects of a fatiguing swimming protocol on shoulder muscle TMG measures and isometric strength in competitive swimmers.

DESIGN

Cross-sectional study.

SETTING

Swimming pool facility.

PATIENTS OR OTHER PARTICIPANTS

A total of 14 young front-crawl competitive swimmers (11 males and 3 females; age = 21 ± 3 years [range, 17-26 years], height = 1.78 ± 0.06 m, mass = 73.1 ± 9.2 kg).

MAIN OUTCOME MEASURE(S)

Participants completed TMG and isometric strength assessments before and after 30-minute, high-intensity swim training. The TMG assessment was performed on 7 muscles of the shoulder according to front-crawl biomechanics and the applicability of the technique to obtain data, such as time to contraction and muscle-belly radial displacement. Isometric strength was assessed using a digital handheld dynamometer during shoulder flexion, extension, external rotation, and internal rotation.

RESULTS

Fatigue induced a smaller radial displacement, mostly observable in latissimus dorsi (-1.0 mm; 95% CI = -1.7, -0.3 mm; P = .007) and pectoralis major muscles (-1.4 mm; 95% CI = -2.4, -0.4 mm; P = .007). Only shoulder extension showed an isometric strength reduction after the fatiguing protocol (-0.03 N/kg; 95% CI = -0.05, -0.01 N/kg; F1,13 = 4.936; P = .045; ηp2 = 0.275).

CONCLUSIONS

This study provides preliminary evidence for the usefulness of TMG to detect fatigue-induced changes in contractile properties of the shoulder muscles in swimmers, in particular the latissimus dorsi and pectoralis major.

Identification of Peripheral Fatigue through Exercise-Induced Changes in Muscle Contractility

The aim of this study was to assess whether tensiomyography is a tool sensitive enough to detect peripheral fatigue. Twenty-six strength-trained men were split into two groups: 1) a fatigued group (FG), who performed a full-squat (SQ) standardized warm-up plus 3 x 8 SQs with 75% 1RM with a 5-min rest interval, and 2) a non-fatigued group (NFG), who only did the SQ standardized warm-up. The countermovement jump (CMJ), maximal isometric force (MIF) in the SQ at 90º knee flexion, and TMG in vastus medialis (VM) and vastus lateralis (VL) muscles were assessed pre- and post-protocols. Data were analyzed through mixed ANOVA, logistic regression analysis, and receiver-operating curves. There were significant group x time interactions (p < 0.01) for CMJ height, MIF, maximal radial displacement (Dm), and radial displacement velocity (Vrd90) since the FG acutely decreased in these variables, while no significant changes were observed for the NFG. The logistic regression showed a significant model for detecting fatigue, whether it used the CMJ or MIF, with only the relative change in VL-Vrd90 as a fatigue predictor. The determination of the area under the curve showed that Dm and Vrd90 had good to excellent discriminative ability. Dm and Vrd90 are sensitive to detect fatigue in VL and VM muscles in resistance training contexts.

Emerging Wearable Ultrasound Technology

This perspective article provides a brief overview on materials, fabrications, beamforming, and applications for wearable ultrasound devices, a rapidly growing field with versatile implications. Recent developments in miniaturization and soft electronics have significantly advanced wearable ultrasound devices. Such devices offer distinctive advantages over traditional ultrasound probes, including prolonged usability and operator independence, and have demonstrated their effectiveness in continuous monitoring, noninvasive therapies, and advanced human-machine interfaces. Wearable ultrasound devices can be classified into three main categories: rigid, flexible, and stretchable, each having distinctive properties and fabrication strategies. Key unique strategies in device design, packaging, and beamforming for each type of wearable ultrasound devices are reviewed. Furthermore, we highlight the latest applications enabled by wearable ultrasound technology in various areas. This article concludes by discussing the outstanding challenges within the field and outlines potential pathways for future advancements.

The association between unilateral and bilateral performance-related measures in elite female soccer players: a multifaceted investigation

Purpose

The present study aimed to investigate a) the associations between bilateral performance utilizing countermovement jump (CMJ), squat jump (SJ), speed and unilateral CMJ, isokinetic peak torque in knee extension and flexion with angular velocities of 60°/s and 180°/s and tensiomyography (TMG) parameters; b) whether the asymmetries derived from unilateral tests are associated with bilateral CMJ, SJ and speed in elite female soccer players.

Methods

Thirty-five elite female soccer players (average age: 20 ± 5 years) completed CMJ, SJ, speed, isokinetic muscle strength and TMG tests.

Results

Compared to the non-dominant leg, the dominant leg demonstrated greater peak torque output in both knee flexion (7.4%) and knee extension (5.6%) isokinetic tasks, as well as m. vastus medialis contraction time (7.6%), and soccer-specific agility test (4.1%). Conversely, the hamstring to quadriceps peak torque ratio at 180°/s (8.5%) was significantly greater in the non-dominant leg. The associations between CMJ, SJ and speed performance were positive and ranged from weak (r = 0.350) to high (r = 0.710). For speed and TMG-derived variables, correlations were negative and ranged from weak (r = -0.345, p = 0.042, for vastus medialis contraction time) to moderate (r = -0.530, p = 0.001, for biceps femoris contraction time). Furthermore, both bilateral CMJ and SJ negatively correlated with TMG-derived variables, ranging from weak (r = -0.350, p = 0.039, for vastus lateralis contraction time) to moderate (r = -0.537, p = 0.003, for rectus femoris contraction time).

Conclusion

The overall significant, albeit inconsistent, correlations between the diverse performance scores obtained highlight the necessity for a multifaceted and thorough diagnostic strategy in female soccer players.

Trunk muscles' characteristics in adolescent gymnasts with low back pain: a pilot study on the effects of a physiotherapy intervention including a postural reeducation program

BACKGROUND

Trunk muscles' function and characteristics are of great importance for both static and dynamic tasks in different sports, and abnormalities of trunk flexors and extensors might be associated with low back pain (LBP). The aim of this study was to provide a comprehensive evaluation of the functional, morphological and contractile properties in trunk flexors and extensors of young gymnasts with and without LBP.

METHODS

Young gymnasts (14/25 females, 14-18 y) were screened for the presence of chronic LBP. Abdominal and lumbar muscles were tested for function (McGill's endurance tests), thickness (ultrasound), and contractile responses (tensiomyography). An 8-sessions physiotherapy intervention including postural reeducation was performed by a subsample of 10 subjects with LBP.

RESULTS

LBP was found to be associated to higher flexors-to-extensors endurance ratio (OR 11.250, 95% CI: 1.647-76.849, p = 0.014), reduced mean lumbar multifidus thickness (OR 16.500, 95% CI: 2.246-121.228, p = 0.006), and reduced mean erector spinae radial displacement (OR 16.500, 95% CI: 2.246-121.228, p = 0.006). The physiotherapy intervention was found to reduce LBP symptoms and it was associated with a significant improvement in the flexors-to-extensors ratio (p < 0.001).

CONCLUSIONS

This study provides preliminary evidence of functional, morphological, and contractile trunk muscles' alterations associated with chronic LBP in young gymnasts, and presents the effects of a postural reeducation program on symptoms and muscles' functional properties.

Electromechanical efficiency index of skeletal muscle and its applicability: a systematic review

Introduction: The electromechanical efficiency of skeletal muscle represents the dissociation between electrical and mechanical events within a muscle. It has been widely studied, with varying methods for its measurement and calculation. For this reason, the purpose of this literature review was to integrate the available research to date and provide more insights about this measure. Methods: A systematic search of the literature was performed across three online databases: PubMed, ScienceDirect, and SPORTDiscus. This yielded 1284 reports, of which 10 met the inclusion criteria. Included studies have used different methods to measure the electromechanical efficiency (EME) index, including electromyography (EMG), mechanomyography and tensiomyography (TMG). Results: The EME index was used to assess muscle conditions such as muscle atrophy, pain syndromes, or to monitor rehabilitation in patients with knee problems, fatigue and the effects of exercise and rehabilitation. TMG has been shown to be one of the most reliable methods to obtain the EME index, but its use precludes obtaining the index during voluntary muscle contractions. Conclusion: Standardizing the EME index is crucial for its diverse applications in clinical, sport, and rehabilitation contexts. Future research should prioritize standardization of measurement protocols for establishing the most repeatable, and reliable approach that can be used for inter-individual comparisons or for assessing an individual for multiple times over a longer period. Systematic Review Registration: https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42023440333 Identifier: CRD42023440333.

Accurate Identification of Motoneuron Discharges From Ultrasound Images Across the Full Muscle Cross-Section

OBJECTIVE

Non-invasive identification of motoneuron (MN) activity commonly uses electromyography (EMG). However, surface EMG (sEMG) detects only superficial sources, at less than approximately 10-mm depth. Intramuscular EMG can detect deep sources, but it is limited to sources within a few mm of the detection site. Conversely, ultrasound (US) images have high spatial resolution across the whole muscle cross-section. The activity of MNs can be extracted from US images due to the movements that MN activation generates in the innervated muscle fibers. Current US-based decomposition methods can accurately identify the location and average twitch induced by MN activity. However, they cannot accurately detect MN discharge times.

METHODS

Here, we present a method based on the convolutive blind source separation of US images to estimate MN discharge times with high accuracy. The method was validated across Ten participants using concomitant sEMG decomposition as the ground truth.

RESULTS

140 unique MN spike trains were identified from US images, with a rate of agreement (RoA) with sEMG decomposition of 87.4 ± 10.3%. Over 50% of these MN spike trains had a RoA greater than 90%. Furthermore, with US, we identified additional MUs well beyond the sEMG detection volume, at up to >30 mm below the skin.

CONCLUSION

The proposed method can identify discharges of MNs innervating muscle fibers in a large range of depths within the muscle from US images.

SIGNIFICANCE

The proposed methodology can non-invasively interface with the outer layers of the central nervous system innervating muscles across the full cross-section.

An Approach to Using Electrical Impedance Myography Signal Sensors to Assess Morphofunctional Changes in Tissue during Muscle Contraction

This present work is aimed at conducting fundamental and exploratory studies of the mechanisms of electrical impedance signal formation. This paper also considers morphofunctional changes in forearm tissues during the performance of basic hand actions. For this purpose, the existing research benches were modernized to conduct experiments of mapping forearm muscle activity by electrode systems on the basis of complexing the electrical impedance signals and electromyography signals and recording electrode systems' pressing force using force transducers. Studies were carried out with the involvement of healthy volunteers in the implementation of vertical movement of the electrode system and ultrasound transducer when the subject's upper limb was positioned in the bed of the stand while performing basic hand actions in order to identify the relationship between the morphofunctional activity of the upper limb muscles and the recorded parameters of the electro-impedance myography signal. On the basis of the results of the studies, including complex measurements of neuromuscular activity on healthy volunteers such as the signals of electro-impedance myography and pressing force, analyses of the morphofunctional changes in tissues during action performance on the basis of ultrasound and MRI studies and the factors influencing the recorded signals of electro-impedance myography are described. The results are of fundamental importance and will enable reproducible electro-impedance myography signals, which, in turn, allow improved anthropomorphic control.

Quantifying muscle contraction with a conductive electroactive polymer sensor: introduction to a novel surface mechanomyography device

Clinicians seek an accurate method to assess muscle contractility during activities to better guide treatment. We investigated application of a conductive electroactive polymer sensor as a novel wearable surface mechanomyography (sMMG) sensor for quantifying muscle contractility. The radial displacement of a muscle during a contraction is detected by the physically stretched dielectric elastomer component of the sMMG sensor which quantifies the changes in capacitance. The duration of muscle activation times for quadriceps, hamstrings, and gastrocnemius muscles demonstrated strong correlation between sMMG and EMG during a parallel squat activity and isometric contractions. A moderate to strong correlation was demonstrated between the sMMG isometric muscle activation times and force output times from a dynamometer. The potential wearable application of an electroactive polymer sensor to measure muscle contraction time is supported.

Assessment of the functional state of the back muscles in girls with C-shaped low-grade scoliosis in a tensiomyographic image: An observational cross-sectional study

PURPOSE

The study aimed to test the feasibility of using tensiomyography to assess the functional status of the latissimus dorsi and erector spinae muscles in girls with C-shaped low back scoliosis.

MATERIALS AND METHODS

Twenty-five girls aged 13-15 took part in an observational (cross-sectional) study. The examination involved measurements using the tensiomyography method (TMG). Two groups of muscles were tested: latissimus dorsi and erector spinae on the concave and convex side of low-grade scoliosis. The following indicators were analyzed: Td-delay time, Tc-contraction time, and Dm-maximal muscle displacement.

RESULTS

The analysis of Td revealed that values of this variable on the concave side were slightly lower compared to the convex side in both tested groups of muscles. Similarly, Tc values on the concave side were slightly lower than on the convex side of the curvature in both groups of muscles. In the case of Dm, lower displacement values and, consequently, greater muscle rigidity were observed on the concave side of the latissimus dorsi and the convex side of the erector spinae.

CONCLUSIONS

The TMG method can be potentially used to diagnose the functional condition of muscles in patients with low-grade scoliosis. There were differences between the functional condition of the muscles on the concave and convex sides of the curvature.

Contraction Velocity of the Elbow Flexors Assessed by Tensiomyography: A Comparison Between Formulas

ABSTRACT

Mesquita, RNO, Latella, C, Ruas, CV, Nosaka, K, and Taylor, JL. Contraction velocity of the elbow flexors assessed by tensiomyography: A comparison between formulas. J Strength Cond Res 37(10): 1969-1977, 2023-Muscle contraction velocity ( Vc ) assessed by tensiomyography is a promising measure for athlete profiling. Multiple formulas are used to estimate Vc , but the most suitable method is yet to be established. Fifteen adults (2 female subjects) underwent tensiomyography assessment of biceps brachii muscle at 10, 45 and 90° of elbow flexion on 2 separate days. Vc was calculated using 6 formulas. Formulas 1 and 2 are measures of the early phase of the twitch; Formulas 3-5 are measures over a wider time-window, with Formula 5 normalizing Vc to maximal displacement ( D m); and we proposed Formula 6 as a measure of peak Vc . Test-retest reliability, the required minimum number of trials, proportional bias, and effects of joint angle were investigated. Higher reliability (coefficient of variation: 2.8-6.9%) was found for Formula 1 (0-2 mm of displacement) and Formula 5 (normalized 10-90% of D m). Overall, a minimum of 6-7 trials was required to obtain reliable estimates. For 10° only, significant positive proportional bias ( r = 0.563-0.670) was found for all formulas except Formula 5. Vc was faster ( p < 0.001) at shorter muscle lengths for all formulas except Formula 5 ( p = 0.06). Vc in the early phase of the twitch was more reliable when calculated using absolute displacement (Formula 1) than a relative threshold (Formula 2). Over a larger time-window, Formulas 3 and 4 were similarly reliable. Because they are derived from different components of the twitch and different parameters, the different formulas should not be used interchangeably. Additionally, more precise nomenclature is required to describe the information obtained from each formula.

Enhanced skeletal muscle contractile function and corticospinal excitability precede strength and architectural adaptations during lower-limb resistance training

PURPOSE

Evolving investigative techniques are providing greater understanding about the early neuromuscular responses to resistance training among novice exercisers. The aim of this study was to investigate the time-course of changes in muscle contractile mechanics, architecture, neuromuscular, and strength adaptation during the first 6-weeks of lower-limb resistance training.

METHODS

Forty participants: 22 intervention (10 males/12 females; 173.48 ± 5.20 cm; 74.01 ± 13.13 kg) completed 6-week resistance training, and 18 control (10 males/8 females; 175.52 ± 7.64 cm; 70.92 ± 12.73 kg) performed no resistance training and maintained their habitual activity. Radial muscle displacement (Dm) assessed via tensiomyography, knee extension maximal voluntary contraction (MVC), voluntary activation (VA), corticospinal excitability and inhibition via transcranial magnetic stimulation, motor unit (MU) firing rate, and muscle thickness and pennation angle via ultrasonography were assessed before and after 2, 4, and 6-weeks of dynamic lower-limb resistance training or control.

RESULTS

After 2-weeks training, Dm reduced by 19-25% in the intervention group; this was before any changes in neural or morphological measures. After 4-weeks training, MVC increased by 15% along with corticospinal excitability by 16%; however, there was no change in VA, corticospinal inhibition, or MU firing rate. After 6-weeks training there was further MVC increase by 6% along with muscle thickness by 13-16% and pennation angle by 13-14%.

CONCLUSION

Enhanced contractile properties and corticospinal excitability occurred before any muscle architecture, neural, and strength adaptation. Later increases in muscular strength can be accounted for by architectural adaptation.

Neuromuscular changes after a Long Distance Triathlon World Championship

ABSTRACTThis study aimed to determine the neuromuscular changes in muscle contractile properties and countermovement jump (CMJ) performance after a long distance (LD) triathlon, inquiring to what extent it is influenced by gender and the evaluated muscle, and to explore for response differences. Four elite (2 females and 2 males) and 18 well-trained triathletes (3 females and 15 males) who competed in the 2019 LD Triathlon World Championship undergone, prior and post-race, a CMJ and a muscle contractile properties assessment in vastus lateralis (VL) and biceps femoris (BF) using tensiomyography. A mixed ANOVA was carried out to detect triathletes' neuromuscular changes after the competition. A large decrease in jump height and flight time was found in CMJ (p = 0.001, ηp2 = 0.767) with gender differences (ηp2 = 0.308). contraction (Tc), delay (Td) and sustain times (Ts) also showed a large decrease (p = 0.001, ηp2 = 0.174-0.413). However, maximum radial muscle belly displacement was not altered by the competition, but did greatly increase radial displacement velocity (p = 0.031; ηp2 = 0.212). No gender differences were found in contractile properties. Correlation analysis between race performance and the jumping and tensiomyography parameters only showed a moderate negative correlation with Tc of the BF in pre- and post-competition (r = -0.44; -0.43; p = 0.05). In conclusion, triathletes after a LD World Championship suffer a sharp drop in jump performance and variations in VL's and BF's contractile properties, showing decreases in Tc, Td and Ts without gender differences. The regular use of these parameters can allow the monitoring of triathlete's neuromuscular fatigue and aid in the distribution of more efficient loads in their training cycles.HighlightsTrainers and researchers in neuromuscular fatigue can have reference data of elite and well-trained triathletes after performing LD race.The magnitude of change in the CMJ and the contractile properties of BF and VL achieved in competition by these elite reference triathletes can guide to modulate triathletes training.The regular use of the parameters using these references can allow an exhaustive neuromuscular fatigue monitoring during the sessions or training cycles throughout the season.

Reproducibility of knee extensor and flexor contraction velocity in healthy men and women assessed using tensiomyography: A registered report

BACKGROUND

Tensiomyography measures the radial displacement of a muscle during an electrically evoked twitch contraction. Different concepts to determine the rate of displacement (Vc) from the maximum twitch exist, but information on their reproducibility is scarce. Further, different inter-stimuli intervals during progressive stimulation are used, but the effect of different intervals on Vc is unclear.

OBJECTIVES

The first aim of this study was to investigate the within and between-day reliability of the five most frequently used Vc concepts. The second aim was to investigate the effect of different inter-stimuli intervals on Vc.

METHODS

On two consecutive days, we determined Vc of the biceps femoris long head and rectus femoris of twenty-four healthy subjects. The maximum displacement was determined twice within three minutes on day one and a third time 24 h later. Also, on day two, we applied three blocks of ten consecutive stimuli at a constant intensity of 50 mA, separated by 3 min each. Inter-stimuli intervals in randomly ordered blocks were 10 s, 20 s or 30 s, respectively.

RESULTS

All Vc concepts displayed good to excellent relative (ICC 0.87-0.99) and generally good absolute within- and between-day reliability for both muscles. Across Vc-concepts, absolute reliability was higher for the rectus femoris (CV% 1.3-7.95%) compared to the biceps femoris (CV% 6.06-15.30%). In both muscles, Vc was generally not affected by different inter-stimuli intervals. For most Vc concepts, repeated stimulation induced an increase regardless of the inter-stimuli interval, but this effect was mainly trivial and small at most.

CONCLUSIONS

The reproducibility of Vc concepts was generally good but varies between different muscles. A rest interval of 10 s seems preferable to longer intervals for less time required per measurement. Following this initial study, the effect of different inter-stimuli intervals on Vc should be further investigated.

Correlation between Physical Performance and Tensiomyographic and Myotonometric Parameters in Older Adults

BACKGROUND

To examine the correlation between physical performance and muscle strength and the variables obtained from tensiomyography and myotonometry.

METHODS

Fifty-two older adults able to complete functional tests participated in this observational study. Variables of maximal radial muscle displacement (Dm) and contraction time (Tc) (using tensiomyography) and muscle stiffness (using myotonometry) of the rectus femoris and vastus lateralis muscles were assessed. Physical performance (Short Physical Performance Battery, Timed Up and Go, Five Times Sit to Stand, and walking speed), isometric knee extension strength, and grip strength were assessed. A correlation analysis was performed between all the variables.

RESULTS

A significant correlation between the Short Physical Performance Battery and the rectus femoris (rho = 0.491) and vastus lateralis Dm (rho = 0.329) was found. Significant correlations between the Five Times Sit to Stand Test and the Dm values of the rectus femoris (rho = -0.340) and Dm (rho = -0.304), and stiffness (rho = -0.345) in the vastus lateralis, were also found. No significant correlations were found between tensiomyography and myotonometry, the Timed Up and Go, and walking speed, nor between tensiomyography and myotonometry and grip strength or isometric knee extension strength.

CONCLUSIONS

Functional tests should be prioritized in the assessment of older adults, but further research into muscle quality using technology is advisable.

Diagnostic accuracy of Tensiomyography parameters for monitoring peripheral neuromuscular fatigue

The diagnostic accuracy of tensiomyography (TMG) parameters compared to the gold standard in neuromuscular fatigue evaluation using voluntary and electrically induced muscle activation is unclear. This study aimed to investigate the diagnostic accuracy of TMG parameters to detect individual changes after interventions that were designed to induce central or peripheral fatigue. Nineteen males (age: 32.2 ± 9.3 years) performed two interventions, consisting of maintaining 25% of maximal voluntary contraction (MViC_25%) and a 30 s all-out cycling test (Wingate), respectively. TMG parameters, maximum voluntary contraction (PtMViC), voluntary activation (VA%) and electrically elicited double twitches (Dtw) were assessed on the knee extensors before (PRE), one minute (POST) and seven minutes after (POST7) the intervention. The diagnostic accuracy (AUC) of TMG parameters were evaluated in comparison to two criteria measures (PtMViC and Dtw). RM ANOVA revealed a significant interaction between the effects of intervention and time on VA% (p = 0.001) and Dtw (p < 0.001) but not for PtMViC (p = 0.420). AUC showed that TMG parameters had a good ability in detecting muscular fatigue assessed by Dtw but not by PtMViC. The results of the current study suggest that TMG parameters can be used to monitor peripheral neuromuscular fatigue.

Tensiomyographic Assessment of Contractile Properties in Elite Youth Soccer Players According to Maturity Status

Little is known about how muscle contractile properties are affected by biological maturation in elite youth soccer players. This study aimed to determine the effects of maturation on contractile properties of rectus femoris (RF) and biceps femoris (BF) muscles assessed by tensiomyography (TMG) and provide reference values for elite youth soccer players. One hundred twenty-one elite youth soccer players (14.98 ± 1.83 years; 167.38 ± 10.37 cm; 60.65 ± 11.69 kg) took part in the study. The predicted peak height velocity (PHV) was used in order to establish players' maturity status (Pre-PHV, n = 18; Mid-PHV, n = 37; Post-PHV = 66). Maximal radial displacement of the muscle belly, contraction time, delay time, and contraction velocity for RF and BF muscles were recorded. One-way ANOVA showed no significant differences between PHV groups for any tensiomyography variables in RF and BF muscles (p > 0.05). Our results established that maturity status did not show a significant effect in mechanical and contractile properties on RF and BF muscles evaluated by TMG in elite youth soccer players. These findings and reference values can be useful for strength and conditioning coaches of elite soccer academies in order to optimize the evaluation of neuromuscular profiles.

The Utility of Myotonometry in Musculoskeletal Rehabilitation and Human Performance Programming

Myotonometry is a relatively novel method used to quantify the biomechanical and viscoelastic properties (stiffness, compliance, tone, elasticity, creep, and mechanical relaxation) of palpable musculotendinous structures with portable mechanical devices called myotonometers. Myotonometers obtain these measures by recording the magnitude of radial tissue deformation that occurs in response to the amount of force that is perpendicularly applied to the tissue through a device's probe. Myotonometric parameters such as stiffness and compliance have repeatedly demonstrated strong correlations with force production and muscle activation. Paradoxically, individual muscle stiffness measures have been associated with both superior athletic performance and a higher incidence of injury. This indicates optimal stiffness levels may promote athletic performance, whereas too much or too little may lead to an increased risk of injury. Authors of numerous studies suggested that myotonometry may assist practitioners in the development of performance and rehabilitation programs that improve athletic performance, mitigate injury risk, guide therapeutic interventions, and optimize return-to-activity decision-making. Thus, the purpose of our narrative review was to summarize the potential utility of myotonometry as a clinical tool that assists musculoskeletal clinicians with the diagnosis, rehabilitation, and prevention of athletic injuries.

Effects of Lumbar Stabilization Exercises on Isokinetic Strength and Muscle Tension in Sedentary Men

Lumbar stabilization exercises (LSE) lead to high levels of erector spinae muscle (ESM) activation, which has a positive effect on improving physical function. The purpose of this study is to identify factors explaining changes in muscle strength after 7 weeks of LSE and to evaluate changes in stiffness and contraction of the ESM. All participants (male: n = 42, age = 28.26 ± 10.97) were assessed for 60°/s isokinetic extensor muscle strength and tension using a tensiomyography (TMG) and isokinetic device before and after LSE. Maximum displacement (Dm) and average velocity up to 90% Dm (Vc 90) were significantly different before and after LSE. Additionally, participants’ 60°/s isokinetic extensor strength was significantly higher after exercise. A regression analysis was conducted to test the explanatory power of the variables, and positive results were obtained in the increase in extensor strength before and after Vc 90 and LSE. Furthermore, statistical significance was set at p < 0.05. After LSE, the increase in 60°/s isokinetic extensor strength and ESM’s Dm and Vc 90 can be interpreted as positive changes post-exercise in endurance muscles with a higher percentage of type I fibers. Our results can contribute to predicting the long-term exercise effect in sedentary workers and developing an individualized strategic exercise program.

Sensor location affects skeletal muscle contractility parameters measured by tensiomyography

Tensiomyography (TMG) is a non-invasive method for measuring contractile properties of skeletal muscle that is increasingly being used in research and practice. However, the lack of standardization in measurement protocols mitigates the systematic use in sports medical settings. Therefore, this study aimed to investigate the effects of lower leg fixation and sensor location on TMG-derived parameters. Twenty-two male participants underwent TMG measurements on the m. biceps femoris (BF) in randomized order with and without lower leg fixation (fixed vs. non-fixed). Measurements were conducted at 50% of the muscle's length (BF-mid) and 10 cm distal to this (BF-distal). The sensor location affected the contractile properties significantly, both with and without fixation. Delay time (Td) was greater at BF-mid compared to BF-distal (fixed: 23.2 ± 3.2 ms vs. 21.2 ± 2.7 ms, p = 0.002; non-fixed: 24.03 ± 4.2 ms vs. 21.8 ± 2.7 ms, p = 0.008), as were maximum displacement (Dm) (fixed: 5.3 ± 2.7 mm vs. 3.5 ± 1.7 mm, p = 0.005; non-fixed: 5.4 ± 2.5 mm vs. 4.0 ± 2.0 mm, p = 0.03), and contraction velocity (Vc) (fixed: 76.7 ± 25.1 mm/s vs. 57.2 ± 24.3 mm/s, p = 0.02). No significant differences were revealed for lower leg fixation (all p > 0.05). In summary, sensor location affects the TMG-derived parameters on the BF. Our findings help researchers to create tailored measurement procedures in compliance with the individual goals of the TMG measurements and allow adequate interpretation of TMG parameters.

Moderate- to fast-walking improves immunocytes through a positive change of muscle contractility in old women: a pilot study

This study aimed to examine whether compared with a program without walking, intervention programs with three types of walking can improve the muscle property and immunocytes in elderly women. Thirty-two subjects were randomly assigned to control group (CON), slow walking group (SWG), moderate walking group (MWG), and fast walking group (FWG). Three types of walking on treadmill were 30 min a day, 5 days/wk for 12 weeks. Muscle contraction time (Tc), maximum displacement (Dm), and immunocytes were tested by tensiomyography and flow cytometry. After the intervention, FWG had an increasing tendency in the muscle mass compared with other three groups. Tc of biceps femoris (BF) decreased in CON and SWG, while Tc of BF in MWG and FWG (30.58%±23.71%) increased. It was similar in the rectus femoris (RF). Although Dm of BF and RF increased in CON and SWG, those decreased in MWG and FWG. Leucocytes of CON and SWG had a decreasing tendency, those of MWG (9.65%±13.01%) and FWG (13.01%± 13.58%) increased. In the neutrophil, only CON decreased, whereas the three groups showed an increasing tendency. Helper T cell was increased only in FWG (19.61%±19.94%), showing significant differences between groups (P=0.009, η ²=0.378). Natural killer cell was improved in SWG and MWG but showed a clear increase in FWG (75.76%±63.57%). It might be confirmed that walking for elderly increases the muscle property of the lower legs as they walk faster, which might be expected to improve the immunocytes function.

Characteristics of muscle contraction of the rectus femoris using tensiomyography by sex in healthy college students: a cross-sectional study

Background

Tensiomyography (TMG) is a non-invasive instrument for measuring mechanical muscle contraction characteristics and measuring the maximum displacement of the muscle belly in the radial direction with respect to the muscle and the time needed to achieve this from electrical stimulation. There have been only been a reports of TMG in healthy adults. A systematic review of TMG reported a low proportion of female participants, with a small sample size. Therefore, it is unclear whether there is a difference in TMG parameters according to sex and between dominant and non-dominant feet. Furthermore, the relationship between TMG parameters and evaluations commonly used in clinical practice has not been clarified. This study aimed to clarify the characteristics of muscle contraction of the rectus femoris using TMG according to sex among healthy college students and its relationship with muscle function evaluation, such as lower limb muscle mass and muscle strength.

Methods

This cross-sectional study included 91 healthy university students (18-24 years). Five tools were used: TMG, lower-limb muscle mass, rectus femoris thickness, isometric knee joint extension torque, and thigh circumference. Each parameter was compared by the generalized linear mixed model (GLMM) and Bonferroni's multiple comparison test, with sex as the without-subject factor and dominant/non-dominant foot as the within-subject factor. The correlation between the TMG parameters and other parameters was examined using Pearson's correlation coefficient for both males and females.

Results

The results of the GLMM, in terms of the TMG parameters, an interaction was observed for maximum displacement (Dm); in the results of the multiple comparison test, Dm for the non-dominant leg was significantly lower in females than in males. A main effect and interaction were not observed for delay time (Td) and contraction time (Tc) by sex, dominant foot, or non-dominant foot. There was a main effect of sex on muscle function evaluation parameters (ρ ≤ 0.05). The correlation between TMG parameters for males and females and lower limb muscle mass, muscle thickness, joint torque, and thigh circumference were significantly correlated with some TMG parameters, lower limb muscle mass and muscle thickness (ρ ≤ 0.05). The absolute value of the correlation coefficient was low overall (0.20-0.38).

Conclusion

In healthy college students, TMG parameters for the rectus femoris showed sex differences in Dm, and there was a weak correlation between TMG parameters and lower limb muscle mass. TMG parameter evaluation may indicate a different function compared to the traditional muscle function assessment used in clinical practice. When using the Dm of the TMG as an evaluation battery for the rectus femoris muscle, it is important to consider sex-related differences.

Muscle Contractile Properties Measured by the Tensiomyography (TMG) Method in Top-Level Football Players of Different Playing Positions: The Case of Serbian Super League

The aim of this study is to investigate the differences in muscle contractile properties measured by the TMG method between top-level football players of different playing positions. The sample consisted of 57 football players from the Serbian Super League, divided into three groups: defenders-DF, midfielders-MF, and forwards-FW. Muscles included in the study were the Rectus Femoris (RF), Vastus Medialis (VM), Vastus Lateralis (VL), Biceps Femoris (BF), and Semitendinosus (ST) of the right (R) and left (L) leg. The TMG parameters used in this study were contraction time (Tc), delay time (Td), relaxation time (Tr), maximal displacement (Dm), and sustain time (Ts). The ANOVA results showed that differences in TMG parameters between top-level football players of different playing positions are small and exist only in the Tr of RF (F = 4.658, p = 0.014), BF (F = 4.433, p = 0.016), and ST muscle (F = 3.808, p = 0.028), and the Tc (F = 3.214, p = 0.048) and Td (F = 3.705, p = 0.031) of the VM muscle. All differences were detected between DF and FW players, and all differences were in the left (non-dominant) leg. The results obtained in this study indicate that the training and selection process in football, from the aspect of functional and mechanical muscle properties, should be similar for all players, regardless of playing position. It has been shown that TMG has relatively low sensitive strength for detecting differences between football players of different playing positions.

Methodical approaches to determine the rate of radial muscle displacement using tensiomyography: A scoping review and new reporting guideline

Tensiomyography is a non-invasive method to assess skeletal muscle contractile properties from the stimulated radial displacement. Many studies have used the rate of displacement (Vc) as an indirect measure of muscle contraction velocity. However, no standardised methodical approach exists to measure displacement and determine Vc. This review aimed to provide an overview of concepts to determine Vc and measurement protocols to foster the development of a standardised methodical approach. This review followed the Preferred Reporting Items for Systematic Reviews and meta-Analyses extension for Scoping Reviews (PRISMA-ScR) guideline. Systematic searches were performed within five electronic databases and additional sources. The included 62 studies reported 10 different concepts to determine Vc, which we summarised in three groups. The determination concepts differed mainly regarding time intervals during the contraction phase considered and criteria used to define these intervals. Essential information on the equipment and raters, measurement setup, electrical stimulation procedure, and data analysis were frequently not reported. In conclusion, no consensus on how to determine Vc existed. Incomplete reporting of measurement protocols hindered study comparison, which obstructs developing a standardised approach. Therefore, we propose a new guideline for reporting measurement protocols, which covers the 1) equipment and rater, 2) measurement setup, including positioning of the subject, sensor and electrodes, 3) electrical stimulation, including initial stimulation amplitude, increment, and endpoint, and 4) data analysis, including selection criteria and number of analysed signals and a definition of derived parameters.

Estimation of contractile parameters of successive twitches in unfused tetanic contractions of single motor units - A proof-of-concept study using ultrafast ultrasound imaging in vivo

During a voluntary contraction, motor units (MUs) fire a train of action potentials, causing summation of the twitch forces, resulting in fused or unfused tetanus. Twitches have been important in studying whole-muscle contractile properties and differentiation between MU types. However, there are still knowledge gaps concerning the voluntary force generation mechanisms. Current methods rely on the spike-triggered averaging technique, which cannot track changes in successive twitches' properties in response to individual neural firings. This study proposes a method that estimates successive twitches contractile parameters of single MUs during low force voluntary isometric contractions in human biceps brachii. We used a previously developed ultrafast ultrasound imaging method to estimate unfused tetanic activity signals of single MUs. A twitch decomposition model was used to decompose unfused tetanic activity signals into individual twitches. This study found that the contractile parameters varied within and across MUs. There was an association between the inter-spike interval and the contraction time (r = 0.49,p < 0.001) and the half-relaxation time (r = 0.58,p < 0.001), respectively. The method shows the proof-of-concept to study MU contractile properties of individual twitches in vivo, which can provide further insights into the force generation mechanisms of voluntary contractions and response to individual neural discharges.

Effects of motor imagery training on skeletal muscle contractile properties in sports science students

Background

Studies on motor imagery (MI) practice based on different designs and training protocols have reported changes in maximal voluntary contraction (MVC) strength. However, to date, there is a lack of information on the effects of MI training on contractile properties of the trained muscle.

Methods

Forty-five physically active sport science students (21 female) were investigated who trained three times per week over a 4-week period in one of three groups: An MI group conducted MI practice of maximal isometric contraction of the biceps brachii; a physical exercise (PE) group physically practiced maximal isometric contractions of the biceps brachii in a biceps curling machine; and a visual imagery (VI) group performed VI training of a landscape. A MVC test of the arm flexors was performed in a biceps curling machine before and after 4 weeks of training. The muscular properties of the biceps brachii were also tested with tensiomyography measurements (TMG).

Results

Results showed an interaction effect between time and group for MVC (p = 0.027, η ² = 0.17), with a higher MVC value in the PE group (Δ5.9%) compared to the VI group (Δ -1.3%) (p = 0.013). MVC did not change significantly in the MI group (Δ2.1%). Analysis of muscle contractility via TMG did not show any interaction effects neither for maximal radial displacement (p = 0.394, η ² = 0.05), delay time (p = 0.79, η ² = 0.01) nor contraction velocity (p = 0.71, η ² = 0.02).

Conclusion

In spite of MVC-related changes in the PE group due to the interventions, TMG measurements were not sensitive enough to detect concomitant neuronal changes related to contractile properties.

Muscle Asymmetries in the Lower Limbs of Male Soccer Players: Preliminary Findings on the Association between Countermovement Jump and Tensiomyography

Strength and power asymmetries have been observed in different sports, including soccer. Such asymmetries, as well as the bilateral deficit (BLD), can be assessed during different tasks, static or dynamic, and with different methods and devices, in order to detect the possible different aspects, as well as the association with physical performance and injuries. The aim of this study was to investigate the association between muscle asymmetries and BLD during a countermovement jump (CMJ), and tensiomyography (TMG) parameters and asymmetries, in the lower limbs of male soccer players. A total of 23 male soccer players (18 ± 4 years) were recruited. Bilateral and unilateral CMJs were performed, and peak power (W) and height (cm) were obtained. TMG was performed on different muscles of the lower limbs, and lateral and functional symmetries were obtained. Playing position and history of injuries were collected. CMJ inter-limb symmetry was found to significantly correlate with biceps femoris (r = 0.574, p = 0.004) and soleus (r = 0.437, p = 0.037) lateral symmetry. Players in central roles presented significantly worse functional symmetry scores of the knee than defense players (-17.5%, 95% CI -31.2--3.9; p = 0.10). Participants reporting a history of injury at the ankle were characterized by significantly lower functional symmetry in both the dominant (43%, 39.5-48.0 vs. 74.5%, 46.5-89.3, p = 0.019) and non-dominant (45%, 42.5-46.0 vs. 81.0%, 45.8-90.3, p = 0.024) ankle. Findings from this preliminary study suggest an association between lower-limb muscle asymmetries during a dynamic task, such as jumping, and muscle contractile properties evaluated with TMG; moreover, functional asymmetries may be present after ankle injuries. Future studies in larger samples should evaluate the presence of such asymmetries as predictors or characteristics of different muscular and joint injuries.

Differences in the Contractile Properties of the Biceps Femoris and Semitendinosus Muscles Throughout a Season in Professional Soccer Players

The aim of this study was to monitor seasonal changes in the mechanical and neuromuscular characteristics of the knee flexor muscles with tensiomyography, the biceps femoris (BF) and semitendinosus (ST) muscles, of 27 soccer players. All male professional soccer players (age 25 ± 4 years) were measured at the beginning of the preseason (second week) and in the competitive season (10 weeks later). The variables contraction time (Tc) and muscle displacement (Dm) showed significant differences in some muscles, and in others they indicated a tendency to change. In general, the BF improved (more explosive and better muscle tone) and the ST worsened (slower and worse muscle tone) its values during the season. The findings of this study suggest that usual daily soccer training and weekly competition might produce antagonistic changes between the knee flexor muscles.

The relationship between external and internal load parameters in 3 × 3 basketball tournaments

Purpose

3 × 3 basketball games are characterized by high-intensity accelerations and decelerations, and a high number of changes of direction and jumps. It is played in tournament form with multiple games per day. Therefore, optimal regeneration is crucial for maintaining a high performance level over the course of the tournament. To elucidate how load of a match affects the athletes' bodies (i.e., internal load), muscular responses to the load of 3 × 3 games were analyzed. We aimed to investigate changes in contractility of the m. rectus femoris (RF) and m. gastrocnemius medialis (GC) in response to the load of single 3 × 3 games and a 3 × 3 tournament.

Methods

Inertial movement analysis was conducted to capture game load in 3 × 3. Changes in contractility were measured using tensiomyography (TMG). During a two-day tournament, TMG measurements were conducted in the morning and after each game. Additionally, off-game performance analysis consisting of jump and change-of-direction (COD) tests was conducted the day before the tournament.

Results

Significant changes of the muscle contractility were found for GC with TMG values being higher in the baseline than in the post-game measurements. In contrast to athletes of the GC group, athletes of the RF group responded with either decreased or increased muscle contractility after a single 3 × 3 game. A significant correlation between external and internal load parameters could not be shown. Concerning off-game performance, significant correlations can be reported for COD test duration, CMJ height and ∆Vc as well as COD test duration and ∆Dm. No systematic changes in muscle contractility were found over the course of the tournament in RF and GC.

Conclusion

The athletes' external 3 × 3 game load and their performance level did not seem to affect muscular contractility after a single 3 × 3 game or a complete 3 × 3 tournament within this investigation. This might indicate that elite athletes can resist external load without relevant local muscular fatigue. With respect to the course of the tournament, it can therefore be concluded that the breaks between games seem to be sufficient to return to the initial level of muscle contractility.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13102-022-00530-1.

Relationship between hypertrophy, strength gains and tensiomyography adaptations: a moderator role of contraction duration

The aim of the study was to investigate how the relationship between resistance training-induced hypertrophy, strength, and passive contractile adaptations is affected by contraction duration. Twenty university students (11 males) were randomly assigned to either the fast eccentric/fast concentric phase group (F/F; 1 s both phases) or the slow eccentric/fast concentric phase group (S/F; 4 s and 1 s, respectively). Both experimental groups completed a 7-week biceps curl training programme with a total of 14 sessions (2 days/week). Elbow flexor muscle thickness (MT), one-repetition maximum (1RM), and tensiomyographic (TMG) parameters (radial displacement-D_m and contraction time-T_c) were assessed. The percentage change (∆) in MT correlated significantly with the ∆1RM only in the S/F group (r = 0.712, p < 0.05). Both groups demonstrated significant negative associations between ∆MT and ∆D_m (r = 0.717-0.760, p < 0.01). Conversely, no significance was found between ∆MT and ∆T_c (F/F: r = -0.398, p = 0.255; S/F: r = 0.410, p = 0.239), ∆1RM and ∆T_c (F/F: r = -0.278, p = 0.436; S/F: r = 0.223, p = 0.536), nor ∆1RM and ∆D_m (F/F: r = - 0.131, p = 0.719; S/F: r = - 0.351, p = 0.320). The main findings indicate that the relationship between hypertrophy and strength gains is significantly stronger when resistance training was paced with slower eccentric contractions comparing to fast ones. On the other hand, reduced D_m values indicate increase in MT regardless of contraction duration, while strength gains are not correlated with corresponding TMG changes.

Age-related differences of vastus lateralis muscle morphology, contractile properties, upper body grip strength and lower extremity functional capability in healthy adults aged 18 to 70 years

Background

There is a lack of of cross-sectional research that has investigated muscle morphology, function, and functional capability in all age-bands of healthy adults. The primary aim of this study was to evaluate age-related differences in indices of vastus lateralis (VL) muscle morphology, function and functional capability in a sample of healthy males and females aged 18-70yrs. Secondary aims were to evaluate relationships between age and VL muscle morphology and function and functional capability.

Methods

B mode Ultrasonography and Tensiomyography were used to measure VL muscle thickness, pennation angle, fascicle length, and contractile properties in 274 healthy adults aged 18-70yrs. Measurements of grip strength and functional capability (1-min chair rise test) were also taken. Data analysis included descriptive statistics, correlations, one-way ANOVAs, and multiple regressions.

Results

Negative correlations were found between age and muscle thickness (r_s = -.56), pennation angle (r_s = -.50), fascicle length (r_s = -.30), maximal displacement (r_s = -.24), grip strength (r_s = -.27) and the 1-min chair rise test (r_s = -.32). Positive correlations were observed between age and the echo intensity of the muscle (r_s = .40) and total contraction time (r_s = .20). Differences in the indices of muscle health were noticeable between the 18–29 age band and the 50–59 and 60–70 age bands (p < 0.05). The interaction of age and level of physical activity predicted changes in the variables (r² = .04—.32).

Conclusion

Age-related differences in muscle health are noticeable at 50 years of age, and age-related differences are larger in females compared to males. It was suggested that the thickness of the VL changed the most with age across the adult lifespan and that physical activity likely acts to abate detrimental change.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12877-022-03183-4.

The Effect of Load and Volume Autoregulation on Muscular Strength and Hypertrophy: A Systematic Review and Meta-Analysis

Background

Autoregulation has emerged as a potentially beneficial resistance training paradigm to individualize and optimize programming; however, compared to standardized prescription, the effects of autoregulated load and volume prescription on muscular strength and hypertrophy adaptations are unclear. Our objective was to compare the effect of autoregulated load prescription (repetitions in reserve-based rating of perceived exertion and velocity-based training) to standardized load prescription (percentage-based training) on chronic one-repetition maximum (1RM) strength and cross-sectional area (CSA) hypertrophy adaptations in resistance-trained individuals. We also aimed to investigate the effect of volume autoregulation with velocity loss thresholds ≤ 25% compared to > 25% on 1RM strength and CSA hypertrophy.

Methods

This review was performed in accordance with the PRISMA guidelines. A systematic search of MEDLINE, Embase, Scopus, and SPORTDiscus was conducted. Mean differences (MD), 95% confidence intervals (CI), and standardized mean differences (SMD) were calculated. Sub-analyses were performed as applicable.

Results

Fifteen studies were included in the meta-analysis: six studies on load autoregulation and nine studies on volume autoregulation. No significant differences between autoregulated and standardized load prescription were demonstrated for 1RM strength (MD = 2.07, 95% CI – 0.32 to 4.46 kg, p = 0.09, SMD = 0.21). Velocity loss thresholds ≤ 25% demonstrated significantly greater 1RM strength (MD = 2.32, 95% CI 0.33 to 4.31 kg, p = 0.02, SMD = 0.23) and significantly lower CSA hypertrophy (MD = 0.61, 95% CI 0.05 to 1.16 cm², p = 0.03, SMD = 0.28) than velocity loss thresholds > 25%. No significant differences between velocity loss thresholds > 25% and 20–25% were demonstrated for hypertrophy (MD = 0.36, 95% CI – 0.29 to 1.00 cm², p = 0.28, SMD = 0.13); however, velocity loss thresholds > 25% demonstrated significantly greater hypertrophy compared to thresholds ≤ 20% (MD = 0.64, 95% CI 0.07 to 1.20 cm², p = 0.03, SMD = 0.34).

Conclusions

Collectively, autoregulated and standardized load prescription produced similar improvements in strength. When sets and relative intensity were equated, velocity loss thresholds ≤ 25% were superior for promoting strength possibly by minimizing acute neuromuscular fatigue while maximizing chronic neuromuscular adaptations, whereas velocity loss thresholds > 20–25% were superior for promoting hypertrophy by accumulating greater relative volume.

Protocol Registration The original protocol was prospectively registered (CRD42021240506) with the PROSPERO (International Prospective Register of Systematic Reviews).

Supplementary Information

The online version contains supplementary material available at 10.1186/s40798-021-00404-9.

Effects of resistance training on hypertrophy, strength and tensiomyography parameters of elbow flexors: role of eccentric phase duration

The aim of the study was to compare the effects of two different training protocols, which differ in the duration of the eccentric phase, on the one-repetition maximum (1RM), thickness and contractile properties of elbow flexors. Twenty untrained college students were randomly divided into two experimental groups, based on the training tempo: FEG (Faster Eccentric Group: 1/0/1/0) and SEG (Slower Eccentric Group: 4/0/1/0). Training intervention was a biceps bending exercise, conducted twice a week for 7 weeks. The intensity (60–70% RM), sets (3–4) and rest intervals (120 s) were held constant, while repetitions were performed until it was not possible to maintain a set duration. In the initial and final measurements, 1RM, muscle thickness and tensiomyography parameters – contraction time (Tc) and radial deformation (Dm) – were evaluated. An ANCOVA model (using baseline outcomes as covariates) was applied to determine between-group differences at post-test, while Pearson’s product-moment correlation coefficient was used to investigate the relationship between absolute changes in muscle thickness and Dm. Muscle strength increase was greater for SEG than for FEG (6.0 ± 1.76 vs. 3.30 ± 2.26 kg, p < 0.01). In both groups muscle thickness increased equally (FEG: 3.24 ± 2.01 vs. SEG: 3.57 ± 1.17 mm, p < 0.01), while an overall reduction in Dm was observed (FEG: 1.99 ± 1.20 vs. SEG: 2.26 ± 1.03 mm, p < 0.01). Values of Tc remained unchanged. A significant negative relationship was observed between changes in muscle thickness and Dm (r = -0.763, Adj.R² = 0.560, p < 0.01). These results indicate that the duration of the eccentric phase has no effect on muscle hypertrophy in untrained subjects, but that slower eccentric movement significantly increases 1RM.

Short-term effects of two different recovery strategies on muscle contractile properties in healthy active men: A randomised cross-over study

The aim of this study was to compare the immediate effects of cold-water immersion (CWI) and hot-water immersion (HWI) versus passive resting after a fatigue-induced bout of exercise on the muscle contractile properties of the Vastus Medialis (VM). We conducted a randomised cross-over study involving 28 healthy active men where muscle contractile properties of the VM wer recorded using Tensiomyography (TMG) before and after CWI, HWI or passive resting and up to one-hour post-application. The main outcomes obtained were muscle displacement and velocity of deformation according to limb size (Dmr and Vdr). Our results showed a significant effect of time (F(3.9,405) =32.439; p <0.001; η²_p =0.29) and the interaction between time and temperature (F(7.9,405) =5.814; p <0.001; η²_p=0.13) on Dmr but no for temperature alone (F(2,81) =2.013; p =0.14; η²_p=0.04) while for Vdr, both time (F(5.2,486) =23.068; p <0.001 η²_p = 0.22) and temperature (F(2,81) =4.219; p = 0.018; η²_p= 0.09) as well as the interaction (F(10.4,486) =7.784; p <0.001; η²_p =0.16) were found significant. Compared to CWI, HWI increased Dmr post-application and Vdr both post-application as well as 15 and 45' thereafter. These findings suggest that applying HWI could be a valid alternative to CWI to promote muscle recovery.

Effects of Foam Rolling Duration on Tissue Stiffness and Perfusion: A Randomized Cross-Over Trial

Despite its beneficial effects on flexibility and muscle soreness, there is still conflicting evidence regarding dose-response relationships and underlying mechanisms of foam rolling (FR). This study aimed to investigate the impact of different FR protocols on tissue perfusion and tissue stiffness. In a randomized crossover trial, two FR protocols (2x1 min, 2x3 min) were applied to the right anterior thigh of twenty healthy volunteers (11 females, 25 ± 4 years). Tissue perfusion (near infrared spectroscopy, NIRS) and stiffness (Tensiomyography, TMG and Myotonometry, MMT) were assessed before and after FR application. Variance analyses revealed a significant interaction of FR duration and tissue perfusion (F_[1,19] = 7.098, p = 0.015). Local blood flow increased significantly from pre to post test (F_[1,19] = 7.589, p = 0.013), being higher (Δ +9.7%) in the long-FR condition than in the short-FR condition (Δ +2.8%). Tissue stiffness (MMT) showed significant main effects for time (F_[1,19] = 12.074, p = 0.003) and condition (F_[1,19] = 7.165, p = 0.015) with decreases after short-FR (Δ -1.6%) and long-FR condition (Δ -1.9%). However, there was no time*dose-interaction (F_[1,19] = 0.018, p = 0.895). No differences were found for TMG (p > 0.05). FR-induced changes failed to exceed the minimal detectable change threshold (MDC). Our data suggest that increased blood flow and altered tissue stiffness may mediate the effects of FR although statistical MDC thresholds were not achieved. Longer FR durations seem to be more beneficial for perfusion which is of interest for exercise professionals designing warm-up and cool-down regimes. Further research is needed to understand probable effects on parasympathetic outcomes representing systemic physiological responses to locally applied FR stimulations.

Muscle Contractile Properties Measured at Submaximal Electrical Amplitudes and Not at Supramaximal Amplitudes Are Associated with Repeated Sprint Performance and Fatigue Markers

Background: The present study analyzes the associations between the muscle contractile properties (MCP) measured at different neuromuscular electrical stimulation amplitudes (NMESa) and the performance or transient fatigue after a bout of repeated sprints. Methods: Seventeen physically active male subjects performed six repeated sprints of 30 m with 30 s of passive recovery. Capillary blood creatine kinase (CK) concentration, knee extension or flexion isometric peak torque, tensiomyography, and repeated sprint performance were assessed. Results: Muscle displacement and contraction time were different in relation to the NMESa used in the rectus femoris and biceps femoris muscles. At rest, significant (p < 0.05) associations were found between muscle displacement and the loss of time in the repeated sprints (sprint performance) at 20 or 40 mA in the rectus femoris. At post +24 h or +48 h, the highest significant associations were found between the muscle displacement or the contraction time and CK or peak torques also at submaximal amplitudes (20 mA). The NMESa which elicits the peak muscle displacement showed lack of practical significance. Conclusion: Although MCP are typically assessed in tensiomyography using the NMESa that elicit peak muscle displacement, a submaximal NMESa may have a higher potential practical application to assess neuromuscular fatigue in response to repeated sprints.

Effects of Kinesio Taping on Muscle Contractile Properties: Assessment Using Tensiomyography

CONTEXT

Although functional effects of kinesio taping (KT) have been widely studied, its effects on contractile properties of the target muscle remain unclear. Tensiomyography is suitable for quantifying muscle stiffness and rate of force development upon imposed twitch contraction.

OBJECTIVE

To test the hypothesis that KT has effects on contractile properties of targeted muscle using tensiomyography.

DESIGN

Prospective cohort study.

SETTINGS

Performance laboratory of a sports rehabilitation center.

PARTICIPANTS

A total of 11 healthy volunteers.

INTERVENTIONS

Tensiomyography measurements before KT facilitation technique applied (pre-KT), 45 minutes, and 24 hours after KT (post-KT1 and post-KT2, respectively) without removing the tape.

MAIN OUTCOME MEASURES

Maximal radial displacement, contraction time, delay time, sustain time, relaxation time, and velocity of contraction.

RESULTS

Significant effects were shown for maximal radial displacement (P = .004), contraction time (P = .013), relaxation time (P = .035), and velocity of contraction (P = .0033), but not for delay time (P = .060) and sustain time (P = .078). Post hoc testing indicated a significant decrease in maximal radial displacement for post-KT1 only (from 6.33 [1.46] to 4.87 [2.14] mm), and a significant increase in contraction time for both post-KT1 and post-KT2 (from 30.87 [11.39] to 39.71 [13.49] ms, and 37.41 [14.73] ms, respectively). Post hoc testing also showed a significant decrease in relaxation time for post-KT2 (from 65.97 [53.43] to 47.45 [38.12] ms), and a significant decrease in velocity of contraction for both post-KT1 and post-KT2 (from 0.22 [0.08] to 0.15 [0.09] mm/s, and 0.16 [0.07] mm/s), respectively.

CONCLUSION

The findings indicate that KT leads to an increased muscle stiffness and a reduced muscle rate of force production despite the facilitation technique applied.

Optimal Spatial Sensor Design for Magnetic Tracking in a Myokinetic Control Interface

BACKGROUND AND OBJECTIVES

Magnetic tracking involves the use of magnetic sensors to localize one or more magnetic objectives, in those applications in which a free line-of-sight between them and the operator is hampered. We applied this concept to prosthetic hands, which could be controlled by tracking permanent magnets implanted in the forearm muscles of amputees (the myokinetic control interface). Concerning the system design, the definition of a sensor distribution which maximizes the information, while minimizing the computational cost of localization, is still an open problem. We present a simple yet effective strategy to define an optimal sensor set for tracking multiple magnets, which we called the Peaks method.

METHODS

We simulated a proximal amputation using a 3D CAD model of a human forearm, and the implantation of 11 magnets in the residual muscles. The Peaks method was applied to select a subset of sensors from an initial grid of 480 elements. The approach involves setting an appropriate threshold to select those sensors associated with the peaks in the magnetic flux density and its gradient distributions. Selected sensors were used to track the magnets during muscle contraction. For validating our strategy, an alternative method based on state-of-the-art solutions was implemented. We finally proposed a calibration phase to customize the sensor distribution on the specific patient's anatomy.

RESULTS

80 sensors were selected with the Peaks method, and 101 with the alternative one. A localization accuracy below 0.22 mm and 1.86° for position and orientation, respectively, was always achieved. Unlike alternative methods from the literature, neither iterative or analytical solution, nor a-priori knowledge on the magnet positions or trajectories were required, and yet the outcomes achieved with the two strategies proved statistically comparable. The calibration phase proved useful to adapt the sensors to the patient's stump and to increase the signal-to-noise ratio against intrinsic noise.

CONCLUSIONS

We demonstrated an efficient and general solution for solving the design optimization problem (i.e. identifying an optimal sensor set) and reducing the computational cost of localization. The optimal sensor distribution mirrors the field shape traced by the magnets on the sensing surface, being an intuitive and fast way of achieving the same results of more complex and application-specific methods. Several applications in the (bio)medical field involving magnetic tracking will benefit from the outcomes of this work.

Detecting subtle yet fast skeletal muscle contractions with ultrasoft and durable graphene-based cellular materials

Human bodily movements are primarily controlled by the contractions of skeletal muscles. Unlike joint or skeletal movements that are generally performed in the large displacement range, the contractions of the skeletal muscles that underpin these movements are subtle in intensity yet high in frequency. This subtlety of movement makes it a formidable challenge to develop wearable and durable soft materials to electrically monitor such motions with high fidelity for the purpose of, for example, muscle/neuromuscular disease diagnosis. Here we report that an intrinsically fragile ultralow-density graphene-based cellular monolith sandwiched between silicone rubbers can exhibit a highly effective stress and strain transfer mechanism at its interface with the rubber, with a remarkable improvement in stretchability (>100%). In particular, this hybrid also exhibits a highly sensitive, broadband-frequency electrical response (up to 180 Hz) for a wide range of strains. By correlating the mechanical signal of muscle movements obtained from this hybrid material with electromyography, we demonstrate that the strain sensor based on this hybrid material may provide a new, soft and wearable mechanomyography approach for real-time monitoring of complex neuromuscular–skeletal interactions in a broad range of healthcare and human–machine interface applications. This work also provides a new architecture-enabled functional soft material platform for wearable electronics.

Quantification of the Link between Timed Up-and-Go Test Subtasks and Contractile Muscle Properties

Frailty and falls are a major public health problem in older adults. Muscle weakness of the lower and upper extremities are risk factors for any, as well as recurrent falls including injuries and fractures. While the Timed Up-and-Go (TUG) test is often used to identify frail members and fallers, tensiomyography (TMG) can be used as a non-invasive tool to assess the function of skeletal muscles. In a clinical study, we evaluated the correlation between the TMG parameters of the skeletal muscle contraction of 23 elderly participants (22 f, age 86.74 ± 7.88) and distance-based TUG test subtask times. TUG tests were recorded with an ultrasonic-based device. The sit-up and walking phases were significantly correlated to the contraction and delay time of the muscle vastus medialis (ρ = 0.55-0.80, p < 0.01). In addition, the delay time of the muscles vastus medialis (ρ = 0.45, p = 0.03) and gastrocnemius medialis (ρ = -0.44, p = 0.04) correlated to the sit-down phase. The maximal radial displacements of the biceps femoris showed significant correlations with the walk-forward times (ρ = -0.47, p = 0.021) and back (ρ = -0.43, p = 0.04). The association of TUG subtasks to muscle contractile parameters, therefore, could be utilized as a measure to improve the monitoring of elderly people's physical ability in general and during rehabilitation after a fall in particular. TUG test subtask measurements may be used as a proxy to monitor muscle properties in rehabilitation after long hospital stays and injuries or for fall prevention.

Tensiomyographic changes of muscle contractile properties in individuals with lower-limb amputation: A pilot study

BACKGROUND

Individuals with a unilateral lower-limb amputation (LLA) rely heavily on their intact limb during daily physical activities. However, there is limited research on the resultant effects of this over-reliance on contractile properties of muscles in the intact limb.

OBJECTIVE

To compare the muscle contractile properties of the intact limb among individuals with a unilateral LLA to those of age-matched able-bodied individuals, using tensiomyography.

STUDY DESIGN

This is a cross-sectional, observational study.

METHODS

Nine men with a unilateral LLA and 10 able-bodied men (control) were included. Tensiomyography measures were obtained for 5 muscles: gastrocnemius lateralis (GL) and medialis (GM), rectus femoris, vastus lateralis (VL), and vastus medialis. Contraction time (Tc), delay time (Td), maximal displacement (Dm), and velocity of deformation (Vd) for each muscle were compared between groups.

RESULTS

Tc and Td for the GL and GM muscles were lower for the LLA than the control group (GL: P = .03, r = -0.51, P < .01, r = 0.67; GM: P = .02, r = 0.53, P = .07, r = 0.54, respectively). Dm and Vd of the VL were significantly smaller in the LLA than the control group (P < .01, r = 0.73, P < .01, r = 0.23, respectively).

CONCLUSIONS

Men with a unilateral LLA seem to have slower deformation of the gastrocnemius muscles and higher stiffness of the VL than able-bodied controls. These findings may be indicative of an overuse of the intact limb as a compensation for the unilateral LLA. The confirmation of these findings in a larger sample size is required to translate these findings to practice.

High-Protein Energy-Restriction: Effects on Body Composition, Contractile Properties, Mood, and Sleep in Active Young College Students

Background: It is often advised to ensure a high-protein intake during energy-restricted diets. However, it is unclear whether a high-protein intake is able to maintain muscle mass and contractility in the absence of resistance training. Materials and Methods: After 1 week of body mass maintenance (45 kcal/kg), 28 male college students not performing resistance training were randomized to either the energy-restricted (ER, 30 kcal/kg, n = 14) or the eucaloric control group (CG, 45 kcal/kg, n = 14) for 6 weeks. Both groups had their protein intake matched at 2.8 g/kg fat-free-mass and continued their habitual training throughout the study. Body composition was assessed weekly using multifrequency bioelectrical impedance analysis. Contractile properties of the m. rectus femoris were examined with Tensiomyography and MyotonPRO at weeks 1, 3, and 5 along with sleep (PSQI) and mood (POMS). Results: The ER group revealed greater reductions in body mass (Δ -3.22 kg vs. Δ 1.90 kg, p < 0.001, partial η ² = 0.360), lean body mass (Δ -1.49 kg vs. Δ 0.68 kg, p < 0.001, partial η ² = 0.152), body cell mass (Δ -0.85 kg vs. Δ 0.59 kg, p < 0.001, partial η ² = 0.181), intracellular water (Δ -0.58 l vs. Δ 0.55 l, p < 0.001, partial η ² = 0.445) and body fat percentage (Δ -1.74% vs. Δ 1.22%, p < 0.001, partial η ² = 433) compared to the CG. Contractile properties, sleep onset, sleep duration as well as depression, fatigue and hostility did not change (p > 0.05). The PSQI score (Δ -1.43 vs. Δ -0.64, p = 0.006, partial η ² = 0.176) and vigor (Δ -2.79 vs. Δ -4.71, p = 0.040, partial η ² = 0.116) decreased significantly in the ER group and the CG, respectively. Discussion: The present data show that a high-protein intake alone was not able to prevent lean mass loss associated with a 6-week moderate energy restriction in college students. Notably, it is unknown whether protein intake at 2.8 g/kg fat-free-mass prevented larger decreases in lean body mass. Muscle contractility was not negatively altered by this form of energy restriction. Sleep quality improved in both groups. Whether these advantages are due to the high-protein intake cannot be clarified and warrants further study. Although vigor was negatively affected in both groups, other mood parameters did not change.

Use of Tensiomyography in Evaluating Sex-Based Differences in Resistance-Trained Individuals After Plyometric and Isometric Midthigh Pull Postactivation Potentiation Protocols

ABSTRACT

Herring, CH, Goldstein, ER, and Fukuda, DH. Use of tensiomyography in evaluating sex-based differences in resistance-trained individuals after plyometric and isometric midthigh pull postactivation potentiation protocols. J Strength Cond Res 35(6): 1527-1534, 2021-The purposes of this study were to determine if there are sex-based differences in muscular contractile properties as measured by tensiomyography (TMG) and to determine if plyometrics or the isometric midthigh pull are effective methods of eliciting postactivation potentiation (PAP). Thirty strong, resistance-trained men (n = 15) and women (n = 15) underwent 3 testing days consisting of a PAP or control protocol, and pre-TMG and post-TMG and performance testing. Contractile properties from TMG were assessed in the gastrocnemius medial head (GMH), gluteus maximus (GM), rectus femoris (RF), and biceps femoris (BF). Performance testing included countermovement jumps (CMJs) and 30-m sprints. A time × sex interaction was found for GM delay time with women primarily influencing changes (mean difference = 2.74 ms) rather than men (mean difference = 1.32 ms). Main effects for time revealed an increase in GMH velocity of contraction (+0.004 mm·ms-1) and reductions in GM contraction time (-2.85 ms), GM delay time (-2.03 ms), RF delay time (-0.65 ms), CMJs (-2.74 cm), and 30-m time (0.05 seconds). Main effects for sex revealed greater values in women for GM contraction time (+15.50 ms), GM delay time (+6.65 ms), RF delay time (+2.26 ms), BF contraction time (+8.44 ms), BF delay time (+4.07 ms), BF maximal displacement (+2.27 mm), and 30-m time (+0.67 seconds), and lower values in women for GM velocity of contraction (-0.039 mm·ms-1) and CMJs (-13.46 cm).These findings may help practitioners optimize performance through enhanced assessments for injury risk, targeting specific muscles for training, and by selecting proper CAs and rest periods when using PAP.

Immediate effects of myofascial release on neuromechanical characteristics in female and male patients with low back pain and healthy controls as assessed by tensiomyography. A controlled matched-pair study

BACKGROUND

Low back pain (LBP) is a major health issue in most industrialised countries. Lumbodorsal fascia has been advocated as a potential source of pain in the lumbopelvic region. Myofascial release constitutes a manual therapeutic approach focussing on the restoration of altered soft tissue function. No previous study has focused on quantifying neuromechanical effects of myofascial release on LBP patients through tensiomyography. The purpose of this study was to quantify immediate neuromechanical alterations of myofascial release on patients with LBP and healthy controls through tensiomyography parameters.

METHODS

The participants' (n = 30) bilateral lumbar erector spinae muscles were assessed via tensiomyography before and after a 6-min myofascial release treatment of the lumbodorsal fascia to evaluate the muscles' mechanical characteristics. Subjects with LBP (n = 15) were eligible to partake if they reported having had LBP for most days in the past 12 weeks. Muscle displacement (Dm [mm]), velocity of contraction (Vc [mm/s]), and lateral symmetry (Ls [%]) were assessed through tensiomyography testing.

FINDINGS

Statistical analyses revealed a significant increase for velocity of contraction in the right (p = .021) and left (p = .041) lumbar erector spinae for the subjects with LBP but not for the healthy controls (both p > .14).

INTERPRETATION

We suggested that myofascial release alters neuromechanical characteristics in subjects with LBP. Tensiomyography may be implemented in clinical settings to monitor intervention effects of the myofascial system, especially the tensiomyography parameter velocity of contraction.

Effects of Velocity Loss Threshold Within Resistance Training During Concurrent Training on Endurance and Strength Performance

PURPOSE

This study analyzed the effects of 3 training interventions: 1 isolated endurance training (ET) and 2 concurrent training (CT), which differed in the velocity loss (VL) magnitude allowed during the resistance training (RT) set: 15% (VL15) versus 45%, on strength and endurance running performance.

METHODS

A total of 33 resistance- and endurance-trained men were randomly allocated into 3 groups: VL15, VL 45%, and ET. ET was similar across all groups. The CT groups differed in the VL allowed during the RT set. Before and after the 8-week training program the following tests were performed: (1) running sprints, (2) vertical jump, (3) progressive loading test in the squat exercise, and (4) incremental treadmill running test up to maximal oxygen uptake.

RESULTS

Significant differences (P < .001) in RT volume (approximately 401 vs 177 total repetitions for VL 45% and VL15, respectively) were observed. Significant "group" × "time" interactions were observed for vertical jump and all strength-related variables: the CT groups attained significantly greater gains than ET. Moreover, a significant "group" × "time" interaction (P = .03) was noted for velocity at maximal oxygen uptake. Although all groups showed increases in velocity at maximal oxygen uptake, the VL15 group achieved greater gains than the ET group.

CONCLUSIONS

CT interventions experienced greater strength gains than the ET group. Although all groups improved their endurance performance, the VL15 intervention resulted in greater gains than the ET approach. Therefore, moderate VL thresholds in RT performed during CT could be a good strategy for concurrently maximizing strength and endurance development.

Velocity Loss as a Critical Variable Determining the Adaptations to Strength Training

PURPOSE

This study aimed to compare the effects of four resistance training (RT) programs with different velocity loss (VL) thresholds: 0% (VL0), 10% (VL10), 20% (VL20), and 40% (VL40) on sprint and jump performance, muscle strength, neuromuscular, muscle hypertrophy, and architectural adaptations.

METHODS

Sixty-four young resistance-trained men were randomly assigned into four groups (VL0, VL10, VL20, and VL40) that differed in the VL allowed in each set. Subjects followed an RT program for 8 wk (two sessions per week) using the full-squat (SQ) exercise, with similar relative intensity (70%-85% 1-repetition maximum), number of sets (3), and interset recovery period (4 min). Before and after the RT program, the following tests were performed: 1) muscle hypertrophy and architecture of the vastus lateralis (VLA), 2) tensiomyography, 3) 20-m running sprint, 4) vertical jump, 5) maximal voluntary isometric contraction in SQ, 6) progressive loading test in SQ, and 7) fatigue test.

RESULTS

No between-group differences existed for RT-induced gains in sprint, jump, and strength performance despite the differences in the total volume performed by each group. VL20 and VL40 showed significant increases (P < 0.001) in muscle hypertrophy (group-time interaction, P = 0.06). However, only VL40 exhibited a significant slowing (P < 0.001) of the delay time in the VLA muscle (group-time interaction, P = 0.05). Moreover, VL40 showed a significant decrease in the early rate of force development (P = 0.04).

CONCLUSIONS

Higher VL thresholds (i.e., VL20 and VL40) maximized hypertrophic adaptations, although an excessive VL during the set (i.e., VL40) may also induce negative neuromuscular adaptations. Therefore, moderate VL thresholds should be chosen to maximize strength adaptations and to prevent negative neuromuscular adaptations.