Maximal Voluntary Isometric Contraction Research Articles

Enhanced inhibitory input to triceps brachii in humans with spinal cord injury.

Most individuals with cervical spinal cord injury (SCI) show increased muscle weakness in the elbow extensor compared to elbow flexor muscles. Although this is a well-known functional deficit, the underlying neural mechanisms remain poorly understood. To address this question, we measured the suppression of voluntary electromyographic activity (svEMG; a measurement thought to reflect changes in intracortical inhibition) by applying low-intensity transcranial magnetic stimulation over the arm representation of the primary motor cortex during 10% of isometric maximal voluntary contraction (MVC) into elbow flexion or extension in individuals with and without chronic cervical SCI. We found that the svEMG latency and duration were not different between the biceps and triceps brachii in controls but prolonged in the triceps in individuals with SCI. The svEMG area was larger in the triceps compared to the biceps in both groups and further increased in SCI participants, suggesting a pronounced intracortical inhibitory input during elbow extension. A negative correlation was found between svEMG area and MVCs indicating that control and SCI participants with lower svEMG area had larger MVCs. The svEMG area was not different between 5% and 30% of MVC, making it less probable that differences in muscle strength between groups contributed to our results. These findings support the existence of strong inhibitory input to corticospinal projections controlling elbow extensor compared to flexor muscles, which is more pronounced after chronic cervical SCI. KEY POINTS: After cervical spinal cord injury (SCI), people often recover function in elbow flexor, but much less in elbow extensor muscles. The neural mechanisms contributing to this difference remain unknown. We measured the suppression of voluntary electromyographic activity (svEMG) elicited through low-intensity transcranial magnetic stimulation of the primary motor cortex (assumed to reflect changes in intracortical inhibition) in the biceps and triceps muscles in controls and individuals with cervical chronic incomplete SCI. We found increased svEMG area in the triceps compared to the biceps in controls and SCI participants, with this measurement being even more pronounced in the triceps after SCI. The svEMG area correlated with maximal voluntary contraction values in both groups, suggesting the people with lesser inhibition had larger motor output. Our results support the presence of strong cortical inhibitory input to corticospinal projections controlling elbow extensor compared to elbow flexors muscles after cervical SCI.

Comparison of muscle activation during quadrupedal movement training and traditional bodyweight exercises

Quadrupedal movement training (QMT) is a unique form of bodyweight training shown to improve flexibility, FMS scores, and proprioception, however, little is known about its muscle activation characteristics. Therefore, the purpose of this study was to compare surface EMG (sEMG) activity of muscles of the trunk, upper, and lower extremity during QMT movements and common traditional bodyweight exercises (TRA). Twenty (males n = 9) participants (age: 27.5 ± 10.8 yrs, height: 169.0 ± 7.0 cm, mass: 66.6 ± 10.9 kg) were prepped and fitted with sEMG electrodes on their right-side bicep brachii, medial deltoid, triceps brachii, pectoralis major, latissimus dorsi, rectus abdominus, rectus femoris and bicep femoris. Following completion of maximal voluntary isometric contraction (MVIC) tests for normalization, participants performed 4 repetitions of 8 QMT exercises (from the Animal Flow™ system) and 3 TRA exercises (pushup, squat and forearm plank) in random order. The pooled peak muscle activations of all QMT exercises resulted in moderate (21–40% MVIC) to very high (>60% MVIC) peak muscle activation levels for each muscle group with significantly higher (p > 0.05) muscle activation for the biceps (47.72 ± 21.41%), deltoid (66.58 ± 11.39%), and latissimus dorsi (62.81 ± 18.14%) than the pushup (23.31 ± 16.95, 45.63 ± 18.59, 29.17 ± 20.58% respectively) and significantly higher activation of the bicep femoris (41.89 ± 13.83%) than the squat (17.79 ± 11.12%). TRA (pushup) showed significantly higher activation of the triceps and pectoralis. There were no differences in rectus femoris or rectus abdominus. Muscle activation levels during QMT are comparable to or higher than common traditional bodyweight exercises and therefore may be an appealing strategy for training multiple muscle groups simultaneously.

Spinal muscle characteristics during three different types of locomotion activities among college students with idiopathic scoliosis

Background contextPhysical activities such as walking and climbing stairs are pervasive in human daily life. Individuals with scoliosis frequently encounter dysfunction in their muscle recruitment. Multiple studies have corroborated the presence of muscle dysfunction in individuals diagnosed with scoliosis. However, there is currently a noteworthy research gap regarding the exploration of changes in muscle characteristics and disparities from those observed in individuals without scoliosis during everyday activities, specifically stair climbing.PurposeThis study aims to examine the unique patterns of muscle activity during daily life in individuals with scoliosis and distinguish the specific differences between scoliosis patients and the healthy controls. The findings of this study are significantly important for the future accurate assessment of scoliosis and the development of rehabilitation treatment plans.Study designCase–control study.Sample sizeTwenty eight idiopathic scoliosis patients and twenty eight controls.Outcome measuresRoot Mean Square(RMS), Maximum Voluntary Isometric Contraction(MVIC)%, RMS ratio(RMS convex / RMS concave).MethodsThe surface electromyography (sEMG) device used in this study was the Delsys Trigno, with a sampling frequency of 1500 Hz. It recorded the activation level, peak contraction, and average activation level of the erector spinae (at T6, T10, and L3 levels), gluteus maximus, gluteus medius, external oblique, and rectus abdominis muscles during three different types of locomotion for both the 28 individuals with idiopathic scoliosis and the 28 control participants.ResultsThe movement patterns of the idiopathic scoliosis patients significantly differ from those of the normal population during level walking and ascending or descending stairs. In level walking, there is an asymmetry in the activation levels of the T6 and L3 erector spinae muscles, with lower activation on the convex side compared to the concave side. Similarly, during stair ascent, the activation of the T6 and T10 erector spinae muscles is asymmetric, with higher activation on the convex side than the concave side. Moreover, during stair descent, the activation of the T6 erector spinae muscle is asymmetric, with higher activation on the convex side than the concave side.ConclusionsDuring level walking and stair activities, idiopathic scoliosis patients exhibit pronounced abnormal movement patterns that significantly differ from those of the control group. Under different activity conditions such as level walking, ascending and descending stairs, idiopathic scoliosis patients demonstrate abnormal muscle activation in different segments of the spine. It is crucial for clinicians to prioritize the symmetry of muscle activation in the spinal region of idiopathic scoliosis patients and consider incorporating symmetry training for these muscles.

Motion Tape Strain During Trunk Muscle Engagement in Young, Healthy Participants

Background: Motion Tape (MT) is a low-profile, disposable, self-adhesive wearable sensor that measures skin strain. Preliminary studies have validated MT for measuring lower back movement. However, further analysis is needed to determine if MT can be used to measure lower back muscle engagement. The purpose of this study was to measure differences in MT strain between conditions in which the lower back muscles were relaxed versus maximally activated. Methods: Ten participants without low back pain were tested. A matrix of six MTs was placed on the lower back, and strain data were captured under a series of conditions. The first condition was a baseline trial, in which participants lay prone and the muscles of the lower back were relaxed. The subsequent trials were maximum voluntary isometric contractions (MVICs), in which participants did not move, but resisted the examiner force in extension or rotational directions to maximally engage their lower back muscles. The mean MT strain was calculated for each condition. A repeated measures ANOVA was conducted to analyze the effects of conditions (baseline, extension, right rotation, and left rotation) and MT position (1–6) on the MT strain. Post hoc analyses were conducted for significant effects from the overall analysis. Results: The results of the ANOVA revealed a significant main effect of condition (p < 0.001) and a significant interaction effect of sensor and condition (p = 0.01). There were significant differences in MT strain between the baseline condition and the extension and rotation MVIC conditions, respectively, for sensors 4, 5, and 6 (p = 0.01–0.04). The largest differences in MT strain were observed between baseline and rotation conditions for sensors 4, 5, and 6. Conclusions: MT can capture maximal lower back muscle engagement while the trunk remains in a stationary position. Lower sensors are better able to capture muscle engagement than upper sensors. Furthermore, MT captured muscle engagement during rotation conditions better than during extension.

Reliability of a standardized protocol of the Single Leg Heel Rise Test

The single leg heel rise (SLHR) test is a widely used method for assessing calf muscle-tendon unit (MTU) endurance in various fields, including medicine, sports, and dance. The objectives of this study were to examine the reliability of a standardized SLHR test protocol with a heel rise measurement device and to investigate the relationship between SLHR repetitions, SLHR total work, and both maximal voluntary isometric contraction (MVIC) and reactive strength index (RSI) outcomes of the plantar flexors. 21 sport students (8 females, 13 males) were assessed for SLHR outcomes (number of repetitions, height of heel rises, total positive work performed) in two data collection sessions, as well as unilateral lower extremity MVIC and RSI. Test-retest reliability showed excellent reliability and low variability for the number of repetitions (Intraclass correlation coefficient (ICC)=0.91, 95% CI: 0.73 to 0.97; coefficient of variability (CV): 8.1- 8.7%), height of the heel rises (ICC=0.92, 95% CI: 0.81 to 0.97; CV: 4.6 - 5.2%) and total positive work performed (ICC=0.96, 95% CI: 0.87 to 0.99; CV: 6.8 - 9.8%) in both feet. No significant correlation was identified between SLHR repetitions, MVIC, and reactive strength outcome measures. A moderate correlation was observed between the total work performed in the SLHR and RSI outcomes that could potentially be explained by the body weight (BW) of the participants. The SLHR test provides reliable measures for lower leg muscular endurance, yet it does not predict plantar flexor maximal strength or reactive strength. In future studies, we advise employing this standardized protocol for screenings of athletes and dancers.

Relationship Between Pain, Muscle Strength, Function, and Quality of Life in Overhead Players With Chronic Internal Shoulder Impingement

Background and Objectives: This study aims to determine the relationship between pain, muscle strength, function, and quality of life (QoL) in overhead players with chronic shoulder internal impingement syndrome. Methods: Forty-seven overhead players consisting of 15 men, 32 and women (mean age 32.45±7.2) with chronic shoulder internal impingement were enrolled. The pain was measured by a visual analogue scale (VAS). Disabilities of the arm, shoulder, and hand (DASH) and shoulder pain and disability index (SPADI) questionnaires were used to measure pain and function, and a short form (SF)-36 questionnaire to measure QoL. Muscle strengths were evaluated in both hands with a hand-held dynamometer and players were asked to hold the maximal voluntary isometric contraction (MVIC) in the middle range for 3 s and rest for 30 s between each test and each contraction was repeated three times on both affected and healthy side and the average of contractions was considered for each side. Results: The study showed a significant relationship between pain, the strength of shoulder muscle groups (-0.354), function (-0.935), and QoL (-0.861) in overhead throwers with chronic shoulder internal impingement syndrome and the strength of internal rotators of the affected shoulder decreased more than others. (P<0.05) Conclusions: This correlational study showed a significant relationship between pain and strength of shoulder muscles and function and QoL in overhead throwers with this syndrome.

Acute effects of resistance exercise on the muscle architecture and tissue organization of the maximal isometrically contracted and uncontracted gastrocnemius medialis muscle

ABSTRACT This study aimed to investigate the acute effects of resistance exercise on muscle architecture and tissue organization at rest and during isometric maximum voluntary contraction (iMVC) of the gastrocnemius medialis muscle. In 16 healthy adults (25 ± 3 y), ultrasound scans were captured before (pre), immediately after (post), and 15 min after (post_15) single-leg calf raises during rest and iMVCs. Measurements included muscle thickness (MT), pennation angle (PA), and fascicle length (FL). Spatial frequency analysis (SFA) assessed tissue organization (e.g. peak spatial frequency radius (PSFR), quality factor (Q6)). MT increased significantly from pre to post (+5.7%) and post_15 (+5.6%) at rest. During iMVC, MT and FL increased significantly from pre to post (MT: +8.1%, FL: +14.9%) and post_15 (MT: +5.2%, FL: +10.5%), while PA decreased significantly from pre to post_15 (−10.2%). PSFR and Q6 decreased significantly from pre to post (−7.0-8.2%) and increased from post to post_15 (+10.3-10.6%) at rest, with no significant changes during iMVC. Resistance exercise led to altered muscle architecture for more than 15 min, while SFA parameters reverted to baseline within 15 min. Thus, SFA potentially enables early differentiation of potential physiological alterations in muscle micro-morphology.

Changes in hamstrings’ active stiffness during fatigue tasks are modulated by contraction duration rather than intensity

Despite the increase in research of hamstring stiffness through the use of ultrasound-based shear wave elastography, the active stiffness of biceps femoris long head (BFlh) and semitendinosus (ST) muscles under fatigue conditions at various contraction intensities has not been sufficiently explored. This study aimed to compare the effects of knee flexor’s isometric contraction until exhaustion performed at 20% vs. 40% of maximal voluntary isometric contraction (MVIC), on the active stiffness responses of BFlh and ST. Eighteen recreationally active males performed two experimental sessions. The knee flexors’ MVIC was assessed before the fatiguing task, which involved a submaximal isometric contraction until failure at 20% or 40% of MVIC. Active muscle stiffness of the BFlh and ST was assessed using shear wave elastography. BFlh active stiffness remained relatively unaltered at 20% of MVIC, while ST active stiffness decreased from ≅ 91% contraction time (55.79 to 44.52 kPa; p < 0.001). No intramuscular stiffness changes were noted in BFlh (36.02 to 41.36 kPa; p > 0.05) or ST (63.62 to 53.54 kPa; p > 0.05) at 40% of MVIC session. Intermuscular active stiffness at 20% of MVIC differed until 64% contraction time (p < 0.05) whereas, at 40% of MVIC, differences were observed until 33% contraction time (p < 0.05). BFlh/ST ratios were not different between intensities (20%=0.75 ± 0.24 ratio vs. 40%=0.72 ± 0.32 ratio; p > 0.05), but a steeper increase in BFlh/ST ratio was found for 20% (0.004 ± 0.003 ratio/%) compared to 40% (0.001 ± 0.003 ratio/%) of MVIC (p = 0.003). These results suggest that contraction duration could play a major role in inducing changes in hamstrings’ mechanical properties during fatigue tasks compared to contraction intensity.

The Effects of Inorganic Nitrate Supplementation on Muscular Power and Endurance Across the Menstrual Cycle.

Oral inorganic nitrate (NO3-) supplementation increases nitric oxide (NO) bioavailability and may improve muscular power in males and females, although data in females is limited. Estrogen increases NO bioavailability and fluctuates throughout the menstrual cycle (MC), with low levels in the early follicular (EF) phase and peaking during the late follicular (LF) phase. The purpose of the present study was to examine the effects of NO3- supplementation on isokinetic peak power, maximal voluntary isometric contraction (MVIC) force, muscular endurance, and recovery from fatigue in healthy young females during the EF and LF phases of the MC. Ten eumenorrheic females were tested in a double-blinded, randomized, placebo-controlled design. Participants consumed ~13mmol NO3-, in the form of 140ml beetroot juice (BRJ), or an identical NO3--depleted placebo (PL), for ~5 days prior to visits and 2 hours prior to testing. Plasma estradiol was elevated in the LF phase, and plasma nitrite and nitrate were elevated in the BRJ condition (p < 0.05). While isokinetic peak power was unchanged, calculated maximal power (Pmax) and maximal velocity (Vmax) was significantly worsened in the BRJ treatment independent of the MC phase (p = 0.02 and 0.03, respectively). Muscular endurance, MVIC, and fatigue recovery were unaltered by BRJ or the MC. These data indicate that NO3- supplementation decreased maximal power and velocity in females and suggest that the benefits of NO3- supplementation previously found in males may not extend to young females.

The influence of Sex on the Effects of Inorganic Nitrate Supplementation on Muscular Power and Endurance.

Inorganic nitrate (NO3-) supplementation increases nitric oxide (NO) bioavailability and may improve muscular power and endurance, although most studies are in males. Therefore, the present double-blind, randomized, placebo-controlled study examined the effects of NO3- supplementation on isokinetic peak power, maximal voluntary isometric contraction (MVIC) force, muscular endurance (time-to-task failure; TTF), and recovery from fatigue in young females (n=12) and males (n=14). Participants consumed ~13mmol NO3- (BRJ), or an identical NO3--depleted beverage (PL), for ~3 days and 2 hours before testing visits. Plasma nitrate and nitrite were elevated in the BRJ condition (p ≤ 0.05). Peak power (W·kg-1) showed a sex effect (p ≤ 0.05) at all angular velocities and a sex-by-treatment effect at 270 and 360°/sec (p ≤ 0.05). Post hoc analysis revealed no significant differences between treatments (p > 0.05). Estimated maximal knee extension power (Pmax) and maximal knee extension velocity (Vmax) demonstrated no sex, treatment, or sex-by-treatment effect (p > 0.05). There were no significant effects for TTF (F: PL; 269±161 vs BRJ; 277±158s and M: PL; 228±171 vs BRJ; 194±100s; p > 0.05). Cohen's d effect sizes for peak power showed moderate to large effect sizes at 270 (d=0.92) and 360 deg/sec (d=0.81), showing a possible differentiated effect of dietary nitrate in females and males. The present data indicate that NO3- supplementation does not significantly affect knee extensor maximal power, maximal contraction velocity, and muscular endurance in either sex. The sex-dependent response to dietary nitrate supplementation requires further investigation as data on females is scarce.

Popliteal plexus block compared with tibial nerve block on rehabilitation goals following total knee arthroplasty: a randomized non-inferiority trial

This trial examined the effectiveness of the popliteal plexus block (PPB) and tibial nerve block (TNB) for early rehabilitation after total knee arthroplasty (TKA). We allocated 136 participants to receive PPB or TNB with 0.25% levobupivacaine 10 mL in a randomized, double-masked manner. The primary outcome was achieving rehabilitation goals with a non-inferiority 9-hour margin, including adequate pain relief, knee flexion angles over 90 degrees, and enabling ambulatory rehabilitation. The time to reach rehabilitation goals showed non-inferiority with 49.7 ± 10.5 h for TNB and 47.4 ± 9.7 h for PPB, whose mean difference (PPB - TNB) was − 2.3 h (95% CI -5.8 to 1.2 h; P < 0.001). PPB showed higher dorsal and plantar percentage of maximum voluntary isometric contraction (dorsal, PPB 87.7% ± 11.4% vs. TNB 74.0% ± 16.5%: P < 0.001; plantar, PPB 90.9% ± 10.3% vs. TNB 72.1% ± 16.0%; P < 0.001) at six hours after nerve block. No significant differences between the two groups emerged in pain scores, knee range of motion, additional analgesic requirements, success in the straight leg raise, and adverse events. PPB exhibited non-inferiority to TNB in achieving postoperative rehabilitation goals and had superiority in preserving foot motor strength after TKA. (200)

Flexibar And Non-Flexibar Exercises And Its Effects On Trunk Activation- A Review Of Literature

Objective: To systematically review the randomised controlled trials to evaluate the effects of flexi-bar and non-flexi-bar exercises, specifically stabilization training, on trunk muscle activity in various postures. Methodology: The study included randomized control trials and clinical trials published between 2007-2018 , focusing on patients with upper trunk muscle weakness aged above 18. Exclusion criteria included a study with overlapping data, a study with associated disorders, or abstract-only papers. The search strategy involved a search of existing literature from databases like PubMed, Google Scholar, Cochrane Library, PEDro, and Research Gate, removing duplicates and identifying relevant articles. The full-text screening was performed, and the remaining relevant articles underwent data extraction. Surface electromyography (EMG) was used to measure the activity of selected trunk muscles, which was then normalized to maximum voluntary isometric contraction. Results: The findings of this study indicate that flexi-bar exercises resulted in higher activation of trunk muscles compared to non-flexi-bar exercises (stabilization training). The unique physical response induced by the vibration created through the swinging motion of the flexi bar triggered reflexive contractions of core muscles, leading to increased muscle activity. This suggests that flexi bar exercises may be beneficial in promoting muscular activation and potentially alleviating low back pain by evening out muscular imbalances.Conclusion: The results of this study support the use of flexi-bar exercises for activating trunk muscles, particularly when compared to non-flexi-bar exercises (stabilization training).

Biomechanics of the Human Knee Joint in Maximum Voluntary Isometric Flexion: Study of Changes in Applied Moment, Agonist-Antagonist Participations, Joint Center, and Flexion Angle.

Estimation of the knee joint strength by maximum voluntary isometric contraction (MVIC) is a common practice to assess strength, coordination, safety to return to work or engage in sports after an injury, and to evaluate the efficacy of treatment modalities and rehabilitation strategies. In this study, we utilize a previously validated coupled finite element-musculoskeletal model of the lower extremity to explore the sensitivity of output measures (posterior cruciate ligament [PCL]/muscle/contact forces and passive moments) in knee MVIC flexion exercises at seated position. To do so, at three knee flexion angles (KFA), input measures (resistance moment and contribution moments of quadriceps and gastrocnemii) were varied at four levels each using the Taguchi design of experiment. Our findings reveal significant increases in PCL forces with KFA (p < 0.01), net MVIC moment (p < 0.01), and resistance moment of quadriceps (p < 0.01). In contrast, they drop at larger activity in gastrocnemii (p < 0.01). Tibiofemoral (TF) contact forces increase with the net MVIC moment (p < 0.01). The passive knee flexion moment, while highly dependent on the location at which computed, also increases with the net MVIC moment (p < 0.01). Changes in KFA, MVIC moment, and proportions thereof carried by quadriceps and/or gastrocnemii substantially affect biomechanics of the joint. Compared with level walking and stair ascent, slightly larger contact forces/stresses and much greater PCL forces are computed. This study improves our understanding of the knee joint behavior during MVIC in effective evaluation and rehabilitation interventions. Besides, it emphasizes the importance of positioning the joint center in model studies.

Eicosapentaenoic Acid and Medium-Chain Triacylglycerol Structured Lipid Supplementation Improves Muscular Endurance Exercise Performance and Reduces Muscle Fatigue in Young Healthy Male

Objective Structured lipids containing medium-chain fatty acids, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) from fish oil (EPA/MCT) and it improve overall endurance. However, their effects on local muscle endurance remain unclear. This study aimed to investigate the effects of EPA/MCT intake on muscle endurance during leg extension exercises and subsequent muscle fatigue. Methods This 8-week, placebo-controlled, randomized, double-blind parallel-group trial involved 20 healthy young men. Subjects were randomly assigned to an EPA/MCT group (10 subjects) and a placebo group (PL group, 10 subjects). They consumed 4560 mg of the test food daily for 8 wk before an exercise intervention. The EPA/MCT supplement contained 600 mg of EPA, 260 mg of DHA, and 1890 mg of MCT (1110 mg of octanoic acid and 780 mg of decanoic acid). After the 8-week intervention, the subjects performed four sets of leg extension exercises at 40% of their body weight until exhaustion. The number of repetitions per set and the total repetitions across the four sets served as indicators of muscle endurance. Isometric maximum voluntary contraction (MVC), range of motion, circumference, muscle thickness, echo intensity, and muscle stiffness were measured before and after exercise to assess muscle fatigue. Results There was no difference between the groups in the number of repetitions for sets 1–4 or in the total number of repetitions during the leg extension exercise. In the EPA/MCT group, a significant negative correlation was observed between the increase in the blood EPA/AA ratio and the rate of decrease in the number of repetitions. Additionally, the decrease in MVC after exercise was significantly smaller in the EPA/MCT group than in the PL group. Conclusion Our study results suggest that an 8-week intake of EPA/MCT can increase the blood EPA/AA ratio and improve muscle endurance performance. Additionally, EPA/MCT intake reduces muscle fatigue after exercise.

Isometric Force-Time Curve Assessment: Accuracy, Precision, and Repeatability of a Mobile Application and Portable and Lightweight Device.

Strength assessment is one of the main fields in sports performance, physical rehabilitation, physical activity, and health. We aimed to compare maximal voluntary isometric contractions (MVICs) and paired voluntary isometric contractions (VICs) of knee extensors between an isokinetic dynamometer (BIODEX) and a portable and lightweight device (DINABANG). From 19 volunteers (age: 28.7 ± 7 years; body mass: 72 ± 10 kg; and height: 173 ± 7 cm) we obtained 114 paired MVIC measures and, from the force-time curves of these repetitions, 22,507 paired VIC measures of knee extensors. We observed "excellent" repeatability for MVICs (ICC:1.00; p < 0.001) between BIODEX (247 ± 79.5 Nm) and DINABANG (247 ± 74.8 Nm), with "trivial" effect (mean difference: 0.12 Nm (0.02%); 95%CI: -0.13 to 0.23 Nm; p = 0.606; d = 0.048). Bland-Altman plots revealed high accuracy for MVIC (bias: 0.12 Nm) and consistent distribution (precision) inside the limits of agreement (-4.81 to 5.06 Nm) and respective 95%CI. "Excellent" repeatability was also observed for VICs (ICC:1.00; p < 0.001) between BIODEX (219 ± 84.1 Nm) and DINABANG (218 ± 84.0 Nm), with "trivial" effect (0.24 Nm (0.11%); 0.08 to 0.11 Nm; p < 0.001; d = 0.100). Bland-Altman plots revealed high accuracy for VICs (bias: 0.24 Nm) and consistent distribution (precision) inside the limits of agreement (-4.5 to 4.9 Nm) and respective 95%CI. DINABANG is accurate, precise, and reliable in torque measurement.

Neural and Muscular Determinants of Performance Fatigability Are Independent of Work and Recovery Durations During High-Intensity Interval Exercise in Males

ABSTRACT The present study aimed to investigate the effect of two protocols of high-intensity interval exercise (HIIE) on performance fatigability and its neural and muscular determinants. On different days, 14 healthy males performed two HIIE protocols with different work and recovery durations (matched for total duration, work and recovery intensities, and density): 1) 4 × 4 min at 90% HRpeak,180-s recovery at 70% HRpeak; and 2) 16 × 1 min at 90% HRpeak, 45-s recovery at 70% HRpeak. Pre- to post-HIIE reduction in maximal voluntary isometric contraction (MVIC) was used as marker of performance fatigability, while voluntary activation (VA) and potentiated quadriceps twitch force (Qtw) as markers of the neural (i.e. central fatigue) and muscular (i.e. peripheral fatigue) determinants, respectively. In addition, pre- to post-HIIE reduction in twitch force stimulated at 100 Hz (Qtw100) and 10:100 Hz ratio (Qtw10:Qtw100) were used as markers of high- and low-frequency performance fatigability, respectively. The MVIC, VA, Tw, Qtw100, and Qtw10:Qtw100 ratio decreased similarly from pre- to post-HIIE in both HIIE protocols (p < .05). The rating of perceived effort, blood pH, and plasma lactate responses were similar between HIIE protocols (p > .05), but the heart rate was higher in the longer HIIE protocol (p < .05). In conclusion, performance fatigability and its neural and muscular determinants seemed to be independent of the work and recovery durations of the HIIE, at least when HIIE protocols were matched for total work duration, work and recovery intensities, and density. Further, HIIE with long work and recovery might be preferable when the intention is to stress the chronotropic response.

Acute effects of local vibration inducing tonic vibration reflex or illusion of movement on maximal wrist force production.

Local vibration (LV) mainly stimulates primary afferents (Ia) and can induce a tonic vibration reflex (TVR) and an illusion of movement. This study aimed to evaluate the effect of these two phenomena on maximal voluntary isometric contraction (MVIC) capacity. LV (80 Hz) was applied to the wrist flexor muscles in two randomized experiments for 6 min. LV conditions were adjusted to promote either TVR (visual focus on the vibrated wrist) or ILLUSION [hand hidden, visual focus on electromyographic activity of the flexor carpi radialis muscle (FCR)]. Mechanical and electromyographic (EMG) responses of the FCR and extensor carpi radialis muscles were recorded during MVIC in flexion and extension and during electrically evoked contractions at supramaximal intensity. Measurements were performed before (10 min and just before) and after (0 and 30 min) LV protocol. An increase in FCR EMG was observed during LV in the TVR condition (+340%) compared with the illusion condition (P = 0.003). In contrast, the movement illusion was greater in the ILLUSION condition (assessed through subjective scales) (P = 0.004). MVIC was reduced in flexion only after the TVR condition ([Formula: see text], all P < 0.034). Moreover, the decrease in force was correlated with the amount of TVR recorded on the FCR muscle (r = -0.64, P = 0.005). Although potentiated doublets of each muscle did not evolve differently between conditions, a decrease was observed between the first and the last measure. In conclusion, when conducting research to assess maximal strength, it is necessary to have better control and reporting of the phenomena induced during LV.NEW & NOTEWORTHY The maximal force production of the vibrated muscle is reduced after 6 min of LV only in TVR condition. Furthermore, the amount of TVR is negatively correlated with this force decrease. When measuring the effects of LV on maximal force production, it is important to control and report any phenomena induced during vibration, such as TVR or movement illusion, which can be achieved by recording EMG activity of vibrated muscle and quantifying illusion.

Surface electromyographic analysis of the bilateral abdomen and back muscle during selected yoga posture

Sedentary lifestyles lead to postural deformities, Lower Back Pain(LBP) and Colorectal cancer(CRC). Practicing Yoga attains definite strength in muscles by activating muscle fibers. The Yoga poses analyzed are often used in strengthening and stability programs for the abdomen and back muscles. ObjectiveTo determine the potential use of Dolphin pose and Dolphin plank in specific strengthening endurance and rehabilitation programs via sEMG analysis in the selected bilateral abdomen and lower back muscles. MethodsSurface electromyographic analysis was conducted on bilateral muscles, including the Rectus Abdominis(RA), External oblique(EO), Internal oblique(IO), and Erector Spinae(ES), resulting in Dolphin pose(DS), Dolphin plank(DP), and High plank(HP). Data were expressed by Root Mean Square(RMS) of each bilateral muscle during each Pose normalized as 100% of maximum voluntary isometric contraction(MVIC). ResultsDolphin plank(DP) generated a very high-level muscle activation than 100% MVIC in all bilateral muscles, and there was a significant main effect of Pose e (p < 0.001). Erector spinae generated more activation in the Dolphin pose (p < 0.05) than in the HP and DS. No significant difference between bilateral activity differences in DP and DS. There was a significant difference between RRA and LRA (p < 0.001) and RIO and LIO (p < 0.0001). ConclusionFindings have suggested that the Dolphin plank could be used for abdomen strengthening, performance enhancement, and rehabilitation programs. Dolphin pose may benefit lower back stability by providing endurance to the Erector spinae muscle. So, this yoga pose can be incorporated into the yoga training module for addressing lower back pain(LBP) caused by longer sitting in a sedentary lifestyle.

Using nonlinear dynamics analysis to evaluate time response of cupping therapy with different intervention timings on reducing muscle fatigue.

Cupping therapy has been indicated effective in reducing muscle fatigue after 24h based on the spectral analyses of surface electromyography (sEMG). However, there is no sufficient evidence showing changes of sEMG nonlinear indexes at more time points after cupping therapy. Furthermore, it is unclear whether the intervention timings of cupping therapy affect the recovery from muscle fatigue. The purpose of this study was to use the sEMG nonlinear analysis to assess the difference of time response of cupping therapy between different intervention timings after muscle fatigue. This randomized controlled trial recruited 26 healthy volunteers. Cupping therapy (-300mmHg pressure for 5min by the 45mm-diameter cup) was applied before (i.e., pre-condition) or after (i.e., post-condition) muscle fatigue induced by performing repeated biceps curls at 75% of the 10 repetitions of maximum (RM) on the non-dominant upper extremity. Subjects were randomly allocated to the pre-condition group or the post-condition group. The sEMG signals during the maximal voluntary isometric contractions (MVC) of the biceps were recorded at four time points (i.e., baseline; post 1: immediate after cupping-fatigue/fatigue-cupping interventions; post 2: 3h after cupping-fatigue/fatigue-cupping interventions; post 3: 6h after cupping-fatigue/fatigue-cupping interventions). Two nonlinear sEMG indexes (sample entropy, SampEn; and percent determinism based on recurrence quantification analysis, %DET) were used to evaluate the recovery from exercise-introduced muscle fatigue. The Friedman test followed by the Nemenyi test and the Mann-Whitney U test were applied in statistics. The SampEn and %DET change rate did not show any significant differences at four time points in the pre-condition group. However, there were significant delayed effects instead of immediate effects on improving muscle fatigue in the post-condition group (SampEn change rate: baseline 0.0000 ± 0.0000 vs. post 2 0.1105 ± 0.2253, p < 0.05; baseline 0.0000 ± 0.0000 vs. post 3 0.0627 ± 0.4665, p < 0.05; post 1-0.0321 ± 0.2668 vs. post 3 0.0627 ± 0.4665, p < 0.05; and %DET change rate: baseline 0.0000 ± 0.0000 vs. post 2-0.1240 ± 0.1357, p < 0.01; baseline 0.0000 ± 0.0000 vs. post 3 0.0704 ± 0.6495, p < 0.05; post 1 0.0700 ± 0.3819 vs. post 3 0.0704 ± 0.6495, p < 0.05). Moreover, the SampEn change rate of the post-condition group (0.1105 ± 0.2253) was significantly higher than that of the pre-condition group (0.0006 ± 0.0634, p < 0.05) at the post 2 time point. No more significant between-groups difference was found in this study. This is the first study demonstrating that both the pre-condition and post-condition of cupping therapy are useful for reducing muscle fatigue. The post-condition cupping therapy can e ffectively alleviate exercise-induced muscle fatigue and there is a significant delayed effect, especially 3h after the interventions. Although the pre-condition cupping therapy can not significantly enhance muscle manifestations, it can recover muscles into a non-fatigued state.

Influence of Changing Hip Position on Electromyographic Activities of Selected Trunk Muscles During Bridging Exercises in Healthy Subjects: A Cross-Sectional Study

Objective: The purpose of this study was to investigate how rectus abdominis, external oblique (EO), internal oblique (IO), erector spinae, multifidus (MF), and gluteus maximus (GMax) muscle activities change with different hip positions during back and side bridging exercises. MethodsThirty-six healthy individuals participated in this cross-sectional study and performed 6 exercises including back bridging (BB) in neutral hip position, BB with internal rotation, BB with external rotation (BB + ER), side bridging with hips in neutral (SB), side bridging with hips in flexion (SB + HF), and side bridging with hips in extension (SB + HE). Muscle activity was observed using surface electromyography, normalized using maximum voluntary isometric contraction. Repeated-measures 1-way analysis of variance compared muscle readings for each position. ResultsBack bridging with internal rotation showed significant differences in EO (P = .01) and IO (P < .001) compared with other BB positions. Multifidus and GMax differed significantly in BB + ER (P = .04). Side bridging exhibited significant differences in EO (P = .02; P < .001) and IO (P < .001) compared with the other 2 SB positions, with peak in SB + HF. Erector spinae, MF, and GMax also differed significantly (P < .001, P = .02, P < .001, respectively) with peak in SB + HE. ConclusionThe findings revealed that EO and IO muscles were most active during BB with internal rotation, whereas the MF and GMax muscles were most active during BB + ER. In terms of SB, the EO and IO muscles were most active with either SB + HF or SB + HE, whereas the erector spinae, MF, and GMax muscles were most active with SB + HE.