Isometric Contraction Research Articles

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.

Effects of low-intensity isometric handgrip training on home blood pressure in hypertensive patients: a randomized controlled trial.

We examined if lower intensity isometric handgrip (IHG) training than usual load could significantly reduce home blood pressure (HBP) in treated Japanese hypertensive patients. Sixty patients (mean age, 66.9 years; 44.6% men) with high blood pressure to grade 1 hypertension level were randomly assigned to an IHG or control group. The IHG group performed IHG training for 12 weeks, followed by a 12 weeks of detraining. The control group did not any IHG training. The IHG training comprised four sets of 2-min isometric contractions at 15% of maximum voluntary contraction (MVC) or half than usual, including 1 min of rest between sets, for ≥3 days a week. At the end of the former phase, both morning and evening systolic HBP (HSBP) and evening diastolic HBP (HDBP) were significantly higher than those at baseline in the control group while neither morning nor evening HSBP remained unchanged in the IHG group. Morning HBPs increased at the end of the latter phase than those at the end of the former phase in the IHG group and remained unchanged in the control group. The change (Δ) in morning HSBP from baseline to the end of the former phase was smaller in the IHG group than that in the control group (Δ4.1 mmHg vs. Δ0.0 mmHg, p = 0.05). A similar tendency was observed after adjusting baseline HSBP and seasonal variation (p = 0.06). In conclusion, a 12-week IHG training at 15% of MVC significantly lowered morning HSBP by approximately 4.0 mmHg in treated Japanese hypertensive patients. This study showed that a 12-week IHG training at 15% of MVC lowered morning HSBP by about 4.0 mmHg in treated Japanese hypertensive patients. Continuous low-intensity IHG training may provide a stable hypotensive effect in high blood pressure to grade 1 hypertensive population.

Impact of contraction intensity and ankle joint angle on calf muscle fascicle length and pennation angle during isometric and dynamic contractions

During muscle contraction, not only are the fascicles shortening but also the pennation angle changes, which leads to a faster contraction of the muscle than of its fascicles. This phenomenon is called muscle gearing, and it has a direct influence on the force output of the muscle. There are few studies showing pennation angle changes during isometric and concentric contractions for different contraction intensities and muscle lengths. Therefore, the aim was to determine these influences over a wide range of contraction intensities and ankle joint angles for human triceps surae. Additionally, the influence of contraction intensity and ankle joint angle on muscle gearing was evaluated. Ten sport students performed concentric and isometric contractions with intensities between 0 and 90% of the maximum voluntary contraction and ankle joint angles from 50° to 120°. During these contractions, the m. gastrocnemius medialis and lateralis and the m. soleus were recorded via ultrasound imaging. A nonlinear relationship between fascicle length and pennation angle was discovered, which can be described with a quadratic fit for each of the muscles during isometric contraction. A nearly identical relationship was detected during dynamic contraction. The muscle gearing increased almost linearly with contraction intensity and ankle joint angle.

The Effect of Isometric Exercise Position on the Effectiveness of Isolated Work of the Thigh Flexor Muscles Based on the Results of the sEMG Study.

The main function of the hamstring muscles is to bend the knee joint and support the function of the hip extensors. Their frequent injuries are the result of overload related to, among others, dynamic running or jumping, and inadequate preparation for athletics activities. The asymmetry of the work of individual flexor muscle groups is clearly marked in the case of valgus or varus of the knee joint, i.e., in different positions of the lower limb. The aim of the study was to determine the position and form of a rehabilitation exercise in which an isolated group of muscles flexing the knee joint will show the greatest bioelectrical activity. The study involved 25 students of the Jagiellonian University Medical College. The students were aged 20-26. The average age was 22.9 (±1.4). The study participants included 17 women with an average age of 23.0 (±1.1) and 8 men with an average age of 22.6 (±1.9). Women constituted 68% and men 32% of all respondents. All participants agreed to participate in the study. Surface electromyography measurements in both lower limbs provided an initial number of 50 cases. The activity of the knee flexor muscles during isometric contraction with resistance was measured in correlation with three foot and lower leg settings: internal rotation, neutral position, and external rotation. The bioelectrical activity of the semitendinosus muscle is significantly higher (p < 0.01) in the internal rotation position than in the neutral position of the lower leg, while the bioelectrical activity of the biceps femoris muscle is inversely higher (p < 0.01) in the external rotation position than in the neutral position. The results are significant for both average and maximum values of muscle stimulation. During isometric contraction with resistance, the semitendinosus muscle shows the greatest bioelectrical activity in the internal rotation position of the lower leg and foot, and the biceps femoris muscle in the external rotation position of the lower leg and foot. The above information has important implicational applications when improving isolated groups of hamstrings. In the future, this may contribute to more effective rehabilitation of patients with injuries of the muscles described in the article.

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.

Cardiovascular handgrip responses during treadmill exercise: randomized pilot trial.

The isometric exercise performed using the handgrip (HG) acutely promotes elevation of systolic blood pressure (SBP) and diastolic blood pressure (DBP), and in a non-consensual manner among articles elevation or maintenance of heart rate (HR). Currently, although there is a vast literature on the hemodynamic effects of interval training and isometric exercise with HG alone, there is still no consistent evidence of such adjustments occurring in the association between the two. Therefore, the objective of this study was to describe the acute hemodynamic responses found only during interval training and when combined with isometric contraction with HG. This is a pilot study of a crossover clinical trial. Seven male volunteers, aged 24±3.9 years, underwent three protocols on an ergometric treadmill, with a 3-minute warm-up at 30% of heart rate reserve (HRR), four sprints 2 minutes at 50% HRR and active intervals at the same speed as the warm-up. Randomization was carried out in a simple random manner. The protocols were classified according to the use of HG during sprints, as follows: PI = without HG; PII = HG 30% of handgrip strength (HGS) and PIII = 60% of HGS). Variations (Δ) in HR, double product (DP), SBP and DBP were evaluated. The presence of HG did not change HR behavior, but it increased DP (PI: 10,472±2,539 vs. PII: 12,217±1,933 vs. PIII: 13,369±3,089) through SBP, which in PI had a plateau behavior of 15±22.2 mmHg, while PII varied with an average of 41±12.2 mmHg and PIII 47±11.1 mmHg, in the 4th sprint. DBP fell in PI with 12±13.2 mmHg, while PII and PIII showed an drop of 0±19.6 and 6±13.0 mmHg in the last sprint, respectively. The use of HG during interval training directly modulates hemodynamic variables, promoting an increase in SBP elevation, attenuation of the drop in DBP and an increase in DP, without an increase in HR. RBR-78fhyrf. Available in https://ensaiosclinicos.gov.br/rg/RBR-78fhyrf.

The effects of different post-activation potentiation strategies on the performance of elite female track cyclists in position 1 of team sprint

The study aimed to optimise post-activation potentiation (PAP) strategies for Rider 1 in elite team sprints to improve performance over 250 m (opening lap), with a focus on female cyclists. Eight national-level track cyclists participated in this study, undergoing four sets of activation strategies: control (CON), dynamic high inertia (DYN, 4 × 4 pedal strokes), isometric contraction (ISO, 4 × 4 s, 4 angles), and back squat activation (BSQ, 4 × 4 rep, 80%1RM). The tests were divided into pre-activation and post-activation phases, including measurements at 4 min, 8 min, and 12 min after activation. The tests included a 250 m time trial (TT) and segment timing, with measurements of peak torque, peak power, average power, and cadence. The mean cadence, torque, and power for the first 62.5 m of pedal revolutions were collected. Paired-sample t-tests were used to assess activation differences. Multiple group comparisons were conducted using analysis of variance (ANOVA). The Bonferroni correction was used to control Type I errors. For significant activation strategies, linear or non-linear regression was applied to extrapolate the torque-cadence and power-cadence profiles, and the parameter differences were examined to investigate profile changes. Cohen’s d and Cohen’s f were used as effect sizes. After DYN activation, the 250 m TT significantly improved (p = 0.018), primarily through a reduction in the 62.5 m time (p = 0.006) and an increase in peak torque (p = 0.018). After 12 min of ISO activation, the 250 m TT showed a large effect but did not reach the significance level under Bonferroni correction (p = 0.135, d = 0.860), with a notable reduction in the 62.5 m time (p = 0.003). PAP can be strategically employed to enhance the performance of elite female Rider 1 in team sprints.

Effects of altered contractile environment on muscle shape change in the triceps surae.

Skeletal muscles change shape when they contract. Current insights into the effects of shape change on muscle function have primarily come from experiments on isolated muscles operating at maximal activation levels. However, when muscles contract and change shape, the forces they apply onto surrounding muscles will also change. The impact of an altered contractile environment (i.e., mechanical behaviour of surrounding muscle) on muscle shape change, remains unknown. To address this, we altered the mechanical contributions of the gastrocnemii during isometric plantarflexion contractions [via changing knee angle] and determined if there were associated changes in how the muscles of the triceps surae bulged in thickness during a ramped contraction. We combined B-mode ultrasound imaging with surface electromyography to quantify the neuromechanical contributions of the medial (MG) and lateral gastrocnemius (MG) and soleus (SOL) muscles during isometric plantarflexion contractions. Our results demonstrated that at the same SOL activity levels, altering knee angle had no influence on the magnitude of muscle shape change (thickness) in the triceps surae muscles. We observed high levels of inter-individual variability in muscle bulging patterns, particularly in the knee flexed position, suggesting a complex relationship between muscle bulging and activation strategies in the triceps surae, which may be related to differences in muscle mechanical properties between participants or across muscles. Our findings highlight the dynamics of in vivo bulging interactions among muscles within the triceps surae and provide insights for future investigations into the impact of altered contractile environments on three-dimensional muscle deformations and force production.

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.

The effects of resistance training to near volitional failure on motor unit recruitment during neuromuscular fatigue.

It is unclear whether chronically training close to volitional failure influences motor unit recruitment strategies during fatigue. We compared resistance training to near volitional failure vs. non-failure on individual motor unit action potential amplitude (MUAP) and surface electromyographic excitation (sEMG) during fatiguing contractions. Nineteen resistance-trained adults (11 males, 8 females) underwent 5 weeks (3×/week) of either low repetitions-in-reserve (RIR; 0-1 RIR) or high RIR training (4-6 RIR). Before and after the intervention, participants performed isometric contractions of the knee extensors at 30% of maximal peak torque until exhaustion while vastus lateralis sEMG signals were recorded and later decomposed. MUAP and sEMG excitation for the vastus lateralis were quantified at the beginning, middle, and end of the fatigue assessment. Both training groups improved time-to-task failure (mean change = 43.3 s, 24.0%), with no significant differences between low and high RIR training groups (low RIR = 28.7%, high RIR = 19.4%). Our fatigue assessment revealed reduced isometric torque steadiness and increased MUAP amplitude and sEMG excitation during the fatiguing task, but these changes were consistent between groups. Both low and high RIR training improved time-to-task failure, but resulted in comparable motor unit recruitment during fatiguing contractions. Our findings indicate that both low and high RIR training can be used to enhance fatiguability among previously resistance-trained adults.

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)

Tale of quadriceps and hamstring muscle strength after ACL reconstruction: a systematic review with longitudinal and multivariate meta-analysis

ObjectiveThis study aimed to investigate how knee extensor and flexor strength change over time after anterior cruciate ligament reconstruction (ACLR).DesignSystematic review with longitudinal meta-analysis.Data sourcesMedline, Embase, CINAHL, Scopus, Cochrane CENTRAL...

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).

Investigating premotor corticospinal excitability in fast and slow voluntary contractions of the elbow flexors.

Corticospinal excitability (CSE) increases prior to a voluntary contraction; however, the relative contributions of premotor cortical and spinal mechanisms are poorly understood. It is unknown whether the intended voluntary contractile rate affects CSE. Eighteen young, healthy participants (nine females) completed isometric elbow flexion contractions targeting 50% maximal voluntary contraction (MVC) torque, at either fast (fast as possible) or slow (25% MVC/s) contractile rates. Participants were cued to contract with warning (red) and "GO" (green) visual signals. Magnetic and electric stimulations were applied to elicit motor evoked potentials (MEPs), cervicomedullary evoked potentials (CMEPs), and M-waves, in the surface electromyogram (EMG) recorded over the biceps brachii. MEPs and CMEPs were collected at 0, 25, 50 and 75% premotor reaction time (RT - defined as the time between the "GO" cue and onset of biceps brachii EMG) and compared to a resting baseline. MEP amplitude was greater than baseline at 75% RT (p=0.009), and CMEP amplitude was significantly increased at all RT points relative to baseline (p≤0.001). However, there were no differences in MEP and CMEP amplitudes when compared between fast and slow conditions (p≥0.097). Normalized to the CMEP, there was no difference in MEP amplitude from baseline in either contractile condition (p≥0.264). These results indicate that increased premotor CSE is a spinally-mediated response. Furthermore, premotor CSE is not influenced by the intended voluntary contractile rate. CMEP amplitudes were larger for females than males within the premotor RT period (p=0.038), demonstrating that premotor spinal excitability responses may be influenced by sex.

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.

Regional changes in the free Achilles tendon volume in response to repeated submaximal contractions

IntroductionThe Achilles tendon (AT) may become smaller in volume following acute bouts of heavy and sustained loading likely because of transient fluid exudation to the periphery and this could augment cellular mechanotransduction and tendon adaptation. Given the structure of the AT is distinct across its length, regional changes in the free AT volume may occur in response to loading. This study aimed to investigate whether the change in tendon volume in response to repeated submaximal loading is distinct across the free AT length. MethodsSixteen ATs of healthy males and females (age 24.4 ± 9.4 years, body mass 70.9 ± 16.1 kg, height 1.7 ± 0.1 m) were scanned at rest using freehand 3D ultrasound. Scanning was done before and immediately after submaximal (75 %) voluntary isometric plantarflexion contractions (8 s) involving four sets of ten repetitions. Regional volumetric changes were assessed across the free AT length by dividing the tendon into distal, mid, and proximal regions. ResultsSignificant reduction in the free AT volume occurred across all tendon regions in response to the intervention, however, the mid- region exhibited the greatest reduction in volume compared to the proximal region (P = 0.025). DiscussionThe fact that volume reduction was greatest in the mid-region compared to the proximal region of the free AT may suggest greater tendon adaptation, via mechanotransduction pathways, in the mid-region and this may be important for tendon health and injury prevention.

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.