Maximal Voluntary Isometric Torque Research Articles

Effect of balance training on neuromuscular function at rest and during isometric maximum voluntary contraction.

This study was directed to investigate the neuromuscular function of the plantar flexors and tibialis anterior (TA) before and after 8 weeks of balance training. Twenty-six young adult subjects were randomly assigned to an intervention group and a control group. During neuromuscular testing, rate of torque development (RTD), isometric maximum voluntary torque (iMVT) and muscle activation were measured. Triceps surae muscle activation and TA muscle co-activation were assessed by normalized root mean square of the EMG signal during the initial phase of contraction (0-100, 0-200 ms) and maximum voluntary contraction (MVC) of the plantar flexors. Furthermore, evoked spinal reflex responses of the soleus muscle (H-reflex evoked at rest and during MVC, V-wave), peak twitch torques induced by electrical stimulation at rest and balance performance were evaluated. We found a significant difference between groups in RTD of the plantar flexors during MVC in the time interval 0-100 ms [37.0 N m s(-1) (4.2-69.9 N m s(-1), P = 0.029)]. This change was accompanied by reduced antagonistic muscle co-activity. The normalized H-reflex of the soleus muscle at rest as well as the sway of the center of pressure during balance performance assessment were significantly lower for the intervention group compared with controls. The training intervention had no effect on iMVT, normalized muscle activity of the plantar flexors, normalized muscle activity of TA, normalized V-wave and normalized H-reflex evoked during MVC. Data suggest that balance training reduced antagonistic muscle co-activity at the onset of triceps surae contraction and, in turn, increased isometric explosive voluntary strength of the plantar flexors.

The acute effect of neuromuscular activation in resistance exercise on human skeletal muscle with the interpolated twitch technique

[Purpose] The purpose of this study was to perform a quantitative assessment of neuromechanical adaptation in skeletal muscles and to propose the scientific underpinnings of the acute effects induced by resistance exercise. [Subjects] The subjects in this study were 11 healthy adult men in their 20s who had no orthopedic history at the time of the study. To examine any signs of resistance exercise-induced changes in the ankle plantar flexor, the subjects were directed to perform a standing barbell calf raise routine. [Methods] Subjects were to carry a load equal to their weights and to perform five sets of ten repetitions. The maximal voluntary isometric contraction torque, resting twitch torque, muscle inhibition, root mean square of muscular activation, contraction time, and half relaxation time were analyzed by synchronizing a dynamometer, an electrical stimulator, and an electromyography system. [Results] The maximal voluntary isometric contraction torque appeared to decline, but the change was not statistically significant. The decline of resting twitch torque, on the other hand, was found to be statistically significant. Muscle inhibition and root mean square of muscular activation were both reduced, but both changes were not statistically significant. Lastly, contraction time and half relaxation time both statistically decreased significantly after resistance exercise. [Conclusion] These results indicate that the acute effects of resistance exercise have a greater impact on the peripheral mechanical system itself, rather than on neurological factors, in terms of the generation of muscle force.

Changes in electrical pain threshold of fascia and muscle after initial and secondary bouts of elbow flexor eccentric exercise.

This study investigated changes in electrical pain threshold (EPT) after repeated eccentric exercise bouts to test the hypothesis that fascia would become more sensitive than muscle when greater delayed onset muscle soreness (DOMS) is induced. Ten young men performed two eccentric exercise bouts (ECC1, ECC2) consisting of ten sets of six maximal isokinetic eccentric contractions of the elbow flexors with the same arm separated by 4 weeks. Maximal voluntary isometric contraction torque, range of motion, muscle soreness assessed by a visual analogue scale (VAS) and pressure pain threshold (PPT) were measured before, immediately after and 1-5 days after exercise. EPT was assessed in the biceps brachii fascia (BBF), biceps brachii muscle, and brachialis fascia (BF) 1 day before, immediately after, and 1, 2 and 4 days after exercise. All measures showed smaller changes (P < 0.05) after ECC2 than ECC1. EPT decreased after both bouts and the largest decreases were evident at 2 days post-exercise (P < 0.05). The decreases in EPT after ECC1 were greater (P < 0.05) for both BBF (Baseline: 1.45 ± 0.23 mA, 2 days post-exercise: 0.13 ± 0.11 mA) and BF (1.64 ± 0.29 mA, 0.26 ± 0.2 mA) than muscle (1.56 ± 0.29 mA, 0.69 ± 0.33 mA). Changes in EPT were correlated with the changes in PPT (r = 0.63-0.87, P ≤ 0.05) but not with VAS (r = -0.01 to 0.50). These results show that fascia becomes more sensitive than muscle to electrical stimulation after the initial eccentric exercise, suggesting that damage inflammation to fascia than muscle fibres is more associated with DOMS.

Quadriceps muscle function after exercise in men and women with a history of anterior cruciate ligament reconstruction.

Sex differences in lower extremity neuromuscular function have been reported after anterior cruciate ligament reconstruction (ACLR). Research evidence supports different levels of fatigability in men and women and between patients with ACLR and healthy controls. The influence of sex on the response to continuous exercise in patients with ACLR is not clear. To compare quadriceps neuromuscular function after exercise between men and women with ACLR. Descriptive laboratory study. Laboratory. Twenty-six active volunteers (13 men [50%]: age = 24.1 ± 4.4 years, height = 179.1 ± 9.8 cm, mass = 80.1 ± 9.4 kg, months since surgery = 43.5 ± 37.0; 13 women [50%]: age = 24.2 ± 5.6 years, height = 163.0 ± 5.9 cm, mass = 62.3 ± 8.3 kg, months since surgery = 45.8 ± 42.7) with a history of unilateral primary ACLR at least 6 months earlier. Thirty minutes of continuous exercise comprising 5 separate 6-minute cycles, including 5 minutes of uphill walking and 1 minute of body-weight squatting and step-ups. Normalized knee-extension maximal voluntary isometric contraction torque, quadriceps superimposed-burst torque, and quadriceps central activation ratio before and after exercise. We performed separate 2 (sex: men, women) × 2 (time: preexercise, postexercise) repeated-measures analyses of variance for the 3 variables. Separate, independent-samples t tests were calculated to compare preexercise with postexercise change in all dependent variables between sexes. A significant group-by-time interaction was present for knee-extension torque (P = .04). The percentage reduction in knee-extension maximal voluntary isometric contraction torque (men = 1.94%, women = -10.32%; P = .02) and quadriceps central activation ratio (men = -1.45%, women = -8.69%; P = .03) experienced by men was less than that observed in women. In the presence of quadriceps dysfunction, female participants experienced greater-magnitude reductions in quadriceps function after 30 minutes of exercise than male participants. This indicates a reduced ability to absorb knee-joint loads, which may have significant implications for reinjury and joint osteoarthritis in women after ACLR.

Phototherapy with combination of super-pulsed laser and light-emitting diodes is beneficial in improvement of muscular performance (strength and muscular endurance), dyspnea, and fatigue sensation in patients with chronic obstructive pulmonary disease.

Phototherapy is an electrophysical intervention being considered for the retardation of peripheral muscular fatigue usually observed in chronic obstructive pulmonary disease (COPD). The objective of this study was to evaluate the acute effects of combination of super-pulsed laser and light-emitting diodes phototherapy on isokinetic performance in patients with COPD. Thirteen patients performed muscular endurance tests in an isokinetic dynamometer. The maximum voluntary isometric contraction (MVIC), peak torque (PT), and total work (TW) of the non-dominant lower limb were measured in two visits. The application of phototherapy or placebo (PL) was conducted randomly in six locations of femoral quadriceps muscle by using a cluster of 12 diodes (4 of 905 nm super-pulsed lasers, 0.3125 mW each; 4 of 875 nm LEDs, 17.5 mW each; and 4 of 640 nm LEDs, 15 mW each, manufactured by Multi Radiance Medical™). We found statistically significant increases for PT (174.7 ± 35.7 N · m vs. 155.8 ± 23.3 N · m, p = 0.003) and TW after application of phototherapy when compared to placebo (778.0 ± 221.1 J vs. 696.3 ± 146.8 J, p = 0.005). Significant differences were also found for MVIC (104.8 ± 26.0 N · m vs. 87.2 ± 24.0 N · m, p = 0.000), sensation of dyspnea (1 [0-4] vs. 3 [0-6], p = 0.003), and fatigue in the lower limbs (2 [0-5] vs. 5 [0.5-9], p = 0.002) in favor of phototherapy. We conclude that the combination of super-pulsed lasers and LEDs administered to the femoral quadriceps muscle of patients with COPD increased the PT by 20.2% and the TW by 12%. Phototherapy with a combination of super-pulsed lasers and LEDs prior to exercise also led to decreased sensation of dyspnea and fatigue in the lower limbs in patients with COPD.

Changes in CEBPB expression in circulating leukocytes following eccentric elbow-flexion exercise.

In mouse models, CCAAT enhancer-binding protein beta (CEBPB) is necessary for M2 macrophage-mediated regeneration after muscle injury. In humans, CEBPB expression in blood was strongly associated with muscle strength. In this study we aimed to test whether CEBPB expression in blood in people is increased 2 days after exercise designed to induce muscle damage and subsequent repair. Sixteen healthy male volunteers undertook elbow flexor exercises designed to induce acute muscle micro-damage. Peripheral blood samples were collected at baseline and days 1, 2, 4 and 7 following exercise. Expression of CEBPB and related genes were analysed by qRT-PCR. Extent of muscle damage was determined by decline in maximal voluntary isometric torque and by plasma creatine kinase activity. Nine subjects had peak (day 4) creatine kinase activity exceeding 10,000 U/l. In this subgroup, CEBPB expression was elevated from baseline to 2 days post exercise (paired-samples t (1,8) = 3.72, p = 0.006). Related expression and selected cytokine changes after exercise did not reach significance. Muscle-damaging exercise in humans can be followed by induction of CEBPB transcript expression in peripheral blood. Associations between CEBPB expression in blood and muscle strength may be consistent with the CEBPB-dependent muscle repair process.Electronic supplementary materialThe online version of this article (doi:10.1007/s12576-014-0350-7) contains supplementary material, which is available to authorized users.

Estudio transversal de fiabilidad y concordancia de un nuevo dispositivo para la evaluación de torsión y tolerancia a la fatiga en flexo extensores cervicales de voluntarios sedentarios asintomáticos

ObjectiveTo determine the reliability and agreement of a method to evaluate maximum voluntary isometric torque (MVIT) and muscle fatigue local tolerance (MFLT) measurement in the cervical flexor-extensor muscles of sedentary life style asymptomatic volunteers. Material and methodFor this observational cross-sectional study, 42 subjects (15 women and 27 men), who were asymptomatic, with sedentary life style, and with no background of cervical pathology were assessed with the cervical muscle testing dynamometer system. The MVIT (Newton-meters; Nm) was recorded with three measurements for each muscle group (n=42). Twenty-four hours later, MFLT (seconds) was measured twice at 60±2.5% of MVIT with two measurements for the cervical flexor and extensor (n=40). After one week, a MVIT and MFLT retest was performed (n=13). ResultsThe general measurement of reliability and agreement for the MVIT show a intra-class correlation coefficient >0.89, coefficient of variation <11% and standard error of measurement <1Nm in both muscle groups. The measurement of MFLT flexor provided intra-class correlation coefficient >0.80, coefficient of variation =20% and standard error of measurement <10seconds; while the results for the extensors were intra-class correlation coefficient <0.50, coefficient of variation =30% and standard error of measurement >20sec. ConclusionsIn both cervical muscle groups, the proposed method and device are reliable and concordant for MVIT evaluation. On its part, gender is a significant scatter factor in MFLT testing.

Knee Muscle Strength Recovery in the Early Period After ACL Reconstruction

Objectives:The aim of this study was to investigate quadriceps and hamstrings isometric strength at 4, 8 and 12 week time points following ACL Reconstruction (ACLR) and to document the strength changes of these muscles over time. The primary hypothesis was that there would be significant increases in quadriceps and hamstring muscle strengths between the 4th, 8th and 12th weeks following ACLR. The secondary hypothesis was that the quadriceps index would be higher than hamstring index at 12th week after ACLR.Methods:Thirty patients (Mean ± SD [age, 29.1±2.3yrs; weight, 77.3±13.2kg; height, 172.1±7.1cm; BMI, 21.2±3.5kg/m2, time to surgery: 7.1±7.2 months]) who underwent ACLR with Hamstring Tendon Autograft (HTG) were enrolled in this study. The isometric strength of quadriceps and hamstring muscles was measured on an isokinetic dynamometer at 60° knee flexion angle at 4th, 8th and 12th weeks after surgery. The recovery of quadriceps and hamstring muscles strength following rehabilitation was expressed as a Quadriceps Index (QI) and Hamstring Index (HI) and calculated with the following formula:[(maximum voluntary isometric torque of the involved limb / maximum voluntary isometric torque by uninvolved limb) × 100]. Torque output of the involved and uninvolved limbs and quadriceps and hamstring indexes were used for the statistical analysis. A repeated measures of ANOVA was used to determine the strength changes of quadriceps and hamstrings over time.Results:Quadriceps and Hamstrings strengths significantly increased over time for both involved (Quadriceps: F (2,46)=58.3, p<0.001, Hamstring: F (2,46)=35.7, p<0.001) and uninvolved limb (Quadriceps: F(2,46)=17.9, p<0.001, Hamstring: F(2,46)=56.9, p=0.001 ). Quadriceps strength was higher at 12th week when compared to the 8 and 4 week time points for the involved limb (p<0.001), and it was higher at 8th week when compared to 4 week time point for the involved limb (p<0.001). For the uninvolved limb, quadriceps strength was also higher at 12th week when compared to the 8 (p=0.02) and 4 week time point (p<0.001), and higher at 8 week when compared to the 4 week time point (p=0.02). Hamstring strength was higher at 12 week when compared to the 8 and 4 week time points (p<0.001) and it was higher at 8 week when compared to 4 week time point for the involved limb (p<0.001). For the uninvolved limb hamstring strength was also higher at 12 week when compared to 4 week time point (p=0.01). There was no significant difference between the 4 and 8 week time points (p>0.05) or between the 8 and 12 week time points (p=0.07). Quadriceps and hamstring indexes significantly changed from 4th weeks (QI:57.9, HI:54.4 ) to 8th weeks (QI:78.8, HI:69.9 ) and from 8th weeks to 12th weeks (QI:82, HI:75.7 ) (p<0.001); however, there was no difference between indexes at the 12-week time point (p=0.17).Conclusion:Isometric strength of quadriceps and hamstring muscles for the involved and uninvolved limb increased during the early period of ACLR. The results of this study could be a baseline for clinicians while prescribing a rehabilitation protocol for ACLR patients with HTG to better appreciate expected strength changes of the muscles in the early phase.

Physiological alterations after a marathon in the first 90-year-old male finisher: case study.

IntroductionEndurance performance decreases during ageing due to alterations in physiological characteristics, energy stores, and psychological factors. To investigate alterations in physiological characteristics and body composition of elderly master athletes in response to an extreme endurance event, we present the case of the first ninety-year-old official male marathon finisher.Case descriptionBefore and directly after the marathon, a treadmill incremental test, dual-energy X-ray absorptiometry, peripheral quantitative computed tomography, mechanography, and dynamometry measurements were conducted. The athlete finished the marathon in 6 h 48 min 55 s, which corresponds to an average competition speed of 6.19 km h-1.Discussion and EvaluationBefore the marathon, was 31.5 ml min-1 kg-1 body mass and peak heart rate was 140 beats min-1. Total fat mass increased in the final preparation phase (+3.4%), while leg fat mass and leg lean mass were slightly reduced after the marathon (-3.7 and -1.6%, respectively). Countermovement jump (CMJ) peak power and peak velocity decreased after the marathon (-16.5 and -14.7%, respectively). Total impulse during CMJ and energy cost of running were not altered by the marathon. In the left leg, maximal voluntary ground reaction force (Fm1LH) and maximal isometric voluntary torque (MIVT) were impaired after the marathon (-12.2 and -14.5%, respectively).ConclusionsSide differences in Fm1LH and MIVT could be attributed to the distinct non-symmetrical running pattern of the athlete. Similarities in alterations in leg composition and CMJ performance existed between the nonagenarian athlete and young marathon runners. In contrast, alterations in total body composition and m1LH performance were markedly different in the nonagenarian athlete when compared to his younger counterparts.

Validity and reliability of an instrumented leg-extension machine for measuring isometric muscle strength of the knee extensors.

Isometric muscle strength of knee extensors has been assessed for estimating performance, evaluating progress during physical training, and investigating the relationship between isometric and dynamic/functional performance. To assess the validity and reliability of an adapted leg-extension machine for measuring isometric knee extensor force. Validity (concurrent approach) and reliability (test and test-retest approach) study. University laboratory. 70 healthy men and women aged between 20 and 30 y (39 in the validity study and 31 in the reliability study). Intraclass correlation coefficient (ICC) values calculated for the maximum voluntary isometric torque of knee extensors at 30°, 60°, and 90°, measured with the prototype and with an isokinetic dynamometer (ICC2,1, validity study) and measured with the prototype in test and retest sessions, scheduled from 48 h to 72 h apart (ICC1,1, reliability study). In the validity analysis, the prototype showed good agreement for measurements at 30° (ICC2,1 = .75, SEM = 18.2 Nm) and excellent agreement for measurements at 60° (ICC2,1 = .93, SEM = 9.6 Nm) and at 90° (ICC2,1 = .94, SEM = 8.9 Nm). Regarding the reliability analysis, between-days' ICC1,1 were good to excellent, ranging from .88 to .93. Standard error of measurement and minimal detectable difference based on test-retest ranged from 11.7 Nm to 18.1 Nm and 32.5 Nm to 50.1 Nm, respectively, for the 3 analyzed knee angles. The analysis of validity and repeatability of the prototype for measuring isometric muscle strength has shown to be good or excellent, depending on the knee joint angle analyzed. The new instrument, which presents a relative low cost and easiness of transportation when compared with an isokinetic dynamometer, is valid and provides consistent data concerning isometric strength of knee extensors and, for this reason, can be used for practical, clinical, and research purposes.

Mechanomyogram amplitude correlates with human gastrocnemius medialis muscle and tendon stiffness both before and after acute passive stretching.

The study aimed to assess the level of correlation between muscle-tendon unit (MTU) stiffness and mechanomyogram (MMG) signal amplitude of the human gastrocnemius medialis muscle, both before and after acute passive stretching. The passive torque (Tpass), electrically evoked peak torque (pT) and myotendinous junction displacement were determined at different angles of dorsiflexion (0, 10 and 20 deg), while maximum voluntary isometric torque (Tmax) was assessed only at 0 deg. Measurements were repeated after a bout of passive stretching. From the MMG signal, the root mean square (RMS) and peak to peak (p-p) were calculated. The MTU, muscle and tendon stiffness were determined by ultrasound and Tpass measurements. Before stretching, correlations between MMG RMS and MTU, muscle and tendon stiffness were found (R(2) = 0.22-0.46). After stretching, Tpass, Tmax, pT and MTU, muscle and tendon stiffness decreased by 25 ± 7, 16 ± 2, 9 ± 2, 22 ± 7, 23 ± 8 and 28 ± 5%, respectively (P < 0.05). During voluntary and electrically evoked contractions, MMG p-p decreased by 9 ± 2 and 5 ± 1%, while MMG RMS increased by 48 ± 7 and 50 ± 8%, respectively (P < 0.05). Correlations between MMG RMS and MTU, muscle and tendon stiffness were still present after stretching (R(2) = 0.44-0.60). In conclusion, correlations between MMG RMS and stiffness exist both before and after stretching, suggesting that a slacker MTU leads to larger muscle fibre oscillations. However, care must be taken in using MMG amplitude as an indirect index to estimate stiffness owing to the relatively small R(2) values of the investigated correlations.

Mechanical, hormonal, and hypertrophic adaptations to 10 weeks of eccentric and stretch-shortening cycle exercise training in old males

The growth promoting effects of eccentric (ECC) contractions are well documented but it is unknown if the rate of stretch per se plays a role in such muscular responses in healthy aging human skeletal muscle. We tested the hypothesis that exercise training of the quadriceps muscle with low rate ECC and high rate ECC contractions in the form of stretch-shortening cycles (SSCs) but at equal total mechanical work would produce rate-specific adaptations in healthy old males age 60–70. Both training programs produced similar improvements in maximal voluntary isometric (6%) and ECC torque (23%) and stretch-shortening cycle function (reduced contraction duration [24%] and enhanced elastic energy storage [12%]) (p<0.05). The rate of torque development increased 30% only after SSC exercise (p<0.05). Resting testosterone and cortisol levels were unchanged but after each program the acute exercise-induced cortisol levels were 12–15% lower (p<0.05). Both programs increased quadriceps size 2.5% (p<0.05). It is concluded that both ECC and SSC exercise training produces favorable adaptations in healthy old males' quadriceps muscle. Although the rate of muscle tension during the SSC vs. ECC contractions was about 4-fold greater, the total mechanical work seems to regulate the hypetrophic, hormonal, and most of the mechanical adaptations. However, SSC exercise was uniquely effective in improving a key deficiency of aging muscle, i.e., its ability to produce force rapidly.

Alteration in neuromuscular function of the plantar flexors following caffeine ingestion.

The aim of this study was to compare the neuromuscular function of the plantar flexors following caffeine or placebo administration. Thirteen subjects (25 ± 3 years) ingested caffeine or placebo in a randomized, controlled, counterbalanced, double-blind crossover design. Neuromuscular tests were performed before and 1 h after caffeine or placebo intake. During neuromuscular testing, rate of torque development, isometric maximum voluntary torque, and neural drive to the muscles were measured. Triceps surae muscle activation was assessed by normalized root mean square of the EMG signal during the initial phase of contraction (0-100 ms, 100-200 ms) and maximal voluntary contraction (MVC). Furthermore, evoked spinal reflex responses of the soleus muscle (H-reflex evoked at rest and during MVC, V-wave) and peak twitch torques were evaluated. The isometric maximum voluntary torque and evoked potentials were not different. However, we found a significant difference between groups for rate of torque development in the time intervals 0-100 ms [41.1 N · m/s (95% CI: 8.3-73.9 N · m/s, P = 0.016)] and 100-200 ms [32.8 N · m/s (95% CI: 2.8-62.8 N · m/s, P = 0.034)]. These changes were accompanied by enhanced neural drive to the plantar flexors. Data suggest that caffeine solely increased explosive voluntary strength of the triceps surae because of enhanced neural activation at the onset of contraction whereas MVC strength was not affected.

Effects of electrical stimulation pattern on quadriceps force production and fatigue

Mixed stimulation programs (MIX) that switch from constant frequency trains (CFT) to variable frequency trains have been proposed to offset the rapid fatigue induced by CFT during electrical stimulation. However, this has never been confirmed with long stimulation patterns, such as those used to evoke functional contractions. The purpose of this study was to test the hypothesis that MIX programs were less fatiguing than CFTs in strength training-like conditions (6-s contractions, 30-min). Thirteen healthy subjects underwent 2 sessions corresponding to MIX and CFT programs. Measurements included maximal voluntary isometric torque and torque evoked by each contraction. There were greater decreases of voluntary and evoked torque (P < 0.05) after CFT than MIX, and mean torque was 13 ± 1% higher during the MIX session (P < 0.05). These findings confirm that combining train types might be a useful strategy to offset rapid fatigue during electrical stimulation sessions with long-duration contractions.

Plantarflexor Weakness Negatively Impacts Walking in Persons With Multiple Sclerosis More Than Plantarflexor Spasticity

ObjectivesTo determine whether plantarflexor (PF) spasticity or ankle strength best predicts variance in walking capacity or self-perceived limitations in walking in persons with multiple sclerosis (MS) and whether persons with MS with PF spasticity are weaker and have greater walking dysfunction than do persons with MS without PF spasticity. DesignCross-sectional study. SettingUniversity research laboratory. ParticipantsForty-two adults with MS (mean age, 42.9±10.1y; Expanded Disability Status Scale score, median=3.0, range=0–6) and 14 adults without disability (mean age, 41.9±10.1y). InterventionNot applicable. Main Outcome MeasuresPF spasticity and dorsiflexion and PF maximum voluntary isometric torque were assessed using the modified Ashworth Scale and a computerized dynamometer, respectively. The Timed 25-Foot Walk Test was the primary outcome measure of walking capacity. Secondary measures included the 6-Minute Walk Test and the 12-item Multiple Sclerosis Walking Scale. ResultsPF strength was the most consistent predictor of variance in walking capacity (Timed 25-Foot Walk Test: R2 change=.23–.29, P≤.001; 6-Minute Walk Test: R2 change=.12–.29, P≤.012), and self-perceived limitations of walking (12-item Multiple Sclerosis Walking Scale: R2 change=.04–.14, P<.18). There were no significant differences (P>.05) between persons with MS with PF spasticity and persons with MS without PF spasticity for any of the outcome measures. ConclusionsOur study suggests a unique contribution of PF weakness to walking dysfunction in persons with MS, and highlights the importance of evaluating PF strength in this clinical population.

Changes in the number of circulating CD34+ cells after eccentric exercise of the elbow flexors in relation to muscle damage

BackgroundIt has been reported that strenuous exercise increases the number of bone marrow-derived progenitor cells such as CD34+ cells in the blood, but no previous studies have investigated the changes in circulating CD34+ cells following resistance exercise. This study tested the hypothesis that the number of CD34+ cells in the blood would increase after eccentric exercise of the elbow flexors, but decrease in recovery, and the magnitude of the changes would be dependent on the magnitude of muscle damage. MethodsNine men (28.0 ± 6.6 years) performed exercises consisting of 10 sets of six maximal voluntary eccentric contractions of the elbow flexors with their non-dominant arm. Six of them performed the same exercise with the same arm 4 weeks later. Changes in indirect markers of muscle damage were measured before, within 10 min after, and at 24, 48, 72, and 96 h after eccentric exercise. Differential leukocyte counts (total leukocytes, neutrophils, lymphocytes, monocytes) and CD34+ cells in the blood were measured before, immediately after, and at 2, 24, 48, 72, and 96 h following the exercises. ResultsAfter eccentric exercise, significant (p < 0.05) decreases in maximal voluntary isometric contraction torque and increases in delayed onset muscle soreness and plasma creatine kinase activity were observed. However, no significant changes in leukocytes and CD34+ cells were evident. The changes in muscle damage markers were significantly (p < 0.05) smaller following the second exercise session as compared with the first exercise session, but the changes in leukocytes and CD34+ cells were not significantly different between sessions. ConclusionThese results did not support the hypothesis, and showed that eccentric exercise-induced muscle damage to the elbow flexors did not influence the number of circulating CD34+ cells.

Electromyographic analysis of upper limb muscles during standardized isotonic and isokinetic robotic exercise of spastic elbow in patients with stroke

Although it has been reported that strengthening exercise in stroke patients is beneficial for their motor recovery, there is little evidence about which exercise method is the better option. The purpose of this study was to compare isotonic and isokinetic exercise by surface electromyography (EMG) analysis using standardized methods.Nine stroke patients performed three sets of isotonic elbow extensions at 30% of their maximal voluntary isometric torque followed by three sets of maximal isokinetic elbow extensions with standardization of mean angular velocity and the total amount of work for each matched set in two strengthening modes. All exercises were done by using 1-DoF planner robot to regulate exact resistive torque and speed. Surface electromyographic activity of eight muscles in the hemiplegic shoulder and elbow was recorded. Normalized root mean square (RMS) values and co-contraction index (CCI) were used for the analysis.The isokinetic mode was shown to activate the agonists of elbow extension more efficiently than the isotonic mode (normalized RMS for pooled triceps: 96.0±17.0 (2nd), 87.8±14.4 (3rd) in isokinetic, 80.9±11.0 (2nd), 81.6±12.4 (3rd) in isotonic contraction, F[1,8]=11.168; P=0.010) without increasing the co-contraction of muscle pairs, implicating spasticity or synergy.

Effect of Plyometric Training on Neural and Mechanical Properties of the Knee Extensor Muscles

This study investigated neuromuscular adaptations of the knee extensors after 8 weeks of plyometric training. 23 subjects were randomly assigned to an intervention group and a control group. We measured isometric maximum voluntary torque (iMVT), rate of torque development (RTD) and impulse (IMP) over different time intervals. The neural drive to muscles was estimated with the interpolated twitch technique and normalized root mean square of the EMG signal. Contractile properties, H reflexes as well as jump height in squat jump (SJ) and countermovement jump (CMJ) were evaluated. Neuromuscular testing was performed at 2 knee angles, i. e., 80° and 45° (0° = full extension). The iMVT at 80° knee flexion was 23.1 N · m (95% CI: 0.1-46.1 N · m, P = 0.049) higher at post-test for the intervention group compared with controls. The same was true for RTD and IMP in the time interval 0-50 ms [308.7 N · m · s(-1) (95% CI: 28.8-588.6 N · m · s(-1), P = 0.033) and 0.32 N · m · s (95% CI: 0.05-0.60 N · m · s, P = 0.026), respectively]. These changes were accompanied by enhanced neural drive to the quadriceps muscle. Jump height in SJ and CMJ was higher at post-test for the intervention group compared with controls. Parameters at 45° knee flexion, contractile properties and evoked potentials did not differ between groups. Although hypertrophic changes were not measured, data suggest that the training regime probably induced mainly neural adaptations that were specifically related to the knee angle. The strength gains at 80° knee flexion likely contributed to the enhanced jump height in SJ and CMJ.

Effect of Short-term Maximal Voluntary Co-contraction Training on Neuromuscular Function

The present study aimed to examine the effect of short-term training utilizing voluntary co-contraction with maximal efforts. 23 healthy young men (training group: TG, n = 13; control group: CG, n = 10) participated in this study. TG conducted a 4-week training program (3 days/week), which consisted of 4 s simultaneous maximal voluntary contractions of elbow flexors and extensors at 90° of the elbow joint, followed by 4 s muscle relaxation (10 repetitions/set, 5 sets/day). Before and after the intervention, maximal voluntary isometric and isokinetic torques and the muscle thicknesses of the elbow flexors and extensors were determined. The electromyograms (EMGs) of the 2 muscle groups during isometric maximal voluntary contraction (MVC) were also recorded. After the intervention, CG did not show any significant changes in all measured variables. In TG, significant increases were found in the agonist EMG activities during MVC, and maximal isometric and isokinetic torques of the elbow flexors and extensors, without significant changes in the muscle thicknesses and involuntary coactivation levels during MVC. The current results indicate that the training mode with maximal voluntary co-contraction is effective for improving the force-generating capabilities of the exercising muscles, without any increases in the level of involuntary coactivation during MVC.

Time Course of the Cross-Over Effect of Fatigue on the Contralateral Muscle after Unilateral Exercise

We investigated the cross-over effect of muscle fatigue and its time course on the non-exercising contralateral limb (NEL) after unilateral fatiguing contractions of the ipsilateral exercising limb (EL). For this purpose, 15 males performed two bouts of 100-second maximal isometric knee extensions with the exercising limb, and neuromuscular function of both the EL and NEL was assessed before (PRE), after a first fatiguing exercise (MID) and after a second fatiguing exercise (POST). Maximal voluntary isometric torque production declined in the EL after the first bout of exercise (−9.6%; p<0.001) while in the NEL, the decrease occurred after the second bout of exercise (−10.6%; p<0.001). At MID, torque decline of the EL was strictly associated to an alteration of the mechanical twitch properties evoked by neurostimulation of the femoral nerve (i.e., peak twitch torque, maximal rate of twitch development). According to these markers, we suggest that peripheral fatigue occurred. At POST, after the second bout of exercise, the voluntary activation level of the knee extensor muscles was altered from PRE (−9.1%; p<0.001), indicating an overall central failure in both the EL and NEL. These findings indicate that two bouts of unilateral fatiguing exercise were needed to induce a cross-over effect of muscle fatigue on the non-exercising contralateral limb. Differential adjustments of the motor pathway (peripheral fatigue vs. central fatigue) might contribute to the respective torque decline in the EL and the NEL. Given that our unilateral fatiguing exercise induced immediate maximal torque reduction in the EL and postponed the loss of torque production in the NEL, it is also concluded that the time course of muscle fatigue differed between limbs.