Peak Maximal Voluntary Contraction Research Articles

Pelvic floor muscle function after grade II tears-Surface electromyography test-retest and differences between nulliparous and primiparous.

Vaginal birth is a risk factor for weakening of the pelvic floor muscles (PFM) and development of pelvic floor dysfunction (PFD). Perineal tears may decrease PFM function. PFM tone can be assessed with surface EMG (sEMG), but reliability studies of sEMG in women with perineal tears are lacking. The aims of this study were to evaluate test-retest and intrarater reliability of sEMG and compare PFM activation between nulliparous and primiparous. A sEMG test-retest was performed in 21 women (12 nulliparous and 9 primiparous with grade II tears) to assess intra-rater reliability during rest and maximal voluntary contraction (MVC) of the PFM. Intraclass Correlation Coefficient (ICC), standard error of measurement (SEM) and minimal detectable change (MDC) were tested. A comparison between nulliparous'and primiparous'PFM activation during rest and MVC was performed. sEMG demonstrated fair reliability in nulliparous (ICC: 0.239; SEM: 5.2; MDC: 14.5) and moderate reliability in primiparous (ICC: 0.409; SEM: 1.5; MDC: 4.2) during rest. For peak MVC very good intrarater reliability was found in nulliparous (ICC: 0.92; SEM: 8.0; MDC: 22.2) and in primiparous (ICC: 0.823; SEM: 8.0; MDC: 22.2). Statistically significant lower PFM activation was found in primiparous women with perineal tear grade II than in nulliparous at rest (mean difference 9.1 µV, 95% confidence interval[CI] 3.0-19.0, p = 0.001), and during MVCpeak (mean difference 50.0 µV, 95% CI 10.0-120.0 p = 0.021). sEMG is reliable when measuring PFM activation in primiparous women with perineal tears grade II. Women with perineal tears grade II have lower PFM activation both during rest and MVC.

Maximal vs. explosive knee extensor strength in professional soccer players: inter-limb asymmetries and relationship with knee function

ABSTRACT The main aims of this study were to compare the magnitude of inter-limb asymmetry (ILA) and the relation with self-reported knee function between maximal and explosive knee extensor strength outcomes in professional soccer players. Forty-six male soccer players completed different maximal isokinetic and isometric contractions of the knee extensors for the assessment of maximal strength (peak torque and maximal voluntary contraction (MVC) torque) and explosive strength (early, intermediate, late, and peak rate of torque development (RTD)). Self-reported knee function was assessed with the International Knee Documentation Committee (IKDC) and Lysholm knee scoring scales. Peak torque and MVC torque showed comparable ILAs (8-9%), both being significantly lower than all RTD ILAs (16% on average; p < 0.001). ILAs for early RTD (21%) and peak RTD (19%) were significantly higher than all the other variables (p < 0.05). Only early and intermediate RTD were significantly correlated – though weakly – with both IKDC (rho = 0.32 for both) and Lysholm (rho = 0.36 and 0.30, respectively) scores. We conclude that explosive knee extensor strength – early RTD in particular – exhibited larger ILAs and better relations with self-reported knee function than peak torque and MVC torque in professional soccer players. These results confirm the validity and functional relevance of early RTD and the need for its inclusion in routine performance testing for soccer players. Highlights Professional soccer players exhibited larger inter-limb deficits in knee extension strength for explosive actions than for the widely-used isokinetic test. Self-reported knee function was significantly correlated with explosive strength of the knee extensor muscles but not with maximal strength. The first 50 ms of an explosive knee extension seem to be crucial for self-perceived sport performance and possibly for injury prevention.

Relationship between Nordic hamstring strength and maximal voluntary eccentric, concentric and isometric knee flexion torque.

Nordic hamstring exercise is performed to prevent knee flexor muscle strain injuries and used to assess their injury risks. However, what exactly Nordic hamstring strength indicates is not clear. We investigated the relationship between Nordic hamstring strength and maximal voluntary contraction (MVC) torque of the knee flexors measured by an isokinetic dynamometer. Sixteen healthy young men who had not experienced hamstring strain injuries participated in the study. In Nordic hamstring, each participant was instructed to lean forward as far as possible in 3 s (approximately 30°/s), and force at the ankle joint of the dominant leg was measured during the movement. The force was multiplied by lower leg length and converted into torque. MVC torque of the knee flexors was measured isometrically at 30°, 45°, 60°, and 90° knee flexion joint angles, and concentrically and eccentrically at 30°/s and 60°/s in 10°–90° knee flexion for the dominant leg in a prone position. Correlations among the dependent variables were assessed using Pearson’s correlation coefficients. Peak Nordic hamstring torque ranged 96.8–163.5 Nm, and peak MVC eccentric torque ranged 50.7–109.4 Nm at 30°/s and 59.2–121.2 Nm at 60°/s. No significant correlations were evident between the peak Nordic hamstring torque and peak eccentric knee flexion torque (r = 0.24–0.3, p = 0.26–0.4). This was also the case for the Nordic hamstring torque and MVC torque of isometric (r = −0.03–0.1, p = 0.71–0.92) and concentric contractions (r = 0.28–0.49, p = 0.053–0.29). These results show that Nordic hamstring strength is not associated with the knee flexor torque measured by an isokinetic dynamometer. It may be that other factors than static and dynamic hamstring strengths affect Nordic hamstring strength.

Modified Pulvertaft on Weave Technique Restores Full Active Knee Extension in Patients With Large Chronic Quadriceps Tendon Rupture: A Case Series

We aimed to investigate the clinical and functional outcomes, including maximal and explosive strength, after chronic quadriceps tendon rupture repair with Modified Pulvertaft on Weave (MPW) technique METHODS: Knee joint range of motion (ROM), patella height, thigh circumference, and Lysholm and International Knee Documentation Committee (IKDC) scores were assessed preoperatively and postoperatively. The knee extensors maximal (isokinetic peak torque and isometric maximal voluntary contraction (MVC) torque) and explosive strength-rate of torque development (RTD) early [RTD50 and RTD100] and late [RTD250]-were performed. We assessed the thigh circumference and vastus lateralis muscle thickness (MT) as indicators of quadriceps muscle mass, and the voluntary quadriceps activation using surface electromyography (EMG50). Nine patients (mean age: 53 ± 11 years) took part in the study. We observed a significant increase in the knee active ROM and a decreased extension deficit (both, P < .001), but not for pain (P= .07), IKDC (P= .07), and Lysholm (P= .21) after the surgery. We did not observe a difference between involved (n= 8) and uninvolved (n= 10) limbs for ROM, thigh circumference, and MT. We observed differences for extensors peak torque, MVC torque, and late RTD (all, P < .05). However, we did not observe differences for early RTD and EMG50. Significant positive correlations were observed for RTD50 (ρ= .80) and RTD100 (ρ= .81) vs EMG50. Both the IKDC and Lysholm were better correlated with the early than with later RTD. The MPW reestablished the active knee extension. The same level of quadriceps muscle mass was observed in both limbs, suggesting a lack of hypotrophy due to the injury. Although the involved limb had demonstrated lower knee extensors maximal strength, they demonstrate an equivalent early RTD when compared to the uninvolved limb. The early RTD seems to be better correlated with the patient's functionality than the later RTD and maximal strength. IV, case series.

Contralateral Effects of Eccentric Exercise and DOMS of the Plantar Flexors: Evidence of Central Involvement

ABSTRACT Purpose: Peripheral and central factors play important roles in the reduction of motor performance following damaging eccentric exercise and delayed onset muscle soreness (DOMS). Following this regime, contralateral limbs could also be affected; however, the factors involved remain inconclusive. The purpose of this study was to distinguish the peripheral and central factors following eccentric contraction and DOMS of the plantar flexors in treated and contralateral homologous limbs. Methods: Ten males (BMI = 25.08 ± 1.69kgm−2; age = 28.70 ± 4.24 years) were randomly assigned to experimental (DOM) or control (CON) groups. The DOM group performed a damaging eccentric exercise, while the CON group rested. Plasma creatine kinase (CK), pain rating scale (PRS), muscle stiffness, maximal voluntary contraction (MVC), and neural voluntary activation (VA) were measured before, after 10 min, and after 24, 48, and 72 hr on treated and contralateral limbs. Results: Following exercise, CK increased until after 48 hr, while PRS increased until after 72 hr compared to the CON group. Importantly, MVC was reduced at all time points, with the greatest reduction observed after 24 hr (−16%), while VA was affected until after 48 hr, with the greatest reduction at after 10 min (−7%). Interestingly, a “cross-over effect” was observed in contralateral limbs when PRS, MVC, and VA were negatively affected following the same pattern (time line) as treated limbs (−13% peak MVC reduction; −3.5% peak VA reduction). Conclusion: These findings suggest a substantial central contribution to the reduction in force immediately following eccentric exercise and to a lesser extent during the latter part of DOMS in both treated and contralateral limbs.

Is there an intermuscular relationship in voluntary activation capacities and contractile kinetics?

The force-generating capacities of human skeletal muscles are interrelated, highlighting a common construct of limb strength. This study aimed to further determine whether there is an intermuscular relationship in maximal voluntary activation capacities and contractile kinetics of human muscles. Twenty-six young healthy individuals participated in this study. Isometric maximal voluntary contraction (MVC) torque, voluntary activation level (VAL), and doublet twitch contractile kinetics (contraction time and half-relaxation time) evoked by a paired supramaximal peripheral nerve stimulation at 100Hz were obtained in elbow flexors, knee extensors, plantar flexors and dorsiflexors of the dominant limb. Peak MVC torque had significant positive correlations between all muscle group pairs (all P values < 0.01). A significant positive correlation for VAL was found only between knee extensors and plantar flexors (r = 0.60, P < 0.01). There were no significant correlations between all muscle group pairs for doublet twitch contraction time and doublet twitch half-relaxation time. These results show that there is a partial common construct of maximal voluntary activation capacities that only concerns muscle groups that have incomplete activation during MVC (i.e., knee extensors and plantar flexors). This suggests that the common construct of MVC strength between these two muscle groups is partly influenced by neural mechanisms. The lack of intermuscular relationship of contractile kinetics showed that there is no common construct of muscle contractile kinetics, as assessed in vivo by investigating the time-course of evoked doublet twitch contractions.

The effects of elevated pain inhibition on endurance exercise performance.

BackgroundThe ergogenic effects of analgesic substances suggest that pain perception is an important regulator of work-rate during fatiguing exercise. Recent research has shown that endogenous inhibitory responses, which act to attenuate nociceptive input and reduce perceived pain, can be increased following transcranial direct current stimulation of the hand motor cortex. Using high-definition transcranial direct current stimulation (HD-tDCS; 2 mA, 20 min), the current study aimed to examine the effects of elevated pain inhibitory capacity on endurance exercise performance. It was hypothesised that HD-tDCS would enhance the efficiency of the endogenous pain inhibitory response and improve endurance exercise performance.MethodsTwelve healthy males between 18 and 40 years of age (M = 24.42 ± 3.85) were recruited for participation. Endogenous pain inhibitory capacity and exercise performance were assessed before and after both active and sham (placebo) stimulation. The conditioned pain modulation protocol was used for the measurement of pain inhibition. Exercise performance assessment consisted of both maximal voluntary contraction (MVC) and submaximal muscular endurance performance trials using isometric contractions of the non-dominant leg extensors.ResultsActive HD-tDCS (pre-tDCS, −.32 ± 1.33 kg; post-tDCS, −1.23 ± 1.21 kg) significantly increased pain inhibitory responses relative to the effects of sham HD-tDCS (pre-tDCS, −.91 ± .92 kg; post-tDCS, −.26 ± .92 kg; p = .046). Irrespective of condition, peak MVC force and muscular endurance was reduced from pre- to post-stimulation. HD-tDCS did not significantly influence this reduction in maximal force (active: pre-tDCS, 264.89 ± 66.87 Nm; post-tDCS, 236.33 ± 66.51 Nm; sham: pre-tDCS, 249.25 ± 88.56 Nm; post-tDCS, 239.63 ± 67.53 Nm) or muscular endurance (active: pre-tDCS, 104.65 ± 42.36 s; post-tDCS, 93.07 ± 33.73 s; sham: pre-tDCS, 123.42 ± 72.48 s; post-tDCS, 100.27 ± 44.25 s).DiscussionDespite increasing pain inhibitory capacity relative to sham stimulation, active HD-tDCS did not significantly elevate maximal force production or muscular endurance. These findings question the role of endogenous pain inhibitory networks in the regulation of exercise performance.

Fatigue-related firing of distal muscle nociceptors reduces voluntary activation of proximal muscles of the same limb

With fatiguing exercise, firing of group III/IV muscle afferents reduces voluntary activation and force of the exercised muscles. These afferents can also act across agonist/antagonist pairs, reducing voluntary activation and force in nonfatigued muscles. We hypothesized that maintained firing of group III/IV muscle afferents after a fatiguing adductor pollicis (AP) contraction would decrease voluntary activation and force of AP and ipsilateral elbow flexors. In two experiments (n = 10) we examined voluntary activation of AP and elbow flexors by measuring changes in superimposed twitches evoked by ulnar nerve stimulation and transcranial magnetic stimulation of the motor cortex, respectively. Inflation of a sphygmomanometer cuff after a 2-min AP maximal voluntary contraction (MVC) blocked circulation of the hand for 2 min and maintained firing of group III/IV muscle afferents. After a 2-min AP MVC, maximal AP voluntary activation was lower with than without ischemia (56.2 ± 17.7% vs. 76.3 ± 14.6%; mean ± SD; P < 0.05) as was force (40.3 ± 12.8% vs. 57.1 ± 13.8% peak MVC; P < 0.05). Likewise, after a 2-min AP MVC, elbow flexion voluntary activation was lower with than without ischemia (88.3 ± 7.5% vs. 93.6 ± 3.9%; P < 0.05) as was torque (80.2 ± 4.6% vs. 86.6 ± 1.0% peak MVC; P < 0.05). Pain during ischemia was reported as Moderate to Very Strong. Postfatigue firing of group III/IV muscle afferents from the hand decreased voluntary drive and force of AP. Moreover, this effect decreased voluntary drive and torque of proximal unfatigued muscles, the elbow flexors. Fatigue-sensitive group III/IV muscle nociceptors act to limit voluntary drive not only to fatigued muscles but also to unfatigued muscles within the same limb.

Neuromuscular fatigue after maximal exercise in patients with cystic fibrosis

The aim of this study was to determine whether patients with cystic fibrosis (CF), despite their ventilatory limitation, would develop neuromuscular fatigue of quadriceps muscles following a maximal cycling exercise. Eleven adults with CF (age = 26.8 ± 6.9 years; forced expiratory volume in 1 s = 54.1 ± 12.8% predicted) and 11 age-matched healthy subjects performed a maximal incremental cycle test with respiratory gas exchange measurements. Maximal voluntary contraction (MVC) and electromyographic (EMG) activity of the vastus medialis muscle were recorded before and after exercise. Neural and contractile properties of the quadriceps were also investigated using femoral nerve electrical stimulation. Patients had lower exercise capacity, peak oxygen uptake and MVC than controls. MVC fell significantly postexercise in both groups (CF: −20 ± 10%, controls: −19 ± 6%; p < 0.01). EMG root mean square values, M-wave amplitude and duration were unchanged in both groups. Peak twitch (−46.9 ± 13.8%), maximal rate of twitch torque development (−50.3 ± 13.8%) and relaxation (−35.2 ± 19.5%) were all reduced after exercise in CF patients. The control group followed the same pattern (−38.4 ± 14.4%, −42.1 ± 14.7% and −15 ± 20.4%) but the statistical significance was not reached for the maximal rate of twitch torque relaxation. In conclusion, CF patients demonstrated lower limb fatigue following symptom-limited cycle exercise, which was comparable to that exhibited by healthy controls. This fatigue may be due to contractile impairments and not to transmission failure. Further studies should be conducted in a larger sample to confirm these preliminary results.

Effect of Long-Acting Testosterone Treatment on Functional Exercise Capacity, Skeletal Muscle Performance, Insulin Resistance, and Baroreflex Sensitivity in Elderly Patients With Chronic Heart Failure: A Double-Blind, Placebo-Controlled, Randomized Study

This study investigated the effect of a 12-week long-acting testosterone administration on maximal exercise capacity, ventilatory efficiency, muscle strength, insulin resistance, and baroreflex sensitivity (BRS) in elderly patients with chronic heart failure (CHF). CHF is characterized by a metabolic shift favoring catabolism and impairment in skeletal muscle bulk and function that could be involved in the pathophysiology of heart failure. Seventy elderly patients with stable CHF-median age 70 years, ejection fraction 31.8 +/- 7%-were randomly assigned to receive testosterone (n = 35, intramuscular injection every 6 weeks) or placebo (n = 35), both on top of optimal medical therapy. At baseline and at the end of the study, all patients underwent echocardiogram, cardiopulmonary exercise test, 6-min walk test (6MWT), quadriceps maximal voluntary contraction (MVC), and isokinetic strength (peak torque) and BRS assessment (sequences technique). Baseline peak oxygen consumption (VO(2)) and quadriceps isometric strength showed a direct relation with serum testosterone concentration. Peak VO(2) significantly improved in testosterone but was unchanged in placebo. Insulin sensitivity was significantly improved in testosterone. The MVC and peak torque significantly increased in testosterone but not in placebo. The BRS significantly improved in testosterone but not in placebo. Increase in testosterone levels was significantly related to improvement in peak VO(2) and MVC. There were no significant changes in left ventricular function either in testosterone or placebo. These results suggest that long-acting testosterone therapy improves exercise capacity, muscle strength, glucose metabolism, and BRS in men with moderately severe CHF. Testosterone benefits seem to be mediated by metabolic and peripheral effects.

Neuro-muscular Fatigue Development During Repeated Cycling Sprints In A Hot Environment

The mechanisms contributing to the alteration in neuromuscular function during repeated sprints have been recently documented. However, the effect of hot environment on these neuro-muscular alterations remains unclear. PURPOSE: To investigate the contributions of central and peripheral factors in the development of neuro-muscular fatigue during repeated sprints in a hot environment METHODS: Ten male subjects (23.1±3 yrs) performed two 38 min repeated sprint trails consisting of eight 6sec sprint of maximal cycling interspaced by 5 min of active recovery (1W/kg body weight.). Trails were performed in control (CON; 24°C - 24% rH) and hot (HOT; 40°C - 40% rH) environmental conditions in random order After each sprint, maximal percutaneous electrical stimulations were applied to the femoral nerve both at rest and during maximal voluntary contraction (MVC). To examine potential impairment in central drive, changes in EMG activity of the vastus lateralis muscle normalized to the M-wave amplitude (RMS/M) as well as muscle activation (VA) were quantified during MVC of knee extensors. Peripheral fatigue was assessed by examining the amplitude of the M-wave and twitch contractile properties following single stimuli. Both Core and skin temperaturs were monitored throughout by telemetric pill and patches respectively. RESULTS: RPE, HR, and skin temperature were significantly (all P< 0.05) higher in HOT compared to CON; RPE: 15±3 vs. 13±3, HR: 141±10 vs. 123±15 bpm. However core temperature, peak power production, MVC and muscle electrical activity during the MVC's or the cycling sprints was not influenced by the environmental condition in this pattern of exercise. CONCLUSION: Despite HR, RPE, and skin temperature being higher in hot than control, the body was able to produce the same power in both conditions. These findings suggest that there are no anticipatory decrements in power production when it comes to repeated sprints even if, RPE do increase in hot environment.

The arm configuration at the point of peak dynamic pull strength

This study examines the effects of velocity and starting position of pull on the configuration of the arm at the point at which peak maximal voluntary contraction (MVC) pull strenght is achived. Ten males performed 15 different isokinetic pulls each, defined by 5 starting positions of the arm in the saggital plane and 3 pull velocities for each position. Some restrictive conditions were applied to body posture and arm motions to facilitate biomechanical analyses of the results. All subjects were tested while seated. The results indicated that pull strength depended strongly on the starting position of the arm and velocity of pull. The angular configuration of the arm at peak strength position was unaffected by the starting position of the arm. This suggests that there may be an optimal arm configuration for dynamic (or even static) pull strength. For each tested velocity of pull, a different optimal configuration was found. Peak strengths attained have been explained by biomechanical principles, but the optimal arm configuration cannot yet be explained in the same way. The empirical relationships are, however, significant