Muscle inactivation: assessment of interpolated twitch technique

Behm, D. G., D. M. M. St-Pierre, and D. Perez. Muscleinactivation: assessment of interpolated twitch technique.J. Appl. Physiol. 81(5):2267-2273, 1996.The validity, reliability, and protocol for theinterpolated twitch technique (ITT) were investigated with isometricplantar flexor and leg extension contractions. Estimates of muscleinactivation were attempted by comparing a variety of superimposed withpotentiated evoked torques with submaximal and maximal voluntarycontraction (MVC) torques or forces. The use of nerve and surfacestimulation to elicit ITT was reliable, except for problems inmaintaining maximal stimulation with nerve stimulation at 20°plantar flexion and during leg extension. The interpolated twitchratio-force relationship was best described by a shallow hyperboliccurve resulting in insignificant MVC prediction errors withsecond-order polynomials (1.1-6.9%). The prediction error under40% MVC was approximately double that over 60% MVC, contributing topoor estimations of MVC in non-weight-bearing postimmobilized anklefracture patients. There was no significant difference in the ITTsensitivity when twitches, doublets, or quintuplets were used.The ITT was valid and reliable when high-intensity contractions wereanalyzed with a second-order polynomial.

     

Reliability and agreement of a dynamic quadriceps incremental test for the assessment of neuromuscular function

The quadriceps-intermittent-fatigue (QIF) test assesses knee extensors strength, endurance and performance fatigability in isometric condition. We aimed to assess reliability and agreement for this test in dynamic conditions and with the use of transcranial magnetic stimulation. On two separate sessions, 20 young adults (25 ± 4 yr, 10 women) performed stages of 100 knee extensors concentric contractions at 120°/s (60° range-of-motion) with 10% increments of the initial maximal concentric torque until exhaustion. Performance fatigability across the test was quantified as maximal isometric and concentric torque loss, and its mechanisms were investigated through the responses to transcranial magnetic and electrical stimulations. Reliability and agreement were assessed using ANOVAs, coefficients of variation (CVs) and intra-class correlation coefficients (ICCs) with 95% CI. Good inter-session reliability and high agreement were found for number of contractions [489 ± 75 vs. 503 ± 95; P = 0.20; ICC = 0.85 (0.66; 0.94); CV = 5% (3; 7)] and total work [11,285 ± 4,932 vs. 11,792 ± 5838 Nm.s; P = 0.20; ICC = 0.95 (0.87; 0.98); CV = 8% (5; 11)]. Poor reliability but high agreement were observed for isometric [–33 ± 6 vs. −31 ± 7%; P = 0.13; ICC = 0.47 (0.05; 0.75); CV = 6% (4;8)] and concentric [−20 ± 11% vs. −19 ± 9%; P = 0.82; ICC = 0.26 (−0.22; 0.63); CV = 9% (6; 12)] torque loss. The dynamic QIF test represents a promising tool for neuromuscular evaluation in isokinetic mode.     

Closed chain assessment of quadriceps activation using the superimposed burst technique

The superimposed burst technique is used to estimate quadriceps central activation ratio during a maximal voluntary isometric contraction, which is calculated from force data during an open-chain knee extension task. Assessing quadriceps activation in a closed-chain position would more closely simulate the action of the quadriceps during activity. Our aim was to determine the test–retest reliability of the quadriceps central activation ratio in the closed chain.MethodsTwenty-two healthy, active volunteers (13M/12F; age = 23.8 ± 3; height = 72.7 ± 14.5 cm; mass = 175.3 ± 9.6 kg) were recruited to participate. Knee extension MVIC torque and the peak torque during a superimposed electrical stimulus delivered to the quadriceps during an MVIC were measured to estimate quadriceps CAR. Interclass correlation coefficients were used to assess test–retest reliability between sessions, and Bland–Altman plots to graphically assess agreement between sessions.ResultsTest–retest reliability was fair for CAR (ICC_2,k = 0.68; P = 0.005), with a mean difference of −2.8 ± 10.3%, and limits of agreement ranging −23.1–18.1%.ConclusionsCAR calculated using the superimposed burst technique is moderately reliable in a closed-chain position using technique-based instruction. Although acceptable reliability was demonstrated, wide limits of agreement suggest high variability between sessions.     

A novel technique for nonvolitional assessment of quadriceps muscle endurance in humans.

Assessment of quadriceps endurance is of interest to investigators studying human disease. We hypothesized that repetitive magnetic stimulation (rMS) of the intramuscular branches of the femoral nerve could be used to induce and quantify quadriceps endurance. To test this hypothesis, we used a novel stimulating coil to compare the quadriceps endurance properties in eight normal humans and, to confirm that the technique could be used in clinical practice, in eight patients with advanced chronic obstructive pulmonary disease (COPD). To validate the method, we compared in vivo contractile properties of the quadriceps muscle with the fiber-type composition and oxidative enzyme capacity. We used a Magstim Rapid(2) magnetic nerve stimulator with the coil wrapped around the quadriceps. Stimuli were given at 30 Hz, a duty cycle of 0.4 (2 s on, 3 s off), and for 50 trains. Force generation and the surface electromyogram were measured throughout. Quadriceps twitch force, elicited by supramaximal magnetic stimulation of the femoral nerve, was measured before and after the protocol. Quadriceps muscle biopsies were analyzed for oxidative (citrate synthase, CS) and glycolytic (phosphofructokinase, PFK) enzyme activity and myosin heavy chain isoform protein expression. The time for force to fall to 70% of baseline (T(70)) was shorter in the COPD group than the control group: 55.6 +/- 26.0 vs. 121 +/- 38.7 s (P = 0.0014). Considering patients and controls together, positive correlations were observed between T(70) and the proportion of type I fibers (r = 0.68, P = 0.004) and CS-to-PFK ratio (CS/PFK) (r = 0.67, P = 0.005). We conclude that quadriceps endurance assessed using rMS is feasible in clinical studies.     

Comparison of twitch potentiation in the gastrocnemius of young and elderly men

The capacity for twitch potentiation in the gastrocnemius muscle was determined following maximal voluntary contractions (MVC) in 11 elderly (means +/- SD; 66.9 +/- 5.3 years) and 12 young (25.7 +/- 3.8 years) men. Potentiation was observed by applying selective stimulation to the muscle belly, 2 s after a 5 s MVC. With this procedure, both groups showed significant (P less than 0.05) increases in twitch tension in the gastrocnemius (ratios of potentiated twitch to baseline were means = 1.68 +/- 0.40 for young vs means = 1.40 +/- 0.20 for the elderly, P less than 0.001). Time to peak tension of the twitch decreased from means = 101.5 +/- 17.9 ms to means = 88.0 +/- 15.8 ms in the young men following potentiation; the respective values for the older men were 136.7 +/- 17.9 ms and 133.1 +/- 28.6 ms. These changes resulted in a greater rate of tension development in the potentiated state. The elderly gastrocnemius thus showed qualitatively similar changes in the isometric twitch following potentiation, but reduced and prolonged responses in comparison to young adults. Slowed muscle contraction and reduced capacity for potentiation may be physiological correlates of the reported morphological changes in aged skeletal muscle.     

Motor point heatmap guide for neuromuscular electrical stimulation of the quadriceps muscle

PurposeTo create an anatomical chart that indicates the probability of finding a motor point (MP) in different areas of the quadriceps muscle.MethodsOn 31 healthy adults, the individual anatomy of the vastus medialis (VM), rectus femoris (RF) and vastus lateralis (VL) was determined using ultrasound. Thereafter, a 3 Hz neuromuscular electrical stimulation (NMES) MP-search with a MP-pen was performed. The thigh anatomy was normalized and divided into 112 (8x14) 3x3cm areas, and the probability of finding a MP in the different areas was calculated to create a MP heat-map.ResultsThe heat-map displayed the two best 3x3cm areas, over VL and VM respectively, each with a probability greater than 50% of finding a MP and a higher probability compared to all other areas (p <.05). RF exhibited two areas with a 29% probability of finding a MP. A higher number of MPs on the quadriceps, mean (±SD) 9.4 ± 1, was in regression analysis found to be significantly associated with two independent factors higher physical activity level and lower body fat (R² = 0.42, p=<.0001).ConclusionLarge inter-individual variations in location, and number of MPs were found, but the heat-map displayed areas with higher probability of finding a MP and can be used to facilitate NMES-application.     

Validity and reliability of isometric,isokinetic and isoinertial modalities for the assessment of quadriceps muscle strength in patients with total knee arthroplasty

Reliability of isometric, isokinetic and isoinertial modalities for quadriceps strength evaluation, and the relation between quadriceps strength and physical function was investigated in 29 total knee arthroplasty (TKA) patients, with an average age of 63 years. Isometric maximal voluntary contraction torque, isokinetic peak torque, and isoinertial one-repetition maximum load of the involved and uninvolved quadriceps were evaluated as well as objective (walking parameters) and subjective physical function (WOMAC). Reliability was good and comparable for the isometric, isokinetic, and isoinertial strength outcomes on both sides (intraclass correlation coefficient range: 0.947–0.966; standard error of measurement range: 5.1–9.3%). Involved quadriceps strength was significantly correlated to walking speed (r range: 0.641–0.710), step length (r range: 0.685–0.820) and WOMAC function (r range: 0.575–0.663), independent from the modality (P < 0.05). Uninvolved quadriceps strength was also significantly correlated to walking speed (r range: 0.413–0.539), step length (r range: 0.514–0.608) and WOMAC function (r range: 0.374–0.554) (P < 0.05), except for WOMAC function/isokinetic peak torque (P > 0.05). In conclusion, isometric, isokinetic, and isoinertial modalities ensure valid and reliable assessment of quadriceps muscle strength in TKA patients.     

Age-related changes in neuromuscular function of the quadriceps muscle in physically active adults

Substantial evidence exists for the age-related decline in maximal strength and strength development. Despite the importance of knee extensor strength for physical function and mobility in the elderly, studies focusing on the underlying neuromuscular mechanisms of the quadriceps muscle weakness are limited.The aim of this study was to investigate the contributions of age-related neural and muscular changes in the quadriceps muscle to decreases in isometric maximal voluntary torque (iMVT) and explosive voluntary strength. The interpolated twitch technique and normalized surface electromyography (EMG) signal during iMVT were analyzed to assess changes in neural drive to the muscles of 15 young and 15 elderly volunteers. The maximal rate of torque development as well as rate of torque development, impulse and neuromuscular activation in the early phase of contraction were determined. Spinal excitability was estimated using the H reflex technique. Changes at the muscle level were evaluated by analyzing the contractile properties and lean mass.The age-related decrease in iMVT was accompanied by a decline in voluntary activation and normalized surface EMG amplitude. Mechanical parameters of explosive voluntary strength were reduced while the corresponding muscle activation remained primarily unchanged. The spinal excitability of the vastus medialis was not different while M wave latency was longer. Contractile properties and lean mass were reduced.In conclusion, the age-related decline in iMVT of the quadriceps muscle might be due to a reduced neural drive and changes in skeletal muscle properties. The decrease in explosive voluntary strength seemed to be more affected by muscular than by neural changes.     

Time course of the effects of vibration on quadriceps function in individuals with anterior cruciate ligament reconstruction

Quadriceps dysfunction is a common, chronic complication following anterior cruciate ligament reconstruction (ACLR) that contributes to aberrant gait biomechanics and poor joint health. Vibration enhances quadriceps function in individuals with ACLR, but the duration of these effects is unknown. This study evaluated the time course of the effects of whole body vibration (WBV) and local muscle vibration (LMV) on quadriceps function. Twenty-four volunteers with ACLR completed 3 testing sessions during which quadriceps isometric peak torque, rate of torque development, and EMG amplitude were assessed prior to and immediately, 10, 20, 30, 45, and 60 min following a WBV, LMV, or control intervention. WBV and LMV (30 Hz, 2g) were applied during six one-minute bouts. WBV increased peak torque 5–11% relative to baseline and control at all post-intervention time points. LMV increased peak torque 6% relative to baseline at 10 min post-intervention and 4–6% relative to control immediately, 10 min, and 20 min post-intervention. The interventions did not influence EMG amplitudes or rate of torque development. The sustained improvements in quadriceps following vibration, especially WBV, suggest that it could be applied at the beginning of rehabilitation sessions to “prime” the central nervous system, potentially improving the efficacy of ACLR rehabilitative exercise.     

Prolonged intermittent high intensity exercise impairs neuromuscular performance of the knee flexors

This study investigated the effect of prolonged intermittent high intensity exercise upon the isokinetic leg strength and electromechanical delay of the knee flexors. Seven male collegiate soccer players were exposed to: (i) a prolonged intermittent high intensity exercise task (PIHIET) which required subjects to complete a single-leg pedalling task, with the preferred limb, (75 rpm for all constant-load portions of the task) consisting of 48 × 1.8 minute cycles of exercise, and (ii) a control task consisting of no exercise. Pre-, mid- and post-PIHIET gravity corrected indices of knee flexion angle-specific torque (0.44 rad knee flexion (AST); 0 rad = full knee extension; [1.05 rad · s⁻¹]) were made for both intervention and control limbs. Electromechanical delay (EMD) of the m. biceps femoris during supine knee flexion movements was evaluated in the preferred leg on both intervention and control days. Repeated measures ANOVAs revealed significant condition (intervention; control) by time (pre; mid; post) interactions for both knee flexor AST (F_[2,12] = 4.8; p<0.03) and EMD (F_[2,12] = 4.1; p<0.05). AST was observed to decrease by 16% and EMD increase by 30% pre to post intervention. These observations suggest an impairment of neuromuscular control and the ability to maintain force generation in the knee flexors, near the extremes of the range of motion during prolonged intermittent high-intensity exercise activities. Changes of this magnitude may pose a threat to the integrity of the knee joint. Accepted: 6 January 1998     

Functional assessment of cryopreserved human femoral arteries for pharmaceutical research

An established method for cryopreservation that might preserve the vascular and endothelial responses of human femoral arteries (HFAs) to be transplanted as allografts was studied. HFAs were harvested from multiorgan donors and stored at 4 degrees C in saline solution before cryostorage. Thirty HFA rings were isolated and randomly assigned to one control group of unfrozen HFAs (eight rings) and one group of cryopreserved HFAs (22 rings).Cryopreservation was performed in RPMI solution containing dimethylsulfoxide (DMSO) and the rate of cooling was -1 degrees C/min until -40 degrees C and faster rates until -150 degrees C was reached. The contractile and relaxant responses of unfrozen and frozen/thawed arteries were assessed in organ bath by measurement of isometric force generated by the HFAs.After thawing, the maximal contractile responses to the contracting agonist tested (noradrenaline) were in the range of 43% of the responses in unfrozen HFAs. The endothelium-independent responses to sodium nitroprusside were not altered whereas the endothelium-dependent relaxant responses to acetylcholine were weakly altered.The cryopreservation method used provided a limited preservation of contractility of HFAs, a good preservation of the endothelium-independent relaxant responses, and a good preservation of endothelium-dependent relaxation. It is possible that further refinements of the cryopreservation protocol, such as a slower rate of cooling and a more controlled stepwise addition of DMSO, might allow better post-thaw functional recovery.     

Time-of-day effect on the torque and neuromuscular properties of dominant and non-dominant quadriceps femoris

The study was conducted first, to determine the possibility of a dichotomy between circadian rhythm of maximal torque production of the knee extensors of the dominant and non-dominant legs, and second, to determine whether the possible dichotomy could be linked to a change in the downward drive of the central nervous system and/or to phenomena prevailing at the muscular level. The dominant leg was defined as the one with which subjects spontaneously kick a football. Tests were performed at 06:00, 10:00, 14:00, 18:00, and 22:00 h. To distinguish the neural and muscular mechanisms that influence muscle strength, the electromyographic and mechanical muscle responses associated with electrically evoked and/or voluntary contractions of the human quadriceps and semi-tendinosus muscles for each leg were recorded and compared. The main finding was an absence of interaction between time-of-day and dominance effects on the torque associated with maximal voluntary contraction (MVC) of both quadriceps. A significant time-of-day effect on MVC torque of the knee extensors was observed for the dominant and non-dominant legs when the data were collapsed, with highest values occurring at 18:00 h (p < 0.01). From cosinor analysis, a circadian rhythm was documented (p < 0.001) with the peak (acrophase) estimated at 18:18 +/- 00:12 h and amplitude (one-half the peak-to-trough variation) of 3.3 +/- 1.1%. Independent of the leg tested, peripheral mechanisms demonstrated a significant time-of-day effect (p < 0.05) on the peak-torque of the single and doublet stimulations, with maximal levels attained at 18:00 h. The central activation of the quadriceps muscle of each leg remained unchanged during the day. The present results confirmed previous observations that muscle torque changes in a predictable manner during the 24 h period, and that the changes are linked to modifications prevailing at the muscular, rather than the neural, level. The similar rhythmicity observed in this study between the dominant and non-dominant legs provides evidence that it is not essential to test both legs when simple motor tasks are investigated as a function of the time of day.     

Scaling effects on the neuromuscular system,twitch kinetics and morphometrics of the cod,Gadus morhua

Size related changes in muscle twitch kinetics, morphometrics and innervation have been examined in cod, Gadus morhua. Fish size ranged from 9 cm to 45 cm in total length (L).

Twitch contraction time (time to 90% relaxation), scaled in proportion to L^0.29. Scaling of morphometric parameters was essentially geometric. Mean cross‐sectional area and weight of the myotomal muscle scaled in proportion to L^2.05 and L^3.08 respectively. These results are discussed in the light of alterations in length specific swimming performance and kinematics as fish grow.

During growth, the number of endplates terminating on each fast fibre increased, from around 10 on fibres 2 mm in length (～10 cm fish) to 20 on 10 mm fibres (—40 cm fish). However, mean spacing between endplates increased from around 0.25 mm to 0.50 mm. The functional significance of polyneuronal innervation in teleost fast muscle fibres is discussed.     

Validity of the jack-knife technique for analysing enzyme kinetic data.

An observation by Duggleby [Biochem. J. (1979) 181, 255-256] that estimates of kinetic parameters by the jack-knife technique [Cornish-Bowden & Wong (1978) Biochem. J. 175, 969--976] are sometimes outside the range of estimates from which they are calculated has been examined. No significant correlation has been found between the occurrence of this behaviour and the actual quality of the estimates.     

Changes in force, cross-sectional area and neural activation during strength training and detraining of the human quadriceps

Four male subjects aged 23-34 years were studied during 60 days of unilateral strength training and 40 days of detraining. Training was carried out four times a week and consisted of six series of ten maximal isokinetic knee extensions at an angular velocity of 2.09 rad.s-1. At the start and at every 20th day of training and detraining, isometric maximal voluntary contraction (MVC), integrated electromyographic activity (iEMG) and quadriceps muscle cross-sectional area (CSA) assessed at seven fractions of femur length (Lf), by nuclear magnetic resonance imaging, were measured on both trained (T) and untrained (UT) legs. Isokinetic torques at 30 degrees before full knee extension were measured before and at the end of training at: 0, 1.05, 2.09, 3.14, 4.19, 5.24 rad.s-1. After 60 days T leg CSA had increased by 8.5% +/- 1.4% (mean +/- SEM, n = 4, p less than 0.001), iEMG by 42.4% +/- 16.5% (p less than 0.01) and MVC by 20.8% +/- 5.4% (p less than 0.01). Changes during detraining had a similar time course to those of training. No changes in UT leg CSA were observed while iEMG and MVC increased by 24.8% +/- 10% (N.S.) and 8.7% +/- 4.3% (N.S.), respectively. The increase in quadriceps muscle CSA was maximal at 2/10 Lf (12.0% +/- 1.5%, p less than 0.01) and minimal, proximally to the knee, at 8/10 Lf (3.5% +/- 1.2%, N.S.). Preferential hypertrophy of the vastus medialis and intermedius muscles compared to those of the rectus femoris and lateralis muscles was observed.(ABSTRACT TRUNCATED AT 250 WORDS)     

Validity of bioelectric impedance for body composition assessment in children

Whole-body bioelectrical impedance analysis (BIA) was evaluated for its reliability and accuracy in estimating body composition in children. The hypothesis that the index, body height2 divided by resistance (RI), can accurately predict fat-free body mass (FFB) and percent fat (%FAT) in children was tested on 94 caucasian children 10-14 yr old. Criterion variables were FFB and %FAT estimated using multicomponent equations developed for children. BIA measurements (resistance and reactance) were found to be reliable. Prediction accuracy (standard error of the estimate, SEE) for FFB from RI alone was 2.6 kg and for %FAT from RI and body weight was 4.2%. For RI, anthropometric variables and reactance, the SEE improved to 1.9 kg FFB. For RI and anthropometric variables, the SEE was 3.3% FAT. For anthropometric variables alone, the SEE's were 2.1 kg FFB and 3.2% FAT. Adult FFB and %FAT prediction equations cross-validated with this sample resulted in SEE's similar to those for adult samples. We conclude that RI together with anthropometry is a reliable and an acceptably accurate method of estimating FFB mass and %FAT in children.     

In vivo behaviour of human muscle architecture and mechanomyographic response using the interpolated twitch technique

This study investigated the origin of curvilinear change in the superimposed mechanomyogram (MMG) amplitude of the human medial gastrocnemius muscle (MG) with increasing contraction intensity. The superimposed twitch amplitude, the superimposed MMG amplitude and the extent of fascicle shortening were measured using ultrasonic images of electrical stimulation during isometric plantar flexions at levels 20%, 40%, 60%, 80%, and 100% of the maximal voluntary contraction (MVC). The superimposed twitch amplitude, the superimposed MMG amplitude and the extent of fascicle shortening decreased with increasing contraction intensity. The superimposed MMG amplitude and the extent of fascicle shortening showed a curvilinear decrease, while the superimposed twitch amplitude showed a linear decrease at levels up to 80% of the MVC. There was a linear relationship between the superimposed MMG amplitude and the extent of fascicle shortening at different contraction intensities. These results indicate that the superimposed MMG amplitude reflects changes in the extent of fascicle shortening at different contraction intensities better than the superimposed twitch amplitude. Our study suggests that the origin of the curvilinear decrease of superimposed MMG amplitude is associated with a curvilinear decrease of the extent of fascicle shortening with increasing contraction intensity in the human MG.     

Quantitative assessment of the accuracy for three interpolation techniques in kinematic analysis of human movement

Marker obstruction during human movement analyses requires interpolation to reconstruct missing kinematic data. This investigation quantifies errors associated with three interpolation techniques and varying interpolated durations. Right ulnar styloid kinematics from 13 participants performing manual wheelchair ramp ascent were reconstructed using linear, cubic spline and local coordinate system (LCS) interpolation from 11–90% of one propulsive cycle. Elbow angles (flexion/extension and pronation/supination) were calculated using real and reconstructed kinematics. Reconstructed kinematics produced maximum elbow flexion/extension errors of 37.1 (linear), 23.4 (spline) and 9.3 (LCS) degrees. Reconstruction errors are unavoidable [minimum errors of 6.7 mm (LCS); 0.29 mm (spline); 0.42 mm (linear)], emphasising careful motion capture system setup must be performed to minimise data interpolation. For the observed movement, LCS-based interpolation (average error of 14.3 mm; correlation of 0.976 for elbow flexion/extension) was most suitable for reconstructing durations longer than 200 ms. Spline interpolation was superior for shorter durations.