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PubMed2005

Effects of prolonged muscle stretching with constant torque or constant angle on hypertonic calf muscles.

OBJECTIVE: To compare the effectiveness of constant-torque prolonged muscle stretching (PMS) treatment in the inhibition of ankle hypertonia with that of constant-angle PMS treatment. DESIGN: Before-after comparison. SETTING: A university-affiliated teaching hospital. PARTICIPANTS: Thirty subjects with hemiplegia and hypertonia in the calf muscles. INTERVENTION: Ankle plantarflexors were stretched using a motor-driven stretching device capable of operating in either a constant-angle or a constant-torque mode for 30 minutes of PMS treatment. MAIN OUTCOME MEASURES: Clinical scales, including the Modified Ashworth Scale (MAS) and passive range of motion (ROM), and biomechanic assessments were used to evaluate the viscoelastic components of the ankle plantarflexors before and after PMS treatment. RESULTS: Both constant-angle and constant-torque PMS treatments significantly improved the clinical scale (MAS, ROM) assessment results and reduced the viscoelastic components of the ankle joint ( P <.05). The degree of change in the viscoelastic components was more evident in subjects with constant-torque PMS than in those with constant-angle PMS ( P <.05). CONCLUSIONS: The present biomechanic assessments indicate that both PMS treatment modes reduced the viscous and elastic components of hypertonic muscles. The proposed constant-torque PMS treatment was more effective than the conventional constant-angle stretching technique.

Adult↗
PubMed2006

Isometric muscle torque in children 5 to 15 years of age: normative data.

OBJECTIVE: To establish reference values of arm and leg muscle strength as measured by isometric torque production in healthy children. DESIGN: Measurement of isometric muscle strength in healthy children. SETTING: Public school. PARTICIPANTS: Healthy children (N=149; 76 boys, 73 girls) ages 5 to 15 years. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Isometric torque values of 12 arm and leg muscle groups of healthy children as measured by a handheld dynamometer. RESULTS: Normative data were obtained for children 5 to 15 years of age. There was an increase in torque with age and weight and a strong correlation with both age and weight. There were few differences between boys and girls. Equations for predicted torque taking into account age, weight, and sex were calculated. The agreement between examiners was excellent. CONCLUSIONS: Studies on growing children require comparison to healthy (normal) children to assess the amount of deviation from normal and to be able to draw conclusions of change over time. The reference values for torque in combination with a predicted value based on the child's age, weight, and sex make it possible to compare over time and between subjects and provide a tool for evaluation of physical status and efficacy of therapy.

Adolescent↗
PubMed2004

Insertion torque pullout strength relationship of soft tissue tendon graft tibia tunnel fixation with a bioabsorbable interference screw.

PURPOSE: The purpose of this study was to evaluate the relationship between insertion torque and the biomechanical characteristics of soft tissue tendon graft tibia fixation with a bioabsorbable interference screw. TYPE OF STUDY: Biomechanical study. METHODS: Doubled tibialis anterior allografts (n = 20, length = 100 mm, diameter = 9 mm) prepared for anterior cruciate ligament (ACL) reconstructions were divided into 3 groups. Maximum insertion torque was measured as grafts were fixed by the same surgeon with a 10-mm diameter, 35-mm long screw in a 7-mm diameter tunnel (dilated to 9 mm) created in either 0.16 or 0.32 g/cm3 dense synthetic bone or cadaveric tibiae (0.84 +/- 0.15 g/cm2). Tensile testing to construct failure was then performed. RESULTS: All constructs failed by tunnel pullout. Higher density synthetic bone had greater load at failure than lower density synthetic bone (486.6 +/- 83.8 v 271.6 +/- 52.6 N, P <.0001) and a slightly greater proportion of variance could be explained in synthetic bone (R2 = 0.74, P <.0001) than in cadaveric tibiae (R2 = 0.64, P =.017). Higher density synthetic bone displayed greater stiffness than lower density synthetic bone (68.1 +/- 21.6 v 37.7 +/- 11.2 N/mm, P =.012) and a higher proportion of variance could be explained in cadaveric tibiae (R2 = 0.72, P =.008) than in synthetic bone (R2 = 0.48, P =.012). Greater insertion torque levels were seen in higher density synthetic bone (2.97 +/- 0.35 v 1.24 +/- 0.06 Nm, P <.0001) than in lower density synthetic bone, and a higher proportion of variance could be explained in synthetic bone (R2 = 0.94, P <.0001) than in cadaveric tibiae (R2 = 0.74, P =.006). CONCLUSIONS: Strong relationships were evident between insertion torque, bone mineral density (BMD) and load to failure across constructs. Differences between the synthetic bone groups and cadaveric tibiae, however, suggest the influence of mixed cortical and cancellous bone, nonuniform structural patterning, and differing BMD levels and distributions in the cadaveric tibiae. CLINICAL RELEVANCE: Soft tissue graft tibial tunnel fixation is directly related to insertion torque and BMD. Synthetic models with mixed bone characteristics are needed to more accurately depict human tibiae during fixation testing.

Absorbable Implants↗
PubMed2005

Vertical torque allows recording of anticipatory postural adjustments associated with slow, arm-raising movements.

BACKGROUND: When performed in the upright position, voluntary arm-raising movements perturb balance. The maintenance of equilibrium requires postural adjustments, some of which can be anticipatory. It is usually suggested that the role of anticipatory postural adjustments is to stabilise the whole body centre of mass. During movements performed at low velocity (i.e. with a lower inertial perturbation), anticipatory postural adjustments have not systematically been detected by classical recording methods (mainly electromyography). The aim of this study was to use vertical torque to characterise anticipatory postural adjustments in slow movement and to determine the significance of this biomechanical parameter. METHODS: Twenty healthy subjects performed self-paced, right arm-raising movements at low and high velocities. Movements were recorded by an optoelectronic system enabling the synchronization of video, force plate and electromyographic data. The force platform provided information on vertical torque and centre of foot pressure anteroposterior displacement. Electromyography activity was recorded from the right anterior deltoid and the bilateral biceps femoris, tibialis anterior and soleus muscles. FINDINGS: Rapid, voluntary, unilateral movements were associated with an early centre of pressure backward shift, anticipatory vertical torque and electromyographic activities. In slow movements, only the anticipatory changes in vertical torque were consistently observed, with the same latency as in rapid movement. INTERPRETATION: The existence of vertical torque in slow movement (when stabilisation of the centre of mass is not necessary) shows that this parameter does not serve to minimise the centre of mass displacement but rather contributes to the generation of arm movement.

Adaptation, Physiological↗
PubMed2006

Activation impairment alters muscle torque-velocity in the knee extensors of persons with post-stroke hemiparesis.

OBJECTIVE: To elucidate mechanisms of impaired force production in post-stroke hemiparesis. METHODS: Knee extensor torque-velocity and activation-velocity relationships were examined in seventeen persons with post-stroke hemiparesis (age 57.5, +/-6.9) and thirteen non-disabled (age 63.0 +/-10.4) persons. RESULTS: Velocity-dependent concentric torque impairment was exaggerated in subjects with hemiparesis relative to control subjects (p<.001). Muscle power was also less in the group with hemiparesis (p<.001), and plateaued at velocities > or =90deg/s (p>.05). In the control group agonist EMG during concentric actions exhibited a positive linear relationship as velocity increased (R(2)=.93, p<.05). The group with hemiparesis produced 34-60% less agonist EMG than controls (p<.02) and modulation was absent (p>.05). Antagonist EMG was either greater in the control (biceps femoris, p<.006) or similar between groups (semimembranosus, p=.95). Under eccentric testing conditions, torque normalized to peak isometric torque (p=.44) and rectus femoris activation (p=.33) were similar between groups, indicating a relative preservation of eccentric torque producing capacity post-stroke. CONCLUSIONS: Certain clinical perspectives assert that weakness following central nervous system injury stems from spastic antagonist restraint. Instead, absence of an antagonist restraint strongly suggests that impaired agonist activation is the principal determinant of hemiparetic weakness. SIGNIFICANCE: These findings have important implications for promoting optimal recovery of motor function in neuro-rehabilitation.

Electromyography↗
PubMed2005

Comparison of a piezoelectric contact sensor and an accelerometer for examining mechanomyographic amplitude and mean power frequency versus torque relationships during isokinetic and isometric muscle actions of the biceps brachii.

The purpose of this study was to compare a piezoelectric contact sensor with an accelerometer for measuring the mechanomyographic (MMG) signal from the biceps brachii during submaximal to maximal isokinetic and isometric forearm flexion muscle actions. Following determination of isokinetic peak torque (PT) and the isometric maximum voluntary contraction (MVC), 10 adults (mean+/-SD age=22.8+/-2.7yrs) performed randomly ordered, submaximal step muscle actions of the dominant forearm flexors in 20% increments from 20% to 80% PT and MVC. Surface MMG signals were recorded simultaneously from a contact sensor and an accelerometer placed over the belly of the biceps brachii muscle. During the isokinetic and isometric muscle actions, the contact sensor and accelerometer resulted in linear increases in normalized MMG amplitude with torque (r(2) range=0.84-0.97) but the linear slope of the normalized MMG amplitude versus isokinetic torque relationship for the accelerometer was less (p<0.10) than that of the contact sensor. There was no significant (p>0.05) relationship for normalized MMG mean power frequency (MPF, %max) versus isokinetic and isometric torque for the contact sensor, but the accelerometer demonstrated a quadratic (R(2)=0.94) or linear (r(2)=0.83) relationship for the isokinetic and isometric muscle actions, respectively. There were also a number of significant (p<0.05) mean differences between the contact sensor and accelerometer for normalized MMG amplitude or MPF values. These findings indicated that in some cases involving dynamic and isometric muscle actions, the contact sensor and accelerometer resulted in different torque-related responses that may affect the interpretation of the motor control strategies involved.

Adult↗
PubMed2003

Quantifying the magnitude of torque physiotherapists apply when stretching the hamstring muscles of people with spinal cord injury.

OBJECTIVE: To quantify the magnitude of stretch that physiotherapists apply to the hamstring muscles of people with spinal cord injury (SCI). DESIGN: Repeated-measures design. SETTING: SCI unit in Australia. PARTICIPANTS: Fifteen individuals with motor complete paraplegia or tetraplegia. INTERVENTION: Twelve physiotherapists manually administered a stretch to the hamstring muscles of each subject. The stretch was applied by flexing the hip with the knee extended. MAIN OUTCOME MEASURE: Applied hip flexor torque. RESULTS: Therapists applied median hip flexor torques of between 30 and 68Nm, although some torques were as large as 121Nm. The stretch applied by different therapists to any 1 subject varied as much as 40-fold. CONCLUSION: There is a large range of stretch torques provided by physiotherapists to patients with SCI. Some therapists provide stretch torques well in excess of those tolerated by individuals with intact sensation.

Activities of Daily Living↗
PubMed1998

Quantification of full-range-of-motion unilateral and bilateral knee flexion and extension torque ratios.

OBJECTIVES: To evaluate the reliability and variability of repeated measurements of isometric knee flexion and extension strength, to quantify the extent of measurement error that may occur due to gravity, and to quantify isometric knee flexion/extension torque ratios at multiple angles through a full range of motion. DESIGN: Reliability assessment. SETTING: A university exercise center. PARTICIPANTS: Seventy-seven healthy men and women recruited from a university and surrounding community. INTERVENTION: Isometric knee flexion and extension strength tests. MAIN OUTCOME MEASURES: Knee flexion/extension strength was measured at 6 degrees, 24 degrees, 42 degrees, 60 degrees, 78 degrees, 96 degrees, and 108 of knee flexion. Before each contraction, subjects were instructed to completely relax the limbs to measure the mass of the lower leg. Torque values obtained during relaxation at each angle were added to or subtracted from "Total Torque" (TTQ) at peak exertion. The adjusted value was recorded as "Net Muscular Torque" (NMT). RESULTS: Reliability for the unilateral and bilateral tests was high (r =.88 to r=.98) and measurement variability low (SEM%=5.1% to 12.6%). There was a statistically significant difference at each angle of measurement between the TTQ and NMT values for both knee flexion and extension. Knee flexion/extension ratios were highly dependent on the angle tested, ranging from 1.30 (at 60) to .31 (at 1080). CONCLUSIONS: Isometric testing, using standardized angles, can reliably quantify knee flexion/extension strength. Furthermore, these findings emphasize the importance of correcting for the mass of the lower leg when assessing muscle function. Angle-specific knee flexion/extension torque ratios should provide clinicians with a more precise method of evaluating muscular balance (imbalance) throughout the range of motion.

Adolescent↗
PubMed2003

Obesity is not associated with increased knee joint torque and power during level walking.

While it is widely speculated that obesity causes increased loads on the knee leading to joint degeneration, this concept is untested. The purpose of the study was to identify the effects of obesity on lower extremity joint kinetics and energetics during walking. Twenty-one obese adults were tested at self-selected (1.29m/s) and standard speeds (1.50m/s) and 18 lean adults were tested at the standard speed. Motion analysis and force platform data were combined to calculate joint torques and powers during the stance phase of walking. Obese participants were more erect with 12% less knee flexion and 11% more ankle plantarflexion in self-selected compared to standard speeds (both p<0.02). Obese participants were still more erect than lean adults with approximately 6 degrees more extension at all joints (p<0.05, for each joint) at the standard speed. Knee and ankle torques were 17% and 11% higher (p<0.034 and p<0.041) and negative knee work and positive ankle work were 68% and 11% higher (p<0.000 and p<0.048) in obese participants at the standard speed compared to the slower speed. Joint torques and powers were statistically identical at the hip and knee but were 88% and 61% higher (both p<0.000) at the ankle in obese compared to lean participants at the standard speed. Obese participants used altered gait biomechanics and despite their greater weight, they had less knee torque and power at their self-selected walking speed and equal knee torque and power while walking at the same speed as lean individuals. We propose that the ability to reorganize neuromuscular function during gait may enable some obese individuals to maintain skeletal health of the knee joint and this ability may also be a more accurate risk indicator for knee osteoarthritis than body weight.

Adult↗
PubMed2003

The removal torque of titanium screw inserted in rabbit tibia treated by dual acid etching.

Chemical acid etching alone of the titanium implant surface have the potential to greatly enhance osseointegration without adding particulate matter (e.g. TPS or hydroxyapatite) or embedding surface contaminants (e.g. grit particles). The aims of the present study were to evaluate any differences between the machined and dual acid etching implants with the removal torque as well as topographic analysis. A total of 40 custom-made, screw-shaped, commercially pure titanium implants with length of 5 mm and an outer diameter of 3.75 mm were divided into 4 groups, 10 screws in each, and chemical modification of the titanium implant surfaces were achieved using HF and HCl/H(2)SO(4) dual acid etching. The first exposure was to hydrofluoric acid and the second was to a combination of hydrochloric acid and sulfuric acid. The tibia metaphysics was exposed by incisions through the skin, fascia, and periosteum. One implant of each group was inserted in every rabbit, 2 in each proximal tibia metaphysics. Every rabbit received 3 implants with acid etched surfaces and 1 implant with a machined surface. Twelve weeks post-surgically, 7 rabbits were sacrificed, Subsequently, the leg was stabilized and the implant was removed under reverse torque rotation with a digital torque gauge (Mark-10 Corporation, USA) (Fig. 1). Twelve weeks after implant placement, the removal torque mean values were the dual acid etched implants (24%HF+HCl/H(2)SO(4), group C) required a higher average force (34.7 Ncm), than the machined surface implants (group A) (p=0.045) (Mann-Whiteney test). Scanning electron micrographs of acid etching of the titanium surface created an even distribution of very small (1-2 microm) peaks and valleys, while machining of the titanium surface created typical microscopically grooved surface characteristics. Nonetheless, there was no difference in surface topography between each acid etched implant groups. Therefore, chemically acid etching implant surfaces have higher strengths of osseointegration than machined implant surfaces. There is less correlation between removal torque and the difference in HF volume%.

Acids↗
PubMed2000

Responses of fine primary afferent nerve fibres innervating the rat knee joint to defined torque.

In total 23 rat knee joint afferent units with conduction velocities of 1.2-17 m/s were recorded extracellularly during inward and outward joint rotations of defined torque using a newly developed torque-meter. There was not a linear relation between the torque and the obtained angle of the joint. The mechanical thresholds of the units ranged from 10 to 60 mNm. During 10 s of stimulation with 60 mNm they responded with 12-300 action potentials. Two mechanosensitive nerve fibres could not be activated via knee joint rotation at any torque at all. The units could be classified according to their response pattern during stimulation: (1) phasic-tonic response behaviour; (2) constant discharge rate; (3) delayed onset of activity. In conclusion, the novel torque-meter allows a precise characterisation of the mechanical threshold and the corresponding response of fine afferent joint units during knee joint rotation.

Animals↗
PubMed1999

Self-adapting washer system for lag screw fixation of mandibular fractures. Part II: In vitro mechanical characterization of 2.3 and 2.7 mm lag screw prototypes and in vivo removal torque after healing.

The aim of this study was to mechanically characterize self-tapping 2.3 and 2.7 mm titanium lag screw prototypes which are part of the newly developed 'self-adapting washer' maxillofacial lag screw osteosynthesis system. In vitro in a screw testing machine the insertion torque, maximum locking torque and axial force and the ultimate torsional strength were assessed. In vivo in six miniature pigs using a mandibular symphyseal fracture model, the removal torques after 3 and 6 months of healing were measured. Additionally the bone-metal contact (BMC) of the screws was assessed histometrically. The maximum insertion torque (0.185 Nm) was far below the mechanical limits of the screws (2.3 mm = 0.96 Nm, 2.7 mm = 1.6 Nm). A tightening of the 2.7 mm screw with an axial force of 1000 N and of the 2.3 mm screw with 500-550 N leaves a safety margin of approximately one-third on the ultimate torsional strength. Clinically these values permit the use of two 2.3 mm lag screws or one 2.7 mm lag screw in mandibular symphysis fractures since 1000 N tensile axial force are required in this indication. During screw removal after 6 months healing, torque levels close to the mechanical limits of the screws were recorded and screw failures were observed. This failure rate may have been due to the BMC of 49.8% which was in the range of titanium dental implants. Accordingly the screw heads were reinforced to prevent fractures.

Animals↗
PubMed2002

Variations in the relationship between the frequency content of EMG signals and the rate of torque development in voluntary and elicited contractions.

Our purpose was to characterize the relationship between EMG mean power frequency (MPF) or median frequency (MF) and rate of torque development in voluntary ballistic and electrically elicited isometric contractions. Twenty-three healthy adults participated in two sets of experiments performed on elbow flexor muscles. For Experiment 1, subjects were asked to generate voluntary ballistic contractions by reaching four different target torque levels (20, 40, 60 and 100% of the maximal voluntary contraction (MVC)) as fast as they could. For Experiment 2, electrical (M-waves) and mechanical (twitches) responses to electrical stimulation of the nerves supplying the biceps brachii and brachioradialis muscles were recorded with the subjects at rest and with a background isometric contraction of 15% MVC. MPF, MF and rate of torque development (% MVC/s) were calculated for both voluntary and elicited contractions. Significant positive correlations were observed between MPF and rate of torque development for the voluntary contractions, whereas significant negative correlations were observed between the two variables for elicited contractions. This suggests that factors other than muscle fiber composition influence the frequency content of EMG signals and/or the rate of torque development, and that the effect of these factors will vary between voluntary and elicited contractions.

Adult↗
PubMed2002

Dynamic torque and apical forces of ProFile.04 rotary instruments during preparation of curved canals.

AIM: To analyse torque and force generated whilst shaping curved canals using rotary instruments. METHODOLOGY: A specially designed computer-controlled testing platform was used to record events during the shaping of straight and curved canals in plastic blocks and in extracted human teeth using ProFile.04 instruments. Size 40 apical stops were prepared using crown-down, apical preparation and step-back procedures. Maximum torque, apically directed force and the numbers of revolutions were recorded at a resolution of 100 samples s-1. Load causing separation as required by the ISO 3630-1 test and cyclic fatigue was also recorded. Mean maximum scores were calculated and statistically tested using one- and two-way analyses of variance. RESULTS: Highest and lowest torque scores were recorded, respectively, in straight canals in plastic blocks at 25 Nmm and in natural canals at 14 Nmm. Significant differences were recorded for canal type and preparation phase (P < 0.0001). Loads causing separation varied from 3.7 to 32.3 Nmm. Apically directed forces ranged from 1 to 7.5 N. Again, there were significant differences depending on canal type and preparation phase (P < 0.0001). The number of revolutions during preparation ranged from 18 to 41. Size 15, 30 and 45 ProFile.04 instruments separated after 581, 430 and 402 revolutions, respectively, in a standard cyclic fatigue test. CONCLUSIONS: The new torque-testing platform details physical parameters during preparation of curved canals. To improve predictability, instrumentation sequences must be tested for excessively high torsional moments or forces. This study indicated that up to 10 curved canals could be safely prepared with a sequence of ProFile. 04 rotary instruments without separation due to cyclic fatigue. Efforts should continue to correlate root canal anatomy with torque and force generated during rotary root canal preparation.

Analysis of Variance↗
PubMed2002

Influence of rotational speed, torque and operator proficiency on failure of Greater Taper files.

AIM: The purpose of this study was to evaluate the influence of rotational speed. torque, and operator experience on the incidence of locking, deformation, and separation of instruments when using a specific Ni-Ti rotary instrumentation technique in extracted human teeth. METHODOLOGY: Greater Taper Ni-Ti rotary instruments (GT) were used in a crown-down technique. In one group (rotational speed evaluation) of canals (n = 300) speeds of 150, 2 50 and 350 r.p.m. (subgroups 1, 2 and 3) were used. Each one of the subgroups included 100 canals. In a second group (evaluation of torque) (n = 300) torque was set at 20, 30 and 55 Ncm (subgroups 4, 5 and 6). In the third group (evaluation of operator proficiency) (n = 300 three operators with varying experience (subgroups 7, 8 and 9) were also compared. Each subgroup included the use of 10 sets of GT rotary instruments and 100 canals of extracted human molars. Each set of instruments was used in up to 10 canals and sterilized before each case. NaOCl 2.5% was used as an irrigant. The number of locked, deformed, and separated instruments was recorded for each group. Statistical analysis was carried out with pairwise comparisons using Fisher's exact tests for each of the failure type. RESULTS: When the influence of rotational speed was evaluated, instrument deformation and separation did not occur in subgroups 1 (150) r.p.m.), 2 (250 r.p.m.), and 3 (350) r.p.m.). Instrument locking occurred in subgroup 3 only. Statistical analysis demonstrated a significant difference between the 150 and 350 r.p.m. groups and between the 250 and 350 r.p.m. groups with respect to instrument locking. In torque evaluation, neither separation, deformation nor locking occurred during the use of the instruments, at 150 r.p.m., and at the different torque values. When the operators were compared, although two instruments were separated in canals prepared by the least experienced operator. Fisher's exact tests did not demonstrate a significant difference between the three subgroups. Instrument locking, deformation, and separation did not occur with the most experienced operator. None of the instruments separated with the trained operator. CONCLUSIONS: Preclinical training in the use of the GT rotary instruments when used with a crown-down technique at 150 r.p.m. was crucial in avoiding instrument separation and reducing the incidence of instrument locking and deformation.

Dental Alloys↗
PubMed2000

The influence of lower extremity joint torque on gait characteristics in elderly men.

OBJECTIVE: To examine the relation between certain lower extremity isokinetic muscle torque capabilities and selected stride characteristics for a group of elderly, sedentary men. STUDY DESIGN: Descriptive analysis of convenience sample. SETTING: Veterans Administration (VA) ambulatory care center. SUBJECTS: Eighty-one elderly men, capable of independent ambulation, were recruited from outpatient clinics and the local community (mean age, 74.7yr). MAIN OUTCOME MEASURES: Maximal isokinetic torque in the sagittal plane of hip, knee, and ankle muscles; stride characteristics of speed, stride length, and cadence recorded during walking at a self-selected velocity. RESULTS: Stepwise regression analysis revealed that hip extension torque was the only significant independent predictor for free walking speed, stride length, and cadence, and accounted for 37% (r = .611), 35% (r = .590), and 12% (r = .341) of the total variance, respectively. Other joint torques correlated with gait parameters but did not add significantly to the multivariate model. CONCLUSIONS: Hip extension torque was the only significant independent predictor for free walking velocity, stride length, and cadence in this group. These results support the idea that strengthening the hip extensors may improve stride characteristics in elderly individuals.

Aged↗
PubMed2006

Plantar flexion torque as a function of time of day.

The possible peripheral and/or central origin in the mechanisms responsible for day-time fluctuation in maximal torque of the triceps surae muscle were investigated with a special emphasis on antagonist muscle coactivation. Eleven healthy male subjects (physical education students) took part in this investigation. The electromechanical properties of the plantar flexor muscles were recorded at two different times of day: between 06:00 h and 08:00 h in the morning and between 17:00 h and 19:00 h in the evening. To investigate peripheral mechanisms, the posterior tibial nerve was stimulated at rest, using percutaneous electrical stimuli, to evoke single twitch, double twitch, and maximal tetanic contraction (100 Hz). Maximal voluntary contraction of the plantar flexors was also assessed by means of the relative electromyographic activity of respective agonist and antagonist muscles (soleus, gastrocnemius medialis, gastrocnemius lateralis, and tibialis anterior). A double twitch was delivered during maximal voluntary plantar flexion to record muscle activation (i.e., interpolated twitch technique). The coactivation level of the tibialis anterior muscle during plantar flexion was calculated. The results indicated a significant decrease in maximal voluntary muscle torque of triceps surae in the evening as compared with the morning (-7.0 %; p < 0.05). Concerning the central command, when extrapolated by the twitch interpolation technique, the decrease in mean activation level of -6.8 % was consistent with the fluctuation in torque (-7.0 %). Soleus muscle electromyographic activity (normalized to the M-wave) showed a significant decline (21.6 %; p < 0.001). Moreover, individual changes in MVC percentage were significantly related to those of normalized electromyographic activity of the soleus muscle (r = 0.688; p < 0.01). Thus, it indicated that the subject's capacity to activate the soleus muscle was affected by the time of day. The coactivation level in the tibialis anterior muscle during plantar flexion did not change significantly in the evening. Concerning peripheral mechanisms, we observed a decrease in maximal M-wave amplitude for soleus and gastrocnemii, associated with unchanged single twitch and tetanus torque. To conclude, impairment in soleus muscle central command seemed to be the mechanism in the origin of torque failure. Such information would be of importance in the investigation of day-time fluctuations in complex motor task performances implicating the triceps surae muscle.

Adult↗
PubMed2006

Effect of ankle joint stiffness during eccentric phase in rebound jumps on ankle joint torque at midpoint.

The purposes of this study were to investigate firstly, the ankle joint stiffness during the eccentric phase in rebound jumps, and secondly, the effect of ankle joint stiffness during the eccentric phase on ankle joint torque at midpoint. Nine active males executed rebound drop jumps from a height of 30 cm (RDJ30) and 50 cm (RDJ50), and 5-repetition rebound jumps (5RJ). Force plate data, limb position and electromyogram (EMG) of the medial head of gastrocnemius (GAS), soleus (SOL), and tibialis anterior (TA) muscles were recorded simultaneously during all jumps. When compared with RDJ30 and RDJ50, 5RJ displayed significantly higher jumping height, ankle joint torque at midpoint, ankle joint stiffness during the eccentric phase, and integrated EMG (IEMG) of GAS and SOL. Furthermore, 5RJ displayed significantly lower contact time and IEMG of TA than RDJ30 and RDJ50 did. The ankle joint torque at midpoint showed a significant positive correlation with jumping height but a significant negative correlation with contact time in rebound jumps. There was a significant positive correlation between the ankle joint stiffness during the eccentric phase and ankle joint torque at midpoint in rebound jumps. These results suggested that for the rebound jumps to be effective, it may be important to enhance the ankle joint torque at midpoint by greater ankle joint stiffness during the eccentric phase. These results also suggested that compared to 5RJ, RDJ30 and RDJ50 may reduce ankle joint stiffness in order to protect the tendomuscular system from the stretch load. However, ankle joint stiffness is possibly increased in 5RJ because the restraint to defend the tendomuscular system is reduced by prediction or adaptation to the stretch load because it is a continuous jump.

Adult↗