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Exercise physiology in the 1990's: mechanistically defining the exercise model.

Definition of the exercise model via a mechanistic approach is a goal which should be of high priority among sport researchers in the 1990's, in an attempt to further qualify previous phenomenological observations of exercising man. Prolonged argument on the "theory-versus-practice" issue is one which is counter-productive in the advancement of knowledge in our discipline, and must be addressed and resolved. With specific emphasis on the neuromuscular control of movement, current research literature suggests that the components limiting to human performance may reside in the muscle, motoneurone and in the supraspinal of movement. Mechanistically defining the limits in each component, related to patterns of movement during exercise, may soon herald a reclassification of exercise types and their limits, defined by the particular system involved. Similarly, new evidence on adaptations throughout the neuromuscular system calls for a systematic study of these adaptations, how they influence structure and function of cell and organ systems, and their effects on the performance of the voluntarily exercising human. A mechanistic approach to these problems, using "simple" experimental models to more precisely define cause-effect, are justifiable and necessary in our field on the basis of the potential applicability of such information in the fields of design of exercise programmes, and the evaluation of their effectiveness, for normal and special populations. The problems associated with increased academic specialization and the communication gap which might result, are not inevitable. An enhancement of the proliferation of this knowledge and its interpretation in practical terms will result through our own awareness of the necessity of doing this, and through sensitization of our students to this issue.

Humans↗

TRPC3 channels confer cellular memory of recent neuromuscular activity.

Skeletal muscle adapts to different patterns of motor nerve activity by alterations in gene expression that match specialized properties of contraction, metabolism, and muscle mass to changing work demands (muscle plasticity). Calcineurin, a calcium/calmodulin-dependent, serine-threonine protein phosphatase, has been shown to control programs of gene expression in skeletal muscles, as in other cell types, through the transcription factor nuclear factor of activated T cells (NFAT). This study provides evidence that the function of NFAT as a transcriptional activator is regulated by neuromuscular stimulation in muscles of intact animals and that calcium influx from the transient receptor potential (TRPC3) channel is an important determinant of NFAT activity. Expression of TRPC3 channels in skeletal myocytes is up-regulated by neuromuscular activity in a calcineurin-dependent manner. These data suggest a mechanism for cellular memory in skeletal muscles whereby repeated bouts of contractile activity drive progressively greater remodeling events.

Animals↗

Neuromuscular and biomechanical coupling in human cycling: adaptations to changes in crank length.

This study exploited the alterations in pedal speed and joints kinematics elicited by changing crank length (CL) to test how altered task mechanics during cycling will modulate the muscle activation characteristics in human rectus femoris (RF), biceps femoris long head (BF), soleus (SOL) and tibialis anterior (TA). Kinetic (torque), kinematic (joint angle) and muscle activity (EMG) data were recorded simultaneously from both legs of 10 healthy adults (aged 20-38 years) during steady-state cycling at ~60 rpm and 90-100 W with three symmetrical CLs (155 mm, 175 mm and 195 mm). The CL elongation (DeltaCL) resulted in similar increases in the knee joint angles and angular velocities during extension and flexion, whilst the ankle joint kinematics was significantly influenced only during extension. DeltaCL resulted in significantly reduced amplitude and prolonged duration of BF EMG, increased mean SOL and TA EMG amplitudes, and shortened SOL activity time. RF activation parameters and TA activity duration were not significantly affected by DeltaCL. Thus total SOL and RF EMG activities were similar with different CLs, presumably enabling steady power output during extension. Higher pedal speeds demand an increased total TA EMG activity and decreased total BF activity to propel the leg through flexion into extension with a greater degree of control over joint stability. We concluded that the proprioceptive information about the changes in the cycling kinematics is used by central neural structures to adapt the activation parameters of the individual muscles to the kinetic demands of the ongoing movement, depending on their biomechanical function.

Adaptation, Physiological↗

Two structural adaptations for regulating transmitter release at lobster neuromuscular synapses.

The distal accessory flexor muscle (DAFM) in the lobster (Homarus americanus) walking leg consists of 5 muscle fiber bundles. All five bundles, one proximal, one distal, and 3 medial, are innervated by one excitatory and one inhibitory motor neuron. Both neurons release more transmitter on the distal bundle than on the proximal bundle. The aim of our studies was to investigate the structural basis of this differentiation. Thin sections cut at 50 microns intervals showed a similar number of excitatory synapses on the two bundles. Freeze-fracture views of excitatory synapses showed that synapse size, active zone number per synapse, and intramembrane particle density in the postsynaptic membrane are similar proximally and distally. Active zones at synapses on the distal bundle are larger and contain about 50% more large intramembrane particles, which are thought to include the voltage-gated Ca2+ channels that couple the action potential to transmitter release, than their counterparts on the most proximal bundle. This difference in channel number appears to produce a disproportionate increase in the probability of transmitter release sufficient to account for most of the proximal-distal disparity in the amplitude of the excitatory postsynaptic potential. In contrast, staining the inhibitor for antibodies to the inhibitory neurotransmitter, GABA, showed that it forms more varicosities on the distal bundle than on the proximal bundle. Because most of the synapses are located in the varicosities, differences in synapse number likely regulate the proximal-distal disparity in the amount of inhibitory transmitter released. Therefore, the regional differentiation in the amount of transmitter released in the DAFM appears to be based on two distinct mechanisms. In the inhibitor, transmitter release appears to be regulated differentially by differences in synapse number. In the excitor, transmitter release appears to be regulated differentially from a similar number of synapses by differences in active zone structure.

Animals↗

Effects of strength training on muscle strength, cross-sectional area, maximal electromyographic activity, and serum hormones in premenopausal women with fibromyalgia.

OBJECTIVE: To examine the effects of strength training on basal concentrations and acute responses of serum hormones, and their possible interrelationships with training induced muscle hypertrophy and strength gains of the knee extensor muscles in women with fibromyalgia (FM) and healthy controls. METHODS: Twenty-one premenopausal women with FM were randomized to 21 week strength training (FMT; n = 11) or control (FMC; n = 10) groups. Twelve premenopausal sedentary healthy women served as controls (HC). Surface electromyographic (EMG) activity, maximal unilateral isometric force of the right knee extensors, and muscle cross-sectional area (CSA) of the quadriceps femoris throughout the lengths of 3/12 to 12/15 of the femur (Lf) were measured. Serum concentrations of total and free testosterone and growth hormone (GH) were analyzed at rest and in pre- and post-exercise conditions, while levels of insulin-like growth factor and dehydroepiandrosterone sulfate were measured at rest only. RESULTS: Mean (SD) maximal force increased by 18% (10%) (p < 0.001) in the FMT group, and by 22% (12%) (p < 0.001) in the HC, while in the FMC it remained unchanged. Maximum integrated EMG of the agonists (VL + VM/2) increased in HC by 22% (p < 0.05) and in the FMT by 19% (p < 0.05). Significant increases in the CSA of the QF were observed at 5 to 12/15 Lf in FMT (p < 0.05-0.01) and at 3 to 12/15 Lf in HC (p < 0.05-0.001), while in FMC the CSA remained unchanged. No training induced changes occurred in the basal concentrations of serum hormones examined. A significant acute increase took place in the mean concentration of GH at pre-training in HC (p < 0.01) and in the FMT (p < 0.05), while at post-training the elevations after the loading (p < 0.001 and 0.05) remained elevated up to 15 min (p < 0.05) in HC and up to 30 min (p < 0.01) post-loading in the FMT. CONCLUSION: Both the magnitude and time course of adaptations of the neuromuscular system to resistance training in women with FM were completely comparable to those taking place in healthy women. Basal levels of the anabolic hormones seem to be similar in women with FM compared to age matched healthy women. Observations recorded during the acute loading conditions might be considered an indication of the training induced adaptation of the endocrine system, showing that the acute GH response may become systematic after strength training in both women with FM and controls.

Adult↗

Implant prostheses for convertibility, stress control, esthetics, and hygiene.

A method of connecting "fixed partial denture" prostheses to osseointegrated implant fixtures has been described. The advantages of this system of restoration for partially and fully edentulous mouths are that it is more effective in addressing the problems of (1) stress-control on abutments, (2) a back-up system for abutment failures, (3) esthetics, and (4) control of bacterial plaques around abutments. To accomplish this procedure, the application of convertible periodontal prosthesis techniques with modifications to some existing implant systems is undertaken. The disadvantages of this method seem insignificant when one considers the complexities and risks involved with the present array of implant prosthesis alternatives. Some patients and dentists might consider the necessity of the prosthesis being detachable as one disadvantage. In reality, the prosthesis can be used as a fixed restoration until the patient has fully adapted to the new proprioception and appearance. A large percentage of patients feel uncomfortable with the word "removable" because it immediately creates a perception of unsightly metallic clasp display, palatal coverage, tongue interference, and negative body image. The use of the term "detachable" coupled with the doctor's offer to perform this task for the patient "whenever necessary" will usually relieve the patient's anxiety and allow the treatment to proceed. Once neuromuscular and esthetic adaptation have occurred and the patient has accepted the prosthesis, daily detaching and home-care hygiene by the patient will follow without incident. Esthetic improvement is obvious (Fig. 3).

Cementation↗

Skeletal muscle responses to unloading with special reference to man.

The limited space flight data suggest that exposure to microgravity decreases muscle strength in humans and muscle mass in lower mammals. Several earth-based models have been used to address the effect of unloading on the human neuromuscular system due to the limited access of biological research to long-term space flight. Bedrest eliminates body weight bearing of both lower limbs. Unilateral lower limb suspension (ULLS), where all ambulatory activity is performed on crutches with an elevated sole on the shoe of one foot, has recently been used to unload one lower limb. The results from studies using these two models support their efficacy. The decrease in strength of m. quadriceps femoris, for example, after four to six weeks of bedrest, ULLS or space flight is 20 to 25%. The results from the earth-based studies show that this response can be attributed in part to a decrease in the cross-sectional area of the KE which reflects muscle fiber atrophy. The results from the ground based studies also support the limited flight data and show that reductions in strength are larger in lower than upper limbs and in extensor than flexor muscle groups. They also raise issue with the generally held concept that postural muscle is most affected by unweighting. Slow-twitch fibers in lower limb muscles of mixed fiber type composition and muscle composed mainly of slow-twitch fibers do not preferentially atrophy after bedrest or ULLS. Taken together, the data suggest that unloading causes remarkable adaptations in the neuromuscular system of humans. It should be appreciated, however, that this area of research is in its infancy.

Adaptation, Physiological↗

Effects of different simulated gravity conditions on neuromuscular control in drop jump exercises.

The neuromuscular characteristics of the triceps surae muscle were investigated during the various types of stretch-shortening cycle (SSC) muscle loading. The analysis concentrated on the preactivation and the contact phases of SSC. Muscle loading was changed unconventionally by artificially changing the condition of the gravity in drop jumps. This was accomplished by using a special lifting block system where the gravity could be modified to control loading and unloading effects of the triceps surae muscle. The normal gravity condition showed an advantage over the other gravity drop jump conditions for the measured parameters. The same tendency could be seen in the activation characteristics of the investigated muscles in the preactivation and eccentric phases. Further, the preactivation EMG was related to the eccentric peak angular velocity of the ankle joint. The correlation coefficients were 0.37 (p < 0.05) and 0.48 (p < 0.01) for the gastrocnemius and the soleus muscles, respectively. All the results emphasized considerable adaptation of the neuromuscular system to the normal gravity condition. However, the overall control of landing may also depend on the vestibular and visual inputs, which might modify even the earlier learned central programs.

Adaptation, Physiological↗

Progressive versus rapid rate of contraction during 7 wk of isometric resistance training.

PURPOSE: The aim of this study was to compare the effects of isometric training performed with progressive versus rapid rate of contraction on the knee extensor neuromuscular properties over a 7-wk period. METHODS: Sixteen healthy male subjects trained quadriceps femoris muscle in a leg extension machine three times a week during 7 wk. The training sessions consisted of six sets of six maximal isometric contractions. A first group trained by performing progressive contractions lasting 4 s, whereas a second group performed contractions with a rapid rate of contraction (i.e., ballistic contractions) lasting about 1 s. RESULTS: Both groups significantly increased the isometric and isokinetic voluntary torque, and the respective absolute or relative gains were comparable. Isometric training performed with progressive rate of contraction affected the evoked action potential (M wave) of the vastus lateralis muscle and not the related twitch properties. On the other hand, the isometric training completed with ballistic contractions significantly modified the twitch contractile properties of the knee extensors and not the associated M waves of both vastus medialis and vastus lateralis. CONCLUSION: Knee extensors adapted specifically their neuromuscular properties to the type of rate of contraction performed during 7-wk isometric resistance training. Progressive isometric contractions produced modifications of the nervous system at peripheral level (i.e., muscle membrane electrical activity), whereas ballistic isometric contractions affected the knee extensor contractile muscle properties (i.e., excitation-contraction coupling).

Adult↗

Task-dependent effect of limb immobilization on the fatigability of the elbow flexor muscles in humans.

Because short-term limb immobilization produces selective adaptations in the neuromuscular system that probably interact with the task-dependent expression of muscle fatigue, the purpose of this study was to determine the effects of limb immobilization on the ability of human subjects to sustain isometric contractions at low and moderate submaximal forces. Four weeks of elbow joint immobilization caused a substantial decrease in the daily activity of biceps brachii during immobilization, a significant reduction in the cross-sectional area and volume of the elbow flexor muscles as measured by magnetic resonance imaging, and a decline in the maximum voluntary contraction (MVC) activation and force of the elbow flexor muscles. Immobilization had a task-dependent effect on muscle fatigue with a substantially increased endurance time (reduced fatigability) at a low force (20% MVC) and no statistical effect at a moderate force (65% MVC). Despite atrophy of the elbow flexor muscles due to the immobilization, the twitch force elicited in biceps brachii by electrical stimulation was greater after immobilization. The selective improvement of fatigue resistance for the low-force contraction and the absence of a change in the time course of the twitch suggests that the immobilization-induced adaptations included an improved efficacy of some excitation-contraction processes and underscored the major role of these mechanisms in determining the endurance time for low-force, long-duration contractions.

Adult↗

Training-induced changes in neuromuscular performance under voluntary and reflex conditions.

To investigate training-induced changes in neuromuscular performance under voluntary and reflex contractions, 11 male subjects went through heavy resistance (high loads of 70-120% of one maximum repetition) and 10 male subjects through explosive type (low loads with high contraction velocities) strength training three times a week for 24 weeks. A large increase (13.9%, p less than 0.01) in voluntary unilateral maximal knee extension strength with only slight and insignificant changes in time of isometric force production were observed during heavy resistance strength training. Explosive type strength training resulted in a small insignificant increase in maximal strength but in considerable shortening (p less than 0.05) in the time of force production. A significant increase (p less than 0.05) noted in the averaged maximal integrated electromyogram (IEMG) of the knee extensors during heavy resistance strength training correlated (p less than 0.01) with the increase in maximal strength. No changes were noted during training in reflex time components, but significant decreases (p less than 0.05) occurred in the peak-to-peak amplitudes of the reflex electromyograms (EMG) in both groups. The individual changes during training in the reflex EMG/force ratio were related (p less than 0.01) to the respective changes in IEMG/force ratio in voluntary contractions. The present observations support the concept of specificity of training, and suggest that specific training-induced adaptations in the neuromuscular system may be responsible for these changes in performance.

Adult↗

Altered impulse activity modifies synaptic physiology and mitochondria in crayfish phasic motor neurons.

1. Crayfish phasic motor synapses produce large initial excitatory postsynaptic potentials (EPSPs) that fatigue rapidly during high-frequency stimulation. Periodic in vivo stimulation of an identified phasic abdominal extensor motor neuron (axon 3) induced long-term adaptation (LTA) of neuromuscular transmission: initial EPSP amplitude became smaller and synaptic depression was significantly reduced. We tested the hypothesis that activity-induced synaptic fatigue-resistance seen during LTA was dependent upon, or correlated with, mitochondrial oxidative competence. 2. Periodic unilateral conditioning stimulation of axon 3 entering each of two adjacent homologous abdominal segments (segments 2 and 3) increased the synaptic stamina in both "conditioned" axons; mean final EPSP amplitudes, recorded after 20 min of 5-Hz test stimulation, were significantly larger than those measured with the same protocol from contralateral unstimulated axons. 3. During 5-Hz test stimulation of the conditioned axon 3 of segment 3, acute superfusion with 0.8 mM dinitrophenol or 20 mM sodium azide [inhibitors of oxidative adenosinetriphosphate (ATP) synthesis] produced increased synaptic depression. Drug-free saline superfusion of the conditioned axon 3 of segment 2 in these same animals did not affect the increased synaptic fatigue resistance seen in this segment. Thus both successful induction (in axon 3 of saline-perfused segment 2) and attenuation (in axon 3 of drug-perfused segment 3) of the increased synaptic stamina can be demonstrated with this twin-segment conditioning protocol. 4. Confocal microscopic imaging of mitochondrial rhodamine-123 (Rh123) fluorescence was used to assess relative oxidative competence of conditioned and unconditioned phasic axons. Conditioned phasic axons showed significantly higher mean mitochondrial Rh123 fluorescence than contralateral unstimulated axons. In the same preparations that showed increased postconditioning Rh123 fluorescence, the synaptic fatigue resistance measured from conditioned axon 3 was also significantly greater than that recorded from contralateral unstimulated axon 3. 5. Axotomy of the phasic extensor nerve root (containing axon 3), before in vivo conditioning stimulation of its decentralized segment, prevented induction of both the increased synaptic stamina in axon 3 and the enhanced mitochondrial fluorescence in decentralized motor axons of the nerve root. Hence, induction of both changes requires axonal transport of materials between the soma and the motor synapses of axon 3. 5. Axotomy of the phasic extensor nerve root (containing axon 3), before in vivo conditioning stimulation of its decentralized segment, Prevented induction of both the increased synaptic stamina in axon 3 and the enhanced mitochondrial fluorescence in decentralized motor axons of the nerve root Hence, induction of both changes requires axonal transport of materials between the soma and the motor synapses of axon 3 6. Because mitochondrial Rh123 fluorescence is primarily dependent upon the oxidative activity of these organelles, our findings suggest that conditioning stimulation of phasic extensor axon 3 increases its mitochondrial oxidative competence and that the enhanced synaptic stamina seen during LTA in axon 3 is correlated with, and dependent upon, oxidative activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Physiological↗

EMG, muscle fibre and force production characteristics during a 1 year training period in elite weight-lifters.

The effects of a 1 year training period on 13 elite weight-lifters were investigated by periodical tests of electromyographic, muscle fibre and force production characteristics. A statistically non-significant increase of 3.5% in maximal isometric strength of the leg extensors, from 4841 +/- 1104 to 5010 +/- 1012 N, occurred over the year. Individual changes in the high force portions of the force-velocity curve correlated (p less than 0.05-0.01) with changes in weight-lifting performance. Training months 5-8 were characterized by the lowest average training intensity (77.1 +/- 2.0%), and this resulted in a significant (p less than 0.05) decrease in maximal neural activation (IEMG) of the muscles, while the last four month period, with only a slightly higher average training intensity (79.1 +/- 3.0%), led to a significant (p less than 0.01) increase in maximum IEMG. Individual increases in training intensity between these two training periods correlated with individual increases both in muscular strength (p less than 0.05) and in the weight lifted in the clean & jerk (p less than 0.05). A non-significant increase of 3.9% in total mean muscle fibre area occurred over the year. The present findings demonstrate the limited potential for strength development in elite strength athletes, and suggest that the magnitudes and time courses of neural and hypertrophic adaptations in the neuromuscular system during their training may differ from those reported for previously untrained subjects. The findings additionally indicate the importance of training intensity for modifying training responses in elite strength athletes.

Adult↗

Alterations in neuromuscular junction morphology during fast-to-slow transformation of rabbit skeletal muscles.

Chronic low frequency stimulation of motor nerves results in transformation of muscle fibre phenotype from fast- to slow-twitch. We examined the light and electron microscopic structure of neuromuscular junctions in normally fast twitch muscles, tibialis anterior and extensor digitorum longus of rabbit after 3 weeks of stimulation to determine whether synaptic structure is also modified during fibre type transformation. Neuromuscular junctions of stimulated and unstimulated (control) tibialis anterior and extensor digitorum longus muscles and unstimulated slow twitch soleus muscle were visualized with rhodamine-conjugated alpha-bungarotoxin. Video light microscopic images of neuromuscular junctions were digitized to allow quantification of their surface areas, perimeters, lengths and widths. Three weeks of stimulation resulted in a decrease in the maximal velocity of muscle fibre shortening and augmentation of mitochondrial volume in fast muscles, demonstrating the efficacy of the stimulation protocol employed in altering muscle fibre phenotype. Neuromuscular junctions of control tibialis anterior and extensor digitorum longus are thin, compact, and continuous, with complex branching patterns. In contrast, those of slow-twitch soleus are thicker and discontinuous. Neuromuscular junctions in control tibialis anterior and extensor digitorum longus are larger than those in soleus. Three weeks of stimulation causes a marked decrease in the size of neuromuscular junctions in tibialis anterior and extensor digitorum longus, as reflected in the significant reduction in neuromuscular junction surface area, length and width. Electron microscopy of these junctions suggests that secondary postsynaptic folds in stimulated muscles are more closely spaced. Also, axon terminals of stimulated muscles appear to contain more densely packed synaptic vesicles and mitochondria than controls. Decreases in neuromuscular junction dimensions can be partly explained by muscle fibre atrophy. However, the decrease in neuromuscular junction size is proportionately greater than that of muscle fibre diameter in both muscles, indicating that factors other than fibre atrophy may contribute to the reduced neuromuscular junction size in stimulated muscles. Neuromuscular junctions of stimulated tibialis anterior and extensor digitorum longus muscles exhibit some features characteristic of normal soleus neuromuscular junctions, indicating structural adaptations consistent with the altered muscle fibre phenotype. On the other hand, neuromuscular junctions of 3 week stimulated tibialis anterior and extensor digitorum longus and their synaptic branches remain as thin and continuous as those of unstimulated controls, suggesting that the transformation of neuromuscular junctions towards a morphology characteristic of slow muscle, is only partial. These results demonstrate that an altered pattern of impulse activity cause significant synaptic remodelling in adult rabbit skeletal muscles.

Animals↗

Studies of biologic parameters for denture design. Part III: Effects of occlusal adjustment, base retention, and fit on masseter muscle activity and masticatory performance.

EMG recordings of ipsilateral and contralateral masseter muscles and standardized masticatory performance tests were made in 20 denture wearers before and after modifications were made to their clinically unsatisfactory dentures. The improvement of retention and stability by correction of gross occlusal prematurities and by the use of a denture adhesive or base reline with a soft tissue-conditioning material did not significantly alter the chewing performance or muscle activity during mastication in denture wearers. The results support our previous findings that the influence of denture factors on chewing ability of denture wearers is limited. To avoid variations in EMG activity caused by changes in electrode positions, all tests for a given subject were made at the same sitting. Thus the study design did not provide time to denture wearers for their neuromuscular mechanism to adapt to the modifications prior to testing masticatory function. A replication of this study that permits sufficient adaptation time after each modification is suggested to validate the findings.

Adhesives↗

Effects of home strength training and stretching versus stretching alone after lumbar disk surgery: a randomized study with a 1-year follow-up.

OBJECTIVE: To assess the adherence to and effects of a 12-month combined strength and stretching home exercise regimen versus stretching alone, on patient outcome after lumbar disk surgery. DESIGN: Randomized controlled trial. SETTING: Departments of physical medicine and rehabilitation and orthopedics at a Finnish hospital. PARTICIPANTS: Patients (N=126) were randomized into either a combined strength training and stretching group (STG, n=65) or a control group (CG, n=61). INTERVENTION: The STG was instructed to perform strength training and both the STG and CG were instructed in the same stretching and stabilization exercises for 12 months. MAIN OUTCOME MEASURES: Pain on the visual analog scale (VAS), the Oswestry and the Million disability indexes, isometric and dynamic trunk muscle strength, mobility in the lumbar spine, and straight-leg raising were measured. RESULTS: The trial was completed by 71% and 77% of the patients from the STG and the CG, respectively. The mean strength training frequency decreased from 1.5 to 0.6 times a week in the STG during the intervention. The mean stretching frequency decreased from 3.7 to 1.6 times a week in both groups. Median back and leg pain varied between 17 and 23 mm (VAS), and the Million and Oswestry indices varied between 14 and 23 points 2 months postoperatively. No statistically significant changes took place in these outcome measures during the 12-month follow-up in both groups. The changes in isometric trunk extension favored the STG ( P =.016) during the first 2 months. However, during the whole 12-month training period, both dynamic and isometric back extension and flexion strength, as well as mobility of the spine and repetitive squat-test results, improved significantly in both groups, and no differences were found in any of the physical function parameters between the STG and CG. CONCLUSIONS: At the 12-month follow-up, no statistically significant changes were found in the physical function, pain, or disability measures between the groups. In the STG, training adherence with regard to training frequency and intensity remained too low to lead to specific training-induced adaptations in the neuromuscular system. Progressive loading, supervision of training, and psychosocial support is needed in long-term rehabilitation programs to maintain patient motivation.

Adult↗

A force-controlled planar haptic device for movement control analysis of the human arm.

This paper describes the design and application of a haptic device to study the mechanical properties of the human arm during interaction with compliant environments. Estimates of the human endpoint admittance can be obtained by recording position deviations as a result of force perturbations. Previous studies attempted to estimate the impedance by recording force as a result of position perturbations, but these experiments do not require a feasible task of human beings. A general problem of force-controlled haptic devices is the occurrence of contact instability, especially where a small virtual mass is required. This negative effect is reduced by the use of a lightweight but stiff manipulator and a robust servo-based admittance controller. The virtual admittance is accurate to at least 13 Hz, attaining a minimum virtual mass of 1.7 kg (isotropic, without damping and stiffness). The properties of known test loads were estimated with an accuracy higher than 98%, up to 20 Hz. The application of the manipulator is evaluated by an experiment with a subject performing a position maintenance task. With this device it is possible to study the adaptability of the neuromuscular system to a variety of environments, enabling a new and functional approach to human motion research.

Adult↗