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In vivo strain gauge analysis demonstrated that tensile bone strain is transmitted along the cranial vault to the parasagittal region during isotonic temporalis contraction. This strain is sufficient to cause measurable separation of the sagittal suture, and thus could influence growth at the sutural margins.
This study concerns the complex interaction between active muscle forces and passive guiding structures during jaw-closing movements. It is generally accepted that the ligaments of the joint play a major role in condylar guidance during these movements. While these ligaments permit a wide range of motions, it was assumed that they are not primarily involved in force transmission in the joints. Therefore, it was hypothesized that muscle forces and movement constraints caused by the articular surfaces imply a necessary and sufficient condition to generate ordinary jaw-closing movements. This hypothesis was tested by biomechanical analysis. A dynamic six-degrees-of-freedom mathematical model of the human masticatory system has been developed for qualitative analysis of the contributions of the different masticatory muscles to jaw-closing movements, it was found that the normally observed movement, which includes a swing-slide condylar movement along the articular eminence, can be generated by various separate pairs of masticatory muscles, among which the different parts of the masseter as well as the medial pterygoid muscle appeared to be the most suitable to complete this action. The results seem to be in contrast to the general opinion that a muscle with a forward-directed force component may not be suitable for generating jaw movements in which the condyle moves backward. The results can be explained, however, by biomechanical analysis which includes not only muscle and joint forces as used in standard textbooks of anatomy, but also the torques generated by these forces.
The purpose of this study was to determine whether a 4-week isotonic resistance training program using Theraband elastic tubing and lightweight dumbbells would significantly increase concentric shoulder rotator strength or velocity of serve or both in a group of elite-level tennis players. Twenty-two male and female varsity college tennis players were randomly assigned to control or 4-week training groups. Subjects were pre- and posttested in concentric internal and external rotation torque using an isokinetic dynamometer. Functional performance was assessed before and after training by recording the peak and average velocities of eight maximal serves. The experimental group exhibited significant gains in internal rotation torque at both slow (120 deg/sec) and fast speeds (300 deg/sec) for total work and in peak torque to body weight ratio and torque acceleration energy at the fast speed. This group also exhibited significant gains in external rotation torque for the same parameters at fast speed. Regarding speed to serve, the experimental group exhibited significantly greater increase in peak speed (+6.0% compared with -1.8%) and average speed (+7.9% compared with -2.3%) compared with the control group. Men exhibited greater internal and external rotation torque on all parameters and in peak and mean speed of serve on both evaluations. Men also exhibited greater imbalance in external to internal rotation torque ratios. In conclusion, resistance training using Theraband tubing and lightweight dumbbells may have beneficial effects on strength and functional performance in college-level tennis players.
Exposure to nitrogen dioxide (NO2), a common oxidant airborne pollutant, has been shown to cause reversible effects on lung function and airway responsiveness, in addition to airways inflammation. However, there have been conflicting reports concerning NO2-induced airway hyperresponsiveness. In the present study, we investigated the isotonic smooth muscle response in isolated human bronchi previously exposed in vitro to NO2. Bronchial segments were obtained from 12 patients who had undergone thoracotomy for lung cancer. Bronchial segments from each patient were exposed to air and to 2.5 parts per million (ppm) NO2 for 4 h. The contractile response of bronchial rings to acetylcholine, neurokinin A (NKA), and substance P was then studied under isotonic conditions. The response to NKA was also studied in rings, with or without epithelium, exposed either to air or 7 ppm NO2. No NO2-induced alteration of the bronchial smooth muscle isotonic response was found under any of the experimental conditions. We conclude that in vitro exposure to up to 7 ppm nitrogen dioxide does not cause alterations of the human bronchial smooth muscle shortening capacity.
BACKGROUND: Skeletal muscle remodeling is a critical component of an organism's response to environmental changes. Exercise causes structural changes in muscle and can induce phase shifts in circadian rhythms, fluctuations in physiology and behavior with a period of around 24 hours that are maintained by a core clock mechanism. Both exercise-induced remodeling and circadian rhythms rely on the transcriptional regulation of key genes. RESULTS: We used DNA microarrays to determine the effects of resistance exercise (RE) on gene regulation in biopsy samples of human quadriceps muscle obtained 6 and 18 hours after an acute bout of isotonic exercise with one leg. We also profiled diurnal gene regulation at the same time points (2000 and 0800 hours) in the non-exercised leg. Comparison of our results with published circadian gene profiles in mice identified 44 putative genes that were regulated in a circadian fashion. We then used quantitative PCR to validate the circadian expression of selected gene orthologs in mouse skeletal muscle. CONCLUSIONS: The coordinated regulation of the circadian clock genes Cry1, Per2, and Bmal1 6 hours after RE and diurnal genes 18 hours after RE in the exercised leg suggest that RE may directly modulate circadian rhythms in human skeletal muscle.
OBJECTIVE: To establish if isokinetic and isotonic muscle stretch (with or without weight-bearing) of the ankle plantar flexors improves gait in hemiplegic patients. A further aim was to compare the effectiveness of these treatment methods. DESIGN: A randomized, parallel group prospective study. SETTING: A stroke rehabilitation unit. SUBJECTS: Ambulatory hemiparetic stroke patients with mild to moderately severe muscle hypertonia of the lower limb and a group of healthy control subjects. INTERVENTION: Subjects were randomized to receive a single 20-min session of isokinetic muscle stretch or isotonic muscle stretch with or without weight-bearing. OUTCOME MEASURES: Selected kinematic, kinetic and spatio-temporal gait parameters were measured at baseline, immediately after the muscle stretch and 24 h later. RESULTS: Sixty-six patients and 21 healthy control subjects were recruited and completed the study. There were statistically significant differences between the patient groups and the healthy subjects on most of the gait parameters studied. However, the differences between the patient groups or between the three measurements over time for each type of muscle stretch did not reach statistical significance. CONCLUSIONS: A single session of isokinetic or isotonic muscle stretch (with or without weight-bearing) of the ankle plantar flexors has no clinically observable effect on the gait of hemiplegic stroke patients.
Smooth muscle cells line the walls of hollow organs and control the organ dimension and mechanical function by generating force and changing length. Although significant progress has been made in our understanding of the molecular mechanism of actomyosin interaction that produces sliding of actin (thin) and myosin (thick) filaments in smooth muscle, the sarcomeric structure akin to that in striated muscle, which allows the sliding of contractile filaments to be translated into cell shortening has yet to be elucidated. Here we show evidence from porcine airway smooth muscle that supports a model of malleable sarcomeric structure composed of contractile units assembled in series and in parallel. The geometric organization of the basic building blocks (contractile units) within the assembly and the dimension of individual contractile units can be altered when the muscle cells adapt to different lengths. These structural alterations can account for the different length-force relationships of the muscle obtained at different adapted cell lengths. The structural malleability necessary for length adaptation precludes formation of a permanent filament lattice and explains the lack of aligned filament arrays in registers, which also explains why smooth muscle is 'smooth'.
We were interested to estimate the maximum mechanical efficiency with which chemical energy derived from ATP hydrolysis is converted into mechanical work by individual cross-bridges when they perform their powerstroke synchronously. Glycerinated rabbit psoas muscle fibres, containing ATP molecules almost equal in number to the cross-bridges within the fibre, were activated to shorten under various afterloads by laser-flash photolysis of caged Ca(2+). In these conditions, almost all the cross-bridges are in the state where the ATP is hydrolyzed but the products have not yet been released from the cross-bridge (M-ADP-P(i)) immediately before activation, and can hydrolyze only one ATP molecule during the flash-induced mechanical response. Power output records of the fibres following activation indicated that the cross-bridges actually started their powerstroke almost synchronously. The amount of ATP utilized at 1 s after activation was estimated from the amount of isometric force developed after interruption of fibre shortening, while the amount of work done was calculated by multiplying the amount of afterload by the distance of fibre shortening. A conservative estimation of the maximum mechanical efficiency at a load of 0.5-0.6 P(o) was 0.7, suggesting that the actual maximum mechanical efficiency of cross-bridge powerstrokes may be close to unity.
Jumping performance at 20 degrees C was assessed in five species of hylid frogs using high-speed cine film. Mean takeoff velocities (Vt) varied from 1.5 to 2.4 ms-1 among the species. Peak Vt varied from 1.9 to 2.9 ms-1. Body-mass-specific power output averaged over the entire takeoff period varied from 29 to 91 W kg-1 during the jumps with the highest takeoff velocities. These values are similar to those predicted from jumping distance. As the mass of muscles available to power the jump probably amounts to no more than 17% of the body mass, average muscle-mass-specific power can be over 500 W kg-1. The performance during jumping is even more impressive in view of the fact that the peak power during takeoff is about twice the average power. These frogs must use elastic storage to redistribute power during takeoff to produce the peak power required and may use pre-storage of elastic energy to boost the average power available.
The compounds in diesel exhaust particles (DEP) that are responsible for vasodilatation were isolated and characterized for the first time. From benzene extract of DEP, 2-methyl-4-nitrophenol, 3-methyl-4-nitrophenl and 4-nitrophenol were isolated, and their vasodilatation activities were confirmed. 3-methyl-4-nitrophenol caused dilatation of rat thoracic artery, and the other two nitrophenols, also showed vasodilatation activities.
OBJECTIVE: To investigate the effectiveness of a body mass reduction programme entailing diet caloric restriction and moderate physical activity with or without supplementary treatment with recombinant (r) GH or steroids to improve body composition and muscle performance in severely obese women aged 61-75 years. METHODS: Twenty women were randomly assigned to one of three groups: body mass reduction alone; body mass reduction plus rGH; body mass reduction plus nandrolone undecanoate. Body composition, isotonic muscle strength and anaerobic power output during jumping were determined before and after the 3-week period. RESULTS: Whatever the experimental group considered, body mass (P<0.01), body mass index (P<0.05) and fat mass (P<0.05) decreased significantly, whereas muscle strength and power increased significantly (P<0.05) after the intervention. CONCLUSION: Small body mass reductions after 3 weeks of energy-restricted diet combined with moderate aerobic and strength exercise are associated with significant improvements in upper and lower limb muscle strength and power and reduction of fat mass in severely obese women aged 61-75 years. Although the association of rGH or nandrolone undecanoate does not appear to exert additional effects on body composition and muscle performance attained by body mass reduction alone, further additional studies with larger study groups, different dosages and more prolonged periods are required for definitive conclusions to be drawn.
We performed a retrospective study of 616 patients (636 shoulders) who had subacromial impingement syndrome to assess the results of non-operative treatment. The diagnosis was made on the basis of a positive impingement sign and the absence of other abnormalities of the shoulder, such as full-thickness tears of the rotator cuff, osteoarthrosis of the acromioclavicular joint, instability of the glenohumeral joint, or adhesive capsulitis. All patients were managed with anti-inflammatory medication and a specific, supervised physical-therapy regimen consisting of isotonic exercises for strengthening of the rotator cuff. The average duration of follow-up was twenty-seven months (range, six to eighty-one months). Over-all, 413 patients (67 per cent) had a satisfactory result. One hundred and seventy-two patients (28 per cent) had no improvement and went on to have an arthroscopic subacromial decompression. Thirty-one patients (5 per cent) had an unsatisfactory result but declined additional treatment. Seventy-four (18 per cent) of the 413 patients who had a successful result had a recurrence of the symptoms during the follow-up period; the symptoms resolved with rest or after resumption of the exercise program. The patients were stratified according to age, the duration of symptoms, and acromial morphology. Patients who were twenty years old or less and those who were forty-one to sixty years old fared better than those who were twenty-one to forty years old. Patients who were more than sixty years old had the poorest results. Sixty-seven (78 per cent) of the eighty-six patients in whom the symptoms had been present for less than four weeks had a satisfactory result, compared with 144 (63 per cent) of the 228 who had had the symptoms for one to six months and with 202 (67 per cent) of the 302 who had had the symptoms for more than six months. Thirty-two (91 per cent) of the thirty-five patients who had a type-I acromion had a successful result, compared with 173 (68 per cent) of the 256 who had a type-II acromion and with 208 (64 per cent) of the 325 who had a type-III acromion. Shoulder dominance, gender, and concomitant tenderness of the acromioclavicular joint did not affect the result significantly (p = 0.084, 0.555, and 0.365, respectively).
Satisfactory results following knee surgery can be obtained only through the combined efforts of the surgeon, patient and therapist. A rehabilitative plan is based upon consideration of the effects of disuse and immobility on musculoskeletal tissues, and knowledge of the healing requirements following injury and specific surgical procedures. A balance must be made between simultaneous demands for protection against undue stress to facilitate healing and the need for stress to retard atrophy of musculoskeletal tissue. A thorough review of these concepts forms the basis for a rational approach to rehabilitation after specific surgical procedures. The phasic approach to knee rehabilitation is based upon progression in a logical fashion through the chronology of immobility, range of motion, progressive weight bearing and strengthening exercises. The latter category can be subdivided into its own progression from isometrics, isotonics, functional exercises through isokinetics. The ultimate goal and final phase is a safe return to full activity. By integrating a thorough knowledge of the healing parameters of musculoskeletal tissues and the simultaneous coexisting needs for protection and controlled stress, specific rehabilitative programmes can then be designed for the most common surgical procedures including: anterior and posterior cruciate ligament reconstruction, meniscal repair and meniscectomy, lateral release and hyaline cartilage procedures.
For successful placement of individuals with mental retardation into community environments, a minimal amount of functional strength is required to promote self-independence. Since muscular strength and power are commonly deficient in these groups, the purpose of this study was to compare isokinetic elbow flexion and extension peak torque (Nm), average power (W), and corresponding flexion/extension ratios of adults males with Down syndrome, with mental retardation without Down syndrome, and sedentary adult males without mental retardation. Subjects with Down syndrome (N = 9), mental retardation without Down syndrome (N = 13), and without mental retardation (N = 13) were tested for elbow flexion and extension peak torque and average power at 60 and 90 degrees/sec on a Cybex 340 isokinetic dynamometer. Results indicated: 1) subjects without mental retardation displayed significantly greater ( p < 0.01) peak torque and average power elbow flexion and extension than subjects with Down syndrome and subjects with mental retardation without Down syndrome at speeds of 60 and 90 degrees/sec, and 2) there were no significant differences between groups in peak torque and average power elbow flexion/extension ratios at both angular velocities. The results of the data analysis support the premise that adults with mental retardation are in need of exercise programs to improve muscular strength.
Strengthening of the evertor muscles is widely advocated as a key component of lateral ankle sprain rehabilitation, but our clinical observation of impaired invertor muscle performance among many patients suggested the need for this study of isokinetic performance deficiencies. Subjects were 30 physically active adolescents, ages 14-19 years, who had recently sustained a lateral ankle sprain or who had symptoms of chronic lateral ankle instability. Eversion/inversion testing was performed on a Biodex isokinetic dynamometer at speeds of 30 and 120 degrees/sec. Analysis of variance results demonstrated significantly greater (p < .05) invertor deficits than evertor deficits for both peak torque and average power at both tests speeds. The findings of this study suggest that a lateral ankle ligament injury may be associated with an invertor muscle performance deficiency, and that restoration of a normal evertor/invertor strength relationship may be accomplished through performance of an isotonic ankle strengthening program.
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Previous studies have shown that voluntary movement diminishes the transmission of cutaneous afferent input through the dorsal column-medial lemniscal system, and also raises the threshold for detecting nonpainful, cutaneous stimuli (electrical shocks). Although there is some evidence that pain elicited by electrical stimulation is diminished during movement, no studies have tested the effect of movement on the perception of pain produced by natural stimulation. For this reason, we tested the effects of voluntary motor activity on the perception of noxious thermal stimuli in human volunteers. We first developed a motor paradigm in which the thermal stimulation could be applied to the immobile limb (isometric elbow flexion-extension). Both isometric and isotonic muscle contractions about the elbow increased the threshold for detecting weak cutaneous stimuli (electrical shocks) applied to the forearm, and to a lesser extent the detection of stimuli applied to the dorsum of the hand. Afterwards, noxious and innocuous heat stimuli were applied to the forearm during isometric contractions and at rest. Magnitude estimates for the intensity of the pain, as well as latency measures of the onset of pain, were recorded. We found no evidence that isometric motor activity diminished either the threshold for pain or the subjective intensity of the noxious and innocuous thermal stimuli. Thus, motor activity decreases the ability to detect weak low-threshold cutaneous inputs, but has no effect on the perception of warmth and heat pain.
In 16 patients, where the diagnosis carpal tunnel syndrome was electrophysiologically confirmed, the pressure between the median nerve and the carpal ligament was measured peroperatively. At rest the pressure was 18-64 mmHg, mean 31 mmHg. Passive volar and dorsal wrist flexion increased the pressure about three times. Isometric or isotonic maximal contractions of wrist and finger muscles, elicited by tetanic nerve stimulation increased the pressure to three to six times the resting value. These high pressures may be one of the causes of the nerve lesion in the carpal tunnel syndrome.