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PubMed2006

Will whole-body vibration training help increase the range of motion of the hamstrings?

Muscle strain is one of the most common injuries, resulting in a decreased range of motion (ROM) in this group of muscles. Systematic stretching over a period of time is needed to increase the ROM. The purpose of this study was to determine if whole-body vibration (WBV) training would have a positive effect on flexibility training (contract-release method) and thereby on the ROM of the hamstring musculature. In this study, 19 undergraduate students in physical education (12 women and 7 men, age 21.5 +/- 2.0 years) served as subjects and were randomly assigned to either a WBV group or a control group. Both groups stretched systematically 3 times per week for 4 weeks according to the contract-release method, which consists of a 5-second isometric contraction with each leg 3 times followed by 30 seconds of static stretching. Before each stretching exercise, the WBV group completed a WBV program consisting of standing in a squat position on the vibration platform with the knees bent 90 degrees on the Nemes Bosco system vibration platform (30 seconds at 28 Hz, 10-mm amplitude, 6 times per training session). The results show that both groups had a significant increase in hamstring flexibility. However, the WBV group showed a significantly larger increase (30%) in ROM than did the control group (14%). These results indicate that WBV training may have an extra positive effect on flexibility of the hamstrings when combined with the contract-release stretching method.

Adult↗

PubMed1989

Measurements of muscle stiffness, the electromyogram and activity in single muscle spindles of human flexor muscles following conditioning by passive stretch or contraction.

In experiments on adult human subjects we examined the effect on passive mechanical properties of a muscle by conditioning it with either an isometric contraction or passive muscle extension. The test measurement was the amount of muscle displacement (stiffness) and the accompanying EMG in response to a brief torque pulse. Two muscles were tested, flexor digitorum profundus (FDP) and brachialis. In FDP the discharge of single muscle spindles was recorded as well. After muscle extension and return to the initial length, passive stiffness was less than after an isometric contraction. The changes in stiffness were accompanied by changes in pattern of EMG and in the responses of muscle spindles. It is suggested that in resting muscle there are stable cross bridges between actin and myosin filaments of muscle fibres which largely determine the passive stiffness. Muscle extension leads to detachment of these cross bridges which then re-form at the longer length. Return of the muscle to its starting length leads to development of slack in muscle fibres because, stiffened by the presence of the stable cross bridges, they are unable to shorten. Slack in muscle fibres lowers their measured stiffness. Muscle contraction, on the other hand, will result in any preexisting slack being taken up by the actively shortening muscle fibres, thereby raising muscle stiffness. Stiffness in intrafusal fibres is likely to follow a similar pattern to that in extrafusal fibres, leading to changes in stretch responsiveness of muscle spindles and consequently in the reflex EMG. It is concluded that the changes in stiffness and accompanying reflexes observed in this study are likely to be seen, at least under some conditions, in normal movements.

Adult↗

PubMedDate not supplied

Assessment of 3-D joint contact load predictions during postural/stretching exercises in aged females.

Our goal was to estimate knee and hip joint contact forces during a variety of unconstrained "stretching" exercises that are often recommended for people with arthritis. The population of interest was aged females with and without significant osteoarthritis (OA). Three-dimensional (3-D) kinematic, force platform, and selected electromyographic (EMG) data were measured. A relatively standard and reasonably efficient technique was used for all subjects and tasks: inverse dynamics to estimate joint reaction forces and net moments, followed by heuristic reductionist techniques for predicting muscle load-sharing. Muscle force predictions were compatible with measured EMG activity for some tasks but less so for others, especially those with significant axial and medio-lateral movement components or high co-contraction. Such results suggest several improvements, which come at computational cost: 3-D joint models which better document muscle and passive tissue loading-sharing in abduction and axial torsion, and dynamic or novel static optimization approaches that can inherently predict muscle co-contraction. Nonetheless, the predicted joint contact loadings provide estimates that are essentially lower bounds on the likely joint contact loads. Based on our results we suggest that the side-kick and back-kick tasks be modified because the loading levels on the support leg are potentially excessive for the aged arthritic population.

Aged↗

PubMed2006

The effect of active warm-up and stretching on the flexibility of adolescent soccer players.

AIM: The purpose of the investigation was to examine in field conditions the acute effects of passive stretching after a general warming-up bout as well as the effects of passive stretching alone. METHODS: Eighteen adolescent team soccer players participated in this study performing 3 different flexibility-training protocols in separate training sessions. In the first treatment stretching protocol a general warm-up was performed where subjects jogged for 20 minutes. The second treatment stretching protocol consisted of the same general warm-up followed by passive stretching of the lower extremities and the trunk, whereas the third and final treatment stretching protocol consisted of passive stretching alone, without any jogging. Passive range of joint motion was examined in hip flexion, hip extension, hip abduction, ankle dorsiflexion, knee flexion and trunk flexion using a goniometer and a flexometer. RESULTS: The general warming-up session induced a significantly increased range of motion only at the ankle dorsiflexion joint (P<0.05). Results also suggest that passive stretching alone and passive stretching after a general warming-up bout both induced a significantly increased range in all lower extremity joints and trunk flexion (P<0.001). CONCLUSIONS: Improvements in flexibility are observed after passive muscle elongation, irrespective of warming-up.

Adolescent↗

PubMed2006

Practical management of iliotibial band friction syndrome in runners.

This article outlines the practical management of iliotibial band friction syndrome (ITBFS) in running athletes. ITBFS is the most common cause of lateral knee pain in runners and is related to repetitive friction of the iliotibial band sliding over the lateral femoral epicondyle. Runners predisposed to this injury are typically in a phase of over training and often have underlying weakness of the hip abductor muscles. The diagnosis of ITBFS is clinical and is based on a thorough patient history and physical exam. In the acute phase, treatment includes activity modification, ice, nonsteroidal anti-inflammatory medication, and corticosteroid injection in cases of severe pain or swelling. During the subacute phase emphasis is on stretching of the iliotibial band and soft tissue therapy for any myofascial restrictions. The recovery phase focuses on a series of exercises to improve hip abductor strength and integrated movement patterns. The final return to running phase is begun with an every other day program, starting with easy sprints and avoidance of hill training with a gradual increase in frequency and intensity. In rare refractory cases that do not respond to conservative treatment, surgery can be considered.

Cumulative Trauma Disorders↗

PubMed2003

Different effects on human skeletal myosin heavy chain isoform expression: strength vs. combination training.

Myosin heavy chain (MHC) isoform expression changes with physical training. This may be one of the mechanisms for muscular adaptation to exercise. We aimed to investigate the effects of different strength-training protocols on MHC isoform expression, bearing in mind that alpha- MHC(slow) (newly identified MHC isoform) mRNA may be upregulated in response to training. Twelve volunteers performed a 6-wk strength training with maximum contractions (Max group), and another 12 of similar age performed combination training of maximum contractions and ballistic and stretch-shortening movements (Combi group). Muscle samples were taken from triceps brachii before and after training. MHC isoform composition was determined by SDS-PAGE silver staining, and mRNA levels of MHC isoforms were determined by RT-PCR. In Max group, there was an increase in MHC(2A) (49.4 to 66.7%, P < 0.01) and a decrease in MHC(2X) (33.4 to 19.5%, P < 0.01) after training, although there was no significant change in MHC(slow). In Combi group, there was also an increase in MHC(2A) (47.7 to 62.7%, P < 0.05) and a decrease in MHC(slow) (18.2 to 9.2%, P < 0.05) but no significant change in MHC(2X). An upregulation of alpha-MHC(slow) mRNA was, therefore, found in both groups as a result of training. The strength training with maximum contractions led to a shift in MHC isoform composition from 2X to 2A, whereas the combined strength training produced an MHC isoform composition shift from slow to 2A.

Adult↗

PubMed2004

Muscle mechanoreflex and metaboreflex responses after myocardial infarction in rats.

BACKGROUND: During exercise, the sympathetic nervous system is activated and blood pressure and heart rate increase. In heart failure (HF), the muscle metaboreceptor contribution to sympathetic outflow is attenuated and the mechanoreceptor contribution is accentuated. Previous studies suggest that (1) capsaicin stimulates muscle metabosensitive vanilloid receptor subtype 1 (VR1), inducing a neurally mediated pressor response, and (2) activation of ATP-sensitive P2X receptors enhances the pressor response seen when muscle mechanoreceptors are engaged by muscle stretch. Thus, we hypothesized that the pressor response to VR1 stimulation would be smaller and the sensitizing effects of P2X stimulation greater in rats with HF due to chronic myocardial infarction (MI) than in controls. METHODS AND RESULTS: Eight to 14 weeks after coronary ligation, rats with infarcts >35% had an increased left ventricular end-diastolic pressure and a marked increase in heart weight. Capsaicin injected into the arterial supply of the hindlimb increased blood pressure by 39% (baseline, 93.9+/-9.5 mm Hg) in control animals but only by 8% (baseline, 94.8+/-10.1 mm Hg) in rats with large MIs (P<0.05). P2X receptor stimulation by alpha,beta-methylene ATP enhanced the pressor response to muscle stretch by 42% in control animals and by 72% in rats with large MIs (P<0.05). CONCLUSIONS: Compared with control animals, cardiovascular responses to VR1 stimulation are blunted and P2X-mediated responses are augmented in rats with HF owing to large MIs.

Achilles Tendon↗

PubMedDate not supplied

[Regulation of cardiac output;an approximation at 3 levels: organic, cellular, and protein].

The heart is the central point for adaptation of the organism to physical exercise because it is the center of the energy support system. Its activity is regulated at three levels; organ, cells and molecular and genetic components. During the development of the heart, the organ adapts in response to chronic and acute overloads by instantaneous functional and chronic changes, leading to a variable degree of cardiac growth. Physical exercise (acute and chronic) is the main example of physiologic overload. The acute response of the heart means a mechanical-hemodynamical and energetic modulation, driving to a final point where oxygen supply fits the increased need. Training, as response to chronic exercise, promotes an increase in energetic capacity (heart rate and stroke volume), structurally reflected in the physiological cardiac hypertrophy. Global functional and structural changes express what is happening at the cellular level. Different stimuli signal through specific receptors and second messengers to the nucleus, regulating gene expression and conditioning structural (size) and functional (contractile) changes. Changes in cellular size explain, by Starling mechanism, the increase in individual contractile strength and in reduction of the ventricular cavity in the systolic period. Other structural changes refer to the interstitium, myocardial vasculature and vascular reactivity. Changes in contractility affect the composition of the contractile elements (isoforms of heavy myosin, light myosin and/or modulatory proteins) and sarcoplasmic Ca2+ regulation, through the increase in Ca2+ flow. Many of the adaptations to chronic exercise studied in vivo in intact heart, isolated heart (Langendorf) or papillary muscle (multicellular preparation), are retained in the cardiomyocyte. Isolated cardiomyocytes can be precisely through the medium, temperature, ionic composition, active substances, etc. Shortening speed without load (Vmax), considered an inotropic index (Sonnenblick) can be measured independently of the initial length. Myocytes shorten against an internal load (restoration force) with viscous and elastic components, although they cannot be loaded externally (stretching is difficult). Cardiomyocyte isolation and maintenance requires strict and controlled conditions. This model offers many possibilities for studying dimensions, contraction-relaxation mechanics, Ca2+ and pH dynamics, beta-adrenergic receptors, electrophysiology, pharmacology, genetics, etc. This kind of studies can deal with normal myocytes or myocytes from trained animals, cardiomyopathies, etc.

Adaptation, Physiological↗

PubMed1985

Physiological characteristics of elite sport parachutists.

The physiological characteristics of 10 male elite sport parachutists (31.6 +/- 3.69 years of age) were determined and compared to 10 male non-sport parachutist controls (30.2 +/- 4.31 years) and other selected elite athletes. The typical sport parachutist was a highly educated (16.4 +/- 2.41 years), first born (9 out of 10), and, more often than not, single individual. During their mean 10.8 years of sport parachuting, these individuals made an average total number of 1,950 jumps (range 980 to 3,100) with a mean of 237.5 jumps during each of the last three years. Mean total free fall time was 22 h and 40 min. Compared to the non-sport parachutist control group, the elite sport parachutists were significantly higher (p less than 0.05) in aerobic power (47.4 +/- 9.04 vs. 37.2 +/- 4.67 ml X kg-1 X min-1), vital capacity (5.27 +/- 0.49 vs. 5.05 +/- 0.31 L), maximum heart rate (203.2 +/- 9.2 vs. 190.1 +/- 7.4 bpm), and back hyperextension flexibility (21.12 +/- 4.1 vs. 18.41 +/- 2.4 in). The elite sport parachutist were also significantly lower (p less than 0.05) in relative (%) body fat when compared to the control group (15.7 +/- 4.51 vs. 20.1 +/- 2.12%). The two groups were not significantly different (p greater than 0.05) with respect to resting heart rate, absolute body weight, dominant hand-grip strength, or lower back/hamstring flexibility as measured by the sit-and-reach test. Regarding somatotype, the elite sport parachutist can be classified as a balanced mesomorph. Compared to other selected elite athletes, the sport parachutists were lower in aerobic power and higher in relative body fat, yet with a summation of triceps, suprailiac, and abdominal skinfolds in the acceptable range for male athletes. The elite sport parachutists were approximately mid-range in absolute body weight and lower back/hamstring flexibility when compared to other selected elite athletes. Based on the findings of this study, there is evidence to suggest that some form of regular aerobic exercise along with a stretching and flexibility program is advisable for those individuals considering frequent participation and desiring peak performance in sport parachuting.

Adult↗

PubMed2004

High-intensity resistance training improves muscle strength, self-reported function, and disability in long-term stroke survivors.

BACKGROUND AND PURPOSE: To evaluate the efficacy of supervised high-intensity progressive resistance training (PRT) on lower extremity strength, function, and disability in older, long-term stroke survivors. METHODS: Forty-two volunteers aged 50 years and above, 6 months to 6 years after a single mild to moderate stroke, were randomized into either a control group of upper extremity stretching or a PRT group that received a 12-week supervised high-intensity resistance training program consisting of bilateral leg press (LP), unilateral paretic and nonparetic knee extension (KE), ankle dorsiflexion (DF), and plantarflexion (PF) exercises. Functional performance was assessed using the 6-minute walk, stair-climb time, repeated chair-rise time, and habitual and maximal gait velocities. Self-reported changes in function and disability were evaluated using the Late Life Function and Disability Instrument (LLFDI). RESULTS: Single-repetition maximum strength significantly improved in the PRT group for LP (16.2%), paretic KE (31.4%), and nonparetic KE (38.2%) with no change in the control group. Paretic ankle DF (66.7% versus -24.0%), paretic ankle PF (35.5% versus -20.3%), and nonparetic ankle PF (14.7% versus -13.8%) significantly improved in the PRT group compared with the control. The PRT group showed significant improvement in self-reported function and disability with no change in the control. There was no significant difference between groups for any performance-based measure of function. CONCLUSIONS: High-intensity PRT improves both paretic and nonparetic lower extremity strength after stroke, and results in reductions in functional limitations and disability.

Aged↗

PubMedDate not supplied

Physical exercise in women with intractable epilepsy.

Fifteen women with pharmacologically intractable epilepsy were given physical exercise (aerobic dancing with strength training and stretching) for 60 min, twice weekly, for 15 weeks. Seizure frequency was recorded by the patients for 3-7 months before the intervention, during the intervention period, and for 3 months after the intervention. Medication and other known seizure-influencing factors were kept as constant as possible. Self-reported seizure frequency was significantly reduced during the intervention period. The exercise also led to reduced level of subjective health complaints, such as muscle pains, sleep problems, and fatigue. The exercise reduced plasma cholesterol ratio and increased maximum O2 uptake. Because most of the patients were unable to continue the exercise on their own after the intervention period, the exercise effects were not maintained during the follow-up period. The patients were not unwilling to continue the exercise, but it was not sufficient to offer them the possibility of continuing similar types of exercise. We believe that 15 weeks is too short a time to establish a life-style change and that continued physical exercise for these patients requires a well-organized and supportive program, requiring experienced and dedicated instructors.

Adolescent↗

PubMed2006

Stage I and II posterior tibial tendon dysfunction treated by a structured nonoperative management protocol: an orthosis and exercise program.

BACKGROUND: Posterior tibial tendon dysfunction (PTTD) is a relatively common problem of middle-aged adults that usually is treated operatively. The purpose of this study was to identify strength deficits with early stage PTTD and to assess the efficacy of a focused nonoperative treatment protocol. METHODS: Forty-seven consecutive patients with stage I or II posterior tibial tendon dysfunction were treated by a structured nonoperative protocol. Criteria for inclusion were the presence of a palpable and painful posterior tibial tendon, with or without swelling and 2) movement of the tendon with passive and active nonweightbearing clinical examination. The rehabilitation protocol included the use of a short, articulated ankle foot orthosis or foot orthosis, high-repetition exercises, aggressive plantarflexion activities, and an aggressive high-repetition home exercise program that included gastrocsoleus tendon stretching. Isokinetic evaluations were done before and after therapy to compare inversion, eversion, plantarflexion, and dorsiflexion strength in the involved and uninvolved extremities. Criteria for successful rehabilitation were no more than 10% strength deficit, ability to perform 50 single-support heel rises with minimal or no pain, ability to ambulate 100 feet on the toes with minimal or no pain, and ability to tolerate 200 repetitions of the home exercises for each muscle group. RESULTS: Before therapy weakness for concentric and eccentric contractures of all muscle groups of the involved ankle was significant (p<0.001). After a median of 10 physical therapy visits over a median period of 4 months, 39 (83%) of the 47 patients had successful subjective and functional outcomes, and 42 patients (89%) were satisfied. Five patients (11%) required surgery after failure of nonoperative treatment. CONCLUSION: This study suggests that many patients with stage I and II posterior tibial tendon dysfunction can be effectively treated nonoperatively with an orthosis and structured exercises.

Adolescent↗

PubMed1985

An electromyographic study of elbow motion during postexercise muscle soreness.

Postexercise muscle soreness was induced in the elbow flexors of human volunteer subjects through the use of a regimen of eccentric contractions. Physical examination before and 48 h after the exercise included measurements of range of elbow motion at the elbow and of arm diameter. Electromyographic (EMG) observations, utilizing fine wire electrodes introduced into each of the elbow flexors, were carried out before and 48 h after the exercise. These observations included resting EMG levels, EMG activity under various isometric loads, and activity during active and passive extensions. The soreness induced was accompanied by a reduction in resting elbow angle while the subjects stood with arms relaxed at their sides, decreased range of both flexion and extension of the elbow, and swelling of the arm. EMG measurements showed no increase in EMG activity as the sore arms were extended passively at the elbow, indicating that the extra resistance to extension associated with the soreness was not a result of stretch receptor-induced activity in the flexors. The results rule out the possibility that neuromuscular activity is responsible for the restriction of motion and are consistent with the idea that edematous changes within the perimuscular connective tissue alter the elastic behavior of the muscles and cause restriction of motion.

Adult↗

PubMed2006

Effects of the transition time between muscle-tendon stretch and shortening on mechanical efficiency.

The net mechanical efficiency of positive work (eta(pos)) has been shown to increase if it is immediately preceded by negative work. This phenomenon is explained by the storage of elastic energy during the negative phase and its release during the subsequent positive phase. If a transition time (T) takes place, the elastic energy is dissipated into heat. The aim of the present study was to investigate the relationship between eta(pos) and T, and to determine the minimal T required so that eta(pos) reached its minimal value. Seven healthy male subjects were tested during four series of lowering-raising of the body mass. In the first series (S (0)), the negative and positive phases were executed without any transition time. In the three other series, T was varied by a timer (0.12, 0.24 and 0.56 s for series S (1), S (2) and S (3), respectively). These exercises were performed on a force platform sensitive to vertical forces to measure the mechanical work and a gas analyser was used to determine the energy expenditure. The results indicated that eta(pos) was the highest (31.1%) for the series without any transition time (S (0)). The efficiencies observed with transition times (S (1), S (2) and S (3)) were 27.7, 26.0 and 23.8%, respectively, demonstrating that T plays an important role for mechanical efficiency. The investigation of the relationship between eta(pos) and T revealed that the minimal T required so that eta(pos) reached its minimal value is 0.59 s.

Adult↗

PubMed2005

Passive stretching does not enhance outcomes in patients with plantarflexion contracture after cast immobilization for ankle fracture: a randomized controlled trial.

OBJECTIVE: To compare the efficacy of short- and long-duration passive stretches with a control treatment for the management of plantarflexion contracture after cast immobilization for ankle fracture. DESIGN: Assessor-blinded, randomized controlled trial. SETTING: Hospital physical therapy outpatient departments. PARTICIPANTS: Adults with plantarflexion contracture (N=150) after cast immobilization for ankle fracture. All subjects were weight bearing or partial weight bearing. INTERVENTIONS: Exercise only, exercise plus short-duration passive stretch, and exercise plus long-duration passive stretch. All subjects had a 4-week course of exercises. In addition, subjects in the short-duration stretch plus exercise group completed 6 minutes of stretching per day, and subjects in the long-duration stretch plus exercise group completed 30 minutes of stretching per day. MAIN OUTCOME MEASURES: Lower Extremity Functional Scale and passive dorsiflexion range of motion with the knee bent and straight at baseline, and at 4 weeks and 3 months postintervention. RESULTS: One hundred thirty-nine (93%) subjects completed the 4-week assessment and 134 (89%) subjects completed the 3-month assessment. There were no statistically significant or clinically important between-group differences for the primary outcomes. CONCLUSIONS: The addition of passive stretching confers no benefit over exercise alone for the treatment of plantarflexion contracture after cast immobilization for ankle fracture.

Adult↗

PubMedDate not supplied

Progressive muscular dystrophy--Duchenne type. Controversies of the kinesitherapy treatment.

The authors carried out a study of children with progressive muscular dystrophy of Duchenne type (DMD), giving special attention to physiatrical follow-up, having in mind that the practice of exercises has been debated very much in the specialized literature. The goal of this study is to try to settle the limits for the utilization of kinesitherapy which should be applied only in specific situations, such as: after skeletal muscular trauma or when the respiratory system is at risk. In this situation the physiatrical procedure would be to restrict physical activity, with early use of wheelchairs and the exclusion of the use of orthoses for orthostatism. DMD, at present, has been considered a result of duplication (60%), deletion (5 to 6%) or point mutations at gen Xp21 (Zatz, 1994), that codifies a protein called Dystrophin (Hoffman et al., 1987). Dystrophin is a cytoskeletal sarcolemmic protein that constitutes about .002% of the total protein of the muscle, present in skeletal fibers concentrated in muscle tendinous joints, which supplies mechanical reinforcement to the surface of the membrane during stretching and shortening physical activity. This protein is absent in DMD cases, wherefore, the sarcolemma undergoes a segmentary necrosis losing its contractile property during eccentric and concentric physical activity. The importance of physiatrical follow-up for DMD patients is to avoid deformities and tendon shortening, to ameliorate the patient's quality of life, to provide respiratory assistance and general counseling to members of the patient's family. The objective of this study is to try to clarify the risks and possibilities of kinesitherapy applied to DMD cases.

Child↗

PubMed1977

Mechanical work and efficiency in level walking and running.

1. The mechanical power spent to accelerate the limbs relative to the trunk in level walking and running, W(int), has been measured at various ;constant' speeds (3-33 km/hr) with the cinematographic procedure used by Fenn (1930a) at high speeds of running.2. W(int) increases approximately as the square of the speed of walking and running. For a given speed W(int) is greater in walking than in running.3. In walking above 3 km/hr, W(int) is greater than the power spent to accelerate and lift the centre of mass of the body at each step, W(ext) (measured by Cavagna, Thys & Zamboni, 1976b). In running W(int) < W(ext) up to about 20 km/hr, whereas at higher speeds W(int) > W(ext).4. The total work done by the muscles was calculated as W(tot) = W(int) + W(ext). Except that at the highest speeds of walking, the total work done per unit distance W(tot)/km is greater in running than in walking.5. The efficiency of positive work was measured from the ratio W(tot)/Net energy expenditure: this is greater than 0.25 indicating that both in walking and in running the muscles utilize, during shortening, some energy stored during a previous phase of negative work (stretching).6. In walking the efficiency reaches a maximum (0.35-0.40) at intermediate speeds, as may be expected from the properties of the contractile component of muscle. In running the efficiency increases steadily with speed (from 0.45 to 0.70-0.80) suggesting that positive work derives mainly from the passive recoil of muscle elastic elements and to a lesser extent from the active shortening of the contractile machinery. These findings are consistent with the different mechanics of the two exercises.

Adult↗

PubMed2001

Reflex cardiovascular responses evoked by selective activation of skeletal muscle ergoreceptors.

It is well known that the exercise pressor reflex (EPR) is mediated by group III and IV skeletal muscle afferent fibers, which exhibit unique discharge responses to mechanical and chemical stimuli. Based on the difference in discharge patterns of group III and IV muscle afferents, we hypothesized that activation of mechanically sensitive (MS) fibers would evoke a different pattern of cardiovascular responses compared with activation of both MS and chemosensitive (CS) fibers. Experiments were conducted in chloralose-urethane-anesthetized cats (n = 10). Passive muscle stretch was used to activate MS afferents, and electrically evoked contraction of the triceps surae was used to activate both MS and CS muscle afferents. No significant differences were shown in reflex heart rate and mean arterial pressure (MAP) responses between passive muscle stretch and evoked muscle contraction. However, when the reflex responses were matched according to tension-time index (TTI), the peak MAP response (67 +/- 4 vs. 56 +/- 4 mmHg, P < 0.05) was significantly greater at higher TTI (427 +/- 18 vs. 304 +/- 13 kg. s, high vs. low TTI, P < 0.05), despite different modes of afferent fiber activation. When the same mode of afferent fiber activation was compared, the peak MAP response (65 +/- 7 vs. 55 +/- 5 mmHg, P < 0.05) was again predicted by the magnitude of TTI (422 +/- 24 vs. 298 +/- 19 kg. s, high vs. low TTI, P < 0.05). Total sensory input from skeletal muscle ergoreceptors, as predicted by TTI and not the modality of afferent fiber activation (muscle contraction vs. passive stretch), is suggested to be the primary determinant of the magnitude of the EPR-evoked cardiovascular response.

Animals↗