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PubMed1990

Evaluation of animal models for the study of exercise-induced muscle enlargement.

Skeletal muscle is known to enlarge in response to high-resistance training programs in humans. Study of the cellular mechanisms of muscle enlargement and the adaptations of muscle to strength-training programs has been difficult because of the need to analyze entire muscles. This precludes the use of human subjects in many experiments of this nature. Several animal models have been developed for the study of muscle enlargement; these models basically fall into three categories: 1) stretch hypertrophy, 2) compensatory hypertrophy, and 3) exercise-induced hypertrophy. This review attempts to analyze these models as models of muscle enlargement produced by strength training in humans. Three areas must be considered when evaluating animal models of human muscle enlargement produced by strength training: 1) response topography, 2) magnitude of enlargement, and 3) muscle fiber adaptations produced as a result of the enlargement. Based on these considerations, it is concluded that none of the animal models currently in use truly represents the human strength-training situation under all conditions. All three models, however, provide valuable information about the plasticity of skeletal muscle in response to a broad spectrum of muscle enlargement.

Animals↗
PubMed1990

Mechanical efficiency of locomotion in females during different kinds of muscle action.

The mechanical efficiencies (ME) of pure positive and pure negative work as well as of stretch-shortening cycle (SSC) exercise were investigated with a special sledge apparatus. The subjects were 20 young females who performed six different types of submaximal exercise: two of pure concentric exercise (positive work), two of pure eccentric exercise (negative work) and two SSC exercises. The work intensities were determined individually, from the recordings of distance obtained during a single maximal concentric exercise. Each exercise involved 60 muscle actions lasting a total of 3 min per testing condition. The MEs of pure positive work with intensities of 30% and 60% maximum (C30 and C60 respectively) were 15.5%, SD 2.6% and 14.3%, SD 1.9%, respectively. In pure negative work, when the dropping heights were 20 cm (E20) and 80 cm (E80), MEs were 28.4%, SD 6.9% and 47.9%, SD 10.1%, respectively. In SSC-exercise, the MEs during the positive phase of the take-off were 31.3%, SD 6.3% (E20/C90) and 35.0%, SD 7.0% (E80/C69). The total MEs in SSC-exercise were 29.1%, SD 4.0% (E20/C90) and 40.1%, SD 5.2% (E80/C60 x 100). In pure negative work, the increased stretching velocity increased the value of ME. In the concentric phase of SSC-exercise, the integrated electromyographic activity (iEMG) of vastus lateralis (VL) and vastus medialis (VM) muscles were lower (P less than 0.05) than in pure concentric work, when the mechanical work was the same (C60 vs E80/C60). During pure eccentric work, iEMGs were lower in comparison to the eccentric phase of SSC-exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed2000

Plasma lactate concentration and muscle blood flow during dynamic exercise with negative-pressure breathing.

This study assessed the hypothesis that increasing cardiac filling pressure (CFP) would enhance contracting muscle blood flow (MBF) by stretching cardiopulmonary baroreceptors and attenuate the increase in plasma lactate concentration ([Lac(-)](p)) during dynamic exercise. Continuous negative-pressure breathing (CNPB) (-15 cmH(2)O) was used to increase the CFP by accelerating the venous return to the heart. In the first series of experiments, 10 men performed a graded exercise seated on a cycle ergometer with (N1) and without CNPB (C1). The increase in [Lac(-)](p) for N1 was attenuated at 60%, 90%, and 100% of maximal exercise intensity compared with that in C1 (P < 0.001). Also, the increases in mean arterial pressure (MAP) and plasma catecholamine concentrations were attenuated in N1 compared with those in C1 throughout the graded exercise (P < 0.05). However, heart rate and pulse pressure were not significantly influenced by CNPB. Second, we studied the impact of CNPB on forearm MBF during a rhythmic handgrip exercise in 5 of the 10 subjects. Forearm MBF was measured immediately after cessation of the exercise by venous occlusion plethysmography at rest, 30%, 50%, and 70% of maximal work load (WL(max)) with (N2) and without CNPB (C2). Forearm MBF and vascular conductance for both trials increased with the increase in intensity, but forearm skin blood flow measured by laser-Doppler flowmetry remained unchanged. MBF and vascular conductance in N2, however, increased more than in C2 at every intensity (P < 0.01) except for MBF at 70% WL(max), whereas the increase in MAP for N2 was attenuated compared with that in C2 (P < 0.05). Thus augmented active muscle vasodilation occurred in N2 with a lower increase in MAP compared with that in C2. These findings suggest that the stretch of intrathoracic baroreceptors, such as cardiopulmonary mechanoreceptors, by CNPB increased MBF by suppressing sympathetic nerve activity. The attenuation of the increase in [Lac(-)](p) might be caused, at least partially, by the increased MBF.

Adult↗
PubMedDate not supplied

Exercise-induced skeletal muscle growth. Hypertrophy or hyperplasia?

Postnatal skeletal muscle growth in humans is generally ascribed to enlargement of existing muscle fibres rather than to cellular proliferation. Some evidence of muscle fibre division or splitting was provided in the nineteenth century. This evidence has more recently been supported by fibres obtained from regenerating muscle, and from muscle which has undergone stress-induced growth. Numerous investigators have reported indirect evidence for exercise-induced hypertrophy and hyperplasia. These findings are largely founded on secondary observations of fibre size or number differences expressed relative to muscle cross-sectional area. Since these observations in humans are open to methodological criticism, researchers have developed 3 animal models to represent exercise-induced human muscle growth. These include compensatory hypertrophy, stretch-induced hypertrophy, and weight lifting in trained animals. The results and criticisms of the experiments which have used these models are discussed in this review. In studies of muscle cross-sectional area, errors are created by fibres terminating intrafascicularly. Longitudinal growth of such fibres result in an overestimation of fibre number, and with the use of penniform muscles where fibres do not run parallel to the longitudinal axis of the muscle, the error is compounded. It was concluded that hyperplasia is not yet substantiated, and that new fibres, if present, may be the result of the development of satellite cells. Further experiments are required before a definitive answer can be provided. It is suggested that rigidly controlled exercise studies using contralateral control, fusiform muscles with analysis of individually teased muscle fibres be performed.

Animals↗
PubMed2005

Effects of viscoelastic properties of tendon structures on stretch-shortening cycle exercise in vivo.

The aim of the present study was to examine the effects of viscoelastic properties of human tendon structures during stretch - shortening cycle exercise. The elongation of tendon and aponeurosis of the medial gastrocnemius muscle of 26 participants was measured by ultrasonography while they performed ramp isometric plantar flexion up to the voluntary maximum, followed by a ramp relaxation. The relationship between estimated muscle force and tendon elongation during the ascending phase was fitted to a linear regression, the slope of which was defined as stiffness. The percentage of the area within the muscle force-tendon elongation loop relative to the area beneath the curve during the ascending phase was defined as hysteresis. In addition, maximal voluntary concentric contractions at 2.09 and 3.14 rad x s(-1) with and without prior eccentric contractions were performed. The difference in the concentric torque at equivalent joint angles with and without prior eccentric contractions (i.e. pre-stretch augmentation) was negatively correlated with stiffness (P < 0.05) and hysteresis (P < 0.05). Furthermore, there was a higher correlation between the pre-stretch augmentation and the viscoelastic properties index--that is, the sum of normalized score values of stiffness and hysteresis (P < 0.01)--than with either stiffness or hysteresis alone. The results of this study suggest that performance during stretch-shortening cycle exercise is significantly affected by the viscoelastic properties of the tendon structures.

Adult↗
PubMed1990

Diagnosis and rehabilitation of the shoulder impingement syndrome in the overhand and throwing athlete.

The shoulder apparatus is of elegant structural design, affording great ROM with substantial power in many planes of movement. It is the underlying anatomic relationships that allow great mobility that also render the shoulder susceptible to injury. Injury in repetitive overhand activities is usually in the form of impingement, which may result from many factors, including multidirectional instability, anterior subluxation, and imbalanced force couple mechanisms, among others. Diagnosis requires a thorough history and physical examination. The impingement sign and test are among the most useful diagnostic maneuvers available. Rehabilitation is individualized, depending upon the cause of impingement, severity of injury, and response to therapy. Overuse syndromes mandate rest and control of inflammation through the use of ice, NSAIDs, and local injections of steroids followed by passive, active-assist, and active ROM; stretching; and mobilization exercises. As pain and inflammation subside, isometric or isotonic exercises are prescribed initially to strengthen the rotator cuff musculature and, therefore, the caudal glide mechanism. Subsequent strengthening exercises then are performed in other planes of movement to strengthen the remaining shoulder-complex muscles. The patient is then advanced to isokinetic training. Stretching is emphasized as an essential preparatory activity for all types of exercise. Maintaining contralateral and lower-limb strength, and cardiovascular conditioning is necessary if athletic activities are to be resumed at the previous level of performance. Following return to athletic performance, an analysis of training habits should be made and a prescription for exercise issued based on the avoidance of aggravating factors and cultivation of activities that enhance existing static and dynamic shoulder stabilizers. Any return of symptoms should prompt an immediate reappraisal with the proper intervention, including adjustment of activity level and exercises as deemed appropriate. With proper conservative therapy, relatively few athletes should require surgical treatment.

Athletic Injuries↗
PubMed1994

Clinical use of neck isometric strength measurement in rehabilitation.

The purpose of this study was to evaluate for diagnostic purposes the isometric strength of the neck flexor and extensor muscles in 56 patients with neck and shoulder pain and to quantify the effect of a specific rehabilitation program. An isometric measurement protocol was performed at the beginning and at the end of a 3-week rehabilitation program that included physiotherapy, stretching, aerobic exercises, and circuit training to improve arm, shoulder, and neck muscle strength. In the beginning, mean neck flexor muscle isometric strength was 83N (+/- 48 SD) and extensor muscle strength 158N (+/- 76 SD), whereas after rehabilitation the strength measurements were 117N (+/- 43 SD) and 207N (+/- 84 SD) respectively. There was a significant increase in the ability to push forward and backward, which correlated with the lessening of neck pain and disability found at the end of the program (p < .05). Isometric strength measurement is a useful and practical method of objectively showing a functional improvement in response to rehabilitation.

Adult↗
PubMed2006

Muscle sympathetic nerve activity responses to dynamic passive muscle stretch in humans.

It is suggested that mechanoreceptors in muscle play an important role in the exercise pressor reflex. However, it has not been verified whether isolated stimulation of the mechanoreceptors can induce responses in muscle sympathetic nerve activity (MSNA) in young healthy individuals. We tested the hypothesis that passive stretch of muscle can evoke an increase in MSNA in healthy individuals. In 12 young subjects, leg calf muscles were passively stretched, or actively contracted for 5 s followed by a 15-25 s (random length) relaxation period. Stretch and contraction were each repeated 25 times. MSNA, heart rate and blood pressure were analysed, and averaged according to the onset of the force on a beat-by-beat basis. At the 1st to the 3rd heart beat from the onset of stretch, MSNA (199 +/- 30%, P < 0.05) as well as heart rate (102.5 +/- 0.7%, P < 0.05) increased transiently but significantly from the prior stretch baseline (100%), followed (from 3rd to 7th beat from the onset of stretch) by a transient increase in mean blood pressure (101.9 +/- 0.3%, P < 0.05) from the baseline. Similar response patterns were observed during active muscle contractions. The present data show that MSNA responses to isolated stimulation of mechanoreceptors are measurable. Because of baroreflex engagement, the magnitude of the response is small and transient, and the haemodynamic consequences using this protocol may be limited.

Adult↗
PubMed2001

The effect of quadriceps femoris muscle strengthening exercises on spasticity in children with cerebral palsy.

BACKGROUND AND PURPOSE: The Bobath neurodevelopmental treatment approach advised against the use of resistive exercise, as proponents felt that increased effort would increase spasticity. The purpose of this study was to test the premise that the performance of exercises with maximum efforts will increase spasticity in people with cerebral palsy (CP). Spasticity, in the present study, was defined as a velocity-dependent hyperexcitability of the muscle stretch reflex. SUBJECTS: Twenty-four subjects with the spastic diplegic form of CP (mean age=11.4 years, SD=3.0, range=7-17) and 12 subjects without known neurological impairments (mean age=11.6 years, SD=3.5, range=7-17) were assessed. METHODS: Knee muscle spasticity was assessed bilaterally using the pendulum test to elicit a stretch reflex immediately before and after 3 different forms of right quadriceps femoris muscle exercise (isometric, isotonic, and isokinetic) during a single bout of exercise training. Pendulum test outcome measures were: (1) first swing excursion, (2) number of lower leg oscillations, and (3) duration of the oscillations. RESULTS: There were no changes in spasticity following exercise between the 2 groups of subjects. DISCUSSION AND CONCLUSION: These results do not support the premise that exercises with maximum efforts increase spasticity in people with CP.

Adolescent↗
PubMed2005

[Is stretching for sports performance still useful? A review of the literature].

Since 1980, according to several authors, it is accepted that increasing flexibility of a muscle-tendon unit allows a better performance and decreases sports injuries. Stretching is regularly included in warm-up and in cooling-down. However, there are contradictory findings in the literature. In contrast, since 1990, there's evidence suggesting that stretching not only does not prevent injuries, but can also decrease the level of performance. Some part of these contradictions can be explained by the various sports activities. Those requesting an increased flexibility, such as gymnastic, dancing or diving, necessitate pre-exercise stretching to optimize the level of performance. In contrary, for sports with slow stretch-shortening cycle such as jogging or cycling, there is no scientific data showing a positive effect of stretching.

Athletic Injuries↗
PubMed2004

Physical activity behaviors and perceived life satisfaction among public high school adolescents.

This study explored relationships between perceived life satisfaction and physical activity behaviors in a statewide sample of adolescents in South Carolina (n = 4,758) using the CDC Youth Risk Behavior Survey (YRBS) and the Brief Multidimensional Student Life Satisfaction Scale (BMSLSS). Adjusted logistic regression analyses and multivariate models constructed separately revealed significant race by gender results. Not exercising for 20 minutes over the past 7 days (sweating and hard breathing), not performing stretching exercising (past 7 days), not exercising to strengthen or tone muscles (past 7 days), spending < 20 minutes actually exercising or playing sports in PE class, not playing on sport teams run by school, and not playing on sport teams run by outside school organizations were associated (p = .05) with reduced life satisfaction for specific race/gender groups. Results suggest implications for school and community-based physical activity programs. Future research should consider measures of life satisfaction as a component of comprehensive assessments of adolescent physical activity behaviors in fieldwork, research, and program evaluation.

Adolescent↗
PubMedDate not supplied

Pathologic synovial plica of the knee. Results of conservative treatment.

Observations of 136 cases of pathologic synovial plica of the knee were analyzed with regard to etiology, symptoms, and the results of conservative treatment. The results obtained with conservative treatment were good in 40% of cases, average in 20%, and poor in 40%. In our opinion, these results justify the treatment of this condition with physical therapy before proceeding with surgical correction. The objective of physical therapy was to decrease the compressive forces in the anterior compartment of the knee by increasing the structural flexibility of the flexor and extensor muscles. This increase in flexibility was obtained by instituting stretching exercises for the hamstrings, gastrocnemius, and quadriceps.

Adolescent↗
PubMed2001

[Anterior knee pain associated with sports and work].

Anterior knee pain is not a disease, but a syndrome with numerous causes. This paper describes its appearance in the patellofemoral joint in sportsmen and in untrained people. Chondromalacia patellae is a condition of the cartilage, not a disease, that is, it is never diagnosed alone. Relative muscular insufficiency, especially of the knee extensors, may occur in children and adolescents, as they grow rapidly. The consequence is a unbalance of active stabilizers and the disturbance of the slippery trail of patella, particularly in the presence of dysplasia of patellofemoral joint. The impingement syndrome pain occurs in sportsmen and people overloading the patellofemoral joint. Other causes of anterior knee pain should be excluded in clinical examination and slippery trail of patella, its position, and signs of instability should be determined. This paper gives an overview of patellar chondromalacia, lateral pressure syndrome, patellar subluxation, patellar acute and recurrent luxation, and idiopathic anterior knee pain. The treatment is basically conservative. Stretching exercises and the strengthening of certain groups of femoral muscles serves to regain the balance, thus normalising the slippery trail and taking off the burden from the patellofemoral joint. If conservative treatment fails, surgery is the alternative.

Athletic Injuries↗