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The effect of pre-stretch on mechanical efficiency of human skeletal muscle.

The mechanical efficiency of positive work was studied in six subjects performing three different types of exercises. On the first occasion the subjects ran on a motor-driven treadmill at 3.33 m s-1; the second and the third exercises consisted of performing rhythmical vertical jumps for 1 min both in rebound (RJ) and no-rebound (NRJ) conditions. The mechanical efficiency calculated in NRJ, which reflects only the conversion of biochemical energy into mechanical work, was found to be lower than the corresponding observation in RJ, 17.2 vs. 27.8% (P less than 0.001), respectively. These differences could not be explained by only the storage and recoil of elastic energy occurring in RJ compared with NRJ. The calculated extra work delivered 'free' was greater than the potential elastic energy which could be stored within the leg extensor muscles (187 vs. 124 J for each jump, P less than 0.05). It is likely that other factors might be responsible for the extra work found in NRJ. It was suggested that the difference in the length of time to perform positive work between a simple shortening contraction and a stretch-shortening muscular activity could be also responsible for the enhanced efficiency observed in RJ. This suggestion was supported by the high relationship (P less than 0.001) found between the time to perform positive work and the mechanical efficiency measured in jumping and estimated during running.

Adult↗

Modulation of stretch reflexes during imposed walking movements of the human ankle.

Our overall objectives were to examine the role of peripheral afferents from the ankle in modulating stretch reflexes during imposed walking movements and to assess the mechanical consequences of this reflex activity. Specifically we sought to define the changes in the electromyographic (EMG) and mechanical responses to a stretch as a function of the phase of the step cycle. We recorded the ankle position of a normal subject walking on a treadmill at 3 km/h and used a hydraulic actuator to impose the same movements on supine subjects generating a constant level of ankle torque. Small pulse displacements, superimposed on the simulated walking movement, evoked stretch reflexes at different phases of the cycle. Three major findings resulted: 1) soleus reflex EMG responses were influenced strongly by imposed walking movements. The response amplitude was substantially smaller than that observed during steady-state conditions and was modulated throughout the step cycle. This modulation was qualitatively similar to that observed during active walking. Because central factors were held constant during the imposed walking experiments, we conclude that peripheral mechanisms were capable of both reducing the amplitude of the reflex EMG and producing its modulation throughout the movement. 2) Pulse disturbances applied from early to midstance of the imposed walking cycle generated large reflex torques, suggesting that the stretch reflex could help to resist unexpected perturbations during this phase of walking. In contrast, pulses applied during late stance and swing phase generated little reflex torque. 3) Reflex EMG and reflex torque were modulated differently throughout the imposed walking cycle. In fact, at the time when the reflex EMG response was largest, the corresponding reflex torque was negligible. Thus movement not only changes the reflex EMG but greatly modifies the mechanical output that results.

Adult↗

Rigidity in parkinsonism: characteristics and influences of passive exercise and electrical nerve stimulation.

Rigidity was measured during sinusoidal passive movements of the ankle joint in 7 patients with parkinsonism. Velocity-dependent changes were observed, less marked than in spasticity and expressed in a different way in flexor and extensor muscles: a mild decrease in resistive torques at faster stretching of dorsal flexors and an increase in resistance on stretching of plantar flexors. Dorsal flexors also frequently showed shortening reactions. Passive exercises and electrical stimulation of the peroneal nerve resulted in decreased electromyographic responses to stretch, smoother passive movements and in improved voluntary contraction.

Aged↗

Comparison of lidocaine injection, botulinum toxin injection, and dry needling to trigger points in myofascial pain syndrome.

BACKGROUND: Myofascial pain syndrome (MPS) is one of the most common causes of chronic musculoskeletal pain. Several methods have been recommended for the inactivation of trigger points (TrP). OBJECTIVES: This prospective, single-blind study was proposed to compare TrP injection with botulinum toxin type A (BTX-A) to dry needling and lidocaine injection in MPS. METHODS: Eighty-seven trigger points (cervical and/or periscapular regions) in 23 female and six male patients with MPS were treated and randomly assigned to three groups: lidocaine injection (n=10, 32 TrP), dry needling (n=10, 33 TrP), and BTX-A injection (n=9, 22 TrP). OUTCOME MEASURES: Clinical assessment including cervical range of motion, TrP pain pressure threshold (PPT), pain scores (PS), and visual analog scales for pain, fatigue, and work disability were evaluated at entry and the end of the 4th week. Additionally, depression and anxiety were evaluated with the Hamilton depression and anxiety rating scales, and quality of life was assessed using the Nottingham health profile (NHP). The subjects were also asked to describe side effects. INJECTION PROCEDURE: One milliliter of 0.5% lidocaine was administered to each TrP in the lidocaine injection group, 10-20 IU of BTX-A to each TrP in the BTX-A group, and dry needling to each TrP in the last group, followed by stretching of the muscle groups involved. The patients were instructed to continue their home exercise programs. RESULTS: Pain pressure thresholds and PS significantly improved in all three groups. In the lidocaine group, PPT values were significantly higher than in the dry needle group, and PS were significantly lower than in both the BTX-A and dry needle groups. In all, visual analog scores significantly decreased in the lidocaine injection and BTX-A groups and did not significantly change in the dry needle group. Disturbance during the injection procedure was lowest in the lidocaine injection group. Quality of life scores assessed by NHP significantly improved in the lidocaine and BTX-A groups but not in the dry needle group. Depression and anxiety scores significantly improved only in the BTX-A-injected group. CONCLUSIONS: Injection is more practical and rapid, since it causes less disturbance than dry needling and is more cost effective than BTX-A injection, and seems the treatment of choice in MPS. On the other hand, BTX-A could be selectively used in MPS patients resistant to conventional treatments.

Adult↗

Effect of cessation and resumption of static hamstring muscle stretching on joint range of motion.

STUDY DESIGN: Single group repeated measures. OBJECTIVES: To determine the effects of cessation and resumption of a hamstring muscle stretching protocol on knee range of motion (ROM). BACKGROUND: It is generally accepted that stretching exercises result in an increase in ROM. The ability to maintain ROM once stretching has ceased and the ability to regain ROM after resumption of the stretching exercise is not well-known. METHODS AND MEASURES: Evaluated the effect of 6 weeks of static hamstring stretching, 4 weeks with cessation from stretching, and 6 weeks with resumption of stretching on knee ROM in 18 inactive college students (12 men, 6 women, mean age 21.0 years). The hamstring stretching consisted of 2 30-second stretches per day, 5 days per week. Knee ROM was measured before and after each of the above phases with an active knee extension test. RESULTS: Mean knee ROM increased after the initial stretching period (143+/-11 to 152+/-9 degrees), decreased to baseline following the cessation period (145+/-8 degrees) and again increased following the resumption of stretching but was not different from the initial gains (154+/-10 degrees). Unlike the stretch limb, the control limb ROM did not change over the 4 measurement times. CONCLUSIONS: There was no retention of knee ROM 4 weeks following a 6-week stretching protocol and a subsequent stretching period did not enhance the gain of knee ROM over the initial stretching period.

Adult↗

Expression of insulin growth factor-1 splice variants and structural genes in rabbit skeletal muscle induced by stretch and stimulation.

1. Skeletal muscle is a major source of circulating insulin growth factor-1 (IGF-1), particularly during exercise. It expresses two main isoforms. One of the muscle IGF-1 isoforms (muscle L.IGF-1) is similar to the main liver IGF-1 and presumably has an endocrine action. The other muscle isoform as a result of alternative splicing has a different 3' exon sequence and is apparently designed for an autocrine/paracrine action (mechano-growth factor, MGF). Using RNase protection assays with a probe that distinguishes these differently spliced forms of IGF-1, their expression and also the expression of two structural genes was measured in rabbit extensor digitorum longus muscles subjected to different mechanical signals. 2. Within 4 days, stretch using plaster cast immobilization with the limb in the plantar flexed position resulted in marked upregulation of both forms of IGF-1 mRNA. Electrical stimulation at 10 Hz combined with stretch (overload) resulted in an even greater increase of both types of IGF-1 transcript, whereas electrical stimulation alone, i.e. without stretch, resulted in no significant increase over muscle from sham-operated controls. Previously, it was shown that stretch combined with electrical stimulation of the dorsiflexor muscles in the adult rabbit results in a marked increase in muscle mass involving increases in both length and girth, within a few days. The expression of both systemic and autocrine IGF-1 growth factors provides a link between the mechanical signal and the marked increase in the structural gene expression involved in tissue remodelling and repair. 3. The expression of the beta actin gene was seen to be markedly upregulated in the stretched and stretched/stimulated muscles. It was concluded that the increased expression of this cytoskeletal protein gene is an indication that the production of IGF-1 may initially be a response to local damage. 4. Switches in muscle fibre phenotype were studied using a specific gene probe for the 2X myosin heavy chain gene. Type 2X expression was found to decrease markedly with stimulation alone and when electrical stimulation was combined with stretch. Unlike the induction of IGF-1 and beta actin, the decreased expression of the 2X myosin mRNA was less marked in the 'stretch only' muscles. This indicates that the interconversion of fibre type 2X to 2A may in some situations be commensurate with, but not under the control of IGF-1.

Actins↗

Can apparent increases in muscle extensibility with regular stretch be explained by changes in tolerance to stretch?

The aim of this study was to determine whether an intensive stretch program increases muscle extensibility or subjects' tolerance to an uncomfortable stretch sensation. Twenty healthy able-bodied individuals with limited hamstring muscle extensibility were recruited. A within-subjects design was used whereby one leg of each subject was randomly allocated to the experimental condition and the other leg was allocated to the control condition. The hamstring muscles of each subject's experimental leg were stretched for 20 minutes each weekday for four weeks. Hamstring muscle extensibility (angle of hip flexion corresponding with a standardised torque) and stretch tolerance (angle of hip flexion corresponding with maximal torque tolerated) were assessed on both legs at the beginning and end of the study. The intervention did not increase the extensibility of the hamstring muscles (mean change in hip flexion was -1 degree, 95% CI -4 to 3 degrees) but did increase subjects' tolerance to an uncomfortable stretch sensation (mean change in hip flexion was 8 degrees, 95% CI 5 to 12 degrees). These results highlight the importance of distinguishing between real and apparent increases in muscle extensibility when assessing the effectiveness of stretch, and indicate that whilst a four-week stretch program increases subjects' tolerance to an uncomfortable stretch sensation it does not increase hamstring muscle extensibility.

Adult↗

Effects of load carrying on metabolic cost and hindlimb muscle dynamics in guinea fowl (Numida meleagris).

The goal of this study was to test whether the contractile patterns of two major hindlimb extensors of guinea fowl are altered by load-carrying exercise. We hypothesized that changes in contractile pattern, specifically a decrease in muscle shortening velocity or enhanced stretch activation, would result in a reduction in locomotor energy cost relative to the load carried. We also anticipated that changes in kinematics would reflect underlying changes in muscle strain. Oxygen consumption, muscle activation intensity, and fascicle strain rate were measured over a range of speeds while animals ran unloaded vs. when they carried a trunk load equal to 22% of their body mass. Our results showed that loading produced no significant (P > 0.05) changes in kinematic patterns at any speed. In vivo muscle contractile strain patterns in the iliotibialis lateralis pars postacetabularis and the medial head of the gastrocnemius showed a significant increase in active stretch early in stance (P < 0.01), but muscle fascicle shortening velocity was not significantly affected by load carrying. The rate of oxygen consumption increased by 17% (P < 0.01) during loaded conditions, equivalent to 77% of the relative increase in mass. Additionally, relative increases in EMG intensity (quantified as mean spike amplitude) indicated less than proportional recruitment, consistent with force enhancement via stretch activation, in the proximal iliotibialis lateralis pars postacetabularis; however, a greater than proportional increase in the medial gastrocnemius was observed. As a result, when averaged for the two muscles, EMG intensity increased in direct proportion to the fractional increase in load carried.

Animals↗

Exercise for health for early postmenopausal women: a systematic review of randomised controlled trials.

Women who pass menopause face many changes that may lead to loss of health-related fitness (HRF), especially if sedentary. Many exercise recommendations are also relevant for early postmenopausal women; however, these may not meet their specific needs because the recommendations are based mainly on studies on men. We conducted a systematic review for randomised, controlled exercise trials on postmenopausal women (aged 50 to 65 years) on components of HRF. HRF consists of morphological fitness (body composition and bone strength), musculoskeletal fitness (muscle strength and endurance, flexibility), motor fitness (postural control), cardiorespiratory fitness (maximal aerobic power, blood pressure) and metabolic fitness (lipid and carbohydrate metabolism). The outcome variables chosen were: bodyweight; proportion of body fat of total bodyweight (F%); bone mineral density (BMD); bone mineral content (BMC); various tests on muscle performance, flexibility, balance and coordination; maximal oxygen consumption (V-dotO(2max)); resting blood pressure (BP); total cholesterol (TC); high-density lipoprotein-cholesterol; low-density lipoprotein-cholesterol; triglycerides; blood glucose and insulin. The feasibility of the exercise programme was assessed from drop-out, attendance and injury rates. Twenty-eight randomised controlled trials with 2646 participants were assessed. In total, 18 studies reported on the effects of exercise on bodyweight and F%, 16 on BMD or BMC, 11 on muscular strength or endurance, five on flexibility, six on balance or coordination, 18 on V-dotO(2max), seven on BP, nine on lipids and two studies on glucose an one on insulin. Based on these studies, early postmenopausal women could benefit from 30 minutes of daily moderate walking in one to three bouts combined with a resistance training programme twice a week. For a sedentary person, walking is feasible and can be incorporated into everyday life. A feasible way to start resistance training is to perform eight to ten repetitions of eight to ten exercises for major muscle groups starting with 40% of one repetition maximum. Resistance training initially requires professional instruction, but can thereafter be performed at home with little or no equipment as an alternative for a gym with weight machines. Warm-up and cool-down with stretching should be a part of every exercise session. The training described above is likely to preserve normal bodyweight, or combined with a weight-reducing diet, preserve BMD and increase muscle strength. Based on limited evidence, such exercise might also improve flexibility, balance and coordination, decrease hypertension and improve dyslipidaemia.

Absorptiometry, Photon↗

Effects of muscle fiber distribution on the mechanical efficiency of human locomotion.

To study the effects of muscle fiber distribution (m. vastus lateralis) on the mechanical efficiency of human locomotion, 12 subjects were observed, six in the slow-twitch (ST) group (38.0% +/- 6.1% FT) and six in the fast-twitch (FT) group (63.8% +/- 5.9% FT). Pure positive, pure negative, and a combination of negative and positive work were performed with a special "sledge ergometer." The mechanical efficiency of the pure positive work (eta) was on the average 16.4% +/- 2.5% and 17.1% +/- 2.1% for the ST and FT groups, respectively. The mechanical efficiency of the pure negative work (eta -) was slightly greater in the ST group (94.0% +/- 30.2% vs 79.6% +/- 32.7%, P = NS). The mechanical efficiency of the positive work in the combined negative/positive work (eta +) was on the average in the ST group 36.4% +/- 5.9% and in the FT group 33.2% +/- 5.5% (t = 2.02, P less than 0.05). The eta + and the calculated elastic parameters (work due to elasticity Wel, utilization of the prestretch %El, and relative Wel) together with the EMG analysis demonstrated that the ST group had a better stiffness regulation and elastic performance. It is suggested that the basic differences in the reflex control between the two types of muscles and functional differences between the respective fiber types could be the possible reasons for the results observed under the conditions of the present slow-type stretch-shortening cycle exercises.

Adult↗

The effect of prolonged skeletal muscle stretch-shortening cycle on recoil of elastic energy and on energy expenditure.

The enhancement of performance in stretch-shortening exercises has been attributed to the recoil of elastic energy stored during the stretching phase. If the time between stretching and shortening (coupling time) is too long the stored elastic energy can be wasted. In the present study, coupling time was increased by asking ten male subjects to run on a treadmill at different speeds (2.2-5.2 m X s-1) using special soft shoes in addition to normal shoes. The results indicated that running with soft shoes required greater energy consumption than running with normal shoes except at slow speed (2.2 m X s-1). When the running speed was increased the extra energy consumed using soft shoes was parallelly enhanced (0.4 J X kg-1/step at 5.2 m X s-1). It was suggested that the effect of coupling time as limiting factor for recoil of elastic energy was relevant in fast twitch (FT) fibers, which were progressively recruited when the running speed was increased. This is consistent to the fact that cross-bridge life time in FT fibers is very short, and therefore more sensitive to coupling time. At slow running speed (2.2 m X s-1) only slow twitch (ST) fibers were recruited and the enhancement of coupling time was not long enough to provocate detachment of cross-bridges of ST fibers, which possess a long cross-bridge life time. It was concluded that the different recruitment of ST and FT fibers influenced the pattern of recoil of elastic energy which was dependent on the running speed.

Adult↗

Potassium and breathing in exercise.

The increase in ventilation caused by exercise is controlled by a combination of neural and chemical events, although the precise contribution and relative importance of these signals is still debated. It is generally agreed that the genesis of exercise hyperpnoea lies within the central nervous system and that peripheral reflexes, both chemical and neural, modulate central drive. Recently, attention has once again focused on the idea that circulating factors, in particular potassium, may play an important role in this modulation by stimulating known areas of peripheral chemoreception. Arterial chemoreceptors, muscle chemoreflex and slowly adapting pulmonary stretch receptors are all excited by hyperkalaemia. When potassium is raised to mimic exercise concentrations it increases ventilation in anaesthetised animals. This response is abolished by surgical denervation of the arterial chemoreceptors and is markedly reduced by chemical denervation with hyperoxia. Hypoxia enhances the ventilatory response to hyperkalaemia, and the stimulatory effects of potassium are further increased when combined with lactic acid or raised concentrations of noradrenaline. Hyperkalaemia can also increase the hypoxic sensitivity of the arterial chemoreflex in exercise. There is a close temporal relationship between potassium and ventilation during exercise, but changes in potassium are not proportionally related to changes in ventilation. When all data are taken together, there is good evidence that potassium has a supporting role in the control of exercise hyperpnoea, predominantly through modulation of the arterial chemoreflex.

Arteries↗

Application of combined botulinum toxin type A and modified constraint-induced movement therapy for an individual with chronic upper-extremity spasticity after stroke.

BACKGROUND AND PURPOSE: Constraint-induced movement therapy (CIMT) is a promising intervention for retraining upper-extremity function after a stroke. The purpose of this case report is to describe the use of a combination of botulinum toxin type A (BtxA) and a modified CIMT program for a patient with severe spasticity who was unable to use his right upper extremity. CASE DESCRIPTION: The 52-year-old patient, who had a stroke 4 years ago, did not meet the minimum motor criteria for CIMT benefit. After receiving BtxA injections targeting the elbow, wrist, and finger flexors, he completed a 4-week program of modified CIMT followed by a 5-month home exercise program. OUTCOMES: The patient exhibited improvement in muscle tone (the velocity-dependent resistance to stretch that muscle exhibits) and in scores on several upper-extremity function tests (Modified Ashworth Scale, Motor Activity Log, Wolf Motor Function Test, Action Research Arm Test, and Fugl-Meyer Assessment of Motor Recovery). He also reported making much progress in the functional use of the involved upper extremity. DISCUSSION: In a patient with severe flexor spasticity and nonuse of the dominant upper extremity after a stroke, a combined treatment of BtxA and modified CIMT may have resulted in improved upper-extremity use.

Botulinum Toxins, Type A↗

Influences of strength, stretching and circulatory exercises on flexibility parameters of the human hamstrings.

The purpose of this study was to compare the effect of resistance training, static and ballistic stretching and stationary cycling on the range of motion (ROM) and end ROM torque of hip joint flexion, resting tension of the hamstrings and stretch-induced electromyographic (EMG) activity of the hamstrings. Four separate experimental groups performed either 15 min resistance training of the hamstrings (n = 12), 15 min static stretching of the hamstrings (n = 14), 15 min ballistic stretching of the hamstrings (n = 16), or 15 min stationary cycling (n = 12). A control group (n = 15) remained resting for 15 min. ROM was increased after static and ballistic stretching and after stationary cycling. ROM remained unchanged in the resistance training group as well as in the control group. End ROM torque showed a significant increase after static and ballistic stretching. Static and ballistic stretching and stationary cycling decreased EMG activity significantly. Resting tension was decreased only after stationary cycling (p < 0.1). The constancy of the muscle resting tension suggests that merely the subjects' tolerance to higher stretching strain brings about the enlargement of ROM after short-term stretching exercises. The enlargement of ROM after stationary cycling could have been caused by the poor decrease of resting tension.

Adult↗

Effects of graded levels of exercise on ipsilateral and contralateral post-exercise resting rectus femoris mechanomyography.

Mechanomyography has shown that "resting" muscle is mechanically active, with greater activity after vigorous exercise. This experiment studied the post-exercise resting mechanomyography activity that results from different levels of exercise; the effects of exercise levels on the contralateral non-exercised limb; and the effects of resting muscle length on post-exercise resting mechanomyographic activity. Ten healthy volunteers had mechanomyography recordings over both mid-rectus femoris, at rest, before and after sets (1, 5, 10, 20, and 30 repetitions) of right leg extensions on an isokinetic dynamometer at 60 s(-1). Sets were performed a week apart, after only sedentary activity during the previous two hours. No definite threshold effect was shown. There was a linear correlation between mechanomyography and work done (R = 0.61, P < 0.01). There was a positive correlation of change of activity between the two thighs (R = 0.62, P < 0.01), with the non-exercised thigh demonstrating about half the activity of the exercised thigh. Finally, we observed that mechanomyographic activity was greater when rectus femoris muscle length was shorter (i.e. when the leg was extended versus flexed). We conclude that resting mechanomyography increases with increasing work and that there is a cross-over for increase in mechanomyography in the non-exercised leg, suggesting a neural mechanism. The greater mechanomyographic activity at shorter muscle lengths suggests that muscle that is less stretched could more freely oscillate, producing higher MMG amplitudes. Altered activity of the muscle spindle gamma loop or Golgi tendon apparatus may also play a role in altered activity with different muscle length.

Adult↗

Continuous low-level heat wrap therapy for the prevention and early phase treatment of delayed-onset muscle soreness of the low back: a randomized controlled trial.

OBJECTIVE: To evaluate the effects of continuous low-level heat wrap therapy for the prevention and early phase treatment (ie, 0-48 h postexercise) of delayed-onset muscle soreness (DOMS) of the low back. DESIGN: Two prospective randomized controlled trials. SETTING: Outpatient medical facility. PARTICIPANTS: Sixty-seven subjects asymptomatic of back pain and in good general health (mean age, 23.5+/-6.6 y). INTERVENTIONS: Participants performed vigorous eccentric exercise to experimentally induce low back DOMS. Participants were assigned to 1 of 2 substudies (prevention and treatment) and randomized to 1 of 2 treatment groups within each substudy: prevention study (heat wrap, n=17; control [nontarget muscle stretch], n=18) and treatment study (heat wrap, n=16; cold pack, n=16). Interventions were administered 4 hours before and 4 hours after exercise in the prevention study and between hours 18 to 42 postexercise in the treatment study. MAIN OUTCOME MEASURES: To coincide with the expected occurrence of peak symptoms related to exercise-induced low back DOMS, hour 24 postexercise was considered primary. Pain intensity (prevention) and pain relief (treatment) were primary measures, and self-reported physical function and disability were secondary measures. RESULTS: In the prevention study, at hour 24 postexercise, pain intensity, disability, and deficits in self-reported physical function in subjects with the heat wrap were reduced by 47% (P<.001), 52.3% (P=.029), and 45% (P=.013), respectively, compared with the control group. At hour 24 in the treatment study, postexercise, pain relief with the heat wrap was 138% greater (P=.026) than with the cold pack; there were no differences between the groups in changes in self-reported physical function and disability. CONCLUSIONS: In this small study, continuous low-level heat wrap therapy was of significant benefit in the prevention and early phase treatment of low back DOMS.

Adult↗