Changes in muscle recruitment patterns during skill acquisition

The control of movement is predicated upon a system of constraints of musculoskeletal and neural origin. The focus of the present study was upon the manner in which such constraints are adapted or superseded during the acquisition of motor skill. Individuals participated in five experimental sessions, ill which they attempted to produce abduction-adduction movements of the index finger in time with an auditory metronome. During each trial, the metronome frequency was increased in eight steps from an individually determined base frequency. Electromyographic (EMC) activity was recorded from first dorsal interosseous (FDI), first volar interosseous (FVI), flexor digitorum superficialis (FDS), and extensor digitorum communis (EDC) muscles. The movements produced on the final day of acquisition more accurately matched the required profile, and exhibited greater spatial and temporal stability, than those generated during initial performance. Tn the early stages of skill acquisition, an alternating pattern of activation in FDI and FVI was maintained, even at the highest frequencies. Tn contrast, as the frequency of movement was increased, activity in FDS and EDC was either tonic or intermittent. As learning proceeded, alterations in recruitment patterns were expressed primarily in the extrinsic muscles (EDC and FDS). These changes took the form of increases in the postural role of these muscles, shifts to phasic patterns of activation, or selective disengagement of these muscles. These findings suggest that there is considerable flexibility in the composition of muscle synergies, which is exploited by individuals during the acquisition of coordination.

Effects of vitamin E and alpha-lipoic acid on skeletal muscle contractile properties

Initial experiments were conducted using an in situ rat tibialis anterior (TA) muscle preparation to assess the influence of dietary antioxidants on muscle contractile properties. Adult Sprague-Dawley rats were divided into two dietary groups: 1) control diet (Con) and 2) supplemented with vitamin E (VE) and alpha -lipoic acid (alpha -LA) (Antiox). Antiox rats were fed the Con rats' diet (AIN-93M) with an additional 10,000 IU VE/kg diet and 1.65 g/kg alpha -LA. After an 8-wk feeding period, no differences existed (P > 0.05) between the two dietary groups in maximum specific tension before or after a fatigue protocol or in force production during the fatigue protocol. However, in unfatigued muscle, maximal twitch tension and tetanic force production at stimulation frequencies less than or equal to 40 Hz were less (P < 0.05) in Antiox animals compared with Con. To investigate which antioxidant was responsible for the depressed force production, a second experiment was conducted using an in vitro rat diaphragm preparation. Varying concentrations of VE and dihydrolipoic acid, the reduced form of -LA, were added either individually or in combination to baths containing diaphragm muscle strips. The results from these experiments indicate that high levels of VE depress skeletal muscle force production at low stimulation frequencies.

Smooth muscle cells of injured rat and rabbit arteries in culture: contractile and cytoskeletal proteins

The aim of this study is to determine whether subpopulations of smooth muscle cells (SMC). as distinguished by variations in contractile and cytoskeletal proteins, appear in the neointima at different times after vascular injury, and/or whether subpopulations develop during serial passaging of these cells. Rat aortae and rabbit carotid arteries were injured with a 2F Fogarty balloon catheter and cultures established from the resulting neointima and the media 2, 6, 12, 16 and 24 weeks later. Cultures were examined at passages 1-5 and subpopulations of SMC categorised by intensity of staining for each protein by immunohistochemistry. Two populations of SMC with different staining intensities ('+ +', '+') were observed for each of the following proteins: alpha -SM actin, SM-myosin, desmin and vimentin. Populations without these proteins were also found. Changes in the percentages of cells expressing these proteins were transitory, indicating that the populations were not limited to a particular tissue (neointima or media), time after injury or passage number. One exception was found in rabbit cultures where the number of desmin-expressing cells quickly decreased with both time after injury and time in culture. Subpopulations of SMC were found at all times after injury in the media and neointima of rat and rabbit arteries, and after multiple passage of these cells. There was no pattern of development of one population suggesting that either no subpopulation has a proliferative or migratory advantage over others, or that only one population exists: that is capable of diverse phenotypic changes. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.

Regulation of LIF receptor expression in vascular smooth muscle

Previous studies in our laboratory have shown that the pleiotropic cytokine leukemia inhibitory factor (LIF) inhibits neointimal formation and the development and progression of atherosclerotic and restenotic lesions in a rabbit model of disease. The present study demonstrates an upregulation of both the LIF receptor (LIFR)-α subunit and the signal transducing subunit gp130 following endothelial denudation of the carotid artery by balloon catheter. Continuous infusion of LIF (30 μg/kg/day) resulted in the downregulation of LIFR-a in injured arteries in vivo. Similarly, smooth muscle cells in vitro treated with LIF exhibited a time-dependent reduction in LIFR-a protein expression and the subsequent reduction in transcription of the TIMP-1 gene. However, in the presence of an intact endothelium, LIFR-a was upregulated in response to LIF, and accordingly the downstream induction of iNOS expression was also increased. Thus, LIF exerts more potent antiatherogenic effects in the vasculature when the endothelium is intact.

Short-term beta-hydroxy-beta-methylbutyrate supplementation does not reduce symptoms of eccentric muscle damage

Purpose: We examined the effects of short-term beta -hydroxy-beta -methylbutyrate (HIM) supplementation on symptoms of muscle damage following an acute bout of eccentric exercise. Methods: Non-resistance trained subjects were randomly assigned to a HMB supplement group (HMB, 40mg/kg bodyweight/day, n = 8) or placebo group (CON, n = 9). Supplementation commenced 6 days prior to a bout of 24 maximal isokinetic eccentric contractions of the elbow flexors and continued throughout post-testing. Muscle soreness, upper arm girth, and torque measures were assessed pre-exercise, 15 min post-exercise, and 1, 2, 3, 4, 7, and 10 days post-exercise. Results: No pre-test differences between HMB and CON groups were identified, and both performed a similar amount of eccentric work during the main eccentric exercise bout (p > .05). HMB supplementation had no effect on swelling, muscle soreness, or torque following the damaging eccentric exercise bout (p > .05). Conclusion: Compared to a placebo condition, short-term supplementation with 40mg/kg bodyweight/day of HMB had no beneficial effect on a range of symptoms associated with eccentric muscle damage. If HMB can produce an ergogenic response, a longer pre-exercise supplementation period may be necessary.

The influence of diet and exercise on muscle and plasma glutamine concentrations

Purpose: This study examined the relationship between muscle glutamine, muscle glycogen, and plasma glutamine concentrations over 3 d of high-intensity exercise during which dietary carbohydrate (CHO) intake varied. Methods: Five endurance-trained men completed two exercise trials in randomized order, over a 14-d period. Each trial required subjects to perform 50 min of high-intensity continuous and interval exercise on three consecutive days while consuming a diet that provided 45% of the energy as CHO or a diet in which CHO provided 70% of the total energy. Four days of inactivity and consumption of a 55% CHO diet separated the two randomized trials. Menus and food were provided for the subjects and all food and drink consumed were weighed and recorded for later analysis. Before exercise on the first day of each trial, at the start of exercise on day 3 and on completion of exercise on day 3, muscle was biopsied from the vastus lateralis for the analysis of glutamine and glycogen concentrations. Venous blood was sampled before and twice after exercise on each day for the analysis of plasma glutamine and cortisol concentrations. Results: Mean plasma glutamine concentration was significantly higher during the 70% CHO exercise trial when compared with the 45% CHO trial (P < 0.05). Glycogen decreased by the same magnitude during both trials and there was no relationship between changes in plasma glutamine and changes in muscle glycogen concentration. Muscle glutamine concentration did not change in either trial. Conclusions: These data suggest that the influence of carbohydrate intake upon the concentration of plasma glutamine is not mediated through the concentration of intramuscular glycogen.

Long-term metabolic and skeletal muscle adaptations to short-sprint training: Implications for sprint training and tapering

The adaptations of muscle to sprint training can be separated into metabolic and morphological changes. Enzyme adaptations represent a major metabolic adaptation to sprint training, with the enzymes of all three energy systems showing signs of adaptation to training and some evidence of a return to baseline levels with detraining. Myokinase and creatine phosphokinase have shown small increases as a result of short-sprint training in some studies and elite sprinters appear better able to rapidly breakdown phosphocreatine (PCr) than the sub-elite. No changes in these enzyme levels have been reported as a result of detraining. Similarly, glycolytic enzyme activity (notably lactate dehydrogenase, phosphofructokinase and glycogen phosphorylase) has been shown to increase after training consisting of either long (> 10-second) or short (< 10-second) sprints. Evidence suggests that these enzymes return to pre-training levels after somewhere between 7 weeks and 6 months of detraining. Mitochondrial enzyme activity also increases after sprint training, particularly when long sprints or short recovery between short sprints are used as the training stimulus. Morphological adaptations to sprint training include changes in muscle fibre type, sarcoplasmic reticulum, and fibre cross-sectional area. An appropriate sprint training programme could be expected to induce a shift toward type Ha muscle, increase muscle cross-sectional area and increase the sarcoplasmic reticulum volume to aid release of Ca2+. Training volume and/or frequency of sprint training in excess of what is optimal for an individual, however, will induce a shift toward slower muscle contractile characteristics. In contrast, detraining appears to shift the contractile characteristics towards type IIb, although muscle atrophy is also likely to occur. Muscle conduction velocity appears to be a potential non-invasive method of monitoring contractile changes in response to sprint training and detraining. In summary, adaptation to sprint training is clearly dependent on the duration of sprinting, recovery between repetitions, total volume and frequency of training bouts. These variables have profound effects on the metabolic, structural and performance adaptations from a sprint-training programme and these changes take a considerable period of time to return to baseline after a period of detraining. However, the complexity of the interaction between the aforementioned variables and training adaptation combined with individual differences is clearly disruptive to the transfer of knowledge and advice from laboratory to coach to athlete.

Reorganization of structural proteins in vascular smooth muscle cells grown in collagen gel and basement membrane matrices (Matrigel): A comparison with their in situ counterparts

When smooth muscle cells are enzyme-dispersed from tissues they lose their original filament architecture and extracellular matrix surrounds. They then reorganize their structural proteins to accommodate a 2-D growth environment when seeded onto culture dishes. The aim of the present study was to determine the expression and reorganization of the structural proteins in rabbit aortic smooth muscle cells seeded into 3-D collagen gel and Matrigel (a basement membrane matrix). It was shown that smooth muscle cells seeded in both gels gradually reorganize their structural proteins into an architecture similar to that of their in vivo counterparts. At the same time, a gradual decrease in levels of smooth muscle-specific contractile proteins (mainly smooth muscle myosin heavy chain-2) and an increase in p-nonmuscle actin occur, independent of both cell growth and extracellular matrix components. Thus, smooth muscle cells in 3-D extracellular matrix culture and in vivo have a similar filament architecture in which the contractile proteins such as actin, myosin, and alpha -actinin are organized into longitudinally arranged myofibrils and the vimentin-containing intermediate filaments form a meshed cytoskeletal network, However, the myofibrils reorganized in vitro contain less smooth muscle-specific and more nonmuscle contractile proteins. (C) 2001 Academic Press.

The effects of stress management on symptoms of upper respiratory tract infection, secretory immunoglobulin A, and mood in young adults

Objective: To investigate the efficacy of a stress management programme on symptoms of colds and influenza in 27 university students before and after the examination period. Method: The incidence of symptoms, levels of negative affect, and secretion rate of secretory immunoglobulin A (sIgA) were recorded for 5 weeks before treatment, for the 4 weeks of treatment, and for 8 weeks after treatment in treated subjects and in 25 others who did not participate in stress management. Results: Symptoms decreased in treated subjects but not in controls during and after the examination period. Although sIgA secretion rate increased significantly after individual sessions of relaxation, resting secretion rate of sIgA did not increase over the course of the study. Negative affect decreased after examinations in both groups, but was not affected by treatment. Conclusion: Stress management reduced days of illness independently of negative affect and sIgA secretion rate. Although the component of treatment responsible for this effect has yet to be identified, psychological interventions may have a role in reducing symptoms of upper respiratory tract infection. (C) 2001 Elsevier Science Inc. All rights reserved.

An investigation of symptom-specific muscle hyperreactivity in upper extremity cumulative trauma disorder

Objective: The study examined symptom-specific muscle hyperreactivity in patients with chronic pain with upper limb cumulative trauma disorder (CTD). Design: Four tasks were presented in counterbalanced order and included neutral, general stressor, personal stressor, and pain stressor tasks. Ratings of stressfulness and recordings of skin conductance level confirmed the effectiveness of the experimental manipulations in inducing stress experiences for all subject groups. Setting: The study was conducted in a university research center. Patients: Thirty patients with CTD were matched as closely as possible for age and gender to control groups of chronic low back pain, arthritis, and pain-Free subjects Outcome Measures: Surface electromyograph recordings were taken from the frontalis, forearm flexors, trapezius, and lower back during baseline and tasks. Results: The study found no evidence of greater muscle tension increases or extended duration of return to baseline for the CTD or low back pain patients at any of the muscle sites for any of the tasks in comparison to control groups. Conclusions: The results indicate that symptom-specific psychophysiological responses may be limited to certain subgroups rather than being characteristic of chronic musculoskeletal pain patients in general.

The use of perineal ultrasound to quantify levator activity and teach pelvic floor muscle exercises

Perineal ultrasound was used to detect and quantify levator activity by measuring the displacement of the internal urethral meatus against the inferoposterior margin of the symphysis pubis, Women who had previously been instructed in pelvic floor muscle exercises were more likely to contract the levator muscle when asked to do so than were those without previous instruction (P

Muscle strength and function before and after anterior cruciate ligament reconstruction using semitendonosus and gracilis

This study assessed the quadriceps and hamstring strength before and 6 months after anterior cruciate ligament (ACL) reconstructive surgery using the hamstrings and related the findings to functional performance. Six months after surgery is a critical time for assessment as this is when players are returning to sport. Maximum isokinetic strength of 31 patients with complete unilateral ACL ruptures was measured at speeds of 60 degrees and 120 degrees per second. Functional assessment included the single hop, the triple hop, the shuttle run, side-step and carioca tests. All patients underwent a controlled quadriceps emphasized home-based physiotherapy program both before and after surgery. Results show that before surgery there was a 7.3% quadriceps strength deficit at 60 degrees per second compared to the uninjured leg but no hamstring strength deficit. After surgery there was a statistically significant but relatively small loss of muscle strength. The quadriceps strength deficit had increased to 12% and there was a 10% hamstring deficit. Post-operatively there was an 11% and 6.3% improvement in the hop tests, a 9% (P < 0.01) improvement in the shuttle run, a 15% (P < 0.001) improvement in the side step and a 24% (P < 0.001) improvement in the carioca tests (P < 0.001) despite the loss of muscle strength. (C) 2001 Elsevier Science B.V. All rights reserved.