Muscle Exertion Research Articles

Sports performance: is there evidence that the body clock plays a role?

Athletic performance shows a time-of-day effect, possible causes for which are environmental factors (which can be removed in laboratory studies), the sleep-wake cycle and the internal "body clock". The evidence currently available does not enable the roles of these last two factors to be separated. Even so, results indicate that the body clock probably does play some role in generating rhythms in sports performance, and that to deny this is unduly critical. Protocols to assess the separate roles of the body clock and time awake are then outlined. A serious impediment to experimental work is muscle fatigue, when maximal or sustained muscle exertion is required. Dealing with this problem can involve unacceptably prolonged protocols but alternatives which stress dexterity and eye-hand co-ordination exist, and these are directly relevant to many sports (shooting, for example). The review concludes with suggestions regarding the future value to sports physiology of chronobiological studies.

Peripheral mechanism of muscle pain: An update

There are many conditions accompanied by muscle pain/hyperalgesia. Despite the large number of people who are suffering from musculoskeletal pain, understanding of its mechanism is quite limited. Many muscle pain conditions are considered to be somehow related to muscle exertion, in the presence or absence of muscle ischemia, therefore, this review introduces recent results obtained from delayed onset muscle soreness model by lengthening contraction (eccentric contraction), together with recent advances in muscle pain research with a focus on topics such as temporomandibular joint disorders and glutamate, nerve growth factor (NGF) and inflammatory pain, the role of protons and lactic acid in ischemic muscular pain, myofascial pain syndrome and trigger points, and fibromyalgia.

Haematological, biochemical and selected acute phase protein reference intervals for weaned female Merino lambs

Merino lambs are currently the subject of much research into the welfare aspects of mulesing and mulesing alternatives. Obtain haematology, biochemistry and acute phase protein reference intervals using modern methodologies for female Merino lambs. Blood was collected from 50, weaned, 9- to 16-week-old, female Merino lambs. Haematology and biochemistry panels were performed using routine automated methods. The acute phase proteins, fibrinogen, serum amyloid A and haptoglobin, were also measured using commercially available techniques. The reference intervals were determined to be the central 95% of results. Differences in the concentrations for some analytes were seen when compared with reported studies in sheep, but may be explained by the use of sheep of a different signalment, as well as different methodologies for analyte measurement. Overall, most analytes gave similar values to those previously reported in other studies. Notable exceptions were alkaline phosphatase, phosphate and globulins, for which the different results were often attributed to the younger age of the sheep in the present study, and platelets and creatine kinase, for which the elevated levels may have been a result of stress and muscle exertion associated with blood collection and husbandry practices. Established haematological, biochemical and acute phase protein reference intervals are necessary for the investigation of the systemic impact of mulesing and mulesing alternatives and for the investigation of systemic diseases affecting weaned, 9- to 16-week-old, female Merino lambs in general.

Poster 82: Rate of Change in Surface Electromyography Median Frequency to Measure Muscle Fatigue

Objective: Determine the rate of change of the median frequency (MF) of the surface electromyography (SEMG) of muscles that were isometrically contracted during a fatiguing effort. Design: SEMG data were recorded from 3 different muscles during a fatiguing isometric exercise from four subjects in 16 trials, ranging in duration from 20 to 60 seconds. Recoding parameters were a band pass of 20 to 450Hz with a sampling rate of 1000 samples per second. The MF of the SEMG Power Spectral Density (PSD) function was computed at 1-second intervals (from onset of muscle exertion) by means of computing the linear regression from the resulting MF time-series.

Effects of abdominal belts on the cross-sectional shape of the trunk during intense contraction of the trunk muscles observed by computer tomography

Background Several mechanisms of how abdominal belts affect the trunk have been postulated, but very little is known about how the belts affect the cross-sectional shape of the trunk during trunk muscle exertions. Methods To evaluate the effects of abdominal belts on the cross-sectional shape of the trunk during contraction of the trunk muscles, CT images at the third lumbar vertebra level of 20 healthy males (age: 23–45 years) under 8 different conditions (combinations of performing or not performing the Valsalva maneuver after full inhalation or at neutral respiratory state, while wearing or not wearing a 100-mm-wide abdominal belt) were evaluated. The cross-sectional shapes of the trunk seen on CT images taken at the level of the 3rd lumbar vertebra were compared using three-way ANOVA. Findings Wearing the belt decreased the cross-sectional area of the trunk, and wearing it while performing the Valsalva maneuver and during inhalation compressed the postero-lateral part of the trunk and made the trunk nearly round by increasing the ratio of the anterior–posterior width to the right–left width. Interpretation A wide belt cinched around the abdomen exerts external hoop tension on the trunk and stiffens the trunk. When the belt is worn during the Valsalva maneuver after deep inhalation, the posterolateral portion of the trunk is compressed and the trunk becomes circular.

Relation Between Ratings of Perceived Exertion and Skeletal Muscle Deoxygenation During Resistance Exercise

Relation Between Ratings of Perceived Exertion and Skeletal Muscle Deoxygenation During Resistance Exercise

Influence of muscular contractions on the stress analysis of distal femoral interlocking nailing

In the literature, the commonly assumed loading conditions on the proximal femur are hip compression and/or gluteus contractions. However, no study has discussed the influence of muscle forces on failure of distal nail holes and locking screws. This finite-element study analyzed the influence of muscular contractions on stress analysis of distal nail holes and locking screws. Three loading conditions were used for comparison, comprised of either hip compression alone or with muscle contractions. The head displacement of intact and fractured femur, the nail and screw stresses vs. fixation depth, and the stress distribution at the distal nail-screw interfaces were chosen as the comparison indices. The addition of trochanteric and diaphysial muscles showed the more physiologically reasonable displacement of the femoral head. However, all loading conditions consistently showed the hole and screw stresses increase as the nail was inserted deeper. The stress distribution at the distal nail-screw interfaces was remarkably different under the condition of with or without the muscular contractions. The exertion of muscles predicted the fatigue cracking originated at the edge of the nail holes on the medial rather than lateral side. Only hip compression and/or gluteus contraction generated a characteristic bending stress pattern and medially deflected nail curvature. Comparatively, the trochanteric and diaphysial muscles stabilized the femoral head and resulted in the higher stress concentration at the distally medial nail-screw interfaces. However, further experimental and clinical studies, focusing on the failure sites of the distal femoral hardware, should be undertaken to validate such findings.

Application of an Entropy-Assisted Optimization Model in Prediction of Agonist and Antagonist Muscle Forces

Many existing optimization based biomechanical models fail to predict antagonist muscle activity. Some optimization models predict such a cocontraction, but either lack a compelling physiological basis or are computationally formidable. The current study takes advantage of the flexible definition of entropy as a scientific measure, and utilizes it in the objective function of an optimization formulation to construct a new optimization model for predicting agonist and antagonist muscle forces. In this model, the objective function of a nonlinear program consists of a weighted sum of two components: a linear or nonlinear term favoring agonist muscle exertions (reciprocal inhibition), and the entropy term enforcing cocontraction. The concept of the current optimization model is based on recent findings in neurophysiology that there exist two separate central nervous systems for generation of two motor patterns: agonist contraction and agonist-antagonist cocontraction.

An in vivo assessment of the low back response to prolonged flexion: Interplay between active and passive tissues

Full flexion lumbar postures maintained over a prolonged period of time have been shown to lead to changes in the supporting passive structures of the spine and it has been hypothesized that this may lead to low back pain/disorders. However, the specific biomechanics and physiology of this link have not been fully developed. Of particular interest is the interplay between the active and passive extensor mechanisms and the role of rest break in this response. Ten healthy participants performed a regimen of a 10-min full lumbar flexion followed by a 10-min upright standing, with a slow speed isokinetic lift every 2.5min. Changes in the full lumbar flexion angle (system creep) and the electromyographic activity of back extensors in the isokinetic lifts were evaluated. Results showed significant increases in the full flexion angle and increased activity of the extensor muscles in the prolonged flexion to compensate for the reduced extension moment producing capability of the passive tissues. A 30-s rest break in the middle of the flexion moderated these viscoelastic responses. The results suggest that prolonged lumbar flexion results in the systematic transfer of an extension moment from passive tissues to active muscles. Heavy lifting or high force exertion of back muscles immediately after prolonged flexion could be a risk factor for low back disorders when the muscles lose their force generating capacity due to passive stretching. This study also indicated the importance of sufficient rest between consecutive full flexion tasks in reducing the risk.

Performance Enhanced Model in Snatch Weightlifting - Using the kinematic factors -

Y.J Moon Korea Institute of Sports Science; email: moonyj@sports.re.kr INTRODUCTION Weightlifting world record has been broken since weightlifting competition was started. Athletes do their best continually for a new record. In order to increase record, coach or sports researcher support them to enhance skill, physical strength or muscle force exertion and so on. For lower recorded athletes as junior athletes than world champion, we can make a training direction for skill, or physiques easily by compared with more nice recorders. But for world recorders, because they have the best skill and physical strength and muscle force exertion, Anybody don’t know What’s method in order to increase the their record. there is an endeavor to enhance present conditions and to have training more and more. Generally, it is hard to enchance physical strength and muscle exertion force for world recorder and elite athletes but skill is relatively easy to improve. If we can seek the optimal motion or skill, we can offer to make the training direction effectively. Birysiewicz(1981) reported the optimization method of weightlifting skill. Borysiewicz (1981) introduced optimization method in weightlifting and he insist that it can help for atheletes to learn skill. The purpose of this study was to develop the performance enhanced model in snatch weightlifting by using optimization method.

Reduced Finger and Wrist Flexor Activity During Propulsion With a New Flexible Handrim

Richter WM, Rodriguez R, Woods KR, Karpinski AP, Axelson PW. Reduced finger and wrist flexor activity during propulsion with a new flexible handrim. Objective To test the hypothesis that finger and wrist flexor activity is lower when pushing with a high-friction flexible handrim than with a standard uncoated handrim. Design Case series. Setting Biomechanics laboratory. Participants Twenty-four manual wheelchair users. Intervention Subjects pushed their own wheelchairs on a research treadmill set to level, 3°, and 6° grades using both a standard uncoated handrim and a high friction flexible handrim. Propulsion speed was self-selected and held constant between handrim trials. Handrim order was randomized. Finger and wrist flexor muscle activity was measured at the forearm using surface electromyography. Main Outcome Measures Electromyographic data were rectified and normalized by each subject’s maximum voluntary contraction. Total muscle exertion was determined by integrating the rectified signal over each push. Peak and total muscle exertion for each push were averaged across grade conditions and compared across handrims using a repeated measures t test. Results The flexible handrim resulted in statistically significant reductions in both peak and total forearm muscle activation. Averaging across all subjects and grade conditions, peak muscle activation was reduced by 11.8% ( P=.026) and overall muscle exertion was reduced by 14.5% ( P=.016). Conclusions The flexible handrim was shown to require less finger and wrist flexor activity than a standard uncoated handrim for the same propulsion conditions.

An evaluation of backpack harness systems in non-neutral torso postures

Much of the research on backpack design has been focused on spinal loading/biomechanics while the wearer is in a neutral/upright trunk posture, such as those employed by outdoor enthusiasts and schoolchildren. This research has led to some important harness design improvements that reduce trunk muscle exertions, fatigue and improve overall comfort. There are number of occupations, however, wherein workers wear back-mounted packs/devices (e.g. air tanks) while working in non-neutral trunk postures. The objective of the current study was to evaluate the effects of these non-neutral postures on biomechanical loading and then reconsider the backpack system design recommendations. Fifteen participants were asked to support a 18.2 kg load on their back while assuming static forward flexed postures of the torso (15°, 30°, 45°, and 60° of sagittal bend). The mass on the back was attached to the participant through two different harness mechanisms: a basic harness design (as seen on college student backpacks) and a more advanced design containing lateral stiffness rods and a weight-bearing hip belt (as seen on backpacks for hikers). While performing these static, posture maintenance tasks, the activation levels of the bilateral trapezius, erector spinae, and rectus abdominis were collected. Participants also provided subjective ratings of comfort. The results showed that there was a significant interaction between harness type and forward flexion angle for the trapezius and the erector spinae muscles. The normalized EMG for the trapezius muscles showed a 14% and 11% reduction in muscle activity at 15° and 30°, respectively, with the advanced design but these positive effects of the advanced design were not found at the greater flexion angles. Likewise the erector spinae muscles showed a 24% and 14% reduction in muscle activity at 15° and 30°, respectively, with the advanced design harness but these effects of the advanced design were not found at the greater forward flexion angles. The level of forward flexion angle affected the rectus abdominis muscle activity, but neither the harness type main effect nor the interaction of harness type and forward flexion angle was significant. The subjective survey results agreed with the EMG results and showed the advanced design harness was generally more comfortable with respect to the shoulder and low back areas. Collectively, the subjective and objective results show a significant improvement with the advanced harness system but also note an interesting interaction with degree of sagittal flexion, indicating a diminished effectiveness of the design improvements at forward flexed postures. Design criteria for harness systems in these forward flexed postures are discussed.

Designing ergonomic interventions for EMS workers, Part I: Transporting patients down the stairs

The objective of the current work was to test ergonomic interventions aimed at reducing the magnitude of trunk muscle exertions in firefighters/paramedics (FFPs) providing emergency medical services (EMS) when transporting patients down the stairs. The interventions, developed using focus groups, were a footstrap to prevent the patient from sliding down on the backboard, a change in the handle configuration on the stairchair, and 2 devices, the “backboard wheeler” and a tank tread-like device (descent control system, DCS) for a stretcher, that change the backboard and stretcher carrying tasks into rolling and sliding tasks. Eleven two-person teams transported a 75 kg dummy with each intervention and its corresponding control condition down a flight of steps. Surface electromyographic (EMG) data were collected from 8 trunk muscles from each participant. Results showed that the backboard footstrap reduced the erector spinae (ERS) activity for the FFP in the “leader” role by 15 percent, on average. The change in handle configuration on the stairchair had no effect on the variables measured. The backboard wheeler reduced the ERS activity bilaterally in the FFP in the leader role and unilaterally for the FFP in the “follower” role, by 28 and 24 percent, respectively. The DCS reduced the 90th percentile ERS activity for both FFPs from 26 to 16 percent MVC, but increased the latissimus dorsi activity in the follower from 11 to 15 percent MVC. The DCS was the only intervention tested that resulted in a reduced rating of perceived exertion relative to the corresponding control condition. In summary, the hypotheses that the proposed interventions could reduce trunk muscle loading were supported for 3 of the 4 transport interventions tested.

背筋力発揮時における咀嚼筋筋活動について

The lower jaw is considered to be fixed during body exercise. However, its mechanism remains to be elucidated. The present study investigated masticatory muscle activity during of the back. The subjects were 9 healthy dentulous patients. The maximum back strength of the patients was measured with a back-dynamometer. Muscle activities of the temporal, masseter and digastric muscles during exertion of the back and mastication of peanuts were measured. Muscle activities of the temporal and masseter muscle during maximum voluntary clenching and that of the digastric muscles during exertion of resistance against forced mouth opening were also measured, and maximum voluntary muscle activities were obtained. The relative percentage of each masticatory muscle against maximum voluntary activity was calculated from the data obtained, and muscle activities during exertion of the back, mastication of peanuts and maximum muscle activity were compared. Muscle activities of the temporal, masseter and digastric muscles during exertion of back muscles against maximum voluntary muscle activity were 32.1%, 26.4% and 97.4% respectively. Muscle activities of these muscles during mastication of peanuts against maximum voluntary muscle activity were 40.7%, 36.0% and 17.3% respectively. Muscle activities during exertion of the back were 30% in the temporal and masseter muscle, and approximately 100% in the digastric muscles. The result suggests that the digastric muscles play a key role in fixing the mandible in all masticatory muscles including jaw-opening and closing muscles. People exert back strength not only in sports but also in daily life. This study demonstrates the stronger involvement of the digastric muscles in fixation of the mandible during exercise than during strong clenching. The results are of interest in terms of mandibular position, occlusal contact and the load on the temporomandibular joint (TMJ) since there is no wide mouth opening.

Laboratory evaluation of belt usage with apple buckets

Migrant and seasonal orchard harvest workers experience musculoskeletal strain caused by carrying heavy loads and holding awkward postures. An ergonomic hip belt designed to redistribute weight from the upper back, neck, and shoulders to the hips was evaluated. A comparison of muscle exertion (using electromyography [EMG]) of four key back and shoulder muscles and shoulder surface pressure (using a surface pressure sensor [PS]) was made among 10 laboratory volunteers under intervention and control conditions, in two postures (standing erect [0 degrees ]) and flexed [45 degrees ]). All but one measure showed a significant reduction in the flexed posture with the intervention. Two of eight measures showed a significant reduction in the erect posture. Correlations with shoulder discomfort were found for deep shoulder EMG (r=0.71, P=0.021) and shoulder surface pressure (r=0.58, P=0.082). The hip belt intervention produces significant reductions in muscle activity while in a posture commonly assumed during orchard work.

Rhabdomyolysis from Simvastatin Triggered by Infection and Muscle Exertion

A 42-year-old woman received a 6-month course of simvastatin (20 mg/d) for hypercholesterolemia. Despite an infection with fever, fatigue, myalgias, and lumbar pain, she continued to perform her regular sports activities. Neurologic examination revealed bilateral ptosis and slight upper limb weakness. Serum creatine kinase was 41,000 U/L. Needle electromyography was nonspecifically abnormal. Discontinuation of simvastatin and reduction of the sports activities was followed by a prompt continual lowering of the elevated muscle enzymes to normal values over a 2-week period. The patient's infection, regular sports activity despite the infection, and a suspected mitochondrial defect were regarded as triggers of rhabdomyolysis.

Trunk muscle activity during bridging exercises on and off a Swissball

BackgroundA Swiss ball is often incorporated into trunk strengthening programs for injury rehabilitation and performance conditioning. It is often assumed that the use of a Swiss ball increases trunk muscle activity. The aim of this study was to determine whether the addition of a Swiss ball to trunk bridging exercises influences trunk muscle activity.MethodsSurface electrodes recorded the myoelectric activity of trunk muscles during bridging exercises. Bridging exercises were performed on the floor as well as on a labile surface (Swiss ball).Results and DiscussionDuring the prone bridge the addition of an exercise ball resulted in increased myoelectric activity in the rectus abdominis and external oblique. The internal oblique and erector spinae were not influenced. The addition of a swiss ball during supine bridging did not influence trunk muscle activity for any muscles studied.ConclusionThe addition of a Swiss ball is capable of influencing trunk muscle activity in the rectus abdominis and external oblique musculature during prone bridge exercises. Modifying common bridging exercises can influence the amount of trunk muscle activity, suggesting that exercise routines can be designed to maximize or minimize trunk muscle exertion depending on the needs of the exercise population.

強度を自己選択した運動中における骨格筋活動と強度認知との関係

When individuals select their own exercise intensity, the factors contributing to the perception of exercise intensity are important. In particular, it is not clear whether the activity of the skeletal muscles influences the self-selected (SS) intensity. Previous investigations have reported that effort sense increases in response to greater neuromotor activity as measured by electromyography (EMG) during dynamic exercise. The purpose of this study was to examine the effects of skeletal muscle activity on SS exercise intensity by investigating the relationship between the ratings of perceived exertion (RPE) and EMG response. Seven healthy men (mean±SD, 22.2±0.4 years) performed two 20-min sessions of cycling exercise with a protocol involving the SS method, which consisted of 5 min of fixed-load cycling at 70% of maximal oxygen uptake followed by 15 min of cycling with the SS method (SSFL_<70%>). RPE in the femoral region (RPE-peripheral: RPEp) was not correlated with the percentage peak wattage (% W_<peak>) and EMG indices in the femoral region during the SS protocol. While correlation coefficients between RPEp and EMG indices showed significantly negative values during the SSFL_<70%> protocol, there was no significant correlation between them during the SS protocol. These results during SSFL_<70%> suggested that the decrease of agonist muscle exertion and stress in the joint were caused by the increase in revolutions per minute during cycling. The increase in revolutions per minute during SSFL_<70%> appears to affect the decrease in the exertion of the agonist muscles and the stress in the joint and subsequent decline in RPEp. Since exercise intensity with the SS method is thought to be selected on the basis of cognitive feedback, these results suggest that tension of the skeletal muscle and agonist muscular exertion do not influence the perception of intensity during exercise with the SS method.

A computer-based system for the use of electromyographic methods for the measurement of physiological costs associated with operating hand-held tools and computer input devices

Electromyography enables the measurement of the intensity of muscle exertions which are demanded when working with hand-held tools and controls as well as when performing repetitive manual movements. Utilizing multi-channel recording devices, comprehensive physiological responses of working muscles can be quantified in figures and numbers, whereby more or less ergonomically designed tools lead to different physiological costs in terms of muscle strain associated with work. A computer-based system was developed for the suitable application of electromyography, a technique which requires differentiated and detailed knowledge of the possibilities and limitations as well as a substantial amount of experience. Software packages provide programs for the recording, analysis, and evaluation of myoelectric data. Knowledge about practical methods of appropriate recording and processing of myoelectric data which has been accumulated and further developed during the last decade has been fed into the program system. The same is true for a set of investigations already carried-out and published. Making use of the specifically developed and well-proven software packages which can be loaded into almost all PCs for recording, analyzing, and standardizing electromyographic data, even a user who until now is less familiar with these tasks gains access to electromyography as an efficient and important ergonomic method which is applicable with reasonable expenditure both in the laboratory and in the field.

Diurnal and oviposition‐related changes in heart rate, body temperature and locomotor activity of laying hens

ABSTRACTDiurnal and oviposition patterns of heart rate (HR), deep body temperature (BT) and locomotor activity (LA) in conscious and unrestrained Rhode Island Red hens were studied by a radiotelemetry system. Behavioral observations were also made on diurnal changes and during the pre‐ and post‐laying period. Heart rate, BT and LA showed characteristic diurnal changes synchronized with a photoperiod of 15 h light and 9 h dark. In the light period, HR, BT, and LA levels were significantly higher than in the dark period (P &lt; 0.001). Furthermore, the highest levels of these parameters were recorded just after they were fed (08.30 hours), while the lowest level was measured after lights‐off and remained stable throughout the dark period. Behavioral observations indicated that during the light period the hens spent most of their time in very active movement, exhibiting various behavioral patterns. However, in the dark period the hens spent almost all their time resting. The present results suggest that performing various behavioral activities cause heat generated by muscle exertion, which plays a significant role in daily HR, BT, and LA in laying hens. However, during the 60 min before and after oviposition, LA appeared to have increased steadily toward the moment of laying, and then regressed gradually in the post‐laying period to a level significantly lower than in the pre‐laying period (P &lt; 0.001). Furthermore, the pre‐laying behavior of hens indicated extreme restlessness and more activity, whereas the post‐laying period is characterized by less activity and increased relaxation. Consequently, laying behavior has a profound but transitory effect on HR and BT, suggesting that oviposition was probably associated with intense LA.