Effect of number of college baseball pitching on movement, performance, physical strength, physiological, and psychological functions of pitchers / 体力科学

This study aimed to examine the effects of college baseball pitching on movement, performance, physical strength, and physiological and psychological functions of pitchers. The participants were 10 right-handed male pitchers from the University baseball team. The number of pitches were 15 per inning and 135 per nine innings. Ball speed and accuracy were measured for each pitching. The grip strength, back muscle strength, and standing long jump were measured before and after all pitches. Blood lactate levels were measured before pitching, at the end of the 5th and 7th innings, and at 3rd, 6th, and 9th minutes after pitching. The participant’s heart rate and subjective exercise intensity were measured at the beginning and end of each inning using the Borg scale measurement. Five high-speed cameras were used to capture the pitching motions. The displacement of the center of gravity, lower and upper limb joint angles, and the speed of each segment were calculated. The baseball speed and accuracy did not change with the increased number of pitches. However, the grip strength decreased. Although blood lactate and heart rate were not altered, subjective exercise intensity was increased. The lower limb kinematics remained unchanged; however, elbow height was reduced in the upper limb. These results suggest that highly competitive pitchers experience subjective fatigue with the increased number of pitches, however, they maintain pitch performance, speed, and accuracy without altering whole-body physiology and lower-body function and form.

Efficacy of the wild-type/Omicron BA.1 bivalent vaccine as the second booster dose against Omicron BA.2 and BA.5

IntroductionIn addition to the original monovalent vaccines available for SARS-CoV-2, bivalent vaccines covering wild-type (WT) and Omicron BA.1 are also available. However, there is a lack of real-world data on the effectiveness of bivalent vaccines as second boosters on the dominant Omicron sublineages, including BA.2 and BA.5. MethodsThis prospective longitudinal cohort study was conducted at Toyama University Hospital, a tertiary medical center in Japan. Participants (n = 565) who received the first booster vaccination were followed up until 2 weeks after the second booster dose of the monovalent mRNA-1273 (WT group, n = 168) and bivalent BNT162b2 (WT+BA.1 group, n = 23) vaccines. Participants with previous SARS-CoV-2 infections were excluded from the study. Anti-receptor-binding domain (RBD) antibody levels and neutralizing activity were measured. Vaccine-related symptoms were also assessed using a questionnaire after the second booster dose. ResultsThe anti-RBD antibody levels after the second booster dose in the WT and WT+BA.1 group were similar (median [inter quartile], 26262.0 [16951.0-38137.0] U/mL vs. 24840.0 [14828.0-41460.0] U/mL, respectively). Although the neutralization activity of the pooled sera of the WT+BA.1 group was the lowest against BA.5, the activities against BA.2 and BA.5 were higher than those of the WT group in both pseudotyped and live virus assays. Vaccine-related symptoms, including systemic and local symptoms, were strongly correlated with anti-RBD antibody levels and neutralizing titers with significant differences. ConclusionThe second booster dose of the bivalent (WT/Omicron BA.1) vaccine induced higher neutralizing activity against BA.2 and BA.5 than that of the original monovalent vaccine.

A novel hamster model of SARS-CoV-2 respiratory infection using a pseudotyped virus

BackgroundSevere acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a biosafety level (BSL)-3 pathogen; therefore, its research environment is strictly limited. Pseudotyped viruses that mimic SARS-CoV-2 have been widely used for in vitro evaluation because they are available in BSL-2 containment laboratories; however, in vivo application is inadequate. Therefore, animal models that can be instigated with animal BSL-2 will increase opportunities for in vivo evaluations. MethodsHamsters (6-to 10-week-old males) were intratracheally inoculated with luciferase-expressing vesicular stomatitis virus (VSV)-based SARS-CoV-2 pseudotyped virus. The lungs were harvested 24 h after inoculation, and luminescence was measured using an in vivo imaging system. ResultsLung luminescence after inoculation with the SARS-CoV-2 pseudotyped virus increased in a dose-dependent manner. VSV-G (envelope [G]) pseudotyped virus also induced luminescence; however, a 100-fold concentration was required to reach a level similar to that of the SARS-CoV-2 pseudotyped virus. ConclusionsThe SARS-CoV-2 pseudotyped virus is applicable to SARS-CoV-2 respiratory infections in a hamster model. Because of the single-round infectious virus, the model can be used to study the steps from viral binding to entry, which will be useful for future research regarding SARS-CoV-2 entry without using live SARS-CoV-2 or transgenic animals.

Dynamics of neutralizing antibody responses in acute-phase COVID-19: A potential relationship between disease progression and rapid neutralizing antibody response

IntroductionAdaptive immunity to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) dynamics remain largely unknown. The neutralizing antibody (NAb) levels in patients with coronavirus disease 2019 (COVID-19) are helpful for understanding the pathology. Patients and MethodsUsing SARS-CoV-2 pseudotyped virus, serum sample neutralization values in symptomatic COVID-19 patients were measured using the chemiluminescence reduction neutralization test (CRNT). At least two sequential serum samples collected during hospitalization were analyzed to assess NAbs neutralizing activity dynamics at different time points. ResultsOf the 11 patients, four (36.4%), six (54.5%), and one (9.1%) had moderate, severe, and critical disease, respectively. Fifty percent neutralization (N50%-CRNT) was observed upon admission in 90.9% (10/11); all patients acquired neutralizing activity 2-12 days after onset. In patients with moderate disease, neutralization was observed at earliest within two days after symptom onset. In patients with severe-to-critical disease, neutralization activity increased, plateauing 9-16 days after onset. Neutralization activity on admission was significantly higher in patients with moderate disease than in patients with severe-to-critical disease (relative % of infectivity, 6.4% vs. 41.1%; P=.0011). ConclusionsNeutralization activity on admission inversely correlated with disease severity. The rapid NAb response may play a crucial role in preventing the progression of COVID-19.

SARS-CoV-2 RNAemia with higher nasopharyngeal viral load is strongly associated with severity and mortality in patients with COVID-19

ObjectiveThis study aimed to determine the frequency of SARS-CoV-2 RNA in serum and its association with the clinical severity of COVID-19. MethodsAn analytical cross-sectional study was performed in a single tertiary care hospital and included consecutive patients with confirmed COVID-19. The prevalence of SARS-CoV-2 RNAemia and the strength of its association with clinical severity variables, including required oxygen supplementation, ICU admission, invasive mechanical ventilation, and in-hospital mortality, were examined. ResultsFifty-six patients were included in the study. The median age was 54.5 years, and individuals with RNAemia were older than those without detectable SARS-CoV-2 RNA in serum (78 vs. 50 years; P = .0013). RNAemia was detected in 19.6% of patients (11/56) and in 1.0% (1/25), 50.0% (6/12), and 100.0% (4/4) of moderate, severe, and critically ill cases, respectively. Patients with RNAemia required more frequent oxygen supplementation (90.0% vs. 13.3%; P < .0001) and ICU admission (81.8% vs. 6.7%; P < .0001) and required invasive mechanical ventilation (27.3% vs. 0.0%; P < .0001). Among patients with RNAemia, the median viral loads of NP swabs that were collected around the same time as the serum were significantly higher in critically ill cases (5.4 Log10 copies/L [IQR: 4.2-6.3]) than in moderate-severe cases (2.6 Log10 copies/L [1.1-4.5]; P =.030) and were significantly higher in nonsurvivor cases (6.2 Log10 copies/L [IQR: 6.0-6.5]) than in survivor cases (3.9 Log10 copies/L [1.6-4.6]; P =.045). ConclusionsThis study demonstrated a relatively high proportion of SARS-CoV-2 RNAemia and an association between RNAemia and clinical severity. Moreover, among the patients with RNAemia, the viral loads of NP swabs were correlated with severity and mortality, thus suggesting the potential utility of combining serum testing with NP tests as a prognostic indicator for COVID-19 with a higher quality than each separate test.

Evaluation of SARS-CoV-2 neutralizing antibodies using a vesicular stomatitis virus possessing SARS-CoV-2 spike protein

SARS-CoV-2 is a novel coronavirus that emerged in 2019 and is now classified in the genus Coronavirus with closely related SARS-CoV. SARS-CoV-2 is highly pathogenic in humans and is classified as a biosafety level (BSL)-3 pathogen, which makes manipulating it relatively difficult due to its infectious nature. To circumvent the need for BSL-3 laboratories, an alternative assay was developed that avoids live virus and instead uses a recombinant VSV expressing luciferase and possesses the full length or truncated spike proteins of SARS-CoV-2. Furthermore, to measure SARS-CoV-2 neutralizing antibodies under BSL2 conditions, a chemiluminescence reduction neutralization test (CRNT) for SARS-CoV-2 was developed. The neutralization values of the serum samples collected from hospitalized patients with COVID-19 or SARS-CoV-2 PCR-negative donors against the pseudotyped virus infection evaluated by the CRNT were compared with antibody titers determined from an immunofluorescence assay (IFA). The CRNT, which used whole blood collected from hospitalized patients with COVID-19, was also examined. As a result, the inhibition of pseudotyped virus infection was specifically observed in both serum and whole blood and was also correlated with the results of the IFA. In conclusion, the CRNT for COVID-19 is a convenient assay system that can be performed in a BSL-2 laboratory with high specificity and sensitivity for evaluating the occurrence of neutralizing antibodies against SARS-CoV-2.

Viral load dynamics in transmissible symptomatic patients with COVID-19

To investigate the relationship between viral load and secondary transmission in novel coronavirus disease 2019 (COVID-19), we reviewed epidemiological and clinical data obtained from immunocompetent laboratory-confirmed patients with COVID-19 at Toyama University Hospital. In total, 28 patients were included in the analysis. Median viral load at the initial sample collection was significantly higher in adults than in children and in symptomatic than in asymptomatic patients. Among symptomatic patients, non-linear regression models showed that the estimated viral load at onset was higher in the index (patients who transmitted the disease to at least one other patient) than in the non-index patients (patients who were not the cause of secondary transmission; median [95% confidence interval]: 6.6 [5.2-8.2] vs. 3.1 [1.5-4.8] log copies/L, respectively). High nasopharyngeal viral loads around onset may contribute to secondary transmission of COVID-19. Article Summary LineHigh nasopharyngeal viral load around the onset may contributes to secondary transmission of COVID-19.

Local Sagittal Alignment of the Lumbar Spine and Range of Motion in 627 Asymptomatic Subjects: Age-Related Changes and Sex-Based Differences

STUDY DESIGN: Prospective cohort imaging study. PURPOSE: This study aimed to evaluate lumbar sagittal alignment and range of motion (ROM) using radiographs in a large asymptomatic cohort and identify sex-based differences and age-related changes in the subjects. OVERVIEW OF LITERATURE: Several researchers have tried to establish normal alignment and kinematic behavior of the lumbar spine, using plain radiographs. Few studies have employed a large and sex-and age-balanced cohort. METHODS: Total 627 healthy volunteers (at least 50 males and 50 females in each age decade, from the 3rd to the 8th decade) underwent whole spine radiography in the standing position; lumbar spine radiography was performed for all subjects in the recumbent position. Lumbar lordosis (LL, T12–S1) and ROM during flexion and extension were measured using a computer digitizer. RESULTS: The mean LL was 36.8°±13.2° in the recumbent position and 49.8°±11.2° in the standing position. The LL was greater in the standing position than in the recumbent position; further, LL was higher in females as compared to that in males. Local lordosis at each disk level increased incrementally with distal progression through the lumbar spine in both the positions. Local lordosis at L4–S1 was 29.8°±8.0° in the recumbent position and 34.2°±8.3° in the standing position and occupied 85.1% and 70.8% of the total LL, respectively. However, local lordosis in the standing position decreased with age at L2–3, L3–4, and L4–5 levels. Total lumbar ROM (T12–S1) decreased with age. The ROM in females was higher than that in males. CONCLUSIONS: We established the standard value and age-related changes in the lumbar alignment and ROM in each age decade in asymptomatic subjects. These data will be useful and provide the normal values for comparison in clinical practice to identify sex-based differences and age-related changes.

Regional Differences in the Safety of Telaprevir-Based Triple Therapy for Chronic Hepatitis C in Japan: / 医薬品情報学

Objective:The objectives were to assess regional differences in the safety outcomes of telaprevir-based triple therapy(T/PR) in Japan and evaluate a suitable generalized linear mixed model for estimating regional differences.Design and Methods:This study targeted individuals infected with genotype 1 chronic hepatitis C virus registered in a nationwide Japanese interferon database from December 2009 to August 2015. The rate of dropout from treatmentattributable to adverse events was calculated in every prefecture where ≥ 20 cases were reported. We constructed the following four models and evaluated the best-fit model based on Akaike information criterion (AIC) and Bayesian information criterion (BIC):1)prefecture as a fixed-effect,2)prefecture and identified confounding factors as fixed-effects,3)prefecture as a random-effect,and 4)prefecture as a random-effect and identified confounding factors as fixed-effects.Results:A total of 25,989 individuals from 38 prefectures were registered during the study period;among them,1,591 from18 prefectures were included as the study population. The dropout rate ranged from 7.0 to 23.1%among 17 prefectures.The model considering prefecture as a random-effect and confounding factors as fixed-effects showed the best-fit for the databased on both the AIC (1,108.06)and BIC (1,113.41).Conclusion:It is difficult to determine if regional differences exist in the safety outcomes of T/PR in Japan because of the limited number of cases. However, the model using prefecture as a random-effect and other confounding factors as fixed-effects would be suitable for estimating parameters that reflect the influence of the prefecture. Further studies using the model would help inform chronic hepatitis C treatment.

Reliability of the Evaluation Methods Used to Assess a Causal Relationship between Dietary Supplement Intake and Changes in Adverse Events / 医薬品情報学

<b>Objective: </b>This study aimed to confirm whether the methods for assessing the reported causal relationship between dietary supplement intake and adverse events are reliable in the clinical setting.<br><b>Design: </b>The relationships between supplement intake and adverse events were assessed using two algorithms proposed in our previous report, and causal relationships were evaluated.<br><b>Methods: </b>Twelve raters with a high probability of handling adverse event information examined 200 records of dialogues with supplement users.  Each rater independently assessed the causal relationship using the two algorithms.  The relationships between supplement intake and adverse events were assessed for all 200 cases.  Variability in the evaluation among raters was analyzed for each occupation and the whole group of raters.  The distributions of evaluation were analyzed, and inter-rater reliability was evaluated using the intraclass correlation coefficient (ICC) and Fleiss’ kappa coefficient.<br><b>Results: </b>All events of 200 cases seemed to be slight and within the range of variation in daily life.  Almost all cases were classified into two categories as “Possible” and “Lack of Information” by each rater.  The ICC values for all raters, pharmacists, dieticians, and health care workers were 0.644, 0.573, 0.678, and 0.694, respectively, and the kappa coefficients using the two algorithms were 0.466, 0.426, 0.468, and 0.519 and 0.481, 0.478, 0.465, and 0.517, respectively.  There were moderate levels of agreement based on the kappa coefficients and ICC values.<br><b>Conclusion: </b>The two algorithms proposed in our previous report may be reliable in the clinical setting.  Their reliability could be enhanced by establishing a unified method of accumulation and recording adverse events for supplement intake, which should be evaluated by more raters using more cases of adverse events.

Submission Rates of Medication Notebooks in Insurance Pharmacies / 医薬品情報学

<b>Objective: </b>To reveal the current use of medication notebooks in clinical practice and the differences in submission rates of medication notebooks among patients with different sociodemographic and medical characteristics.<br><b>Methods: </b>We conducted a survey of the submission rates by studying the medication history, from June 19, 2014, to July 3, 2014.<br><b>Results: </b>The overall submission rate of returning patients was 57.1% and the submission rate of patients who visit a single medical institution was significantly lower than patients who visit more than two (55.4% vs. 67.7%, <i>p</i><0.001).  Multivariate logistic regression also indicated significant differences between the single and multiple medical institution visit group (adjusted OR=2.74 [95% CI: 1.93-3.89], <i>p</i><0.001).  Submission rates for patients in their 20, 30, and 50 s who visit a single medical institution were lower than 40%.<br><b>Conclusions: </b>To improve the usefulness of the community pharmacy and increase the submission rate, we need to increase awareness of the importance of medication notebooks among patients who visit a single medical institution.  Additionally, future studies need to focus on factors such as age-related issues that might affect submission rates.

A New Electrophysiological Method for the Diagnosis of Extraforaminal Stenosis at L5-S1

STUDY DESIGN: A retrospective study. PURPOSE: To examine the effectiveness of using an electrodiagnostic technique as a new approach in the clinical diagnosis of extraforaminal stenosis at L5-S1. OVERVIEW OF LITERATURE: We introduced a new effective approach to the diagnosis of extraforaminal stenosis at the lumbosacral junction using the existing electrophysiological evaluation technique. METHODS: A consecutive series of 124 patients with fifth lumbar radiculopathy were enrolled, comprising a group of 74 patients with spinal canal stenosis and a second group of 50 patients with extraforaminal stenosis at L5-S1. The technique involved inserting a pair of needle electrodes into the foraminal exit zone of the fifth lumbar spinal nerves, which were used to provide electrical stimulation. The compound muscle action potentials from each of the tibialis anterior muscles were recorded. RESULTS: The distal motor latency (DML) of the potentials ranged from 11.2 to 24.6 milliseconds in patients with extraforaminal stenosis. In contrast, the DML in patients with spinal canal stenosis ranged from 10.0 to 17.2 milliseconds. After comparing the DML of each of the 2 groups and at the same time comparing the differences in DML between the affected and unaffected side of each patient, we concluded there were statistically significant differences (p<0.01) between the 2 groups. Using receiver operating characteristic curve analysis, the cutoff values were calculated to be 15.2 milliseconds and 1.1 milliseconds, respectively. CONCLUSIONS: This approach using a means of DML measurement enables us to identify and localize lesions, which offers an advantage in diagnosing extraforaminal stenosis at L5-S1.

A Case Report of Left Ventricular Myxoma and a Review of Literatures / 日本心臓血管外科学会雑誌

A 61-year-old woman underwent a regular echocardiography in October 2008 in which a mass of 1 cm in diameter was pointed out in the left ventricle apex. It did not dcrease, in spite of anticoagulation therapy, and therefore we performed surgery. The tumor was confirmed on the septal side of the cardiac apex by intraoperative cholangioscopy, and it was excised through the mitral valve. It was diagnosed as myxoma on immediate intraoperative pathological examination, and we confirmed that there was no tumor remnants on the resected stump histologically. The patient was discharged on the 13th day after the operation and 2 years later she was alive without recurrence of the tumor. This is the 25th case of left ventricular myxoma in Japan. In these reports, an initial resection of the tumor in the left ventricle was performed in 23 cases and the approach methods were described in 20 cases. The evaluation of the resected stump, regardless of remaining tumor, was described in only 3 cases. There were no reports of relapse after the operation. There are many reports which emphasize the usefulness of echocardiography, which is very helpful not only in the diagnosis, but also in periodic evaluations after the operation.

A Case of Tricuspid Valve Repair with Artificial Chordae after Resection of Tricuspid Valve Myxoma / 日本心臓血管外科学会雑誌

A 76-year-old-woman, who had undergone endoscopic resection of a gastric polyp 2 years previously, had a cardiac tumor incidentaly pointed out on an abdominal ultrasonographic image. Echocardiography showed a solid round mass (34×25 mm in diameter), attached by a short stalk and which was floating on the right ventricular outflow tract and prolapsing over the pulmonary valve during systole. We suspected right ventricular myxoma. Urgent surgery was performed under cardiopulmonary bypass. After aortic clamping, the trunk of the pulmonary artery was opened near the right ventricule. The tumor was found under the pulmonary valve, attached to the anterior papillary muscle and chordae of the tricuspid valve. The tumor was completely excised with a piece of the papillary muscle and chordae. After right atriotomy, mild tricuspid regurgitation was seen on a water test. After we performed tricuspid annuloplasty and chordplasty with artificial chordae, a second water test did not show any tricuspid regurgitation. The postoperative course was uneventful, and she was discharged on the 13th postoperative day.

CAUSAL EFFECT OF STRENGTH TO WALKING ABILITY DEVELOPMENT BY EXERCISE PARTICIPATION OF ELDERLY PEOPLE IN A COMMUNITY / 体力科学

The purpose of this study was to confirm the causal effect model of strength on walking ability development as a result of exercise participation among elderly people in a community, utilizing the latent curve model (LCM) in structural equation modeling (SEM) . Twenty-six male and 57 female subjects, 83 in total, aged 67.8±5.7, 63.9±7.1 and 65.1±6.9 in a pooled sample participated in the exercise program which lasted for two years. Grip strength and sit-ups used in the Japan Fitness Test were measured for muscular strength, 10-m hurdle walk and 6-min walk for walking ability, and the fitness test score for physical ability. The data analysis procedures were as follows : a) analysis of test-retest reliability and construct validity of measurement items, b) analysis of causal structure model of aging, muscular strength and walking ability, c) analysis of variance for repeated measurement of walking performance by sex, age and year, d) analysis of LCM for walking performance development. The highest goodness-of-fit indices of SEM were obtained in the LCM of 10-m hurdle walk performance development (GFI=0.989, AGFI=0.920, CFI=0.998, RMSEA=0.038) . The path coefficient of sit-ups at pre-test effect on the intercept of 10-m hurdle walk performance development was significant (<I>p</I><0.05) . The path coefficients of age to intercept and slope of 10-m hurdle walk development were also significant (<I>p</I><0.05) . It was concluded that walking ability development through participation in exercise age and strength level was more effective for maintaining walking ability in older age.

RELIBILITY AND VALIDITY OF PHYSICAL FITNESS QUESTIONNAIRE WITH SELF-RATING FOR ELDERLY PEOPLE / 体力科学

The purpose of this study was to confirm the reliability and validity of a physical fitness questionnaire (PFQ) with self-rating for elderly people applying structural equation modeling (SEM) . As subjects, 105 community-dwelling older men and women aged 67.1±6.1 years participated in the study to measure 13 PFQ items and 13 performance tests. The data analysis procedures were as follows : a) testing reliability of PFQ ; b) testing of construct validity of PFQ using exploratory factor analysis (EFA) and confirmatory factor analysis (CFA) ; c) testing of criterion-related validity of PFQ to the performance tests using SEM ; d) testing of correlations of the PFQ to walking ability using SEM. Cronbaeh's alpha coefficient for consistency reliability of the PFQ was .83. Four common factors of muscle strength-power, endurance, coordination, and flexibility were extracted in EFA. The high and enough goodness of fit indices were obtained in the confirmatory factor structure model, and in each sub-domain of criterion-related validity to performance tests and correlation to walking ability models. The criterion-related validity coefficient of muscle strength and power was .77, followed by .66 for endurance, .59 for coordination and .82 for flexibility. The correlation coefficient of muscle strength and power to walking ability was -.51, followed by -.58 for coordination, - .43 for endurance and - . 28 for flexibility. These results indicated that the PFQ consisting of 13 items and 4 sub-domains satisfied reliability and construct validity although criterion related validity to performance tests was insufficient. It was concluded that the PFQ is of useful for physical fitness checking of elderly people.

CAUSAL STRUCTURE BETWEEN MUSCLE, MOTOR AND LIVING FUNCTIONS IN COMMUNITY DWELLING ELDERS / 体力科学

The purpose of this study was to confirm the causal structure model of muscle, motor and living functions utilizing structural equation modeling (SEM) . As subjects, 103 community-dwelling older men and women, aged 65.7±6.9years of age, participated in the study to measure muscle cross-sectional area, maximum voluntary contractions, muscle power, 4 physical performance tests, and 16 questionnaires regarding ability of activities of daily living. The causal structure model of muscle, motor and living functions was hypothesized to be a hierarchical causal structure. The causal structure model of muscle function was hypothesized to be a hierarchical causal structure consisting of 3 sub-domains of muscle mass, muscle strength, and muscle power. Data analysis procedures were as follows : a) testing of construct validity of muscle function variables using confirmatory factor analysis (CFA) in SEM ; b) testing of causal structure using SEM ; c) testing of factor invariance using multi-group analysis for gender. The highest goodness of fit indices was obtained in the causal structure model of muscle, motor and living functions (NFI= .928, CFI= .978, RMSEA =.061) . The causal coefficient of muscle function to motor function was .98 (<I>p</I><.05), followed by.34 for motor function to living function. From the results of multi-group analysis, the measurement invariance model indicated the highest goodness of fit indices (TLI=.968, CFI .977) . It was concluded that the hierarchical causal relation was among muscle, motor and living functions, and in which muscle function was consisted of 3 sub-domains.

FATIGABILITY OF MOTOR UNITS IN FIRST DORSAL INTEROSSEUS MUSCLE EVALUATED USING COLLISION METHOD / 体力科学

We evaluated motor unit (MU) fatigue in the first dorsal interosseous muscle (FDI) using the collision principle. Eight healthy men exerted 70% (short-duration fatigue task: SDF task) and 30% (long-duration fatigue task: LDF task) maximum voluntary contraction of isometric abductions in the left FDI until exhausted. Before and after voluntary contractions, the ulnar nerve was stimulated at the wrist and elbow with supramaximal intensity, and a pair of M-waves was obtained. Fatiguerelated changes were studied in mean power frequency (MPF), averaged rectified value (ARV) calculated from surface EMG, and motor nerve conduction velocity (MCV) and distribution of motor nerve conduction velocity (DMCV) calculated from M-waves. The MPF of voluntary EMG decreased, whereas ARV increased significantly during SDF and LDF tasks, indicating fatigue had developed in the FDI. Endurance was significantly shorter in the SDF task than in the LDF task (p<0.01), whereas differences between tasks were not seen in MPF and ARV changes. Tasks did not affect MCV, but lower components in DMCV increased for both tasks. Increased lower components were larger in the LDF task than in the SDF task. The shift in DMCV indicated that fatigued MUs stopped activity and enduring MUs, which had lower axon conduction velocity, were activated selectively. These results suggest that the collision principle is applicable in evaluating motor unit fatigability.

Effects of Short-Term Immobilization on the Maximum Voluntary Contraction Force Analyzed by the Twitch Interpolation Method / 体力科学

The purpose of this study was to examine the effects of short-term immobilization on the maximum voluntary contraction (MVC) force. The first dorsal interosseus (FDI) of 10 healthy male adults was immobilized for 1 week using casting tape. Atrophy of the muscle was estimated from a cross sectional view of magnetic resonance images (MRI) . To clarify the factors of a peripheral neuromuscular system contributing to the change in the MVC force, twitch force at rest was measured. The contribution of central factors was estimated from a voluntary activation (VA) index, which was obtained by the twitch interpolation method.<BR>The MRI showed no significant changes in the cross sectional area. The MVC force declined after immobilization (p<0.01), and recovered after 1 week from the termination of immobilization (p<0.01) . Both the twitch force at rest and the VA at MVC declined after immobilization (p<0.01), and recovered after 1 week (p<0.05) .<BR>The results indicate that the temporary decline of the MVC force was not accompanied by atrophy of the muscle. Furthermore the decline of the MVC was caused both by the deterioration of peripheral and central functions in the neuromuscular system. Possible factors in the peripheral and central neuromuscular systems affected by the immobilization were discussed.

Mechanism for Slowing Surface Electromyography During Fatiguing Contraction Revealed by Superimposed M-Wave Analysis / 体力科学

We studied the mechanism for slowing surface electromyography (EMG) during fatiguing contraction using superimposed M-wave analysis. Seven healthy male subjects exerted 60% maximum voluntary contraction of isometric abductions in the left first dorsal interosseous muscle (FDI) until exhaustion. Simultaneously with voluntary contractions, the ulnar nerve was electrically stimulated at supramaximal intensity, and volitional EMG and superimposed M-waves were obtained. We examined the behavior of muscle fiber conduction velocity (MFCV) and median frequency (MDF) for both EMG, with the following results:<BR>1) MFCV calculated from volitional EMG of FDI was about 6 m/s during 60% MVC.<BR>2) The waveform of voluntary EMG detected from FDI slowed in all subjects during fatiguing contraction at 60% MVC, indicating fatigue had developed in the muscle.<BR>3) As fatigue progressed, the waveform of the superimposed M-wave tended to decrease in amplitude and increase in duration.<BR>4) As fatigue progressed, MDF and MFCV in volitional EMG decreased significantly (p<0.04) . The rate of change was larger in MDF than in MFCV (p<0.01) .<BR>5) As fatigue progressed, MDF and MFCV in the superimposed M-wave decreased significantly (p<0.01) . The rate of change was larger in NIDF than in MFCV (p<0.05) .<BR>These results suggested that MFCV and other peripheral factors affected the slowing of volitional EMG. Elongation of the depolarization zone in muscle fiber is proposed as a peripheral factor.