Detrended fluctuation analysis detects altered coordination of running gait in athletes following a heavy period of training

Objectives

To investigate whether functional overreaching affects locomotor system behaviour when running at fixed relative intensities and if any effects were associated with changes in running performance.

Chronic fatigue of the small enterprise workers participating in an occupational health checkup center in southern Taiwan

Purpose  There has been increasing interest in the occupational health of workers in small enterprises, especially in developing countries. This study examines the association between psychosocial job characteristics and fatigue, and attempts to identify risk factors for fatigue among workers of small enterprises in southern Taiwan. Methods  A structured questionnaire was administered to workers receiving regular health examinations between August 2005 and January 2006. The questionnaire collected demographic information and data on working conditions, personal health status and life styles. It also collected information on psychosocial job characteristics, fatigue and psychological distress using three instruments. Results  A total of 647 workers with mean age of 43.7 were completed. Probable fatigue was found in 34.6% of the sample. Fatigue was found by multiple logistic regressions to be associated with the lack of exercise, working in shifts, depression score and lack of social support at workplace. Conclusions  This study found associations between life style, psychosocial job characteristics and fatigue. Because the high prevalence of probable fatigue was found in such small enterprises, the authors suggest that a short interview with some quick questionnaires in health checkup for these small enterprise workers are helpful to early detect psychosocial and fatigue problems.     

薄壁构件的高温低周疲劳寿命的预测与验证

提出了文题的计算模型,它采用非线性弹塑性蠕变有限元法,计算构件危险点在高温及周期保载的交变载荷谱作用下的应力应变响应,以应变范围区分法累积损伤,从而求出构件的疲劳寿命,并以带孔矩形薄板为例作了计算与验证,结果吻合较好,可供工程应用。     

Fatigue in multiple sclerosis is not due to sleep apnoea

Fatigue is a frequent and disabling phenomenon among patients with multiple sclerosis (MS). Daytime sleepiness is a typical symptom of the sleep apnoea/hypopnoea syndrome due to nocturnal hypoxia and recurrent arousals causing sleep fragmentation. Since MS plaques are often found in the midbrain, brain stem and upper cervical cord on magnetic resonance imaging (MRI) we hypothesized that fatigue in MS patients might be caused by a central respiratory dysfunction. We investigated 10 patients with definite MS by oligography, two questionnaires assessing fatigue (Fatigue Severity Scale, FSS) and daytime sleepiness (Epworth Sleepiness Scale, ESS), MRI and pulmonary function tests. A total of six patients had either an elevated FSS and/or an elevated ESS. None of the six patients with an elevated FSS and/or ESS has an apnoea index > 5/hour. CT₉₀ was normal in nine patients. We conclude that fatigue and daytime sleepiness in MS cannot be explained by nocturnal apnoeas or oxygen desaturations. The Fatigue Severity Scale should be integrated to the extended Barthel index, which is a new instrument for disability assessment in MS patients.     

Experimental In Situ Conditioning of the Latissimus Dorsi Muscle for Circulatory Assist by Multichannel Stimulation

Abstract: This study was undertaken to survey the changes in force and fatigue of the latissimus dorsi muscle during transformation into a fatigue–resistant muscle by indirect or nervous multichannel stimulation. In sheep, a silicone chamber connected to a pressure–transducing system was implanted under the left latissimus dorsi muscle. Muscle conditioning was performed by multichannel (carousel) stimulation of the thoracodorsal nerve. The program was started with active periods of 10 min/h producing 10 tetanic contractions/min. It was increased until 70 contractions/min could be performed during 24 h. The changes of muscle force and fatigue were monitored by the silicone balloon system. After a mean period of 22 weeks, fatigue resistance was reached. The fatigueresistant muscle was able to produce a pressure of about 100 mm Hg in the balloon. After finishing the conditioning procedure, muscle forces and the fatigue resistance of the conditioned muscle were evaluated. The conditioned muscle showed only a minimal decrease of force during 20 min. Under a preload of 20 N, it exhibited a maximum tetanic tension of 95 N.     

A comparison of surgeons' posture during laparoscopic and open surgical procedures

Background: There is increasing recognition of surgeons' physical fatigue in the new ergonomic environment of laparoscopic surgery. The purpose of this study was to determine what the differences are in the movement of the surgeon's axial skeleton between laparoscopic and open operations. Methods: Surgeons' body positions were recorded on videotape during four laparoscopic (LAP) and six open (OP) operations. The percent of time the head and back were in a normal, bent, or twisted position as well as the number of changes in head and back position were tabulated using a computer program. A separate laboratory study was performed on four surgeons ``walking' a 0.5-inch polyethylene tubing forward and backward using laparoscopic and open techniques. The movements of the surgeons' head, trunk, and pelvis were measured using a three-camera kinematic system (Kin). The center of pressure was recorded using a floor-mounted forceplate (Fp). Results: In the operating room surgeons' head and back positions were more often straight in laparoscopic procedures and more often bent in open operations. The number of changes in back position per minute were significantly decreased when the laparoscopic-only part of surgery was analyzed. In the laboratory the subjects' head position was significantly (p= 0.02) more upright and the anteroposterior (AP) and rotational range of motion of the head was significantly reduced during laparoscopy. Subjects' CP was more anterior and there was a significant reduction in the AP range of motion of the CP during laparoscopy. Conclusions: Our study suggests that surgeons exhibit decreased mobility of the head and back and less anteroposterior weight shifting during laparoscopic manipulations despite a more upright posture. This more restricted posture during laparoscopic surgery may induce fatigue by limiting the natural changes in body posture that occur during open surgery. Received: 3 March 1996/Accepted: 2 July 1996     

Recovery from short term intense exercise: Its relation to capillary supply and blood lactate concentration

Summary Muscle force recovery from short term intense exercise was examined in 16 physically active men. They performed 50 consecutive maximal voluntary knee extensions. Following a 40-s rest period five additional maximal contractions were executed. The decrease in torque during the 50 contractions and the peak torque during the five contractions relative to initial torque were used as indices for fatigue and recovery, respectively. Venous blood samples were collected repeatedly up to 8 min post exercise for subsequent lactate analyses. Muscle biopsies were obtained from m. vastus lateralis and analysed for fiber type composition, fiber area, and capillary density. Peak torque decreased 67 (range 47–82%) as a result of the repeated contractions. Following recovery, peak torque averaged 70 (47–86%) of the initial value. Lactate concentration after the 50 contractions was 2.9±1.3 mmol·l⁻¹ and the peak post exercise value averaged 8.7±2.1 mmol·l⁻¹. Fatigue and recovery respectively were correlated with capillary density (r=−0.71 and 0.69) but not with fiber type distribution. A relationship was demonstrated between capillary density and post exercise/peak post exercise blood lactate concentration (r=0.64). Based on the present findings it is suggested that lactate elimination from the exercising muscle is partly dependent upon the capillary supply and subsequently influences the rate of muscle force recovery. Dr. Tesch was on leave from Department of Clinical Physiology, Karolinska Hospital, Stockholm, Sweden     

The reproducibility of estimates of critical power and anaerobic work capacity in upper-body exercise

The purposes of this study were to apply the linear power versus inverse of time relationship to high-intensity upper-body exercise and to assess the repeatability of the parameters critical power (CP) and anaerobic working capacity (AWC), using limits of agreement (Bland and Altman 1986). Sixteen active male subjects (aged 20–34 years), performed two sets of five constant-power exercises on an adapted cycle ergometer. There were no significant differences between mean estimates of CP [96 (16) W and 95 (17) W] and AWC [7457 (2011) J and 7608 (1684) J] from the first and second sets of bouts. Despite the lack of systematic bias, there was evidence of large random error. Ratio limits of agreement for time to exhaustion during constant-power exercises suggested that a repeat measurement might be expected in 95% of cases to be between 0.64 and 1.59 times the original measurement. The 95% limits of agreement for CP were –15 W to +17 W. The ratio limits of agreement for AWC suggest that in 95% of cases a repeat measurement might be between 0.57 and 1.67 times the original estimate. The results of this study suggest a poor repeatability of constant-power upper-body exercises to exhaustion, which may contribute to a poor repeatability of CP and AWC determined from the linear power versus inverse of time model. Electronic Publication     

Effects of resistance training in humans on neck muscle performance, and electromyogram power spectrum changes

The purpose of this study was to quantify the neuromuscular cervical adaptations to an 8 week strength training programme. Seven healthy men, with no pathological conditions of the neck, performed a lateral flexion isometric resistance-training programme three times a week. The training sessions consisted of one set of ten contractions, each of 6 s duration, at 60% of the predetermined maximal voluntary isometric torque (MVT_im) (warm-up) and two sets of eight contractions, each of 6 s duration, at 80% MVT_im. The training effects were evaluated in three ways: muscle size, strength and fatigability. The cross-sectional areas (CSA) of the trapezius (TRP) and sternocleidomastoideus (SCM) muscles were determined using a computerised tomographic scanner. Results showed an increase in the CSA of TRP and SCM muscles after training, 8.8% at C5 level and 6.4% at C7 level for SCM muscle and 12.2% at C7 level for TRP muscle. Strength increased significantly under both isometric and isokinetic conditions (35% and 20%, respectively). Muscle fatigability in lateral flexion was quantified during a sustained isometric contraction at 50% of MVT_im. The shift of the mean power frequency of the electromyogram power spectrum density function of SCM muscle toward lower frequencies was less after training (14.6% compared to 6.8%). These results indicate the beneficial effect of a strength-training programme which increases neck muscle size and strength during lateral flexion, and decreases the fatigability of the superficial muscles of the neck. Electronic Publication