Effects of stretching velocity on passive resistance developed by the knee musculo-articular complex: contributions of frictional and viscoelastic behaviours

The purpose of the study was to confirm the trends in right and left side muscle blood volume (Mbv) and muscle oxygenation (Mox) during the Biering-Sorensen muscular endurance (BSME) test, compare right and left side Mbv and Mox responses, and predict BSME time via Mox variables. Research suggests that during moderate intensity (∼20% of maximal volitional contraction) muscle contraction blood flow will decrease as a result of increased intramuscular pressure. Moreover, decreased muscle oxygenation is believed to be associated with diminished musculoskeletal endurance time, but until the development of near infrared spectroscopy (NIRS) it was not possible to non-invasively monitor these changes in erector spinae muscle. Nineteen healthy males completed the BSME in a prone position. The NIRS probes were placed on the left and right erector spinae muscle at the third lumbar vertebra level. The test protocol was: 2 min resting baseline, BSME to volitional fatigue, and 4 min recovery. The results indicated Mbv initially increased reaching asymptote before returning to baseline at termination. The Mox increased then declined systematically until BSME termination, returning to near baseline in recovery. No significant difference between sides was noted for Mbv or Mox. Mox best predicted BSME time. In conclusion, Mbv increased and then reaches asymptote as indicated in previous research, and oxygen availability was associated with the duration of erector spinae static contraction. Thus, prolonged static postures using the erector spinae muscles may diminish muscle oxygenation increasing susceptible to fatigue and injury.     

Relationship between erector spinae static endurance and muscle oxygenation-blood volume changes in healthy and low back pain subjects

The purposes of this study were to: (1) compare the muscle blood volume (Mbv) and oxygenation (Mox) responses on the right and left side erector spinae during the Biering-Sorensen muscle endurance (BSME) test between healthy, low back pain active (LBP-A) and LBP-sedentary (LBP-S) subjects using near infrared spectroscopy (NIRS), and (2) determine the relationships between the BSME time and Mbv and Mox. Informed consent was obtained from 30 healthy and 30 chronic LBP subjects. The latter group was subdivided into an active (LBP-A; n = 18) and sedentary (LBP-S; n = 12) subgroups based on physical activity patterns. The groups were age and sex matched. The NIRS probes were placed bilaterally on the erector spinae muscle at the level of the third lumbar vertebrae. The testing protocol was: 2-min resting baseline, BSME to voluntary fatigue, and 4-min recovery. During the BSME Mbv immediately increased for approximately 30-60 s, then showed an asymptote, and a steady decline towards the baseline at termination. Mox demonstrated either an initial increase followed by a systematic decrease until the termination of the BSME, or a systematic decrease throughout the BSME until termination. The LBP-S subjects showed a reduced Mox-range and slower Mox (1/2) recovery time on the left side suggesting a reduced aerobic capacity of the erector spinae muscle in this group. Significant correlations were noted between BSME time and the pooled values of Mox-delta and-range only in the LBP-A group. These observations suggest that factors other than erector spinae aerobic capacity can influence BSME performance.     

Monitoring individual erector spinae fatigue responses using electromyography and near infrared spectroscopy.

This study examined the utility of electromyography and near-infrared spectroscopy (NIRS) in assessing m. erector spinae activity during the Biering-Sorensen Back Muscle Endurance (BSME) test. Six men and four women (27.0 +/- 7.1 years of age) performed the BSME test (time = 131.5 +/- 43.5 s). EMG was used to quantify neuromuscular activity of the right and left side at the L3 level, and root mean square was scaled for maximum value at the start of the exercise. NIRS was used to evaluate blood volume (BV) and oxygenation (OX) simultaneous with EMG bilaterally at the L3 level. There was a decrease to 49+/- 8% of initial median frequency (mean= 83 Hz) on both right and left sides when the exercise was 90% complete, and the slope of the median frequency/time relationship was significantly related to BSME time (r = 0.82). Group means for BV increased during back exercise while OX decreased and was significantly different between right and left sides of the lower back. However, large OX response differences among individuals and between right and left sides were noted. OX and median frequency were moderately related (r = 0.27-0.38). It appears that NIRS combined with EMG is a promising tool for assessing localized metabolic and neuromuscular activity during static contractions of the lower back.     

Cardiorespiratory and hemodynamic responses during repetitive incremental lifting and lowering in healthy males and females

The purposes of this study were twofold. First, to evaluate the cardiorespiratory and muscle oxygenation (OXY)/blood volume (BV) responses during repetitive incremental lifting and lowering (RILL) in healthy males and females. Second, to develop a predictive equation for predicting peak aerobic power (O_2peak) during RILL from the cardiorespiratory, OXY/BV and body composition variables. Fourteen males and 18 females [mean (SD) for age, height and body mass were: 29.6 (8.2) years; 1.75 (0.07) m; 78.9 (10.4) kg and 23.9 (2.1) years; 1.63 (0.06) m; 62.3 (6.3) kg, respectively] completed a RILL from floor to table height at 10 lifts/min to voluntary fatigue. Cardiorespiratory responses were measured using open circuit spirometry and hemodynamic trends were monitored bilaterally at the third lumbar vertebra via near infrared spectroscopy. Significant sex differences (p<0.05) were observed for the peak values of oxygen uptake (O_2peak), ventilation rate ( _E), oxygen pulse, BV-max and BV-delta. Erector spinae OXY decreased systematically until O_2peak was attained, while BV decreased until ~50% of O_2peak and then leveled off. Stepwise regression analysis indicated that ~75% of the variance in O_2peak was predicted from cardiorespiratory, hemodynamic and body composition variables, with the most important predictors for absolute and relative O_2peak being _E (r=0.75) and fat mass (r=−0.63) respectively. Inclusion of left side OXY/BV responses increased the predictability of the common variance in O_2peak from 40% to 74%, implying that muscle hemodynamics play an important role in determining O_2peak during RILL.     

青少年椎旁肌耐力及左右侧对称性测评指标和方法的建立

文题释义： 平均功率频谱斜率(SlopeMPF)：最早由Nagamachi等提出,从肌肉运动学的角度作为评价肌肉疲劳的指标。在持续收缩过程中,肌电图频谱的负向斜率不易受干扰的影响,对与肌肉疲劳相关的生理变化较为敏感,特别是动作电位传导速度的降低,是测量局部肌肉疲劳的客观指标。 多裂肌：是人体正常的肌肉组织,存在于腰背部,位于竖脊肌的深部,比较厚实,它的纤维主要是纵向走行,并且有很大的力量。肌肉承担身体对侧的转体运动,对维持脊柱的稳定性具有非常重要的作用。长时间的一个姿势,长时间的重复某种动作,比如低头弯腰长时间的坐立等等,就会导致多裂肌的肌肉痉挛,充血水肿,形成无菌性的炎症会导致局部的疼痛。背景：研究表明通过表面肌电测试,非特异性慢性下腰痛患者腰部脊柱两侧竖脊肌活动的变化不一致。在体质测量评价中侧重对腰部整体力量的测评,对青少年椎旁肌的测评方法和指标并未有研究报道。 目的：拟建立评定青少年椎旁肌耐力及左右侧对称性的方法和指标,初步制定评价等级标准。 方法：于北京市某中学随机抽取200名学生,其中初中生100名,高中生100名;年龄13-18岁,男女各半。受试者采用Biering-Sorensen(B-S)实验动作,保持椎旁肌等长收缩,采用表面肌电技术记录L₃-L₄双侧竖脊肌、L₅-S₁双侧多裂肌肌电,上身无法维持水平姿势或经3次提醒仍低于水平位时停止测试。筛选指标并建立评价指数,按离差法确定各年龄段椎旁肌耐力及左右侧对称性评价等级标准。研究方案的实施符合北京体育大学的相关伦理要求,受试者及其监护人对试验过程完全知情同意。 结果与结论：①根据解剖姿势分析和肌肉动员比测试,确定B-S动作左/右竖脊肌、左/右多裂肌为原动肌;肌电指标平均功率频谱随时间延续线性下降(R < -0.97,P < 0.01);重复性检验,平均功率频谱斜率(Slope MPF)差异检验P > 0.05,组内相关系数ICC>0.80(P < 0.01),SlopeMPF重复性良好;②拟合复合指数,椎旁肌耐力指数v=slopeMPF(左竖脊肌+右竖脊肌+左多裂肌+右多裂肌)/4,评价青少年椎旁肌耐力;对称性指数u=slopeMPF(左竖脊肌-右竖脊肌)/slopeMPF(左竖脊肌+右竖脊肌)+slopeMPF(左多裂肌-右多裂肌)/slopeMPF (左多裂肌+右多裂肌),评价青少年椎旁肌左右侧对称性;③评价结果显示,同性别高中生较初中生椎旁肌耐力均有增加(P < 0.01);高中组男、女生椎旁肌耐力具有显著性差异;青少年椎旁肌耐力及对称性测试结果均呈现正态分布并可利用离差法进行评价等级划分;④研究初步建立了评定椎旁肌耐力及左右侧对称性的指标和方法,并采用离差法初步制定青少年椎旁肌耐力和左右侧对称性评价标准。 ORCID: 0000-0003-0779-4459(邱丹) 中国组织工程研究杂志出版内容重点：组织构建;骨细胞;软骨细胞;细胞培养;成纤维细胞;血管内皮细胞;骨质疏松;组织工程     

Open-field behavior is not related to treadmill performance in exercising rats

We examined the association between open-field behavior and treadmill performance in 39 adult male Sprague-Dawley rats. Three daily, five-minute trials were conducted in an open field of 49 19 cm squares. The objectivity of the open-field test was established by intraclass correlations (R) for observer agreement on total squares traversed (R = .99) and a subjective behavioral rating scale for anxiety (R = .92). As expected, total squares were inversely correlated (r = -.86) with the subjective anxiety ratings. An independent observer also rated animals on treadmill performance across six daily, five-minute trials of level running at 15 m/min. Performance ratings were objective (rs = .89) and reproducible (R = .91). A volitional endurance run at 30 m/min on level grade was also conducted on a subsequent day. Extreme groups of low anxious (N = 7) and high anxious (N = 7) animals were then identified from convergent responses on total square traversals and the subjective behavioral ratings that were reproducible (R = .72 to .78) of trials two and three of the open-field test. Repeated measures ANOVA showed no group differences (p greater than 0.10) on mean treadmill performance across trials. Endurance was also the same for each group (p greater than 0.05). Our findings indicate that the open-field test is objective and reliable, and it does not reveal a selection bias effect on treadmill performance or endurance. Thus, open-field behavior can be used as a dependent or subject-matching variable in studies of adult male Sprague-Dawley rats when motor-driven treadmill running is a behavioral intervention or outcome measure.     

Drink temperature influences fluid intake and endurance capacity in men during exercise in a hot, dry environment

The effect of different drink temperatures on the perception of exertion and exercise endurance has not been extensively investigated. Consequently, the purpose of the present study was to examine the effect of drink temperature on fluid intake and endurance during cycling in the heat. Eight healthy, non-acclimated males (26 +/- 7 years; maximum oxygen uptake, 54 +/- 5 ml kg(-1) min(-1); mean +/- S.D.) cycled to exhaustion at 34 degrees C and at 65% of their peak aerobic power, consuming a drink at either 19 degrees C (CON) or 4 degrees C (COLD). Six of the eight subjects cycled for longer during COLD, with exhaustion occurring at 62 +/- 4 min, compared to 55 +/- 4 min for CON (P < 0.05; mean +/- S.E.M.). Subjects consumed significantly more fluid during COLD compared to CON (1.3 +/- 0.3 l h(-1) compared to 1.0 +/- 0.2 l h(-1); P < 0.05). Heart rate tended to be lower by approximately 5 beats min(-1) during COLD, and rectal temperature during the second half of the exercise period was approximately 0.25 degrees C lower during the COLD trial; however, these trends were not significant (P = 0.08 and P = 0.07, respectively). No differences were observed between trials for ventilation, concentrations of prolactin, glucose and lactate or perceived exertion. It is concluded that a drink at 4 degrees C during exercise in the heat enhances fluid consumption and improves endurance by acting as a heat sink, attenuating the rise in body temperature and therefore reducing the effects of heat stress.     

Back extensor muscle oxygenation and fatigability in healthy subjects and low back pain patients during dynamic back extension exertion

The purpose of this study was to assess if chronic low back pain patients have impaired paraspinal muscle O₂ turnover and endurance capacity as compared to healthy control subjects during dynamic exercise. Middle-aged healthy male subjects (n = 12, control) and male patients with chronic low back pain (n = 17, CLBP) participated in the study. L4–L5 level paraspinal muscle fatigue was objectively assessed during earlier validated 90 s dynamic back endurance test (spectral EMG, MPF_slope). Also EMG amplitude (EMG_amplitude) and initial MPF (MPF_initial) were assessed from the initial 5 s of the endurance contraction. Simultaneously near infrared spectroscopy (NIRS) was used for quantitative measurement of local L4–L5 paraspinal muscle O₂ consumption. Subcutaneous tissue thickness (ATT) was measured from the EMG and NIRS recording sites. The results indicated that control and CLBP groups were compatible as regarding anthropometric variables, paraspinal muscle activation levels (EMG_amplitude), initial MPF (MPF_initial) and ATT. When the ATT was used as a covariate in the ANOVA analysis, CLBP group did not show significantly greater paraspinal muscle fatigability (right MPF_slope – 12.2 ± 10.7%/min, left right MPF_slope – 12.6 ± 13.3%/min) or O₂ consumption (right NIRS_slope – 52.8 ± 79.6 μM/l/s) as compared to healthy controls (right MPF_slope – 11.9 ± 7.6%/min, left MPF_slope – 12.7 ± 8.6%/min, right NIRS_slope – 53.7 ± 95.2 μM/l/s). As a conclusion, these CLBP male patients did not show any impaired rate of paraspinal muscle oxygen consumption or excessive paraspinal muscle fatigability during dynamic exercise as compared with healthy controls. Subcutaneous tissue thickness has a strong influence on the NIRS and EMG amplitude measurements and, if unchecked, it could result in the false interpretation of the results.     

Shoulder muscle strength and fatigability in patients with frozen shoulder syndrome: the effect of 4-week individualized rehabilitation

The effect of 4-week individualized rehabilitation on shoulder muscle strength and fatigability was evaluated in 10 patients with frozen shoulder syndrome (FSS) in comparison of 10 age- and gender-matched healthy control subjects. Isometric maximal voluntary contraction (MVC) force of the shoulder flexors was measured by hand-held dynamometer. Isometric endurance of the shoulder muscles was characterized by endurance time and net impulse (NI) assessed during weight (30% MVC) holding in hand until exhaustion. Fatigability of deltoideus, infraspinatus and trapezius muscles during isometric endurance test was assessed by electromyogram (EMG) power spectrum median frequency (MF) slope per minute. Rehabilitation in patients with FSS consisted of exercise therapy in swimming pool and gymnasium, electrical therapy and massage. Before rehabilitation, patients with FSS had less (p < 0.05) isometric MVC force and NI during endurance test compared to the control. MF slope in patients with FSS for involved extremity was higher (p <0.05) for the deltoideus muscle and less for the infraspinatus muscle before rehabilitation compared to the controls. Shoulder pain was decreased (p < 0.05) and isometric MVC force and NI in endurance test in patients for involved extremity were increased after rehabilitation. No significant changes in endurance time and MF slope for infraspinatus and trapezius muscles in patients for involved extremity were observed after rehabilitation, whereas MF slope for deltoideus muscle was increased. It was concluded that in patients with FSS, 4-week rehabilitation decreased shoulder pain and improved MVC force of the shoulder flexors and isometric working capacity of these muscles during endurance test.     

Prior endurance exercise attenuates growth hormone response to subsequent resistance exercise

This study examined the influence of prior endurance exercise on hormonal responses to subsequent resistance exercise. Ten males exercised on a cycle ergometer at 50% of maximal oxygen uptake for 60 min and subsequently completed a resistance exercise (bench and leg press, four sets at ten repetitions maximum with an interset rest period of 90 s). Alternatively, the subjects performed the protocol on a separate day with prior endurance exercise limited to 5 min. Blood was obtained before and after the endurance exercise, and 10, 20, and 30 min after the resistance exercise. Maximal isometric torque measured before and after endurance and resistance exercises showed no significant difference between trials. No significant difference was seen in the concentrations of glucose, lactate, testosterone, and cortisol between the trials, but free fatty acids (FFA) and growth hormone (GH) increased (P<0.01 and P<0.05, respectively) after 60 min of endurance exercise. Conversely, after the resistance exercise, GH was attenuated by 60 min of prior exercise (P<0.05). These results indicate that the GH response to resistance exercise is attenuated by prior endurance exercise. This effect might be caused by the increase in blood FFA concentration at the beginning of resistance exercise.     

Assessment of lower-back muscle fatigue using electromyography, mechanomyography, and near-infrared spectroscopy

We have investigated the etiology of lower-back muscle fatigue using simultaneous recordings of electromyography (EMG), mechanomyography (MMG), and near-infrared spectroscopy (NIRS) in an attempt to shed some light on the electrophysiological, mechanical, and metabolic characteristics, respectively. Eight male subjects performed isometric back extensions at an angle of 15° with reference to the horizontal plane, for a period of 60 s. Surface EMG, MMG and NIRS signals were recorded simultaneously from the center of the erector spinae at the level of L3. NIRS was measured to determine the level of muscle blood volume (BV) and oxygenation (Oxy-Hb). The root mean square amplitude value (RMS) of the EMG signal was significantly increased at the initial phase of contraction and then fell significantly, while mean power frequency (MPF) of the EMG signal decreased significantly and progressively as a function of time. There were also significant initial increases in RMS-MMG that were followed by progressive decreases at the end of fatiguing contractions. MPF-MMG remained unchanged. Muscle BV and Oxy-Hb decreased dramatically at the onset of the contraction and then remained almost constant throughout the rest of the contraction. These results, obtained by simultaneous recordings of EMG, MMG, and NIRS, demonstrate that the restriction of blood flow due to high intramuscular mechanical pressure is one of the most important factors in muscle fatigue in the lower-back muscles. In addition, the simultaneous recording system described here can be used to obtain more reliable information regarding the mechanism(s) of lower-back muscle fatigue. Accepted: 4 October 2000     

Effect of static stretch on fatigue of lumbar muscles induced by prolonged contraction

Low back pain (LBP) is believed to be the result of fatigue of the back extensor muscles induced by prolonged contraction. Although static stretch has been considered to promote recovery from such muscle fatigue by relaxation, little is known about the effect of stretch on muscle fatigue, especially in the back extensor muscles. The purpose of this study was to investigate the effect of static stretch on prolonged contraction-inducedfatigue of the back extensor muscles using electromyographic (EMG) spectral analysis in ten healthy volunteers. Bipolar surface electrodes were placed on the longissimus and the multifidus muscles. EMG signals were collected during two trials of a Sorensen trunk-holding test for two minutes, with a five-minute rest period between the two trials (control test). All subjects were asked to perform the same trials, with one-minute of static stretch and a four-minute rest period (stretch test). Maintaining the knees toward the chest in supine position resulted in static stretch. The median frequency (MF) was calculated using a spectrum analysis program, and the MF slope over time was computed by linear regression analysis, and normalized with the y-intercept. The decreasing rate of the normalized MF slope between two trials in two tests was compared. The decreasing rate of the normalized MF slope of the second trial was larger than that of the first trial in the control test (p < 0.05), but no significant difference was observed in the stretch test. The results indicated that static stretch had a significant effect on the recovery from fatigue of the back extensor muscles, since it influenced the decreasing rate of the normalized MF slope.     

Reliability of near infrared spectroscopy (NIRS) for measuring forearm oxygenation during incremental handgrip exercise

The purpose of this study was to test the reliability of a new handgrip exercise protocol measuring forearm oxygenation in 20 healthy subjects on two occasions. The retest took place 48 h later and at the same time of the day. The incremental exercise consisted of 2 min steps of cyclic handgrip contraction (1/2 Hz) separated by 1 min of recovery. The exercise started at 20% MVC, was increased with 10% MVC each step and was performed until exhaustion (69.5 and 73% MVC). Near infrared spectroscopy (NIRS) was used to measure deoxygenation (deoxy[Hb + Mb]) and oxygen saturation (SmO(2)) in the forearm muscles. Prior to the exercise protocol an arterial occlusion of the forearm was performed until deoxy(Hb + Mb) did no longer increase. Maximal increase in deoxy[Hb + Mb] during 10 s of each exercise bout was expressed relative to the occlusion amplitude. ICC was used to examine the test-retest reliability. Significant ICC's were reported at 50% (r = 0.466, p = 0.017) and 60% MVC (r = 0.553, p = 0.005). The group mean of the maximum increase in oxygen extraction was 45.6 ± 16.7% and at the retest 44.9 ± 17.0% with an ICC of r = 0.867 (p < 0.001) which could be classified (Landis and Koch 1979) as almost perfect. The absolute SmO(2) values showed reliable ICC's for every submaximal intensity except at 60% MVC. An ICC of r = 0.774 (p < 0.001) was found at maximal intensity. The results of the present study show that deoxy[Hb + Mb] and SmO(2) responses during this protocol are highly reliable and indicate that this protocol could be used to get insight into deoxygenation and oxygen saturation in a population with low exercise tolerance.     

Left ventricular volumes during exercise in endurance athletes assessed by contrast echocardiography

AIM: The objective was to assess left ventricular (LV) volumes at rest and during upright submaximal exercise in endurance athletes to see whether changes in heart volume could explain the large predicted increase in cardiac output in endurance athletes. METHOD: Contrast echocardiography was used to assess changes in LV volumes during upright bicycle exercise in 24 healthy male endurance athletes. Maximal oxygen uptake and oxygen pulse were measured by using cardiopulmonary exercise testing. RESULTS: From rest to exercise at a heart rate of 160 beats min(-1) end-diastolic volume increased by 18% (P < 0.001) and end-systolic volume decreased by 21% (P = 0.002). Stroke volume showed an almost linear increase during exercise (45% increase, P < 0.001). The increase in end-diastolic volume contributed to 73% of the increase in stroke volume. No significant differences were observed between stroke volume calculated from LV volumes with contrast echocardiography and stroke volume calculated from oxygen pulse at heart rates of 130 and 160 beats min(-1). Using the linear regression equation between oxygen uptake and cardiac output assessed by echocardiography during exercise (r=0.87, P=0.002), cardiac output at maximal exercise was estimated at 33 +/- 3 L min(-1), with an estimated increase in stroke volume by 69% from rest to maximal exercise. CONCLUSION: By using contrast echocardiography, a large increase in stroke volume in endurance athletes could be explained by an almost linear increase in end-diastolic volume and an initial small decrease in end-systolic volume during incremental upright exercise.     

Maximal voluntary hyperpnoea increases blood lactate concentration during exercise

Ventilatory work during heavy endurance exercise has not been thought to influence systemic lactate concentration. We evaluated the effect of maximal isocapnic volitional hyperpnoea upon arterialised venous blood lactate concentration ([lac⁻]_B) during leg cycling exercise at maximum lactate steady state (MLSS). Seven healthy males performed a lactate minimum test to estimate MLSS, which was then resolved using separate 30 min constant power tests (MLSS=207±8 W, mean ± SEM). Thereafter, a 30 min control trial at MLSS was performed. In a further experimental trial, the control trial was mimicked except that from 20 to 28 min maximal isocapnic volitional hyperpnoea was superimposed on exercise. Over 20–28 min minute ventilation, oxygen uptake, and heart rate during the control and experimental trials were 87.3±2.4 and 168.3±7.0 l min⁻¹ (P<0.01), the latter being comparable to that achieved in the maximal phase of the lactate minimum test (171.9±6.8 l min⁻¹), 3.46±0.20 and 3.83 ± 0.20 l min⁻¹ (P<0.01), and 158.5±2.7 and 166.8±2.7 beats min⁻¹ (P<0.05), respectively. From 20 to 30 min of the experimental trial [lac⁻]_B increased from 3.7±0.2 to 4.7±0.3 mmol l⁻¹ (P<0.05). The partial pressure of carbon dioxide in arterialised venous blood increased approximately 3 mmHg during volitional hyperpnoea, which may have attenuated the [lac⁻]_B increase. These results show that, during heavy exercise, respiratory muscle work may affect [lac⁻]_B. We speculate that the changes observed were related to the altered lactate turnover in respiratory muscles, locomotor muscles, or both.     

PNMT inhibition decreases exercise performance in the rat.

The purpose of this investigation was to examine the effect of phenylethanolamine N-methyltransferase (PNMT) inhibition on the regulation of peripheral metabolic and hormonal responses during treadmill exercise in the rat. Changes in plasma catecholamine (epinephrine, norepinephrine, and dopamine), glucagon and glucose, and the glycogen content of the liver and two skeletal muscles were studied in four groups of rats. Two groups of rats were studied at rest: one group had been treated with LY134046, an inhibitor of PNMT, and the second group was treated with physiological saline. A third group treated with LY134046 was studied after treadmill exercise (28 m.min-1 and 8% slope). In this group of rats, exhaustion came after 37.5 +/- 7.9 minutes of exercise. In order to make appropriate comparisons, a fourth group of rats treated with physiological saline was exercised for 37.5 min. Running endurance during the treadmill exercise was thus reduced in LY134046-treated rats. Plasma epinephrine and glucagon concentrations and other metabolic (plasma glucose and gastrocnemius lateralis and superficial vastus lateralis muscles and liver glycogen contents) responses were similar between LY134046- and saline-treated rats at rest and after exercise. These results suggest that PNMT inhibition in epinephrine brain neurons might be the principal factor involved in the LY134046-induced reduction of exercise endurance.     

Decreased exercise blood lactate concentrations after respiratory endurance training in humans

For many years, it was believed that ventilation does not limit performance in healthy humans. Recently, however, it has been shown that inspiratory muscles can become fatigued during intense endurance exercise and decrease their exercise performance. Therefore, it is not surprising that respiratory endurance training can prolong intense constant-intensity cycling exercise. To investigate the effects of respiratory endurance training on blood lactate concentration and oxygen consumption (V˙O₂) during exercise and their relationship to performance, 20?healthy, active subjects underwent 30?min of voluntary, isocapnic hyperpnoea 5 days a week, for 4 weeks. Respiratory endurance tests, as well as incremental and constant-intensity exercise tests on a cycle ergometer, were performed before and after the 4-week period. Respiratory endurance increased from 4.6 (SD 2.5) to 29.1?(SD 4.0)?min (P?P?V˙O₂ did not change at any exercise intensity whereas blood lactate concentration was lower at the end of the incremental [10.4 (SD 2.1) vs 8.8?(SD 1.9)?mmol?·?l^?1, P??1, P?相似文献   

Intra-abdominal pressure increases during exhausting back extension in humans

The aim of this study was to investigate in humans the effect of maintained spinal load on the intra-abdominal pressure (IAP), low back kinematics and trunk muscle activity. This study consisted of two endurance tests for the low back muscles performed 3 weeks apart. Nine healthy subjects participated in the study. In the first test (upright-test), the subject had to pull with the back muscles at a constant force in an upright position, and in the second test (incline-test), the subject had to resist a constant forward pulling force while standing with a 45° inclination of the back in relation to vertical. The IAP, rate of perceived exertion and electromyogram (EMG) from the erector spinae, iliocostalis lumborum, rectus abdominus and the external and internal oblique muscles were measured using surface electrodes. There was no significant difference in endurance time between the two tests. Both tests showed a significant increase in EMG amplitude with time for all muscles except the erector spinae muscle. A decrease in the median frequency for the erector spinae muscle was found indicating fatigue, and since no increase in EMG amplitude was found a decrease in force output from the muscle must be assumed. The IAP increased significantly during both tests. There was a considerable variation between the subjects in the size of this development, but the pattern was the same for all subjects. In conclusion it was found that trunk extension until exhaustion initiates an increase in the activity of the abdominal muscles and an increase in the IAP as the low back muscles become fatigued. Electronic Publication     

Muscle recovery from a short fatigue test and consequence on the reliability of EMG indices of fatigue

The purpose of the present study was to evaluate if rest intervals of 10 or 15 min allow the back muscles to recover completely, from an electromyographic (EMG) point of view, after performing a fatiguing contraction. Twelve healthy males stood in a dynamometer with the trunk in a vertical position and performed three trunk extension fatiguing trials (30 s contractions sustained at 75% of the maximal voluntary contraction) separated successively by a 15 min (between trial 1 and 2) and a 10 min (between trial 2 and 3) rest period. The EMG signals from four pairs of back muscles were collected at 2,048 Hz with active surface electrodes. Different EMG indices computed from the temporal and frequency domains of the EMG signal were considered to evaluate muscular fatigue and recovery from trial 1 to trial 2 and from trial 2 to trial 3. No significant differences (one-way ANOVAs between the three trials, α=0.05) were obtained for the different EMG indices computed. The percentage of variance explained by the inter-trial effect was none in most cases, corroborating that no systematic error was present between the trials and suggesting that complete muscle recovery was allowed with 10 or 15 min rest periods. These results support the use of rest periods of 10 to 15 min between multiple fatigue tests, at least for back muscles and for high intensity short duration fatigue tasks as the one used in the present study. Electronic Publication     

Reproducibility of near-infrared spectroscopy parameters measured during brachial artery occlusion and reactive hyperemia in healthy men

Near-infrared spectroscopy (NIRS) is a noninvasive technique evaluating microvascular function. The aim of this study was to assess the reproducibility of NIRS parameters during reactive hyperemia induced by a 5 min brachial artery occlusion. Twenty-four healthy young males (mean 34±8 years old) had two microvascular function evaluations by NIRS over a 7 to 30-day period (mean 16±10 days). Intra-subject and inter-observer reproducibility were evaluated with intraclass correlation coefficient (ICC), coefficient of variation (CV), and standard error of measurement (SEM%) for every parameter. Mean NIRS parameters did not differ between both evaluations. Reproducibility was greatest for muscle oxygen consumption (ICC: 0.84; CV: 6.51%; SEM: 7.11%), time to basal O(2)Hb (ICC: 0.63, CV: 20.04%, SEM 27.22%), time to maximal O(2)Hb (ICC: 0.71; CV: 15.61%; SEM: 19.27%), peak of O(2)Hb (ICC: 0.63, CV: 6.68%, SEM 8.53%), time to maximal tHb (ICC: 0.73, CV: 19,61%, SEM 24.56%) and area under the O(2)Hb and tHb curves (ICC: 0.68, CV: 16.15%, SEM 22.93% and ICC: 0.62, CV: 18.59%, SEM 26.64%, respectively). Moreover, inter-observer reproducibility ranged from excellent to perfect (ICC from 0.85 to 1.00) for every parameter. NIRS parameters during reactive hyperemia are highly reproducible which enables their repeated measurement to study microvascular function in healthy subjects.