遥测肌电图在工效学研究中的应用

采用遥测技术对受试者进行了两种负重方式(A 和B)的研究。在负重重量相同(25Kg),但重量在身体上分配不同的情况下,受试者以5Km/h的速度步行1小时。结果表明,在步行1小时期间A 方式IEMG 呈持续性增大,而B 方式IEMG 无持续性增大,并在步行45～60分钟时基本保持稳定。步行后A 方式肌拉力比值相对减小,而B 方式无改变。实验表明,B方式可相对减轻工作肌疲劳,提高肌肉工作能力。     

Biomechanical effect of a two-segment anterior cruciate ligament graft with separate femoral attachments and differing levels of prescribed load sharing.

The objective of this study was to analyze the biomechanical effect of varying the level of prescribed load sharing between two segments of an anterior cruciate ligament (ACL) graft, and of separating the femoral attachments of these segments. Total anterior-posterior (AP) laxity was measured using an instrumented spatial linkage. Forces in graft segments were measured using buckle transducers. The two-segment graft was formed using the middle third of the patellar tendon with bone blocks and a synthetic augmentation device. Proximal fixation was obtained using a fixture which allowed changing the individual locations of the femoral attachments of the tendon and augmentation segments. Distal fixation was achieved using a force-setting device which allowed the loads in each segment to be set to prescribed levels. Total graft force, load sharing, and total AP laxity were recorded during the application of 100-N AP tibial loads at 0 degrees, 30 degrees, 60 degrees, 90 degrees, and 110 degrees flexion, for various combinations of load sharing set at extension and locations of femoral attachment sites. The load sharing, total graft force, and AP laxity during AP loading at the five test flexion angles were not significantly affected by changing the prescribed level of load sharing set at extension for a given femoral attachment configuration. However, varying the separate hole locations of the graft segments for a given level of load sharing significantly affected load sharing, total graft force, and AP laxity. If the tendon graft was located posteriorly (on the medial surface of the lateral femoral condyle) and the augmentation segment proximally, the augmentation carried a greater portion of the total force in flexion. If the augmentation segment was changed to a more posterosuperior location and the tendon posteroinferior, the tendon carried a higher percentage of the total force in flexion. AP laxity in most reconstruction states was significantly greater than in the normal joint with an intact ACL. The nature of the load sharing between the graft segments under AP tibial load over the flexion range can be controlled by the appropriate choice of the segments' femoral attachment locations.     

In vivo load sharing among the quadriceps components.

Knee extension is always performed with coordinated contractions of multiple quadriceps muscle components; however, how the load is shared among them under normal and pathological conditions is unclear. We hypothesized that: the absolute moment generated by each quadriceps component increases with the total knee extension moment; the relative contribution and its dependence on the total knee extension moment are different for different quadriceps components; and the centrally located large vastus intermedius (VI) is favored by the central nervous system at low levels of activation. Electrical stimulation was used to activate each quadriceps component selectively in six human subjects. The relationship between the knee extension moment generated by an individual quadriceps component and the corresponding compound muscular action potential (M-wave) over various contraction levels was established for each quadriceps component. This relationship was used to calibrate the corresponding EMG signal and determine load sharing among quadriceps components during submaximal isometric voluntary knee extension. The VI contributed the most (51.8-39.6%) and vastus medialis the least (9.5-12.2%) to knee extension moment (P<0.05). As the knee extension moment increased, the relative contribution of the VI decreased (P=0.017) while the relation contribution of the vastus lateralis and medialis increased (P相似文献   

Biochemical and structural correlates in unloaded and reloaded cat myocardium

Cardiocytes of unloaded myocardium rapidly lose structural and functional integrity through a combined loss of myofibrils and contractile activity; both changes are reversible with load restoration. The present study correlates the biochemical composition of unloaded and reloaded myocardium with these alterations in structure and function. Cardiac muscle was unloaded by transecting the chordae tendineae of a cat right ventricular papillary muscle and was reloaded by suturing these same chordae tendineae to the ventricular wall at the base of the valve; an adjacent intact muscle served as the control. Muscles unloaded for 1 to 14 days were assayed for DNA, protein, total creatine and hydroxyproline content. The ratios of wet weight/DNA and creatine/DNA decreased by 30 and 22% respectively, in parallel with a 38% reduction in cardiocyte cross-sectional area. Protein/unit wet weight was decreased by 50% after 14 days of unloading, so that both protein/DNA and protein/creatine were markedly reduced. Reloading of the muscle restored cardiocyte size, protein per unit wet weight and protein/DNA to normal. Parallel reductions in both contractile filaments and contractile proteins after unloading and parallel increases in each following load restoration were demonstrated by morphometric analysis of electron micrographs and analysis of actin and myosin by gel electrophoresis. In summary, the myocardium undergoes marked, parallel changes in structure, function and biochemical composition in response to the removal and restoration of load.     

负荷对运动试验结果的影响

本文研究了低、高负荷仰卧踏车运动试验和食管调搏试验对ST和QT_c的影响。结果表明,运动后即刻时,三种试验方法之间的ST和QF_c无显著性差异(P>0.05)。2min和4min时,低负荷与食管调搏,高负荷与食管调搏之间均有显著性差异(P<0.01),而低、高负荷之间无显著性差异,相关良好。     

空腹甘油三酯正常的2型糖尿病患者餐后血脂的动态变化

目的探讨空腹甘油三酯正常的2型糖尿病患者脂肪餐后血脂水平的动态变化。方法通过脂肪餐负荷试验对25例空腹甘油三酯正常的2型糖尿病患者和20例健康对照者进行餐后血脂代谢的研究。分别于餐前、餐后2、4、6和8h用酶法测定总胆固醇和甘油三酯,一步法测定高低密度脂蛋白,葡萄糖氧化酶法测定血糖,化学发光免疫分析法测定免疫反应胰岛素,计算曲线下甘油三酯面积和增加面积。结果两组餐后甘油三酯平均值都有所升高,峰值在餐后4h。但糖尿病组餐后8h甘油三酯仍明显高于空腹水平(P<0.05),而对照组在餐后8h甘油三酯已恢复接近空腹水平(P>0.05)。两组的高密度脂蛋白在餐后4h都有一个轻微的低谷出现,但无组间差异(P>0.05)。总胆固醇和低密度脂蛋白在餐后无明显变化。两组曲线下甘油三酯面积和增加面积与餐后4h血清甘油三酯水平的相关性最显著(P<0.05)。结论2型糖尿病患者餐后脂代谢异常发生在空腹血脂异常之前。有必要联合检测空腹与餐后4h的甘油三酯水平来全面反映甘油三酯代谢是否存在异常。     

Effects of walking with loads above the ankle on gait parameters of persons with hemiparesis after stroke

Background

Walking with a load at the ankle during gait training is a simple way to resist lower limb movements to induce functional muscle strengthening. This study investigated the effects of walking with different loads attached above the paretic ankle on biomechanical gait parameters during over ground walking in post-stroke participants.

Methods

Ten participants with moderate chronic hemiparesis were evaluated while walking over ground with three different loads (0.5, 1.0, and 1.5 kg) attached above the paretic ankle. Gait speed, cadence, step lengths as well as hip and knee angular displacements, joint moments and power of the paretic limb were compared while walking with and without loads.

Findings

Walking with a load led to an increased in gait speed (+ 0.03–0.05 m/s), and in step length of the paretic leg (+ 5.6 to 9.4% step length, effect size = 0.49–0.63), but not of the non-paretic leg. The proportion of the stance and swing phases did not change. Maximal joint moments (+ 20 to 48%, effect size = 0.26–0.55) and power (+ 20 to 114%, effect size = 0.30–0.57) increases varied across participants but were mostly affected in early stance at the hip and during the late swing phase at the knee. Mean angular displacement changes were less than 4°.

Interpretation

Post-stroke participants are able to increase hip and knee power bursts to meet the increased mechanical demand of added loads attached to the paretic ankle, while preserving the basic pattern of walking. Further study is needed before using loading to functionally strengthen paretic muscles.     

沙漠干热环境不同负荷和速度行军对人体血浆一氧化氮的影响

为探讨沙漠干热环境应激行军人体一氧化氮(NO)的变化规律,对沙漠干热环境中以不同速度和时间徒手和负荷行军的135名战士血浆NO进行了检测.结果发现,不论是15kg负重还是徒手行军,35km/h和50km/h各行军时间组血浆NO明显低于对照组(P<0.01);徒手行军时,仅3.5km/h行军3小时组NO明显低于1小时组(P<0.05);负重行军时,35km/h行军3小时组NO明显低于1小时和2小时组(P<0.05);行军时间相同时,仅5.0km/h徒手行军3小时组NO明显高于3.5km/h徒手行军3小时组(P<0.01).     

Heart rate and oxygen uptake relationship: a comparison of loaded marching and running in women

Heart rate (beats · min^–1;f _c) measured during marching with a load is often used to predict the oxygen cost (1·min^–1; VO₂) of the activity. The prediction comes from thef _c/VO₂ relationship determined from laboratory measures off _c and VO₂ during treadmill running. Studies in men have suggested that this may not be appropriate although this has yet to be examined in women. This study, therefore, compared thef _c/VO₂ relationship between loaded marching and maximal running protocols in women. Sixteen female subjects [mean (SD), age 21.9 (2.3) years, height 6 (0.06) m, weight 62.6 (7.6) kg] had theirf _c (from three-lead chest electrodes) and VO₂ measured first during standard treadmill run protocols, and again 1 week later during loaded marching protocols. The slopes and intercepts determined from linear regression off _c on VO₂ for each individual for each protocol were compared as were the maximalf _c(f _cmax), VO₂ and ratings of perceived exertion (RPE) from the last work period of each protocol in pairedt-tests. The VO₂ slopes (P < 0.01) and intercepts (P < 0.05) differed significantly between loaded marching and running.f _cmax for loaded marching were 90% off _cmax for running (P < 0.01) and VO₂ for loaded marching were 80% of those for running (P < 0.01). However, RPE at the final levels for the two protocols were not significantly different. The data suggest that in women the VO₂ relationships for loaded marching and for running are different. This difference is similar to that found in men when speed is held constant and the load and gradient are varied. The results suggest that it would be erroneous to usef _c and VO₂ measured during running protocols in the laboratory to estimate energy expenditure and work intensity during loaded marching in the filed.     

Effects of load placement on back muscle activity in load carriage

Summary The effect of two different load placements (just below mid-back or just above shoulder level) on erector spinae EMG, trapezius EMG, and heart rate were investigated during load carriage. The EMG and heart rates were telemetered from 11 subjects while they walked on a smooth level surface at an average velocity of 5.6 km·h^–1 carrying a load of 19.5 kg in a specially designed backpack. The average rectified EMG amplitude was calculated digitally for both load placements. The high load placement resulted in significantly higher levels of muscle activity than did the lower placement. Heart rate was not significantly different between the two placements. A qualitative biomechanical analysis suggests that the EMG differences are primarily due to differences in the moments and forces arising from the angular and linear accelerations of the load and trunk. The results indicate that metabolic measures alone are not sufficient to adequately assess tasks which evoke primarily local muscle demands.