Biomechanical analysis during single-leg squat in individuals with knee osteoarthritis

Backgroud: The single-leg squat (SLS) is a functional task to evaluate the abnormal movement patterns and potential neuromuscular deficits in the lower limbs. Still, it is unknown if SLS could provide information to older adults with knee osteoarthritis (KOA). The study’s objective was to analyze the EMG pattern, kinematics, and postural control in individuals with and without KOA during SLS.Methods: Participated in this study, 60 volunteers of both sexes, 30 had KOA (allocated into the KOA group - KOAG), and 30 were healthy (allocated into the Healthy Group - HG) performing the single-leg squat. Surface electromyography (EMG) was assessed for the gastrocnemius medialis (GM), biceps femoris (BF), gluteus medius (GLM), rectus femoris (RF), vastus medialis (VM), vastus lateralis (VL), and tibialis anterior (TA) in two phases (downward – P1 and upward – P2). The kinematic data was evaluated using an electrogoniometer. The center of pressure (CoP) was obtained using data collected from a force plate.Results: EMG activity was increased for GM and TA muscles during the P1 of the movement and the GM and GLM muscles during P2 of the movement. The angular displacement of the KOAG was lower when compared with the HG. There was no statistical difference for the co-contraction and postural control data.Conclusions: The SLS analysis showed that EMG activity of the muscles TA, GM, and GLM was increased in the KOAG, but this pattern could be affected by fear of movement leading to reduced knee angular displacement.     

Entrainment of Intestinal Slow Waves with Electrical Stimulation Using Intraluminal Electrodes

The aim of this study was to investigate whether the intestinal stimulation would be feasible using a less invasive method: intraluminal electrodes. The study was performed in nine healthy hound dogs (15–26 kg). Four pairs of electrodes were implanted on the serosa of the jejunum at an interval of 5 cm with the most proximal pair 35 cm beyond the pylorus. An intestinal fistula was made 20 cm beyond the pylorus. Simultaneous recordings of intestinal myoelectrical activity were made for 2 h in the fasting state from both intraluminal and serosal electrodes. Various pacing parameters were tested. The frequency of the intestinal slow wave recorded from the intraluminal electrodes was identical to that from the serosal electrodes , p < 0.001), and so was the percentage of normal 17–22 cycles/min waves (95.8±33.9% vs 98.16±1.33%, r=0.96, p<0.01).p < 0.01). A complete entrainment of the intestinal slow wave was achieved in every dog with electrical stimulation using intraluminal ring electrodes. The effective pacing parameters were pulse width of 70 ms, amplitude of 4 mA and frequency of 1.1 IF (intrinsic frequency). The time required for the entrainment of the intestinal slow wave with intraluminal pacing was 25.0±2.1s. The maximum driven frequency was found to be 1.43±0.01 IF. The results reveal that intraluminal pacing is an effective and efficient method for the entrainment of intestinal slow waves. It may become a potential approach for the treatment of intestinal motor disorders associated with myoelectrical abnormalities. © 2000 Biomedical Engineering Society. PAC00: 8754Dt, 8719Ff, 8717Nn     

Motor unit recruitment and rate coding in response to fatiguing shoulder abductions and subsequent recovery

The purpose of the present study was to investigate motor unit (MU) recruitment and firing rate, and the MU action potential (MUAP) characteristics of the human supraspinatus muscle during prolonged static contraction and subsequent recovery. Eight female subjects sustained a 30° shoulder abduction, requiring 11–12% of maximal voluntary contraction (MVC), for 30 min. At 10 and 30 min into the recovery period, the shoulder abduction was repeated for 1 min. The rating of perceived exertion for the shoulder region increased to “close to exhaustion” during the prolonged contraction, and the surface electromyography (EMG) recorded from the deltoid and trapezius muscles showed signs of local muscle fatigue. From the supraspinatus muscle, a total of 23,830 MU firings from 265 MUs were identified using needle electrodes. Of the identified MUs, 95% were continuously active during the 8-s recordings, indicating a low degree of MU rotation. The mean (range) MU firing rate was 11.2 (5.7–14.5) Hz, indicating the relative force contribution of individual MUs to be larger than the overall mean shoulder muscle load. The average MU firing rate remained stable throughout the prolonged abduction, although firing rate variability increased in response to fatigue. The average concentric MUAP amplitude increased by 38% from the beginning (0–6 min) to the end (24–29 min) of the contraction period, indicating recruitment of larger MUs in response to fatigue. In contrast, after 10 min of recovery the average MU amplitude was smaller than seen initially in the prolonged contraction, but not different after 30 min, while the MU firing rate was higher during both tests. In conclusion, MU recruitment plays a significant role during fatigue, whereas rate coding has a major priority during recovery. Furthermore, a low degree of MU rotation in combination with a high relative load at the MU level may imply a risk of overloading certain MUs during prolonged contractions. Accepted: 6 June 2000     

An inverted seated posture decreases elbow flexion force and muscle activation

The purpose of this study was to determine if discrepancies exist between upright and inverted seated positions in isometric maximal voluntary contraction (MVC) elbow flexor force, MVC force produced in the first 100 ms (F100), MVC rate of force development, electromyographic (EMG) activity of the biceps and triceps as well as heart rate and blood pressure. The results showed significantly (p < 0.01) higher MVC force (543.6 ± 29.6 vs. 486.5 ± 23.0 N), F100 (328.3 ± 94.5 vs. 274.6 ± 101.8 N), rate of force development (p = 0.003) (1,851.9 ± 742.2 vs. 1,591.0 ± 719.6 N s⁻¹) and biceps brachii EMG activity (48%, p < 0.01) in the upright versus inverted condition. There were relatively greater co-contractions with the inverted position (p < 0.01) due to the lack of change in triceps’ EMG and the substantial decrease in biceps’ EMG. There were no significant changes in trunk EMG activity. With inversion, there were significant decreases in heart rate (16.8%), systolic (11.6%) and diastolic (12.1%) blood pressures (p < 0.0001). These results illustrate decrements in neuromuscular performance with an inverted seated posture which may be related to an altered sympathetic response.     

肌萎缩侧索硬化症患者临床与肌电图特点分析

目的：探讨肌萎缩侧索硬化症（ALS）患者的临床特点、肌电图（EMG）和神经传导速度（NCV）对ALS的诊断价值。方法：对42例ALS患者回顾性分析其临床特点、NCV及其胸锁乳突肌、胸段脊旁肌及肢体肌EMG资料。结果：42例患者均呈广泛神经原性损害,胸锁乳突肌EMG异常率为90％,胸椎旁肌EMG异常率为88％,两者异常率均低于上、下肢肌EMG的异常率（100％,98％）,而胸椎旁肌自发电位异常率又高于胸锁乳突肌。结论：早期EMG及NCV检查有助于ALS的早期确诊,行胸锁乳突肌及胸椎脊旁肌EMG检测对ALS的诊断及鉴别诊断有重要价值。     

Neuromuscular adaptations in older males and females with knee osteoarthritis during weight-bearing force control

Background

Females exhibit significantly greater incidence, prevalence, and severity of osteoarthritis (OA) compared to males. Despite known biological, morphological, and functional differences between males and females, there has been little sex-related investigation into sex-specific biomechanical and neuromuscular responses to OA.

人体头低脚高仰卧时下肢被动运动对背部肌肉疲劳的影响

目的研究人体头低位状态下肢被动运动对背部主要肌肉肌电(electromyogram,EMG)活动性的影响。方法选取30名健康受试者,分析竖脊肌和斜方肌在不同头低位角度(0°、10°、20°、27°)下静止状态、120次/min和140次/min足部摆动模式和680次/min足部颤动模式下EMG变化趋势。结果在头低位静止状态时,4种头低位角度下中位频率(media frequency,MF)随角度增加均呈下降趋势;摆动模式下,4种头低位角度的MF值均小于静止状态,且当摆动速度为120次/min时,MF值随角度增加而减小;速度为140次/min时,MF值无规律性变化。颤动模式下,MF值随头低位角度增大而增大,且均大于静止状态。结论静止状态下,肌肉疲劳程度随头低位角度增加而增加;颤动模式下应选择较小的头低位角度可更好达到锻炼治疗效果,摆动模式下可选择较大的头低位角度有助于较好达到锻炼治疗效果。此外,为避免肌肉过度疲劳造成劳损,摆动速度应不大于120次/min。     

Impact of laparoscopic surgery on thoracoabdominal mechanics and inspiratory muscular activity

Objective

To evaluate the effect of laparoscopic surgery on pulmonary volume distributions and inspiratory muscles activity. Respiratory consequences associated with postoperative pain were also evaluated.

Methods

This study enrolled 20 patients without lung disease performed spirometry and chest wall kinematic analyses (i.e., chest wall, upper and lower ribcage and abdominal volumes), and measured the activity of inspiratory muscular before and 2 days after laparoscopic surgery. Pain was also assessed.

Results

After laparoscopy, the patients demonstrated decreased volumes in all three thoracoabdominal compartments: abdomen (ABD), upper and lower rib cage (URC and LRC, respectively) compared with the pre-operative measurements: ABD = 0.38 ± 0.20 L vs. 0.55 ± 0.25 L; URC = 0.45 ± 0.18 L vs. 0.55 ± 0.21 L; and LRC = 0.31 ± 0.18 L vs. 0.41 ± 0.23 L; p < 0.05. A reduction in the inspiratory muscular activity after surgery was also observed (sternocleidomastoid: 10.6 ± 5.1 × 10⁻³ mV vs. 12.8 ± 6.3 × 10⁻³ mV; intercostals: 16.8 ± 12.4 × 10⁻³ mV vs. 25.1 ± 21.3 × 10⁻³ mV; p < 0.05). In addition, lower volumes during deep breathing were observed in patients who reported significant pain than those who did not (0.51 ± 0.17 L vs. 0.79 ± 0.29 L; p < 0.05, respectively).

Conclusion

Laparoscopic surgery reduces chest wall ventilation and inspiratory muscular activity during deep breathing. The effects appear to depend on the patient's reported pain level.     

Sequential activation of axial muscles during different forms of rhythmic behavior in man

In humans, studies of back muscle activity have mainly addressed the functioning of lumbar muscles during postural adjustments or rhythmic activity, including locomotor tasks. The present study investigated how back muscles are activated along the spine during rhythmical activities in order to gain insights into spinal neuronal organization. Electromyographic recordings of back muscles were performed at various trunk levels, and changes occurring in burst amplitudes and phase relationships were analyzed. Subjects performed several rhythmic behaviors: forward walking (FW), backward walking (BW), amble walking (where the subjects moved their arms in phase with the ipsilateral leg), walking on hands and knees (HK) and walking on hands with the knees on the edge of a treadmill (Hand). In a final task, the subjects were standing and were asked to swing (Swing) only their arms as if they were walking. It was found that axial trunk muscles are sequentially activated by a motor command running along the spinal cord (which we term “motor waves”) during various types of locomotion or other rhythmic motor tasks. The bursting pattern recorded under these conditions can be classified into three categories: (1) double-burst rhythmic activity in a descending (i.e., with a rostro-caudal propagation) motor wave during FW, BW and HK conditions; (2) double-burst rhythmic activity with a stationary motor wave (i.e., occurring in a single phase along the trunk) during the ‘amble’ walk condition; (3) monophasic rhythmic activity with an ascending (i.e., with a caudo-rostral propagation) motor wave during the Swing and Hands conditions. Our results suggest that the networks responsible for the axial propagation of motor activity during locomotion may correspond to those observed in invertebrates or lower vertebrates, and thus may have been partly phylogenetically conserved. Such an organization could support the dynamic control of posture by ensuring fluent movement during locomotion.