The placement of skin surface markers for non-invasive measurement of scapular kinematics affects accuracy and reliability

Abnormal scapular movement is widely believed to be an important factor in clinical pathology of the shoulder joint complex. Validated non-invasive techniques for measuring scapular movement have been developed, but the effect of marker placement on accuracy is unknown. The objective of this study was to determine the accuracy and reliability of different groupings of markers to achieve the best accuracy and reliability for measuring scapular kinematics. Eight healthy young adult subjects were recruited. An optoelectronic marker grid was applied to the skin overlying the scapula. Two bone pins with optoelectronic marker carriers were inserted into the scapula. The accuracy of six surface marker configurations was determined by comparing the measured kinematics with scapular bone pins (the gold standard). Four humeral movements were tested: glenohumeral abduction, glenohumeral horizontal adduction, hand behind back, and forward reaching. All three rotations had a significant difference in the accuracy of the patches (p = 0.04 to p < 0.0001). For posterior tipping there was a significant effect of movement (p = 0.003) and a significant interaction (p < 0.0001). There was also a significant interaction for external rotation (p = 0.001). The marker grouping with the largest cranio-caudal spread had the highest accuracy for measuring posterior tilting (RMS 1.9°). Markers closer to the scapular spine were more accurate for tracking external rotation (RMS 2.0°) while an intermediate grouping of markers were most accurate for quantifying upward rotation (RMS 1.9°). The reliability between days ranged between 3.8° and 7.5° (based on RMS difference between trials) and there was a significant interaction between patch and movement (p < 0.0001). Intraclass correlation coefficients show moderate to good agreement for most arm movements and scapular rotations. Thus, there exists distinct optimal configurations of non-invasive marker locations for accurately measuring scapular kinematics.     

Enhancing the weight training experience: a comparison of limb kinematics and EMG activity on three machines

The aim of the study was to compare the kinematics and the timing and amount of electromyographic (EMG) activity during the lat-pull down exercise performed on machines that afforded one, two, or three degrees of freedom for the movement. Seven healthy men (age 29.4 ± 5.6 years) participated in the study. The exercise was performed with a 30% 1-RM load. Three types of machines with varying degrees of freedom were used: Type 1, the conventional device that restricted the movement to a frontal plane; Type 2, the addition of forearm supination–pronation; Type 3, the addition of forearm supination–pronation and horizontal extension–flexion about the shoulder. All exercises involved a technique known as beginning movement load (BML) training in which light loads are lifted with a relaxation-lengthening-shortening sequence of muscle activation. The Type-3 machine showed: (1) the greatest vertical displacement of the wrist (p < 0.05); (2) the greatest abduction–adduction displacement about the shoulder (p < 0.01); (3) the least flexion–extension displacement about the elbow joint (p < 0.01); (4) a peak vertical velocity for the shoulder that preceded (p < 0.01) those for the elbow and then wrist during the pull-down phase; (5) a progressive proximal-to-distal sequence of EMG activation involving the serratus anterior, posterior deltoid, latissimus dorsi, and triceps brachii muscles; (6) a reversal of the roles for biceps and triceps brachii during the pull-down phase. These results suggest that BML exercises with greater degrees of freedom can enhance the association between training actions and functional activities.     

Amplitude and frequency measures of surface electromyography during dual task elbow torque production

Summary Studies of motor unit recruitment thresholds have demonstrated the existence of task-specific motor units within the muscles controlling the elbow. Two degree-of-freedom (df) task specificity was investigated at higher levels of elbow torque using the amplitude and frequency characteristics of surface electromyography (EMG). Flexion and supination torque data were collected together with EMG from electrode pairs on the brachioradialis (BRAD), biceps brachii short head, and medial and lateral aspects of biceps brachii long head, while subjects (n=14) performed the following four combinations of isometric tasks: (1) maximum voluntary contraction (MVC) flexion (F) and (2) MVC supination (S), each with a targeted torque of zero in the second d f; (3) MVC flexion with targeted MVC supination (FS); and (4) MVC supination with targeted MVC flexion (SF). Median power frequency (MEDF) and root mean square (RMS) amplitude under steady-state torque conditions were calculated and analyzed using ANCOVA models with planned contrasts (=0.05). A significant main effect for task was found in RMS, but not in MEDF. Contrasts showed a significant increase in RMS response in the dual MVC tasks (FS and SF) over the single MVC tasks of F and S. The lack of frequency changes with alterations in RMS data indicates that the underlying recruitment/rate coding scheme in use for dual-d f tasks may be different than in single-d f tasks, and provides possible support for the notion of motor unit task groups. Task-by-site interactions were found for both MEDF and RMS, and illustrated that the three biceps sites differed from BRAD in their responses to the F versus S tasks. These results provide further support that the synergy between biceps and BRAD is not fixed, and that the concept of flexor equivalence at the elbow does not hold under all torque task conditions     

Relationship between shot put performance and triceps brachii fiber type composition and power production

It is commonly accepted that shot put performance is mainly determined by the ability of the lower body to produce power. The purpose of the present study was to investigate the relationship between shot put performance and triceps brachii muscle fiber type composition and strength capacity. Thirteen male physical education students were selected to participate in the study based upon their shot put performance after 5 weeks of shot put technique instruction. At the completion of this technique-instruction period, they performed the following tests: shot put with a 6-kg shot, isokinetic torque measurements of the elbow extensors at 0, 0.52, 1.04, 1.57, 2.09, 3.14, and 4.19 rad·s⁻¹, maximal strength (1 RM) and explosive-throwing bench-press tests, one-arm seated shot put with 1-, 2-, 3-, 4-, 5- and 6-kg shot. Whole-body and dominant upper-arm bioimpedance measurements were used to estimate whole-body and upper-arm muscle mass. Muscle biopsy samples from the long head of the dominant triceps brachii were obtained and analyzed for fiber type composition with ATPase histochemistry. Shot put performance was significantly correlated with type II fiber area (r=0.70, P<0.01), one-arm seated shot put (range r=0.60 to r=0.79, P<0.05), elbow extensors' isokinetic torque (range r=0.65 to r=0.78, P<0.05), bench-press tests (r>0.86, P<0.01) and estimated arm muscle cross-sectional area (r=0.68, P<0.05). These results suggest that fiber type composition and the functional capacity of triceps brachii muscle (e.g., isokinetic torque) explain a part of shot put performance. The magnitude of the correlation coefficients between shot put and the upper-body power tests suggests that other body parts (e.g., lower extremities) may play a significant role in this event.     

The accuracy of volume estimates using ultrasound muscle thickness measurements in different muscle groups

This study aimed to investigate the accuracy of estimating the volume of limb muscles (MV) using ultrasonographic muscle thickness (MT) measurements. The MT and MV of each of elbow flexors and extensors, knee extensors and ankle plantar flexors were determined from a single ultrasonographic image and multiple magnetic resonance imaging (MRI) scans, respectively, in 27 healthy men (23–40 years of age) who were allocated to validation (n=14) and cross-validation groups (n=13). In the validation group, simple and multiple regression equations using MT and a set of MT and limb length, respectively, as independent variables were derived to estimate the MV measured by MRI. However, only the multiple regression equations were cross-validated, and so the prediction equations with r ² of 0.787–0.884 and the standard error of estimate of 22.1 cm³ (7.3%) for the elbow flexors to 198.5 cm³ (11.1%) for the knee extensors were developed using the pooled data. This approach did not induce significant systematic error in any muscle group, with no significant difference in the accuracy of estimating MV between muscle groups. In the multiple regression equations, the relative contribution of MT for predicting MV varied from 41.9% for the knee extensors to 70.4% for the elbow flexors. Thus, ultrasonographic MT measurement was a good predictor of MV when combined with limb length. For predicting MV, however, the unsuitability of a simple equation using MT only and the difference between muscle groups in the relative contribution of MT in multiple regression equations indicated a need for further research on the limb site selected and muscle analyzed for MT measurement.     

Scanning plane comparison of ultrasound‐derived morphological characteristics of the vastus lateralis

Muscle morphological characteristics obtained via ultrasonography have been used to quantify the size, architecture, and quality of skeletal muscle. Previous research has utilized varying ultrasonographic techniques, however there is little information comparing these different techniques. Muscle morphological characteristics, including cross‐sectional area (CSA), muscle thickness (MT), echo intensity (EI), and subcutaneous adipose tissue thickness (SubQ) were assessed in 24 males (20.2 ± 1.6 y) via three panoramic‐images captured in the transverse plane (PTI) and three still‐images captured in the longitudinal plane (SLI). Cross‐sectional area of PTI was significantly greater than CSA of SLI (P < 0.001), however positive correlations existed between the two measurements (r = 0.752, P < 0.001). Echo intensity of PTI was significantly lower than EI of SLI (P = 0.002), however, positive correlations existed between the two measurements (r = 0.681, P < 0.001). MT of PTI was significantly greater than MT of SLI (P = 0.003), but positive correlations existed between measurements (r = 0.809, P < 0.001). However, SubQ of PTI was significantly lower than SubQ of SLI (P < 0.001), but positive correlations existed between measurements (r = 0.915, P < 0.001). In conclusions, PTI and SLI yield significantly different CSA, EI, MT, and SubQ measurements but these values are highly correlated. Still longitudinal images require less time, cost, and expertise, and therefore may be preferred over PTI in future studies. Clin. Anat. 30:533–542, 2017. © 2016 Wiley Periodicals, Inc.     

Mixed-type gastric carcinomas exhibit more aggressive features and indicate the histogenesis of carcinomas

To investigate the pathobiological behaviors of gastric mixed-type (MT) carcinomas and gastric carcinogenesis, the clinicopathological characteristics of MT carcinomas were analyzed and compared with intestinal-type (IT) and diffuse-type (DT) carcinomas. The expression of Ki-67, caspase-3, p53, fragile histine triad (FHIT), maspin, extracellular matrix metalloproteinase inducer (EMMPRIN), vascular growth factor (VEGF), MUC-2, 4, 5AC and 6, CD44, E-cadherin, β-catenin, and phosphorylated glycogen synthase kinase 3β-ser⁹ (P-GSK3β-ser⁹) was examined on tissue microarrays using immunohistochemistry. It was found that MT carcinomas exhibited large size, deep invasion, frequent local invasion, and lymph node metastasis in comparison with IT and DT carcinomas (p < 0.05). All the markers except MUC-5AC showed higher expression in IT than DT carcinomas (p < 0.05). The expression of maspin, EMMPRIN, VEGF, MUC-4, and membrane E-cadherin was stronger in MT intestinal than diffuse component (p < 0.05). Immunoreactivities to Ki-67, EMMPRIN, and VEGF were weaker in IT carcinoma than in the MT intestinal portion (p < 0.05), while the opposite was true for CD44, MUC-2, and MUC-6 (p < 0.05). The MT diffuse component displayed a higher expression of FHIT, VEGF, and P-GSK3β-ser⁹ than DT carcinoma (p < 0.05). The accumulative survival rate of the IT carcinoma patients was higher than the other types (p < 0.05). The invasive depth, venous invasion, lymph node, peritoneal or liver metastasis, and Lauren's classification were independent prognostic factors for gastric carcinomas (p < 0.05). These findings suggested that MT carcinomas were also indicated to be more aggressive than IT and DT carcinomas. Significant differences were observed in the proliferation, apoptosis, angiogenesis, mucin secretion, and cell adhesion between IT and DT carcinomas, whereas only a few of these characteristics showed differences between the MT intestinal and diffuse parts, thus suggesting that both the MT components might originate from the stem cells with similar genetic traits, but follow different histogenic pathways.     

Determining natural arm configuration along a reaching trajectory

Owing to the flexibility and redundancy of neuromuscular and skeletal systems, humans can trace the same hand trajectory in space with various arm configurations. However, the joint trajectories of typical unrestrained movements tend to be consistent both within and across subjects. In this paper we propose a method to solve the 3-D inverse kinematics problem based on minimizing the magnitude of total work done by joint torques. We examined the fit of the joint-space trajectories against those observed from human performance in a variety of movement paths in 3-D workspace. The results showed that the joint-space trajectories produced by the method are in good agreement with the subjects’ arm movements (r ²>0.98), with the exception of shoulder adduction/abduction (where, in the worst case, r ² ∼0.8). Comparison of humeral rotation predicted by our algorithm with other models showed that the correlation coefficient (r ²) between actual data and our predictions is extremely high (mostly >0.98, 11 out of 15 cases, with a few exceptions, 4 of 15, in the range of 0.8–0.9) and the slope of linear regression is much closer to one (<0.05 distortion in 12 out of 15 cases, with only one case >0.15). However, the discrepancy in shoulder adduction/abduction indicated that when only the hand path is known, additional constraint(s) may be required to generate a complete match with human performance.     

Kinesthetic perceptions of earth- and body- fixed axes

 The major purpose of this research was to determine whether kinesthetic/proprioceptive perceptions of the earth-fixed vertical axis are more accurate than perceptions of intrinsic axes. In one experiment, accuracy of alignment of the forearm to earth-fixed vertical and head- and trunk-longitudinal axes by seven blindfolded subjects was compared in four tasks: (1) Earth-Arm – arm (humerus) orientation was manipulated by the experimenter; subjects aligned the forearm parallel to the vertical axis, which was also aligned with the head and trunk longitudinal axis; (2) Head – head, trunk, and upper-limb orientations were manipulated by the experimenter, subjects aligned the forearm parallel to the longitudinal axis of the head using only elbow flexion/extension and shoulder internal/external rotation; (3) Trunk – same as (2), except that subjects aligned the forearm parallel to the trunk-longitudinal axis; (4) Earth – same as (2), except that subjects aligned the forearm parallel to the earth-fixed vertical. Head, trunk, and gravitational axes were never parallel in tasks 2, 3, and 4 so that subjects could not simultaneously match their forearm to all three axes. The results showed that the errors for alignment of the forearm with the earth-fixed vertical were lower than for the trunk- and head-longitudinal axes. Furthermore, errors in the Earth condition were less dependent on alterations of the head and trunk orientation than in the Head and Trunk conditions. These data strongly suggest that the earth-fixed vertical is used as one axis for the kinesthetic sensory coordinate system that specifies upper-limb orientation at the perceptual level. We also examined the effects of varying gravitational torques at the elbow and shoulder on the accuracy of forearm alignment to earth-fixed axes. Adding a 450 g load to the forearm to increase gravitational torques when the forearm is not vertical did not improve the accuracy of forearm alignment with the vertical. Furthermore, adding small, variably sized loads (between which the subjects could not distinguish at the perceptual level) to the forearm just proximal to the wrist produced similar errors in aligning the forearm with the vertical and horizontal. Forearm-positioning errors were not correlated with the size of the load, as would be expected if gravitational torques affected forearm-position sense. We conclude that gravitational torques exerted about the shoulder and elbow do not make significant contributions to sensing forearm-orientation relative to earth-fixed axes when the upper-limb segments are not constrained by external supports. Received: 26 March 1998 / Accepted: 21 December 1998     

可穿戴上肢康复机器人的设计及其运动仿真和动力学分析

目的针对目前台式上肢康复机器人体积庞大、不便移动的缺点,设计了一款新型的可穿戴式上肢康复机器人,并通过对其运动特性的分析和关节力矩的计算,验证设计的合理性。方法首先,根据模块化设计原理,进行总体结构设计;然后,利用SOILDWORKS进行三维建模,并运用SOILDWORKS Motion对机器人肘关节屈曲/伸展运动、肩关节屈曲/伸展运动、肩肘关节联动运动进行运动仿真;最后,基于拉格朗日方法建立系统的动力学方程,并应用MATLAB软件计算得到机械臂关节力矩的变化曲线。结果仿真结果证实了肩关节、肘关节、腕关节运动仿真曲线平滑,动力学分析证实关节力矩变化曲线平滑且最大关节力矩均小于电机经减速后输出的额定转矩。结论该可穿戴式上肢康复机器人设计合理,为后续上肢康复机器人的研究奠定了理论基础。     

Force synchrony enhances the stability of rhythmic multi-joint arm coordination

Although rhythmic coordination has been extensively studied in the literature, questions remain about the correspondence of constraints that have been identified in the related contexts of inter-limb and intra-limb coordination. Here we used a 2-DOF robot arm which allows flexible manipulation of forces to investigate the effect on coordination stability of intra-limb coordination of: (i) the synchrony of force requirements and (ii) the involvement of bi-functional muscles. Ten subjects produced simultaneous rhythmic flexion–extension (FE) and supination-pronation (SP) elbow movements in two coordination patterns: (1) flexion synchronized with supination/extension with pronation (in-phase pattern) and (2) flexion synchronized with pronation/extension with supination (anti-phase pattern). The movements were produced with five different settings of the robot arm: a neutral setting that imposed balanced force requirements, and four other settings that increased the force requirements for one direction in both DOF. When combined with specific coordination patterns, these settings created conditions in which either synchronous or alternate patterns of forcing were necessary to perform the task. Results showed that synchronous tasks were more stable than asynchronous tasks (P < 0.05). Within the synchronous tasks, some robot settings were designed to either increase or decrease the use of bi-functional muscles. Although there was no difference for the bi-functional muscle biceps brachii, the coordination was more stable for the condition in which the greatest force requirements corresponded to the mechanical action of the bi-functional pronator teres (P < 0.05). In conclusion, force synchrony increases the stability of rhythmic intra-limb coordination, but further research is needed to clarify the role of bi-functional muscles in this effect.     

Relationship between gluteal muscle activation and upper extremity kinematics and kinetics in softball position players

As the biomechanical literature concerning softball pitching is evolving, there are no data to support the mechanics of softball position players. Pitching literature supports the whole kinetic chain approach including the lower extremity in proper throwing mechanics. The purpose of this project was to examine the gluteal muscle group activation patterns and their relationship with shoulder and elbow kinematics and kinetics during the overhead throwing motion of softball position players. Eighteen Division I National Collegiate Athletic Association softball players (19.2 ± 1.0 years; 68.9 ± 8.7 kg; 168.6 ± 6.6 cm) who were listed on the active playing roster volunteered. Electromyographic, kinematic, and kinetic data were collected while players caught a simulated hit or pitched ball and perform their position throw. Pearson correlation revealed a significant negative correlation between non-throwing gluteus maximus during the phase of maximum external rotation to maximum internal rotation (MIR) and elbow moments at ball release (r = ?0.52). While at ball release, trunk flexion and rotation both had a positive relationship with shoulder moments at MIR (r = 0.69, r = 0.82, respectively) suggesting that the kinematic actions of the pelvis and trunk are strongly related to the actions of the shoulder during throwing.     

Relationship between perceived exertion and mean power frequency of the EMG signal from the upper trapezius muscle during isometric shoulder elevation

The aim of the study was to investigate the relationship between a fatigue-induced increase of perceived exertion in the neck with a decrease of mean power frequency (MPF) in the surface electromyography (sEMG) signal during repeated shoulder elevation endurance tasks. About Thirty-two healthy women (age range 20–62) performed two maximum 6-min shoulder elevation endurance tasks at 30% of their maximal voluntary contraction (MVC) level, separated by a rest of 6 min. During these exercises, perceived exertion was estimated using the Borg scale (range 0–10), whereas the MPF of the sEMG signal from the upper trapezius was simultaneously detected. Linear regression analysis was applied over time for each trial and subject for both MPF and Borg scale rating values. The MPF was normalized by the intercept of the linear regression analysis. The resulting slopes of normalized mean power frequency (nMPF) and Borg scale rating were correlated with each other by linear regression for both trials. In order to investigate the individual behavior of fatigue effects between trials, Δ _{trial 2-trial 1} slopes of nMPF and Borg scale ratings were calculated for each subject. These slopes of nMPF and Borg scale ratings were correlated with each other as well by linear regression. The increase of Borg scale ratings, as well as the decrease of nMPF, were significantly higher in trial 2 than trial 1 (P<0.01). The results show a linear correlation between slopes of nMPF and Borg scale ratings for both trials 1 and 2 (r=0.76, P<0.01). Trial-to-trial slopes (Δ _{trial 2-trial 1}) of nMPF and Borg scale rating, were also significantly correlated (r=0.68, P<0.05). Thus, the individually sensed increase of perceived exertion in the neck during trial 2 was accompanied by a simultaneously higher detected decrease of nMPF. These findings indicate a close relationship between subjective perception of exertion in the neck and objectively assessed muscle fatigue of the upper trapezius.     

Analysis of a sprint ski race and associated laboratory determinants of world-class performance

This investigation was designed to analyze the time-trial (STT) in an international cross-country skiing sprint skating competition for (1) overall STT performance and relative contributions of time spent in different sections of terrain, (2) work rate and kinematics on uphill terrain, and (3) relationships to physiological and kinematic parameters while treadmill roller ski skating. Total time and times in nine different sections of terrain by 12 world-class male sprint skiers were determined, along with work rate and kinematics for one specific uphill section. In addition, peak oxygen uptake (VO_2peak), gross efficiency (GE), peak speed (V_peak), and kinematics in skating were measured. Times on the last two uphill and two final flat sections were correlated to overall STT performance (r = ~−0.80, P < 0.001). For the selected uphill section, speed was correlated to cycle length (r = −0.75, P < 0.01) and the estimated work rate was approximately 160% of peak aerobic power. VO_2peak, GE, V_peak, and peak cycle length were all correlated to STT performance (r = ~−0.85, P < 0.001). More specifically, VO_2peak and GE were correlated to the last two uphill and two final flat section times, whereas V_peak and peak cycle length were correlated to times in all uphill, flat, and curved sections except for the initial section (r = ~−0.80, P < 0.01). Performances on uphill and flat terrain in the latter part were the most significant determinants of overall STT performance. Peak oxygen uptake, efficiency, peak speed, and peak cycle length were strongly correlated to overall STT performance, as well as to performance in different sections of the race.     

Recumbent stepping has similar but simpler neural control compared to walking

The purpose of this study was to compare muscle activation patterns and kinematics during recumbent stepping and walking to determine if recumbent stepping has a similar motor pattern as walking. We measured joint kinematics and electromyography in ten neurologically intact humans walking on a treadmill at 0 and 50% body weight support (BWS), and recumbent stepping using a commercially available exercise machine. Cross correlation of upper and lower limb electromyography patterns between conditions revealed high correlations for most muscles. A principal component analysis revealed that the first factor accounted for more muscle activation signal content during recumbent stepping (81%) than during walking (70%). This indicates that the motor pattern during walking is more complex than during stepping. Cross correlation analysis found a high correlation between factors for recumbent stepping and walking (R = 0.54), though not as high as the correlation between factors for walking at 0% BWS and walking at 50% BWS (R = 0.68). There were substantial differences in joint kinematics between walking and recumbent stepping, most notably in hip, elbow, and shoulder motions. These results suggest that although the two tasks have different kinematic patterns, recumbent stepping relies on similar neural networks as walking. Individuals with neurological impairments may be able to improve walking ability from recumbent stepping practice given similarities in neural control between the two tasks.     

The relationship between oxygenation and myoelectric activity in the forearm and shoulder muscles of males and females

The aim was to investigate the relationship between oxygen saturation (StO₂%) measured with near-infrared spectroscopy (NIRS) and myoelectric activity (root mean square, RMS) for the extensor carpi radialis (ECR) and trapezius muscles. In addition, gender differences were examined for submaximal (10–70% MVC) and sustained (10% MVC for 5 min) isometric contractions. Thirteen males and 15 females participated. Changes in StO₂% (∆StO₂%) and RMS, expressed as percentages of maximum, were calculated for each submaximal contraction. A good correlation between ∆StO₂% and RMS was seen for the ECR (r = −0.53) and a moderate correlation seen for the trapezius muscle (r = −0.44). The ANOVA showed a significant decrease in ECR-∆StO₂% over force with females demonstrating a tendency for larger changes than males. ECR-RMS increased over force with no impact of gender. For the trapezius, ∆StO₂% decreased over force but was not gender dependent. Trapezius-RMS increased over force with females demonstrating a tendency for greater change than males. For the sustained contraction, ECR-StO₂% changed over time but was not gender dependent. ECR-RMS increased over time with females showing a greater response than males. Trapezius-StO₂% changed over time and differed between genders, i.e., males increased while females decreased. RMS increased over time similarly for both genders. In conclusion, our data show that the ECR and trapezius aerobic demands during isometric contractions are negatively correlated to electromyography (EMG) RMS. The present study also suggests some gender specificity for forearm and shoulder myoelectric activity and oxygenation for submaximal and sustained contractions.     

Age and Gender Effects on the Proximal Propagation of an Impulsive Force Along the Adult Human Upper Extremity

We tested the null hypotheses that neither age, gender nor muscle pre-cocontraction state affect the latencies of changes in upper extremity kinematics or elbow muscle activity following an impulsive force to the hand. Thirty-eight healthy young and older adult volunteers lay prone on an apparatus with shoulders flexed 75° and arms slightly flexed. The non-dominant hand was subjected to three trials of impulsive loading with arm muscles precontracted to 25, 50, or 75% of maximum pre-cocontraction levels. Limb kinematic data and upper extremity electromyographic (EMG) activity were acquired. The results showed that pre-cocontraction muscle level (p < 0.001) and gender (p < 0.05 for wrist and shoulder) affected joint displacement onset times and age affected EMG onset times (p < 0.05). The peak applied force (F ₁) occurred a mean (± SD) 27 (± 2) ms after impact. The latencies for the wrist, elbow, and shoulder displacements were 21 ± 3, 29 ± 5, and 34 ± 7 ms, respectively. Because the latencies for elbow flexion and lateral triceps EMG were 23 ± 5 and 84 ± 8 ms, respectively, muscle pre-activation rather than stretch reflexes prevent arm buckling under impulsive end loads.     

Influence of cold shivering on fine motor control in the upper limb

The aim of the investigation was to determine the effects of cold shivering on the accuracy of force output in distal, middle and proximal muscles of the upper limb. Tests of hand grip strength, elbow flexion and shoulder flexion (each done at 10% maximal voluntary contraction for 15 s) were done under three conditions: (1) thermoneutral air (27 °C), a condition of thermal comfort; (2) cold air (10 °C), a condition eliciting an increase in tonic muscle activity; (3) and cold air (10 °C) with a cold drink (8 °C), a condition that causes visible shivering. The averaged (root mean square) electromyogram (AEMG) and mean power frequency (MPF) were measured from proximal, middle and distal arm muscles during the tests and compared. The control of force output was highly effective at thermoneutral condition for all motor tasks. During the cold air condition, all muscles were tonically active but there was no effect on accuracy of test performance. However, AEMG increased ≈20% (P < 0.05) with respect to test performance in thermoneutral condition. During the cold air/cold drink condition, all muscles were shivering to a different extend. AEMG during test performance increased 30–150% in comparison to thermoneutral condition (P < 0.05). In this case, hand grip and elbow flexion were not adversely affected (these tests require middle and distal muscles) by cold shivering. However, the accuracy of performance of shoulder flexion was adversely affected. This is consistent with the fact that proximal muscles are more active during cold shivering.     

Relationship between lipoprotein(a) levels, oxidative stress, and blood pressure levels in patients with essential hypertension

High plasma levels of lipoprotein(a) [Lp(a)] are considered a risk factor for the development of coronary artery disease. In vitro experiments have shown that oxidized Lp(a) is able to impair the arterial endothelium-dependent dilation, thus suggesting a possible role of Lp(a) in the genesis of essential hypertension. The aim of our work was to investigate the correlation of blood pressure levels with plasma Lp(a) concentration, apo(a) isoform size, and peroxidative stress in patients with essential hypertension. The study was performed in 54 untreated hypertensive patients whose blood pressure was monitored for 24 h by ambulatory blood pressure monitoring. Lp(a) concentration was measured by a double monoclonal antibody-based enzyme immunoassay demonstrated to be insensitive to apo(a) size heterogeneity. Apo(a) isoforms were determined by a high-resolution SDS-agarose gel electrophoresis followed by immunoblotting. A significant correlation was found between Lp(a) levels and the night-time systolic and diastolic pressures (r=0.32, P<0.05, and r=0.30, P<0.05, respectively), as well as with the mean night-time fall in systolic and diastolic blood pressures (r=0.28, P<0.05 and r=0.29, P<0.05, respectively). These relationships were further potentiated when peroxidative stress data were taken into consideration (r=0.37 and r=0.40, P<0.01 for the night-time systolic and diastolic pressures, respectively and r=0.34 and r=0.38, P<0.01 for the night-time fall in systolic and distolic blood pressures, respectively). Apo(a) isoform size did not affect these relationships. Our data suggest that Lp(a) and peroxidative stress may be involved as cofactors in essential hypertension, with a mechanism that remains to be elucidated. Received: 16 July 2001 / Accepted: 15 September 2001     

Time-dependent adaptations to posture and movement characteristics during the development of repetitive reaching induced fatigue

Repetitive movements are common to many daily activities but often lead to the development of fatigue. We have previously shown that fatigue leads to changes in tridimensional spatial characteristics of the whole body. However, temporal aspects of these posture and movement adaptations have yet to be investigated. Healthy subjects (N = 14) performed a continuous reaching task by pointing between two targets placed at shoulder height, at 100 and 30% arm’s length, anterior to the subject’s midline until fatigue (assessed using the Borg CR-10 scale). Whole body kinematics and upper Trapezius EMG were recorded and analyzed at 1-min intervals to document the progression of fatigue on outcome variables. For all upper limb and postural variables analyzed, changes began to occur approximately midway to fatigue and were followed by an increase in Trapezius activity from baseline. Reach-to-reach variability of joint average positions and range of motion (ROM) increased in multiple directions for shoulder and elbow parameters. Reach-to-reach variability of the center-of-mass ROM also increased in several directions. Changes were also observed in within-movement inter-segmental timing. The peak velocities of elbow and endpoint occurred closer together in time during fatigue while the shoulder peak velocity occurrence showed a greater reach-to-reach variability. Our results suggest that the effects of fatigue on repetitive movement kinematics can be observed across three temporal dimensions of the task: (1) within individual movements, (2) from one movement to the next, and (3) as fatigue develops. Each observed change is discussed as a potential contributor to task-specific control strategies to prolong task performance.