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At least 181 records · Page 10Linked to original sources
PubMed2006

Mechanical energetic contributions from individual muscles and elastic prosthetic feet during symmetric unilateral transtibial amputee walking: a theoretical study.

Energy storage and return (ESAR) foot-ankle prostheses have been developed in an effort to improve gait performance in lower-limb amputees. However, little is known about their effectiveness in providing the body segment mechanical energetics normally provided by the ankle muscles. The objective of this theoretical study was to use muscle-actuated forward dynamics simulations of unilateral transtibial amputee and non-amputee walking to identify the contributions of ESAR prostheses to trunk support, forward propulsion and leg swing initiation and how individual muscles must compensate in order to produce a normal, symmetric gait pattern. The simulation analysis revealed the ESAR prosthesis provided the necessary trunk support, but it could not provide the net trunk forward propulsion normally provided by the plantar flexors and leg swing initiation normally provided by the biarticular gastrocnemius. To compensate, the residual leg gluteus maximus and rectus femoris delivered increased energy to the trunk for forward propulsion in early stance and late stance into pre-swing, respectively, while the residual iliopsoas delivered increased energy to the leg in pre- and early swing to help initiate swing. In the intact leg, the soleus, gluteus maximus and rectus femoris delivered increased energy to the trunk for forward propulsion in the first half of stance, while the iliopsoas increased the leg energy it delivered in pre- and early swing. Thus, the energy stored and released by the ESAR prosthesis combined with these muscle compensations was able to produce a normal, symmetric gait pattern, although various neuromuscular and musculoskeletal constraints may make such a pattern non-optimal.

Amputation, Surgical↗
PubMed2005

The quasi-static response of compliant prosthetic sockets for transtibial amputees using finite element methods.

The finite element method (FEM) is a very powerful tool for analyzing the behavior of structures, especially when the geometry and mechanics are too complex to be modeled with analytical methods. This study focuses on the analysis of patellar tendon bearing prosthetic sockets with integrated compliant features designed to relieve contact pressure between the residual limb and socket. We developed a FEM model composed of a socket, liner and residual limb and analyzed it under quasi-static loading conditions derived from experimentally measured ground reaction forces. The geometry of the residual limb, liner and socket were acquired from computed tomography (CT) data of a transtibial amputee. Three different compliant designs were analyzed using FEM to assess the structural integrity of the sockets and their ability to relieve local pressure at the fibula head during normal walking. The compliant features consisted of thin-wall sections and two variations of spiral slots integrated within the socket wall. One version of the spiral slots produced the largest pressure relief, with an average reduction in local interface pressure during single-leg stance (20-80% of the stance phase) from 172 to 66.4 kPa or 65.8% compared to a baseline socket with no compliant features. These results suggest that the integration of local compliant features is an effective method to reduce local contact pressure and improve the functional performance of prosthetic sockets.

Amputation, Surgical↗
PubMed2005

The human papillomavirus type 11 E1--E4 protein is a transglutaminase 3 substrate and induces abnormalities of the cornified cell envelope.

The human papillomavirus (HPV) E1--E4 protein is detected in the cytoplasm of differentiated keratinocytes, near the cornified cell envelope. HPV does not induce lysis of the infected keratinocyte, and the normally durable cornified cell envelope that forms during keratinocyte differentiation would seemingly inhibit viral egress. HPV infection induces abnormalities of the cornified cell envelope, but the exact mechanisms involved are not well understood. We tested whether the HPV 11 E1--E4 protein, which co-localizes the cell envelope and co-purifies with cell envelope fragments, could serve as an in vitro substrate for transglutaminases. We found evidence of E1--E4 cross-linking by endogenous transglutaminases in an in situ assay using frozen sections of human foreskin, and in addition, E1--E4 protein was cross-linked by recombinant transglutaminase 3 (but not transglutaminase 1) in an in vitro cross-linking assay. We also tested whether expression of E1--E4 in differentiated keratinocytes would induce morphologic alterations of cornified cell envelopes. Differentiated keratinocytes expressing E1--E4 were disorganized and pleomorphic compared to control cells, and cell envelopes purified from E1--E4-expressing cells were small, fragmented, and rough bordered compared to the round, smooth bordered cell envelopes from control cells. We conclude from these in vitro experiments that the E1--E4 protein is cross-linked by transglutaminase 3, and that E1--E4 expression in differentiated keratinocytes induces morphologic abnormalities of the cornified cell envelope.

Cell Fractionation↗
PubMed1987

Pancoast tumors: improved survival with preoperative and postoperative radiotherapy.

Long-term survival after treatment of Pancoast tumors has been limited in most series to those patients without positive lymph nodes or residual tumor. In our series of 18 consecutive patients treated with preoperative irradiation and resection, 14 underwent supplemental postoperative radiotherapy because of positive lymph nodes, tumor at the resection margin, or both. No hospital deaths occurred. Eight patients subsequently died, 6 because of metastatic disease; only 2 deaths were secondary to local recurrence. Ten patients are alive at 6 months to 13 years after resection, and 9 of the 10 have no evidence of tumor recurrence. The overall five-year observed survival (Kaplan-Meier) for the entire series was 56.1 +/- 12.7% (+/- standard error). Although the number of patients is small, the addition of postoperative radiotherapy for those with unfavorable operative findings resulted in long-term survival comparable to that of patients with negative nodes and margins.

Adult↗
PubMed1983

Intraaortic balloon pump morbidity: a comparative analysis of risk factors between percutaneous and surgical techniques.

We reviewed our concurrent experience with percutaneous insertion versus surgical placement of the intraaortic balloon pump over a two-year period both to compare morbidity and to provide guidelines for the choice of method in particular patient groups and clinical settings. The effects on morbidity of sex, age, emergency placement, coexisting peripheral vascular disease, and duration of counterpulsation were determined. Sex was a highly significant factor, with low complication rates (3/29 or 10.3%) for percutaneous insertion in men and an inordinately high morbidity (12/17 or 70.6%) in women (Fisher exact test: p = 4.611 X 10(-5)). This difference may be due to the smaller size of the femoral artery in women. We conclude that percutaneous insertion is the preferred technique for most men but that direct exposure of the femoral artery should be employed in women. Given the serious morbidity encountered with each technique, there is no justification to broaden the indications for intraaortic balloon counterpulsation.

Assisted Circulation↗
PubMed1986

Transthoracic versus extrathoracic esophagectomy: mortality, morbidity, and long-term survival.

Extrathoracic esophagectomy for carcinoma is an acceptable substitute for transthoracic resection if it can be shown to have comparable or superior safety and no adverse effect on long-term survival. To test this hypothesis, we employed extrathoracic esophagectomy in 30 consecutive patients with carcinoma of the esophagus from January, 1978, to July, 1984. During this period, 65 comparable patients underwent transthoracic resection through a left thoracotomy for lower esophageal lesions or a right thoracotomy and laparotomy for upper thoracic lesions. Only patients with carcinoma limited to the gastric cardia were excluded from the study. Overall morbidity was higher in the extrathoracic than in the transthoracic group (13 of 30 or 43.3% versus 15 of 65 or 23.1%; p = 0.05), but the differences in hospital mortality (4 of 65 or 6.2% for the transthoracic group versus 4 of 30 or 13.3% for the extrathoracic group) and duration of hospital stay (17.4 +/- 11.7 days for the transthoracic group versus 20.5 +/- 13.4 days for the extrathoracic group) were not statistically significant. Considering all patients who either died or sustained a postoperative complication, we found significant differences favoring transthoracic resection in those subgroups of patients who were able to undergo primary reconstruction at the time of resection (12 of 57 or 21.1% versus 15 of 28 or 53.6%; p = 0.004), those with advanced Stage III lesions (11 of 47 or 23.4% versus 12 of 20 or 60%; p = 0.006), those with tumor of the lower esophagus (8 of 35 or 22.9% versus 6 of 10 or 60%; p = 0.04), and those with tumor that could be resected through a left thoracotomy (2 of 18 or 11.1% versus 17 of 30 or 56.7%; p = 0.002). Actuarial survival curves for all transthoracic and extrathoracic resections and separate analysis for Stage I and Stage III tumors revealed no statistically significant differences between these two techniques.

Aged↗
PubMed1975

Primary cancer of the lung. A 42-year experience.

Between April, 1932, and July, 1974, 3,808 patients with primary lung cancer were studied and 1,848 underwent resection. Among untreated patients, 95% were dead with a year. Unresected cancer of the lung is so lethal that efforts to streamline surgical management should not be neglected. In good-risk patients with isolated lesions the approach can be direct. If surgical excision is indicated, regardless of a positive or negative sputum cytology, bronchoscopic biopsy, or brush biopsy, such investigations become superfluous. Needle biopsy is also inconclusive and in addition is hazardous. Preoperative investigation should focus on cardiopulmonary reserve more than on ways to obtain tissue for verification. With the passage of time, the extent of resection has become more conservative. The value of palliative resection is now better appreciated in terms of quality of life, its prolongation, and, for some, a possibility for cure.

Humans↗
PubMed2001

Contributions of the individual ankle plantar flexors to support, forward progression and swing initiation during walking.

Walking is a motor task requiring coordination of many muscles. Previous biomechanical studies, based primarily on analyses of the net ankle moment during stance, have concluded different functional roles for the plantar flexors. We hypothesize that some of the disparities in interpretation arise because of the effects of the uniarticular and biarticular muscles that comprise the plantar flexor group have not been separated. Furthermore, we believe that an accurate determination of muscle function requires quantification of the contributions of individual plantar flexor muscles to the energetics of individual body segments. In this study, we examined the individual contributions of the ankle plantar flexors (gastrocnemius (GAS); soleus (SOL)) to the body segment energetics using a musculoskeletal model and optimization framework to generate a forward dynamics simulation of normal walking at 1.5 m/s. At any instant in the gait cycle, the contribution of a muscle to support and forward progression was defined by its contribution to trunk vertical and horizontal acceleration, respectively, and its contribution to swing initiation by the mechanical energy it delivers to the leg in pre-swing (i.e., double-leg stance prior to toe-off). GAS and SOL were both found to provide trunk support during single-leg stance and pre-swing. In early single-leg stance, undergoing eccentric and isometric activity, they accelerate the trunk vertically but decelerate forward trunk progression. In mid single-leg stance, while isometric, GAS delivers energy to the leg while SOL decelerates it, and SOL delivers energy to the trunk while GAS decelerates it. In late single-leg stance through pre-swing, though GAS and SOL both undergo concentric activity and accelerate the trunk forward while decelerating the downward motion of the trunk (i.e., providing forward progression and support), they execute different energetic functions. The energy produced from SOL accelerates the trunk forward, whereas GAS delivers almost all its energy to accelerate the leg to initiate swing. Although GAS and SOL maintain or accelerate forward motion in mid single-leg stance through pre-swing, other muscles acting at the beginning of stance contribute comparably to forward progression. In summary, throughout single-leg stance both SOL and GAS provide vertical support, in mid single-leg stance SOL and GAS have opposite energetic effects on the leg and trunk to ensure support and forward progression of both the leg and trunk, and in pre-swing only GAS contributes to swing initiation.

Adult↗
PubMed1997

Pedal and knee loads using a multi-degree-of-freedom pedal platform in cycling.

To provide a scientific basis for the design of bicycle pedals which possibly alleviate over-use knee injuries, two hypotheses were tested in the present study. The two hypotheses were: (1) that the three-dimensional pedal constraint loads; and (2) that the three-dimensional intersegmental knee loads would be reduced more significantly by a foot/pedal platform allowing both adduction/abduction and inversion/eversion rotations simultaneously than by a platform which allowed either rotation individually. To test these hypotheses, pedal load and lower limb kinematic data were collected from 10 subjects who pedaled with four pedal platforms which allowed zero, one, and two degrees of freedom. A number of quantities describing both pedal loads and intersegmental knee loads was computed for each of the four pedal platforms using a previously reported biomechanical model. The quantities included the positive and negative extremes, averages, and areas, as well as the total absolute area and RMS. Quantities were compared using analysis of variance techniques. The key results were that there were significant reductions in the coupled nondriving moments at the pedal for the dual-rotation platform compared to each of the single-rotation cases. The significant reductions in the coupled moments at the pedal were not manifest at the knee. However, a general nonsignificant reduction in both coupled knee moments was evident. Also, the valgus knee moment was significantly reduced by the dual-rotation platform compared to the inversion/eversion only design. Although the axial knee moment was not significantly reduced by the dual-rotation platform over the adduction/abduction design, there was a general nonsignificant reduction. The lack of significance in knee load results occurred because of high intersubject variability. Accordingly, load reduction benefits made by introducing the second degree of freedom need to be considered individually.

Adult↗
PubMed1997

The effect of pedaling rate on coordination in cycling.

To further understand lower extremity neuromuscular coordination in cycling, the objectives of this study were to examine the effect of pedaling rate on coordination strategies and interpret any apparent changes. These objectives were achieved by collecting electromyography (EMG) data of eight lower extremity muscles and crank angle data from ten subjects at 250 W across pedaling rates ranging from 45 to 120 RPM. To examine the effect of pedaling rate on coordination, EMG burst onset and offset and integrated EMG (iEMG) were computed. In addition, a phase-controlled functional group (PCFG) analysis was performed to interpret observed changes in the EMG patterns in the context of muscle function. Results showed that the EMG onset and offset systematically advanced as pedaling rate increased except for the soleus which shifted later in the crank cycle. The iEMG results revealed that muscles responded differently to increased pedaling rate. The gastrocnemius, hamstring muscles and vastus medialis systematically increased muscle activity as pedaling rate increased. The gluteus maximus and soleus had significant quadratic trends with minimum values at 90 RPM, while the tibialis anterior and rectus femoris showed no significant association with pedaling rate. The PCFG analysis showed that the primary function of each lower extremity muscle remained the same at all pedaling rates. The PCFG analysis, which accounts for muscle activation dynamics, revealed that the earlier onset of muscle excitation produced muscle activity in the same region of the crank cycle. Also, while most of the muscles were excited for a single functional phase, the soleus and rectus femoris were excited during two functional phases. The soleus was classified as an extensor-bottom transition muscle, while the rectus femoris was classified as a top transition-extensor muscle. Further, the relative emphasis of each function appeared to shift as pedaling rate was increased, although each muscle remained bifunctional.

Adult↗
PubMed1998

Standard mechanical energy analyses do not correlate with muscle work in cycling.

The goal of this study was to assess the utility of experimental methods to quantify mechanical energy expenditure (MEE) in human movement. To achieve this goal, a theoretical model of steady-state cycling driven by individual muscle actuators was used to produce two distinct pedal simulations. The simulations yielded the same pedaling rate and power output, but one reduced the MEE by avoiding eccentric muscle contractions. Contractile element force and length change in the individual muscles was used to quantify the total positive and negative work produced by the muscles. Three methods using external measurements were applied to the simulated movement. The three methods to quantify MEE were based on: (1) segment kinematic measurements, (2) work done by total joint powers and (3) intercompensated joint powers, i.e. negative work from one joint is transferred to an adjacent joint where energy is being generated (positive work) via biarticular muscles. The results showed that none of the MEE analyses were correlated to the MEE of the individual muscles, with errors reaching 40%. Errors were mainly attributed to the inability of the MEE methods to account for co-contractions of antagonistic muscle groups. This phenomenon occurred primarily when one muscle generated force during activation while the antagonist generated force during deactivation.

Bicycling↗
PubMed1999

A theoretical analysis of preferred pedaling rate selection in endurance cycling.

One objective of this study was to investigate whether neuromuscular quantities were associated with preferred pedaling rate selection during submaximal steady-state cycling from a theoretical perspective using a musculoskeletal model with an optimal control analysis. Specific neuromuscular quantities of interest were the individual muscle activation, force, stress and endurance. To achieve this objective, a forward dynamic model of cycling and optimization framework were used to simulate pedaling at three different rates of 75, 90 and 105 rpm at 265 W. The pedaling simulations were produced by optimizing the individual muscle excitation timing and magnitude to reproduce experimentally collected data. The results from these pedaling simulations indicated that all neuromuscular quantities were minimized at 90 rpm when summed across muscles. In the context of endurance cycling, these results suggest that minimizing neuromuscular fatigue is an important mechanism in pedaling rate selection. A second objective was to determine whether any of these quantities could be used to predict the preferred pedaling rate. By using the quantities with the strongest quadratic trends as the performance criterion to be minimized in an optimal control analysis, these quantities were analyzed to assess whether they could be further minimized at 90 rpm and produce normal pedaling mechanics. The results showed that both the integrated muscle activation and average endurance summed across all muscles could be further minimized at 90 rpm indicating that these quantities cannot be used individually to predict preferred pedaling rates.

Adult↗
PubMed1999

The influence of pedaling rate on bilateral asymmetry in cycling.

The objectives of this study were to (1) determine whether bilateral asymmetry in cycling changed systematically with pedaling rate, (2) determine whether the dominant leg as identified by kicking contributed more to average power over a crank cycle than the other leg, and (3) determine whether the dominant leg asymmetry changed systematically with pedaling rate. To achieve these objectives, data were collected from 11 subjects who pedaled at five different pedaling rates ranging from 60 to 120 rpm at a constant workrate of 260 W. Bilateral pedal dynamometers measured two orthogonal force components in the plane of the bicycle. From these measurements, asymmetry was quantified by three dependent variables, the percent differences in average positive power (%AP), average negative power (%AN), and average crank power (%AC). Differences were taken for two cases--with respect to the leg generating the greater total average for each power quantity at 60 rpm disregarding the measure of dominance, and with respect to the dominant leg as determined by kicking. Simple linear regression analyses were performed on these quantities both for the subject sample and for individual subjects. For the subject sample, only the percent difference in average negative power exhibited a significant linear relationship with pedaling rate; as pedaling rate increased, the asymmetry decreased. Although the kicking dominant leg contributed significantly greater average crank power than the non-dominant leg for the subject sample, the non-dominant leg contributed significantly greater average positive power and average negative power than the dominant leg. However, no significant linear relationships for any of these three quantities with pedaling rate were evident for the subject sample because of high variability in asymmetry among the subjects. For example, significant linear relationships existed between pedaling rates and percent difference in total average power per leg for only four of the 11 subjects and the nature of these relationships was different (e.g. positive versus negative slopes). It was concluded that pedaling asymmetry is highly variable among subjects and that individual subjects may exhibit different systematic changes in asymmetry with pedaling rate depending on the quantity of interest.

Adult↗
PubMed1999

The association between negative muscle work and pedaling rate.

The objective of this research was to use a pedal force decomposition approach to quantify the amount of negative muscular crank torque generated by a group of competitive cyclists across a range of pedaling rates. We hypothesized that negative muscular crank torque increases at high pedaling rates as a result of the activation dynamics associated with muscle force development and the need for movement control, and that there is a correlation between negative muscular crank torque and pedaling rate. To test this hypothesis, data were collected during 60, 75, 90, 105 and 120 revolutions per minute (rpm) pedaling at a power output of 260 W. The statistical analysis supported our hypothesis. A significant pedaling rate effect was detected in the average negative muscular crank torque with all pedaling rates significantly different from each other (p < 0.05). There was no negative muscular crank torque generated at 60 rpm and negligible amounts at 75 and 90 rpm. But substantial negative muscular crank torque was generated at the two highest pedaling rates (105 and 120 rpm) that increased with increasing pedaling rates. This result suggested that there is a correlation between negative muscle work and the pedaling rates preferred by cyclists (near 90 rpm), and that the cyclists' ability to effectively accelerate the crank with the working muscles diminishes at high pedaling rates.

Adult↗
PubMed2000

Adaptation of muscle coordination to altered task mechanics during steady-state cycling.

The objective of this work was to increase our understanding of how motor patterns are produced during movement tasks by quantifying adaptations in muscle coordination in response to altered task mechanics. We used pedaling as our movement paradigm because it is a constrained cyclical movement that allows for a controlled investigation of test conditions such as movement speed and effort. Altered task mechanics were introduced using an elliptical chainring. The kinematics of the crank were changed from a relatively constant angular velocity using a circular chainring to a widely varying angular velocity using an elliptical chainring. Kinetic, kinematic and muscle activity data were collected from eight competitive cyclists using three different chainrings--one circular and two different orientations of an elliptical chainring. We tested the hypotheses that muscle coordination patterns (EMG timing and magnitude), specifically the regions of active muscle force production, would shift towards regions in the crank cycle in which the crank angular velocity, and hence muscle contraction speeds, were favorable to produce muscle power as defined by the skeletal muscle power-velocity relationship. The results showed that our hypothesis with regards to timing was not supported. Although there were statistically significant shifts in muscle timing, the shifts were minor in absolute terms and appeared to be the result of the muscles accounting for the activation dynamics associated with muscle force development (i.e. the delay in muscle force rise and decay). But, significant changes in the magnitude of muscle EMG during regions of slow crank angular velocity for the tibialis anterior and rectus femoris were observed. Thus, the nervous system used adaptations to the muscle EMG magnitude, rather than the timing, to adapt to the altered task mechanics. The results also suggested that cyclists might work on the descending limb of the power-velocity relationship when pedaling at 90 rpm and sub-maximal power output. This finding might have important implications for preferred pedaling rate selection.

Adaptation, Physiological↗
PubMed2000

Muscle contributions to specific biomechanical functions do not change in forward versus backward pedaling.

Previous work had identified six biomechanical functions that need to be executed by each limb in order to produce a variety of pedaling tasks. The functions can be organized into three antagonistic pairs: an Ext/Flex pair that accelerates the foot into extension or flexion with respect to the pelvis, an Ant/Post pair that accelerates the foot anteriorly or posteriorly with respect to the pelvis, and a Plant/Dorsi pair that accelerates the foot into plantarflexion or dorsiflexion. Previous analyses of experimental data have inferred that muscles perform the same function during different pedaling tasks (e.g. forward versus backward pedaling) because the EMG timing was similar, but they did not present rigorous biomechanical analyses to assess whether a muscle performed the same biomechanical function, and if so, to what degree. Therefore, the objective of this study was to determine how individual muscles contribute to these biomechanical functions during two different motor tasks, forward and backward pedaling, through a theoretical analysis of experimental data. To achieve this objective, forward and backward pedaling simulations were generated and a mechanical energy analysis was used to examine how muscles generate, absorb or transfer energy to perform the pedaling tasks. The results showed that the muscles contributed to the same primary Biomechanical functions in both pedaling directions and that synergistic performance of certain functions effectively accelerated the crank. The gluteus maximus worked synergistically with the soleus, the hip flexors worked synergistically with the tibialis anterior, and the vasti and hamstrings functioned independently to accelerate the crank. The rectus femoris used complex biomechanical mechanisms including negative muscle work to accelerate the crank. The negative muscle work was used to transfer energy generated elsewhere (primarily from other muscles) to the pedal reaction force in order to accelerate the crank. Consistent with experimental data, a phase shift was required from those muscles contributing to the Ant/Post functions as a result of the different limb kinematics between forward and backward pedaling, although they performed the same biomechanical function. The pedaling simulations proved necessary to interpret the experimental data and identify motor control mechanisms used to accomplish specific motor tasks, as the mechanisms were often complex and not always intuitively obvious.

Bicycling↗