Tension Output Research Articles

Mere tension output from spring-linkage-based mechanical metamaterials.

Metamaterials whose properties are inaccessible with conventional materials offer powerful tools for unprecedentedly manipulating physical signals. However, an effective design strategy of metamaterials still remains a challenge for changing the compression or tension characters of stress waves during forward propagation. Here, we introduce a class of spring-linkage-based metamaterials exhibiting mere tension output at the distal end, no matter that the input is an axial impact, a sudden tension, or even alternating tension-compression. The metamaterials can turn compressive waves into pure tension and filter them out from the tension-compression mixed ones while allowing tensile signal stably propagating in soliton form. This is achieved by combining nonuniform and nonlinear properties of the proposed cells. In particular, these extraordinary functions of the metamaterial can be turned on or off and adjusted by tuning a key switch cell; thus, it is anticipated to serve as a start for more complex manipulation and utilization of mechanical signals.

Effect of khat leaves extract (Catha edulis) on the excitability of frog gastrocnemius.

This study was held on the isolated excitable tissue of frog's gastrocnemius muscle. Experiments were down by determining the dose dependent of leaves of khat extract. Work down in accordance with personal presupposition since reported that khat have psycho stimulant effects accordingly we thought khat might have effects on systemically biology that mediated by chticol amines. Results showed the effect of khat leaves extract on excitability of muscle contraction that was easily attested when the electrical stimuli were applied either through the nerve or directly to the muscle. Whereas khat treatment showed a significant increase in the contraction period of the gastrocnemius muscle and both of the relaxation periods and half relaxation time were shortened. Also it was found that pretreatment by khat leaves extract caused changes in the tension output, increased the height of effect intensity with prolonged the contraction period, while the latent period was decreased and reduced slightly the half relaxation period of the twitch comparison with the normal control muscle. These experimental results indicated that khat had highly stimulant effects on muscle, whereas caused liberation of thermoenzymatic and chemical energy during contraction which converted into mechanical energy, which manifested its self as work.

Peripheral Nerve Regeneration Using a Cytokine Cocktail Secreted by Skeletal Muscle-Derived Stem Cells in a Mouse Model

Severe peripheral nerve injury, which does not promise natural healing, inevitably requires clinical treatment. Here, we demonstrated the facilitation effect of peripheral nerve regeneration using a cytokine cocktail secreted by skeletal muscle-derived stem cells (Sk-MSCs). Mouse sciatic nerve was transected with a 6 mm gap and bridged collagen tube, and the culture supernatant of Sk-MSCs with 20% adult mouse serum (AMS)/Iscove’s modified Dulbecco’s medium (IMDM) was administered into the tube immediately after the operation, followed by an injection once a week for six weeks through the skin to the surrounding tube of the cytokine (CT) group. Similarly, 20% AMS/IMDM without cytokines was administered to the non-cytokine control (NT) group. Tension recovery in the plantar flexor muscles via electrical stimulation at the upper portion of the damaged nerve site, as well as the numerical recovery of axons and myelinated fibers at the damaged site, were evaluated as an index of nerve regeneration. Specific cytokines secreted by Sk-MSCs were compared with damaged sciatic nerve-derived cytokines. Six weeks after operation, significantly higher tension output and numerical recovery of the axon and myelinated fibers were consistently observed in the CT group, showing that the present cytokine cocktail may be a useful nerve regeneration acceleration agent. We also determined 17 candidate factors, which are likely included in the cocktail.

Voluntary Exercise Positively Affects the Recovery of Long-Nerve Gap Injury Following Tube-Bridging with Human Skeletal Muscle-Derived Stem Cell Transplantation.

The therapeutic effects of voluntary exercise on the recovery of long-gap nerve injury following the bridging of an acellular conduit filled with human skeletal muscle-derived stem cells (Sk-SCs) have been described. Human Sk-SCs were sorted as CD34+/45− (Sk-34) cells, then cultured/expanded under optimal conditions for 2 weeks. Surgery to generate a long-gap sciatic nerve injury was performed in athymic nude mice, after which the mice were divided into exercise (E) and non-exercise (NE) groups. The mice were housed in standard individual cages, and voluntary exercise wheels were introduced to the cages of the E group one week after surgery. After 8 weeks, the human Sk-34 cells were actively engrafted, and showed differentiation into Schwann cells and perineurial cells, in both groups. The recovery in the number of axons and myelin in the conduit and downstream tibial nerve branches, and the lower hindlimb muscle mass and their tension output, was consistently higher by 15–25% in the E group. Moreover, a significantly higher innervation ratio of muscle spindles, reduced pathological muscle fiber area, and acceleration of blood vessel formation in the conduit were each observed in the E group. These results showed that the combined therapy of tube-bridging, Sk-34 cell transplantation, and voluntary exercise is a potentially practical approach for recovery following long-gap nerve injury.

The development of the experimental setup for measuring the cell membrane electrical potential by Sucrose-Gap Technique

This article describes the development of the experimental setup for measuring the cell membrane electrical potential by Double -Sucrose-Gap Technique. The double-gap isolation method allows the simultaneous measurement of electrical activity and tension output from contracting segments of muscle fibers. This technique has been widely used as a convenient tool for recording of the membrane activities from myelinated or unmyelinated nerves and muscle preparations. This device can be an effective way to provide undergraduate biomedical engineering students with invaluable experiences in neurophysiology. The installation design and its main characteristics are described. The advantages of the described device are the simplicity of the experiment, relatively low cost, the possibility of long-term experiment.

Reconstitution of the complete rupture in musculotendinous junction using skeletal muscle-derived multipotent stem cell sheet-pellets as a “bio-bond”

Background. Significant and/or complete rupture in the musculotendinous junction (MTJ) is a challenging lesion to treat because of the lack of reliable suture methods. Skeletal muscle-derived multipotent stem cell (Sk-MSC) sheet-pellets, which are able to reconstitute peripheral nerve and muscular/vascular tissues with robust connective tissue networks, have been applied as a “bio-bond”.Methods. Sk-MSC sheet-pellets, derived from GFP transgenic-mice after 7 days of expansion culture, were detached with EDTA to maintain cell–cell connections. A completely ruptured MTJ model was prepared in the right tibialis anterior (TA) of the recipient mice, and was covered with sheet-pellets. The left side was preserved as a contralateral control. The control group received the same amount of the cell-free medium. The sheet-pellet transplantation (SP) group was further divided into two groups; as the short term (4–8 weeks) and long term (14–18 weeks) recovery group. At each time point after transplantation, tetanic tension output was measured through the electrical stimulation of the sciatic nerve. The behavior of engrafted GFP+ tissues and cells was analyzed by fluorescence immunohistochemistry.Results. The SP short term recovery group showed average 64% recovery of muscle mass, and 36% recovery of tetanic tension output relative to the contralateral side. Then, the SP long term recovery group showed increased recovery of average muscle mass (77%) and tetanic tension output (49%). However, the control group showed no recovery of continuity between muscle and tendon, and demonstrated increased muscle atrophy, with coalescence to the tibia during 4–8 weeks after operation. Histological evidence also supported the above functional recovery of SP group. Engrafted Sk-MSCs primarily formed the connective tissues and muscle fibers, including nerve-vascular networks, and bridged the ruptured tendon–muscle fiber units, with differentiation into skeletal muscle cells, Schwann cells, vascular smooth muscle, and endothelial cells.Discussion. This bridging capacity between tendon and muscle fibers of the Sk-MSC sheet-pellet, as a “bio-bond,” represents a possible treatment for various MTJ ruptures following surgery.

Immune-inspired self-adaptive collaborative control allocation for multi-level stretching processes

For multi-level stretching processes in large industrial production lines exhibiting complicated non-linear dynamics and interconnected control variables, a novel immune-based self-adaptive collaborative control allocation (ICCA) method is proposed to deal with the tension output fluctuations and some uncertainties. The allocation strategies for coupled stretching ratios at different levels are implemented in the ICCA to achieve the best stable tension performance. The stretching ratio of single level is determined by minimizing the error between the proposed reference model and the actual stretching plant. Compared with distributed control for individual sub-processes, the reversing dynamic programming on each level is introduced which is operated from the last level sequentially. The gain-tuning strategy is directly driven by the optimization result, namely, the self-adaptive allocation algorithm, is just the execution level for operating the solutions of reversing optimization. The optimization and self-adaptive controller are designed to cope with the presence of actuator imperfections and tension tracking fluctuations in the neighboring non-linear process. In addition, the criterion is an important factor in evaluating the control performance of this system, which consists of the objective function. Simulation results show that the ICCA method exhibits better performances than the centralized PI control and the cytokine network-inspired cooperative control in dealing with the desired tension tracking and fluctuations reducing by the control algorithm.

ESTIMASI PARAMETER MODEL FUNGSI ALIH ORDE 4 PADA ROL PENGUMPAN SISTEM TRANSPORTASI WEB MATERIAL BERBASIS FORGETTING FACTOR DENGAN MATLAB 7.04

Web Materials Transport system appears in variety of industrial applications such as paper and plastics industries. The main part of web transport system is unwind roll section. The dynamic model for unwind roll section is derived from the Newton’s laws, the Hooke’s law and conservations of mass principle. This model gives a relationship between web tension output and torque input. Futhermore this relationship is expressed in transfer function form. This transfer function contains a phisical time-varying parameter namely the radius of the unwind roll. Usually before designing control system, a model parameter estimation is needed. This on-line estimation problem is investigated in this paper using RLS (recursive least square) method with forgetting factor. The estimation needs data in the form of discrete and the initial value covariance matrix diagonal (P). This research uses discrete ZOH method with sampling period T = 0.4 sec; 0.35 sec; 0.3 sec; 0.25 sec; 0.2 sec for convert transfer function from s-domain to z-domain. Parameters estimation with mean square error (MSE) in the range 2x10-5 ≤ MSE ≤ 3x10-5 are obtained using initial value covariance matrix diagonal P in the range 102 ≤ P ≤ 108 using forgetting factor 0.95.

Muscle sparing in muscle RING finger 1 null mice: response to synthetic glucocorticoids

Skeletal muscle atrophy occurs under a variety of conditions and can result from alterations in both protein synthesis and protein degradation. The muscle-specific E3 ubiquitin ligases, MuRF1 and MAFbx, are excellent markers of muscle atrophy and increase under divergent atrophy-inducing conditions such as denervation and glucocorticoid treatment. While deletion of MuRF1 or MAFbx has been reported to spare muscle mass following 14 days of denervation, their role in other atrophy-inducing conditions is unclear. The goal of this study was to determine whether deletion of MuRF1 or MAFbx attenuates muscle atrophy after 2 weeks of treatment with the synthetic glucocorticoid dexamethasone (DEX). The response of the triceps surae (TS) and tibialis anterior (TA) muscles to 14 days of DEX treatment (3 mg kg(-1) day(-1)) was examined in 4 month-old male and female wild type (WT) and MuRF1 or MAFbx knock out (KO) mice. Following 14 days of DEX treatment, muscle wet weight was significantly decreased in the TS and TA of WT mice. Comparison of WT and KO mice following DEX treatment revealed significant sparing of mass in both sexes of the MuRF1 KO mice, but no muscle sparing in MAFbx KO mice. Further analysis of the MuRF1 KO mice showed significant sparing of fibre cross-sectional area and tension output in the gastrocnemius (GA) after DEX treatment. Muscle sparing in the MuRF1 KO mice was related to maintenance of protein synthesis, with no observed increases in protein degradation in either WT or MuRF1 KO mice. These results demonstrate that MuRF1 and MAFbx do not function similarly under all atrophy models, and that the primary role of MuRF1 may extend beyond controlling protein degradation via the ubiquitin proteasome system.

Temperature jump induced force generation in rabbit muscle fibres gets faster with shortening and shows a biphasic dependence on velocity.

We examined the tension responses to ramp shortening and rapid temperature jump (<0.2 ms, 3-4 degrees C T-jump) in maximally Ca(2+)-activated rabbit psoas muscle fibres at 8-9 degrees C (the fibre length (L(0)) was approximately 1.5 mm and sarcomere length 2.5 microm). The aim was to investigate the strain sensitivity of crossbridge force generation in muscle. The T-jump induced tension rise was examined during steady shortening over a wide range of velocities (V) approaching the V(max) (V range approximately 0.01 to approximately 1.5 L(0) s(1)). In the isometric state, a T-jump induced a biphasic tension rise consisting of a fast (approximately 50 s(1), phase 2b) and a slow (approximately 10 s(1), phase 3) component, but if treated as monophasic the rate was approximately 20 s(1). During steady shortening the T-jump tension rise was monophasic; the rate of tension rise increased linearly with shortening velocity, and near V(max) it was approximately 200 s(1), approximately 10x faster than in the isometric state. Relative to the tension reached after the T-jump, the amplitude increased with shortening velocity, and near V(max) it was 4x larger than in the isometric state. Thus, the temperature sensitivity of muscle force is markedly increased with velocity during steady shortening, as found in steady state experiments. The rate of tension decline during ramp shortening also increased markedly with increase of velocity. The absolute amplitude of T-jump tension rise was larger than that in the isometric state at the low velocities (<0.5 L(0) s(1)) but decreased to below that of the isometric state at the higher velocities. Such a biphasic velocity dependence of the absolute amplitude of T-jump tension rise implies interplay between, at least, two processes that have opposing effects on the tension output as the shortening velocity is increased, probably enhancement of crossbridge force generation and faster (post-stroke) crossbridge detachment by negative strain. Overall, our results show that T-jump force generation is strain sensitive and becomes considerably faster when exposed to negative strain. Thus the crossbridge force generation step in muscle is both temperature sensitive (endothermic) and strain sensitive.

Application of SMA in Membrane Structure Shape Control

Shape memory alloy (SMA) actuators have found a wide range of applications due to their unique properties such as high force, long stroke, small size, light weight, and silent operation, etc. However, their strong nonlinear properties make them a challenge to achieve accurate actuations. A simple control strategy is presented based on the idea of adjusting the SMA wire temperature as rapidly as possible. This strategy is simple, stable, and requires no hysteresis model or thermal model. The strategy is tested first on tracking displacement outputs, and effects of updating rate and input current on control accuracy are also discussed. It is then used for active shape control of a membrane structure model by adjusting its boundary tensions. Results indicate that under the developed control strategy, SMA wire actuators can offer very good accuracy in tracking displacement outputs and tension outputs. For the membrane structure shape control, the structure shape precision is improved greatly.

Disturbance Rejection in Parameter-varying Web-winding Systems

We propose a control scheme to reject disturbances in web tension that are caused by reel eccentricities in parameter-varying web-winding systems. When the web winds from one reel to the other, the nominal reel radii vary. In addition to this, the reels are not perfectly circular and the eccentricities introduce disturbances to the tension output. If the web is thin enough, in a certain time span, the nominal reel radii can be considered as constants and the reel eccentricities are periodic. In our design, the entire web winding process in which the whole pack of web winds from a full source reel to an empty take-up reel is investigated at a certain number of operating points. At each operating point, an adaptive controller that synthesizes the inverse input whose system response cancels the disturbances is developed. Gain-scheduling control is then used between different operating points. The scheme is simulated on a decoupled tension loop of an example reel-to-reel web-winding system that represents a digital tape system.

Evaluation of morphological and functional regeneration of rat nerve-muscle units after temporary and permanent tubulization.

We compared the ability of temporary and permanent tubing to achieve morphological and functional recovery of nerve-muscle units, following experimental nerve transection (8-mm gap) in rat tibial nerve. Electrical stimulation of the sciatic nerve was used to analyze tension output, evoked electromyogram and conduction-transmission time (CTT) of denervated nerve-muscle units. Morphological analysis of the nerve and muscle was also performed. Within 6 weeks, the nerve gap had been bridged by a thin nerve trunk, and a few myelinated fibers were observed, although there was still no functional recovery. The rats were divided into two groups: permanent tubing (PT) and temporary tubing (TT; tubing subsequently removed). At 10 weeks after the operation, the TT group showed apparently greater thickness of regenerated nerve trunks, significantly higher tension output of plantar flexors, shorter CTT, and heavier muscle mass. These results were consistent with the presence of myelinated fibers in the regenerated nerve trunks, as shown histologically. Thus, removal of the silicone chamber results in faster and better recovery than tubing left permanently in place.

Relationship between functional deficit and severity of experimental fast-strain injury of rat skeletal muscle.

We developed a rat model of fast-strain muscle injury to examine the relationship between functional deficit and the degree of muscle damage. A single fast strain was applied to the right plantaris (Plt) muscle of adult male rats. A tetanic contraction was induced by stimulating the sciatic nerve. Three types of strain injuries were produced by manipulating the timing of strain and contraction conditions, including applying the strain at: (1) the shortening phase (SP), (2) the full contraction phase (FCP) during tetanic contraction and (3) when the muscle is not contracting, i.e. non-contraction (NC). The contralateral Plt muscle was used as the control. Morphological and functional analysis were performed and the severity of strain injury was estimated by measuring [3H]thymidine labelling 48 h after the strain was applied. The results show a significant decrease in tension output in all three groups at 5 min after strain application (P < 0.01). The functional deficit lasted for 3 weeks in the NC group, while rats of the SP and FCP groups showed recovery 1 week after strain. Increased uptake of [3H]thymidine was similar in SP and FCP groups, but 3.5-fold higher in NC than in SP and FCP groups (P < 0.01). Histological analysis revealed an increase in the size of interstitial spaces of the muscle in NC compared to SP and FCP groups (P<0.05). Our results suggest that the contraction of muscle fibres limits the severity of connective tissue damage, and that muscle damage accompanied by disruption of the muscle connective tissue network requires a relatively longer recovery time.

Mechanical and metabolic determination of VO2 and fatigue during repetitive isometric contractions in situ.

Repetitive isometric tetanic contractions (1/s) of the canine gastrocnemius-plantaris muscle were studied either at optimal length (Lo) or short length (Ls; approximately 0.9 . Lo), to determine the effects of initial length on mechanical and metabolic performance in situ. Respective averages of mechanical and metabolic variables were (Lo vs. Ls, all P < 0.05) passive tension (preload) = 55 vs. 6 g/g, maximal active tetanic tension (Po) = 544 vs. 174 (0.38 . Po) g/g, maximal blood flow (Q) = 2.0 vs. 1.4 ml . min-1 . g-1, and maximal oxygen uptake (VO2) = 12 vs. 9 micromol . min-1 . g-1. Tension at Lo decreased to 0.64 . Po over 20 min of repetitive contractions, demonstrating fatigue; there were no significant changes in tension at Ls. In separate muscles contracting at Lo, Q was set to that measured at Ls (1.1 ml . min-1 . g-1), resulting in decreased VO2 (7 micromol . min-1 . g-1), and rapid fatigue, to 0.44 . Po. These data demonstrate that 1) muscles at Lo have higher Q and VO2 values than those at Ls; 2) fatigue occurs at Lo with high VO2, adjusting metabolic demand (tension output) to match supply; and 3) the lack of fatigue at Ls with lower tension, Q, and VO2 suggests adequate matching of metabolic demand, set low by short muscle length, with supply optimized by low preload. These differences in tension and VO2 between Lo and Ls groups indicate that muscles contracting isometrically at initial lengths shorter than Lo are working under submaximal conditions.

EXPERIMENTAL MODEL FOR MUSCLE STRAIN INJURY: RELATION BETWEEN CONTRACTILE CONDITION AND SEVERITY

570 We developed a new model for muscle strain injury to examine a relationship between contractile condition and severity on fast muscle strain. Wistar male rats (15-20 week-old, n=38) were used in this study. Distal tendons of plantaris (PLA) muscle in both legs were exposed and isolated (not sectioned), then silk blade (1.0 grade, Nihonshyoji, Japan) was tied. An acute fast strain(22.5 ± 0.4 N) was applied for right-side PLA muscle. Contralateral left-side PLA was saved for control. Tetanic contraction was induced by a stimulation for sciatic nerve. Three kinds of strain injuries were produced by a combination of the timing of strain and contractile condition as follows; 1) strained at non-contraction phase (NCP), 2) initial contraction phase (ICP) and 3) full contraction phase (FCP) during tetanic tension. Tension output, before and after 5 min of strain, were measured and then suture operation was performed. After 2, 3, and 4 weeks recovery period, PLA muscles were excised after the re-measurement of tetanic tension, and prepared for histological analysis. In addition, [3H]-thymidine labeling at 2 days after strain was performed as a marker for a severity of strain injuries. Results suggest that the severity of muscle strain injury is not always reflect for the reduction of tetanic tension, and it is alleviated by the contraction. TableTable

Effects of chronic low frequency stimulation on contractile and elastic properties of hindlimb suspended rat soleus muscle.

Chronic low frequency stimulation (10 Hz, 8 h x day[-1]) was used in this study to prevent the changes in the contractile and elastic properties of rat soleus muscles induced by 3 weeks of hindlimb suspension (HS). Results showed that electrostimulation was able to counteract in part the decrease in soleus muscle mass and tension output induced by unweighting. On the other hand, the increases in maximal shortening velocity and twitch speed following HS were not prevented by stimulation. Unweighting was responsible for an increase in series elastic compliance of soleus muscle. Chronic stimulation successfully counteracted this increase in series compliance probably by changing the properties of the tendon. The partial recovery of muscle mass and tension output as a result of stimulation enhanced the role of contractile activity in preventing muscle atrophy. Moreover, the inefficiency of the tonic activity imposed by stimulation in preventing the increase in twitch speed of soleus muscle during HS demonstrated the primacy of neuronal activity. Discrepant results concerning changes in contraction kinetics deduced from the twitch could have been due to the fact that such myograms also depend on the series compliance.

Early metabolic adaptations of rabbit fast-twitch muscle to chronic low-frequency stimulation.

To investigate early adaptive responses to chronic low-frequency stimulation (CLFS), rabbit tibialis anterior (TA) muscles were continuously stimulated at 10 Hz for 8 days, allowed to rest for 1 h, and then subjected to a 15-min fatigue test at 10-Hz stimulation. The contralateral TA muscles which had not been exposed to CLFS, served as controls during the fatigue test. Compared to the controls, the initial tension output of the 8-day prestimulated muscles was reduced by 25%. However, these muscles maintained higher tensions during the fatigue test than the controls. Citrate synthase activity, an indicator of aerobic-oxidative capacity, was only slightly elevated (40%) in the 8-day stimulated muscles. Unlike the controls, the prestimulated muscles failed to produce potentiation during the fatigue test. Control muscles responded to the fatigue test with pronounced reductions in contents of adenosine 5'-triphosphate (ATP), phosphocreatine (PCr), and glycogen, as well as with large increases in contents of inosine monophosphate (IMP), inorganic phosphate (Pi), creatine (Cr), and lactate. Under the same conditions contents of ATP, PCr, Cr, glycogen, lactate, Pi, and IMP were unaltered in the 8-day prestimulated muscles. These findings demonstrated that CLFS for 8 days elicited pronounced alterations in energy metabolism and contractile properties. These adaptive changes occurred prior to fibre type transitions and substantial increases in aerobic-oxidative potential.

A gap isolation method to investigate electrical and mechanical properties of fully contracting skeletal muscle fibers

We describe here a single-gap isolation method that allows the simultaneous measurement of electrical activity and tension output from fully contracting segments of frog skeletal muscle fibers. By using single pulses and pulse trains of varying frequency (5-100 Hz), records obtained for both electrical and mechanical fiber response demonstrate that the physiological properties of the fiber segments have been preserved. Action potentials could be recorded free of movement artifacts, even while segments were in fused tetani and developing maximum tensions of more than 600 kN/m2. Single current pulses evoked action potentials that averaged 144 +/- 16 mV (mean +/- SD, n = 8) in amplitude and twitches that averaged 285 +/- 66 kN/m2 and 55 +/- 5 ms (mean +/- SD, n = 20) in magnitude and time to peak, respectively. Trains of action potentials elicited patterns of tension development that exhibited summation, unfused tetani, and fused tetani in a frequency-dependent manner. The AC and DC electrical properties of the single grease gap were modeled with a simple Thévenin equivalent circuit, which satisfactorily predicted the experimental results. Our methodology is easily implemented and potentially applicable to any muscle preparation in which fiber segments with an intact end attached to a piece of tendon can be dissected.

Effect of zidovudine (AZT) on the structure and function of rat skeletal muscle

The role of the anti-HIV agent zidovudine (ZDV = AZT) in the generation of mitochondrial myopathies and subsequent skeletal muscle contractile deficiencies was evaluated in male rats given ZDV in drinking water (1 mg/mL). After 6 weeks, there was no difference in treadmill run time between experimental (n = 6) and control (n = 6) rats. ZDV did not affect tension output by the gastrocnemius-plantaris-soleus muscle group when stimulated in situ at frequencies of 15, 30, 45, and 75 tetani/min, nor did the drug affect the cytochrome oxidase activity of fast glycolytic, fast oxidative glycolytic, or slow oxidative fiber types after 6 or 15 weeks of treatment. A group of female rats, similarly evaluated after 6 weeks of ZDV at 1 (n = 4) or 2 (n = 4) mg/mL, also did not display any discernable deficiencies. However, when the data from all 10 control rats were compared with those of the 19 ZDV rats, the cytochrome oxidase activity of fast oxidative glycolytic muscle of the ZDV rats was significantly higher (35.0 +/- 1.36 versus 40.7 +/- 1.14 mumol.min-1.g-1; p < 0.05). No ultrastructural abnormalities were observed in 15-week ZDV-treated cardiac muscle or in any of the three skeletal muscle fiber types. These results suggest that ZDV-related myopathies observed in AIDS patients may be due to interactions between the drug and complications associated with HIV infection.