Limb Kinematics, Kinetics and Muscle Dynamics During the Sit-to-Stand Transition in Greyhounds

Standing up from a prone position is a critical daily activity for animals: failing to do so effectively may cause an injurious fall or increase predation susceptibility. This sit-to-stand behaviour (StS) is biomechanically interesting because it necessitates transitioning through near-maximal joint motion ranges from a crouched (i.e., poor mechanical advantage) to a more upright posture. Such large joint excursions should require large length changes of muscle-tendon units. Here we integrate experimental and musculoskeletal simulation methods to quantify the joint motions, limb forces, and muscle fibre forces, activations and length changes during StS in an extreme athlete-the greyhound-which has large hindlimb muscles bearing short-fibred distal muscles and long tendons. Study results indicate that hindlimb anti-gravity muscle fibres operate near their ~50% limits of length change during StS; mostly by starting at highly lengthened positions. StS also requires high muscle activations (>50%), in part due to non-sagittal motions. Finally, StS movements require passive non-muscular support in the distal hindlimb where short-fibred muscles are incapable of sustaining StS themselves. Non-locomotor behaviours like StS likely impose important trade-offs between muscle fibre force capacity and length changes, as well as active and passive mechanisms of support, that have been neglected in locomotor biomechanics studies.

Muscle contributions to propulsion and braking during walking and running: insight from external force perturbations

There remains substantial debate as to the specific contributions of individual muscles to center of mass accelerations during walking and running. To gain insight, we altered the demand for muscular propulsion and braking by applying external horizontal impeding and aiding forces near the center of mass as subjects walked and ran on a treadmill. We recorded electromyographic activity of the gluteus maximus (superior and inferior portions), the gluteus medius, biceps femoris, semitendinosus/membrinosus, vastus medialis, lateral and medial gastrocnemius and soleus. We reasoned that activity in a propulsive muscle would increase with external impeding force and decrease with external aiding force whereas activity in a braking muscle would show the opposite. We found that during walking the gastrocnemius and gluteus maximus provide propulsion while the vasti are central in providing braking. During running, we found that the gluteus maximus, vastus medialis, gastrocnemius and soleus all contribute to propulsion.

Activity and functions of the human gluteal muscles in walking, running, sprinting, and climbing

It has been suggested that the uniquely large gluteus maximus (GMAX) muscles were an important adaptation during hominin evolution based on numerous anatomical differences between humans and extant apes. GMAX electromyographic (EMG) signals have been quantified for numerous individual movements, but not across the range of locomotor gaits and speeds for the same subjects. Thus, comparing relative EMG amplitudes between these activities has not been possible. We assessed the EMG activity of the gluteal muscles during walking, running, sprinting, and climbing. To gain further insight into the function of the gluteal muscles during locomotion, we measured muscle activity during walking and running with external devices that increased or decreased the need to control either forward or backward trunk pitch. We hypothesized that 1) GMAX EMG activity would be greatest during sprinting and climbing and 2) GMAX EMG activity would be modulated in response to altered forward trunk pitch demands during running. We found that GMAX activity in running was greater than walking and similar to climbing. However, the activity during sprinting was much greater than during running. Further, only the inferior portion of the GMAX had a significant change with altered trunk pitch demands, suggesting that the hip extensors have a limited contribution to the control of trunk pitch movements during running. Overall, our data suggest that the large size of the GMAX reflects its multifaceted role during rapid and powerful movements rather than as a specific adaptation for a single submaximal task such as endurance running.

The metabolic and mechanical costs of step time asymmetry in walking

Animals use both pendular and elastic mechanisms to minimize energy expenditure during terrestrial locomotion. Elastic gaits can be either bilaterally symmetric (e.g. run and trot) or asymmetric (e.g. skip, canter and gallop), yet only symmetric pendular gaits (e.g. walk) are observed in nature. Does minimizing metabolic and mechanical power constrain pendular gaits to temporal symmetry? We measured rates of metabolic energy expenditure and calculated mechanical power production while healthy humans walked symmetrically and asymmetrically at a range of step and stride times. We found that walking with a 42 per cent step time asymmetry required 80 per cent (2.5 W kg(-1)) more metabolic power than preferred symmetric gait. Positive mechanical power production increased by 64 per cent (approx. 0.24 W kg(-1)), paralleling the increases we observed in metabolic power. We found that when walking asymmetrically, subjects absorbed more power during double support than during symmetric walking and compensated by increasing power production during single support. Overall, we identify inherent metabolic and mechanical costs to gait asymmetry and find that symmetry is optimal in healthy human walking.

Physical, hematologic, biochemical, and immunologic effects of supranutritional supplementation with dietary selenium in Holstein cows

OBJECTIVE

To measure responses of cows to supplemental Se intake in excess of nutritional requirements, but lower than recognized toxic dosages.

ANIMALS

24 healthy adult Holstein cows.

PROCEDURE

Cows were allotted to 4 groups and fed sodium selenite to provide 0, 3, 20, or 50 mg of Se/cow/d for 90 days. Subsequently, the dosage for the group receiving 50 mg/cow/d was increased to 100 mg/cow/d for 28 d. Blood, liver specimens, feces, and urine were obtained at points during the trial.

RESULTS

Serum and blood Se concentrations in groups receiving 20 or 50 mg/cow/d increased over time, compared with controls (P < 0.01). Increasing supplemental Se intake to 100 mg/cow/d further increased serum and blood Se concentrations (P < 0.05). Urine, fecal, and liver Se concentrations increased more markedly in response to treatment than did those of serum or blood. No effect of Se treatment was seen on blood cell counts or serum activities of hepatocellular enzymes. Likewise, neither titer response to rabies vaccination nor lymphocyte blastogenic response to nonspecific mitogens was affected by Se treatment. Objective or subjective physical signs of Se toxicosis were not observed at any Se dosage.

CONCLUSIONS

Inorganic Se intakes of up to 50 mg/d for 90 days or 100 mg/d for 28 days by adult Holstein cows do not affect the variables measured.

CLINICAL RELEVANCE

Intakes of Se as sodium selenite in amounts 10 to 30 times the nutritional requirements are unlikely to cause health problems in adult cows. Urine and feces are good test samples for detection of Se supplementation greater than requirements.

An automated clinic management system for a family planning network

The medical information, financial, and logistic aspects of a comprehensive computer-based Appointment, Registration, Information System, and Evaluation (ARISE) are analyzed for the management of a family planning program serving 30,000 patients annually. An overview of the existing computer system network is presented with descriptions of the interactive master patient index, the batch appointment process, the management statistics package, and Department of Health, Education, and Welfare (HEW) reporting. Emphasis is placed on the financial management control system which includes 1) procedures for third-party submission of claims for payment, in particular Titles IVA, XX, and XIX (Social Security Act), together with discussion of related administrative requirements; 2) technics of auditing data integrity including systematic sampling of collected data; and 3) the process of billing and receipts collection. Methodology and implementation aspects of ARISE may have wide applicability to other family planning and similarly structured clinical programs.

Rentran. An on-line computer-based regional kidney transplant matching system

An interactive on-line computerized renal transplant matching system called RENTRAN which serves the Southwest Kidney Transplant Region is described. The region consists of one transplant center in Arkansas, two in Oklahoma, and six in Texas. The computer used is the DECsystem-10 located in the Medical Computing Resources Center at Dallas. RENTRAN participants have remotely located standard interactive computer terminals and gain access to the computer by dialing over normal telephone lines. Functions provided by RENTRAN include obtaining instructions, performing a donor-recipient match, obtaining a list of potential recipients, making a user comment or adding, updating or deleting a potential recipient record. Either long or short formats for dialog with the computer system are available for inexperienced and experienced and users, respectively. In the time period from August 1,1973, when the system went into production on February 1, 1976, there have been in excess of 232 matches attempted and approximately 142 kidneys have been transplanted according to RENTRAN results. There are about 361 recipients currently on the data base. The system was developed with funds provided by the Texas Regional Medical Program. Expenses of maintaining the system as well as occasional programmed improvements as deemed appropriate by the Southwest Kidney Transplant Region Registry Committee on the basis of user comments are provided through a $25 per year charge to patients for being listed on the data base.