Biomedical subjects

S J Wickler

Publications and source records attributed to S J Wickler.

At least 19 recordsLinked to original sources

PubMed2004

Energetic and kinematic consequences of weighting the distal limb.

REASON FOR PERFORMING STUDY: It is well known that adding a load to a horse's back increases its energetic costs of locomotion, but the magnitude of increase obtained by loading the most distal portion of limb has not been measured. OBJECTIVES: To measure oxygen consumption in horses with mass added to the back and hooves. Because such mass distribution alters inertial parameters of the limbs, kinematic measurements were made to quantify the magnitude of change in limb movement. METHODS: Steady-state oxygen consumption was measured in 6 horses with a load of 2.4 kg. The load was either carried on the back or distributed equally between the 4 limbs. Modified bell boots kept the mass at the level of P3. Horses trotted on a treadmill at speeds ranging from 2 to 5 m/sec (in 0.5 m/sec increments). High-speed (250 Hz) digital images were recorded in a sagittal plane and the positions of retroreflective markers located on standard positions on the limbs were digitised for kinematic analysis. RESULTS: Loading of the distal limbs produced a 6.7% increase in metabolic rate, an order of magnitude higher than when the mass was added over the back. Although the stride period was 2% longer in horses with loads on the distal limbs, time of contact and duty factor were not different. Distal limb loading increased the range of motion in hind- but not forelimbs. CONCLUSIONS: The costs of swinging the limbs in the horse are considerable and the addition of weights to the distal limb can have a profound effect on not only the energetics of locomotion but also the kinematics, at least in the hindlimb. POTENTIAL RELEVANCE: The use of weighted shoes, intended to increase animation of the gait, increases the metabolic effort of performance horses a disproportionate amount. The additional mass also increases the joint range of motion and, potentially, the likelihood of injury.

Animals↗

PubMed2002

A lactate-guided conditioning programme to improve endurance performance.

Blood lactate measurements are used widely in horses to assess athletic performance, but there are few published data on using lactate as a guide for endurance improvement. The velocity at which blood lactate concentration ([LA]) of 4 mmol/l is reached (v4) is widely used to determine fitness. In an earlier study of v4, exercise at low intensities for longer duration was more effective at improving endurance than shorter, higher intensities. However, the prescription was unchanged during the study (6 weeks). We hypothesised that, to produce greater improvement in v4 in the same time frame, it is necessary to adjust conditioning regimes more frequently. Six horses underwent an initial treadmill-based standard exercise test (SET). A regression analysis [LA]-speed relationship was used to calculate v2. Horses were then conditioned for 45 min at their calculated v2 3 times/week (6% incline). Every 2 weeks the horses performed an SET to evaluate the v2 conditioning protocol which ended with SET 4. Mean v4 increased 17% from SET 1 to SET 4 (P = 0.003; 5.8 +/- 03 to 6.8 +/- 0.4 m/s). This study demonstrates that a lactate-guided conditioning programme can significantly enhance endurance performance over a 6-week time peroid when the conditioning protocol is adjusted every 2 weeks based on v4 improvement.

Animals↗

PubMed2002

The cost of transport in an extended trot.

We hypothesised that trotters during an extended trot have lower energetic costs of locomotion (CT) than horses not bred for this behaviour. VO2 was measured as a function of speed in 7 Arabian horses (3 trained to extend their trotting speeds) and in 2 horses, of similar mass, bred to trot (Hackney). Both oxygen consumption and CT increased with speed and there was, contrary to our hypothesis, no difference between breeds. In Arabians at 6.5 m/s, CT had increased 25% above the CT at 5.0 m/s (normal transition speed). For Hackneys at 6.8 m/s, the CT was almost 35% higher. Stride frequencies increased linearly in all horses up to 5.0 m/s. At the canter at 5.0 m/s, the frequency increased 9% to 111 strides/min, but then increased minimally with speed. In the Hackneys and the Arabians that extended the trot, stride frequencies were approximately 102 and did not increase with speed. Stride length (SL) increased linearly with speed in both trotting and cantering horses, and cantering SL were lower than trotting (at 5.0 m/s, SL for trotting = 3.04 m and for cantering SL = 2.68 m). There were no differences between breeds in stride frequency or stride length. Extending the trot can have profound energetic requirements that could limit athletic performance and may lead to increased concussive impact on the limbs.

Animals↗

PubMed2002

Effect of trotting speed, load and incline on hindlimb stance-phase kinematics.

The objective was to understand how the stance-phase kinematics of the hindlimb of trotting horses change with speed under 3 conditions (level, loaded and incline), to compare our results with the predictions of the spring-mass model and to help focus our future studies of muscle function. Video recordings were made of 5 Arabian horses trotting on a treadmill. Five consecutive strides were digitised and averaged for each trial. The angle-time diagrams were qualitatively similar to those reported previously. As speed increases, the range of motion of the hindlimb increases, as predicted by the spring-mass model. This is the result of increased range of motion in the coxofemoral and tarsal joints. The hindlimb does not 'land short-take off long'. When trotting up an incline, the hindlimb undergoes a greater range of motion because of increased retraction resulting from increased extension of the coxofemoral joint. At hoof contact on an incline, the 3 proximal joints are more flexed than on the level. Carrying a load had no effect on kinematics. These results suggest that there may be larger changes in strain with speed in muscles acting at the coxofemoral and tarsal joints than at the femorotibial joint, and that locomotion up an incline will change muscle strain more than carrying a load.

Animals↗

PubMed2002

Hindlimb net joint energies during swing phase as a function of trotting velocity.

Net joint powers and energies have been described in walking horses during the swing phase of the stride in the fore- and hindlimb (Clayton et al. 2001). During trotting, swing phase net joint powers have been described in the forelimb but not in the hindlimb. The effects of velocity on power profiles and energy patterns are important in relation to locomotor energetics. The objective of this study was to evaluate velocity-dependent changes in hindlimb net energy profiles of the swing phase during trotting. Inverse dynamic analysis was used to calculate net joint energies at the hindlimb joints of 6 horses trotting overground at velocities ranging from 2.27-5.17 m/s. At all velocities, there was net energy generation at the hip and tarsus and net energy absorption at the stifle, fetlock and coffin joints. Velocity-dependent bursts of energy generation at the hip actively protracted the limb in early swing and initiated retraction in late swing. Synchronous with the bursts of energy generation at the hip were velocity-dependent bursts of energy absorption across the stifle that acted to control flexion in early swing and extension in late swing. The distal limb was raised and lowered by velocity-dependent bursts of energy generation that flexed the tarsus in early swing and extended it in late swing. The energy bursts in early swing increased linearly with velocity, whereas the energy bursts in late swing increased as a function of the square or cube of velocity. The results contribute to understanding the mechanisms used to accelerate and decelerate the limbs more rapidly as velocity increases, which is an important consideration in racing and sporting performance.

Animals↗

PubMed2002

Metabolic and osmoregulatory function at low and high (3800 m) altitude.

Altitude evokes physiological adjustments that include not only respiratory and cardiovascular properties, but also metabolic function, renal and endocrine responses. The purpose of the present study was designed to expand our understanding of the physiological process involved with acclimatisation to high altitude in equids. The study examined temporal effects on metabolic and osmoregulatory function in horses (n = 6) at rest and postexercise at 3800 m. Animals were studied at 225 m (Pb = 743 mmHg) and during a 10 day stay at altitude (Pb = 487 mmHg). Rest samples were taken 90 min postprandial at 0830 h and immediately after the gallop phase of a standard exercise test. Changes in glucose, insulin, cortisol, thyroxine, sodium, potassium, chloride and total protein were assessed at both altitudes. Exercise stimulated increases in cortisol, thyroxine, potassium, and chloride; while the concentrations of glucose, insulin, sodium and total protein (regardless of altitude) decreased. Acute (Day 2) altitude exposure (following transport stress) produced significant increases in glucose, cortisol, thyroxine, chloride and protein at rest and exercise. All variables (except cortisol) appeared to stabilise by Day 4 of altitude exposure. Observations from these data (coupled with haematological and blood gases data) indicate that equids acutely acclimate within 2-3 days to this altitude.

Acclimatization↗

PubMed2001

Effect of load on preferred speed and cost of transport.

Horses have a tendency to utilize a relatively narrow set of speeds near the middle of a much broader range they are capable of using within a particular gait, i.e., a preferred speed. Possible explanations for this behavior include minimizing musculoskeletal stresses and maximizing metabolic economy. If metabolic economy (cost of transport, CT) and preferred speeds are linked, then shifts in CT should produce shifts in preferred speed. To test this hypothesis, preferred speed was measured in trotting horses (n = 7) unloaded on the level and loaded with 19% of their body weight on the level. The preferred speed on the level was 3.33 +/- 0.09 (SE) m/s, and this decreased to 3.13 +/- 0.11 m/s when loaded. In both conditions (no load and load), the rate of O2 consumption (n = 3) was a curvilinear function of speed that produced a minimum CT (i.e., speed at which trotting is most economical). When unloaded, the speed at which CT was minimum was very near the preferred speed. With a load, CT decreased and the minimum was also near the preferred speed of horses while carrying a load.

Animals↗

PubMed2000

Milk ceruloplasmin and its expression by mammary gland and liver in pigs.

Concentrations of ceruloplasmin and copper in milk and blood plasma, the nature of milk ceruloplasmin, and the effects of lactation and gestation on these parameters, as well as the expression of ceruloplasmin mRNA by the mammary gland, were examined in pigs. As seen previously in humans, ceruloplasmin and copper concentrations in sow milk were much higher a few days after birth than 1 month later, averaging 26.5 and 6.6 mg ceruloplasmin/L (by immunoassay) and 1.67 and 0.34 mg total Cu/L, on days 3 and 33 postpartum, respectively. Values for ceruloplasmin oxidase activity (measured with p-phenylene diamine) were 7.8 and 1.3 nmol/min/L, respectively. Daily milk ceruloplasmin production went from 61 to 22 mg/day and daily copper output from 38 to 12 mg/day. In contrast, there was little or no variation in serum ceruloplasmin concentration during lactation or gestation, although total plasma copper was high at the end of gestation. Milk ceruloplasmin was of the same apparent size as serum ceruloplasmin, as determined by SDS-PAGE and immunoblotting, and ceruloplasmin mRNAs of liver and mammary gland were indistinguishable by Northern analysis and RT-PCR of the various exons. Expression of total RNA and ceruloplasmin mRNA, as detected in biopsies of mammary gland, increased markedly upon onset of lactation and then declined during the next month in conjunction with a drop in milk ceruloplasmin production. The results indicate that milk ceruloplasmin, while being the same protein as in plasma, is not derived from the plasma but is produced by the mammary gland.

Age Factors↗

PubMed2000

Hematological changes and athletic performance in horses in response to high altitude (3,800 m).

This study had two goals: 1) measure hematologic changes with high-altitude acclimatization in horses; and 2) assess the effect of 9 days at high altitude on subsequent athletic performance at low altitude. Six horses performed standardized exercise tests on a dirt track (before and during time at altitude) and treadmill (pre- and postaltitude exposure). Resting and immediate postexercise blood samples were measured for blood volume, lactate, red cell number, packed cell volume, and 2,3-diphosphoglycerate (DPG) concentrations at 225 m, over a 9-day period at 3,800 m, and shortly after returning to 225 m. Acclimatization produced increases in total red cell volume (38.2 +/- 2.4 to 48.1 +/- 2.9 ml/kg, P = 0.004) and DPG/hemoglobin concentrations (19.4 +/- 1.7 increased to 29.4 +/- 0. 4 micromol/g, P = 0.004). Two performance variables, heart rate recovery postexercise and lactate recovery, were faster after acclimatization.

2,3-Diphosphoglycerate↗

PubMed2000

Preferred speed and cost of transport: the effect of incline.

Preferred speed is the behavioral tendency of animals to utilize a relatively narrow set of speeds near the middle of a much broader range that they are capable of using within a particular gait. Possible explanations for this behavior include minimizing musculoskeletal stresses and maximizing energetic economy. If preferred speed is determined by energetic economy (cost of transport, C(T)), then shifts in preferred speed should produce shifts in C(T). To test this hypothesis, preferred speeds were measured in trotting horses on the level and on an incline. The preferred trotting speed decreased from 3.29+/-0.24 m s(-)(1) on the level to 3.05+/-0.30 m s(-)(1) (means +/- s.d., N=6) on an 11.8 % incline. The rate of oxygen consumption was measured as a function of trotting speed on a treadmill and was a curvilinear function of speed in all horses under both conditions (level and 10 % incline). This curvilinear relationship resulted in a C(T) that was a U-shaped function of speed. The speed at which C(T) was minimal (i.e. at which trotting was most energetically economical) was very near the preferred speed on the level and decreased on the incline, again to a speed near the preferred speed on the incline.

Animals↗

PubMed2000

Time of contact and step length: the effect of limb length, running speed, load carrying and incline.

Using published values for twelve species of birds and mammals, we investigated the effects of limb length and running speed on time of contact and step length. In addition, we measured the time of contact in horses trotting up a 10 % incline and when carrying a load averaging 19 % of their body mass. From these values, we calculated stride period and step length. Our analysis of the interspecific data yielded the following relationship between time of contact (t(c) in s) and leg length (L in m) and running speed (v in m s(-)(1)): t(c)=0.80L(0.84)/v(0.87) (r(2)=0.97). Both exponents in this relationship are significantly different from 1.0, indicating that step length increases with speed and that small species use a step length that, relative to their leg length, is longer than the relative step length used by larger species. Time of contact increased when a horse carried a load but not when it trotted up an incline.

Animals↗

PubMed1999

High-altitude effects on respiratory gases, acid-base balance and pulmonary artery pressures in equids.

Arterial and venous blood were analysed at rest and post exercise for pH, PCO2, and PO2, and bicarbonate ([HCO3-]), base excess (BE), and strong ion difference (SID) were calculated in response to a 10 day sojourn to 3800 m. Pulmonary artery pressures (PAP) were measured at rest. Post exercise samples were restricted to venous blood. The equids (n = 6) experienced a profound hypoxia-hypocapnia and a respiratory alkalosis. PaO2 decreased 42% and PaCO2 41%. PaCO2 increased to 80% of initial values after 8 days at altitude. Arterial [HCO3-] decreased by 34%; however, it returned to normal by Day 4. Base excess decreased initially, but increased at altitude with time. Strong ion difference was decreased during the altitude exposure and continued to be depressed even after return to low altitude. Pulmonary artery pressure increased 63% on Day 1 of exposure (from 27.9 +/- 2 to 45.4 +/- 3 mmHg); Days 2 and 6 averaged 36.3 +/- 3 and 37.5 +/- 3 mmHg. Thirty-six hours after return to 225 m, most variables (except [SID] and post exercise BE) returned to normal. The most profound changes in the indicators of gas exchange, at altitude, occurred during the first 3 days and only [HCO3-] returned to normal during the subsequent acclimatization to altitude.

Acid-Base Equilibrium↗

PubMed1993

Lactate and glucose metabolism in mouse (Mus musculus) and reptile (Anolis carolinensis) skeletal muscle.

The reliance on anaerobic metabolism during exercise in lizards has been the subject of a growing body of literature in activity metabolism. Prior studies have demonstrated that lizards rely more on postexercise lactate to regenerate depleted glycogen stores than do many mammals. These studies prompted an in vitro comparison between the metabolic mechanisms for the handling of lactate and glucose in the muscles of a small mammal and lizard. Hindlimb muscles of Mus and Anolis were stimulated to fatigue and then incubated in the presence of 15 mM lactate and either 5.5 (mice) or 8.5 (anoles) mM glucose. Oxidation rates of lactate and glucose were seven to eight times higher in mice. Both species oxidized more lactate than glucose (8 to 9 times). However, anole muscle showed a preference for lactate as a substrate for glycogenesis, incorporating 1.5 times as much lactate (expressed in glucose equivalents) as glucose. In contradistinction, mice incorporated 2.8 times as much glucose into glycogen as lactate. The quantitative differences in metabolic scope of mammals and reptiles are accompanied by fundamental differences in the capacity and patterns of skeletal muscle metabolism of lactate and glucose.

Animals↗

PubMed1993

Plasma catecholamine and corticosterone and their in vitro effects on lizard skeletal muscle lactate metabolism.

Lizard skeletal muscles utilize primarily lactate as a gluconeogenic substrate for glycogen replenishment following exercise. To understand the influence of selected hormones on this process, we measured changes in plasma catecholamines and corticosterone resulting from exercise in the lizard Dipsosaurus dorsalis and then investigated the physiological effects of those hormones on skeletal muscle lactate and glucose metabolism in vitro. Plasma epinephrine (Epi), norepinephrine, and corticosterone (Cort) increased 5.8, 10.2, and 2.2 times, respectively, after 5 min of exhaustive exercise. Epi and Cort levels remained elevated after 2 h of recovery. Skeletal muscle fiber bundles isolated from the red and white regions of the iliofibularis muscle were incubated 2 h at 40 degrees C in the presence of postexercise concentrations of [14C]lactate (15 mM) and glucose (8.5 mM) in the presence and absence of Epi or Cort. Red muscle oxidized both substrates at 2-3 times the rate of white muscle, and both red and white fibers oxidized lactate at 5-10 times the rate of glucose oxidation. Epi had a stimulatory effect on lactate oxidation by white muscle. Lactate incorporation into glycogen proceeded at 2-3 times the rate of glucose incorporation in both muscle types, with rates in red muscle again 2-3 times that for white muscle. Epi stimulated lactate carbon incorporation into glycogen by 50-140% in both red and white muscle but had no effect on glucose incorporation into glycogen in either tissue. We interpret these data as evidence that epinephrine stimulates lactate removal by skeletal muscle. Cort had no effect on lactate metabolism in either muscle type.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Free fatty acids in exercising Arabian horses fed two common diets.

Four Arabian geldings were used in a randomized, repeated measure design to study the effect of two different diets on plasma free fatty acids at rest and during exercise. On each of four sampling days, two horses were fed one of two isoenergetic diets, either 100% corn or 100% alfalfa, at 22% of their estimated daily energy requirement. Two hours after the consumption of the diet, each horse participated in a submaximal standard exercise test consisting of three consecutive 10-min runs of increasing intensity at heart rates of 132, 140 and 147 beats/min, respectively. There were no significant (P greater than 0.05) differences between the two groups (corn-fed vs. alfalfa-fed) in pre-meal (0.554 +/- 0.031 vs. 0.629 +/- 0.033 mmol/L), post-meal (0.520 +/- 0.027 vs. 0.609 +/- 0.041 mmol/L), and basal (0.392 +/- 0.036 vs. 0.401 +/- 0.052 mmol/L) free fatty acid concentrations. However, free fatty acids were significantly higher in the horses fed alfalfa (0.608 +/- 0.038 mmol/L) rather than corn (0.484 +/- 0.031 mmol/L) during exercise.

Animals↗

PubMed1992

Temporal effects of plasmapheresis on serum proteins in horses.

The temporal response of blood and serum proteins to chronic plasmapheresis was determined in 8 horses used in a commercial antibody enterprise. Plasmapheresis of between 4 and 11 L induced significant decreases in total protein, albumin, and IgG values. With the exception of a high hematocrit value for the first postplasmapheresis blood sample, there were no changes in erythrocyte or leukocyte measurements, and no changes in the proportions of serum protein in an electrophoretic profile. Regression equations generated for recovery of proteins after plasmapheresis indicated a return to preplasmapheresis values of total protein and albumin at approximately 1 month. Complications of repeated plasmapheresis were not detected when plasma extractions were done between 7 and 19 times at 30-day intervals.

Animals↗

PubMed1991

Disuse atrophy in the hibernating golden-mantled ground squirrel, Spermophilus lateralis.

Disuse (inactivity, bed rest, and spaceflight) may lead to a loss of muscle mass and a decrease in oxidative capacity in skeletal muscle. If such changes were to occur in hibernating animals, both locomotor and thermogenic function would be compromised. Muscle masses and oxidative capacities (as assessed by citrate synthase activity) were measured in the gastrocnemius and semitendinosus muscles, cardiac muscle (ventricle), and brown fat (axillary pad) in a group (n = 7) of prehibernating ground squirrels (Spermophilus lateralis) and after 6 mo of hibernation (n = 8). Hibernation produced significant atrophy in the gastrocnemius (14%) and semitendinosus (42%) muscles. Cardiac tissue increased (21%) in mass, as did brown adipose tissue (150%). That such changes were not due simply to fluid shifts was evidenced by similar protein concentrations between groups. In contrast to many other disuse studies, oxidative capacity was increased significantly in the gastrocnemius (65%) and semitendinosus (37%). Citrate synthase was also higher in cardiac tissue of hibernators (20%) but was not significantly different in brown fat.

Adipose Tissue↗

PubMed1988

Nonshivering thermogenesis and brown fat in spontaneously hypertensive rats.

Oxygen consumption was measured before and during infusion of the catecholamine isoproterenol in age-matched spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) normotensive rats. Mass-independent rates of oxygen consumption of anesthetized 7-week-old rats were similar in the WKY and SHR rats (11.08 +/- 0.74 and 11.33 +/- 0.82 ml O2 min-1 kg-.67, respectively). Catecholamine infusion elicited increased total oxygen consumption in both WKY and SHR animals (15.0 +/- 1.0 and 14.9 +/- 1.2 ml O2 min-1 kg-.67, respectively), and the magnitude of these increases did not significantly differ. To assess whether there were changes in the metabolic state of brown adipose tissue, the major site of catecholamine-induced thermogenesis in rats, enzymes whose activity is proportional to aerobic capacity were assayed in vitro. In both the interscapular and cervical brown fat depots, maximal citrate synthase and maximal HOAD (beta-hydroxyacyl-CoA dehydrogenase) activities were similar in SHR and WKY rats. There were also no significant differences in brown fat protein content, suggesting no differential growth of this tissue in the two rat strains. Our results indicate that the nonshivering thermogenic capacity of the hypertensive SHR rats does not differ from that of the normotensive WKY animals.

Adipose Tissue, Brown↗