Blood circulation of long bones in trained growing rats and mice.

The effect of physical training on the blood circulation of long bones was studied in growing rats and mice of NMRI-strain. The animals to be trained and their controls were about 2 weeks old at the beginning of the training. The training took place on a 5 degree inclined treadmill 5 days a week for 3 weeks in experiment I and 7 weeks in experiments II and III. The duration of the daily exercise was progressively increased over 3 weeks. The final exercise bouts were 80 min for moderate and 180 min for intensive training programs. The circulating red cell volume (ml/100 g bone) of the humeral, femoral and tibial bones of the trained animals was lower compared to the controls in all three experiments mainly due to reduced hematocrit values. The circulating blood volume (ml/100 g bone) decreased in the tibial bones of the trained animals in experiment I and showed a decreasing tendency in experiment III, but no significant differences between the groups were observed in the humeral and femoral bones. Yet, when related to the volume of the bones the circulating blood volume (ml/100 ccm bone) was significantly higher in the femoral bones of the trained animals, while the changes in the humeral bones were negligible (experiment III). The results suggest that the vascularity of long bones is affected by physical training. The varying responses in different bones are perhaps due to the amount of mechanical stress during physical activity.     

Physical training and connective tissues in young mice: biochemistry of long bones

The effect of physical training on collagen, ground substance, and nucleic acid concentrations in long bones was studied in male mice of NMRI strain. The mice to be trained and their controls were about 2 wk old at the beginning of training, which took place on a 5 degrees inclined treadmill 5 days/wk for 3-22 wk. The duration of daily exercise was increased progressively over 3 wk. The final daily exercise bouts were 50 and 80 min for moderate programs and 180 min for the intensive program at a speed of 30 cm/s. Increased concentrations of nitrogen and hexosamines were found at both training intensities, especially after prolonged training. No conclusive changes in nucleic acid concentrations were observed after training. The hexosamine-hydroxyproline ratio was higher and the hydroxyproline-nitrogen ratio lower in the long bones of trained animals compared to the controls. In conclusion these data suggest that prolonged physical activity affects the organic matrix of long bones by maintaining above average concentrations of glycosaminoglycans in matured bones.     

Bone mechanical properties after exercise training in young and old rats

The effects of a 10-wk training regimen on the mechanical properties of the femur and humerus were evaluated in 2.5- and 25-mo-old Fischer 344 female rats. The rats trained on a rodent treadmill 5 days/wk for 10 wk. Duration, grade, and speed increased until the rats maintained 1 h/day at 15% grade and either 15 m/min (old rats) or 36 m/min (young rats). Excised bones were mechanically tested with a 3-point flexure test for mechanical properties of force, stress, and strain. Fat-free dry weight (FFW) and moment of inertia were also obtained. With aging, similar increases were observed in both the femur and humerus for FFW, moment of inertia, and force. Ultimate stress was reduced in the senescent femur while strain was elevated; a similar but nonsignificant trend was observed in the humerus. Irrespective of age, training increased FFW in the femur and, to a lesser degree, in the humerus. Breaking force was elevated for both bones after training. In young and old bones, the training-induced differences in bone mass and force were similar, despite differences in training intensity. In the old trained rats, femur ultimate stress was greater than that in control rat femurs and similar to that in young rat femurs. The results of the present study indicate that training effects were not limited by age.     

Effect of training on skeletal muscle injury from downhill running in rats

Experiments were conducted to test the hypothesis that injury to skeletal muscle in rats resulting from prolonged downhill running is prevented to a greater extent by prior downhill training than by either uphill or level training. Changes in plasma creatine phosphokinase (CPK) activity and glucose-6-phosphate dehydrogenase (G-6-PDase) activity in the soleus (S), vastus intermedius (VI), and medial head of triceps brachii (TM) muscles were evaluated as markers of muscle injury 48 h after 90 min of intermittent downhill running (16 m . min -1). Prior to this acute downhill run, groups of rats were trained by either downhill (-16 degrees), level (0 degrees), or uphill (+16 degrees) running (16 m . min -1) for 30 min/day. Training duration was either 5 days or 1 day. A training effect (i.e., reduced muscle injury) was indicated if muscle G-6-PDase or plasma CPK activity in a trained group following the 90-min downhill run was not different from that of nonexercised control animals and/or if it was lower than that of nontrained runners. A significant training effect was achieved in all three muscles with 5 days of either downhill or level training, but only in S after 5 days of uphill training. Elevation of plasma CPK activity was prevented by 5 days of training on all three inclines.(ABSTRACT TRUNCATED AT 250 WORDS)     

Glucose uptake and oxidation in fat cells of trained and sedentary pregnant rats

The purpose of this investigation was to examine the relationship between an exercise program and fetal development to determine whether training could influence insulin sensitivity in the pregnant rat. Prior to impregnation one group of animals was exercise trained on a Quinton shock-stimulus rodent treadmill. The exercised group was trained to run 5 days/wk, for 2.0 h/day at 31 m/min up an 8 degree incline for 8 wk before mating. Following mating the training intensity was reduced to 27 m/min up a 5 degree incline, and the exercise period decreased to 1 h/day. On day 19 of gestation, 24 h postexercise for the trained mothers, the animals were killed in the fed state and the parametrial fat pads were removed. The parametrial depot of the trained mother was smaller than the sedentary control dam. This was due to a change in cell size and did not involve alterations in cell number. Isolated adipocytes of the parametrial fat pads were used to measure the rates of 2-deoxy-D-[3H]glucose uptake and D-[1-14C]glucose oxidation to 14CO2. The results indicated that the adipocytes from the dam trained prior to and during pregnancy were significantly (P less than 0.05) more responsive to insulin than those of animals remaining sedentary during the same period. At the maximal insulin concentration tested, the fat cells from trained mothers were able to take up and metabolize approximately twice as much glucose as the sedentary control dams. However, the increase in insulin responsiveness induced by the training program did not match the changes observed in trained nonpregnant rats of prior investigations.     

The effect of fatigue and training status on firefighter performance

Firefighting is a strenuous occupation that requires optimal levels of physical fitness. The National Fire Protection Association suggests that firefighters should be allowed to exercise on duty to maintain adequate fitness levels. However, no research has addressed the effect of exercise-induced fatigue on subsequent fire ground performance. Therefore, the primary purpose of this study was to determine the effect that a single exercise session had on the performance of a simulated fire ground test (SFGT). Secondarily, this study sought to compare the effect of physical training status (i.e., trained vs. untrained firefighters) on the performance of an SFGT. Twelve trained (age: 31.8 ± 6.9 years; body mass index [BMI]: 27.7 ± 3.3 kg·m(-2); VO2peak: 45.6 ± 3.3 ml·kg(-1)·min(-1)) and 37 untrained (age: 31.0 ± 9.0 years; BMI: 31.3 ± 5.2 kg·m(-2); VO2peak: 40.2 ± 5.2 ml·kg(-1)·min(-1)) male career firefighters performed a baseline SFGT. The trained firefighters performed a second SFGT after an exercise session. Time to complete the SFGT, heart rate, and blood lactate were compared between baseline and exercise SFGT (EX-SFGT) conditions. In the trained firefighters, time to complete the SFGT (9.6% increase; p = 0.002) and heart rate (4.1% increase; p = 0.032) were greater during the EX-SFGT compared with baseline, with no difference in post-SFGT blood lactate (p = 0.841). The EX-SFGT time of the trained firefighters was faster than approximately 70% of the untrained firefighters' baseline SFGT time. In addition, the baseline SFGT time of the trained firefighters was faster than 81% of the untrained firefighters. This study demonstrated that on-duty exercise training reduced the work efficiency in firefighters. However, adaptations obtained through regular on-duty exercise training may limit decrements in work efficiency because of acute exercise fatigue and allow for superior work efficiency compared with not participating in a training program.     

Influence of exercise training on maternal and fetal morphological characteristics in the rat

Evidence in both humans and animals has shown that exercise before or during pregnancy may effect fetal outcome. The purpose of this investigation was to examine the effects of an exercise program on fetal development in the rat. Prior to impregnation one group of animals was exercise-trained on a Quinton shock-stimulus rodent treadmill. The exercised group was trained to run 5 days/wk, for 2.0 h/day at 31 m/min up an 8 degree incline for 8 wk before mating. Following mating the training intensity was reduced to 27 m/min up a 5 degree incline, and the exercise period decreased to 1 h/day. On day 19 of gestation, 24 h postexercise for the trained mothers, the animals were killed in the fed state and the maternal and fetal characteristics were measured. The sedentary controls gained significantly (P less than 0.05) more body weight during pregnancy. This can be attributed to three factors: higher number of fetuses, 14.83 +/- 0.04 vs. 12.2 +/- 0.85 for the trained; larger litter weights, 44.25 +/- 4.97 vs. 26.17 +/- 1.82 g/dam for the trained; and slightly larger lipid stores. In addition to having fewer pups the trained mothers had a greater number of fetal resorptions; 0.9/dam as opposed to 0.17/dam for the sedentary control. Analysis of fetal body composition showed no difference in total body water, protein, or fat between the pups of sedentary and trained dams. The results of this study indicate that exercise training prior to and during pregnancy influences fetal development in the rat.     

Effects of endurance moderate physical training on basal metabolism of young adult rats

In order to clarify the conclusion that the change of basal metabolism affected by physical training, effect of endurance training for 8 weeks on basal metabolism of young adult rats were investigated. Results are as follows. Endurance training increased significantly running ability of rats, for instance the running time at a speed of 25 m/min on the control and training groups were 53.7 +/- 18.8 min, 232.8 +/- 32.8 min, respectively. The ratio of soleus's weight to the body weight in trained rats was high significantly (p less than 0.05). The glycogen contents of trained rats under the condition of feeding have higher than the control rats. Especially, glycogen contents of the soleus and red-gastrocnemius significant increased (p less than 0.05), and liver glycogen content under the same condition increased significantly (p less than 0.02). The oxygen consumption in trained rats increased significantly compared with control rats (p less than 0.03). The basal metabolism of trained rats showed 1.24-fold increase compared with those of control (p less than 0.02). Oxygen consumption of sliced ventricle in trained rats increased significantly (p less than 0.03), it's rate was 118% of control. However those of other tissues did not change significantly.     

Effects of training on biochemical and functional properties of rodent neonatal heart

This study was undertaken to determine biochemical and functional (in vivo) adaptations of the rodent neonatal heart in response to a training program of endurance running. Ten day-old rats were progressively trained on a treadmill (final intensity, 21 m/min, 30% grade, 1 h/day) until 75 days of age. The training program induced 14, 57, and 24% increases in relative heart mass, skeletal muscle citrate synthase activity, and whole-body maximal O2 uptake, respectively (P less than 0.05). Cardiac myosin (ATPase) and Ca2+-regulated myofibril ATPase were both reduced by approximately 15% in trained vs. sedentary animals (P less than 0.05). In the majority of trained hearts examined, the myosin isozyme profile reflected an estimated 14 +/- 3% shift toward the V3 or low ATPase isozyme. Left ventricular functional indices during submaximal exercise, derived from a fluid-filled indwelling cannula, indicated that the trained animals maintained similar left ventricular (LV) systolic pressure, LV + the time derivative of pressure, and systemic arterial mean blood pressure compared with their sedentary counterparts. These functional parameters were maintained even though the trained animals performed with lower submaximal exercise heart rate. These findings suggest that maximal exercise capacity can be enhanced in neonatal rats even though the biochemical potential for ATP degradation in the cardiac contractile system is lowered. We speculate that the trend to maintain the myosin isozyme pattern further in the direction of the V3 isozyme in the trained neonatal rat heart may reflect a means to economize cross-bridge cycling while maintaining normal levels of ventricle performance at a given submaximal work load.     

Effects of racetrack exercise on third metacarpal and carpal bone of New Zealand thoroughbred horses

The response of equine bone to training has not been quantified in racetrack trained horses, only in treadmill exercised horses. Seven two-year-old thoroughbred fillies were trained on sand and grass at a racetrack, in a typical New Zealand flatrace training regime. The horses were exercised 6 days per week for up to 13 weeks. During the day the horses were confined in 4 x 4m sand yards, and were stalled at night. Another 7 fillies of the same age were allowed free exercise in grass yards. The bones of the animals were available after the 13 week experimental period, and were examined using a Siemens Somatom AR CT scanner. To quantify the response of epiphyseal bone, 3mm thick sagittal plane images of the carpus (through the middle of the medial condyle of distal radius) and the distal third metacarpal bone (Mc3) (immediately lateral and medial to the junction of the condyle and the median sagittal ridge) were studied. Appropriate areas of interest were chosen, and the mean tissue density equivalent (Houndsfield Units) was determined. In the carpus, there was a significant effect of exercise in the dorso-distal aspect of the radius (p<0.01), dorsal aspect of radial and third carpal bones (p<0.01 and p<0.001 respectively). In palmaro-distal subchondral bone of Mc3, there was a significant effect on the medial/lateral site (p<0.01), which differed between right and left legs, probably due to the effect of the horses having been trained in one direction around the training track. The mean tissue density of the Mc3 epiphysis of the exercised group was 36.8% greater than that of the non-exercised group (p<0.001). The study demonstrates that bone response is both rapid and substantial, which should prompt the use of non-invasive diagnostic aids to determine the stage of training in which tissue density changes occur.     

Training increases muscle blood flow in rats with peripheral arterial insufficiency

This study investigated the effect of physical training on muscle blood flow (BF) in rats with peripheral arterial insufficiency during treadmill running. Bilateral stenosis of the femoral artery of adult rats (300-350 g) was performed to reduce exercise hyperemia in the hindlimb but not limit resting muscle BF. Rats were divided into normal sedentary, acute stenosed (stenosed 3 days before the experiment), stenosed sedentary (limited to cage activity), and stenosed trained (run on a treadmill by a progressively intense program, up to 50-60 min/day, 5 days/wk for 6-8 wk). Hindlimb BF was determined with 85Sr- and 141Ce-labeled microspheres at a low (20 m/min) and high treadmill speed (30-40 m/min depending on ability). Maximal hindlimb BF was reduced to approximately 50% normal in the acute stenosed group. Total hindlimb BF (81 +/- 5 ml.min-1.100 g-1) did not change in stenosed sedentary animals with 6-8 wk of cage activity, but a redistribution of BF occurred within the hindlimb. Two factors contributed to a higher BF to the distal limb muscle of the trained animals. A redistribution BF within the hindlimb occurred in stenosed trained animals; distal limb BF increased to approximately 80% (P less than 0.001) of the proximal tissue. In addition, an increase in total hindlimb BF with training indicates that collateral BF has been enhanced (P less than 0.025). The associated increase in oxygen delivery to the relatively ischemic muscle probably contributed to the markedly improved exercise tolerance evident in the trained animals.     

Development of the time conditioned reflex in various phases of the day cycle in rats

Outbred rats (n = 60) were trained to count 20-s intervals (by the technique developed by J. Bures) with drinking reinforcement. The animals were divided in three groups, which were subjected to conditioning from 7.00 to 9.00 a.m, from 1.00 to 3.00 p.m., and from 8.00 to 10.00 p.m, respectively. Conditioning was most efficient in the morning and least efficient in the day-time. Thus, the better capability of rats for time perception and conditioning on the basis of time perception in transitional phases of a day (from light to darkness and on the contrary) is in agreement with circadian rhythm of locomotion of these nocturnal animals.     

Running during recovery from hindlimb suspension induces transient muscle injury

The objectives were to study morphological adaptations of soleus muscle to decreased loading induced by hindlimb suspension and the effect of run training during the subsequent recovery period. Adult female Wistar rats were kept for 28 days with hindlimbs suspended. For the next 28 days, rats were assigned to a cage-sedentary or daily running group. Compared with control soleus muscles, 28 days of hindlimb suspension reduced the mass and fiber cross-sectional area to 58 and 53% of control values, respectively, and decreased type I fibers from 92 +/- 2 to 81 +/- 2%. During recovery, clusters of damaged fibers were observed in the soleus muscle, and this observation was more pronounced in trained animals. Type IIc fibers appeared transiently during recovery, and their presence was exacerbated with training, as IIc fibers increased to approximately 20% of the total by day 14 of recovery and were no longer evident at day 28. Although muscle wet mass does not differ as a result of mode of recovery at day 14, training transiently decreased the overall fiber area compared with sedentary recovery at this point. By day 28 of recovery the morphological characteristics of soleus muscle in the trained group did not differ from control muscle, whereas in the sedentary group muscle mass and overall fiber cross-sectional area were approximately 14% less than control values.     

"Live high-train low" using normobaric hypoxia: a double-blinded, placebo-controlled study

The combination of living at altitude and training near sea level [live high-train low (LHTL)] may improve performance of endurance athletes. However, to date, no study can rule out a potential placebo effect as at least part of the explanation, especially for performance measures. With the use of a placebo-controlled, double-blinded design, we tested the hypothesis that LHTL-related improvements in endurance performance are mediated through physiological mechanisms and not through a placebo effect. Sixteen endurance cyclists trained for 8 wk at low altitude (<1,200 m). After a 2-wk lead-in period, athletes spent 16 h/day for the following 4 wk in rooms flushed with either normal air (placebo group, n = 6) or normobaric hypoxia, corresponding to an altitude of 3,000 m (LHTL group, n = 10). Physiological investigations were performed twice during the lead-in period, after 3 and 4 wk during the LHTL intervention, and again, 1 and 2 wk after the LHTL intervention. Questionnaires revealed that subjects were unaware of group classification. Weekly training effort was similar between groups. Hb mass, maximal oxygen uptake (VO(2)) in normoxia, and at a simulated altitude of 2,500 m and mean power output in a simulated, 26.15-km time trial remained unchanged in both groups throughout the study. Exercise economy (i.e., VO(2) measured at 200 W) did not change during the LHTL intervention and was never significantly different between groups. In conclusion, 4 wk of LHTL, using 16 h/day of normobaric hypoxia, did not improve endurance performance or any of the measured, associated physiological variables.     

Effect of training on fibre composition and phosphate metabolites in rest measured in vitro in muscles of young pigs.

1. Fibre type composition and phosphate metabolites were studied in m. longissimus thoracis (MLT), m. rectus femoris (MRF) and m. triceps brachii (MTB) in trained (N = 6) and sedentary (N = 6) pigs. 2. Samples were analyzed histochemically and by means of in vitro 31P NMR spectroscopy. 3. Training (duration 11 weeks) consisted of treadmill running at a speed of 1.1 m/sec. The daily exercise time of trained animals gradually increased from 10 min during the very first days to 60 min at the end of the 4th week. 4. During the final 7 weeks exercise time remained unchanged. Sedentary animals were not subjected to training. 5. A higher proportion of type beta R fibres in MRF, MTB and MLT and a lower proportion of type alpha W fibres were found in the trained group of animals compared to the control group. 6. In MLT no significant differences in the proportion of type alpha W were observed between both groups. 7. No significant differences in average fibre diameter of muscle fibres were found between groups. 8. No differences in concentration of phosphate compounds were observed between trained and sedentary groups. 9. Muscles with a higher proportion of type IIb fibres in both groups of pigs contained higher amounts of phosphocreatine (PCr) and were also characterized by a higher ratio of PCr to inorganic phosphate (Pi).     

Muscle atrophy and hypoplasia with aging: impact of training and food restriction

The purpose of this work is to study the influence of aging, training, and food restriction on skeletal muscle mass and fiber number. Male Fischer 344 rats (n = 49) at 3 mo postpartum were assigned to three groups: 1) sedentary control (confined to cage), 2) exercise trained (18 m/min, 8 degrees grade, 20 min/day, 5 days/wk), or 3) food restricted (alternate days of free access and no access to food). At 12 and 27 mo postpartum the soleus and extensor digitorum longus (EDL) muscles were excised, weighed, and fiber number was quantified after HNO3 digestion. At 27 mo the masses of soleus and EDL muscles of sedentary control rats were 83 and 70%, respectively, of 12-mo values (138 +/- 5 and 151 +/- 4 mg). At 27 mo, soleus muscle mass of trained rats was 113% of sedentary control values, whereas EDL muscle mass was unaffected by training. At 27 mo, food restriction had no effect on the mass of both muscles compared with 27-mo sedentary control values. Fiber number was not affected by training or food restriction in both muscles. Fiber number for soleus and EDL muscles of combined groups declined with age by 5.6 and 4.2%, respectively. With aging, the small loss of muscle fibers can account at most for approximately 25% of the observed skeletal muscle atrophy.     

Is exhaustive training adequate preparation for endurance performance?

Our purpose was to test the significance of exhaustive training in aerobic or endurance capacity. The extent of adaptations to endurance training was evaluated by assessing the increase in physical performance capability and oxidative markers in the organs of rats trained by various exercise programs. Rats were trained by treadmill running 5 days.week-1 at 30 m.min-1 for 8 weeks by one of three protocols: T1-60 min.day-1; T2-120 min.day-1; and T3-120 min.day-1 (3 days.week-1) and to exhaustion (2 days.week-1). Groups T2 and T3 ran for longer than T1 in an endurance exercise test (P less than 0.05), in which the animals ran at 30 m.min-1 to exhaustion; no difference was observed between groups T2 and T3. All 3 trained groups showed a similar increase (20-27%) in the fast-twitch oxidative-glycolytic (FOG) fibers with a concomitant decrease in the fast-twitch glycolytic (FG) fiber population in gastrocnemius (p less than 0.05). The capillary supply in gastrocnemius increased with the duration of exercise (p less than 0.05): no difference was found between groups T2 and T3. Likewise, no distinction was seen between groups T2 and T3 in the increase in succinate dehydrogenase activity in gastrocnemius and the heart. These results suggest that the maximal adaptive response to endurance training does not require daily exhaustive exercise.     

Imbalance in SOD/CAT activities in rat skeletal muscles submitted to treadmill training exercise

The association between physical exercise and oxidative damage in the skeletal musculature has been the focus of many studies in literature, but the balance between superoxide dismutase and catalase activities and its relation to oxidative damage is not well established. Thus, the aim of the present study was to investigate the association between regular treadmill physical exercise, oxidative damage and antioxidant defenses in skeletal muscle of rats. Fifteen male Wistar rats (8-12 months) were randomly separated into two groups (trained n=9 and untrained n=6). Trained rats were treadmill-trained for 12 weeks in progressive exercise (velocity, time, and inclination). Training program consisted in a progressive exercise (10 m/min without inclination for 10 min/day). After 1 week the speed, time and inclination were gradually increased until 17 m/min at 10% for 50 min/day. After the training period animals were killed, and gastrocnemius and quadriceps were surgically removed to the determination of biochemical parameters. Lipid peroxidation, protein oxidative damage, catalase, superoxide dismutase and citrate synthase activities, and muscular glycogen content were measured in the isolated muscles. We demonstrated that there is a different modulation of CAT and SOD in skeletal muscle in trained rats when compared to untrained rats (increased SOD/CAT ratio). TBARS levels were significantly decreased and, in contrast, a significant increase in protein carbonylation was observed. These results suggest a non-described adaptation of skeletal muscle against exercise-induced oxidative stress.     

Enhanced efficiency of lactate removal after endurance training

The effects of endurance training (running 1 h/day at 40 m/min, 10% grade) on net lactate removal at various lactate concentrations were assessed in resting rats by use of constant exogenous lactate infusion (0, 69.3, 123.6, and 175.0 mumol.kg-1.min-1). No consistent difference in resting lactate concentrations, 1.17 +/- 0.09 mM, was observed between control and trained animals with no exogenous infusion of lactate. With increasing lactate infusion rates, control animals demonstrated a twofold greater increase in blood lactate concentration (range 1.2-11.4 mM) compared with trained animals (range 1.0-5.5 mM). This response resulted from a more rapid rise in net lactate removal with changes in blood lactate concentration for trained animals. The estimated maximal reaction velocity for net lactate removal in trained animals was 19% lower than in control animals; however, the Michaelis-Menten constant was greater than 66% lower in trained animals (4 mM) compared with controls (12 mM). Control animals also demonstrated a twofold greater increase in lactate concentration as a function of the tracer-estimated lactate turnover. The ratio of 14CO2 yield to lactate specific activity as a function of total tracer removal was not significantly different between groups, suggesting that the relative contributions of oxidation and gluconeogenesis to lactate removal were similar for both groups. At blood concentrations greater than 1 mM, trained animals achieve higher rates of lactate removal for any given lactate concentration.     

Papillary mechanics and cardiac morphology of infarcted rat hearts after training

Infarction of the left ventricle was induced by ligation of the coronary artery in male Sprague-Dawley rats under ketamine-xylazine anesthesia. Three weeks after surgery, animals were assigned to a trained (n = 21; running at 20 m/min, 10% grade, 1 h/day, 5 days/wk) or nontrained group (n = 23) for an additional 8 wk. A third, sham-operated control group (n = 16) remained cage sedentary for 11 wk. Ventricular mass was greater in the trained and nontrained infarct groups [1,335 +/- 57.3 and 1,414 +/- 56.1 mg, respectively (mean +/- SE)] compared with the control group (1,155 +/- 50.9 mg) (P less than or equal to 0.05). The diameter of septal fibers was 13% greater in the trained and 17% greater in the nontrained infarct groups compared with control. The specific peak developed force and maximum rate of force development of left ventricular papillary muscle in vitro were 75 and 62% greater in both infarcted groups compared with the control group; these variables were unaffected by training. Myofibrillar adenosine triphosphatase activity of septum was 20% lower in both infarct groups compared with sham-operated animals. We conclude that exercise training did not alter the magnitude of morphological and physiological adaptations to infarction.