The effect of endurance exercise on bone dimensions, collagen, and calcium in the aged male rat

Skeletal site-specific effects of endurance running on structure and strength of tibia, lumbar vertebrae, and mandible in male Sprague–Dawley rats

Bone microarchitecture, bone mineral density (BMD), and bone strength are affected positively by impact activities such as running; however, there are discrepancies in the magnitude of these effects. These inconsistencies are mainly a result of varying training protocols, analysis techniques, and whether or not the skeletal sites measured are weight bearing. This study’s purpose was to determine the effects of endurance running on sites that experience different weight bearing and load. Eight-week-old male Sprague–Dawley rats (n = 20) were randomly assigned to either a group with a progressive treadmill running protocol (25 m/min for 1 h, incline of 10%) or a nontrained control group for 8 weeks. The trabecular structure of the tibia, lumbar vertebra (L3), and mandible and the cortical structure at the tibia midpoint were measured using microcomputed tomography to quantify bone volume fraction (i.e., bone volume divided by total volume (BV/TV)), trabecular number (Tb.N), trabecular thickness (Tb.Th), trabecular separation (Tb.Sp), and cortical thickness. BMD at the proximal tibia, lumbar vertebrae (L1–L3), and mandible was measured using dual energy X-ray absorptiometry. The tibia midpoint strength was measured by 3-point bending using a materials testing system. Endurance running resulted in superior bone structure at the proximal tibia (12% greater BV/TV (p = 0.03), 14% greater Tb.N (p = 0.01), and 19% lower Tb.Sp (p = 0.05)) but not at other sites. Contrary to our hypothesis, mandible bone structure was altered after endurance training (8% lower BV/TV (p < 0.01) and 15% lower Tb.Th (p < 0.01)), which may be explained by a lower food intake, resulting in less mechanical loading from chewing. These results highlight the site-specific effects of loading on the skeleton.

Effects of skim milk powder intake and treadmill training exercise on renal, bone and metabolic parameters in aged obese rats

PURPOSE

we aim to examine whether adding exercise has impact on obesity prevention and bone metabolism in senior rats, to which dietary obesity was induced through skim milk intake.

METHODS

We used 47, 14-week old Sprague -Dawley (SD) female rats (CLEA Japan, Inc.). The Rats were separated into four random groups: 1) a Non-Ex group with a normal diet (n = 12), 2) an Ex group with a normal diet (n = 12), 3) a Non-Ex group with a skim milk diet (n = 11), and 4) an Ex group with a skim milk diet (n = 12). As the exercise for each Ex group, rats ran on a treadmill starting at 27-week old (TREADMILL CONTROL LE8710 and TREADMILL CONTROL LE8700, Harvard Bioscience). Training protocol stipulated a frequency of five times a week for 12 weeks.

RESULTS

The leptin concentration differed with dietary content: compared to the Ex group with a skim milk diet, Non-Ex and Ex groups with a normal diet showed significantly higher values (p < 0.05). The Ex group had significantly lower values in both the normal diet and skim milk diet groups with or without exercise (p < 0.05). Compared to the Non-Ex group with a normal diet, BS/BV (mm(2)/mm(3)), BV/TV (%), Tb.Th (μm), TBPf (/mm) and Tb.N (/mm) had significantly lower in the Ex group, the Ex and Non-Ex groups with a whey protein diet, and the Ex group with a skim milk protein diet (p < 0.05).

CONCLUSION

These findings suggest that senior female rats fed SMP would have higher bone structural and strength parameters than rats fed a normal diet.

Effects of chronic heavy alcohol consumption and endurance exercise on cancellous and cortical bone microarchitecture in adult male rats

BACKGROUND

Bone health is influenced by numerous lifestyle factors, including diet and exercise. Alcohol is a major nonessential constituent of diet and has dose- and context-dependent effects on bone. Endurance exercise is associated with increased risk of stress fractures. The purpose of this study was to determine the long-term independent and combined effects of chronic heavy alcohol consumption and endurance exercise (treadmill running) on bone mass and microarchitecture in young adult male Sprague-Dawley rats.

METHODS

Six-month-old male rats were randomized into 4 groups (9 to 13 rats/group): sedentary + control diet, sedentary + ethanol (EtOH) diet, exercise + control diet, or exercise + EtOH diet. EtOH-fed rats consumed a liquid diet (EtOH comprised 35% of caloric intake) ad libitum. Control rats were pair-fed the same diet with isocaloric substitution of EtOH with maltose-dextran. Exercise was conducted on a motorized treadmill (15% grade for 30 minutes) 5 d/wk for 16 weeks. Femur and 12th thoracic vertebra were analyzed for bone mineral content (BMC) and density (BMD) using densitometry and cortical and cancellous bone architecture using microcomputed tomography.

RESULTS

EtOH consumption resulted in lower femur length, BMC, and BMD, and lower midshaft femur cortical volume, cortical thickness, and polar moment of inertia. In addition, trabecular thickness was lower in vertebra of EtOH-fed rats. Endurance exercise had no independent effect on any end point evaluated. A significant interaction between endurance exercise and EtOH was detected for several cancellous end points in the distal femur metaphysis. EtOH-consuming rats that exercised had lower distal femur metaphysis bone volume/tissue volume, trabecular connectivity density, and trabecular thickness compared to exercising rats that consumed control diet.

CONCLUSIONS

The results obtained in this model suggest that chronic heavy alcohol consumption may reduce skeletal integrity by reducing bone size, mass, and density, and by negatively altering bone microarchitecture and may increase fracture risk associated with endurance exercise at weight-bearing skeletal sites.

Genistein and exercise do not improve cardiovascular risk factors in the ovariectomized rat

OBJECTIVE

To investigate the effect of either genistein, or exercise, or both, on parameters that are indicators of cardiovascular health.

METHODS

We investigated the effect of genistein treatment (300 mg genisten/kg body weight/day), or exercise training, or combined genistein and exercise training, for a period of 6 weeks on physical characteristics, cardiovascular plasma markers, blood pressure, aortic morphology, cardiac structure and oxidative stress in the ovariectomized (OVX) Sprague-Dawley rat. Comparisons were made with intact rats.

RESULTS

Ovariectomy (compared to intact) resulted in significant decreases in uterine weight (6-fold, p < 0.0001), insulin levels (4-fold, p = 0.0214), insulin/glucose ratio (3-fold, p = 0.0029), and tumor necrosis factor-α plasma levels (2-fold, p < 0.0001). Similarly, aortic blood pressure was significantly increased (by 8%, p < 0.0033) in OVX rats, without changes in aortic luminal or wall dimensions. Heart surface area was significantly increased (by 16%, p = 0.0160) in OVX rats and this was without changes in non-protein thiol levels (a marker of oxidative stress). Physical characteristics were not altered by treatment with genistein, or genistein with exercise, with the exception of increased uterine weight in OVX rats treated under these same conditions. There were no effects of genistein or exercise on indices of blood pressure and aortic morphology in the OVX rat. However, right ventricular nuclei count was reduced in sedentary genistein-treated rats compared to non-treated control OVX rats.

CONCLUSION

Our results indicate that administration of genistein at this dose, treadmill running, or the combination of both, are not associated with any improvement in cardiovascular function and structure, and risk factors in an ovariectomy model of postmenopause.

The critical size bony defect in a small animal for bone healing studies (I): Comparative anatomical study on rats' femur / Der kritische Knochendefekt am Kleintier zur Untersuchung der Knochenheilung: Vergleichende Anatomie am Rattenfemur

Laboratory rats are small animal models which are often used for scientific investigations in medicine. So far there are only few scientific data about the meaning of these small animal models for in vivo bone healing studies available in literature. Although the rat's femur with its cyclic loadings during gait is an appropriate model for investigations in the field of experimental orthopaedics and traumatology there is a lack of morphometric information with respect to its anatomy. The aim of this study is to evaluate the anatomy of rat femurs in two species, which are often performed in animal experimental medicine. These morphometric data should contribute to develope an appropriated osseous fragment fixation system in the rat's femur. The femurs of Wistar (WR) and Sprague Dawley (SDR) cadavers were prepared and analysed by x-rays in two standard planes. The results were compared with the corresponding data for humans by literature. It could be demonstrated that SDR showed a higher caput-collum-diaphyseal and antetorsion angle, but a lower transcondylar femur valgus angle compared to WR. Cortical thickness, bone marrow cavity diameter and femur length were higher in WR. Wistar rat's femur anatomy shows more similarities to human anatomy than Sprague Dawley rats.

Effects of preservation on the mechanical strength and chemical composition of cortical bone: an experimental study in sheep femora

Preservation methods have enabled bone banks to furnish cortical bone grafts to orthopaedic surgeons. However, cortical bone preserved by freezing and autoclaving, may be weakened by these treatments. To test this hypothesis we compared the ultimate tensile strength of freshly harvested sheep femora with that of femora which were frozen at -20 degrees C for 60 days, or autoclaved at 134 degrees C for 8 min. We measured the collagen and mineral contents (calcium, phosphorus, magnesium) and hydroxyproline of the specimens and tested for changes induced by preservation. Mechanical three point tests showed that frozen femora were significantly stronger than either fresh or autoclaved femora (p<0.05). Frozen specimens also had the highest phosphorus level, indicating these measures are related to strength. Cortical bone is not significantly weakened by autoclaving or freezing. This result does not imply that preserved grafts are clinically interchangeable with fresh grafts, rather, it suggests that future studies should focus on post surgical issues, such as the rate of remodeling and integration, which may be sensitive to preservation technique.

Increased bone volume and bone mineral content in xylitol-fed aged rats

BACKGROUND

Our previous studies have shown that dietary xylitol supplementation protects against the loss of bone mineral after ovariectomy. The ovariectomy-induced decrease in trabecular bone volume is significantly retarded by dietary xylitol.

OBJECTIVE

To study whether dietary xylitol can protect against bone loss also during aging, a long-term experimental study was performed with rats.

METHODS

Twenty-four male Sprague-Dawley rats were divided into two groups. The rats in the control group were fed a basal RM1 diet, while the rats in the experimental group were continuously fed the same diet supplemented with 10% (w/w) xylitol. The rats were killed after 20 months. Their tibiae were used for the analyses of bone density and trabecular bone volume, and their femurs were used for the scanning analyses with peripheral quantitative computed tomography (pQCT).

RESULTS

The tibial density of the xylitol-fed aged group (1.73 +/- 0.14 g/mm(3)) was significantly greater than that of the aged group without xylitol (1.56 +/- 0.14 g/ mm(3)). The trabecular bone volume of the xylitol-fed rats was 21.2 +/- 4.0%. It was significantly greater than that of the rats not receiving xylitol (9.3 +/- 4.3%). The pQCT-measured cortical bone mineral density and the pQTC-measured cortical bone mineral content of the femoral diaphysis were significantly greater in the xylitol-fed group than in the control group. The trabecular bone mineral density and the trabecular bone mineral content of the femoral distal metaphysis were also significantly greater in the xylitol-fed group than in the non-xylitol group. The total bone mineral density and the total bone mineral content of the femoral neck in the xylitol-fed aged group significantly exceeded those in the aged group without xylitol supplementation.

CONCLUSIONS

A continuous moderate dietary xylitol supplementation leads to increased bone volume and increased bone mineral content in the long bones of aged rats. This indicates a xylitol-induced protection against aging-related osteoporotic changes.

Endurance training and bone metabolism in middle-aged rats

This study was performed to observe the influence of moderate treadmill running on bone of middle-aged male rats. Seventy 15-month-old Wistar rats were used. Ten initial controls (IC) were killed on day 0. Among the 60 others, three groups of ten exercised rats (E) run 1 h/day, 6 days/week at 60% of their maximum aerobic capacity. On days 30, 60 and 90 of the training period, 20 rats, ten E and ten R (resting animals), were killed. Femoral failure stress never varied and was never different in E and R during the experiment. On day 90 whole body mineral content and mineral density were higher in E than R. Simultaneously, total, diaphyseal and metaphyseal femoral densities were lower in R than IC or than in E. No difference was observed between IC and E. In resting rats, urinary deoxypyridinoline excretion (a marker of bone resorption) increased between days 0 and 90, while it did not change in runners. These results indicate that in middle-aged rats, moderate running prevents decrease in bone mineral density, probably by inhibiting bone resorption.

Five jumps per day increase bone mass and breaking force in rats

The effects of jump training on bone morphological and mechanical properties were investigated in immature bones of female Fischer 344 rats. Five-week-old rats were divided into control or five jump-trained groups comprised of 5-, 10-, 20-, 40-, and 100-jump groups, representing the number of jumps per day. The rats were jump-trained 5 days/week for 8 weeks, and the height of jump was increased to 40 cm progressively. The femur and tibia in the 5-jump group had significantly greater fat-free dry weights per body weight and maximum loads at the fracture tests than those in the control group. The tibia in the 5-jump group also had significantly larger cortical area at the cross-sectional analysis. Although a slight tendency toward increase according to the number of jumps per day was observed, there were few differences in bone morphological and mechanical parameters among the 10-, 20-, and 40-jump groups. The present results indicate that a large number of strains per day is not necessary for bone hypertrophy to develop in rats.

Mechanical loading stimulates rapid changes in periosteal gene expression

Although mechanical forces regulate bone mass and morphology, little is known about the signals involved in that regulation. External force application increases periosteal bone formation by increasing surface activation and formation rate. In this study, the early tibial periosteal response to external loads was compared between loaded and nonloaded contralateral tibia by examining the results of blot hybridization analyses of total RNA. To study the impact of external load on gene expression, RNA blots were sequentially hybridized to cDNAs encoding the protooncogene c-fos, cytoskeletal protein beta-actin, bone matrix proteins alkaline phosphatase (ALP), osteopontin (Op), and osteocalcin (Oc), and growth factors insulin-like growth factor I (IGF-I) and transforming growth factor-beta (TGF-beta). The rapid yet transient increase in levels of c-fos mRNA seen within 2 hours after load application indirectly suggests that the initial periosteal response to mechanical loading is cell proliferation. This is also supported by the concomitant decline in levels of mRNAs encoding bone matrix proteins ALP, Op, and Oc, which are typically produced by mature osteoblasts. Another early periosteal response to mechanical load appeared to be the rapid induction of growth factor synthesis as TGF-beta and IGF-I mRNA levels were increased in the loaded limb with peak levels being observed 4 hours after loading. These data indicate that the acute periosteal response to external mechanical loading was a change in the pattern of gene expression which may signal cell proliferation. The altered pattern of gene expression observed in the present study supports previous evidence of increased periosteal cell proliferation seen both in vivo and in vitro following mechanical loading.

Effects of free mobilization and low- to high-intensity treadmill running on the immobilization-induced bone loss in rats

After an immobilization period of 3 weeks, the effects of free remobilization (8 weeks) as well as low- and high-intensity treadmill running on the bone mineral content (BMC) and density (BMD) of the hindlimbs of Sprague-Dawley rats (n = 70) were studied using a dual-energy x-ray absorptiometric scanner. In the low-intensity running program, the rats were allowed to move freely in the cage for 1 week, after which they started to run on a treadmill twice a day for 7 weeks. The speed of the treadmill was 20 cm/s, with an uphill inclination of 10 degrees. The running time was gradually increased from 20 minutes per session to 45 minutes per session. In the high-intensity group, the program was similar, with the exception that the speed of the treadmill was 30 cm/s, with an uphill inclination of 30 degrees. Immobilization for 3 weeks produced a significant BMC and BMD loss in the immobilized left femur and tibia (mean loss 9.6%, p < 0.001) but did not affect the right free limbs. Both low- and high-intensity running restored mineral content in the immobilized limb; however, an average 5% difference (p < 0.05) in mineral content of the right and left limb bones persisted. In the running groups, the values for the immobilized left limbs were at the same level or exceeded (range 3.8-11.6%, p < 0.05-0.01) and those of the free right limbs exclusively exceeded (range 5.3-15.9%, p < 0.05-0.01) the corresponding values of the age-matched control rats.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of long-term exercise on vertebral and femoral bone mass, dimensions, and strength--assessed in a rat model

The rat model has previously been used to test the effect of ovariectomy and of PTH administration on vertebral bone mass, size, and biomechanical competence. In this study, we used the same "biomechanical rat model" to assess the effect of long-term exercise on vertebral bone mass and quality and also on femoral bone mass, dimensions, and strength. Sixty female Fischer rats were randomized into four groups. Two groups were exercised for 5 days a week on a treadmill with a running distance of 2 km per day. The exercise program was initiated at the age of 2 months. The two exercise groups were investigated after 4 and 10 months. Two sedentary groups (observed for 4 and 10 months) served as controls. At death, three lumbar vertebral bodies (L4-L6) and the left femur were obtained from each rat, and changes in bone mass (ash density, trabecular bone volume [BV/TV]), bone size, and biomechanical competence were assessed. The results revealed an age-related (4-10 months) increase in vertebral bone mass and strength. The additional effect of exercise on the vertebral bodies was an increase in cross-sectional area and bone biomechanical competence. In the femoral bone specimens, an age-related increase in bone mass, size, and strength was also disclosed, and while exercise by itself had no significant influence on biomechanical parameters it did reduce cortical-endosteal bone resorption. The study has demonstrated an anabolic effect of a light exercise regimen on both femoral cortical bone and vertebral bodies (mainly trabecular bone).(ABSTRACT TRUNCATED AT 250 WORDS)

Bone response to alternate-day mechanical loading of the rat tibia

Mechanical loading of the living skeleton influences bone formation, mass, and strength. The primary purpose of the present study was to examine the influence of different loading schedules (days/week) on the bone response to external loading using an in vivo rat tibia four-point bending model. Three studies were conducted to (1) characterize the loaded region, (2) examine the variation of the response within the loaded region, and (3) test the response to different loading schedules. In all studies adult female retired breeder Sprague-Dawley rats were used (6 months, 285 g). First, the location of the loaded region during four-point bending was determined by radiogrammetry of 7 rats. Second, 5 rats were externally loaded for 8 of 10 days at 31 N, 36 cycles, and 2 Hz (1349 +/- 244 mu epsilon). The extent of labeled (forming) periosteal and endocortical surface in the loaded region was compared both among four serial sections from the same tibia and between the loaded and the contralateral tibiae. Finally, 50 rats were randomized into five groups: two nonloaded, control and sham, and three loaded, alternate day, Monday, Wednesday, and Friday, and daily. The rats were externally loaded for 3 weeks at 35 N, 36 cycles, and 2 Hz (1533 +/- 308 mu epsilon). The tibia and fibula were studied for labeled surfaces and mineral apposition rate. For adult female rats with tibial length 39 mm, the loaded region was located 3.5-14 (+/- 0.7) mm proximal to the tibia-fibula junction (TFJ).(ABSTRACT TRUNCATED AT 250 WORDS)

Physical activity and bone mass: exercises in futility?

Growing bone responds to low or moderate exercise through significant additions of new bone in both cortical and trabecular moieties and results in adaptation through periosteal expansion and endocortical contraction. Intracortical activation frequency declines in growing bone in response to exercise, reducing porosity and the remodelling space. These adaptations can be maintained into and throughout adulthood. Young bones have a greater potential for periosteal expansion than aging bone, allowing them to adapt more rapidly and efficiently to an acute need for increased strength, but a threshold level of activity exists above which some bones respond negatively by suppressing normal growth and modelling activity, reducing geometric, mechanical and material properties in cortical and trabecular bone. From cross-sectional studies, differences in bone mass between exercising and non-exercising adults are generally less than 10%, but do not account for exercise history which may be very important, and often fail to consider important confounding variables. There is sufficient longitudinal data to demonstrate that moderate to intensive training can bring about modest increases of about 1-3% in bone mineral content (BMC) of men and premenopausal women. In young adults very strenuous training may increase BMC of the tibia up to 11% and its bone density (BD) by 7%, but may represent periosteal woven bone formation in response to excessive strain. Some evidence shows that exercise can also add bone mass to the post-menopausal skeleton, although the amounts are site-specific and relatively modest. Increases as high as 5-8% can be found after 1-2 years of intensive exercise, but additions of bone to the femur and radius are generally less than 2%, well within the range of the remodelling space and measurement precision. Although increases in bone mass of the post-menopausal skeleton may be extremely modest, physical activity is important to preserve bone mass and muscle function. Detraining reduces any bone mass increase to pre-existing values so that long-term benefits are only retained with continuing exercise. Most importantly, the amount of bone gain that can be achieved appears dependent primarily on the initial bone mass suggesting that individuals with extremely low initial bone mass may have more to gain from exercise than those with moderately reduced bone mass.

Effects of two non-endurance exercise protocols on established bone loss in ovariectomized adult rats

The effects of non-endurance exercise on bone properties were evaluated in 9-month-old sham-operated (SH) and ovariectomized (OVX) rats. The studies were started 3 months postsurgery, after bone mass was decreased in OVX rats. The sham and OVX rats were either kept sedentary (SED) or were trained to run with one of two protocols: 12 m/minute, 50 minutes/day, 4 days/week (low intensity, frequent, EX-1); or 21 m/minute, 40 minutes/day, 1 day/week (moderate intensity, infrequent, EX-2). A group of seven rats evaluated at the beginning of the study served as baseline control. The bone mineral was assessed by the ash weight of the left femur, tibia, and 4th lumbar vertebra. Biomechanical (strength, deformation, stress, strain, and stiffness) and morphometric (length, cortical and medullary area, moment of inertia) properties were evaluated for the right femur. There was a significantly lower bone mineral and mechanical properties in OVX-SED (n = 7) than in SH-SED (n = 10) rats. The OVX-EX-1 (n = 6) rats had higher ash content of femur and tibia than OVX-SED rats, but the change was significant only for tibia. The EX-2 had no effect on the ash content, but femur stress was higher in OVX-EX-2 (n = 8) than in OVX-SED rats. The femur yield force and deformation were improved in OVX rats with both exercise protocols, whereas the vertebra ash weight, femur strain, modulus of elasticity, length, cortical area, and moment of inertia were not changed.(ABSTRACT TRUNCATED AT 250 WORDS)

Can vigorous exercise play a role in osteoporosis prevention? A review

Part of the reduction in bone density observed in older people is due to disuse rather than the aging process itself. While some mechanical stress is needed to maintain optimal bone density, it is not clear just which types of exercise are most valuable or whether appropriate exercise might reduce the need for estrogen therapy in postmenopausal women. Cross-sectional studies. Physical activity, aerobic fitness, and strength have all been correlated with bone density. Young people who use a specific part of the body in vigorous exercise exhibit enhanced bone density in that part of the body, but not necessarily in other regions. Older people who have been active for many years seem to exhibit generally enhanced bone density. Prospective studies. Most regimens which used vigorous aerobic and strength training enhanced bone density, but walking is relatively ineffective for prevention of postmenopausal bone loss. Most studies using specific bone-loading exercise have shown substantial increases in bone density at the specific sites loaded. Elderly people seem capable of responding favorably to vigorous exercise. No direct comparisons of exercise and estrogen therapy have been reported. Excessive exercise. Extremely high volumes of exercise may overwhelm a person's adaptive capacity, leading to stress fractures. For example, young women athletes who suffer from menstrual dysfunction exhibit reduced bone density and musculoskeletal disorders. Clinical implication. Although the evidence is far from conclusive, an exercise regimen should probably include vigorous total body exercise, including strength and aerobic training.

Effect of swimming on prednisolone-induced osteoporosis in elderly rats

We investigated the possible ameliorating and preventive effect of swimming on prednisolone-induced osteoporosis in elderly rats. A total of 48 female Sabra strain rats were randomly assigned to the following groups and treatments: (1) control (C), (2) swimming (S), (3) prednisolone-treated (CP), and (4) swimming + prednisolone (SP). An additional 8 rats were sacrificed and examined at the onset of the study. Groups C and S were sham injected; groups CP and SP were injected with prednisolone (Ultracorten), 80 mg/kg three times per week for 10 weeks. Groups S and SP swam 1 h daily, 5 days per week for 10 weeks. SP rats swam simultaneously with prednisolone administration. At the end of the swimming period, in vivo bone mineral content (BMC) measurements were performed on rat vertebrae L4-5 by single-photon absorptiometry. Later, the humerus and femur were removed for the following measurements: morphometric, bone density (BD) by Compton scattering technique, bone ion content by atomic absorption, and hydration fraction by proton magnetic resonance (PMR). We found that the humeral BD of S rats was greater by 14% for group S over C and 3% greater for group SP over CP (P less than 0.05). Vertebral BMC was higher by 15% in group S over C and 11% higher for group SP over CP (P less than 0.05). Femoral calcium (mg/g dry bone) ion content was higher by 5% in group S over C and 8% in group SP over CP group (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of function on rat femora

We evaluated the mechanical effects of different degrees of function and weight bearing on intact rat femora. Thirty rats were allocated to either an exercising, a nonweight-bearing, or a control group. The exercising rats were trained on a treadmill with a 6 weeks' running program of progressive intensity and duration. In the nonweight-bearing group, the left achilles tendon was severed at its insertion. The control rats were allowed normal activity. After 6 weeks, the animals were killed. The maximum bending moment and bending rigidity were increased in the exercised rats, whereas no differences were found between the control and nonweight-bearing rats. Bone weight and bone dimensions did not differ in the three groups. In the nonweight-bearing group, the maximum bending moment and bending rigidity were higher in the nonoperated on limb, as well as the outer and inner bone dimensions and the area moment of inertia. Our results indicate that exercise improves the mechanical characteristics of bone.

A histomorphometric study of cortical bone activity during increased weight-bearing exercise

To quantify cortical bone response to weight-bearing exercise, bone size, mineral content, and formation were measured at the femoral midshaft in swine. Bone formation was measured histomorphometrically on the periosteal, endosteal, and osteonal surfaces. Sedentary adult crossbred sows (3 years, 229 kg) were randomly assigned to basal (B, n = 6), control (C, n = 7), or trained (T, n = 7) groups. The basal and control groups did not exercise and were killed initially (B) or after 20 weeks (C). The trained group walked on a treadmill 20 minutes/day at 5 km/h and 5% grade, 5 days/week for 20 weeks. Bone length, area, or fat-free dry weight was not different with time (B versus C) or with training (C versus T). Periosteal modeling was stimulated by walking. Periosteal formation surface and mineral apposition rate (MAR) were greater in trained than control femora. No effects of walking were measured on the endosteal surface. Intracortical remodeling was not affected by walking. The number of labeled osteons (22.4 cm-2) was not different among groups, but osteonal MAR was greater in trained (1.18 microns/day) than control (0.96 mu/day) femora. Walking for 20 weeks in the previously sedentary sows was not a sufficient stimulus to create differences in gross measures of bone size or mineral content but did increase periosteal and intracortical MAR. The primary effect of increased exercise appeared to be osteoblast activation.

Effects of voluntary exercise on bone mineral content in rats

We used a voluntary running model to explore the relationship between average daily running distance and bone mineral status of rats. A total of 60 male Sprague-Dawley rats were randomly assigned at 6 weeks of age to a sedentary control group (n = 22) or to a group with unlimited access to a running wheel (n = 38). The running distance of exercising rats was monitored daily, and steady-state running levels ranged from 3.2 to 18.1 km/day. At the end of the experimental period, femora and tibiae were dissected and bone mineral content (BMC, g/cm) and bone mineral density (BMD, g/cm2) were measured by single-photon absorptiometry. Cross-sectional morphometry was examined by taking a transverse section of the femoral middiaphysis. Hindlimb percentage fat was significantly higher in controls than in runners (20.0 +/- 1.2 versus 11.1 +/- 0.6, p less than 0.001), and soleus mass was greater in runners than in controls (371 +/- 8.1 versus 320 +/- 0.8 mg, p less than 0.001). Femoral and tibial lengths, weights, and volumes were significantly higher in runners than in controls (p less than 0.005). BMC and BMD were higher in runners than in controls at all sites apart from the distal femur. Cross-sectional areas at the femoral midshaft were greater in running rats than in sedentary controls (6.26 +/- 0.1 versus 5.45 +/- 0.3 mm2, p less than 0.02), as was the polar moment of inertia (15.6 +/- 0.6 versus 12.7 +/- 0.2 mm4, p less than 0.05). No positive correlation was found between distance run and BMC, BMD, cross-sectional area, or polar moment of inertia.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of swimming on bone modeling and composition in young adult rats

The purpose of this study was to investigate the adaptability of long bones of young adult rats to the stress of chronic aquatic exercise. Twenty-eight female Sabra rats (12 weeks old) were randomly assigned to two groups and treatments: exercise (14 rats) and sedentary control (14 rats) matched for age and weight. Exercised animals were trained to swim in a water bath (35 degrees +/- 1 degree C, 1 hour daily 5 times a week) for 12 weeks loaded with lead weights on their tails (2% of their body weight) (BW). At the end of the training period following blood sampling for alkaline phosphatase, all rats were sacrificed and the humeri and tibiae bones were removed for the following measurements: bone morphometry, bone water compartmentalization, bone density (BD), bone mineral content (BMC), and bone ions content (Ca, Pi, Mg, Zn). The results indicate that exercise did not significantly affect the animals' body weight, bone volume, or length and diameters. However, bone hydration properties, BD, bone mass, and mineralization revealed significant differences between swim-trained rats and controls (P less than 0.05). Longitudinal (R1) measurement was higher by 43% for both humerus and tibia, and Transverse (R2) relaxation rates of hydrogen proton were higher by 117 and 76% for humerus and tibia, respectively; fraction of bound water was higher by 36 and 46% for humerus and tibia, respectively. BD, bone weight, and ash were higher by 13%. BMC and bone ions content were higher by 10%, and alkaline phosphatase was higher by 67%.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of swimming on bone growth and development in young rats

The effect of chronic swimming on bone modelling was studied. Forty female Sabra rats (5 weeks old) were randomly assigned to the following experimental groups: 30 rats were trained to swim (water bath 35 +/- 1 degree C, one h daily, five times a week) for 20 weeks--20 of them loaded with lead weights (1% body weight) while the rest (10 animals) swam load free. Ten sedentary rats matched for age and weight served as controls. At the end of the twenty-week swimming period, all rats were sacrificed, both humeri bones were dissected and prepared for the following examinations: morphometric, bone density (BD), bone mineral content (BMC), compression tests and cross-sectional geometrical parameters, histomorphometry and biochemical analysis of minerals (Ca, Pi, Mg, Zn). All measured parameters were found to be significantly higher (P less than 0.05) in the swimming rats irrespective of load, as compared with the controls. Bone weight was higher by 19%, bone volume by 11%, bone length by 2.8%, cortical area by 16%, BD by 7% and BMC by 15%. The compression breaking force at the distal shaft of the humerus was higher by 24% in the trained group, while the ultimate compressive stress was not significantly different. Maximal and minimal moment of inertia at the distal diaphysis were 33.4 and 40% higher, respectively, for the swimming groups than the controls. Ca, Pi, Mg and Zn levels per total humeral bone were significantly higher in the exercising rats. The histomorphometry and cross-sectional data emphasize longitudinal and transversal growth. These data indicate that swimming exercise exerts a positive effect on bone growth and development in young rats.

Effect of long-distance running on bone mass in women

The effect of long-distance running on bone mass was assessed in 10 premenopausal and 9 estrogen-deprived postmenopausal women and compared to that in closely matched sedentary control women. Vertebral trabecular bone density (VBD) was determined by computed tomography and radial cortical bone density (CBD) by single-photon absorptiometry. Physical fitness was assessed by determining maximal oxygen consumption (VO2max) on a treadmill run to exhaustion. VBD was 183 +/- 7 mg/cm3 and VO2max was 48 +/- 1 ml/kg per minute in young women runners and 163 +/- 8 mg/cm3 and 32 +/- 2 ml/kg per minute in sedentary young women. A positive correlation was noted between VBD and VO2max in these groups (r = 0.509, p less than 0.03). Despite a significantly higher VO2max in postmenopausal women runners compared with sedentary controls (37 +/- 2 versus 24 +/- 2 ml/kg per minute), VBD was identical (112 +/- 5 versus 111 +/- 5 mg/cm3) and no correlation was seen between VBD and VO2max (r = 0.187, p = 0.457). Radial cortical bone density was not different between the runners or sedentary groups in young women (0.738 +/- 0.01 versus 0.732 +/- 0.1 g/cm2) or postmenopausal women (0.617 +/- 0.3 versus 0.665 +/- 0.4 g/cm2). These results suggest that although physical fitness enhances vertebral bone density in premenopausal women, it does not appear to prevent age- and/or sex steroid deficiency-induced bone loss in postmenopausal women.

The aging athlete

In summary, the purpose of this material is to demonstrate that the aging athlete does differ from the younger competitor in many facets. There are physiological, structural, and psychosocial differences which distinguish them as a unique entity in the athletic world. Despite the unavoidable alterations that the passage of time imposes on our bodies, these competitors are still capable of incredible performances of strength, skill, and endurance. In reference to injury, these athletes are at risk from both their current program and their past indiscretions. The literature strongly suggests that the greatest threat to the health of the aging athlete is not the aging process itself but rather inactivity. Astrand concurs with this and states that "there is less risk in activity than in continuous inactivity--it is more advisable to pass a careful physical examination if one intends to be sedentary in order to establish whether one's state of health is good enough to stand the inactivity." It appears that the body systems were designed to reinforce activity and when there is disuse, a large number of atrophic changes take place. It has been estimated that regular exercise may be able to retard the physiologic decline associated with old age as much as 50%. Taken in this light, exercise is truly a fountain of youth from which we can all rejuvenate ourselves. Science has proven that life does not begin at 40, but it has also demonstrated that it does not have to end there. As one author so aptly states, "Not too many years ago the words grandma and grandpa conjured images of rocking chairs and inactivity."(ABSTRACT TRUNCATED AT 250 WORDS)

Endurance training and bone loss in calcium-deficient and ovariectomized rats

We examined interactions among physical training, estrogen deficiency, and calcium deficiency with respect to the maintenance of femoral bone in five groups of 10 to 11-month-old female Fischer 344 rats: sedentary intact, sedentary ovariectomized, trained intact, trained ovariectomized, and control. All rats, except controls, were maintained on a calcium-deficient diet (0.02%) for 8 weeks, and had lower femoral weight, density, ash weight, and ash weight/volume than control rats. Ovariectomy combined with calcium deficiency decreased bone density more than did calcium deficiency alone. Treadmill training for 8 weeks resulted in an increase in maximal functional capacity, endurance time, heart weight and heart/body weight and attenuated the decrease in femoral density observed when ovariectomy and calcium deficiency both were present such that it was similar to that observed in calcium deficiency alone. We concluded that calcium-deficient ovariectomized rats undergo some of the bone changes characteristic of osteoporosis, and of these changes, a decrease in femoral density was attenuated by endurance training.

Bone status of senescent male rats: chemical, morphometric, and mechanical analysis

The bone status of male rats 6, 12, and 24 months of age (n = 10) was examined. Femur calcium (Ca), phosphorus (P), and osteocalcin contents; serum chemistry; and mechanical properties of the bone were measured and correlated. Diaphyseal Ca, P, and osteocalcin contents were not different in animals 6 and 12 months of age but decreased significantly at 24 months: -7.4% for Ca, -4.2% for P, and -24% for osteocalcin compared to 12 months. Femurs from 24-month-old (senescent) rats were characterized by a scalloped appearance of the midfemoral endosteal surface and by cortical porosities. These age-associated changes coincided with nearly two-fold increases in serum immunoreactive parathyroid hormone (PTH) and osteocalcin. Serum Ca did not change with age, whereas serum P decreased (-14.8%) from 6 to 24 months. Maximum breaking force required to fracture femurs at midshaft did not change with age. Hence, the strength of the femur as an intact organ was not compromised with age despite the loss of diaphyseal Ca and P in the senescent animal. However, ultimate stress, a parameter that normalizes for differences in bone geometry and size, decreased 35% in femurs from 12- compared with 24-month-old animals. These mechanical results might be explained by the morphometric finding that, in contrast to the small but progressive age-associated increases in femur weight and length, the cortical and medullary areas increased at least two-fold. Therefore, the strength of the intact femur was maintained by architectural compensations, even though normalized tissue strength decreased with age. These findings suggest that bone status was compromised in the aged male rat.