Effects of exercise on bone mineral density in mature osteopenic rats

Time of day of exercise does not affect the beneficial effect of exercise on bone structure in older female rats

Background: Circadian clock genes are expressed in bone and biomarkers of bone resorption and formation exhibit diurnal patterns in animals and humans. Disruption of the diurnal rhythms may affect the balance of bone turnover and compromise the beneficial effects of exercise on bone. Objective: This study investigated whether the time of day of exercise alters bone metabolism in a rodent model. We hypothesized that exercise during the active phase results in greater bone mass than exercise during the rest phase in older female rats. Methods: Fifty-five, female 12-month-old Sprague Dawley rats were randomly assigned to four treatment groups (n = 13-14/group). Rats were subjected to no exercise or 2 h of involuntary exercise at 9 m/min and 5 days/wk for 15 weeks using motor-driven running wheels at Zeitgeber time (ZT) 4-6 (rest phase), 12-14 (early active phase), or 22-24 (late active phase). ZT 0 is defined as light on, the start of the rest phase. A red lamp was used at minimal intensity during the active, dark phase exercise period, i.e., ZT 12-14 and 22-24. Bone structure, body composition, and bone-related cytokines in serum and gene expression in bone were measured. Data were analyzed using one-way ANOVA followed by Tukey-Kramer post hoc contrasts. Results: Exercise at different ZT did not affect body weight, fat mass, lean mass, the serum bone biomarkers, bone structural or mechanical parameters, or expression of circadian genes. Exercise pooled exercise data from different ZT were compared to the No-Exercise data (a priori contrast) increased serum IGF-1 and irisin concentrations, compared to No-Exercise. Exercise increased tibial bone volume/total volume (p = 0.01), connectivity density (p = 0.04), and decreased structural model index (p = 0.02). Exercise did not affect expression of circadian genes. Conclusion: These data indicate that exercise is beneficial to bone structure and that the time of day of exercise does not alter the beneficial effect of exercise on bone in older female rats.

Alleviative Effects of Exercise on Bone Remodeling in Fluorosis Mice

Fluorine is widely present in nature in the form of fluoride. Prolonged high-dose fluoride exposure can cause skeletal fluorosis, resulting in osteosclerosis, osteoporosis or osteomalacia. It has been proved that exercise is one of the important factors affecting the health of the bone and promoting bone formation. To investigate the effects of exercise on bone remodeling in fluorosis mice, 120 male 3-week-old ICR mice were randomly divided into four groups: control group (C), exercise group (E), fluoride group (F), fluoride plus exercise group (F + E). After 8-week physical exercise and/or fluoride exposure, we evaluated the content of fluorine, the histopathological structure and microstructure of femur, bone metabolism biochemical indexes and oxidative stress related parameters, and the mRNA and protein levels of genes in BMP-2/Smads and OPG/RANKL/RANK signaling pathways. Our results showed that 100 mg/L NaF exposure increased the accumulation of fluoride in bone, altered histology of bone, and enhanced the activities of ALP and TRACP. Meanwhile, excessive fluoride induced oxidative stress in bone tissue by increasing the content of ROS and MDA, and decreasing the activities of antioxidant enzymes. In addition, the results of qRT-PCR suggested that NaF significantly increased the mRNA expression of BMP-2, Smad-5, Col IA1, Col IA2, OPG, RANKL and RANK, as well as the elevated proteins of OPG, RANKL and RANK. However, these fluoride-induced changes were alleviated after moderate exercise. Taken together, these findings indicated that moderate exercise decreased the toxicity of fluoride by reducing the accumulation of fluorine in the body to relieve the bone damage caused by fluorosis.

Effects of Interval Exercise Training on Serum Biochemistry and Bone Mineral Density in Dogs

Simple Summary

In this study, six male beagle dogs underwent 12 weeks of interval exercise following the Frequency, Intensity, Time/duration, Type, Volume, and Progression (FITT-VP) training principle. The heart rate (HR) response was measured during the entire exercise period, and changes in bone mineral density (BMD), muscle volume (MV), and hematology and serum biomarkers were evaluated at the pre-exercise training period and post-exercise training period. We showed that exercise training increased BMD in the femur and serum total alkaline phosphatase (TALP), aspartate aminotransferase, and creatine kinase levels. In addition, our data suggest a positive correlation between BMD and TALP, demonstrating that increased TALP might be an important contributing factor for enhancing BMD with physical training in dogs.

Abstract

Exercise has been suggested as a powerful intervention for health care and fitness management in humans; however, few studies have demonstrated the benefits of exercise training in dogs. The purpose of this study was to examine the effects of exercise training on heart rate (HR), bone mineral density (BMD), muscle volume (MV), and hematological and serum biomarkers in dogs. Six healthy beagles completed the interval treadmill exercise, developed on the basis of the FITT principle, two times a week for 12 weeks. To evaluate the physiological parameters, the HR values were analyzed using the Polar H10 system during the entire exercise period. At pre-and post-exercise, quantitative computed tomography and hematological and serum biochemical parameters were analyzed. The interval exercise resulted in a normal HR response and no adverse behavioral or physiological effects on the dogs. We showed that exercise improved BMD in the femur (541.6 ± 16.7 vs. 610.2 ± 27.8 HA, p < 0.01) and increased serum total alkaline phosphatase (TALP; 68.6 ± 9.2 vs. 81.3 ± 17.2, p < 0.01), aspartate aminotransferase (23.5 ± 1.0 vs. 33.5 ± 1.6, p < 0.01), and creatine kinase (114.8 ± 5.3 vs. 214.0 ± 20.8, p < 0.01) levels. There was a positive relationship between BMD and TALP (femur: r = 0.760, p = 0.004; vertebrae: r = 0.637; p = 0.025). Our findings suggest that interval exercise training is beneficial to increase BMD in the femur, and an increased TALP level would be a concomitant mechanism for enhancing BMD with exercise in dogs.

Does Physical Exercise Always Improve Bone Quality in Rats?

For decades, the osteogenic effect from different physical activities on bone in rodents remained uncertain. This literature review presents for the first time the effects on five exercise models (treadmill running, wheel running, swimming, resistance training and vibration modes) in three different experimental rat groups (males, females, osteopenic) on bone quality. The bone parameters presented are bone mineral density, micro-architectural and mechanical properties, and osteoblast/osteocyte and osteoclast parameters. This review shows that physical activities have a positive effect (65% of the results) on bone status, but we clearly observed a difference amongst the different protocols. Even if treadmill running is the most used protocol, the resistance training constitutes the first exercise model in term of osteogenic effects (87% of the whole results obtained on this model). The less osteogenic model is the vibration mode procedure (31%). It clearly appears that the gender plays a role on the bone response to swimming and wheel running exercises. Besides, we did not observe negative results in the osteopenic population with impact training, wheel running and vibration activities. Moreover, about osteoblast/osteocyte parameters, we conclude that high impact and resistance exercise (such jumps and tower climbing) seems to increase bone formation more than running or aerobic exercise. Among the different protocols, literature has shown that the treadmill running procedure mainly induces osteogenic effects on the viability of the osteocyte lineage in both males and females or ovariectomized rats; running in voluntary wheels contributes to a negative effect on bone metabolism in older male models; whole-body vertical vibration is not an osteogenic exercise in female and ovariectomized rats; whereas swimming provides controversial results in female models. For osteoclast parameters only, running in a voluntary wheel for old males, the treadmill running program at high intensity in ovariectomized rats, and the swimming program in a specific ovariectomy condition have detrimental consequences.

Influence of physical training on markers of bone turnover, mechanical properties, morphological alterations, density and mineral contents in the femur of rats exposed to cadmium and/or alcohol

The aim of the study was to investigate the effect of physical training on bone parameters of rats exposed to alcohol (Al) and/or cadmium (Cd). Young female rats were divided into one control group and six groups exposed to Cd and/or Al. Al (36% calories of diet) and Cd (20 mg Cd/kg feed) were administered with liquid diet. Half of the rats from the treated groups were subjected to treadmill training (20 m/min for 0.5 h, 4 days a week). The experiment was carried out for 5 months. Al decreased the concentration of calcium (Ca) and iron (Fe) in the femur, whereas Cd and Cd + Al intake reduced the contents of Ca, Fe and zinc. Al and/or Cd caused an increase in both C-terminal telopeptide of type I collagen (CTX1; bone resorption marker) and osteocalcin (OC; formation indicator) and enhanced the degree of porosity and flexural strength of the femur. Al partially prevented the loss of Fe from the bone caused by Cd, but intensified the inhibition of growth of body weight in comparison with separate exposure to Cd. In rats co-exposed to Cd + Al, the levels of CTX1 were greater compared with those treated with Al or Cd separately, and the density was less than that in rats exposed to Al separately. The training caused increases of magnesium and Ca contents, decreases in CTX1, as well as increases in OC and bone density, decreasing their porosity. The effect of training on the bone status, however, was limited (especially in rats co-exposed to Cd and Al) because of the increase in their mineralization, stimulated by exercises, was insufficient in relation to collagen production intensity. In conclusion, training had favourable effects on some bone parameters, but did not compensate for the negative effects of Al and/or Cd exposure on the poor mineralization and histopathological and morphological changes in the femur.

Compromised Exercise Capacity and Mitochondrial Dysfunction in the Osteogenesis Imperfecta Murine (oim) Mouse Model

Osteogenesis imperfecta (OI) is a heritable connective tissue disorder that most often arises from type I collagen-COL1A1 and COL1A2-gene defects leading to skeletal fragility, short stature, blue-gray sclera, and muscle weakness. Relative to the skeletal fragility, muscle weakness is much less understood. Recent investigations into OI muscle weakness in both patients and mouse models have revealed the presence of an inherent muscle pathology. Understanding the mechanisms responsible for OI muscle weakness is critical, particularly in light of the extensive cross-talk between muscle and bone via mechanotransduction and biochemical signaling. In the following study we initially subjected WT and oim/oim mice, modeling severe human OI type III, to either weight-bearing (voluntary wheel-running) or non-weight-bearing (swimming) exercise regimens as a modality to improve muscle strength and ultimately bone strength. The oim/oim mice ran only 35% to 42% of the distance run by age- and sex-matched WT mice and exhibited little improvement with either exercise regimen. Upon further investigation, we determined that oim/oim gastrocnemius muscle exhibited severe mitochondrial dysfunction as characterized by a 52% to 65% decrease in mitochondrial respiration rates, alterations in markers of mitochondrial biogenesis, mitophagy, and the electron transport chain components, as well as decreased mitochondrial citrate synthase activity, relative to age- and sex-matched WT gastrocnemius muscle. Thus, mitochondrial dysfunction in the oim/oim mouse likely contributes to compromised muscle function and reduced physical activity levels. © 2019 American Society for Bone and Mineral Research.

Multiscale experimental study on the effects of different weight-bearing levels during moderate treadmill exercise on bone quality in growing female rats

Background

Bone tissue displays a hierarchical organization. Mechanical environments influence bone mass and structure. This study aimed to explore the effects of different mechanical stimuli on growing bone properties at macro–micro–nano scales.

Methods

Sixty five-week-old female Wistar rats were treadmill exercised at moderate intensity with the speed of 12 m/min, and then randomly divided into five groups according to weight-bearing level. After 8 weeks of experiment, femurs were harvested to perform multiscale tests.

Results

Bone formation was significantly increased by weight-bearing exercise, whereas bone resorption was not significantly inhibited. Trabecular and cortical bone mineral densities showed no significant increase by weight-bearing exercise. The microstructure of trabecular bone was significantly improved by 12% weight-bearing exercise. However, similar positive effects were not observed with further increase in weight-bearing levels. The nanomechanical properties of trabecular bone were not significantly changed by weight-bearing exercise. The macrostrength of whole femur and the nanomechanical properties of cortical bone significantly decreased in the 19% and 26% weight-bearing exercise groups.

Conclusion

When rats ran on the treadmill at moderate intensity during growth period, additional 12% weight-bearing level could significantly increase bone formation, improve microstructure of trabecular bone, as well as maintain the structure and mechanical properties of cortical bone. Excessive weight-bearing level caused no positive effects on the trabecular bone microstructure and properties of cortical bone at all scales. In addition, increased weight-bearing level exerted no significant influence on trabecular and cortical bone mineral densities.

Young and healthy C57BL/6 J mice performing sprint interval training reveal gender- and site-specific changes to the cortical bone

Physical exercise is considered to impede the bone loss associated with physiological ageing however, a training program that efficiently leads to bone accrual in the healthy does not yet exist. We turned to the C57BL/6 J mouse and designed a sprint interval training for treadmill that was tailored to the individual performance limits. It consisted of four weeks with five training sessions each, followed by another four weeks with three. After completion of the training period, mice were sacrificed and the hind legs were analyzed via µCT and MRI for changes in bone parameters and muscle volume, respectively. Increased performance limits in both sexes confirmed an effect of the treadmill training. However, while male tibiae after eight weeks revealed a significant reduction of cortical bone mass at the distal metaphysis, the cross sectional analysis of female tibiae showed a transient decrease of cortical bone mass after four weeks that was reversed into a significant accrual after eight weeks of training and occurred over the entire length of the tibia. The observed net reduction of female bone mass after four weeks of training is suggestive of a remodelling process which may be delayed in the males.

Morphological and Microstructural Alterations of the Articular Cartilage and Bones during Treadmill Exercises with Different Additional Weight-Bearing Levels

The aim of this study was to investigate the morphological and microstructural alterations of the articular cartilage and bones during treadmill exercises with different exercise intensities. Sixty 5-week-old female rats were randomly divided into 10 groups: five additional weight-bearing groups (WBx) and five additional weight-bearing with treadmill exercise groups (EBx), which were subjected to additional weight bearing of x% (x = 0, 5, 12, 19, and 26) of the corresponding body weight of each rat for 15 min/day. After 8 weeks of experiment, the rats were humanely sacrificed and their bilateral intact knee joints were harvested. Morphological analysis of the cartilages and microcomputed tomography evaluation of bones were subsequently performed. Results showed that increased additional weight bearing may lead to cartilage damage. No significant difference was observed among the subchondral cortical thicknesses of the groups. The microstructure of subchondral trabecular bone of 12% and 19% additional weight-bearing groups was significantly improved; however, the WB26 and EB26 groups showed low bone mineral density and bone volume fraction as well as high structure model index. In conclusion, effects of treadmill exercise on joints may be associated with different additional weight-bearing levels, and exercise intensities during joint growth and maturation should be selected reasonably.

THE INFLUENCE OF PASSIVE TOBACCO EXPOSURE AND PHYSICAL EXERCISE ON BONE TISSUE OF YOUNG RATS

OBJECTIVE

The objective of this study is to investigate the effect of passive smoking during pregnancy and associated with swimming on bone area growth, bone mineral density (BMD), and bone mineral content (BMC).

METHODS

The offspring was grouped by control matrices (G1) and passive smokers (G2). The offspring was regrouped in eight subgroups, with exposure to smoking (2x/day) and physical exercise (1 session/day), respecting the group of matrices in: sedentary control (G1CS and G2CS), swimming control (G1CN and G2CN), sedentary passive smoker (G1FS and G2FS), and passive smoker swimmer (G1FN and G2FN). The area, BMD and BMC were measured by the tibia and femur and analyzed by densitometer. The results were analyzed by One-Way ANOVA test with Tukey post-test, with a significance level of 5%.

RESULTS

In the tibia BMC study, a better rate was observed in G2CN group when compared to G1CS, G1CN and G1FN (p ≤ 0.023). When assessing BMD in the femur, a higher density ratio was observed in G1FS group when compared to G2CS, G2CN, G2FS and G2FN (p<0.008). In the tibia study, the animals of the G1FS group had higher rates when compared to G2CS and G2FN groups (p≤0.007).

CONCLUSIONS

The model of male offspring exposed to passive smoking during fetal development showed a strong decrease in the analyzed parameters. Level of Evidence I, Randomized High Quality Clinical Trial With or Without Statistically Significant Difference, But Narrow Confidence Intervals.

High-impact exercise in rats prior to and during suspension can prevent bone loss

High-impact exercise has been considered an important method for treating bone loss in osteopenic experimental models. In this study, we investigated the effects of osteopenia caused by inactivity in femora and tibiae of rats subjected to jump training using the rat tail suspension model. Eight-week-old female Wistar rats were divided into five groups (n=10 each group): jump training for 2 weeks before suspension and training during 3 weeks of suspension; jump training for 2 weeks before suspension; jump training only during suspension; suspension without any training; and a control group. The exercise protocol consisted of 20 jumps/day, 5 days/week, with a jump height of 40 cm. The bone mineral density of the femora and tibiae was measured by double energy X-ray absorptiometry and the same bones were evaluated by mechanical tests. Bone microarchitecture was evaluated by scanning electron microscopy. One-way ANOVA was used to compare groups. Significance was determined as P<0.05. Regarding bone mineral density, mechanical properties and bone microarchitecture, the beneficial effects were greater in the bones of animals subjected to pre-suspension training and subsequently to training during suspension, compared with the bones of animals subjected to pre-suspension training or to training during suspension. Our results indicate that a period of high impact exercise prior to tail suspension in rats can prevent the installation of osteopenia if there is also training during the tail suspension.

Biomechanical and microstructural benefits of physical exercise associated with risedronate in bones of ovariectomized rats

Several treatments have been developed aiming the prevention of bone loss. There are discussions about the best prophylactic and therapeutic procedures for osteoporosis. This study evaluated the effects of physical exercise associated with risedronate as a prophylactic and therapeutic procedure in osteopenic bones of rats submitted to ovariectomy. We used 48 Wistar rats divided into: ovariectomized or subjected to sham surgery. Ovariectomized rats were divided into the following sub-groups: OVX, 12 weeks sedentary; OVX-EX, treadmill training for 12 weeks; OVX-RA, 12 weeks with risedronate administration; and OVX-EX-RA, 12 weeks with risedronate administration and treadmill training. Rats subjected to sham surgery were divided into the following sub-groups: SH, 12 weeks sedentary; SH-EX, treadmill training for 12 weeks; SH-RA, 12 weeks with risedronate administration; and SH-EX-RA, 12 weeks with risedronate administration and training on the treadmill. The effectiveness of the treatment was evaluated in tibias using biomechanical, radiological, histomorphometric, and immunohistochemical analyses. Data were analyzed by statistical tests, with significance level of P < 0.05. Results of mechanical tests showed that the SH-RA group had lower values compared with OVX-RA group; densitometry showed no significant differences; according to histomorphometric methods, OVX group presented lower results than the SH-EX, OVX-RA, SH-EX-RA, and OVX-EX-RA groups, and SH-EX-RA and OVX-EX-RA groups showed values higher than SH-RA, SH, and OVX-EX groups. The SH-EX-RA and OVX-EX-RA groups had decreased immunostaining for tartrate-resistant acid phosphatase and receptor activator of nuclear factor kappa-B ligand and increased osteoprotegerin immunostaining. In this experimental model, it was concluded that the physical training associated with use of risedronate exerted positive effects on biomechanical and microstructural properties in bones of ovariectomized rats.

A well-balanced diet combined or not with exercise induces fat mass loss without any decrease of bone mass despite bone micro-architecture alterations in obese rat

The association of a well-balanced diet with exercise is a key strategy to treat obesity. However, weight loss is linked to an accelerated bone loss. Furthermore, exercise is known to induce beneficial effects on bone. We investigated the impact of a well-balanced isoenergetic reducing diet (WBR) and exercise on bone tissue in obese rats. Sixty male rats had previously been fed with a high fat/high sucrose diet (HF/HS) for 4months to induce obesity. Then, 4 regimens were initiated for 2months: HF/HS diet plus exercise (treadmill: 50min/day, 5days/week), WBR diet plus exercise, HF/HS diet plus inactivity and WBR diet plus inactivity. Body composition and total BMD were assessed using DXA and visceral fat mass was weighed. Tibia densitometry was assessed by Piximus. Bone histomorphometry was performed on the proximal metaphysis of tibia and on L2 vertebrae (L2). Trabecular micro-architectural parameters were measured on tibia and L2 by 3D microtomography. Plasma concentration of osteocalcin and CTX were measured. Both WBR diet and exercise had decreased global weight, global fat and visceral fat mass (p<0.05). The WBR diet alone failed to alter total and tibia bone mass and BMD. However, Tb.Th, bone volume density and degree of anisotropy of tibia were decreased by the WBR diet (p<0.05). Moreover, the WBR diet had involved a significant lower MS/BS and BFR/BS in L2 (p<0.05). Exercise had significantly improved BMD of the tibia possibly by inhibiting the bone resorption, as evidenced by no change in plasma osteocalcin levels, a decrease of CTX levels (p<0.005) and trabecular osteoclast number (p<0.05). In the present study a diet inducing weight and fat mass losses did not affected bone mass and BMD of obese rats despite alterations of their bone micro-architecture. The moderate intensity exercise performed had improved the tibia BMD of obese rats without any trabecular and cortical adaptation.

Long-term aerobic exercise and omega-3 supplementation modulate osteoporosis through inflammatory mechanisms in post-menopausal women: a randomized, repeated measures study

BACKGROUND

Evidence indicates that dietary fats and physical activity influence bone health. The purpose of this study was to examine the effects of long-term aerobic exercise and omega-3 (N-3) supplementation on serum inflammatory markers, bone mineral density (BMD), and bone biomarkers in post-menopausal women.

METHODS

Seventy-nine healthy sedentary post-menopausal women aged 58-78 years participated in this study. Subjects were randomized to one of 4 groups: exercise + supplement (E+S, n = 21), exercise (E, n = 20), supplement (S, n = 20), and control (Con, n = 18) groups. The subjects in the E+S and E groups performed aerobic exercise training (walking and jogging) up to 65% of HRmax, three times a week for 24 weeks. Subjects in the E+S and S groups consumed 1000 mg/d N-3 for 24 weeks. The lumbar spine (L2-L4) and femoral neck BMD, serum tumor necrosis factor (TNF) α, interleukin (IL) 6, prostaglandin (PG) E2, estrogen, osteocalcin, 1, 25-dihydroxyvitamin D3 (1, 25 Vit D), C-telopeptide (CTX), parathyroid hormone (PTH) and calcitonin (CT) were measured at baseline, the end of week 12 and 24.

RESULTS

Serum estrogen, osteocalcin, 1, 25 Vit D, CT, L2-L4 and femoral neck BMD measures increased (P < 0.05) and the serum CTX, PTH, TNF-α, IL-6, and PGE2 decreased (P < 0.05) in E + S group after the 24 wk intervention but not in the E or S intervention groups. L2-L4 and femoral neck BMD, estrogen, osteocalcin, and CT were negatively (P < 0.05) correlated with TNF-α and PGE2. PTH and CT were correlated positively and negatively with IL-6, respectively (P < 0.05).

CONCLUSIONS

The present study demonstrates that long-term aerobic exercise training plus N-3 supplementation have a synergistic effect in attenuating inflammation and augmenting BMD in post-menopausal osteoporosis.

Effects of different swimming exercise intensities on bone tissue composition in mice: a Raman spectroscopy study

OBJECTIVE

Raman spectroscopy was employed to evaluate the effect of different swimming intensities on femoral bone composition in an animal model.

BACKGROUND DATA

Intense swimming exercise may affect bone mineralization, and Raman technique has been shown to be effective in evaluating tissue composition (phosphate minerals and carbonate apatites - bands at 960 and 1170 cm(-1), as well as collagen matrix - amide I band at 1660 cm(-1)).

MATERIALS AND METHODS

Eighteen female Swiss Webster mice were separated into three groups (n = 6 per group) of sedentary (SED), and swimming with an intensity of 40% (PT-40) and 80% (PT-80) of the maximum load, with 6 weeks of training. Near-infrared Raman spectra (830 nm wavelength and 80 mW laser power) were obtained with a dispersive Raman spectrometer using a CCD camera and imaging spectrograph with 30-s integration time. Spectra were collected in the medial and lateral diaphysis of the femur and principal components analysis (PCA) was employed to extract features of the Raman bands of bone and to perform quantitative analysis.

RESULTS

PC1 vector resembles Raman spectra and carries information about apatite minerals and some contribution from organic matrix. A statistically significant difference was found in the PC1 scores (ANOVA, p < 0.05), indicating lower mineral concentrations in the femur in both the PT-40 and PT-80 groups compared to the SED group. These results corroborated with the radiographic assessment of bone density.

CONCLUSION

Raman technique associated with PCA statistics showed that intense swimming exercise may affect bone mineralization and remodeling in a mouse model of training.

Restoration of bone turnover rate after decompression surgery in patients with symptomatic lumbar spinal stenosis: preliminary report

STUDY DESIGN

Prospective short-term longitudinal study.

OBJECTIVE

To investigate changes in the bone turnover rate in patients with lumbar spinal stenosis (LSS) before and after decompression surgery. SUMMARY OF BACK GROUND DATA: Decompression surgery enables elderly patients with LSS to participate in daily activities and physical exercise by reducing or alleviating leg and back pain. However, there have been no studies to date regarding the effect of decompression surgery on bone metabolism in such patients.

METHODS

Twenty-three patients with spinal stenosis who were scheduled to undergo decompression surgery were enrolled in our study. Ten patients were given oral bisphosphonates after the operation (B+ group), while the remaining 13 patients did not receive oral bisphosphonate (B- group). In both groups, walking distance without rest, the Oswestry Disability Index (ODI) scores, duration of symptoms, bone formation, and resorption markers, and bone mineral density were recorded before surgery. Three months after surgery, bone turnover markers, a single trial for walking distance without rest and ODI scores were measured for both groups.

RESULTS

Three months after the operation, the bone resorption marker u-NTx was decreased significantly for both groups. Although there was a decrease in bALP, a bone formation maker, in both groups, the change in each group was not statistical significant. Distance in a single trial walk was increased and ODI scores were decreased significantly for both groups.

CONCLUSION

This study suggests that decompression surgery has a beneficial effect on bone metabolism in patients with LSS who have walking intolerance and limited physical activity.

Selective breeding as a tool to probe skeletal response to high voluntary locomotor activity in mice

We present a novel mouse-model for the study of skeletal structure and evolution, based on selective breeding for high levels of voluntary wheel running. Whereas traditional models (originally inbred strains, more recently knockouts and transgenics) rely on the study of mutant or laboratory-manipulated phenotypes, we have studied changes in skeletal morphometrics resulting from many generations of artificial selection for high activity in the form of wheel running, in which mice engage voluntarily. Mice from the four replicate High Runner (HR) lines run nearly three times as many revolutions during days 5 and 6 of a 6-day exposure to wheels (1.12 m circumference). We have found significant changes in skeletal dimensions of the hind limbs, including decreased directional asymmetry, larger femoral heads, and wider distal femora. The latter two have been hypothesized as evolutionary adaptations for long-distance locomotion in hominids. Exercise-training studies involving experimental groups with and without access to wheels have shown increased diameters of both femora and tibiafibulae, and suggest genetic effects on trainability (genotype-by-environment interactions). Reanalysis of previously published data on bone masses of hind limbs revealed novel patterns of change in bone mass associated with access to wheels for 2 months. Without access to wheels, HR mice have significantly heavier tibiafibulae and foot bones, whereas with chronic access to wheels, a significant increase in foot bone mass that was linearly related to increases in daily wheel running was observed. Mice exhibiting a recently discovered small-muscle phenotype ("mini-muscle," [MM] caused by a Mendelian recessive gene), in which the mass of the triceps surae muscle complex is ∼50% lower than in normal individuals, have significantly longer and thinner bones in the hind limb. We present new data for the ontogenetic development of muscle mass in Control, HR, and MM phenotypes in mice of 1-7 weeks postnatal age. Statistical comparisons reveal highly significant differences both in triceps surae mass and mass-corrected triceps surae mass between normal and MM mice at all but the postnatal age of 1 week. Based on previously observed differences in distributions of myosin isoforms in adult MM mice, we hypothesize that a reduction of myosin heavy-chain type-IIb isoforms with accounts for our observed ontogenetic changes in muscle mass.

Modified activity-stress paradigm in an animal model of the female athlete triad

The exercising woman with nutritional deficits and related menstrual irregularities is at risk of compromising long-term bone health, i.e., the female athlete triad. There is no animal model of the female athlete triad. The purpose of this study was to examine long-term energy restriction in voluntary wheel-running female rats on estrous cycling, bone mineral content, and leptin levels. Twelve female Sprague-Dawley rats (age 34 days) were fed ad libitum and given access to running wheels during an initial 14-wk period, providing baseline and age-related data. Daily collection included dietary intake, body weight, estrous cycling, and voluntary running distance. At 4 mo, rats were randomized into two groups, six restrict-fed rats (70% of ad libitum intake) and six rats continuing as ad libitum-fed controls. Energy intake, energy expenditure, and energy availability (energy intake - energy expenditure) were calculated for each animal. Serum estradiol and leptin concentrations were measured by RIA. Femoral and tibial bone mineral density and bone mineral content (BMC) were determined by dual-energy X-ray absorptiometry. Restrict-fed rats exhibited a decrease in energy availability during Weight Loss and Anestrous phases (P = 0.002). Compared with controls after 12 wk, restrict-fed rats showed reduced concentrations of serum estradiol (P = 0.002) and leptin (P = 0.002), lower ovarian weight (P = 0.002), and decreased femoral (P = 0.041) and tibial (P = 0.05) BMC. Decreased energy availability resulted in anestrus and significant decreases in BMC, estrogen and leptin levels, and body weight. Finally, there is a critical level of energy availability to maintain estrous cycling.

Doping dose of salbutamol and exercise training: impact on the skeleton of ovariectomized rats

Previous studies in healthy rats have demonstrated a deleterious bone impact of β-agonist treatment. The purpose of this study was to examine the trabecular and cortical effects of β2-agonists at doping dose on treadmill exercising rats with estrogen deficiency. Adult female rats were ovariectomized (OVX; n = 44) or sham operated ( n = 12). Then, OVX rats received a subcutaneous injection of salbutamol (SAB) or vehicle with (EXE) or without treadmill exercise for 10 wk. Bone mineral density (BMD) was analyzed by densitometry. Microcomputed tomography and histomorphometric analysis were performed to study trabecular bone structure and bone cell activities. After 10 wk, SAB rats presented a much more marked decrease of BMD and trabecular parameters. Exercise did not change the high level of bone resorption in OVX EXE SAB compared with OVX SAB group (both on COOH-terminal collagen cross-links and osteoclast number). These results confirm the deleterious effect of β2-agonists on bone quantity (femoral BMD gain: OVX EXE, +6.8%, vs. OVX EXE SAB, −1.8%; P < 0.01) and quality (−8.0% of femoral trabecular thickness in OVX EXE SAB vs. OVX EXE), indicating that SAB suppresses the effect of EXE in OVX rats. Furthermore, we notice that the slight beneficial effect of exercise was mainly localized in the tibia. These findings indicate the presence of a bone alteration threshold below which there is no more alteration in structural bone quantity and quality. The negative effects of SAB on bone observed in this study in trained rats may indicate potential complications in doping female athletes with exercise-induced amenorrhea.

Effects of chronic NH4Cl dosage and swimming exercise on bone metabolic turnover in rats

To determine the effects of ammonium chloride (NH4Cl) dosage and swimming exercise training during 4 weeks on bone metabolic turnover in rats, seven-week-old female 24 Wister-Kyoto (WKY) rats were investigated by bone status including bone mineral density (BMD) and biomechanical markers from blood and urine. Twenty-four rats (initial weight: 191.2+/-7.6 g) were randomly divided into four groups: baseline (8 weeks old) control group (n=6, BC), 4-week control group (n=6, Con), 4-week swimming exercise loading group (n=6, Swim) and 4-week chronic NH4Cl dosage group (n=6, Acid). All rats were fed an AIN93M diet (Ca: 0.5%, P: 0.3%), and both Con and Swim groups were pair-fed by feeding volume of the NH4Cl dosage group. The acid group only received 0.25 M NH4Cl distilled water ad libitum. At the end of the experimental period, rats were sacrificed with blood drawn and femur and tibia were removed for analysis of bone mineral density (BMD) by dual energy X-ray absorptiometry (DEXA). In the Swim group, 24-hour urinary deoxypiridinoline (Dpd) excretion, reflecting bone resorption, was significantly increased (p<0.05) with a tendency towards decrease of BMD (N.S.), and body weight and abdominal fat weight were decreased in approximately 7% (p<0.05) and 58% (p<0.001), as compared with age matched Con rats. In the Acid group, 24-hour urinary calcium (Ca) and phosphorus (P) excretion were increased approximately 2.1-fold (p<0.05) and 2.0-fold (p<0.01), respectively, with increase of kidney weight as much as in the Con groups. Serum Ca and P concentration, as well as urinary Dpd excretion were, however, not significantly changed. These results suggest that blood Ca and P concentrations in the chronic acidosis condition during the 4-weeks might be maintained by hypercalciuria and hyperphosphaturia with kidney disorder, and swimming exercise training leads to decrease in BMD with stimulation of bone resorption and reduction of body fat.

Effects of creatine supplementation on body composition and renal function in rats

BACKGROUND

The aim of the present study was to evaluate the long-term effects of oral creatine supplementation on renal function and body composition (fat and lean mass) in an experimental model.

METHODS

Male Wistar rats were supplemented with creatine (2 g.kg(-1) of food) for 10 wk in combination with treadmill exercise, 12 m.min(-1), 1 h.d(-1) (CREAT + EX, N = 12) or not (CREAT, N = 10), and compared with exercised animals without creatine supplementation (EX, N = 7) and CONTROL animals, N = 7. Body composition and bone mineral density (BMD) were determined by dual x-ray absorptiometry and glomerular filtration rate (GFR) and renal plasma flow (RPF) were measured by inulin and paraaminohippurate clearance, respectively.

RESULTS

At the end of the study (post), CREAT+EX presented higher lean mass and lower fat mass than CREAT, EX or CONTROL (349.7 +/- 19.7 vs 313.3 +/- 20.3, 311.9 +/- 30.8, 312.4 +/- 21.0 g and 5.7 +/- 2.3 vs 10.0 +/- 3.3, 9.8 +/- 1.5, 10.0 +/- 3.5%, P < 0.05, respectively). Post lean/fat mass ratio was higher than baseline only in CREAT + EX (18.9 +/- 7.2 vs 8.6 +/- 1.8, P < 0.05). Post BMD was significantly higher than baseline in all groups. GFR and RPF were lower in CREAT versus CONTROL (0.5 +/- 0.1 vs 1.0 +/- 0.1 and 1.5 +/- 0.2 vs 2.4 +/- 0.5 mL.min(-1), P < 0.05, respectively).

CONCLUSION

Creatine supplement in combination with exercise increased the proportion of lean mass more than EX or CREAT alone. The use of creatine alone induced an important and significant reduction of both RPF and GFR.

Experimental evolution and phenotypic plasticity of hindlimb bones in high-activity house mice

Studies of rodents have shown that both forced and voluntary chronic exercise cause increased hindlimb bone diameter, mass, and strength. Among species of mammals, "cursoriality" is generally associated with longer limbs as well as relative lengthening of distal limb segments, resulting in an increased metatarsal/femur (MT/F) ratio. Indeed, we show that phylogenetic analyses of previously published data indicate a positive correlation between body mass-corrected home range area and both hindlimb length and MT/F in a sample of 19 species of Carnivora, although only the former is statistically significant in a multiple regression. Therefore, we used an experimental evolution approach to test for possible adaptive changes (in response to selective breeding and/or chronic exercise) in hindlimb bones of four replicate lines of house mice bred for high voluntary wheel running (S lines) for 21 generations and in four nonselected control (C) lines. We examined femur, tibiafibula, and longest metatarsal of males housed either with or without wheel access for 2 months beginning at 25-28 days of age. As expected from previous studies, mice from S lines ran more than C (primarily because the former ran faster) and were smaller in body size (both mass and length). Wheel access reduced body mass (but not length) of both S and C mice. Analysis of covariance (ANCOVA) revealed that body mass was a statistically significant predictor of all bone measures except MT/F ratio; therefore, all results reported are from ANCOVAs. Bone lengths were not significantly affected by either linetype (S vs. C) or wheel access. However, with body mass as a covariate, S mice had significantly thicker femora and tibiafibulae, and wheel access also significantly increased diameters. Mice from S lines also had heavier feet than C, and wheel access increased both foot and tibiafibula mass. Thus, the directions of evolutionary and phenotypic adaptation are generally consistent. Additionally, S-line individuals with the mini-muscle phenotype (homozygous for a Mendelian recessive allele that halves hindlimb muscle mass [Garland et al., 2002, Evolution 56:1,267-1,275]) exhibited significantly longer and thinner femora and tibiafibulae, with no difference in bone masses. Two results were considered surprising. First, no differences were found in the MT/F ratio (the classic indicator of cursoriality). Second, we did not find a significant interaction between linetype and wheel access for any trait, despite the higher running rate of S mice.

Effect of treadmill exercise on bone mass in female rats

Increasing peak bone mass at skeletal maturity, minimizing bone loss during middle age and after menopause, and increasing bone mass and preventing falls in advanced age are important measures for preventing osteoporotic fractures in women. Exercise has generally been considered to have a positive influence on bone health. This paper reviews the effects of treadmill exercise on bone in young, adult, ovariectomized, and osteopenic female rats. Treadmill exercise increases cortical and cancellous bone mass of the tibia as a result of increased bone formation and decreased bone resorption in young and adult rats. The increase in lumbar bone mass seems to be more significant when long-term exercise is applied. Treadmill exercise prevents cancellous bone loss at the tibia as a result of suppressed bone resorption in ovariectomized rats, and increases bone mass of the tibia and mechanical strength of the femur, as a result of suppressed bone resorption and increased bone formation in osteopenic rats after ovariectomy. Treadmill exercise transiently decreases the serum calcium level as a result of accumulation of calcium in bone, resulting in an increase in serum 1,25-dihydroxyvitamin D(3) level and a decrease in serum parathyroid hormone level. We conclude that treadmill exercise may be useful to increase bone mass in young and adult rats, prevent bone loss in ovariectomized rats, and increase bone mass and bone strength in osteopenic rats, especially in the long bones at weight-bearing sites. Treadmill exercise may have a positive effect on the skeleton in young, and adult, ovariectomized, and osteopenic female rats.

How many days per week should rats undergo running exercise to increase BMD?

The aim of the present study was to examine the effect of different frequencies of running exercise on increasing bone mineral density (BMD) and improving bone histomorphology at various sites of the skeleton (tibia, femur, and second lumbar vertebra) in young rats. Twenty-five female Wistar rats, 8 weeks old, were divided into five groups, of 5 animals each according to running load: control group, no running (A group); running load (RL), 4 days per week (d/w; B group); RL, 5 d/w (C group); RL, 6 d/w (D group); and RL, 7 d/w (E group). Rats ran on a treadmill at a speed of 15 m/min for 30 min per day over an 8-week period. The results indicated that the BMD of the tibia in the B, C, D, and E groups and that of the femur in the B and E groups increased significantly over that of the A group. However, the cortical BMD and trabecular BMD of the second lumbar vertebra did not change. In regard to bone histomorphometry of the tibia, a parameter of bone resorption (eroded surface/bone surface) was significantly lower in the B and D groups than in the A group. There were no differences in the parameters of bone formation. Tartaric acid-resistant acid phosphatase (TRACP) values were significantly lower in the B and C groups than in the A group. There were significant increases in body weight in the B group and in muscle weight in the C group. From the data obtained in this study, it was concluded that increases in BMD were obtained by a moderate running load at frequencies of 4 and 5 days per week.

Evaluation of serum concentrations of biochemical markers of bone metabolism and insulin-like growth factor I associated with treadmill exercise in young horses

OBJECTIVE

To evaluate changes in serum concentrations of biochemical markers of bone metabolism and insulin-like growth factor I (IGF-I) associated with treadmill exercise in young horses.

ANIMALS

12 two-year-old Thoroughbred mares.

PROCEDURE

During a 20-week study period, 6 horses were exercised on a treadmill 3 times a week (exercise group) and 6 horses received walking exercise 6 days a week (controls). Serum concentrations or activity of biochemical markers and IGF-I were assessed biweekly. Bone mineral density and content of the first phalanx were measured by dual-energy X-ray absorbiometry (DEXA) on completion of the study.

RESULTS

Compared with values in controls, bone mineral density and content were higher and serum concentrations of osteocalcin (a marker of bone formation) and the carboxy-terminal telopeptide of type I collagen (a marker of bone resorption; ICTP) were lower in exercised horses. Serum concentration and activity of the bone formation markers carboxy-terminal propeptide of type I collagen and bone-specific alkaline phosphatase (BAP) were not different between the 2 groups. Serum IGF-I concentration was lower in the exercise group, compared with control values; there was a significant correlation between change in IGF-I values and changes in osteocalcin, ICTP, and BAP values at the end of the study.

CONCLUSIONS AND CLINICAL RELEVANCE

Treadmill exercise over 20 weeks induced adaptive changes in bones of 2-year-old Thoroughbreds; training appears to increase bone mineral density, thereby enhancing mechanical strength of bone, but decreases bone turnover. Results indicated an association between changes in serum IGF-I concentration and bone cell activity in horses.

High-impact exercise strengthens bone in osteopenic ovariectomized rats with the same outcome as Sham rats

The effect of jump exercise on middle-aged osteopenic rats was investigated. Forty-two 9-mo-old female rats were either sham-operated (Sham) or ovariectomized (OVX). Three months after surgery, the rats were divided into the following groups: Sham sedentary, Sham exercised, OVX sedentary, and OVX exercised. Rats in the exercise groups jumped 10 times/day, 5 days/wk, for 8 wk, with a jumping height of 40 cm. Less than 1 min was required for the jump training. After the experiment, the right tibia and femur were dissected, and blood was obtained from each rat. OVX rats were observed to have increased body weights and decreased bone mass in their tibiae and femurs. Jump-exercised rats, on the other hand, had significantly increased tibial bone mass, strength, and cortical areas. The bone mass and strength of OVX exercised rats increased to approximately the same extent as Sham exercised rats, despite estrogen deficiency or osteopenia. Our data suggest that jump exercise has beneficial effects on lower limb bone mass, strength, bone mineral density, and morphometry in middle-aged osteopenic rats, as well as in Sham rats.

Combined intervention of exercise and genistein prevented androgen deficiency-induced bone loss in mice

There is evidence that estrogen plays an important role in skeletal tissue in males as well as females. We have reported that phytoestrogens, such as genistein, selectively act on bone and exhibit cooperative effects on bone mass when combined with exercise in ovariectomized mice. In this study, we examined whether both interventions exhibit cooperative effects on bone loss in androgen-deficient mice similar to those in estrogen-deficient mice. Male mice aged 7 wk were either sham operated or orchidectomized (ORX) and divided into six groups: 1) sham; 2) ORX; 3) ORX and treated with genistein (0.4 mg/day) subcutaneously; 4) ORX, exercised on a treadmill daily for 30 min/day at 12 m/min; 5) ORX, given genistein, and exercised (ORX+ExG); and 6) ORX and treated with 17beta-estradiol (E(2)). Four weeks after the intervention, seminal vesicle weight strikingly decreased in ORX mice, and it was not affected by administration of genistein or E(2). Bone mineral density of whole femur was significantly reduced by ORX, and bone loss was prevented by the combined intervention. Histomorphometric analysis showed that bone volume and trabecular thickness in the distal femoral cancellous bone were significantly lower in the ORX group than in the Sham group, and they were completely restored in the ORX+ExG group, as in the ORX with E(2) group. These results indicate that the combined intervention of moderate exercise and a low dose of genistein administration shows an additive effect in preventing bone loss in ORX mice similar to that in ovariectomized mice.

Tower climbing exercise started 3 months after ovariectomy recovers bone strength of the femur and lumbar vertebrae in aged osteopenic rats

To determine both the preventive and recovery effects of tower climbing exercise on mass, strength, and local turnover of bone in ovariectomized (OVX) rats, we carried out two experiments. In experiment I, 60 Sprague-Dawley rats, 12 months of age, were assigned to four groups: a Baseline Control, Sham-Operated Sedentary, OVX-Sedentary and OVX-Exercise rats. Rats voluntarily climbed a 200-cm tower to drink water from a bottle set at the top. At 3 months, OVX elevated both the femoral cortex and lumbar trabecular turnover, leading to a reduction in bone mass and strength. However, in OVX-Exercise rats, those values were maintained at the same level as in the Sham-Sedentary rats. Thus, the climbing exercise, started after 3 days of OVX, prevented OVX-induced cortical and trabecular bone loss by depressing turnover elevation. After confirming the preventive effect, we evaluated the recovery effect of exercise. In experiment II, 90 Sprague-Dawley rats, 12 months of age, were assigned to six groups: a Baseline control, two groups of Sham-Operated Sedentary and OVX-Sedentary, and OVX-Exercise rats. The exercise started 3 months after the OVX operation. At 3 months, OVX increased the trabecular bone formation rate and osteoclast surface, leading to a decrease in compressive strength. In the midfemur, the cross-sectional area, moment of inertia, and bending load values decreased. At 6 months, in the OVX-Exercise rats, the parameters of breaking load in both the lumbar and midfemur, lumbar bone mass, and the total cross-sectional area recovered to the same levels as those in the Sham-Sedentary rats. However, the cortical bone area did not recover. Periosteal bone formation increased, while endosteal bone formation decreased. These results showed that the climbing exercise had both a preventive and recovery effect on bone strength in OVX rats. In the mid-femur, effects on bone formation were site-specific, and the cross-sectional morphology was improved without an increase in cortical bone area, supporting cortical drift by mechanical stimulation.

Preventive effects of running exercise on bones in heavy ion particle irradiated rats

We examined the effects of running exercise on preventing decreases in bone mineral and tissue volume after heavy ion particle irradiation in rats. Male Wistar rats experienced whole-body irradiation by heavy ion particle beam (C-290 MeV) at doses of 0.5, 1.0, and 5.0 Gy and were divided into voluntary running groups and control groups. Rats in the running groups ran on the treadmill 15 m/min, 90 min/day for 35 days after exposure. At the end of the experiment, a tibia was obtained from each rat for measurement of bone mineral density (BMD) and cross-sectional area, strength strain index, and bone histomorphometric analysis. The weights of muscles and concentration of serum calcium were measured. Total BMD and trabecular BMD in the metaphysis and cortical BMD of the diaphysis of tibia in the running groups increased. Bone volume and trabecular thickness increased while trabecular separation decreased in the running groups compared to those in the control groups at respective doses. However, the osteoid surface and eroded surface varied in the running groups compared to those of the respective corresponding groups. The dynamic parameters such as mineralizing surface, mineral apposition rate, and bone formation rate in the running groups were varied, probably due to the differences in radiation-induced sensitivities of bones following radiation exposure. The overall results suggest that running exercise might have a beneficial effect on preventing bone mineral loss and changes in bone structure induced by space radiation, but it is necessary to examine the optimal conditions of running exercise response to doses.

Short- and long-term effects of calcium and exercise on bone mineral density in ovariectomized rats

At the level of prevention of bone mineral loss produced by ovariectomy, the aim of the present study was to determine the effect produced by supplementation of Ca in the diet and a moderate exercise programme (treadmill), simultaneously or separately, in ovariectomized rats, an experimental model of postmenopausal bone loss. Female Wistar rats (n 110, 15 weeks old) were divided into five groups: (1) OVX, rats ovariectomized at 15 weeks of age, fed a standard diet; (2) SHAM, rats sham operated at 15 weeks of age, fed a standard diet; (3) OVX-EX, ovariectomized rats, fed a standard diet and performing the established exercise programme; (4) OVX-Ca, ovariectomized rats fed a diet supplemented with Ca; (5) OVX-EXCa, ovariectomized rats with the exercise programme and diet supplemented with Ca. The different treatments were initiated 1 week after ovariectomy and were continued for 13 weeks for subgroup 1 and 28 weeks for subgroup 2, to look at the interaction of age and time passed from ovariectomy on the treatments. Bone mineral density (BMD) was determined, at the end of the study, in the lumbar spine (L2, L3 and L4) and in the left femur using a densitometer. Bone turnover was also estimated at the end of the study, measuring the serum formation marker total alkaline phosphatase (AP) and the resorption marker serum tartrate-resistant acid phosphatase (TRAP). As expected, OVX rats showed a significant decrease (P<0.05) in BMD, more pronounced in subgroup 2, and a significant increase in AP and TRAP with regard to their respective SHAM group. The simultaneous treatment with Ca and exercise produced the best effects on lumbar and femoral BMD of ovariectomized rats, partially avoiding bone loss produced by ovariectomy, although it was not able to fully maintain BMD levels of intact animals. This combined treatment produced a significant increase in AP, both in subgroups 1 and 2, and a decrease in TRAP in subgroup 1, with regard to OVX group. The exercise treatment alone was able to produce an increase in BMD with regard to OVX group only in subgroup 1 of rats (younger animals and less time from ovariectomy), but not in subgroup 2. In agreement with this, there was an increase of AP in both subgroups, lower than that observed in animals submitted to exercise plus Ca supplement, and a decrease of TRAP in subgroup 1, without significant changes in this marker in the older rats. Ca treatment did not produce any significant effect on BMD in OVX rats in both subgroups of animals, showing a decrease of AP and TRAP levels in the younger animals with no significant variations in markers of bone remodelling in the older female rats compared with their respective OVX group.

Cooperative effects of exercise training and genistein administration on bone mass in ovariectomized mice

We reported that genistein, a soybean isoflavone, prevents bone loss caused by estrogen deficiency, without undesirable effects on the uterus. In this study, we examined cooperative effects of genistein administration and running exercise on bone mass in ovariectomized (OVX) mice. Female mice aged 7 weeks were either sham-operated or OVX and divided into six groups: (1) sham; (2) OVX; (3) OVX, treated with genistein at a submaximal dose (0.4 mg/day) subcutaneously (G); (4) OVX, exercised on a treadmill daily for 30 minutes/day at 12 m/minute on a 10 degree uphill slope (Ex); (5) OVX, given genistein and exercised (ExG); and (6) OVX, treated with 17beta-estradiol (0.03 microg/day) in the same manner as genistein (E2). Four weeks after intervention, bone mass was estimated by dual-energy X-ray absorptiometry (DXA) and peripheral quantitative computed tomography (pQCT). Bone mineral density (BMD) of the whole femur measured by DXA was higher in both the G and the Ex groups than in the OVX group. Furthermore, BMD in the ExG group was significantly higher than that in the groups receiving either intervention alone. Bone area in distal region of the femur was significantly higher in Ex and ExG groups as compared with those in the OVX and G groups. pQCT analysis showed that the cross-sectional areas (CSAs) and periosteum perimeter at midshaft of the femur did not differ in the sham and OVX groups but were significantly higher in Ex and ExG groups. Histomorphometric analysis showed that bone formation rate/bone surface (BFR/BS) was significantly higher in both Ex and ExG groups as compared with that in non-exercised groups. The bone volume (BV/TV) in the distal femoral cancellous bone was lower in the OVX than that in the sham group, and it was restored completely in the ExG group, as in the E2 group. Thickness of the trabecular bone (Tb.Th) was higher in Ex and ExG groups than that in the OVX and G groups. These results indicate that the combined intervention of moderate exercise and the submaximal dose of genistein administration show a cooperative effect in preventing bone loss in OVX mice.

Effect of high-impact and low-repetition training on bones in ovariectomized rats

This study was designed to investigate the effect of high-impact and low-repetition jump training on bones in ovariectomized (OVX) rats. Forty female Wistar rats were sham-operated (sham) or OVX at the age of 11 weeks. The rats were divided randomly into the following four groups: sham-sedentary (SS; n = 10), sham-exercised (SE; n = 10), OVX-sedentary (OS; n = 10), and OVX-exercised (OE; n = 10). The rats started the jump training at the age of 12 weeks. The jump-training protocol was 10 times/day, 5 days/week and the jumping-height was 40 cm. After 8 weeks of training, the mass and breaking force in the tibia and ulna, cross-sectional areas of diaphysis in the tibia, and serum bone turnover markers were measured. The jump training significantly increased the fat-free dry weight, ash weight, and ultimate breaking force in the tibia. The rate of increase in these parameters was similar in both the sham and the OVX groups. On the other hand, in the ulna, there were no significant changes in the ultimate breaking force. The jump training significantly increased the periosteal perimeter and cortical area, although the increase in these parameters in OE compared with OS was lower than that in SE compared with SS. The jump training significantly increased serum osteocalcin in the OVX groups, as well as in the sham groups. These results suggest that high-impact and low-repetition training had beneficial effects on bone formation and bone biomechanical properties in OVX rats, as well as in sham rats.

Prolonged swimming exercise training induce hypophosphatemic osteopenia in stroke-prone spontaneously hypertensive rats (SHRSP)

Stroke-prone spontaneously hypertensive rats (SHRSP) induce spontaneous osteoporosis. To elucidate the specific characteristics of bone metabolism, the SHRSP was compared with age matched Wistar-Kyoto (WKY) rats. We investigated the effects of prolonged swimming exercise training on bone mineral density (BMD) and metabolism in the SHRSP. Seven-week-old male SHRSP and WKY were divided into three groups; the sedentary control WKY group (n = 6, WKY), the sedentary control SHRSP group (n = 6, SP) and the swimming exercise training SHRSP group (n = 6, SWIM) (in pool with 60 min./day, 5 days/week for 12 weeks). The femoral BMD, bone mineral content (BMC), strength, Ca and P contents (%) of SHRSP were approximately 17, 27, 25, 20 and 9%, respectively, lower than that of WKY (p < 0.001). Serum alkaline phosphatase (AlP) had not changed between both of SP and WKY, but tartrate-resistant acid phosphatase (TrAcP) of SP approximately 3-fold higher than that of WKY (p < 0.05). Both serum calcium (Ca) and intact parathyroid hormone (i-PTH) were similar between SP and WKY. However, serum phosphate (P) of SP was approximately 18% lower than that of WKY (N.S.). These results suggested that SHRSP induces osteopenia by the bone turnover of the promoted osteoclast activity with disturbed phosphate homeostasis. On the other hand, the femoral BMD and strength were approximately 7% and 20%, respectively, decreased in the SWIM (p < 0.001), and femoral bone Ca and P contents (%) were also approximately 11% and 14%, respectively, lower than that of SP (p < 0.001). There were no significant difference between SWIM and SP on serum Ca, but serum P of SWIM was significantly lower than that of SP (p < 0.05). These results suggested that the prolonged swimming exercise training in the SHRSP induces more cruelly hypophosphatemia, and leading to osteopenia eventually. We conclude that SHRSP induces osteopenia with disturbance of phosphate homeostasis, and the prolonged swimming exercise in the SHRSP might deteriorate hypophosphatemia and osteopenia.

Effect of deconditioning on cortical and cancellous bone growth in the exercise trained young rats

Exercise enhances bone growth and increases peak bone mass. The aim of this study was to determine whether or not 4 weeks of deconditioning after 8 weeks of exercise in growing rats would result in a decrease in bone gain or reverse the benefits of exercise. Fifty 4-week-old female Sprague-Dawley rats were randomized by a stratified weight method into 5 groups with 10 rats in each group: 8 weeks exercise (8EX), 8 weeks sedentary control (8S), 12 weeks exercise (12EX), 8 weeks exercise followed by 4 weeks sedentary (8EX4S), and 12 weeks sedentary control (12S). The exercise consisted of running on a treadmill with a 5 degrees slope at 24 m/minute for 1 h/day and 5 days/week. After each period of exercise, cancellous and cortical bone histomorphometry were performed on double fluorescent labeled 5-microm-thick sections of the proximal tibia and 40-microm-thick sections of the tibial shaft, respectively. Eight and 12 weeks of exercise resulted in a significant increase in the body weight and gastrocnemius muscle weight by two-way analysis of variance (ANOVA). The femoral wet weight (mg; mean +/- SD; 8EX, 781 +/- 45.1 vs. 8S, 713 +/- 40.5; p < 0.05; 12EX, 892 +/- 41.6 vs. 12S, 807 +/- 19.8; p < 0.05) was significantly higher in the exercise group than that in the respective control groups. The femoral wet weight and bone volume (BV) of the 8EX4S group (818 +/- 46.2 mg and 531 +/- 31.2 microl, respectively) were significantly lower than those of the 12EX group (p < 0.05) and did not differ significantly from those of the 12S groups. The cancellous BV was significantly higher in the 8EX and 12EX groups than that in the respective sedentary groups (p < 0.05). The cortical bone area of the tibial shaft was also significantly higher in the 12EX than that in the 12S group (p < 0.05). The increase in the cancellous BV or cortical bone area was caused by an increase in the mineral apposition rate (MAR), without a significant effect in the labeled perimeter. The bone formation rate (BFR; microm3/microm2 per day) in the cancellous bone (12EX, 27.9 +/- 7.74 vs. 12S, 15.4 +/- 4.56; p < 0.05) or periosteal surface (12EX, 127.6 +/- 27.7 vs. 12S, 79.5 +/- 18.6; p < 0.05) was significantly higher in the exercised groups than that in the respective control group (p < 0.05). Again, deconditioning resulted in a decrease in the cancellous BFR, BV, periosteal BFR, and cortical bone area to levels not significantly different from the 12S group. In conclusion, our findings showed that exercised growing rats, when deconditioned, lost the benefits gained through exercise and their bone parameters were reduced to levels not different from the sedentary control. Thus, continued exercise is required to maintain high bone mass.

Does the mechanical milieu associated with high-speed running lead to adaptive changes in diaphyseal growing bone?

Exercise during growth can be important for attaining optimal bone mass. High-intensity long-duration protocols, however, can have detrimental effects on immature bone morphology and mechanics. The underlying mechanisms are poorly understood. Here, we quantified the mechanical environment of the middiaphyseal rooster tarsometatarsus during high-speed running and examined whether short bouts of this exercise-related mechanical milieu can induce positive changes in cortical bone morphology, mechanics, and mineral ash content. At 9 weeks of age, roosters were assigned to controls (n = 9) and runners (n = 8). Treadmill running was applied in loading sessions of 5 min, three times per day (approximately 2600 cycles/day) for 8 weeks. Both controls and runners received double-fluorochrome labels during weeks 3 and 8 of the protocol. Middiaphyseal distributions of tarsometatarsal longitudinal normal strain, strain rate, and strain gradients engendered by walking and running were determined via in vivo strain gauges. Compared with walking, running elevated mean peak strain magnitude by 19%, peak strain rates by 136%, and peak strain gradients by approximately 18%. After 8 weeks of running, middiaphyseal areal and mechanical properties and normalized ash weight were no different between runners and controls. Transient and focal reductions in periosteal mineral apposition rates occurred during the exercise protocol. Our current data suggest that reducing the number of loading cycles can mitigate the adverse response previously observed in this model with long-duration running. This study also supports the tenet that the exercise-generated mechanical milieu must differ substantially from the habitual milieu to induce significant adaptations.

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.