The effects of repetitive physiologic loading on bone turnover and mechanical properties in adult female and male rats

Perspectives from research and practice: A survey on external load monitoring and bone in sport

Introduction

There is limited information regarding the association between external load and estimated bone load in sport, which may be important due to the influence exercise can have on bone accrual and injury risk. The aim of this study was to identify external load measuring tools used by support staff to estimate bone load and assess if these methodologies were supported in research.

Methods

A survey was comprised of 19 multiple choice questions and the option to elaborate on if/how they monitor external load and if/how they used them to estimate bone load. A narrative review was performed to assess how external load is associated to bone in research.

Results

Participants were required to be working as support staff in applied sport. Support staff (n = 71) were recruited worldwide with the majority (85%) working with professional elite athletes. 92% of support staff monitored external load in their organisation, but only 28% used it to estimate bone load.

Discussion

GPS is the most commonly used method to estimate bone load, but there is a lack of research assessing GPS metrics with bone load. Accelerometry and force plates were among the most prevalent methods used to assess external load, but a lack of bone specific measurements were reported by support staff. Further research exploring how external load relates to bone is needed as there is no consensus on which method of external load is best to estimate bone load in an applied setting.

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.

Protocol of a randomised controlled trial assessing the impact of physical activity on bone health in children with inflammatory bowel disease

INTRODUCTION

Low bone mineral density (BMD) is a frequent issue in children and adolescents with inflammatory bowel disease (IBD). Several studies in healthy populations have reported a positive impact of physical activity (PA) on bone health. Recently, an observational study in paediatric patients with IBD showed a significant positive relationship between daily PA and BMD. However, intervention studies investigating a causal relationship between PA and BMD are warranted to confirm these results. The aim of this randomised controlled trial will be to investigate the effect of a PA programme on BMD in paediatric patients with IBD.

METHODS AND ANALYSIS

This trial is a multicentre (four centres), randomised, controlled, blinded end-point study. Eighty children with IBD will be randomly assigned in a 1:1 ratio to receive a programme with adapted physical exercises (intervention group) or usual PA (control group) during a 9-month period. The primary outcome is the change from baseline at 9 months (the end of the study) in whole-body BMD assessed by dual-energy X-ray absorptiometry. Secondary efficacy outcomes include the changes from baseline at 9 months in: BMD assessed in the lumbar spine and trochanter; daily PA (time spent in moderate-to-vigorous PA); body composition (fat mass and fat-free mass); fatigue resistance; quality of life and activity of IBD.

ETHICS AND DISSEMINATION

The study was approved by the Research Ethics Committee in France (Comité de Protection des Personnes, Sud-Ouest and Outre-Mer III, Bordeaux, France, No 2018/27). All procedures will be performed according to the ethical standards of the Helsinki Declaration of 1975, as revised in 2008, and the European Union's Guidelines for Good Clinical Practice. Written informed consent will be obtained from the parents or legal guardian and from the children. Research findings will be disseminated in peer-reviewed journals and scientific meetings.

TRIAL REGISTRATION NUMBER

NCT03774329.

Physical activity is associated with improved bone health in children with inflammatory bowel disease

BACKGROUND & AIMS

Bone health is an important concern in patients with inflammatory bowel disease (IBD). Low bone mineral density (BMD) is a powerful predictor of fracture risk in IBD patients. Physical activity (PA) plays an important role in bone health. However, PA data for children and adolescents with IBD are scarce. The primary aim is to evaluate the relationship between PA and BMD in children with IBD. The secondary aim was to assess the relationship between PA and quality of life.

METHODS

Eighty-four IBD paediatric patients (45 boys) aged 14.3 ± 2.7 years were included (disease activity: (i) remission, n = 62; (ii) mild, n = 18; (iii) severe disease, n = 1). BMD was measured using dual-energy X-ray absorptiometry and expressed as age- and sex-based Z-scores. Each patient wore a triaxial accelerometer for seven consecutive days for objective PA quantification. Quality of life was assessed using the PedsQL™ and energy intake was assessed prospectively for three days using a dietary diary.

RESULTS

BMD Z-score was -0.96 ± 1.11. Only five patients (6%) fulfilled the recommendation of 60 min of daily moderate-to-vigorous PA (MVPA). The proportion of children with osteopenia and osteoporosis was 51% and 4%, respectively. After adjustment for confounders (pubertal status and body mass index), total PA and time in MVPA were positively associated with BMD (regression coefficient per one standard deviation increase in PA parameters = 0.26; P < 0.05). There was no association between time spent in MVPA and total PA, and total quality of life score.

CONCLUSIONS

PA likely is associated with improved bone health in IBD children. Intervention studies investigating a causal relationship between PA and BMD in paediatric patients with IBD are warranted.

Resveratrol Is Not as Effective as Physical Exercise for Improving Reproductive and Metabolic Functions in Rats with Dihydrotestosterone-Induced Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a reproductive and metabolic disorder associated with obesity and insulin resistance that often precedes the development of type-2 diabetes. Rats continuously exposed to dihydrotestosterone from prepuberty display typical reproductive and metabolic PCOS characteristics including anovulation, polycystic ovaries, insulin resistance, and obesity. Our aim was to investigate if resveratrol improves reproductive and metabolic functions in PCOS rats. The effect was compared to exercise. Control and PCOS rats were treated with vehicle or resveratrol (400 mg · kg−1 · day−1) for 5-6 weeks. Another group of PCOS rats received vehicle treatment and exercised for 5-6 weeks. Insulin sensitivity was determined by euglycemic-hyperinsulinemic clamp. The glucose infusion rate was lower in the PCOS-vehicle group compared to control-vehicle rats (P<0.05). Exercise increased insulin sensitivity compared with PCOS-vehicle rats (P<0.05), but resveratrol did not. Resveratrol treatment and exercise resulted in smaller adipocytes, upregulated estrogen-related receptorαgene expression in subcutaneous fat, and improved estrus cyclicity in the previously acyclic PCOS rats. Although resveratrol had positive effects on adiposity and cyclicity in a similar manner to exercise, resveratrol does not seem to be a good candidate for treating insulin resistance associated with PCOS because no improvement in insulin sensitivity was observed in PCOS rats on normal chow.

Effect of fatigue loading and associated matrix microdamage on bone blood flow and interstitial fluid flow

Functional adaptation of bone to cyclic fatigue involves a complex physiological response that is targeted to sites of microdamage. The mechanisms that regulate this process are not understood, although lacunocanalicular interstitial fluid flow is likely important. We investigated the effect of a single period of cyclic fatigue on bone blood flow and interstitial fluid flow. The ulnae of 69 rats were subjected to cyclic fatigue unilaterally using an initial peak strain of -6000 muepsilon until 40% loss of stiffness developed. Groups of rats (n=23 per group) were euthanized immediately after loading, at 5 days, and at 14 days. The contralateral ulna served as a treatment control, and a baseline control group (n=23) that was not loaded was also included. After euthanasia, localization of intravascular gold microspheres within the ulna (n=7 rats/group) and tissue distribution of procion red tracer were quantified (n=8 rats/group). Microcracking, modeling, and remodeling (Cr.S.Dn, microm/mm(2), Ne.Wo.B.T.Ar, mm(2), and Rs.N/T.Ar, #/mm(2) respectively) were also quantified histologically (n=8 rats/group). Cyclic fatigue loading induced hyperemia of the loaded ulna, which peaked at 5 days after loading. There was an associated overall decrease in procion tracer uptake in both the loaded and contralateral control ulnae. Tracer uptake was also decreased in the periosteal region, when compared with the endosteal region of the cortex. Pooling of tracer was seen in microdamaged bone typically adjacent to an intracortical stress fracture at all time points after fatigue loading; in adjacent bone tracer uptake was decreased. New bone formation was similar at 5 days and at 14 days, whereas formation of resorption spaces was increased at 14 days. These data suggest that a short period of cyclic fatigue induces bone hyperemia and associated decreased lacunocanalicular interstitial fluid flow, which persists over the time period in which osteoclasts are recruited to sites of microdamage for targeted remodeling. Matrix damage and development of stress fracture also interfere with normal centrifugal fluid flow through the cortex. Changes in interstitial fluid flow in the contralateral ulna suggest that functional adaptation to unilateral fatigue loading may include a more generalized neurovascular response.

Exercise-induced changes in the cortical bone of growing mice are bone- and gender-specific

Fracture risk and mechanical competence of bone are functions of bone mass and tissue quality, which in turn are dependent on the bone's mechanical environment. Male mice have a greater response to non-weight-bearing exercise than females, resulting in larger, stronger bones compared with control animals. The aim of this study was to test the hypothesis that short-term weight-bearing running during growth (21 days starting at 8 weeks of age; 30 min/day; 12 m/min; 5 degrees incline; 7 days/week) would similarly have a greater impact on cross-sectional geometry and mechanical competence in the femora and tibiae of male mice versus females. Based on the orientation of the legs during running and the proximity of the tibia to the point of impact, this response was hypothesized to be greatest in the tibia. Exercise-related changes relative to controls were assayed by four-point bending tests, while volumetric bone mineral density and cross-sectional geometry were also assessed. The response to running was bone- and gender-specific, with male tibiae demonstrating the greatest effects. In male tibiae, periosteal perimeter, endocortical perimeter, cortical area, medial-lateral width and bending moment of inertia increased versus control mice suggesting that while growth is occurring in these mice between 8 and 11 weeks of age, exercise accelerated this growth resulting in a greater increase in bone tissue over the 3 weeks of the study. Exercise increased tissue-level strain-to-failure and structural post-yield deformation in the male tibiae, but these post-yield benefits came at the expense of decreased yield deformation, structural and tissue-level yield strength and tissue-level ultimate strength. These results suggest that exercise superimposed upon growth accelerated growth-related increases in tibial cross-sectional dimensions. Exercise also influenced the quality of this forming bone, significantly impacting structural and tissue-level mechanical properties.

Dual energy X ray absorptiometry of ex vivo HcB/Dem mouse long bones: left are denser than right

Dual energy X ray absorptiometry (DXA) has become a popular analytical technique in mice and other small animals. Comparative study of bone properties at different anatomical sites is an active area of study in model organisms. Such investigations require that site-specific data be generated and interpreted. There are no published data addressing the degree to which contralateral mouse bones resemble each other in the absence of an experimental intervention, nor are there data addressing the correlation of bone densitometry measurements between anatomically distant sites. To address these gaps in our knowledge, we used DXA to compare excised mouse femora and humeri. At the population level, left bones were slightly but significantly denser than right bones, with an overall adjusted bone mineral density (BMD) difference of 0.7 +/- 0.3 and 0.5 +/- 0.2 mg/cm2 at the femur and humerus, respectively. At the level of bone pairs from a single animal, absolute adjusted BMD disparities between the right and left sides were 2.3 +/- 1.9 mg/cm2 at the femur and 1.7 +/- 1.4 mg/cm2 at the humerus. Correlation coefficients between left and right sides were 0.78 for adjusted BMD at both sites. The correlation coefficient between side-averaged femoral and humeral BMD was 0.81, but ranged between 0.70 and 0.75 when limited to ipsilateral or contralateral femur-humerus pairs. Our findings suggest the desirability of randomizing limbs for treatment in studies using contralateral limb controls. These observations may represent the densitometric manifestation of behavioral and neuroanatomical lateralization in laboratory mice.