[Physical exercise and the skeleton]

Comparative effects of various running exercise modalities on femoral bone quality in rats

BACKGROUND

It is now well established that physical exercise is an effective preventive method to reduce and treat certain chronic diseases, particularly musculoskeletal disorders. At the bone level, running exercise is well known for its positive effects on various parameters of bone quality. There is, however, no consensus regarding the effects of different running exercise modalities on bone quality.

AIM

The objective of this study was to compare the effects of three treadmill running modalities: intermittent, moderate continuous, and a combination of both-on bone quality parameters in rats.

METHODS

Thirty-nine, 5-week-old, male Wistar rats were randomly divided in 4 groups: sedentary control (SED; n = 10), intermittent running exercise (IE; n = 10), continuous running exercise (CE; n = 10) and combined running exercise (COME; n = 9). Rats in running groups were exercised 45 min/day, 5 days/week, for 8 consecutive weeks. Femoral micro-architectural parameters were assessed by micro-CT; femoral osteocyte apoptosis, osteoclast resorption and bone histomorphometry were assessed by histology.

RESULTS

Femoral trabecular thickness in the combined running group was increased (p < 0.0001) compared to respective results in the other running groups (0.13 mm vs 0.11 mm). The cortical thickness, osteocyte lacunae occupancy rate in the whole femur, numbers of apoptotic osteocytes and osteoclastic resorption surfaces were not significantly different between groups. Statistical differences were occasionally noted depending on the femoral anatomical region.

CONCLUSION

These results suggest that the femur should not be considered as the better bone to study the effects of running protocols.

Grip strength is a predictor of bone mineral density among adolescent combat sport athletes

The aim of this study was firstly to investigate the correlation between bone parameters and grip strength (GS) in hands, explosive legs power (ELP), and hormonal parameters; second, to identify the most determinant variables of bone mineral density (BMD) among adolescent combat sport athletes. Fifty combat sport athletes aged 17.1 ± 0.2 year were compared with 30 sedentary subjects matched for age, height, and pubertal stage. For all subjects, the BMD in deferent sites associated with anthropometric parameters were measured by dual-energy X-ray absorptiometry. The growth hormone (GH) and testosterone (TESTO) concentrations were tested. The GS in dominant (GSDA) and nondominant arms (GSNDA) and ELP were evaluated. All BMD measured were greater in athletes than in sedentary group (p<0.01). The GS and ELP showed higher values in athletes than in sedentary group (p<0.01). The BMD in all sites were correlated with weight, but without correlation with height. The GSNDA and ELP were significantly correlated with BMD of both spine and legs. The GH was correlated with the BMD of whole body and spine (p<0.05). The TESTO was only correlated with BMD of the arms (p<0.01). The best predictor of BMD measurements is GSNDA. This study has proved the osteogenic effect of combat sports practice, especially judo and karate kyokushinkai. Therefore, children and adolescent should be encouraged to participate in combat sport. Moreover, it suggested that the best model predicting BMD in different sites among adolescent combat sports athletes was the GSNDA.

Distance of walking in childhood and femoral bone density in perimenopausal women

Kuopio osteoporosis risk factor and prevention (OSTPRE) study is a population-based study from Eastern Finland. At baseline in 1989-91, bone densitometry of lumbar spine and femoral neck as assessed by DXA was carried out on women aged 48-58 (n = 3,222). In 1993, menarcheal age and health habits during adolescence were inquired from a postal inquiry. In 1996, a random sample of 254 women who had been premenopausal at baseline was interviewed over phone. They were asked how many kilometers per day they had walked to school and back, in each grade of primary school. The study sample (N = 185) was formed by excluding women with menarcheal age of >14 or <11 years. Women with any reported HRT history were also excluded. The mean age of the study sample was 50.7 (1.63) years, weight 70.8 (13.1) kg, height 161.5 (5.0) cm, and mean walking distance to and fro from the school at ages from 9 to 11 years was 2.7 (1.7) km. In regression analysis, the walking distance was associated with femoral BMD (r = 0.18, P = 0.015). After adjusting for baseline age, weight and height, this association persisted (P = 0.025). When walking distance was categorized as I = 0-0.549 km, II = 0.55-1.99 km, III = 2.0-4.99 and IV = 5.0 km and more, the respective means for femoral BMDs were 0.92, 0.97, 0.98 and 1.01 g/cm(2). Statistical significance persisted after adjusting for height, weight, age, grip strength, calcium intake, smoking, place of residence, use of contraceptive pills, physical load of work and baseline physical activity (P = 0.032). A 10 year follow-up revealed no changes in bone loss rate between the groups and femoral BMD benefits persisted (repeated measures analysis = NS). Walking distance was not associated with spinal bone density. Even though walking is a low impact activity, walking before menarche may have a moderate but long-lasting positive effect on femoral peak bone density. Lack of walking and similar low impact physical activities during peak growth years may have a negative effect on peak bone mass formation.

Bone anabolic responses to mechanical load in vitro involve COX-2 and constitutive NOS

Mechanical stimulation is essential for maintaining the homeostasis and architecture of connective tissues including bone. The purpose of our study was to test the importance of several potential signaling intermediates in the anabolic responses of bone to loads applied with a newly developed micromechanical loading device. Tibial bones excised from 7- to 8-day-old CD-1 mice were cyclically loaded at 1 Hz, 1000 muepsilon (microstrain) at a peak load of 100 mN. DNA and protein synthesis were evaluated by measuring the incorporation of 3H-thymidine and 14C-proline, respectively. The roles of cyclooxygenase (COX) isoforms, nitric oxide synthase (NOS) isoforms, and glutamate receptor-gated Ca2+ channeling were examined by incubating the bones in the presence of each of their specific inhibitors. The results indicate that COX-2 and constitutive NOS are important signaling molecules in the anabolic responses of neonatal tibial bone to the micromechanical load in vitro.

Influence of clenbuterol on bone metabolism in exercised or sedentary rats

This paper reports that the selective beta(2)-adrenergic receptor agonist clenbuterol affects bone metabolism in growing 3-mo-old male Wistar rats treated over 8 wk. Thirty-two 3-mo-old growing Wistar rats weighing 234 +/- 2 g were assigned to a progressive isometric force, strength-training exercise program plus oral clenbuterol (2 mg x kg body wt(-1) x day(-1)) for 5 days each week, exercise program without clenbuterol 5 days each week, no exercise program plus oral clenbuterol (2 mg x kg(-1) x day(-1)) for 5 days each week, or no exercise without clenbuterol 5 days each week. At the end of 8 wk, lean mass, fat mass, and right total femoral, distal metaphyseal femoral, and diaphyseal femoral bone mineral density were measured by Hologic QDR 4,500 dual X-ray absorptiometry (DEXA) technique. Left femoral bones were harvested after death on day 58, and femoral resistance was determined by three-point bending testing. We found that fat mass was decreased in rats given strength training exercise and decreased further in rats treated with clenbuterol. Lean mass was increased in clenbuterol-treated animals. Strength-training exercise appeared to have no effect on bone mineral density, serum osteocalcin, or urinary deoxypyridinoline. However, clenbuterol treatment decreased femoral length, diameter, bone mineral density, and mechanical resistance. Clenbuterol had no effect on osteocalcin but increased urinary deoxypyridinoline. We concluded that clenbuterol treatment decreased bone mineral density and increased bone resorption independent of the level of exercise rats were given.