Quick benefits of interval training versus continuous training on bone: a dual-energy X-ray absorptiometry comparative study

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.

Low-intensity pulsed ultrasound enhances the positive effects of high-intensity treadmill exercise on bone in rats

INTRODUCTION

Moderate exercise benefits bone health, but excessive loading leads to bone fatigue and a decline in mechanical properties. Low-intensity pulsed ultrasound (LIPUS) can stimulate bone formation. The purpose of this study was to explore whether LIPUS could augment the skeletal benefits of high-intensity exercise.

MATERIALS AND METHODS

MC3T3-E1 osteoblasts were treated with LIPUS at 80 mW/cm2 or 30 mW/cm2 for 20 min/day. Forty rats were divided into sham treatment normal control (Sham-NC), sham treatment high-intensity exercise (Sham-HIE), 80 mW/cm2 LIPUS (LIPUS80), and high-intensity exercise combined with 80 mW/cm2 LIPUS (LIPUS80-HIE). The rats in HIE group were subjected to 30 m/min slope treadmill exercise for 90 min/day, 6 days/week for 12 weeks. The LIPUS80-HIE rats were irradiated with LIPUS (1 MHz, 80 mW/cm2) for 20 min/day at bilateral hind limb after exercise.

RESULTS

LIPUS significantly accelerated the proliferation, differentiation, mineralization, and migration of MC3T3-E1 cells. Compared to 30 mW/cm2 LIPUS, 80 mW/cm2 LIPUS got better promotion effect. 12 weeks of high-intensity exercise significantly reduced the muscle force, which was significantly reversed by LIPUS. Compared with the Sham-NC group, Sham-HIE group significantly optimized bone microstructure and enhanced mechanical properties of femur, and LIPUS80-HIE further enhanced the improvement effect on bone. The mechanisms may be related to activate Wnt/β-catenin signal pathway and then up-regulate the protein expression of Runx2 and VEGF, the key factors of osteogenesis and angiogenesis.

CONCLUSION

LIPUS could augment the skeletal benefits of high-intensity exercise through Wnt/β-catenin signal pathway.

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.

Impact of long-lasting spontaneous physical activity on bone morphogenetic protein 4 in the heart and tibia in murine model of heart failure

Bone morphogenetic protein 4 (BMP4) plays an important role in bone remodeling and in heart failure pathogenesis. The aim of this study was to evaluate the effect of spontaneous physical activity on the expression of BMP4 in the heart and tibia of the transgenic (Tgαq*44) mice, representing a model of chronic heart failure. Tgαq*44 and wild-type FVB mice (WT) were randomly assigned either to sedentary or to trained groups undergoing 8 weeks of spontaneous wheel running. The BMP4 protein expression in heart and tibiae was evaluated using Western immunoblotting and the phosphorus and calcium in the tibiae was assessed using the X-ray microanalysis. BMP4 content in the hearts of the Tgαq*44-sedentary mice was by ~490% higher than in the WT-sedentary mice, whereas in tibiae the BMP4 content of the Tgαq*44-sedentary mice was similar to that in the WT-sedentary animals. Tgαq*44 mice revealed by ~28% poorer spontaneous physical activity than the WT mice. No effect of performed physical activity on the BMP4 content in the hearts of either in the Tgαq*44 or WT mice was observed. However, 8-week spontaneous wheel running resulted in a decrease in the BMP4 expression in tibiae (by ~43%) in the group of Tgαq*44 mice only, with no changes in their bone phosphorus and calcium contents. We have concluded that prolonged period of spontaneous physical exercise does not increase the risk of the progression of the BMP4-mediated pathological cardiac hypertrophy and does not affect bone mineral status in the chronic heart failure mice.

Interval running training improves age-related skeletal muscle wasting and bone loss: Experiments with ovariectomized rats

NEW FINDINGS

What is the central question of this study? What is the effect and mechanism of interval running training on age-related muscle wasting and bone loss in an ovariectomized rat model? What is the main finding and its importance? Interval running training improved muscle growth and osteogenic differentiation by enhancing the expression of bone morphogenic proteins and sirtuins in ageing-induced ovariectomized rats. Therefore, the repetition of low and high intensities within a single exercise bout, such as interval running training, may be recommended as a practical intervention to prevent skeletal muscle wasting and bone loss in the elderly.

ABSTRACT

Effective prophylactic strategies are needed for the suppression of age-related muscle wasting and bone loss after menopause. Exercise training is attractive due to its potential for improving energy metabolism, as well as age-related muscle wasting and bone loss. In particular, interval running (IR) training involves a repetition of low and high intensities within a single exercise bout. Therefore, this study elucidated the effect of interval training on muscle and bone health, as well as anti-ageing, in ovariectomized (OVX) rats. The anti-ageing effect of IR on muscle and bone was tested using western blotting and micro-computed tomography analysis, tartrate-resistant acid phosphatase and immunohistochemical staining. IR significantly inhibited the expression of inflammatory molecules, and improved antioxidant activity via down-regulation of mitogen-activated protein kinases (MAPKs) in the ageing-induced OVX rats skeletal muscle. IR compared with continuous running (CR) improved muscle mass and growth in OVX rats by the promotion of muscle growth-related factors including MyoD, myogenin, phospho-mechanistic target of rapamycin (p-mTOR), sirtuins (SIRTs), and bone morphogenic proteins (BMPs). IR also effectively recovered OVX-induced bone loss via the down-regulation of bone resorption and osteoclast formation in receptor activator of nuclear factor κB ligand (RANKL)-treated bone marrowmacrophages (BMMs). In particular, IR led to high expression of SIRT1 and 6, which promoted osteogenic differentiation and bone formation via modulating the BMP signalling pathway compared with CR training. The in vivo effect of IR was confirmed by immunohistochemical staining with the improvement of bone formation molecules such as BMPs and SIRTs. These results suggested that IR training affected myogenic and osteogenic formation. So, IR training may be considered for prevention of muscle wasting and bone loss for the elderly.