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

Are associations between physical activity and bone mineral density in adults sex- and age-dependent? An analysis of the UK Biobank study

Although physical activity (PA) is recognized as a key bone mass determinant across life, athlete studies suggest that it may be less effective in women and older individuals. This has not been explored within the general population. We aimed to address this knowledge gap using data from the UK Biobank Study, a large population-based study of middle-aged and older adults. Free-living PA data collected at 100 Hz for 7 d using wrist-worn accelerometers were classified as sedentary behavior (0-29 milligravities [mg]), light (30-124 mg), or moderate-to-vigorous PA (125 + mg). LS and FN-BMD were assessed using DXA. The associations between PA and BMD were assessed using linear regression models, with formal assessments of sex and age interactions undertaken and adjustments made for accelerometer wear time, height, body mass index, education, ethnicity, disability, and (in women only) menopausal status. In total, 15 133 UK Biobank participants (52% women) had complete PA, bone, and covariate data. In this sample, greater overall and moderate-to-vigorous PA was associated with higher LS BMD. In women, these associations were typically weaker in older individuals, for example, regression coefficients in women aged 70 yr or older were ~50% lower than at 45-54 yr (age-by-PA interactions P < .01 in all models). Similar associations were observed in basic but not full models for FN BMD. Greater sedentary time was associated with lower LS BMD in men only, and greater light PA and sedentary time were associated with higher and lower FN BMD, respectively, in both sexes. These results suggest that associations between PA and bone health at clinically-relevant sites are weaker in older than younger women. That positive associations are evident between overall and moderate-vigorous PA and FN BMD even in women ≥70 yr suggests that PA for bone health should still be promoted in older women.

How to Suppress Mineral Loss and Stimulate Anabolism in Postmenopausal Bones with Appropriate Timing of Exercise and Nutrients

Background. Bone Health and Osteoporosis Foundation (BHOF) reports that as of 2023, approximately 10 million of older Americans have osteoporosis and another 44 million have low bone density. Osteoporosis is a serious handicap for the elderly and, in particular, for estrogen-deficient postmenopausal women, as it increases the risk of debilitating bone weakness and fractures. The BHOF recommendations for prevention of osteopenia, osteoporosis and bone fractures are to perform weight-bearing and muscle-strengthening exercises and to take recommended amounts of daily calcium and vitamin D. Methods. The purpose of this review is to describe and discuss recent evidence-based research on how to effectively utilize timing of exercise and calorie intake for stimulation of postmenopausal bone anabolism, and to provide this new information in the form of specific and actionable recommendations. Results. The five evidence-based recommendations are as follows: 1. Select an appropriate circadian time of day for exercise; 2. Increase walking speed to raise the movement momentum; 3. Eat a weight-maintenance meal one or two hours before the exercise bout; 4. Sustain the duration of walking activity (impulse) for 40 to 45 min; and 5. Repeat effective exercise stimulus 7 to 8 h after the first one to double the anabolic effect. Osteogenesis can also be increased with subthreshold mechanical loading, where needed, under several special circumstances. Conclusions. This review should provide pragmatic actionable pointers on how to utilize the idiosyncratic bone responsiveness to timing of movement and meals to prevent osteoporosis and encourage research toward a better understanding of how bone detects adequacy of a mechanical stimulus and determines duration of necessary rest to recover its sensitivity to mechanical stimulation and nutrients.

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.

Breed and loading history influence in vivo skeletal strain patterns in pre-pubertal female chickens

The influence of loading history on in vivo strains within a given specie remains poorly understood, and although in vivo strains have been measured at the hindlimb bones of various species, strains engendered during modes of activity other than locomotion are lacking, particularly in non-human species. For commercial egg-laying chickens specifically, there is an interest in understanding their bones' mechanical behaviour, particularly during youth, to develop early interventions to prevent the high incidence of osteoporosis in this population. We measured in vivo mechanical strains at the tibiotarsus midshaft during steady activities (ground, uphill, downhill locomotion) and non-steady activities (perching, jumping, aerial transition landing) in 48 pre-pubescent female (egg-laying) chickens from two breeds that were reared in three different housing systems, allowing varying amounts and types of physical activity. Mechanical strain patterns differed between breeds, and were dependent on the activity performed. Mechanical strains were also affected by rearing environment: chickens that were restricted from performing dynamic load bearing activity due to caged-housing generally exhibited higher mechanical strain levels during steady, but not non-steady activities, compared to chickens with prior dynamic load-bearing activity experience. Among chickens with prior experience of dynamic load bearing activity, those reared in housing systems that allowed more frequent physical activity did not exhibit lower mechanical strains. In all groups, the tibiotarsus was subjected to a loading environment consisting of a combination of axial compression, bending, and torsion, with torsion being the predominant source of strain. Aerial transition landing produced the highest strain levels with unusual strain patterns compared to other activities, suggesting it may produce the strongest anabolic response. These results exemplify how different breeds within a given specie adapt to maintain different patterns of mechanical strains, and how benefits of physical activity in terms of resistance to strain are activity-type dependent and do not necessarily increase with increased physical activity. These findings directly inform controlled loading experiments aimed at studying the bone mechanoresponse in young female chickens and can also be associated to measures of bone morphology and material properties to understand how these features influence bone mechanical properties in vivo.

Computational modeling for osteogenic potential assessment of physical exercises based on loading-induced mechanobiological environments in cortical bone remodeling

Osteoporosis and disuse can cause bone loss which reduces the weight-bearing strength of long bones. Physical exercise or mechanical loading prevents bone loss as it promotes bone modeling through osteogenesis, i.e., new bone formation. Several studies have observed distinct bone remodeling responses to physical exercises; nevertheless, the underlying mechanism behind such responses is not well established. Loading-induced pore-pressure and fluid motion act as mechanobiological stimuli to bone cells namely osteocytes which further initiate osteoactivities. The shape of loading waveforms also affects the poromechanical environment of bone. Accordingly, the present study hypothesizes that loading waveforms associated with physiological exercises may expose the bone to different mechanobiological stimuli resulting in distinct bone remodeling. A poromechanical finite element model is developed to compute pore-pressure and interstitial fluid velocity in femoral cortical bone tissue (healthy and osteoporotic) subjected to loading waveforms of three physiological exercises namely walking, running, and jumping. The model also computes the mechanobiological stimulus as a function of fluid velocity. The outcomes indicate that pore-pressure and fluid velocity decrease significantly in osteoporotic bone tissue in comparison with healthy tissue. Jumping and running both improve pore-pressure and fluid velocity in healthy and osteoporotic tissues, whereas running significantly enhances mechanobiological stimulus in both the tissues which indicates a possible explanation for distinct bone remodeling to different physical exercises. The present work also suggests that running may be recommended as a potential biomechanical therapeutic to prevent bone loss. Overall, the present work contributes to the area of orthopedic research to develop effective designs of prophylactic exercises to improve bone health.

Unraveling the physiologic paradoxes that underlie exercise prescription for stress fracture prevention

The effects of exercise on stress fracture risk are paradoxical. Exercise can promote both bone formation and resorption, which in turn, can reduce and increase risk of stress fractures, respectively. We review classic and current literature that suggests that the processes that underlie these responses to exercise are distinct. Bone remodeling involves osteoclastic resorption of fatigue-damaged bone, coupled with subsequent bone deposition to replace the damaged tissue. Bone modeling involves the independent action of osteoblasts and osteoclasts forming or resorbing bone, respectively, on a surface. In the formation mode, modeling results in increased bone stiffness, strength, and resistance to fatigue. Both the remodeling and modeling responses to exercise require significant time for newly deposited bone to fully mineralize. We propose that recognizing these two distinct physiologic pathways and their related time courses reveals the theoretical basis to guide exercise prescription to promote bone health during periods of heightened stress fracture risk. Such guidance may include minimizing rapid increases in the duration of repetitive exercises that may cause fatigue damage accrual, such as long-distance running and marching. Rather, limiting initial exercise characteristics to those known to stimulate bone formation, such as short-duration, moderate-to-high impact, dynamic, and multidirectional activities with rest insertion, may increase the fatigue resistance of bone and consequently minimize stress fracture risk.

Adolescent Bone Advantages 3 Years After Resistance Training Trial

PURPOSE

We assessed maintenance of skeletal advantages 3 years after completion of a 2-year, school-based, controlled exercise trial in adolescent girls.

METHOD

Middle-school girls participated in a resistance training program embedded in physical education classes. Effort groups (low-effort group [LO] and high-effort group [HI]) were identified; the control group (CON) participated in standard physical education at a separate school. Baseline and follow-up (FU) assessments at 6, 18, and 54 (FU3) months included densitometry, anthropometry, and questionnaires assessing physical maturity and nonintervention organized physical activity. Linear mixed effects models were fit to evaluate bone outcomes across all FU time points for CON versus LO/HI.

RESULTS

Sixty-eight girls (23 CON/25 HI/20 LO) were 11.6 (0.3) years at baseline. Bone parameters did not differ at baseline, except femoral neck bone mineral density (LO < HI/CON, P < .05). Forty-seven participants provided FU3 assessment: 17 CON/16 HI/14 LO. After adjusting for height, gynecologic age, baseline bone, and organized physical activity, bone gains across all time points were greater for HI versus CON for legs bone mineral content, femoral neck bone mineral content/bone mineral density, and third lumbar vertebra bone mineral content/bone mineral density (P ≤ .05). At FU3, bone values were greater for HI versus CON at subhead, legs, femoral neck, and third lumbar vertebra (P < .03).

CONCLUSION

Adolescent girls who exerted high effort in a school-based resistance training program demonstrated significant skeletal benefits 3 years after program completion.

Interactive effects of various loading parameters on the fluid dynamics within the lacunar-canalicular system for a single osteocyte

The osteocyte lacunar-canalicular system (LCS) serves as a mechanotransductive core where external loading applied to the skeleton is transduced into mechanical signals (e.g., fluid shear) that can be sensed by mechanosensors (osteocytes). The fluid velocity and shear stress within the LCS are affected by various loading parameters. However, the interactive effect of distinct loading parameters on the velocity and shear stress in the LCS remains unclear. To address this issue, we developed a multiscale modeling approach, combining a poroelastic finite element (FE) model with a single osteocytic LCS unit model to calculate the flow velocity and shear stress within the LCS. Next, a sensitivity analysis was performed to investigate individual and interactive effects of strain magnitude, strain rate, number of cycles, and intervening short rests between loading cycles on the velocity and shear stress around the osteocyte. Lastly, we developed a relatively simple regression model to predict those outcomes. Our results demonstrated that the strain magnitude or rate alone were the main factors affecting the velocity and shear stress; however, the combination of these two was not directly additive, and addition of a short rest between cycles could enhance the combination of these two related factors. These results show highly interactive effects of distinct loading parameters on fluid velocity and shear stress in the LCS. Specifically, our results suggest that an enhanced fluid dynamics environment in the LCS can be achieved with a brief number of load cycles combined with short rest insertion and high strain magnitude and rate.

Effect of External Mechanical Stimuli on Human Bone: a narrative review

Bone is a living composite material that has the capacity to adapt and respond to both internal and external stimuli. This capacity allows bone to adapt its structure to habitual loads and repair microdamage. Although human bone evolved to adapt to normal physiologic loading (for example from gravitational and muscle forces), these same biological pathways can potentially be activated through other types of external stimuli such as pulsed electromagnetic fields, mechanical vibration, and others. This review summarizes what is currently known about how human bone adapts to various types of external stimuli. We highlight how studies on sports-specific athletes and other exercise interventions have clarified the role of mechanical loading on bone structure. We also discuss clinical scenarios, such as spinal cord injury, where mechanical loading is drastically reduced, leading to rapid bone loss and permanent alterations to bone structure. Finally, we highlight areas of emerging research and unmet clinical need.

Effects of Different Types of Mechanical Loading on Trabecular Bone Microarchitecture in Rats

Mechanical loading is generally considered to have a positive impact on the skeleton; however, not all types of mechanical loading have the same beneficial effect. Many researchers have investigated which types of mechanical loading are more effective for improving bone mass and strength. Among the various mechanical loads, high-impact loading, such as jumping, appears to be more beneficial for bones than low-impact loadings such as walking, running, or swimming. Therefore, the different forms of mechanical loading exerted by running, swimming, and jumping exercises may have different effects on bone adaptations. However, little is known about the relationships between the types of mechanical loading and their effects on trabecular bone structure. The purpose of this article is to review the recent reports on the effects of treadmill running, jumping, and swimming on the trabecular bone microarchitecture in small animals. The effects of loading on trabecular bone architecture appear to differ among these different exercises, as several reports have shown that jumping increases the trabecular bone mass by thickening the trabeculae, whereas treadmill running and swimming add to the trabecular bone mass by increasing the trabecular number, rather than the thickness. This suggests that different types of exercise promote gains in trabecular bone mass through different architectural patterns in small animals.

Free-fall landing and interval running have different effects on trabecular bone mass and microarchitecture, serum osteocalcin, biomechanical properties, SOST expression and on osteocyte-related characteristics

The effects of treadmill interval training (IT) and free-fall exercise were evaluated on bone parameters including osteocyte related characteristics. Thirty-eight 4-month-old male Wistar rats were randomly divided into a control (C) group and exercise groups: IT, 10 free-fall impacts/day with a 10-s (FF10) or 20-s interval between drops (FF20), 5 days/week, for 9 weeks. We assessed bone mineral density (BMD); microarchitecture by µCT; mechanical strength by a 3-point bending test; density and occupancy of the osteocyte lacunae by toluidine blue staining; osteocalcin and NTx systemic levels by ELISA; and bone tissue Sost messenger RNA (mRNA) expression by RT-PCR. NTx levels were significantly lower in exercise groups as compared with the C group. In exercise groups the Sost mRNA expression was significantly lower than in C. Tb.N was significantly higher for IT and FF20 compared with the C group. Tb.Sp was significantly lower in FF10 compared with the C group. Both IT and FF20 were associated with higher tibial lacunar density as compared with FF10. compared with FF10, IT fat mass was lower, while tibial osteocyte lacunae occupancy and systemic osteocalcin level were higher. All exercise modes were efficient in reducing bone resorption. Both IT and free-fall impact with appropriate recovery periods, which may be beneficial for bone health and osteocyte-related characteristics. Novelty: Interval training is beneficial for bone mineral density. Exercises decreased both bone resorption and inhibition of bone formation (Sost mRNA). Longer interval recovery time favors osteocyte lacunae density.

Anabolic Bone Stimulus Requires a Pre-Exercise Meal and 45-Minute Walking Impulse of Suprathreshold Speed-Enhanced Momentum to Prevent or Mitigate Postmenopausal Osteoporosis within Circadian Constraints

Osteoporosis currently afflicts 8 million postmenopausal women in the US, increasing the risk of bone fractures and morbidity, and reducing overall quality of life. We sought to define moderate exercise protocols that can prevent postmenopausal osteoporosis. Our previous findings singled out higher walking speed and pre-exercise meals as necessary for suppression of bone resorption and increasing of markers of bone formation. Since both studies were amenable to alternate biomechanical, nutritional, and circadian interpretations, we sought to determine the relative importance of higher speed, momentum, speed-enhanced load, duration of impulse, and meal timing on osteogenic response. We hypothesized that: (1) 20 min of exercise one hour after eating is sufficient to suppress bone resorption as much as a 40-min impulse and that two 20 min exercise bouts separated by 7 h would double the anabolic effect; (2) early morning exercise performed after eating will be as effective as mid-day exercise for anabolic outcome; and (3) the 08:00 h 40-min. exercise uphill would be as osteogenic as the 40-min exercise downhill. Healthy postmenopausal women, 8 each, were assigned to a no-exercise condition (SED) or to 40- or 20-min exercise bouts, spaced 7 h apart, for walking uphill (40 Up and 20 Up) or downhill (40 Down and 20 Down) to produce differences in biomechanical variables. Exercise was initiated at 08:00 h one hour after eating in 40-min groups, and also 7 h later, two hours after the midday meal, in 20-min groups. Measurements were made of CICP (c-terminal peptide of type I collagen), osteocalcin (OC), and bone-specific alkaline phosphatase (BALP), markers of bone formation, and of the bone resorptive marker CTX (c-terminal telopeptide of type 1 collagen). The osteogenic ratios CICP/CTX, OC/CTX, and BALP/CTX were calculated. Only the 40-min downhill exercise of suprathreshold speed-enhanced momentum, increased the three osteogenic ratios, demonstrating the necessity of a 40-min, and inadequacy of a 20-min, exercise impulse. The failure of anabolic outcome in 40-min uphill exercise was attributed to a sustained elevation of PTH concentration, as its high morning elevation enhances the CTX circadian rhythm. We conclude that postmenopausal osteoporosis can be prevented or mitigated in sedentary women by 45 min of morning exercise of suprathreshold speed-enhanced increased momentum performed shortly after a meal while walking on level ground, or by 40-min downhill, but not 40-min uphill, exercise to avoid circadian PTH oversecretion. The principal stimulus for the anabolic effect is exercise, but the prerequisite for a pre-exercise meal demonstrates the requirement for nutrient facilitation.

Modeling the musculoskeletal loading in bone remodeling at the hip of a child

BACKGROUND AND OBJECTIVES

The mechanical load associated with physical activity affects the bone adaptation process. The bone adaptationeffect varies with age, being more effective during childhood and adolescence, particularly during pre-pubertal years. Bone-strengthening physical activity is recommended for children and adolescents. The number of time periods (bouts) per day of vigorous physical activity seems to be more important than the total cumulative time for optimal bone strength. So, the aim of this study was to evaluate the effects of weight-bearing physical activity on bone mineral density (BMD) of the proximal femur through computational simulation considering the intensity, exposure time (bouts) and regionalization of the results.

METHODS

For this purpose, a finite element model of a 7 year-old child femur was developed based on computed tomography images. Musculoskeletal loads were obtained from experimental kinematic data of weight-bearing physical activity performed by children of the same age (standing, walking, running, jumping). The effects of physical activity on BMD of several regions of interest of the femur were analyzed using a bone remodeling model. A daily accumulation of 400 min of physical activity (200 min walking and 200 min standing) was considered as reference, against with which the effects of additional 10 min loading bouts were compared: 10 min bouts of vigorous intensity physical activity vs. 10 min bouts of light to moderate intensity physical activity.

RESULTS

The simulations revealed greater increases in BMD associated with higher intensity and longer duration of physical activity. The largest BMD increases occurs during the first 10 min bout compared to longer durations and in less mineralized central regions compared to regions far from the neutral axis of the bone.

CONCLUSION

Weight bearing physical activity is more effective in bone remodeling when the musculoskeletal loading is more intense and of short duration and, under these conditions, less mineralized regions are more positively impacted.

The Efficacy of Brief School-Based Exercise Programs in Improving Pubertal Bone Mass and Physical Fitness: A Randomized Controlled Trial

PURPOSE

To examine the effects of three types of school-based exercises on bone health and physical fitness function in Chinese boys and girls.

METHODS

One hundred and seventy-four Chinese boys and girls were randomly assigned into four groups: (1) sham exercise (ShEx); (2) high-impact exercise (HiEx); (3) high-impact exercise with various directions (HiExVi); and (4) high-intensity interval exercise (HiInEx). Speed of sound (SOS) and physical fitness parameters were determined before and after six-month intervention.

RESULTS

At the end of six-month intervention, participants in all groups show an increment of SOS compared with the baseline (p < 0.05), and the changes were higher in HiEx (mean: 38.878 m/s, 95% CI: 32.885~44.872, p = 0.001) and HiExVi groups (49.317 m/s, 42.737~55.897, p < 0.001) compared with ShEx group (20.049 m/s, 13.751~26.346). Six-month exercise training generated a reduction of percent of body fat (PBF) and waist-hip ratio (WHR) (p < 0.05). The decrease of PBF was greater in HiExVi (-1.222%, -1.820~-0.624, p = 0.012) and HiInEx groups (-1.395%, -1.809~-0.982, p = 0.003), whereas the reduction of WHR was larger in HiEx (-0.026, -0.039~-0.014, p = 0.009), HiExVi (-0.024, -0.036~-0.012, p = 0.021), and HiInEx groups (-0.035, -0.046~-0.024, p < 0.001) compared with ShEx group. Balance function (BLF), vital capacity (VC), standing long jump (SLJ), and sit up (SU) increased in all intervention groups (p < 0.05). The BLF increased in HiEx (6.332 s, 4.136~8.528, p = 0.001), HiExVi (10.489 s, 8.934~12.045, p < 0.001), and HiInEx groups (9.103 s, 7.430~10.776, p < 0.001) showed a greater change than that of ShEx group (1.727 s, 0.684~2.770). The increment of VC (273.049 mL, 199.510~346.587, p < 0.001) and SU (2.537 times/min, 0.639~4.435, p = 0.017) was higher in HiInEx group, whereas the accrual in SLJ was larger in HiExVi (7.488 cm, 4.936~10.040, p = 0.007) compared with ShEx group (58.902 mL, 7.990~109.814; -0.463 times/min, -2.003~1.077; 1.488 cm, -0.654~3.630).

CONCLUSION

The brief school-based exercises were effective in improving schoolchildren's health, but they showed different effects, with HiEx mostly improving bone health, HiInEx largely benefiting physical fitness function, and HiExVi enhancing both bone and physical fitness.

The Diminishing Returns of Mechanical Loading and Potential Mechanisms that Desensitize Osteocytes

Adaptation to mechanical loading is critical to maintaining bone mass and offers therapeutic potential to preventing age-related bone loss and osteoporosis. However, increasing the duration of loading is met with "diminishing returns" as the anabolic response quickly becomes saturated. As a result, the anabolic response to daily activities and repetitive bouts of loading is limited by the underlying mechanisms that desensitize and render bone unresponsive at the cellular level. Osteocytes are the primary cells that respond to skeletal loading and facilitate the overall anabolic response. Although many of osteocytes' signaling mechanisms activated in response to loading are considered anabolic in nature, several of them can also render osteocytes insensitive to further stimuli and thereby creating a negative feedback loop that limits osteocytes' overall response. The purpose of this review is to examine the potential mechanisms that may contribute to the loss of mechanosensitivity. In particular, we examined the inactivation/desensitization of ion channels and signaling molecules along with the potential role of endocytosis and cytoskeletal reorganization. The significance in defining the negative feedback loop is the potential to identify unique targets for enabling osteocytes to maintain their sensitivity. In doing so, we can begin to cultivate new strategies that capitalize on the anabolic nature of daily activities that repeatedly load the skeleton.

Promoting adaptive bone formation to prevent stress fractures in military personnel

Mechanical loading leads to adaptive bone formation - the formation of new bone on existing skeletal surfaces - which increases bone strength and fatigue resistance. The same mechanical loading can also cause microdamage to bone and development of a stress fracture through targeted remodelling. Stress fractures are common in military recruits and cause significant morbidity, lost training time, and discharge from military service. This narrative review proposes strategies to promote adaptive bone formation as a novel approach to mitigate the risk of stress fracture injuries during arduous military training. Exercise that is unaccustomed, dynamic, high-impact, multidirectional, intermittent, and includes extended rest periods to restore bone mechanosensitivity, is most osteogenic. New bone formation can take up to one year to mineralize, and so new exercise training programmes should be initiated well in advance of military activities with high risk of stress fracture. Bone mechanosensitivity is highest in adolescence, before puberty, and so increasing physical activity in youth is likely to protect skeletal health in later life, including for those in the military. Recent data show that adaptive bone formation takes place during initial military training. Adaptive bone formation can also be supported with adequate sleep, vitamin D, calcium, and energy availability. Further evidence on how strategies to promote adaptive bone formation affect stress fracture risk are required. Adaptive bone formation can be optimized with a range of training and nutritional strategies to help create a resilient skeleton, which may protect against stress fracture throughout military service.

Effects of exercise frequency and training volume on bone changes following a multi-component exercise intervention in middle aged and older men: Secondary analysis of an 18-month randomized controlled trial

Progressive resistance training (PRT) combined with weight-bearing impact exercise are recommended to optimize bone health, but the optimal frequency and dose of training remains uncertain. This study, which is a secondary analysis of an 18-month intervention in men aged 50-79 years, examined the association between exercise frequency and the volume of training with changes in DXA and QCT-derived femoral neck (FN) and lumbar spine (LS) bone outcomes, respectively. Men were allocated to either thrice-weekly PRT plus impact exercise training (n = 87) or a non-exercising (n = 85) group. Average weekly exercise frequency (ExFreq) and training volume per session [PRT volume (weight lifted, kg), number of weight-bearing impacts (jumps completed) and total training volume] over the 18-months were calculated from the participants' exercise cards. Regression analysis showed that average weekly ExFreq and training volume per session were positively associated with the 18-month changes in FN BMD and LS trabecular volumetric BMD. Men completing on average 1 to <2 and ≥2 sessions/week had a 1.6 to 2.2% greater net gain in FN BMD relative to non-exercising men, while those completing ≥2 sessions/week had 3.9 to 5.2% net gain in LS trabecular vBMD compared to non-exercising men and those completing <1 session/week. Further analysis showed that the average number of impact loads per session, but not the average PRT weight-lifted, was positively associated with changes in BMD. Every 10 impact loads per session over 18 months was associated with a 0.3% and 1.3% increase in FN BMD and LS trabecular vBMD, respectively. In conclusion, this study indicates that exercise frequency and training volume were predictors of the changes in hip and spine BMD following a multi-component exercise program, and that the number of impact loads rather than PRT weight lifted per session was more important for eliciting positive skeletal responses in middle-aged and older men.

Effect of Various Types of Muscle Contraction with Different Running Conditions on Mouse Humerus Morphology

How various types of muscle contraction during exercises affect bone formation remains unclear. This study aimed to determine how exercises with different muscle contraction types affect bone morphology. In total, 20 mice were used and divided into four groups: Control, Level, Down Slow, and Down. Different types of muscle contraction were induced by changing the running angle of the treadmill. After the intervention, micro-computed tomography (Micro-CT), tartrate-resistant acid phosphatase/alkaline phosphatase (ALP) staining, and immunohistochemical staining were used to analyze the humerus head, tendon-to-bone attachment, and humerus diaphyseal region. Micro-CT found that the volume ratio of the humeral head, the volume of the tendon-to-bone attachment region, and the area of the humeral diaphyseal region increased in the Down group. However, no difference was detected in bone morphology between the Level and Down Slow groups. In addition, histology showed activation of ALP in the subarticular subchondral region in the Down Slow and Down groups and the fibrocartilage region in the tendon-to-bone attachment. Moreover, Osterix increased predominantly in the Down Slow and Down groups.Overall bone morphological changes in the humerus occur only when overuse is added to EC-dominant activity. Furthermore, different type of muscle contractile activities might promote bone formation in a site-specific manner.

Transmission of whole body vibration - Comparison of three vibration platforms in healthy subjects

The potential of whole body vibration (WBV) to maintain or enhance musculoskeletal strength during ageing is of increasing interest, with both low and high magnitude WBV having been shown to maintain or increase bone mineral density (BMD) at the lumbar spine and femoral neck. The aim of this study was to determine how a range of side alternating and vertical WBV platforms deliver vibration stimuli up through the human body. Motion capture data were collected for 6 healthy adult participants whilst standing on the Galileo 900, Powerplate Pro 5 and Juvent 100 WBV platforms. The side alternating Galileo 900 WBV platform delivered WBV at 5-30 Hz and amplitudes of 0-5 mm. The Powerplate Pro 5 vertical WBV platform delivered WBV at 25 and 30 Hz and amplitude settings of 'Low' and 'High'. The Juvent 1000 vertical WBV platform delivered a stimulus at a frequency between 32 and 37 Hz and amplitude 10 fold lower than either the Galileo or Powerplate, resulting in accelerations of 0.3 g. Motion capture data were recorded using an 8 camera Vicon Nexus system with 21 reflective markers placed at anatomical landmarks between the toe and the forehead. Vibration was expressed as vertical RMS accelerations along the z-axis which were calculated as the square root of the mean of the squared acceleration values in g. The Juvent 1000 did not deliver detectable vertical RMS accelerations above the knees. In contrast, the Powerplate Pro 5 and Galileo 900 delivered vertical RMS accelerations sufficiently to reach the femoral neck and lumbar spine. The maximum vertical RMS accelerations at the anterior superior iliac spine (ASIS) were 1.00 g ±0.30 and 0.85 g ±0.49 for the Powerplate and Galileo respectively. For similar accelerations at the ASIS, the Galileo achieved greater accelerations within the lower limbs, whilst the Powerplate recorded higher accelerations in the thoracic spine at T10. The Powerplate Pro 5 and Galileo 900 deliver vertical RMS accelerations sufficiently to reach the femoral neck and lumbar spine, whereas the Juvent 1000 did not deliver detectable vertical RMS accelerations above the knee. The side alternating Galileo 900 showed greater attenuation of the input accelerations than the vertical vibrations of the Powerplate Pro 5. The platforms differ markedly in the transmission of vibration with strong influences of frequency and amplitude. Researchers need to take account of the differences in transmission between platforms when designing and comparing trials of whole body vibration.

Resistance Training Modulates the Matrix Metalloproteinase-2 Activity in Different Trabecular Bones in Aged Rats

Background

Aging decreases osteogenic ability, inducing harmful effects on the bone extracellular matrix (ECM), while exercise training has been indicated as a tool to counteract bone disorders related to advancing age. The modulation of bone ECM is regulated by several types of matrix metalloproteinase (MMP); however, MMP-2 activity in different trabecular bones in response to resistance training (RT) has been neglected. Remodeling differs in different bones under the application of the same mechanical loading. Thus, we investigated the effects of 12 weeks of RT on MMP-2 activity in the lumbar vertebra (L6), tibia, and femur of young (3 months) and older rats (21 months).

Methods

Twenty Wistar rats were divided into four groups (five animals per group): young sedentary or trained and older sedentary or trained. The 12-week RT consisted of climbing a 1.1-m vertical ladder three times per week with progressive weights secured to the animals’ tails. The animals were killed 48 h after the end of the experimental period. The MMP-2 activity was assessed by the zymography method.

Results

The aging process induced lower MMP-2 activity in the lumbar vertebrae and tibia (p=0.01). RT upregulated pro, intermediate, and active MMP-2 activity in the tibia of young rats (p=0.001). RT also upregulated pro and active MMP-2 activity in the lumbar vertebrae and tibia with advancing age (p=0.01). There was no significant difference (p>0.05) between groups for MMP-2 of the femur, regardless of age and RT.

Conclusion

The aging process impairs MMP-2 activity, but RT is a potential therapeutic approach to minimize the deleterious effects of ECM degeneration in different aged bones. Distinct MMP-2 responses to exercise training may result in specific remodeling processes.

Changes in Volumetric Bone Mineral Density Over 12 Months After a Tibial Bone Stress Injury Diagnosis: Implications for Return to Sports and Military Duty

BACKGROUND

Bone stress injuries (BSIs) occur in up to 20% of runners and military personnel. Typically, after a period of unloading and gradual return to weightbearing activities, athletes return to unrestricted sports participation or military duty approximately 4 to 14 weeks after a BSI diagnosis, depending on the injury location and severity. However, the time course of the recovery of the bone's mechanical competence is not well-characterized, and reinjury rates are high.

PURPOSE

To assess the bone microarchitecture and volumetric bone mineral density (vBMD) over 12 months after a tibial BSI diagnosis.

STUDY DESIGN

Case-control study; Level of evidence, 3.

METHODS

We enrolled 30 female athletes from the local community (aged 18-35 years) with a tibial BSI (grade ≥2 of 4 on magnetic resonance imaging) for this prospective observational study. Participants completed a baseline visit within 3 weeks of the diagnosis. At baseline and 6, 12, 24, and 52 weeks after the BSI diagnosis, we collected high-resolution peripheral quantitative computed tomography scans of the ultradistal tibia (4% of tibial length) of the injured and uninjured legs as well as pain and physical activity assessment findings.

RESULTS

From baseline to 12 weeks after the diagnosis, total, trabecular, and cortical vBMD declined by 0.58% to 0.94% (P < .05 for all) in the injured leg. Total and trabecular vBMD also declined by 0.61% and 0.67%, respectively, in the uninjured leg (P < .05 for both). At 24 weeks, mean values for all bone parameters were nearly equivalent to baseline values, and by 52 weeks, several mean values had surpassed baseline values. Of the 30 participants, 10 incurred a subsequent BSI during the course of the study, and 1 of these 10 incurred 2 subsequent BSIs. Participants who suffered an additional BSI were younger and had a later age of menarche, a greater incidence of previous fractures, and lower serum parathyroid hormone levels (P < .05 for all).

CONCLUSION

Bone density declined in both the injured and the uninjured legs and, on average, did not return to baseline for 3 to 6 months after a tibial BSI diagnosis. The observed time to the recovery of baseline vBMD, coupled with the high rate of recurrent BSIs, suggests that improved return-to-sports and military duty guidelines may be in order.

Association of objectively measured physical activity and bone health in children and adolescents: a systematic review and narrative synthesis

The influence of day-to-day physical activity on bone in adolescence has not been well characterized. Forty articles were identified that assessed the relationship between accelerometry-derived physical activity and bone outcomes in adolescents. Physical activity was positively associated with bone strength in peri-pubertal males, with less consistent evidence in females. Physical activity (PA) is recommended to optimize bone development in childhood and adolescence; however, the influence of day-to-day PA on bone development is not well defined. The aim of this review was to describe the current evidence for objectively measured PA on bone outcomes in healthy children and adolescents. MEDLINE, Embase, Cochrane Library, Scopus, Web of Science, CINAHL, PsycInfo, and ClinicalTrials.gov were searched for relevant articles up to April 2020. Studies assessing the relationship between accelerometry-derived PA and bone outcomes in adolescents (6-18 years old) were included. Two reviewers independently screened studies for eligibility, extracted data, and rated study quality. Forty articles met inclusion criteria (25 cross-sectional, 15 longitudinal). There was significant heterogeneity in accelerometry methodology and bone outcomes measured. Studies in males indicated a significant, positive relationship between moderate to vigorous PA (MVPA) and bone outcomes at the hip and femur, particularly during the peri-pubertal years. The results for MVPA and bone outcomes in females were mixed. There was a paucity of longitudinal studies using pQCT and a lack of data regarding how light PA and/or impact activity influences bone outcomes. The current evidence suggests that objectively measured MVPA is positively associated with bone outcomes in children and adolescents, especially in males. However, inconsistencies in methodology make it difficult to determine the amount and type of PA that leads to favorable bone outcomes. Given that the majority of research has been conducted in Caucasian adolescents, further research is needed in minority populations.

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.

Bone Adaptation in Adult Women Is Related to Loading Dose: A 12-Month Randomized Controlled Trial

Although strong evidence exists that certain activities can increase bone density and structure in people, it is unclear what specific mechanical factors govern the response. This is important because understanding the effect of mechanical signals on bone could contribute to more effective osteoporosis prevention methods and efficient clinical trial design. The degree to which strain rate and magnitude govern bone adaptation in humans has never been prospectively tested. Here, we studied the effects of a voluntary upper extremity compressive loading task in healthy adult women during a 12-month prospective period. A total of 102 women age 21 to 40 years participated in one of two experiments: (i) low (n = 21) and high (n = 24) strain magnitude; or (ii) low (n = 21) and high (n = 20) strain rate. Control (n = 16) no intervention. Strains were assigned using subject-specific finite element models. Load cycles were recorded digitally. The primary outcome was change in ultradistal radius integral bone mineral content (iBMC), assessed with QCT. Interim time points and secondary outcomes were assessed with high resolution pQCT (HRpQCT) at the distal radius. Sixty-six participants completed the intervention, and interim data were analyzed for 77 participants. Likely related to improved compliance and higher received loading dose, both the low-strain rate and high-strain rate groups had significant 12-month increases to ultradistal iBMC (change in control: -1.3 ± 2.7%, low strain rate: 2.7 ± 2.1%, high strain rate: 3.4 ± 2.2%), total iBMC, and other measures. "Loading dose" was positively related to 12-month change in ultradistal iBMC, and interim changes to total BMD, cortical thickness, and inner trabecular BMD. Participants who gained the most bone completed, on average, 128 loading bouts of (mean strain) 575 με at 1878 με/s. We conclude that signals related to strain magnitude, rate, and number of loading bouts contribute to bone adaptation in healthy adult women, but only explain a small amount of variance in bone changes. © 2020 The Authors. Journal of Bone and Mineral Research published by American Society for Bone and Mineral Research.

Terrestrial acclimation and exercise lead to bone functional response in Polypterus senegalus pectoral fins

The ability of bones to sense and respond to mechanical loading is a central feature of vertebrate skeletons. However, the functional demands imposed on terrestrial and aquatic animals differ vastly. The pectoral girdle of the basal actinopterygian fish Polypterus senegalus was previously shown to exhibit plasticity following terrestrial acclimation, but the pectoral fin itself has yet to be examined. We investigated skeletal plasticity in the pectoral fins of P. senegalus after exposure to terrestrial loading. Juvenile fish were divided into three groups: a control group was kept under aquatic conditions without intervention, an exercised group was also kept in water but received daily exercise on land, and a terrestrial group was kept in a chronic semi-terrestrial condition. After 5 weeks, the pectoral fins were cleared and stained with Alcian Blue and Alizarin Red to visualize cartilage and bone, allowing measurements of bone length, bone width, ossification and curvature to be taken for the endochondral radial bones. Polypterus senegalus fin bones responded most strongly to chronic loading in the terrestrial condition. Fish that were reared in a terrestrial environment had significantly longer bones compared with those of aquatic controls, wider propterygia and metapterygia, and more ossified metapterygia and medial radials, and they showed changes in propterygial curvature. Exercised fish also had longer and more ossified medial radials compared with those of controls. Polypterus senegalus fin bones exhibit plasticity in response to novel terrestrial loading. Such plasticity could be relevant for transitions between water and land on evolutionary scales, but key differences between fish and tetrapod bone make direct comparisons challenging.

Skeletal effects of plyometric exercise and metformin in ovariectomized rats

Estrogen deficiency causes bone loss and skeletal muscle dysfunction, and attenuates the musculoskeletal effects of exercise. The anti-diabetic drug metformin has been suggested to promote beneficial skeletal effects. To explore whether metformin can improve musculoskeletal training response during estrogen deficiency, we investigated the skeletal effects of plyometric exercise and metformin, in an ovarectomized (OVX) rat model of osteoporosis. Female Sprague Dawley rats, 12 weeks of age, rats were allocated to a sham-operated group (Sham), and four OVX groups; metformin (OVX-Met), exercise (OVX-Ex), combined metformin and exercise (OVX-MetEx) and a control group (OVX-Ctr), n = 12/group. Dual X-ray absorptiometry, micro computed tomography, fracture toughness testing, histomorphometry and plasma analyses were performed to explore skeletal effects. All intervention groups exhibited a higher gain in femoral bone mineral density (BMD) than OVX-Ctr (p < .01). The combined intervention also resulted in a higher gain in femoral and spine BMD compared to OVX-Met (p < .01). Both exercise groups displayed improved microarchitecture, including both cortical and trabecular parameters (p < .05). This was most evident in the OVX-MetEx group where several indices were at sham level or superior to OVX-Ctr (p < .05). The OVX-MetEx group also exhibited an enhanced toughening effect compared to the other OVX groups (p < .05). The beneficial skeletal effects seemed to be mediated by inhibition of bone resorption and stimulation of bone formation. The training response (i.e. jumping height) was also greater in the metformin treated rats compared to OVX-Ex (p < .01), indicating a performance-enhancing effect of metformin. Both exercise groups displayed higher lean mass than OVX-Ctr (p < .05). In conclusion, the combination of plyometric exercise and metformin improved trabecular microarchitecture and bone material properties relative to OVX controls. However, no additive effect of the combined intervention was observed compared to exercise alone.

Occupational Activities: Factors That Tip the Balance From Bone Accrual to Bone Loss

Bone adaptation to persistent overloading can be counteracted by superimposed inflammatory and loading-induced damage that can tip the balance from bone accrual to loss.

Supplemental digital content is available in the text.

It is commonly assumed that beneficial adaptations in bone occur with vigorous exercise, yet any adaptive re/modeling in bone undergoing persistent overloading can be counteracted by superimposed inflammatory, compressive, and tensile loading–induced damage responses above thresholds of tissue fatigue failure and repair. This leads to a tenuous balance between achieving bone accrual and loss.

Murine Axial Compression Tibial Loading Model to Study Bone Mechanobiology: Implementing the Model and Reporting Results

In vivo, tibial loading in mice is increasingly used to study bone adaptation and mechanotransduction. To achieve standardized and defined experimental conditions, loading parameters and animal-related factors must be considered when performing in vivo loading studies. In this review, we discuss these loading and animal-related experimental conditions, present methods to assess bone adaptation, and suggest reporting guidelines. This review originated from presentations by each of the authors at the workshop "Developing Best Practices for Mouse Models of In Vivo Loading" during the Preclinical Models Section at the Orthopaedic Research Society Annual Meeting, San Diego, CA, March 2017. Following the meeting, the authors engaged in detailed discussions with consideration of relevant literature. The guidelines and recommendations in this review are provided to help researchers perform in vivo loading experiments in mice, and thus further our knowledge of bone adaptation and the mechanisms involved in mechanotransduction. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:233-252, 2020.

An Overview of the Beneficial Effects of Exercise on Health and Performance

Life expectancy is steadily increasing in modern societies, and so are noncommunicable diseases such as cardiovascular diseases, diabetes, obesity, and cancer, accounting for more than 70% of all deaths globally. The costs associated with these diseases are enormous, but it has been estimated that the majority of these noncommunicable diseases are preventable. In addition to an unhealthy diet, tobacco use, and harmful use of alcohol, physical inactivity is a key risk factor. Consequently, physical activity is a logical remedy, and in this chapter an overview of the numerous beneficial effects of physical activity on health and performance is given.The chapter is divided into three parts: First, the basics of physical activity and exercise are discussed, for instance exercise classification, exercise intensity operationalization, energy supply, and the acute effects of exercise such as blood flow redistribution and increased cardiac output. In the second part, the effects of exercise on physical performance are summarized. Specifically, it is discussed how endurance, strength, power, and balance can be improved. This discussion includes recommendations regarding the type, intensity, and duration of the exercise leading to improvements in one of these aspects of physical performance, as well as the mechanisms causing these adaptations. In the third part, the beneficial effects of physical activity on physical and mental health are outlined, with particular attention to cardiovascular diseases, the metabolic syndrome, musculoskeletal diseases, mood, anxiety, depression, and dementia.It can be concluded that with adequate programming, regular physical activity is an effective way to improve physical performance, improve physical and mental health, and reduce the risk factors for many noncommunicable diseases such as cardiovascular diseases, metabolic syndrome, sarcopenia, osteoporosis, and depression. In contrast to medication, physical exercise has no negative side effects, costs very little, and targets many health issues at once. If the multitude of beneficial effects of regular exercise were to be combined in a single low-cost drug, it would be prescribed for almost all types of physical and mental health issues.

Jump Exercise and Food Restriction on Bone Parameters in Young Female Rats

We examined the effect of jump exercise on bone parameters in young female rats under food restriction. Seven-week-old female rats were divided into four groups: a sedentary and ad libitum feeding group (n = 10), a jump exercise and ad libitum feeding group (n = 9), a sedentary and 30% food restriction group (n = 9), and a jump exercise and 30% food restriction group (n = 10). The jump groups jumped 20 times/day, 5 times/week. The experiment lasted for 13 weeks. There were no interactions of jump exercise and food restriction on bone. Jump exercise under food restriction conditions induced higher bone strength, bone mineral content, bone area, bone mineral density (BMD), and cortical bone volume in young female rats, similar to rats under ad libitum feeding conditions. Bone strength parameters were not significantly different between ad libitum intake and food restriction with jump exercise training; however, BMD, bone size, and bone mass in the food restriction groups did not reach the levels of those in the ad libitum conditions group with jump exercise training. Neither jump exercise nor food restriction had a significant effect on serum estradiol or IGF-1. Our study reveals jump exercise attenuates loss of biomechanical properties and some bone sites with food restriction in young female rats.

Skeletal loading score is associated with bone microarchitecture in young adults

Physical activity that involves high strain magnitudes and high rates of loading is reported to be most effective in eliciting an osteogenic bone response. Whether a history of participation in osteogenic activities during youth, as well as current participation in osteogenic activities, contributes to young adult bone microarchitecture and strength is unknown.

PURPOSE

We determined the association between a new skeletal loading (SkL) score reflecting physical activity from age 11 to adulthood, the bone specific physical activity questionnaire (BPAQ) and bone microarchitecture in young Black and White men and women.

METHODS

We conducted a cross-sectional study of young ([mean ± SD] 23.7 ± 3.3 years) Black (n = 51 women, n = 31 men) and White (n = 50 women, n = 49 men) adults. Microarchitecture and estimated bone strength (by micro-finite element analysis) were assessed at the ultradistal tibia using high-resolution peripheral quantitative computed tomography (HR-pQCT). Physical activity questionnaires were administered and a SkL score was derived based on ground reaction force, rate of loading, frequency, duration, and life period of participation per activity from age 11 onwards. BPAQ score was also calculated. We used multiple linear regression to determine associations between both SkL score and BPAQ score and bone outcomes, adjusting for age, height, weight, sex, and race.

RESULTS

We found that SkL score, which accounts for current and historical physical activity, was significantly associated with most cortical bone parameters at the tibia including area, area fraction, porosity, thickness, and tissue mineral density (R² = 0.27-0.55, all p < 0.01). Further, trabecular thickness, separation, number, and bone mineral density (R² = 0.22-0.32, all p < 0.01), as well as stiffness and failure load (R² = 0.63-0.65, all p < 0.01), were associated with the SkL score. The BPAQ was also significantly associated with most bone parameters, but to a lesser degree than SkL score.

CONCLUSION

These findings suggest that among young adults, greater amounts of osteogenic physical activity, as assessed by the SkL score and BPAQ are associated with improved bone microarchitecture and strength. With the potential to predict bone parameters in young adults, these scores may ultimately serve to identify those most vulnerable to fracture.

Assessment of acute bone loading in humans using [18F]NaF PET/MRI

PURPOSE

The acute effect of loading on bone tissue and physiology can offer important information with regard to joint function in diseases such as osteoarthritis. Imaging studies using [¹⁸F]-sodium fluoride ([¹⁸F]NaF) have found changes in tracer kinetics in animals after subjecting bones to strain, indicating an acute physiological response. The aim of this study is to measure acute changes in NaF uptake in human bone due to exercise-induced loading.

METHODS

Twelve healthy subjects underwent two consecutive 50-min [¹⁸F]NaF PET/MRI examinations of the knees, one baseline followed by one post-exercise scan. Quantification of tracer kinetics was performed using an image-derived input function from the popliteal artery. For both scans, kinetic parameters of K_i^NLR, K₁, k₂, k₃, and blood volume were mapped parametrically using nonlinear regression with the Hawkins model. The kinetic parameters along with mean SUV and SUV_max were compared between the pre- and post-exercise examinations. Differences in response to exercise were analysed between bone tissue types (subchondral, cortical, and trabecular bone) and between regional subsections of knee subchondral bone.

RESULTS

Exercise induced a significant (p < <0.001) increase in [¹⁸F]NaF uptake in all bone tissues in both knees, with mean SUV increases ranging from 47% in trabecular bone tissue to 131% in subchondral bone tissue. Kinetic parameters involving vascularization (K₁ and blood volume) increased, whereas the NaF extraction fraction [k₃/(k₂ + k₃)] was reduced.

CONCLUSIONS

Bone loading induces an acute response in bone physiology as quantified by [¹⁸F]NaF PET kinetics. Dynamic imaging after bone loading using [¹⁸F]NaF PET is a promising diagnostic tool in bone physiology and imaging of biomechanics.

Inverse remodelling algorithm identifies habitual manual activities of primates based on metacarpal bone architecture

Previously, a micro-finite element (micro-FE)-based inverse remodelling method was presented in the literature that reconstructs the loading history of a bone based on its architecture alone. Despite promising preliminary results, it remains unclear whether this method is sensitive enough to detect differences of bone loading related to pathologies or habitual activities. The goal of this study was to test the sensitivity of the inverse remodelling method by predicting joint loading histories of metacarpal bones of species with similar anatomy but clearly distinct habitual hand use. Three groups of habitual hand use were defined using the most representative primate species: manipulation (human), suspensory locomotion (orangutan), and knuckle-walking locomotion (bonobo, chimpanzee, gorilla). Nine to ten micro-computed tomography scans of each species ([Formula: see text] in total) were used to create micro-FE models of the metacarpal head region. The most probable joint loading history was predicted by optimally scaling six load cases representing joint postures ranging from [Formula: see text] (extension) to [Formula: see text] (flexion). Predicted mean joint load directions were significantly different between knuckle-walking and non-knuckle-walking groups ([Formula: see text]) and in line with expected primary hand postures. Mean joint load magnitudes tended to be larger in species using their hands for locomotion compared to species using them for manipulation. In conclusion, this study shows that the micro-FE-based inverse remodelling method is sensitive enough to detect differences of joint loading related to habitual manual activities of primates and might, therefore, be useful for palaeoanthropologists to reconstruct the behaviour of extinct species and for biomedical applications such as detecting pathological joint loading.

Exogenous skeletal muscle satellite cells promote the repair of levator palpebrae superioris mechanical damage in rat

AIM OF THE STUDY

Blepharoptosis is a drooping of the upper eyelid, usually due to dysfunction of the levator palpebrae superioris (LPS). Recently, skeletal muscle satellite cells (SSCs) have been reported to promote the repair of damaged skeletal muscle. This study aims to investigate the potential contribution of exogenous SSCs to the regeneration of mechanically damaged LPS.

MATERIALS AND METHODS

Thirty-two rats were randomly divided into four groups, including control group, SSCs-treated group, SSCs-treated injury group and non-treated injury group. After rats in injury groups were artificially lacerated on both the left and right LPS, HBBS (Hank's Balanced Salt Solution) containing SSCs was injected into upper eyelid tissue. After 7 days, the LPS muscle tissues were excised. In addition, skeletal muscle cells (SMCs) and SSCs were cocultured for use as an in vitro model, and the protective effects of SSCs on cultured SMCs were also investigated.

RESULTS

Histological staining revealed that exogenous SSCs repaired the damaged muscle fibers and attenuated the fibrosis of LPS, possibly due to the increased level of IGF-1. In contrast, the level of IL-1β, IL-6, TGF-β1 and Smad2/3 (phospho-T8) were significantly reduced in the SSCs-treated group. The in vitro model using coculture of skeletal muscle cells (SMCs) and SSCs also revealed an increased level of IGF-1 and reduced level of inflammatory factors, resulting in a better cell survival rate.

CONCLUSIONS

This study found that exogenous SSCs can promote the repair of LPS mechanical damage and provides new insight into the development of novel therapeutic approaches for blepharoptosis.

Treadmill running and targeted tibial loading differentially improve bone mass in mice

Treadmill running and tibial loading are two common modalities used to assess the role of mechanical stimulation on the skeleton preclinically. The primary advantage of treadmill running is its physiological relevance. However, the applied load is complex and multiaxial, with observed results influenced by cardiovascular and musculoskeletal effects. In contrast, with tibial loading, a direct uniaxial load is applied to a single bone, providing the advantage of greater control but with less physiological relevance. Despite the importance and wide-spread use of both modalities, direct comparisons are lacking. In this study, we compared effects of targeted tibial loading, treadmill running, and their combination on cancellous and cortical architecture in a murine model. We show that tibial loading and treadmill running differentially improve bone mass, with tibial loading resulting in thicker trabeculae and increased cortical mass, and exercise resulting in greater number of trabeculae and no cortical mass-based effects. Combination of the modalities resulted in an additive response. These data suggest that tibial loading and exercise may improve mass differentially.

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Tibial loading increased trabecular thickness while exercise increased number.

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Combined effects of loading and exercise were additive in cancellous bone.

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In cortical bone, loading increased cross-sectional area.

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No mass-based effects were noted due to exercise.

Exercise for the prevention of osteoporosis in postmenopausal women: an evidence-based guide to the optimal prescription

BACKGROUND

Osteoporosis and related fragility fractures are a global public health problem in which pharmaceutical agents targeting bone mineral density (BMD) are the first line of treatment. However, pharmaceuticals have no effect on improving other key fracture risk factors, including low muscle strength, power and functional capacity, all of which are associated with an increased risk for falls and fracture, independent of BMD. Targeted exercise training is the only strategy that can simultaneously improve multiple skeletal and fall-related risk factors, but it must be appropriately prescribed and tailored to the desired outcome(s) and the specified target group.

OBJECTIVES

In this review, we provide an overview of the general principles of training and specific loading characteristics underlying current exercise guidelines for the prevention of osteoporosis, and an update on the latest scientific evidence with regard to the type and dose of exercise shown to positively influence bone mass, structure and strength and reduce fracture risk in postmenopausal women.

Effects of Single or Multiple Sessions of Whole Body Vibration in Stroke: Is There Any Evidence to Support the Clinical Use in Rehabilitation?

Background and Purpose

Recently new technologies and new techniques, such as Whole Body Vibration (WBV), have been introduced by the health and fitness industry to pursue therapeutic or physical performance goals. The aim of this systematic review is to investigate the effectiveness of single or multiple WBV sessions alone or in association with traditional rehabilitation, compared to traditional rehabilitation therapy or with sham therapy in poststroke patients.

Methods

Randomized Control Trials and controlled clinical trials written in English between January 1st, 2003, and December 31st, 2017, were selected from PubMed, Cochrane-Central-Register-of-Controlled-Trials, and Physiotherapy-Evidence-Database (PEDro). The single WBV session and multiple sessions' effects were assessed. Study characteristics, study population, intervention protocols, effects of WBV sessions, and adverse events were investigated with a descriptive analysis.

Results

The search reported 365 articles and after screening and removal of duplicates, 11 manuscripts with PEDro score≥6/10 were selected (391 poststroke patients). Study characteristics, study population, intervention protocols (frequencies, amplitude of vibration, and peak acceleration), effects of a single or multiple WBV sessions, and adverse events were analyzed. They have been investigated with particular attention to bone turnover, structure and muscle functions, spasticity, postural control and risk of falls, functional mobility, somatosensory threshold, and activity and participation. Comparing WBV group with control group no significant benefits emerged.

Discussion

This systematic review included studies involving participants with non homogeneous characteristics, just considering the incorporation of studies on individuals with chronic and postacute stroke. Despite these limits, WBV treatment has no significant risks for patients and shows interesting effects of WBV treatment in Structure and muscle functions, Spasticity and Postural control.

Conclusions

Even though treatment with WBV appears safe and feasible, there is insufficient evidence to support its clinical use in poststroke rehabilitation at this point. More studies assessing other functional tests and with more specific treatment protocols are needed.

Total and regional bone mineral and tissue composition in female adolescent athletes: comparison between volleyball players and swimmers

Background

Exploring the osteogenic effect of different bone-loading sports is particular relevant to understand the interaction between skeletal muscle and bone health during growth. This study aimed to compare total and regional bone and soft-tissue composition between female adolescent swimmers (n=20, 15.71±0.93 years) and volleyball players (n=26, 16.20±0.77 years).

Methods

Dietary intake was obtained using food frequency questionnaires. Body size was given by stature, sitting height, and body mass. Six skinfolds were measured. Bone mineral content (BMC) and density (BMD), lean soft tissue, and fat tissue were assessed using dual-energy X-ray absorptiometry. Pearson’s product moment correlation coefficients were calculated to examine the relationships among variables, by type of sport. Comparisons between swimmers and volleyball players were performed using student t-tests for independent samples and multivariate analysis of covariance (controlling for age, training history and body size).

Results

Swimmers (BMC: 2328±338 g) and volleyball players (BMC: 2656±470 g) exceeded respectively by 2.1 and 2.8 standard deviation scores the average of international standards for whole body BMC of healthy adolescents. Years of training in swimmers were positively related to the upper limbs BMC (r=+0.49, p<0.05). In volleyball players, years of training correlated significantly with lower limbs BMD (r=+0.43, p<0.05). After adjustments for potential confounders, moderate differences (ES-r=0.32) between swimmers and volleyball players were noted in BMD at the lower limbs (volleyball players: +0.098 g∙cm^-2, +7.8%).

Conclusions

Youth female athletes who participate in high-intensity weight-loading activities such as volleyball exhibit moderately higher levels of BMD at the lower limbs compared to non-loading sports such as swimming.

Electronic supplementary material

The online version of this article (10.1186/s12887-018-1182-z) contains supplementary material, which is available to authorized users.

Transient peak-strain matching partially recovers the age-impaired mechanoadaptive cortical bone response

Mechanoadaptation maintains bone mass and architecture; its failure underlies age-related decline in bone strength. It is unclear whether this is due to failure of osteocytes to sense strain, osteoblasts to form bone or insufficient mechanical stimulus. Mechanoadaptation can be restored to aged bone by surgical neurectomy, suggesting that changes in loading history can rescue mechanoadaptation. We use non-biased, whole-bone tibial analyses, along with characterisation of surface strains and ensuing mechanoadaptive responses in mice at a range of ages, to explore whether sufficient load magnitude can activate mechanoadaptation in aged bone. We find that younger mice adapt when imposed strains are lower than in mature and aged bone. Intriguingly, imposition of short-term, high magnitude loading effectively primes cortical but not trabecular bone of aged mice to respond. This response was regionally-matched to highest strains measured by digital image correlation and to osteocytic mechanoactivation. These data indicate that aged bone’s loading response can be partially recovered, non-invasively by transient, focal high strain regions. Our results indicate that old murine bone does respond to load when the loading is of sufficient magnitude, and bones’ age-related adaptation failure may be due to insufficient mechanical stimulus to trigger mechanoadaptation.

Distal radius microstructure and finite element bone strain are related to site-specific mechanical loading and areal bone mineral density in premenopausal women

While weight-bearing and resistive exercise modestly increases aBMD, the precise relationship between physical activity and bone microstructure, and strain in humans is not known. Previously, we established a voluntary upper-extremity loading model that assigns a person's target force based on their subject-specific, continuum FE-estimated radius bone strain. Here, our purpose was to quantify the inter-individual variability in radius microstructure and FE-estimated strain explained by site-specific mechanical loading history, and to determine whether variability in strain is captured by aBMD, a clinically relevant measure of bone density and fracture risk. Seventy-two women aged 21–40 were included in this cross-sectional analysis. High resolution peripheral quantitative computed tomography (HRpQCT) was used to measure macro- and micro-structure in the distal radius. Mean energy equivalent strain in the distal radius was calculated from continuum finite element models generated from clinical resolution CT images of the forearm. Areal BMD was used in a nonlinear regression model to predict FE strain. Hierarchical linear regression models were used to assess the predictive capability of intrinsic (age, height) and modifiable (body mass, grip strength, physical activity) predictors. Fifty-one percent of the variability in FE bone strain was explained by its relationship with aBMD, with higher density predicting lower strains. Age and height explained up to 31.6% of the variance in microstructural parameters. Body mass explained 9.1% and 10.0% of the variance in aBMD and bone strain, respectively, with higher body mass indicative of greater density. Overall, results suggest that meaningful differences in bone structure and strain can be predicted by subject characteristics.

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Areal bone mineral density (aBMD) explains 51% of the variability in bone strain.

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Adult bone loading predicts greater cortical porosity and trabecular density.

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Greater body mass predicts greater aBMD and lower bone strain.

A mathematical multiscale model of bone remodeling, accounting for pore space-specific mechanosensation

While bone tissue is a hierarchically organized material, mathematical formulations of bone remodeling are often defined on the level of a millimeter-sized representative volume element (RVE), "smeared" over all types of bone microstructures seen at lower observation scales. Thus, there is no explicit consideration of the fact that the biological cells and biochemical factors driving bone remodeling are actually located in differently sized pore spaces: active osteoblasts and osteoclasts can be found in the vascular pores, whereas the lacunar pores host osteocytes - bone cells originating from former osteoblasts which were then "buried" in newly deposited extracellular bone matrix. We here propose a mathematical description which considers size and shape of the pore spaces where the biological and biochemical events take place. In particular, a previously published systems biology formulation, accounting for biochemical regulatory mechanisms such as the rank-rankl-opg pathway, is cast into a multiscale framework coupled to a poromicromechanical model. The latter gives access to the vascular and lacunar pore pressures arising from macroscopic loading. Extensive experimental data on the biological consequences of this loading strongly suggest that the aforementioned pore pressures, together with the loading frequency, are essential drivers of bone remodeling. The novel approach presented here allows for satisfactory simulation of the evolution of bone tissue under various loading conditions, and for different species; including scenarios such as mechanical dis- and overuse of murine and human bone, or in osteocyte-free bone.

Evaluation of loading parameters for murine axial tibial loading: Stimulating cortical bone formation while reducing loading duration

Classic studies in bone mechanobiology have established the importance of loading parameters on the anabolic response. Most of these early studies were done using loading methods not currently in favor, and using non-murine species. Our objective was to re-examine the effects of several loading parameters on the response of cortical bone using the contemporary murine axial tibial compression model. We subjected tibias of 5-month old, female C57Bl/6 mice to cyclic (4 Hz) mechanical loading and examined bone formation responses using dynamic and static histomorphometry. First, using a reference protocol of 1,200 cycles/day, 5 days/week for 2 weeks, we confirmed the significant influence of peak strain magnitude on periosteal mineralizing surface (Ps.MS/BS) and bone formation rate (Ps.BFR/BS) (p < 0.05, ANOVA). There was a significant induction of periosteal lamellar bone at a lower threshold of approx. -1,000 μϵ and a transition from lamellar-woven bone near -2,000 μϵ. In contrast, on the endocortical surface, bone formation indices did not exhibit a load magnitude-dependent response and no incidence of woven bone. Next, we found that reducing daily cycle number from 1,200 to 300 to 60 did not diminish the bone formation response (p > 0.05). On the other hand, reducing the daily frequency of loading from 5 consecutive days/week to 3 alternate days/week significantly diminished the periosteal response, from a loading-induced increase in Ps.MS/BS of 38% (loaded vs. control) for 5 days/week to only 15% for 3 days/week (p < 0.05). Finally, we determined that reducing the study duration from 2 to 1 weeks of loading did not affect bone formation outcomes. In conclusion, cyclic loading to -1,800 μϵ peak strain, at 4 Hz and 60 cycles/day for 5 consecutive days (1 week) induces an increase in periosteal lamellar bone formation with minimal incidence of woven bone in 5-month-old C57Bl/6 female mice. Our results provide a basis for reduction of loading duration (daily cycles and study length) without loss of anabolic effect as measured by dynamic histomorphometry. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:682-691, 2018.

Effects of Body Mass Index on Bone Loading Due to Physical Activity

The aim of the current study was to compare bone loading due to physical activity between lean, and overweight and obese individuals. Fifteen participants (lower BMI group: BMI < 25 kg/m², n = 7; higher BMI group: 25 kg/m² < BMI < 36.35 kg/m², n = 8) wore a tri-axial accelerometer on 1 day to collect data for the calculation of bone loading. The International Physical Activity Questionnaire (short form) was used to measure time spent at different physical activity levels. Daily step counts were measured using a pedometer. Differences between groups were compared using independent t-tests. Accelerometer data revealed greater loading dose at the hip in lower BMI participants at a frequency band of 0.1-2 Hz (P = .039, Cohen's d = 1.27) and 2-4 Hz (P = .044, d = 1.24). Lower BMI participants also had a significantly greater step count (P = .023, d = 1.55). This corroborated with loading intensity (d ≥ 0.93) and questionnaire (d = 0.79) effect sizes to indicate higher BMI participants tended to spend more time in very light activity, and less time in light and moderate activity. Overall, participants with a lower BMI exhibited greater bone loading due to physical activity; participants with a higher BMI may benefit from more light and moderate level activity to maintain bone health.

Hip and spine bone mineral density are greater in master sprinters, but not endurance runners compared with non-athletic controls

We examined bone density in older athletes and controls. Sprinters had greater hip and spine bone density than endurance athletes and controls, whereas values were similar in the latter two groups. These results could not be explained by differences in impact, muscle size or power between sprint and endurance athletes.

PURPOSE

We examined the relationship between prolonged participation in regular sprint or endurance running and skeletal health at key clinical sites in older age, and the factors responsible for any associations which we observed.

METHODS

We recruited 38 master sprint runners (28 males, 10 females, mean age 71 ± 7 years), 149 master endurance runners (111 males, 38 females, mean age 70 ± 6 years) and 59 non-athletic controls (29 males, 30 females, mean age 74 ± 5 years). Dual X-ray absorptiometry was used to assess hip and spine bone mineral density (BMD), body composition (lean and fat mass), whilst jump power was assessed with jumping mechanography. In athletes, vertical impacts were recorded over 7 days from a waist-worn accelerometer, and details of starting age, age-graded performance and training hours were recorded.

RESULTS

In ANOVA models adjusted for sex, age, height, body composition, and jump power, sprinter hip BMD was 10 and 14% greater than that of endurance runners and controls respectively. Sprinter spine BMD was also greater than that of both endurance runners and controls. There were no differences in hip or spine BMD between endurance runners and controls. Stepwise regression showed only discipline (sprint/endurance), sex, and age as predictors of athlete spine BMD, whilst these variables and starting age were predictive of hip BMD.

CONCLUSIONS

Regular running is associated with greater BMD at the fracture-prone hip and spine sites in master sprinters but not endurance runners. These benefits cannot be explained by indicators of mechanical loading measured in this study including vertical impacts, body composition or muscular output.

Plausibility and parameter sensitivity of micro-finite element-based joint load prediction at the proximal femur

A micro-finite element-based method to estimate the bone loading history based on bone architecture was recently presented in the literature. However, a thorough investigation of the parameter sensitivity and plausibility of this method to predict joint loads is still missing. The goals of this study were (1) to analyse the parameter sensitivity of the joint load predictions at one proximal femur and (2) to assess the plausibility of the results by comparing load predictions of ten proximal femora to in vivo hip joint forces measured with instrumented prostheses (available from www.orthoload.com ). Joint loads were predicted by optimally scaling the magnitude of four unit loads (inclined [Formula: see text] to [Formula: see text] with respect to the vertical axis) applied to micro-finite element models created from high-resolution computed tomography scans ([Formula: see text]m voxel size). Parameter sensitivity analysis was performed by varying a total of nine parameters and showed that predictions of the peak load directions (range 10[Formula: see text]-[Formula: see text]) are more robust than the predicted peak load magnitudes (range 2344.8-4689.5 N). Comparing the results of all ten femora with the in vivo loading data of ten subjects showed that peak loads are plausible both in terms of the load direction (in vivo: [Formula: see text], predicted: [Formula: see text]) and magnitude (in vivo: [Formula: see text], predicted: [Formula: see text]). Overall, this study suggests that micro-finite element-based joint load predictions are both plausible and robust in terms of the predicted peak load direction, but predicted load magnitudes should be interpreted with caution.

Bouts of Vigorous Physical Activity and Bone Strength Accrual During Adolescence

PURPOSE

We examined the influence of vigorous physical activity (VPA) bout frequency on bone strength accrual across adolescence, independent of total volume of VPA.

METHODS

We measured VPA (6 metabolic equivalents; total volume and bout frequency <5 min in duration) annually using waist-worn accelerometers (ActiGraph GT1M) in 309 adolescents (9-20 y at baseline: 99, <13 y; 126, 13-18 y; 84, >18 y) over a maximum of 4 years. We applied finite element analysis to high-resolution peripheral quantitative computed tomography scans of the distal tibia (8% site) to estimate bone strength (failure load; F.Load, Newtons). We fit a mixed effects model with maturity offset (years from age at peak height velocity) as a random effect and sex, ethnicity, tibia length, lean body mass, and VPA (volume and bout frequency) as fixed effects.

RESULTS

VPA volume and bout frequency were positively associated with F.Load across adolescence; however, VPA volume did not predict F.Load once VPA bout frequency was included in the model. Participants in the upper quartile of VPA bout frequency (∼33 bouts per day) had 10% (500 N) greater F.Load across adolescence compared with participants in the lowest quartile (∼9 bouts per day; P = .012). Each additional daily bout of VPA was associated with 21 N greater F.Load, independent of total volume of VPA.

CONCLUSION

Frequent VPA should be promoted for optimal bone strength accrual.

HIGH-IMPACT DROP EXERCISE ALTERS MECHANICAL PROPERTIES IN OSTEOPENIC BONE

ABSTRACT Introduction: Osteopenia is a reversible condition and precedes osteoporosis. Physical activity and mechanical loading appear to play an important role in the regulation of bone homeostasis, without the side effects of targeted drug therapy. However, there is controversy as to which type of stimulus promotes more effective adaptations with respect to mechanical properties of bones. Objective: To investigate the effects of high-impact drop training on bone structure after ovariectomy-induced osteopenia in 40 10-week-old female Wistar rats. Methods: Twenty female rats (prevention program) were randomly assigned into two groups (n=10): Ovariectomized sedentary (OVXs), and OVX trained (OVX+Dropt). OVX+Dropt animals began training 3 days after surgery. Another twenty female rats (treatment program) were randomly assigned to two other groups (n=10): Ovariectomized sedentary (OVXs), and OVX trained (OVX+Dropt). OVX+Dropt animals began training 60 days after surgery. The rats in the trained groups were dropped from 40 cm height 20 times/day, 5 days/week over a period of 12 weeks period. At the end, the biomechanical tests were analyzed. Results: The final load and stiffness of the left tibia in the trained groups were higher than in the sedentary groups (p<0.05). Conclusions: Dropping exercise induced favorable changes in bone mechanical properties. High-impact drop exercise is effective to prevent bone loss after ovariectomy even when osteopenia is already established.