Paradoxical adaptation of mature radius to unilateral use in tennis playing

Inter-arm bone mass and size asymmetries in children tennis players are maturity status specific: a 9-month study on the effects of training time across pubertal change and somatic growth

PURPOSE

Bone growth with exercise is best assessed by tennis-induced inter-arm asymmetries. Yet, the effects of training and maturation across puberty were unclear. This study explored arm bone growth across 9 months of training in 46 tennis players 7-14 years (25 boys, 21 girls).

METHODS

Bone mineral content (BMC) and bone area (BA) were measured from DXA scans. Pubertal status was assessed by Tanner stage (TS) and somatic growth by maturity offset (MO). Children were grouped as pre- (TS I-I), early (TS I-II), and mid/late pubertal (TS II-III).

RESULTS

Training time (TT) change in the three groups was 160-170, 190-230, and 200-220 h, respectively. Bone asymmetries were large in all groups (d > 0.8, P < 0.001): 5-18 g (9-21%) and 9-17 g (17-23%) in girls and boys, respectively, for BMC, and 5-15 cm2 (6-13%) and 9-15 cm2 (12-15%) in girls and boys (10-13%), respectively, for BA. BMC and BA change asymmetry peaked at pre-puberty in girls (56%, 46%) and at early puberty in boys (57%, 43%). Asymmetry gains varied with baseline asymmetry (41%) and change in TT (38%) and TS (17%) in BMC, and with baseline asymmetry (58%) and change in MO (17%) and TS (12%) in BA.

CONCLUSION

All bone asymmetries were substantial. Tennis-induced bone gains were higher at pre- to early puberty in girls and at early to mid/late puberty in boys. Training enhanced mostly bone mass and maturity status enhanced mostly bone size; sex was not bone-change modeling impactful. Implications are discussed considering certain limitations.

Bone asymmetries in the limbs of children tennis players: testing the combined effects of age, sex, training time, and maturity status

This study estimated upper and lower limb bone mineral content (BMC) and bone area (BA) in 48 children tennis players (24 boys, 24 girls) aged 7-13 years. The sample comprised four age groups (8.2 ± 0.44, 9.5 ± 0.13, 10.5 ± 0.33, 12.2 ± 0.58). BMC and BA were measured via DXA, and sexual maturity by the Tanner scale, then used as a binary: prepubertal vs peripubertal. Total training time (TTT) included all playing years. Arms were asymmetric and legs symmetric. Boys were more asymmetric than girls in BMC (18% vs 13%) and BA (11% vs 8%). Pre-pubertal children were less asymmetric than peri-pubertal in BMC (14% vs 18%) and in BA (9.4% vs 10%). Bone growth changed with age and TTT markedly better in the dominant arm. The linear combination of TTT, sex, and maturity binary extracted 59% of BMC asymmetry and only 21% of BA asymmetry. For both bone parameters the sex effect was significant only for the pre-pubertal children. Training time constitutes the best predictor of bone asymmetry compared to age, sex, and maturity; when adequate, playing arm bone hypertrophy may be detectable at the age of 7-8 years. These results have health and performance implications.

Study of human radius construction systematics: evaluation by DXA in dry bone

This study has been undertaken in order to describe the bone mass distribution of the dry human radius via dual x-ray absorptiometry (DXA) with a Norland XR-800 densitometer machine. A sample of 39 dry radius bones was used. Two projections were made: antero-posterior and lateral, and five regions of interest were selected. The bone densities and the bone mineral contents of the various regions of the radius in the two projections were compared using Student's t tests for paired samples, with statistically significant differences being found in all of the values, except in the proximal extremity (P Ext). The area of greatest bone mineral content (BMC) was the medial diaphysis (M Diaph), followed by the distal extremity (D Ext), with the lowest value being found in the proximal extremity (P Ext). As for bone mineral density (BMD), a great symmetry is observed if we take the mean point of the longitudinal axis as a reference, with it being distributed from highest to lowest from the central part to the extremities. A correlation study of the BMD and BMC values between the segments themselves and with the total, in both positions, provides us with a high correlation (p ≤ 0.01), with the highest correlation value being found for the proximal diaphysis (P Diaph) region, indicating the heterogeneous nature of the distribution of the radius bone mass. Bone densitometry via DXA is useful in order to establish an overview of the structural construction of the human radius.

Effects of age and starting age upon side asymmetry in the arms of veteran tennis players: a cross-sectional study

While tennis playing results in large bone strength benefits in the racquet arm of young players, the effects of tennis playing in old players have not been investigated. Large side asymmetries in bone strength were found in veteran players, which were more pronounced in men, younger players and childhood starters.

INTRODUCTION

Regular tennis results in large racquet arm bone and muscle strength advantages; however, these effects have not been studied in old players. The non-racquet arm can act as an internal control for the exercising racquet arm without confounding factors, e.g. genotype. Therefore, veteran tennis player side asymmetries were examined to investigate age, sex and starting age effects on bone exercise benefits.

METHODS

Peripheral quantitative computed tomography (pQCT) scans were taken at the radius, ulna and humerus mid-shaft and distal radius in both arms of 88 tennis players (51 males, 37 females; mean age 63.8 ± 11.8 years). Thirty-two players began playing in adulthood, thereby termed 'old starters'; players were otherwise termed 'young starters'.

RESULTS

Muscle size and bone strength were greater in the racquet arm; notably, distal radius bone mineral content (BMC) was 13 ± 10% higher and humeral bone area 23 ± 12% larger (both P < 0.001). Epiphyseal BMC asymmetry was not affected by age (P = 0.863) or sex (P = 0.954), but diaphyseal asymmetries were less pronounced in older players and women, particularly in the humerus where BMC, area and moment of resistance asymmetries were 28-34 % less in women (P < 0.01). Bone area and periosteal circumference asymmetries were smaller in old starters (all P < 0.01); most notably, no distal radius asymmetry was found in this group (0.4 ± 3.4%).

CONCLUSIONS

Tennis participation is associated with large side asymmetries in muscle and bone strength in old age. Larger relative side asymmetries in men, younger players and young starters suggest a greater potential for exercise benefits to bone in these groups.

Effects of repetitive loading on the growth-induced changes in bone mass and cortical bone geometry: a 12-month study in pre/peri- and postmenarcheal tennis players

Pre- and early puberty may be the most opportune time to strengthen the female skeleton, but there are few longitudinal data to support this claim. Competitive female premenarcheal (pre/peri, n = 13) and postmenarcheal (post, n = 32) tennis players aged 10 to 17 years were followed over 12 months. The osteogenic response to loading was studied by comparing the playing and nonplaying humeri for dual-energy X-ray absorptiometry (DXA) bone mineral content (BMC) and magnetic resonance imaging (MRI) total bone area (ToA), medullary area (MedA), cortical area (CoA), and muscle area (MCSA) at the humerus. Over 12 months, growth-induced gains (nonplaying arm) in BMC, ToA, and CoA were greater in pre/peri (10% to 19%, p < .001) than in post (3% to 5%, p < .05 to .001) players. At baseline, BMC, ToA, CoA, and MCSA were 8% to 18% greater in the playing versus nonplaying arms in pre/peri and post players (all p < .001); MedA was smaller in the playing versus nonplaying arms in post only players (p < .05). When comparing the annual gains in the playing arm relative to changes in the nonplaying arm, the increases in ToA and CoA were greater in pre/peri than post players (all p < .05). The smaller the side-to-side differences in BMC and CoA at baseline, the larger the exercise benefits at 12 months (r = -0.39 to -0.48, p < .01). The exercise-induced change in MCSA was predictive of the exercise benefits in BMC in pre/peri players only (p < .05). In conclusion, both pre/peri- and postmenarcheal tennis players showed significant exercise-induced skeletal benefits within a year, with greater benefits in cortical bone geometry in pre/perimenarcheal girls.

Association of physical activity with trabecular microstructure and cortical bone at distal tibia and radius in young adult men

CONTEXT

The relationship between physical activity, trabecular microstructure, and cortical geometry in weight-bearing and non-weight-bearing bone has not previously been studied in men.

OBJECTIVE

The aim of this study was to investigate whether present (type and amount) and previous duration of physical activity were associated with trabecular microstructure and cortical cross-sectional area (CSA) in weight-bearing bone in young men.

DESIGN AND SETTING

This was a cross-sectional, population-based study.

PARTICIPANTS

Participants included a cohort of 829 Swedish men between 22.8 and 25.7 yr old (24.1 +/- 0.6 yr, mean +/- SD).

MAIN OUTCOME MEASURES

Several microstructural trabecular and cortical traits were assessed with high-resolution three-dimensional peripheral quantitative computed tomography at distal tibia and radius. A standardized questionnaire was used to collect information about physical activity amount (hours per year), duration (years), and type (strain score 0-3, based on ground reaction forces).

RESULTS

Men with the highest physical activity strain score had higher tibial trabecular bone volume fraction (13.9Delta%) and trabecular number (12.7%) than men with the lowest strain score (P < 0.001). Men in the group with the longest duration of physical activity had higher tibial cortical CSA (16.1%) than the sedentary men (P < 0.001). Inclusion of all physical activity variables in a linear regression model revealed that strain score independently predicted trabecular bone volume fraction, and trabecular number (P < 0.001) and that duration of previous physical activity independently predicted cortical CSA (P < 0.001) of the tibia.

CONCLUSIONS

In this large cohort of young men, the degree of mechanical loading due to type of physical activity was predominantly associated with trabecular microstructure, whereas duration of previous physical activity was mainly related to parameters reflecting cortical bone size in weight-bearing bone.

Genetic selection for fast growth generates bone architecture characterised by enhanced periosteal expansion and limited consolidation of the cortices but a diminution in the early responses to mechanical loading

Bone strength is, in part, dependent on a mechanical input that regulates the (re)modelling of skeletal elements to an appropriate size and architecture to resist fracture during habitual use. The rate of longitudinal bone growth in juveniles can also affect fracture incidence in adulthood, suggesting an influence of growth rate on later bone quality. We have compared the effects of fast and slow growth on bone strength and architecture in the tibiotarsi of embryonic and juvenile birds. The loading-related biochemical responses (intracellular G6PD activity and NO release) to mechanical load were also determined. Further, we have analysed the proliferation and differentiation characteristics of primary tibiotarsal osteoblasts from fast and slow-growing strains. We found that bones from chicks with divergent growth rates display equal resistance to applied loads, but weight-correction revealed that the bones from juvenile fast growth birds are weaker, with reduced stiffness and lower resistance to fracture. Primary osteoblasts from slow-growing juvenile birds proliferated more rapidly and had lower alkaline phosphatase activity. Bones from fast-growing embryonic chicks display rapid radial expansion and incomplete osteonal infilling but, importantly, lack mechanical responsiveness. These findings are further evidence that the ability to respond to mechanical inputs is crucial to adapt skeletal architecture to generate a functionally appropriate bone structure and that fast embryonic and juvenile growth rates may predispose bone to particular architectures with increased fragility in the adult.

Previous sport activity during childhood and adolescence is associated with increased cortical bone size in young adult men

Physical activity during growth has been associated with altered cortical bone geometry, but it remains uncertain if the physical activity-induced increments in cortical bone size remain when the level of physical activity is diminished or ceased. The aim of this study was to investigate if physical activity during growth is associated with cortical bone geometry in currently inactive young men. In this study, 1068 men (18.9 +/- 0.6 [SD] yr) were included. Cortical bone geometry at the tibia and radius were measured using pQCT. A standardized questionnaire was used to collect information about current and previous sport activity. Subjects who continued to be active (n = 678) and who had been previously active (n = 285) in sports had a wider cortical bone (periosteal circumference [PC], 4.5% and 3.2%, respectively) with increased cross-sectional area (CSA; 12.5% and 6.9%) of the tibia than the always inactive subjects (n = 82). In the currently inactive men (n = 367), regression analysis (including covariates age, height, weight, calcium intake, smoking, and duration of inactivity) showed that previous sport activity was independently associated with cortical bone size of the tibia (CSA and PC). Amount of previous sport activity explained 7.3% of the total variation in cortical CSA. Subjects, who ceased their sport activity for up to 6.5 yr previously, still had greater cortical PC and CSA of the tibia than always inactive subjects. The results from this study indicate that sport activity during growth confers positive effects on bone geometry even though sport activity is ceased.

Exercise for optimising peak bone mass in women

Physical activity is one of the major non-pharmacological methods for increasing and maintaining bone mineral density (BMD) and geometry. As such, it has an important role in maintaining peak bone mass and strength, thus reducing the risk of future osteoporotic fracture. However, not all exercise is effective, so a prescription in terms of optimal type, intensity, frequency and duration is required. Studies using animal models suggest that loading that is high in magnitude, rapidly applied and novel is most effective, whilst duration is less important beyond a threshold number of cycles. In human subjects cross-sectional studies comparing different athletic populations suggest that those who participate in high- or odd-impact sports have higher BMD; whilst impact exercise, strength training and brief high-impact-jump training interventions increase BMD in premenopausal women. In order to further elucidate exercise recommendations to optimise bone health in this population, the usefulness of brief high-impact unilateral exercises has been evaluated. Brief hopping exercises were shown to be feasible for sedentary premenopausal women, producing ground-reaction forces as high as those from jumping. Regularly performing these hopping exercises over 6 months was found to increase femoral-neck BMD of the trained leg relative to the control leg. Unilateral high-impact exercise may therefore improve bone strength of the trained limb and provide a useful model for comparing exercise prescriptions to help define the most efficient and effective exercise recommendations for the bone health of premenopausal women.

Health benefits of tennis

The aim of the study was to explore the role of tennis in the promotion of health and prevention of disease. The focus was on risk factors and diseases related to a sedentary lifestyle, including low fitness levels, obesity, hyperlipidaemia, hypertension, diabetes mellitus, cardiovascular disease, and osteoporosis. A literature search was undertaken to retrieve relevant articles. Structured computer searches of PubMed, Embase, and CINAHL were undertaken, along with hand searching of key journals and reference lists to locate relevant studies published up to March 2007. These had to be cohort studies (of either cross sectional or longitudinal design), case-control studies, or experimental studies. Twenty four studies were identified that dealt with physical fitness of tennis players, including 17 on intensity of play and 16 on maximum oxygen uptake; 17 investigated the relation between tennis and (risk factors for) cardiovascular disease; and 22 examined the effect of tennis on bone health. People who choose to play tennis appear to have significant health benefits, including improved aerobic fitness, a lower body fat percentage, a more favourable lipid profile, reduced risk for developing cardiovascular disease, and improved bone health.

Side differences in the bone density of the distal radius and calcaneus in Koreans aged 4-86 years

Although bone mineral density (BMD) measurements of peripheral bone have been widely used due to practical and economic factors, a consensus does not exist as to whether the dominant or nondominant side is preferable for diagnosing osteoporosis and predicting fracture risk. Thus, we evaluated BMD differences of the distal radius and calcaneus between dominant and nondominant sides in the Korean population. Data were collected from 1794 subjects (979 females and 815 males) aged 4-86 yr, who were not taking any medication that affected bone metabolism or had a history of fracture. All subjects completed a questionnaire, and anthropometric and BMD measurements were taken. BMD values at the distal radii and calcanei were measured by dual-energy X-ray absorptiometry using a Lunar instrument. Significant correlations were observed between the dominant and nondominant distal radii (r=0.92; p<0.0001) and calcanei (r=0.94; p<0.0001). A side difference for the distal radius was not observed, whereas a significant side difference for the calcaneus was detected (p<0.05). Our findings provide information for recommending a sampling site upon measuring the distal radius and calcaneus during clinical or community-based studies.

Intraskeletal variability in bone mass

For methodological or other reasons, a variety of skeletal elements are analyzed and subsequently used as a basis for describing general bone loss and mass. However, bone loss and mass may not be uniform within and among skeletal elements of the same individual because of biomechanical factors. We test the hypothesis that a homogeneity in bone mass exists among skeletal elements of the same individual. Measures indicative of bone mass were calculated from the midshafts of six skeletal elements from the same individuals (N = 41). The extent of intraskeletal variability in bone mass (relative cortical area) was then examined for the entire sample, according to age, sex, and pathological status. The results of the analysis showed that all measures reflect a heterogeneity in bone mass (P </= 0.001). Specifically, differences were observed between the bones of the upper limb and those of the lower limb. Both sexes showed intraskeletal variability in bone mass, but the difference between the sexes is not significant (P = 0.509). When the sample is subdivided according to age, all groups show intraskeletal variability in bone mass, but the difference did not differ significantly among the groups (P = 0.217). However, significant differences in intraskeletal variability are observed between individuals below and above the age of 50. Pathological individuals show intraskeletal variability in bone mass, but the difference between the pathological and non-pathological groups is not significant (P = 0.095). These results indicate that the bone mass of any particular skeletal element is intricately tethered to its specific mechanical loading environment.

Side-to-side differences in cortical bone mineral density of tibiae in young male athletes

The importance of physical activity in the development and maintenance of bone mineral density (BMD) is widely accepted. However, the effects on cortical BMD have not been clarified in detail. The present study examined bilateral asymmetries in cortical BMD of the tibia using peripheral quantitative computed tomography. Subjects comprised 37 young male athletes and 57 controls (age range, 18-28 years). BMD and geometrical indices were determined in bilateral tibiae. Cortical and trabecular BMD were calculated at the diaphysis and distal metaphysis, respectively. Cortical width, periosteal cross-sectional area, and cross-sectional moment of inertia were calculated using tomographic data of the tibial diaphysis. In athletes, the non-dominant leg showed greater cortical BMD than the dominant leg (mean difference, 5.42%; P < 0.0001). Cortical width and moment of inertia were also greater in the non-dominant leg. Periosteal area displayed no significant difference between legs. The control group exhibited similar results except for cortical BMD. No differences in trabecular BMD were noted between legs in either athletes or controls. These results implies the existence of mechanisms for the mechanical adaptation of cortical BMD. Dominant leg is used for mobility or manipulation whereas the non-dominant leg contributes to support the actions of the dominant leg. Loading differences in bilateral legs in young athletes might affect the remodeling rate leading to the side-to-side differences in cortical BMD.

Short-term and long-term site-specific effects of tennis playing on trabecular and cortical bone at the distal radius

Mechanical loading during growth magnifies the normal increase in bone diameter occurring in long bone shafts, but the response to loading in long bone ends remains unclear. The aim of the study was to investigate the effects of tennis playing during growth at the distal radius, comparing the bone response at trabecular and cortical skeletal sites. The influence of training duration was examined by studying bone response in short-term (children) and long-term (young adults) perspectives. Bone area, bone mineral content (BMC), and bone mineral density (BMD) of the radius were measured by DXA in 28 young (11.6 +/- 1.4 years old) and 47 adult tennis players (22.3 +/- 2.7 years old), and 70 age-matched controls (12 children, 58 adults) at three sites: the ultradistal region (trabecular), the mid-distal region, and the third-distal region (cortical). At the ultradistal radius, young and adult tennis players displayed similar side-to-side differences, the asymmetry in BMC reaching 16.3% and 13.8%, respectively (P < 0.0001). At the mid- and third-distal radius, the asymmetry was much greater in adults than in children (P < 0.0001) for all the bone parameters (mid-distal radius, +6.6% versus +15.6%; third-distal radius, +6.9% versus +13.3%, for BMC). Epiphyseal bone enduring longitudinal growth showed a great capacity to respond to mechanical loading in children. Prolonging tennis playing into adulthood was associated with further increase in bone mineralization at diaphyseal skeletal sites. These findings illustrate the benefits of practicing impact-loading sports during growth and maintaining physical activity into adulthood to enhance bone mass accrual and prevent fractures later in life.

Influence of physical activity and maturation status on bone mass and geometry in early pubertal girls

This study aimed to evaluate the influence of leisure-time physical activity on the development of bone mass and density in early pubertal girls. Scores of physical activity were obtained from 242 Finnish girls (10-12 years old within Tanner Stages I-II) using a questionnaire. Bone mass and density were assessed using different densitometric techniques. At Tanner Stage I, active girls had significantly higher bone mineral mass (BMC) and areal bone mineral density (aBMD) of the whole body and cortical volumetric BMD and thickness of the tibial shaft compared with sedentary girls (P<0.05). On the other hand, the active girls at Tanner Stage II showed significantly higher values only in BMC and aBMD at the lumbar spine (P=0.017 and P=0.007, respectively). These indicated that girls at Tanner Stage I with higher leisure-time physical activity level benefited more from physical activity in terms of their bone development than their less active counterparts. Our results provide evidence that the most beneficial time for physical exercise to exhibit its effect on bone development is in the earlier pubertal period for normal school children, but the positive effect on the lumbar spine is also demonstrated in Tanner Stage II.

Inter-arm asymmetry in bone mineral content and bone area in postmenopausal recreational tennis players

OBJECTIVE

To determine whether long-term recreational tennis participation is associated with increased bone and muscle mass in the dominant compared to the non-dominant arm, in postmenopausal tennis players.

METHODS

Dual-energy X-ray whole body scans were performed in 10 postmenopausal tennis players (mean +/- S.D.; 59.7 +/- 4.8 years) and 12 postmenopausal non-active women (62.8 +/- 7.2 years) matched for age and height. Tennis players started in this sport at 31.4 +/- 8.8 years, and had been playing for 26.8 +/- 6.8 years, at least 3 h per week. In addition, shoulder isokinetic muscular strength was also evaluated.

RESULTS

Tennis participation resulted in a lower whole mass and fat mass in both arms (P < 0.05). Dominant arm muscle mass and shoulder joint isokinetic strength were essentially similar in both groups, however, the tennis players showed 8% greater bone mineral content and 7% greater osseous area in the dominant than in the non-dominant arm (P < 0.05). No inter-arm differences were found in bone mineral density. A relationship was observed between the length of tennis participation and the degree of inter-arm asymmetry in bone mineral content (r = 0.81, P < 0.01) and bone area (r = 0.78, P < 0.01). However, the BMD of the arms was essentially similar in both groups. No differences were observed in femoral and lumbar bone mass and density between groups.

CONCLUSIONS

Long-term tennis participation is associated with increased bone mass, but not BMD, in the dominant arm of postmenopausal tennis players. The magnitude of the inter-arm asymmetry of postmenopausal tennis players is proportional to the length of tennis participation.

Cortical and trabecular bone at the forearm show different adaptation patterns in response to tennis playing

Bone responds to impact-loading activity by increasing its size and/or density. The aim of this study was to compare the magnitude and modality of the bone response between cortical and trabecular bone in the forearms of tennis players. Bone area, bone mineral content (BMC), and bone mineral density (BMD) of the ulna and radius were measured by dual-energy X-ray absorptiometry (DXA) in 57 players (24.5 +/- 5.7 yr old), at three sites: the ultradistal region (50% trabecular bone), the mid-distal regions, and third-distal (mainly cortical bone). At the ultradistal radius, the side-to-side difference in BMD was larger than in bone area (8.4 +/- 5.2% and 4.9 +/- 4.0%, respectively, p < 0.01). In the cortical sites, the asymmetry was lower (p < 0.01) in BMD than in bone area (mid-distal radius: 4.0 +/- 4.3% vs 11.7 +/- 6.8%; third-distal radius: 5.0 +/- 4.8% vs 8.4 +/- 6.2%). The asymmetry in bone area explained 33% of the variance of the asymmetry in BMC at the ultradistal radius, 66% at the mid-distal radius, and 53% at the third-distal radius. The ulna displayed similar results. Cortical and trabecular bone seem to respond differently to mechanical loading. The first one mainly increases its size, whereas the second one preferentially increases its density.

Effects of physical training on cortical bone at midtibia assessed by peripheral QCT

Effects of long-term exercise on volumetric bone mineral density (vBMD), bone mineral content, bone geometric properties, and the strength indexes of bone were examined in a cross-sectional study of athletes and controls. Tibias of 25 jumpers (13 women), 30 swimmers (15 women), and 25 controls (15 women), aged 18-23 yr, were scanned at midsite by using peripheral quantitative computed tomography. The cortical vBMD of female athletes was lower than that of the controls (2.00 +/- 0.05, 1.90 +/- 0.08, and 1.92 +/- 0.12 g/cm3, respectively, for controls, swimmers, and jumpers). On the other hand, periosteal areas of male jumpers and female athletes were greater than that of controls (460 +/- 50, 483 +/- 46, and 512 +/- 55 mm2, respectively, for male controls, swimmers, and jumpers, and 283 +/- 52, 341 +/- 73, and 378 +/- 75 mm2, respectively, for female controls, swimmers, and jumpers). The endocortical area of female swimmers was greater than that of controls (103 +/- 29, 148 +/- 52, and 135 +/- 54 mm2, respectively, for controls, swimmers, and jumpers). The polar moment of inertia and strength strain index of male jumpers and female athletes were significantly greater than those of controls, except for the difference in strength strain index between male jumpers and controls. We conclude that the improvement of mechanical properties of young adult bone in response to long-term exercise is related to geometric adaptation and not to vBMD.