Me: It is important to note that only two sports were compared side by side, specifically soccer and swimming for the first study. What we see is that when the swimmers and soccer players are compared to control groups, the loading from weight by the soccer players resulted in an increase in bone mineral density (BMD) which results in an increase in bone strength, and increased thickness of the cortical area. Apparently the bone strength of swimmers seems to be even lower than the controls, which makes sense since we have seen astronauts who go into space will increase in height from decompression of spine but will drop dramatically bone mineral density, bone loss, and bone strength. This might suggest that the viscoelastic nature of water might do a similar effect on the human body allowing for it to expand longitudinally in the water but probably goes back to normal when the swimmer gets out of the water just like how the astronaut gets back to their normal height after spending time back on earth. We know the loading from soccer leads to stronger bones and thicker bones. However we are not clear whether it would lead to longer bones as well, which is what we have been trying to achieve.
For the second study, it seems that with old age, the medullary cavity decreases in apposition and increase in size. Exercise can help increase the endocortical apposition and cortical area from the inside thus resulting in slight shrinkage of the cavity. With boys, during puberty and post puberty, the periosteal apposition is higher than the cortical resorption so for males, the cortical area is larger. With females from the tennis study, the periostral apposition is also higher from exercise and loading before puberty but the cavity seems to increase from endocortical resorption. What is important to note is that the rising estrogen levels in the pubertal tennis players will result in less bone sensitivity to loading.
From PubMed study link HERE
Bone geometry and strength adaptations to physical constraints inherent in different sports: comparison between elite female soccer players and swimmers.
Laboratoire Interuniversitaire de Biologie des APS, EA 3533, PRES Clermont Université, Université Blaise Pascal, 24 avenue des Landais, BP 80026, 63177 Aubiere Cedex, France.
Sports training characterized by impacts or weight-bearing activity is well known to induce osteogenic effects on the skeleton. Less is known about the potential effects on bone strength and geometry, especially in female adolescent athletes. The aim of this study was to investigate hip geometry in adolescent soccer players and swimmers compared to normal values that stemmed from a control group. This study included 26 swimmers (SWIM; 15.9 ± 2 years) and 32 soccer players (SOC; 16.2 ± 0.7 years), matched in body height and weight. A group of 15 age-matched controls served for the calculation of hip parameter Z-scores. Body composition and bone mineral density (BMD) were assessed by dual-energy X-ray absorptiometry (DXA). DXA scans were analyzed at the femoral neck by the hip structure analysis (HSA) program to calculate the cross-sectional area (CSA), cortical dimensions (inner endocortical diameter, ED; outer width and thickness, ACT), the centroid (CMP), cross-sectional moment of inertia (CSMI), section modulus (Z), and buckling ratio (BR) at the narrow neck (NN), intertrochanteric (IT), and femoral shaft (FS) sites. Specific BMDs were significantly higher in soccer players compared with swimmers. At all bone sites, every parameter reflecting strength (CSMI, Z, BR) favored soccer players. In contrast, swimmers had hip structural analysis (HSA) Z-scores below the normal values of the controls, thus denoting weaker bone in swimmers. In conclusion, this study suggests an influence of training practice not only on BMD values but also on bone geometry parameters. Sports with high impacts are likely to improve bone strength and bone geometry. Moreover, this study does not support the argument that female swimmers can be considered sedentary subjects regarding bone characteristics.
- PMID: 20963459 [PubMed – indexed for MEDLINE]
From another perspective article entitled “The structural adaptations of cortical bone to loading during different stages of maturation ”
Changes in bone geometry during growth
Growth in the external size of a long bone, its cortical thickness and the distribution of cortical bone about the neu- tral axis is determined by the absolute and relative behavior of the periosteal and endocortical bone surfaces along the length of the bone8,13. Before puberty, periosteal apposition accounts for most of the increase in cortical area, this is part- ly offset however by the enlarging marrow cavity due to endocortical resorption. The net result is an enlarged corti- cal area located further from the neutral axis, leading to increased resistance to bending4. Late in puberty, periosteal apposition continues and is now accompanied by endocorti- cal apposition14, leading to an increase in cortical thickness.
The temporal sequence of events in boys tracks that of girls before puberty. Sexual dimorphism occurs during puberty and is characterized by boys exhibiting greater perisoteal expansion late in and post-puberty, and the absence of any endocortical contraction. Thus, in boys, the net result is the attainment of a greater cortical area that is located further from the axis of rotation compared to girls13.
The skeleton’s temporal sequence of events due to growth are not only surface-specific but also region-specific with more rapid maturation of distal than proximal regions. Distal segments of the appendicular skeleton mature before the proximal segments14. Similarly, contraction of the medullary cavity occurs in a distal to proximal pattern8,14.
The effect of additional loading on bone geome- try during growth
If additional loading does enhance the effect of growth then it would follow that exercise during childhood would result in an increase in periosteal but not endocortical apposition. Late in puberty, and in the immediate years following puberty the predominant effect would be narrowing of the medullar cavity due to endocortical apposition. This maturity-dependent preferential change in cortical surfaces with mechanical loading has been demonstrated in animals15-17. Younger animals showed greater periosteal expansion, while older animals showed greater medullar cavity narrowing. Reduced mechanical loading through limb immobilization or weightlessness also leads to preferential changes at the cortical surfaces: younger animals show a greater periosteal response (inhibition of bone formation), while older animals showed a greater endocortical response (increased resorption)7,16,18.
The results of human studies however are equivocal; for instance, consistent with this proposal is the finding that pre- pubertal female gymnasts had a larger total bone area (periosteal expansion) of the forearm despite a smaller stature19. While the playing arm in adult tennis players resulted in no detectable change to the total bone area of the radius, it did however result in thicker trabeculae20. Exercise also led to medullary contraction (but no periosteal expan- sion) at the tibia in adult military recruits21. In contrast, load- ing in pre-pubertal female gymnasts and non-athletic boys resulted in increased cortical area at the mid-femoral shaft due to endocortical contraction, not periosteal expansion2.
The aforementioned inconsistencies in the literature are likely to partly reflect the limitations imposed by two-dimen- sional measures (i.e., X-ray) of a three-dimensional struc- ture (i.e., bone). Radiographs and dual energy X-ray absorp- tiometry (DEXA) provide a two-dimensional projection of bone in the coronal plane which integrates periosteal and endocortical changes in the medio-lateral, not antero-poste- rior direction. Predicting changes using two-dimensional projections makes the flawed assumption that the bone is cylindrical and that the osteogenic response is uniform. These measurements in one plane do not provide informa- tion about changes that may occur cross-sectionally because of bone modelling. The cortical bone could be contracting in one plane but expanding in the other to resist bending moments. For this reason analysis of the cross sectional bone geometry is imperative. Furthermore, inferences from one or two measures at a site may not provide an accurate representation of changes that occur along the length of the bone8,22. Measuring techniques (MRI or CT) that provide a cross sectional view in the transverse plane is required for a more accurate assessment of surface specific changes in long bones. MRI is useful (particularly in children) because of the ability to collect images along the whole length of the bone without any radiation exposure.
In a recent study, MRI was used to compare the side-to- side differences in bone traits in the arms of competitive female tennis players during different stages of maturation8. The key findings were that loading did magnify the structural changes produced during growth. Prior to puberty, loading
magnified periosteal apposition along the length of the shaft; at the mid-humerus loading resulted in increased endocorti- cal resorption (medullary expansion). During the post-puber- tal period loading magnified the effect of endocortical appo- sition (medullary contraction), which makes an important contribution to cortical thickness in females. In fact, endo- cortical apposition accounted for most of the greater side-to- side difference attained in the post-pubertal years.
Most of the structural changes due to loading occurred early in the pre-pubertal years because adaptive changes in response to loading were sufficient to reduce the strains in bone that may lead to microdamage if not decreased23,24. The only additional benefit achieved from tennis training later in puberty was contraction of the medullary cavity. The rising estrogen levels during puberty are thought to lower the bone (re)modeling threshold on this surface, and thus sensitize bone next to marrow to the effect of mechanical loading25. Interestingly, medullary contraction did not confer any addi- tional increase in the structural rigidity of the bone.