Site-Speci®c Skeletal Response to Long-Term Weight Training Seems to be Attributable to Principal Loading Modality: A pQCT Study of Female Weightlifters A. Heinonen, H. SievaÈnen, P. Kannus, P. Oja, I. Vuori Bone Research Group, UKK Institute, Tampere, Finland Received: 20 February 2001 / Accepted: 31 October 2001 / Online publication: 20 May 2002 Abstract. Physical training may be able to improve bone strength through site-speci®c changes in the composi- tion, size and structure of the bone without notable in- creases in volumetric density. To address this possibility speci®cally, we compared 14 competitive female weightlifters with 14 female physical therapy students. Peripheral quantitative computed tomographic scans pQCT) were taken from the distal radius, radial shaft, distal femur, and tibial midshaft of the dominant limb. Analysis of covariance ANCOVA) was used to estimate the intergroup dierences, using body weight and age as covariates. Cortical density did not dier between the weightlifters and controls at any site, whereas trabecular density was greater in the weightlifters, the bene®t being 10% P= 0.186) at the distal radius and 11% P = 0.040) at the distal femur compared with the controls. Weightlifters' cortical cross-sectional area was 38% P = 0.029) larger at the distal radius, 26% larger P = 0.001) at the radial shaft, and 9% larger at the tibial midshaft P = 0.034). Consequently, the weight- lifters' forearm bone strength indices were also signi®- cantly higher, the intergroup dierence being 41% P = 0.001) at the distal radius and 43% P = 0.004) at the radial shaft. Thus, the observed intergroup dier- ence at the distal radius was mainly due to enlarged bone, particularly its cortex, rather than higher volu- metric bone density. Findings at the radial shaft were similar. In contrast, weightlifters' trabecular tissue at the distal femur was denser but the bone per se was not clearly bigger than that of the controls' intergroup dierence 5%, P = 0.117). We suggest that bones sub- jected to exceptionally high bending-loading distal ra- dius and radial shaft) are larger than their normal counterparts while at sites experiencing axial, compres- sive-loading e.g., distal femur), a denser trabecular structure more load-carrying area) may be sucient and any substantial enlargement in bone size may not be necessary. Key words: pQCT Ð Bone geometry Ð Trabecular density Ð Cortical density Ð Mechanical loading. The dynamic nature of bone is re¯ected in the ability of the bone to adapt to altered mechanical loading by ad- justing its size, geometry, structure, and microarchitec- ture in a way that keeps the internal eective strains within a reasonable and safe range [1, 2]. It follows that ``dense'' bones i.e., trabecular bones with a large load- bearing cross-sectional area per unit of volume) can eciently combine the axial compressive loading ca- pacity and the ability to absorb mechanical energy, whereas a typical tubular shape of the long bone cortices results from the bending loading exerted on the diaph- ysis and from the fact that the diaphyses should be sti in nature [3]. However, pertinent information regarding the eects of speci®c loading on human bone structure has remained sparse [4±8]. This may mirror the limited sensitivity of the common bone densitometric technique e.g., planar dual-energy X-ray absorptiometry, DXA) to reveal the speci®c structural adaptation strategies of bone to meet the demands of incident mechanical loading, as well as the lack of deeper understanding of bone responsiveness to physical exercise. Regarding the latter issue, athletes provide a wealth of natural experi- ments for examining this topic in humans. The considerable dierences seen in the bone mineral mass of athletes representing dierent sports [9, 10] can be explained, at least partly, by a large variation in the type, intensity, frequency, and duration of mechanical loading inherent in these sports. In terms of skeletal loading, weightlifting, for instance, creates extreme torques in the upper extremities whereas the lower ex- tremities experience large compressive stresses [11]. Hence, it is expected that the response to long-term athletic weight training at dierently loaded skeletal sites should re¯ect the speci®c loading modality. Should such a loading-speci®c response exist, it would provide new and more relevant information on the potential causality between the loading and the special charac- teristics in bone structure. Therefore, this study focused on assessing whether there are site-speci®c dierences in Calcif Tissue Int 2002) 70:469±474 DOI: 10.1007/s00223-001-1019-9 Calci®ed Tissue International Ó 2002 Springer-Verlag New York Inc. Correspondence to: A. Heinonen, UKK Institute for Health Promotion Research Kaupinpuistonkatu 1, 33500 Tampere, Finland email: ukarhe@uta.®