Bilateral bone characteristics of the humerus (proximal, shaft, and distal sites) and radius (shaft and distal sites) in 12 former Finnish national-level male tennis players (mean age 30 years) and their 12 age-, height-, and weight-matched controls were measured with peripheral quantitative computed tomography (pQCT). The pQCT variables analyzed were bone mineral content (BMC), total cross-sectional area of bone (Tot.Ar), cross-sectional area of the marrow cavity (M.Cav.Ar), cortical bone (Co.Ar) and trabecular bone (Tr.Ar), volumetric density of cortical (Co.Dn) and trabecular (Tr.Dn) bone, cortical wall thickness (Co.Wi.Th), bone strength index (BSI), and principal moments of inertia (I min and I max ). In the players, significant side-to-side differences, in favor of the dominant (playing) arm, were found in BMC (ranging 14%-27%), Tot.Ar (16%-21%), Co.Ar (12%-32%), BSI (23%-37%), I min (33%-61%), and I max (27%-67%) at all measured bone sites, and in Co.Wi.Th. (5%-25%) at the humeral and radial shafts, and distal humerus. The side-to-side M.Cav.Ar difference was significant at the proximal humerus (19%) and radial shaft (29%). Concerning the players' Co.Dn and Tr.Dn, the only significant side-toside difference was found in the Co.Dn of the distal humerus, with the playing arm showing a slightly smaller Co.Dn than the nonplaying arm (؊2%). In controls, significant dominant-tonondominant side differences were also found, but with the majority of the differences being rather small, and significantly lower than those of the players. In conclusion, despite the large side-to-side differences in BMC, the volumetric bone density (Co.Dn, Tr.Dn) was almost identical in the dominant and nondominant arms of the players and controls. Thus, the players' high playing-arm BMC was due to increases in the Tot.Ar, M.Cav.Ar, Co.Ar, and CW.Th. In other words, the playing arm's extra bone mineral, and thus increased bone strength, was mainly due to increased bone size and not due to a change in volumetric bone density. These upper arm results may not be generalized to the entire skeleton, but the finding may give new insight into conventional dual-energy X-ray absorptiometry (DXA)-based bone density measurements when interpreting the effects of exercise on bone. (Bone 27:351-357; 2000)

This randomized cross-over study was designed to investigate the effects of a 4-min vibration bout on muscle performance and body balance in young, healthy subjects. Sixteen volunteers (eight men, eight women, age 24-33 years) underwent both the 4-min vibration- and sham-interventions in a randomized order on different days. Six performance tests (stability platform, grip strength, isometric extension strength of lower extremities, tandem-walk, vertical jump and shuttle run) were performed 10 min before (baseline), and 2 and 60 min after the intervention. The effect of vibration on the surface electromyography (EMG) of soleus, gastrocnemius and vastus lateralis muscles was also investigated. The vibration-loading, based on a tilting platform, induced a transient (significant at the 2-min test) 2.5% net benefit in the jump height (P = 0.019), 3.2% benefit in the isometric extension strength of lower extremities (P=0.020) and 15.7% improvement in the body balance (P = 0.049). In the other 2-min or in the 60-min tests, there were no statistically significant differences between the vibration- and sham-interventions. Decreased mean power frequency in EMG of all muscles during the vibration indicated evolving muscle fatigue, while the root mean square voltage of EMG signal increased in calf muscles. We have shown in this study that a single bout of whole body vibration transiently improves muscle performance of lower extremities and body balance in young healthy adults.

Bone characteristics of the humeral shaft and distal radius were measured from 64 female tennis and squash players and their 27 age-, height-, and weight-matched controls with peripheral quantitative tomography (pQCT) and DXA. The players were divided into two groups according to the starting age of their tennis or squash training (either before or after menarche) to examine the possible differences in the loading-induced changes in bone structure and volumetric density. The used pQCT variables were bone mineral content (BMC), total cross-sectional area (TotA) of bone, cross-sectional area of the marrow cavity (CavA) and that of the cortical bone (CoA), cortical wall thickness (CWT), volumetric density of the cortical bone (CoD) and trabecular bone (TrD), and torsional bone strength index (BSIt) for the shaft, and compressional bone strength index (BSIc) for the bone end. These bone strength indices were compared with the DXA-derived areal bone mineral density (aBMD) to assess how well the latter represents the effect of mechanical loading on apparent bone strength. At the humeral shaft, the loaded arm's greater BMC (an average 19% side-to-side difference in young starters and 9% in old starters) was caused by an enlarged cortex (CoA; side-to-side differences 20% and 9%, respectively). The loaded humerus seemed to have grown periosteally (the CavA did not differ between the sites) leading to 26% and 11% side-to-side BSIt difference in the young and old starters, respectively. CoD was equal between the arms (؊1% difference in both player groups). The side-to-side differences in the young starters' BMC, CoA, TotA, CWT, and BSIt were 8 -22% higher than those of the controls and 8 -14% higher than those of the old starters. Old starters' BMC, CoA, and BSIt side-to-side differences were 6 -7% greater than those in the controls. The DXA-derived side-to-side aBMD difference was 7% greater in young starters compared with that of the old starters and 14% compared with that in controls, whereas the difference between old starters and controls was 6%, in favor of the former. All these betweengroup differences were statistically significant. At the distal radius, the player groups differed significantly from controls in the side-to-side BMC, TrD, and aBMD differences only; the young starters' BMC difference was 9% greater, TrD and aBMD differences were 5% greater than those in the controls, and the old starters' TrD and aBMD differences were both 7% greater than those in the controls. In summary, in both of the femaleThe authors have no conflict of interest.

The 4-month whole body vibration-intervention enhanced jumping power in young adults, suggesting neuromuscular adaptation to the vibration stimulus. On the other hand, the vibration-intervention showed no effect on dynamic or static balance of the subjects. Future studies should focus on comparing the performance-enhancing effects of a whole body vibration to those of conventional resistance training and, as a broader objective, on investigating the possible effects of vibration on structure and strength of bones, and perhaps, incidence of falls of elderly people.

Recent animal studies have given evidence that vibration loading may be an efficient and safe way to improve mass and mechanical competence of bone, thus providing great potential for preventing and treating osteoporosis. Randomized controlled trials on the safety and efficacy of the vibration on human skeleton are, however, lacking. This randomized controlled intervention trial was designed to assess the effects of an 8-month whole body vibration intervention on bone, muscular performance, and body balance in young and healthy adults. Fifty-six volunteers (21 men and 35 women; age, 19 -38 years) were randomly assigned to the vibration group or control group. The vibration intervention consisted of an 8-month whole body vibration (4 min/day, 3-5 times per week). During the 4-minute vibration program, the platform oscillated in an ascending order from 25 to 45 Hz, corresponding to estimated maximum vertical accelerations from 2g to 8g. Mass, structure, and estimated strength of bone at the distal tibia and tibial shaft were assessed by peripheral quantitative computed tomography (pQCT) at baseline and at 8 months. Bone mineral content was measured at the lumbar spine, femoral neck, trochanter, calcaneus, and distal radius using DXA at baseline and after the 8-month intervention. Serum markers of bone turnover were determined at baseline and 3, 6, and 8 months. Five performance tests (vertical jump, isometric extension strength of the lower extremities, grip strength, shuttle run, and postural sway) were performed at baseline and after the 8-month intervention. The 8-month vibration intervention succeeded well and was safe to perform but had no effect on mass, structure, or estimated strength of bone at any skeletal site. Serum markers of bone turnover did not change during the vibration intervention. However, at 8 months, a 7.8% net benefit in the vertical jump height was observed in the vibration group (95% CI, 2.8 -13.1%; p ‫؍‬ 0.003). On the other performance and balance tests, the vibration intervention had no effect. In conclusion, the studied whole body vibration program had no effect on bones of young, healthy adults, but instead, increased vertical jump height.