EFFECTS OF UNILATERAL STRENGTH TRAINING AND DETRAINING ON BONE-MINERAL MASS AND ESTIMATED MECHANICAL CHARACTERISTICS OF THE UPPER-LIMB BONES IN YOUNG-WOMEN
A. Heinonen et al., EFFECTS OF UNILATERAL STRENGTH TRAINING AND DETRAINING ON BONE-MINERAL MASS AND ESTIMATED MECHANICAL CHARACTERISTICS OF THE UPPER-LIMB BONES IN YOUNG-WOMEN, Journal of bone and mineral research, 11(4), 1996, pp. 490-501
The aims of this study were to examine the effects of 12 months unilat
eral high-resistance strength training and 8-month detraining on bone
mineral content (BMC), density (BMD) and estimated mechanical characte
ristics of upper limb bones, and also to estimate consequent loading i
nduced strains on forearm bone shafts. Thirteen female physiotherapy s
tudents (mean 23.8 +/- 5.0 yrs, 166 +/- 7 cm, 64.4 +/- 13.3 kg) traine
d their left upper limbs with dumbbells on average 2.8 times per week
for 12 months, followed by eight months detraining. Nineteen students
served as controls (mean 25.7 +/- 5.2 yrs, 165 +/- 4 cm, 62.1 +/- 7.0
kg). BMC, BMD, and bone width and estimated cortical wall thickness (C
WT) were measured at five different sites in both upper extremities (p
roximal humerus, humeral shaft, radial shaft, ulnar shaft, and distal
forearm) using dual energy x-ray absorptiometry (DXA) scanner. In addi
tion, cross-sectional moment of inertia (CSMI) was estimated from DXA
data. The maximal isometric strength of the upper extremities was meas
ured with an arm flexion-extension dynamometer. The training increased
significantly the flexion strength by 14% (p = 0.001). During the det
raining period, all measured strength values in the training group dec
reased in both limbs with respect to values after training. Despite th
e clear effect on muscular strength, no significant intergroup differe
nces were observed in BMC, BMD, bone width, CWT, or CSMI values at any
measured site after the training or detraining period. The estimated
loading-induced strains remained within customary loading, and the cha
nge in strain level was only 15%. In conclusion, this study indicated
that using high-resistance strength training may not provide an effect
ive osteogenic stimulus for bone formation and geometric changes in up
per limb bones of young, healthy, adult women. The interaction of bone
s and muscles may play an important and relatively unrecognized role i
n the development of bone strength, suggesting that the entire biomech
anical environment should be carefully considered when evaluating the
osteogenic efficiency of physical loading.