Abstract
The skeletal response to exercise and training on bone is
exceptionally good during the growing years. However, it is not known whether
the benefit of training on bone is maintained after the training. This 20-month
follow-up study assessed the effect of a 9-month jumping intervention on bone
gain and physical performance in 99 girls (mean age
12.5 ± 1.5 years at the beginning of the study) one year
after the end of the intervention. Both bone mineral content (BMC), by dual
energy X-ray absorptiometry (DXA) at the lumbar spine and proximal femur, and
physical performance parameters (standing long jump, leg extension strength,
and shuttle run tests) were measured at baseline and at 20 months. A
multivariate regression analysis was first used to determine the best
predictors of the BMC accrual by time. Analysis showed that age at baseline and
square of age, changes in height and weight, and pubertal development into
Tanner stages 4 and 5 during the follow-up explained the majority of the BMC
gain. Then, the effect of participation in the 9-month exercise intervention on
BMC accrual and physical performance was analysed adding this variable
(participation: yes/no) into the model. The regression analysis showed that the
trainees (N = 50) had 4.9 %
(95 % CI, 0.9 % to 8.8 %,
p = 0.017) greater BMC increase in the lumbar spine than
the controls (N = 49). The mean 20-month BMC increase in
the lumbar spine was 28 % (SD 19) in the trainees compared to
22 % (12) increase in the controls. In the proximal femur, the
trend was similar but the obtained 2 to 3 % higher BMC accrual in
the trainees (compared to that in controls) were statistically insignificant.
Among the performance variables, using the same model that best predicted the
BMC accrual, the only statistically significant between-groups difference, in
favour of the trainees, was the improvement in the standing long jump test
(6.4 %, 95 % CI, 2.3 % to
10.4 %, p = 0.002). Improvements in the leg
extension strength and shuttle run tests showed no between-groups difference.
In conclusion, although the greatest proportion of bone mineral accrual in
growing girls is attributable to growth, an additional bone gain achieved by
jumping training is maintained at the lumbar spine at least a year after the
end of the training.
Key words
Exercise - jumping - bone-gain - BMC - maintenance - growing girls
References
