Abstract
Introduction: The skeletal system is submitted to a lifelong active conversion process, with bone mass and architecture being adapted to changing mechanical strain. In older subjects, the necessary intensities for that probably exceed the level of a systematical resistance training. Muscular contractions caused by vibrating stimuli lead to an enhanced co-activation of agonists and antagonists and, thus, possibly to a higher pressure on bone tissue as well. In this study, effects of this mechanism on bone mass and strength index (BSI) were examined. Methods: 73 post- menopausal women were randomized into one group of conventional resistance training or, resp., another group of oscillating resistance training (25 Hz, amplitude of max. 1.5 cm) (GALILEO). The training was performed twice a week with an intensity of up to 50-60% (month 1-6) and 60-70% (month 7-12) of the 1-repetition maximum in 2 sets each during a 12-month period in both groups. 50% of the participants of each group decided to take a definite hormone replacement therapy (estradiol 2 mg, MPA 10 mg) whereas the other 50% did not. In the beginning and in the end of the study, quadriceps muscle torque was measured at the knee joint, and lumbar and femoral neck BMD were assessed by DXA. Every 3 months, geometrical and density parameters of the tibia were obtained by pQCT at three measuring sites ( 4, 14, and 38% tibial length from the distal end). Results: In the end of the study, data of 51 subjects could be evaluated. In both groups, a significant increase of the torque could be noticed. Lumbar and femoral neck BMD values showed no significant changes comparing the two groups. The significant decrease of BSI values in the 14% range of the GALILEO group led to a significant difference between the two training groups within the second term of the study. Regarding HRT administration, a decrease of BSI could be noticed in both GALILEO subgroups after 9 months, a BSI rise after 12 months, however, only in the HRT subgroup. In the subgroups without HRT, the decrease in BMD values led to a significant difference in the lumbar range. At all measuring sites, a positive influence of HRT could be proved. Discussion: Total changes could be interpreted as a synergism of GALILEO and HRT, with a greater influence of HRT. The simultaneous decrease of BSI in the GALILEO training subgroups allows the hypothesis of a synchronization of the ARF cycles by more intensive training on the GALILEO device after 6 months, effecting a muscular co-activation and an additional acceleration by the oscillation. |
