No abstract

No abstract

No abstract

No abstract

Ageing compromises locomotor capacity and is associated with an increased risk of falls. Several lines of evidence indicate that both changes in muscle mass and performance are causative. Most studies, however, do not discern between effects of ageing, sedentarism and comorbidity. The present study compares the age effects in muscle cross section, force and power in physically competent self-selected subjects of different age groups. A total of 169 women and 89 men between 18 and 88 years, without any disease, impairment or medication affecting the musculoskeletal system were enrolled in this study. Calf muscle cross-sectional area was assessed by computed tomography. Muscle force and power were assessed by jumping mechanography. No significant correlation between muscle cross section and age was found in the men. A weak correlation in the women disappeared after correction for height. Close correlations with age, however, were found for peak force and peak power. Correction for muscle cross section or body weight further increased these correlation coefficients, particularly for peak power specific to body weight (r = 0.81 in women and r = 0.86 in men). The non-sedentarian population investigated here depicted a reduction of >50% between the age of 20 and 80 without a reduction in muscle cross section. This suggests a crucial role for muscular power in the ageing process. Possibly, the jumping mechanography as a measurement of anti-gravitational power output is a promising extension of the chair-rising test, known to be predictive for immobilization and the risk of falls.

In this study we investigated metabolic power during whole-body vibration exercise (VbX) compared to mild resistance exercise. Specific oxygen consumption (VO2) and subjectively perceived exertion (rating of perceived exertion, RPE; Borg scale) were assessed in 12 young healthy subjects (8 female and 4 male). The outcome parameters were assessed during the last minute of a 3-min exercise bout, which consisted of either (1) simple standing, (2) squatting in cycles of 6 s to 90 degrees knee flexion, and (3) squatting as before with an additional load of 40% of the subject's body weight (35% in females). Exercise types 1-3 were performed with (VbX+) and without (VbX-) platform vibration at a frequency of 26 Hz and an amplitude of 6 mm. Compared to the VbX- condition, the specific VO2 was increased with vibration by 4.5 ml x min(-1) x kg(-1). Likewise, squatting and the additional load were factors that further increased VO2. Corresponding changes were observed in RPE. There was a correlation between VbX- and VbX+ values for exercise types 1-3 (r = 0.90). The correlation coefficient between squat/no-squat values (r = 0.70 without and r = 0.71 with the additional load) was significantly lower than that for VbX-/VbX+. Variation in specific VO2 was significantly higher in the squatting paradigm than with vibration. It is concluded that the increased metabolic power observed in association with VbX is due to muscular activity. It is likely that this muscular activity is easier to control between individuals than is simple squatting.

Bed rest is a recognized model for muscle atrophy and bone loss in space flight and in clinical medicine. We hypothesized that whole body vibration in combination with resistive exercise (RVE) would be an effective countermeasure. Twenty healthy male volunteers underwent horizontal bed rest for 56 days and were randomly assigned either to a group that performed RVE 11 times per week or to a group that underwent bed rest only (Ctrl). Bone mineral content (BMC) was assessed by peripheral quantitative computed tomography (pQCT) in the tibia and the radius and by dual x-ray absorptiometry (DXA) in the hip and lumbar spine at baseline and at regular intervals during bed rest and a 12-month follow-up. RVE appeared to protect muscle size and function, and it also prevented bone loss (p-values between <0.001 and 0.01). Bone losses were largest in the distal tibia epiphysis, where BMC declined from 421.8 mg/mm (SD 51.3) to 406.6 mg/mm (SD 52.7) in Ctrl, but only from 411.1 mg/mm (SD 56.6) to 409.6 mg/mm (SD 66.7) in RVE. Most of the BMC losses were recovered by 12-month follow-up. Analyses showed that the epiphyseal cortex, rather than spongiosa, depicted the most pronounced changes during bed rest and recovery. These results suggest that the combined countermeasure applied in this study is effective to prevent bone losses from the tibia. This underlines the importance of mechanical usage for the maintenance of the human skeleton.

Assessment of maximum power in jumping mechanography appears to have good test-retest reliability with negligible learning effects. Moreover, it results in a comparatively large intersubject variability, which makes it an interesting method in the assessment of aging effects in middle-aged to older subjects and patients.