Underweight women must walk further than normal to achieve skeletal benefit
MedWire News: Women with below-average body weight (BW) need to walk almost four times as many steps per day as average-weight women in order to maintain normal bone mineral density (BMD), US study findings indicate.
"This analysis suggests that the goal of 10,000 steps per day - that has been advocated by some as a target for a healthy lifestyle - should be re-examined when used in the context of skeletal health," remark Katherine Boyer (Stanford University, California) and colleagues.
The researchers examined the relationship between habitual walking activity and femoral BMD in 105 healthy men and women aged 49-64 years.
First, they tested for a correlation between BMD and an index of cumulative loading - the bone density index (BDI) - which is calculated using speed, step-count, and ground reaction force (GRF) data. The relationship between BDI and BMD was then used to predict, for a range of BWs and walking speeds, the number of steps per day required to maintain normal BMD (T-score >-1.0).
Boyer and team found that BDI was significantly correlated with BMD in women but not men. This meant they could only perform further calculations in the female cohort (n=66).
As reported in the journal Osteoporosis International, a woman with the average BW of the study cohort (65.1 kg), walking at 1.00 m/s, would need to take 4892 steps per day to maintain a T-score of -1.0.
However, a woman weighing 20% less than the average weight (52.5 kg) would need to take a substantially greater 18,568 steps per day to maintain the same T-score.
"This (18,568 steps) is an ambitious steps per day goal, and thus, to increase success of an activity-modifying intervention in lower BW females, higher intensity activities or devices to artificially increase BW during walking might be necessary," the authors suggest.
Increasing the walking speed to 1.32 m/s meant that the recommended 10,000 steps would be required to maintain normal BMD, but only two of the 66 women reached this speed during the study.
The researchers conclude that walking interventions for osteoporosis are sensitive to gender, weight, and speed.
"Future research should explore interventions to safely increase the GRF magnitudes during everyday activities, which may provide significant benefit for healthy skeletal aging," they add.
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By Laura Dean