LEGS UNDER STRAIN

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As young animals develop and grow, their spindly limbs must adjust to their increasing bulk. Russell Main and Andrew Biewener were curious how young goat's bones altered as they aged. Wondering whether bone strain changed as the youngsters developed and whether their skeleton growth matched their weight gain, the team put groups of kids through their paces(p. 2577).Working with 6-week- and 15-week-old domestic goats, the team fitted strain gauges to one of the youngsters' radius bones and filmed them as they walked,trotted and galloped. Comparing the young animals' strain measurements with measurements from adults, the team found that the strain in the foreleg's radius bone increased as they grew, which surprised Main and Biewener as they had thought that the bone strains would remain unchanged as the animals developed. However, when they looked closer at the strain distributions, they realised that the pattern of strain in the bones remained unchanged as the young animals gained weight. And when the team looked at the girth of the developing animal's bones, instead of thickening to support their increased weight, the bone became relatively slim as the animals grew!Main and Biewener suspect that the youngster's bones are relatively bulky to protect their limbs from high strains incurred while keeping up with their elders. They explain that as younger animals have to trot, or even gallop, to keep pace with older animals, their forelimbs experience much higher strains,but the relatively large cross sectional area of their shorter limbs`maintains strains at comparably safe levels, even when the young goats move quickly for their size'.