The Year in Fitness: Exercise, Add Intensity, Live to See Another Yearbr In that study, which I wrote about in March (which became my most popular column this year), scientists at the Mayo Clinic compared differences in gene expression inside muscle cells after youngerbr and older people had completed various types of workouts.br But in people older than 64, more than 400 genes were working differently nowbr and many of those genes are known to be related to the health and aging of cells.br Other studies this year reinforced the notion that age need not be a deterrent to hard exercise and that such workouts could be key to healthy aging.br Perhaps most striking, “the animals had tolerated the high-intensity interval training well,” one of the scientists who conducted the study told me.br His efforts help to belie a number of entrenched beliefs about older people, includingbr that physical performance and aerobic capacity inevitably decline with age and that intense exercise is inadvisable, if not impossible, for the elderly.br The greatest differences were seen in the operations of genes after people had practiced high-intensity interval training for 12 weeks.br After four months of this kind of training, the exercised animals were strongerbr and more aerobically fit than other mice of the same age, and few remained physically frail.