Columnist: A recent research report suggests that by exercising vigorously, one significantly lowers one' s chances of developing certain cardiorespiratory illnesses. But exercise has this effect, the report concludes, only if the exercise is vigorous. Thus, one should not heed older studies purporting to show that nonstrenuous walking yields the same benefits. The reasoning in the columnist's argument is most vulnerable to criticism on the grounds that this argument ['fails to show that a certain conclusion of the recent report is better justified than an opposing conclusion reached in older studies', 'fails to consider that those who exercise vigorously are at increased risk of physical injury caused by exercise', 'fails to consider the possibility that the risk of developing certain cardio-respiratory illnesses can be reduced by means other than exercise', 'fails to consider the possibility that those who engage in vigorous physical exercise are more likely than others to perceive themselves as healthy']