In order to determine the effect of muscle fatigue on the ability of students to squeeze a clothespin, five male students did jumping jacks for three minutes and then squeezed a clothespin as many times
as possible in a minute. Three other male students ran up and down the stairs for 30 seconds and then
squeezed a clothespin as many times as possible for one minute. The results of the two groups were
recorded. Identify one change that could be made to the experiment to increase the validity of the
conclusion made from these results.