To determine the effect of fatigue on the action of muscles, each of five boys was given a 10cm clothespin. the student squeezed the clothespins for 30 seconds and recorded the results. after the first trail, the girls rested and the boys jogged in place for 1 minute. a second trail was then done to determine how many times each student could squeeze the clothespins in 45 seconds. identify one error in the design of this experiment.