Identify the error in the sentence: "When she went to the gym, Maudie liked to run on the treadmill for 45 minutes, lifting weights, then to take a yoga class."

The phrase "lifting weights" in the sentence creates an inconsistency in the parallel structure of the activities Maudie is described as doing. The sentence mentions multiple actions she engages in at the gym: running on the treadmill, lifting weights, and taking a yoga class. For clarity and grammatical consistency, all actions should be presented in the same form.

In this case, "to take a yoga class" is an infinitive phrase, and so are the phrases "to run on the treadmill" and "to lift weights" (the latter would ideally be "to lift weights" to maintain the parallel structure). The presence of "lifting weights" interrupts this pattern by using a gerund instead of an infinitive. Therefore, the sentence would be clearer and grammatically correct if all activities followed the same structure, such as "to run on the treadmill, to lift weights, and to take a yoga class." This uniformity ensures that readers understand the relationship between the actions more fluidly.