During the summer, Doug performed in choir competitions throughout the state. Local businesses helped the students pay for the long distance trips through generous donations. Once a week, the choir group would travel to another city and perform for an audience and a panel of judges. Although they had a strenuous summer, the singers were thrilled to bring home a state championship trophy. Their demanding efforts had truly paid off. Based on the meaning of "demanding," what does strenuous mean in the passage?