[Purpose] This study aimed to determine the effects of a mobile health application, and exercise instructions by a physical therapist on exercise frequency, duration, and intensity for middle-aged and older adults. [Participants and Methods] The study included males and females in their 50s to 70s, who provided consent to participate. Thirty-six people who wished to participate in the online group were divided into groups of five or six each, with a physical therapist as group leader. The frequency, intensity, duration of exercise, and group activities were surveyed using questionnaires: before coronavirus disease (COVID-19) (before March 2020, when the novel coronavirus began to spread in Japan), during COVID-19 (after April 2020), after digital versatile disc (DVD) distribution, and after online group initiation (3 weeks after DVD distribution for the control group). [Results] The online group received significantly more frequent instructions by a physiotherapist than the control group. The control group did not show significant changes over time, whereas the online group exercised significantly, more frequently after the intervention. [Conclusion] The online mode and physical therapist intervention resulted in a significant increase in exercise frequency. Exercise advice from professionals and peer presence to continue exercising together were beneficial.