University of Queensland researcher has found that restructuring our daily routine to include exercise can have unexpected effects on health.
The study by UQ and University of South Australia researchers is the first of its kind to investigate changes of time use after starting an exercise program.
UQ School of Human Movement Studies research fellow Dr Sjaan Gomersall said that while it was important to make time for physical activity, where this time came from could have positive or negative health outcomes.
"When people undertake a new exercise program, the time spent in other domains, such as sleep or screen time, must be reduced to accommodate the new activity," Dr Gomersall said.
"If a new exerciser chooses to reduce screen time to accommodate exercise, for example, then there will presumably be additional health benefits, given that sedentary time is a risk factor for mortality and cardiovascular disease.
"Conversely, if they choose to sleep less, the benefits of physical activity may be reduced and ultimately lead to negative health outcomes such as obesity and depression."
The study involved 129 inactive adults aged 18 to 60 in a six-week exercise program, taking part in circuit training, boxing or bushwalking.
Participants were randomly allocated to one of three groups – a moderate or extensive exercise group (150 and 300 extra minutes of exercise a week, respectively), or a control group.
They were regularly surveyed to determine how the program affected their lifestyle.
Dr Gomersall said findings suggested that introducing a moderate or extensive exercise program could reduce the time spent watching television by about 50 minutes a day.
"This is significant, as watching two or more hours of television daily can increase the risk of cardiovascular disease by 125 per cent," she said.
"However, results also showed that this positive health outcome was offset by participants spending an extra 30 minutes a day using computers.
"This may indicate they were taking work home because they left early to exercise.
"Sleep levels also decreased by around 40 minutes a day during the study, meaning participants lost 20 hours of sleep during the six weeks."
Dr Gomersall said that it was also possible that abandoning exercise was more about an inability to lose time for other activities rather than the exercise load.
"Educating people about the exchange in time may help to maximise the health gains associated with physical activity," she said.
The study was done by Dr Gomersall and led by Professor Timothy Olds from the University of South Australia.
The study appear in the Journal of Science and Medicine in Sport.
Sjaan R. Gomersall, Kevin Norton, Carol Maher, Coralie English, Tim S. Olds, "In search of lost time: When people undertake a new exercise program, where does the time come from? A randomized controlled trial," Journal of Science and Medicine in Sport, Available online 6 February 2014, ISSN 1440-2440, DOI: 10.1016/j.jsams.2014.01.004.