Using smartphones as you run or walk on the treadmill lowers the intensity of the exercise, resulting in overall less health benefits, says a study.
The findings are important because poor cardiorespiratory fitness is associated with an increased prevalence of cardiovascular disease risk factors such as higher cholesterol and blood pressure levels, which could potentially lead to early death.
"Exercising at a lower intensity has been found to reduce the health benefits of exercise and fitness improvements over time," said researcher Jacob Barkley from Kent State University.
In the present study, 44 students participated in four, separate 30-minute exercise sessions on a treadmill.
The researchers assessed the effects of common smartphone functions such as music, talking and texting and a control condition where the students had no access to their smartphones.
Using the phone exclusively for listening to music increased the average treadmill speed, heart rate and enjoyment of a bout of exercise.
Talking increased enjoyment, maintained heart rate but reduced speed.
Texting reduced both speed and heart rate but it did not alter enjoyment.
It appears as if listening to music and, to a lesser extent, talking may have benefits on the duration and frequency of exercise owing to their ability to increase enjoyment.
"However, if an individual's opportunity for exercise is constrained by time, then it appears best to avoid talking on a smartphone during planned exercise," the authors said.
The researchers did not find any fitness-related benefits of texting while exercising.
"If one is looking to get the most benefits and improvements out of their workout, leave the smartphone in the locker room and enjoy your music with another type of device," the authors said.
The study was published in the journal PLOS ONE.