Australian study of 1,983 participants in a 12-year health monitoring program tracked television viewing habits over time using group-based trajectory modeling
Tests of lower limb strength at the end of the study revealed significantly higher scores among the lowest-viewing groups; however, a high-viewing subgroup also scored well
Researchers believe high-viewer scores may be related to "training stimulus" associated with adiposity
No differences between viewing groups was noted for timed up-and-go test
Results point to need for early intervention, and importance of tracking viewing patterns over time, not just at a single point
It's no secret that large amounts of sedentary behavior, such as is associated with extensive television viewing, can have a negative effect on physical function and overall health. Now researchers in Australia have amassed 12 years' worth of data that shows how extended viewing habits can impact knee extensor strength, and the results are about what you'd expect—with 1 exception.
Researchers drew data from the Australian Diabetes, Obesity, and Lifestyle Study, a longitudinal project that began in 1999 and attempts to track its 11,000 participants over time. The most recent wave of data collection, which involves participants coming to onsite testing centers, was conducted 2011-2012. A total of 1,983 participants who had been with the program since the beginning were included in the current study, allowing researchers to follow television viewing patterns over time using group-based trajectory modeling (GBTM). Results were e-published ahead of print in Medicine & Science in Sports & Exercise (abstract only available for free).
Using data collected over the 12-year time span, researchers grouped participants into 3 major viewing time "trajectories" consisting of 2 subgroups each: consistently low and low-increasing (0-5.75 hours/week), moderate-increasing and moderate-decreasing (6-11.6 hours/week), and consistently high and high-increasing (18-115 hours/week). No participants were added to the data pool, so the study could focus on seeing what happens as a group ages, from an average participant age of 57.6 in 1999 to 69.5 at the time of the last collection point.
Researchers then analyzed results from 2 tests administered during the 2011-2012 sessions: the 8-foot timed up-and-go test (TUG), and the knee extensor strength test (KES).
Data showed few differences among groups for the TUG, but researchers noted significantly higher lower-limb isometric strength among the lowest-viewing subgroups compared with the middle group. However, 1 other group also showed better results on the KES—the subset whose viewing hours were consistently high.
The lower-limb strength associated with the high-volume viewers didn't necessarily surprise researchers, who write that high viewing time has been associated with adiposity, "which may provide a training stimulus (by carrying more weight during incidental and planned activity) and thereby maintain muscle strength." As for the lack of differences in TUG results, authors speculate that the average age of the group hadn't yet reached 70, the point where they assert reduction in gait speed begins to rapidly accelerate.
Researchers believe the results help to demonstrate how viewing habits can change over time, "a concept that is poorly captured through traditional statistical approaches" that focus on a single snapshot of viewing. "[The current study results] suggest that historic TV time may be more predictive of physical performance than current TV time, evidenced by participants in the moderate-increasing and moderate-decreasing TV time trajectories performing similarly on both tests of physical function," authors write.
"With the majority of adults in the moderate-increasing trajectory of TV-time, action is needed to counteract this negative trend," authors write, suggesting that that there may be "opportunities for intervention at critical life stages."
Bottom line: those interventions shouldn't wait. "Collectively, these results suggest that excessive TV time should be addressed earlier rather than later in life," authors write.