Rat study reveals exercise changes body at molecular level

The researchers hope that their findings could one day be used to tailor human exercise to an individual's health status or to develop treatments that mimic the effects of physical activity for people who are unable to exercise.

"This is the first whole-organism map looking at the effects of training in multiple different organs," says Steve Carr, from the Broad Institute of MIT and Harvard and co-senior author of the study published in Nature.

"The resource produced will be enormously valuable and has already produced many potentially novel biological insights for further exploration."

Scientists with the Molecular Transducers of Physical Activity Consortium (MoTrPAC) collected samples from male and female rats (Rattus norvegicus) during 8 weeks of endurance treadmill training.

"A lot of large-scale studies only focus on 1 or 2 data types," says Natalie Clark, a computational scientist in Carr's group, which analysed proteins.

In this study, the teams performed nearly 10,000 assays to make about 15 million measurements from blood and 18 solid tissues.

They found the most extreme changes occurred in the adrenal gland, which produces hormones to regulate important processes such as immunity, metabolism, and blood pressure.

They also observed many tissues showed sex differences in their response to exercise. For example, most pro-inflammatory cytokines (immune-signalling molecules) unique to female rats showed changes in levels between 1-2 weeks of training. Whereas those in males showed differences between 4-8 weeks.

Carr's team also found changes in the proteins in the liver.

"Even though the liver is not directly involved in exercise, it still undergoes changes that could improve health," says co-first author Pierre Jean-Beltran, a postdoctoral researcher in Carr's group.

"No one speculated that we'd see these … changes in the liver after exercise training. This highlights why we deploy all of these different molecular modalities — exercise is a very complex process, and this is just the tip of the iceberg."

Additional ongoing studies are investigating the effects of exercise on young adult and older rats, as well as the short-term effects of 30-minute bouts of physical activity. Recruitment of about 1,500 individuals for a clinical trial to study the effects of both endurance and resistance exercise in children and adults is also currently underway.