You’ve likely found (either anecdotally or through your own experiences) that resistance training builds muscle mass while endurance training seems to do the exact opposite. A new study published in Physiological Reports highlighted the reasoning behind how the body adapts to different stressors.

Scientists have observed that one gene, peroxisome proliferator-activated receptor-gamma coactivator PGC-1α, controls many of the adaptations that take place during exercise. The new research shows that, although both resistance and endurance training activate the PGC-1α gene, different adaptation processes are stimulated depending on the type of training.

Subjects were divided into a resistance exercise (RE) group and an endurance exercise (EE) group. The RE group performed 10 sets of their 10 repetition maximum on a leg press machine. The EE test consisted of strenuous walking on a treadmill. Both tests were performed over the course of 50 minutes. Muscle biopsies were then taken from the thigh muscles of each group.

Results showed that both forms of exercise produced variations of the PGC-1α gene that increased blood vessel growth. However, only resistance training activated genes responsible for encouraging muscle growth.

The results of the study also confirmed the role of the PGC-1α in exercise and recovery.

“Our results support that gene expression responses of PGC-1α isoforms may have an important role in exercise-induced muscle adaptations,” the researchers said in their report.

This research builds on an earlier study from the University of Basel, which found that endurance exercise alters the metabolic profile of muscles via the PGC-1α gene.