If you’re someone who has dabbled in various forms of exercise, you’ve probably noticed how differently your body responds to each one. If you’re lifting weights frequently, you’ve noticed an increase in muscle mass as opposed to running, where you’re more likely to achieve a leaner frame and increased stamina. But what is responsible for these varying results? According to a recent study, one specific gene may be the determining factor in how the body responds to your workout style.

Researchers divided 19 physically active men into two groups. One group did a 50 minute sesh on the treadmill, the other group did 50 minutes of leg press exercises. Biopsies of the men’s thigh muscles were taken pre- and post workout. They found that both endurance and resistance training initiated the gene, peroxisome proliferator-activated receptor-gamma coactivator 1α (PGC-1α), which then created various isoforms. They noticed that only endurance training released an isoform called PGC-1α exon 1a.

READ MORE: Should You Actually Work Out Every Day?