According to the following research, lifting weights can help the body become more flexible. For 10 weeks, two separate group of individuals were asked to do 3 workouts per week with 1 control group doing nothing

Group A – Did 1 set of strength training that involved 9 exercises for 8 to 12 reps.

Group B – Did 3 set of strength training that involved 9 exercises for 8 to 12 reps

Group C- A control group that did not train at all

Result: Doing one set of strength training 3 times per week increase sit and stretch flexibility by 5 cm while doing three set of strength training increase flexibility by 8 cm

Link to source journal:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3588898/

Infographic Summary provided by “Strength & Conditioning Research”