Progressive and Regressive Angular Isometric Loading (PAILs/RAILs) is a tool I implement with clients in order to improve active range of motion over time. Unlike most "mobility" drills (which are usually not actual mobility drills), PAILs/RAILs use voluntary contractions to help pull you deeper into ranges of motion that you're not able to initially build tension in.
Just like any other modalities, you'll see transient effects with PAILs/RAILs that'll wear off rather quickly if they're not performed on a consistent basis with intent. It's also imperative to hold passive stretches for longer periods of times than you normally would to allow stretch tolerance to improve.
While active contractions help improve your mobility, you can't reach your true mobility potentials without first having the prerequisite flexibility necessary. When attacking both PAILs/RAILs and passive stretching daily, you'll be amazed how quickly you could make physiological adaptations with your current range of motion.
Mobility is just like any other training stimulus we're trying to achieve. Force needs to be present in order to make adaptations. Similar to strength training, connective tissue also has to be introduced to progressive overload in an intelligent manner to see results. Interested in learning more? Check out the Par Four Performance Virtual Kinstretch Group to improve your mobility today!