Is there anything I should be doing to help increase my pull up capacity whilst hanging around?
Stretching Muscle Prior To Exercise
1) Agonist Muscle Stretching
The Agonist Muscles in an exercise are the ones used in the movement.
As an example. in the case of a Pull Up or Chin is that the working Agonist Muscles are primarily the Posterior Chain: Lats, Posterior Deltoids, Rhomboids with the exception being the Biceps.
Research has demonstrates that stretching the Agonist Muscles too much prior to performing an Agonist Exercises, decreases Maximum Strength and Power.
Base on the research, Agonist Muscle Stretching prior to or between Set of an Agonist Exercise needs to limited to 30 seconds or less.
Agonist Stretching for Muscle Mass
1) John Parrillo, Bodybuilding Coach
Parrillo was a pioneer with Bodybuilding stretching between Agonist Exercises.
Parrillo's empirical data indicated it increased muscle mass.
2) Dr Jose Antonio
Antonio's research with Loaded Stretching of the Wings of Bird, determined it increase muscle mass.
3) Dr Jacob Wilson
Research by Wilson (University of Tampa Human Performance) with athlete determined that Antonio's finding were effective for increasing muscle mass in humans
As per Wilson's finding, Stretching around 30 seconds between Sets was effective in the working Agonist Muscle.
General Agonist Stretching Exercise Recommendation
Stretching the Agonist Stretch in an Agonist Exercise is effective at increasing muscle mass without decreasing Strength and/or Power.
Antagonist Muscle Stretching Prior To An Agonist Exercise
In Upper Body Exercises the Antagonist Muscle in an Agonist Exercise provides a "Braking Effect".
That means in a Pull Up/Chin the Anterior Muscles (Pecs and Anterior Shoulder along with the Triceps (Anterior Muscle) limit Strength and Power Production.
Think of the Antagonist Muscles like the Emergency Brake on your car.
Diving with the Emergency Brake on limits how fast you go.
The Key To Increasing Agonist Muscle Force Production
The key to increasing Agonist Exercise Force Production is to take the "Antagonist Brake Off".
1) Stretching The Antagonist Muscles Prior to An Agonist Exercise
Doing so "Releases The Antagonist Brake", allowing greater Agonist Muscle Force Production.
Length of Antagonist Muscle Stretch
Stretching of the Antagonist Muscle 30 seconds or longer is the most effective.
Stretching Example
Stretching the Pecs, Anterior Shoulders and Triceps prior to performing a Pull Up/Chin.
2) Performing An Antagonist Exercise prior to a Agonist Muscle Exercise.
Doing so, is another method of "Releasing The Antagonist Brake".
Antagonist Exercise Example
Performing a Dumbbell Bench Press prior to a Pull Up or Chin.
A Dumbbell Bench Press relaxes the Antagonist Muscles along with allowing them to be Stretched before Pull Ups or Chins.
The objective is to "Release The Antagonist Brake". Thus, Light to Moderate Loads are effective; which allows you to place your focus and maximum effort on your Agonist Pull Up or Chin.