Without getting too scientific on this subject, Author L. Rea goes into some depth about this in his book, “Building The Perfect Beast”.
Many of these charts that I have seen often suggest you use, for example, the bench press for determining fiber type in your chest. The problem with using the major compound moves is that for most people, triceps and delts tire way before your pecs. Therefore, your results will be somewhat inaccurate.
A better way to do this is to use isolation exercises:
Pecs: Pec-Dec or DB Flyes
Ant. Delts: Pulley Raise or BB Raise
Lat. Delts: Seated DB Laterals or Cable Laterals
Pos. Delts: Reverse Pec Dec or Reverse Inclined Rear Laterals
Bi’s: 90-degree Preacher Curl
Tri’s: Superstrict Triceps Pushdowns
Lats: Straight Arm Cable Pullover or Machine Pullovers
Traps: Full Range DB Shrugs
Erectors: Weighted Hyper Extensions
Hams: Leg Curls (lying, seated, standing, your choice)
Quads: Leg Ext. or Parallel Squats
Calves: Seated Calf Raise or Strict Donkey Raise
***Try to utilize a 1.5-2.0 second positive, and a 1.5-2.0 second negative rep speed.
Find the single rep max (SRM) for each body part.
Reduce the weight to 85% of SRM and do a set to positive failure with reasonable form.
If you are able to complete more than a higher number of reps, then that bodypart is predominantly type-I slow twitch endurance fibers.
If you can only complete a lower number of reps, it would be obvious that there is an existing higher ratio of type-II fibers and the greater potential for growth, in most cases.
As we age, the ratio of fiber types changes toward an increase in type-I fibers. This is usually not a problem with life-long weight trainers. The good news is that fiber type ratios can be altered as can muscle cell number and fiber number/size. Training stimuli and hormones greatly influence this as well due to specific intent training techniques. However, hormones, intermediates, and ATP have the greater potential for influence.
Hope this helps. A lot of it was taken directly from Building The Perfect Beast and a some other sources.
Just remember that this is not always an exact science, it is only meant to be an approximation and somewhat of a guideline on what rep ranges your body responds to best.