Some people tend to thrive on very little exercise, while others seem to be incapable of making gains no matter how hard, long and frequently they train. Learn how to design a program custom tailored to your needs.
One of my favorite lines is, "I can pass by the weight room, smell the iron inside, and instantly begin to grow." Simply, some people tend to thrive on very little exercise, while others seem to be incapable of making gains no matter how hard, long and frequently they train. This was referred to as one's "tolerance to exercise," a term coined by Arthur Jones years ago.

One's "tolerance" is high if more exercise is needed, and low if less is needed. There are many variables that can affect your exercise tolerance. Of course, "genetics" ranks highest on the list below, and you'll notice several such factors. Others, on the other hand, are able to be manipulated in various ways.

Factors That Affect Your Exercise Tolerance:

Red vs White Fiber Ratio
Tolerance To Pain
Level Of "Psych"
Amount Of Rest Since Last Workout
Perceived Exertion
Amount Of Eccentric Stress (Which Causes Connective Tissue Microtrauma)
Incentive Level
Strength-To-Weight Ratio
Time Of Last Meal (Energy)
Type Of Foods Eaten At Last Meal (Glycemic Index)
Use Of Ergogenic Techniques Or Substances
Musculoskeletal Leverage Factors
Motor Unit Recruitment Capabilities
Skill Level At Exercise Being Performed (If Such Is Required; e.g., Cleans)
Equipment Quality & Design
Environmental Factors (e.g., Heat, Cold, etc.)
Size Of Muscle Being Exercised
Various Intra- and Extracellular Biochemical Factors
How close you are to your maximum potential in size or strength

All these factors, and perhaps several more as yet undreamed of, will variably affect how frequently you should train each body part and how best to split your routine.

Several years ago, after chatting with Arthur and reading some of his thinking on the topic, I began charting other lifters' reps at 80 percent max. I found that guys who were so-called "fast" gainers were only able to do 4-6 reps at 80 percent, while lifters who seemingly never made great gains were able to rep out at around 15-20 reps with 80 percent of their max. Apparently, so-called "fast gainers" have rather poor anaerobic strength endurance. This is explainable in part by the fact that they're probably mostly white muscle fiber, which has fast twitch/low oxidative capabilities. Conversely, slow gainers are probably mostly red muscle fiber (slow twitch/high oxidative) and therefore may possess greater ability for rapid during-set recovery.

The problem is, however, that each muscle group's tolerance to exercise probably differs. Each exercise you do for each body part can - and often does - possess an entirely individual rep ability at 80 percent max.

To Discern Your Specific Tolerance Level For Each Body Part, Follow These Simple Instructions:

1. Determine your approximate one rep maximum (1RM) for each exercise.

2. Load 80 percent on the bar (machine) & rep out with it for one all-out effort to see how many reps you can do.

3. Apply this information to the table below to determine each body part's exercise tolerance.

4. Take into account ALL of the factors listed above that can affect your exercise tolerance.

5. Critically evaluate whether your predicted exercise tolerance levels stand up to what you know from experience to be true. Remember, "low tolerance" means that you probably make easy gains for that body part, and "high tolerance" means that you're probably a hard gainer for that body part.

Here is an example of what I've found in regards to exercise tolerances for fast gainers, average gainers and slow gainers. Perhaps you'll find these figures and estimations to be pretty close estimates. But perhaps you won't. One thing is clear, you must look! Your continued progress toward your maximum potential may well depend on it!