TUL / TCF and Weight Progression

By Tim Ryan and Fred Hahn


Tim Ryan began the presentation by discussing several proposed methods of determining a subject's ideal time under load (TUL) that have been promoted by various exercise professionals.  These are:

  1. Arthur Jones 20 Percent Inroad Theory -- Nautilus Research, Ellington Darden's Field Testing

  2. MedX® Fatigue Response Test (FRT)

  3. Brian Johnston's Fiber Typing Field Test

  4. Dr. Doug McGuff's "Signature Time Under Load"

Tim discussed and highlighted the numerous flaws and problems inherent in all the above referenced methods of determining an individual's ideal TUL and/or fiber type.  He concluded that though it may be helpful and desirable to have a test to individually determine a subject's ideal TUL/fiber type, unfortunately the technology does not currently exist to allow us to "know".  Furthermore, the currently proposed methods are inaccurate and misleading and thus are best discarded.

Fred Hahn then defined TUL and TCF:

TUL is the total time the muscle is under tension (i.e., from the instant the muscle begins to contract against the resistance until the time the weightload is released at the end of the set and the muscle relaxes.

TCF is the total time from the start of muscle contraction against resistance until movement against the resistance becomes impossible and the subject is unable to complete the rep (i.e., muscular failure).

Fred noted that TCF is a valuable performance variable and important for record keeping to analyze with regard to a subject's improvement and progression.

Fred then began a discussion of the current theories relating to what is believed to be the correct TUL/TCF for optimal muscle fiber recruitment and stimulation.  He also discussed several instructional related obstacles that arise when attempting to teach clients high intensity strength training and getting them to "behave" properly or perform competently with resistance levels that will render momentary muscle failure within the prescribed time frame.

Fred and Tim concluded by outlining the following points:

  1. The general scientific consensus is that muscular failure should be achieved within 1:00 to 2:00 minutes.

  2. Although stimulation of strength increases is possible with TUL/TCF less than or greater than 1:00 to 2:00 minutes, safety becomes an issue with TUL/TCF less than one minute, and time efficiency, muscle fiber recruitment, and client concentration/pain tolerance may be compromised at higher TUL/TCF. 

  3. It is thought possible that muscle failure with high TUL/TCF may be caused by "chemical congestion" in a muscle, rather than true muscle fiber fatigue, and that less muscle fibers are called upon and fatigued when using the lighter weight loads necessary to permit high TUL/TCF.

  4. In order to assure a maximum amount of muscle fiber recruitment, subjects should train with a weight load that is as heavy as possible to elicit muscle failure within the prescribed time, provided proper lifting form is not compromised. 

  5. Weight loads must be continually progressed over time to ensure continued muscle strength stimulation.

  6. Rep cadence must be standardized and all repetitions should be performed slowly and smoothly.  The NCES suggests a rep cadence of 10/10, but not less than 6/6.

  7. Instructors should understand that due to genetic differences it may be necessary to tailor TUL/TCF to the individual.  However, valid scientific evidence in this area is lacking, as are guidelines.  Approximately 80 percent of the population will respond best to the 1:00 to 2:00 minute guideline.  Therefore, the vast majority of subjects should be trained according to this guideline.