Time Under Load, a New Standard of Measurement

by M. Doug McGuff, M.D.

concept by Terry Carter

When I first met Terry Carter, I had no idea what a fortuitous event this would be. We met at the 1997 SuperSlow convention. I was there to speak and to gather information in preperation for opening my own facility. Terry offered to become involved with me and to provide the majority of personal training to be done at my facility as my emergency medicine career did not allow much time for me to train clients. One of Terry's few conditions for working with me at Ultimate Exercise was that we use stopwatches to record progress using time under load (TUL) rather than count repetitions. This seemed like a strange condition but Terry offered several sound reasons as detailed in this article.

Terry felt that counting reps is meaningless under most normal protocols as 6 reps done with the standard 2 second positive, 4 second negative would total 48 seconds TUL. But rep form is seldom that stable, thus 6 reps one workout might represent a vastly different TUL at another workout. SuperSlow standardizes your rep so that your record keeping is more precise when counting reps, but a single SuperSlow rep takes 20 seconds. Terry argued that you could do 4 SuperSlow reps one workout for 92 seconds time under load, and then at the next workout the same number of reps might actually be 80 seconds. This could be a first early warning of overtraining but it would be buried within that 20 second rep and never seen. Terry held that using a smaller unit of measure would provide more precise information to use when modulating volume and frequency. Terry said that counting reps for record-keeping purposes is "like using miles to measure the length of your house".

Terry then argued that TUL served to motivate clients better than rep counting. If you get 6 reps at one workout, and 6 the next you might feel dejected. But using TUL you would see that the first workout was 120 seconds and the second was 129 seconds. This is real progress and it is highly motivating. Further TUL tends to enforce the correct behavior in the client. Imagine your just a few inches short of completing your 6th rep when you fail. If you can't complete it you have to face the frustration of having to record 5 reps and knowing subconsiously that there are about 18 seconds of TUL that you don't get credit for. This situation drives many clients towards form descrepancies so they can complete the rep and "get credit". TUL however encourages good form because the client gets credit for every second he spends under load. Thus there are no sneaky attempts to change form or speed up the movement in order to complete a rep...indeed a common phrase at our facility is "slow....milk it for time".

The most intriguing reason Terry offered for using TUL was what I felt to be a rather bold statement. Terry claimed he expected to find an optimal TUL for each client on any particular movement. He even said he thought he could narrow it down to a 10 second window of time and then make small resistance increases within that window on an almost continuous basis. It sounded interesting but unlikely....was I ever wrong. As we started training clients and collecting data a pattern started to develop. Once the resistance became meaningful in a particular movement the client's TUL for that movement became very constant. This became apparent when one client recorded a TUL of 1:43 on 4 successive workouts even though he used more resistance every time. Over time the "window" of ideal TUL appears much more narrow than 10 seconds, in fact it is sometimes 1-3 seconds. Once we find a client's ideal TUL for a given movement we then just keep adding resistance on a workout by workout basis, and lo-and-behold their TUL remains relatively constant. If we had been using a rep range the client would have to endured 40-60 seconds more TUL in many cases before a weight graduation would have occurred.

Review of the scientific facts illustrates why enforcing a rep-range is counterproductive. Arthur Jones and Ellington Darden, PhD came up with a way of calculating an ideal rep- range by taking 80% of a one rep max and doing as many reps as you can. Then your rep range would be that plus or minus that number of reps x 0.15. They were very close (plus or minus 0.15 I would say). When a muscle is under significant load it recruits motor units (groups of muscle fibers innervated by a single motor nerve). It recruits these motor units sequentially in a particular order. In general recruitment begins with the slowest twitch fibers and ends with the fastest twitch fibers. Slow/fast twitch (contrary to popular notions) does not refer to speed of contraction but instead refers to how quickly a fiber fatigues. Slow twitch have a lower force output but lasts longer...fast twitch have high force output but fatigue quickly. So, if the resistance is meaningful, the fibers are recruited in a fixed order slowest, slow, fast, fastest.....each subtype having a fixed "staying power". Thus, if the load is meaningful, failure will occur at a fairly fixed TUL. I recalled that my chest press stayed stuck at 6 reps for almost 9 months, I even lightened the weight 20lbs to try to make 8 reps but was still stuck at 6 reps. It turns out my optimal TUL is 81 seconds....almost on the money every time. Now as long as my TUL is close to 81 seconds I progress the weight. Now I am making rapid progress on chest press. These TUL trends occurred in a blinded fashion....we don't look at TUL recordings on our clients until after the workout is done (each machine has a stopwatch hanging on it). When we go back to record what the client did we are often amazed to find that their TUL was duplicated to the second even though we jumped the resistance 10lbs from the last session.

We now believe the concept of double progression (increasing weight and reps) is actually mistaken. Instead one should find the signature TUL for a given person in that movement and then carry out single progression. That is, progress weight at a fixed TUL as is determined by a particular fiber type and motor unit recruitment pattern. Once you know the ideal TUL single progression (increasing resistance) appears to be the way to rapid gains. We find that if recovery is adequate that the resistance increase can be increased in fairly large increments. For males 8-10lb jumps on upper body and 14-20lb jumps on Leg Press. Female incremental changes are about half that of males.

For any individual signature TUL will vary from movement to movement. Mine are as follows Leg Press 2:54-3:00, Chest Press 1:21-1:23, Pulldown 2:10-2:20, Overhead Press 1:54-2:00. Terry on the other hand is about 1:00 on almost all movements except Pulldown where he trends towards 1:15. Finding a signature TUL is helped by recording your workout on a chart where you can see trends as your eye scans from left to right across the record.

I have had many tell me that varying rep range has brought them new progress and a recent article by Ellington Darden, PhD advocates varying rep speed and rep range. This is offered as a way of overcoming "exercise immunity". I believe that people may experience improvement when they vary their rep range and rep speed because in the process of doing so they have chance encounters with their ideal TUL. Why not deliberately seek out your ideal TUL and give single progression a try...I think you will be pleasantly surprised.

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