Metrics of Training Stress by Mark Langley


Mark Langley

There is as much an art to coaching as there is science. While we can go by objective metrics to guide our training, there is a certain intuitive aspect that qualitatively separates coaching from a grocery list of exercises to perform. It takes some degree of feeling to understand the impact a training program will have on your athletes, and trying to quantify how it feels objectively might be hard.

To put it simply, 3,225 total pounds of volume load can be meaningless if you don’t understand the context, and there are some important questions to ask. Are the athletes performing compound movements or simple movements? What’s the number of sets, reps, and length of their rest intervals? Volume load needs some sort of asterisk that denotes all of these details. Take for example these two work outs:

The first workout looks like it’s searching for a 1 rep max (1RM) and then doing sets around 90% 1RM. The second session on the other hand is completing something more in terms of endurance. They have equal volumes, but entirely different outcomes. Trying to compare these two is like comparing apples to oranges. It only makes sense to compare workouts that have similar objectives.

We can try to compare the two according to density or total weight over time:

In this scenario, going strictly by the numbers can also be misleading. We can’t draw conclusions based off of this information. We’ve gone from comparing apples and oranges to entire orchards of each. If we were to jump to conclusions we might be convinced that one training stimulus had more impact or requires more recovery than another. Again, comparisons only make sense if we compare similar modes of work. Making cross comparisons is moot.

A more relevant method of comparing the two can be through work. Work is the product of mass accelerated over distance, and alternatively force and distance.

The equations above are rough examples of what work is, but of course it’s always more complicated because that’s how physics tends to be. Doing the math on this isn’t simple or clean. Luckily, PUSH does the math on its own, and produced the following data:

We’ve now identified a metric which makes the two workouts not only comparable, but almost equal to one another. Had the endurance training not completed it’s final set, or the strength training added a couple of reps, the work totals for each could even be equal. The important note to take from this equation is that acceleration can play as much of a role as total reps when determining total work. Had strength increased - or endurance decreased - its acceleration, then the work values of the equations would have also ended closer to one another.

Any change of the applicable variables of the work equation (mass, acceleration, distance), could result in the two work values becoming attenuated. . The volume of training is just as important as the qualitative parts, or the parts that make different types of resistance training unique. This gives some metric of training stress.1

Since we’ve now found a comparable metric for these equations we can look at the densities of each. On the surface, this seems no different than volume density. Density can describe the energetic system targeted by the training, something not at all illustrated by this example. This example shows just strength and endurance, but really shines when comparing reps or pause sets, where the eccentric portion of the lift is emphasized. Thusly, it gives a method of comparison that is advantageous in certain methodologies such as hypertrophy, power, or speed training.

Figure 1: Monod H, Scherrer J. The Work Capacity of a Synergic Muscular Group. Ergonomics. 1965;8(3):329-338. doi:10.1080/00140136508930810.

Figure 1: Monod H, Scherrer J. The Work Capacity of a Synergic Muscular Group. Ergonomics. 1965;8(3):329-338. doi:10.1080/00140136508930810.


In the context of weight training, dynamic work capacity is the maximum amount of work one is able to accomplish.2 Since this can be done aerobically or anaerobically, it levels the playing field across different modes of training.3 It also gives us some modicum of understanding when we’re talking about the upper limits of training and performance. There has been some research on the difference between volume and work,4 but few studies have defined work capacity in this specific way. Many think of work capacity as a given mass being moved until failure in a single set, or a capacity of work that is limited upon its work dimension.5–7 This has fostered some definitions that describe exactly what volume is used for: disregarding dynamic work. With the advent of accelerometers, linear position transducers, and other weightroom technologies, we’re able to look at this issue in a more mechanical way.

One point worth mentioning is that although work may be a useful metric for training stress, work capacity (the upper limit) may have limitations. As previously mentioned, there isn’t an abundance of foundational understanding of dynamic work capacity in biomechanical terms and how it pertains to resistance training. It does however give us a great basis to compare the quality of one day’s training to another.

PUSH calculates work and volume load, charting it over time via the web Portal. This gives users a gauge of their progress. The portal can be used to help gauge whether a high-low scheme is actually high or low beyond simpler measures of intensity or volume. It can also identify specialization if the programming is split by muscular emphasis or location on the body. Lastly, It can identify specialization by energy system, with certain loads being more efficient than others.

Overall, the ability to measure a workout based on the measure of work - as opposed to simply intensity or volume - allows a much deeper and measured approach to any weight training program. However the complexity of the work equation makes it a difficult metric to account for day-to-day. It is the simplicity, convenience, and immediacy of PUSH to measure work, which makes it an invaluable product for the optimization of fitnss routines.

Figure 2: Note the major differences between day two and day four

Figure 2: Note the major differences between day two and day four


  1. Hu M, Finni T, Zou L, et al. Effects of strength training on work capacity and parasympathetic heart rate modulation during exercise in physically inactive men. Int J Sports Med. 2009;30(10):719-724. doi:10.1055/s-0029-1225329.
  2. Monod H, Scherrer J. The work capacity of a synergic muscular group. Ergonomics. 1965;8(3):329-338. doi:10.1080/00140136508930810.
  3. Pujol TJ, Mayhew JL, Brechue WF, Smith AE, Reneau P, Barnes JT. Effect of heavy resistance training on low- and high-intensity upper body work capacity in college women. Med Sci Sport Exerc. 2011;43(Suppl 1):837-838. doi:10.1249/01.MSS.0000402333.96006.cb.
  4. McBride JM, McCaulley GO, Cormie P, Nuzzo JL, Cavill MJ, Triplett NT. Comparison of methods to quantify volume during resistance exercise. J Strength Cond Res. 2009;23(1):106-110. doi:10.1519/JSC.0b013e31818efdfe.
  5. Mayhew JL, Brechue WF, Smith AE, Kemmler W, Lauber D, Koch AJ. Impact of testing strategy on expression of upper-body work capacity and one-repetition maximum prediction after resistance training in college-aged men and women. J Strength Cond Res. 2011;25(10):2796-2807. doi:10.1519/JSC.0b013e31822dcea0.
  6. Brechue WF, Mayhew JL. Lower-body work Capacity and one-repetition maximum squat prediction in college football players. J Strength Cond Res. 2012;26:364-372. doi:10.1519/JSC.0b013e318225eee3.
  7. Taylor SA, Batterham AM. The reproducibility of estimates of critical power and anaerobic work capacity in upper-body exercise. Eur J Appl Physiol. 2002;87(1):43-49. doi:10.1007/s00421-002-0586-4.