Courtesy of Daniel L. Carl, Ph.D.
Why setting repeat intervals is crucial, and why often times I rely on rest intervals instead.
Close your eyes, think for a moment about a practice when poor little Susie is training in your group and is simply not ready to appropriately handle the workload you have established. You assign a set of 10 x 100 on 1:30 where a majority of the team will repeat 1:10s and have about 20s rest. Now Susie is tough and determined and she can make the 1:30 interval but is doing so while repeating in the low 1:20s and getting 5 – 10s rest. A simple repeat interval set that fits everyone doesn’t it? But does it? Let’s take a closer look at some of the numbers.
In the scenario just described most coaches will simply create another interval in a different lane. Maybe Susie and her teammates will have a 1:35 or even 1:40 cycle. Unfortunately, due to lane space and varying talent levels not all programs and coaches will have the flexibility to create all the space and intervals that are needed.
So does the muscle cell really know the difference between 20s and 5s of rest? What about 5-10s versus 45s recovery time? Research suggests that there is at least a biphasic ATP recovery pattern in muscle and possibly a tri-phasic pattern. With confidence, there is a rapid recovery rate where ATP stores are regenerated to ~50% in the first 20-25s. This is primarily through a combination of the relatively instantaneous phosphagen system and through glycolysis with some aerobic respiration. Additional ATP stores are regenerated at a slower recovery rate with about 75% restored in 40 seconds; 85-90% in 60 seconds and for the most part 100% in 3 minutes.
Back to our example regarding Susie. Because of the timeline in our scenario her recovery of ATP is insufficient relative to her faster teammates. What options does she have in this set? They’re not favorable, the bottom line is she is going to have to slow down or possibly fail in the set you designed. For sure she is not training her muscles in the same manner that the faster swimmers are. Even more likely Susie will shift to a different neural firing pattern including muscle fiber type.
One way I have used to address swimmers like Susie is to simply provide the swimmers with specific rest intervals rather than repeat intervals. If you were to provide the set as 10 x 100 @ 10s rest in theory all swimmers will be training in the same manner.
One negative of a rest interval set is that you run the risk of swimmers slacking off and repeating times slower than they should be. It does require that you as the coach instill into your program an environment where the individual is personally responsible for their training and you as the coach need to stay engaged in their training.
One positive of the rest interval set is that you can eliminate a potentially negative training environment. Rather than Susie feeling like she is slow and doesn’t belong, she is now being held to the same training responsibility as the fastest swimmers in the pool. Susie and all swimmers are engaged and training within the set as you desire.
Do you have a Susie or two in your practice? I encourage you to consider providing a rest interval on some training sets or even entire days in place of our standard repeat intervals. Use rest intervals to provide variety in your practices and to control the training parameters that you have designed. As a result, you may find the extra added benefit of team bonding when all members within a team are training together each with their own personal responsibility to be the best they can be. Good luck.
Baker JS, McCormick MC, Robergs RA. Interaction among skeletal muscle metabolic energy systems during intense exercise. J Nutr Metab. 2010;2010:905612. doi: 10.1155/2010/905612.
Barclay, C.J. J Muscle Res Cell Motil (2017). https://doi.org/10.1007/s10974-017-9467-7
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- Casey, D. Constantin-Teodosiu, S. Howell, E. Hultman, and P. L. Greenhaff, “Metabolic response of type I and II muscle fibers during repeated bouts of maximal exercise in humans,” American Journal of Physiology, vol. 271, no. 1, pp. E38–E43, 1996
Daniel L. Carl Ph.D. Bio
Dan Carl is an Associate Professor of Exercise Physiology in the Department of Rehabilitation, Exercise and Nutrition Sciences at the University of Cincinnati. Dr. Carl also works as a Senior Coach and consultant with the Cincinnati Marlins and as head coach at Sycamore HS. Prior to his 13 years in Cincinnati, Dr. Carl worked 14 years as a Division I coach at Miami Univ., Univ. of Delaware, Ohio State Univ. and Valparaiso University.