Is Repeat Sprinting an Aerobic Activity?

It’s great to be back in the gym after a relaxing weekend. My mom came to visit Emily and I from Raleigh, NC so it was nice to have some down time to hang out with her. As you can imagine, my schedule keeps my pretty busy, so I don’t get to spend as much time with friends and family as I’d like!

As I mentioned last week, I’ve been reading quite a bit of research on energy systems recently. Understanding where energy for certain activities comes from will help make training more specific and appropriate to the demands of the sport (and the position in some cases). In general, it is traditionally thought that:

  1. The ATP-PCr System contributes to high intensity activities ranging from 0-12 seconds.
  2. The Anaerobic Glycolytic System contributes to moderate-high intensity activities ranging from ~13s-~30-45s
  3. The Aerobic Glycolytic System contributes to moderate intensity activities ranging from ~30s-3 minutes
  4. The Aerobic Beta-Oxidation System contributes to low-moderate intensity activities from 3-minutes on

Naturally, this is a grossly oversimplified view of energy systems training, which is the major reason for this discussion. It’s important to realize that the intensity of movement is equally, if not more important in determining energy system contribution than the duration of the activity. In other words, if you walk for 12 seconds, you won’t be relying on the ATP-PCr System as your primary energy source; it’s a low intensity activity that doesn’t require a huge surge of energy production. As your body performs work, it breaks down ATP. Replenishment of ATP is needed to continue to do work. Naturally, the higher the intensity of the activity, the faster the breakdown of ATP and therefore, the faster the replenishment source needs to be. This is why high intensity activities rely on the ATP-PCr system; it’s the fastest replenishment source. Unfortunately, this supply is limited, so as stores become depleted, the body must rely on other energy systems for the replenishment of ATP. Because these other systems cannot replenish ATP as rapidly, performance decreases. This is an underlying reason why someone can run a 4.3s 40-yard dash (120 feet at 27.9 ft/second), but not a 3:09 mile (5,280 feet at 27.9 ft/second). Simply, the rate at which energy can be resupplied is a limiting factor in maintaining high level performance.

After reading the above paragraph, it’s reasonable to think that the systems are activated in the presented sequence; the next being activated when the former is depleted. In other words, Anaerobic Glycolysis System becomes active when the ATP-PCr System depletes, the Aerobic Glycolysis System becomes active when the Anaerobic Glycolysis System depletes, and so on. In fact, this isn’t too far off of how this is typically presented in undergraduate academic programs. In reality, almost ALL systems are always active to some degree during every activity and preceding activity will play a role in which system predominates.

One illustration of this comes from a 1999 study from Parolin et al. titled “Regulation of skeletal muscle glycogen phosphorylase and PDH during maximal intermittent exercise.” As an aside, I find that I’m a little embarrassed when research of this magnitude is over 10 years old before I come across it!

The study looked at the contribution of ATP regeneration from PCr, glycolysis, and oxidative (aerobic) systems during a repeat high intensity sprint task. More specifically, the subjects were asked to perform 3 30-second maximum effort cycling sprints at 100 RPMs, separated by 4 minutes of rest. The authors compared the first and third cycling effort using the following time periods:

  1. “Rest”: Immediately before the 1st and 3rd trials
  2. 0-6 second time block of the 1st and 3rd trials
  3. 6-15 second time block of the 1st and 3rd trials
  4. 15-30 second time block of the 1st and 3rd trials

What they found was fascinating.

Results:

  1. Total power decreased from 622+/-27 W to 459+/-32W from the 1st to 3rd work bouts respectively.
  2. Total PCr hydrolysis was greater in the 1st trial compared to the 3rd (80.7 vs. 59.9 mmol/kg/dry wt). Before the 3rd trial, PCr availability was 79% of what it was before the 1st trial, indicating incomplete replenishment.
  3. Muscle glycogen utilization was 89.2+/-31.3 mmol/kg dry wt during the 1st trial, but reduced to a negligible 4.2+/-28.5 mmol/kg dry wt during the 3rd trial.
  4. The rate of pyruvate production was highest in the first 15s of the 1st trial, but dropped to <1/3-1/6 in the last 15s of the 1st trial and through throughout the 3rd trial. However, pyruvate oxidation increased for than 3x during the last 15s of the first bout.
  5. During the 1st trial, concentrations of lactate, pyruvate, and H+ increased progressively during the first 15s, and then leveled off across the final 15s. Levels of these metabolic byproducts remained high during the 3rd bout, but DID NOT increase further.
  6. However, the concentration of ATP was UNCHANGED during exercise AND between bouts.

This is just a snapshot of a myriad of results from the authors’ analyses, but taken together this study demonstrates:

  1. After 15s of a single 30s bout, oxidative phosphorylation becomes the primary contributor of ATP replenishment.
  2. Oxidative energy systems provide an increasing proportion of total ATP replenishment with repeated high intensity efforts.

In other words:

  1. The oxidative system provides a significant amount of energy almost immediately, even during high intensity efforts.
  2. Oxidative systems become increasingly important with repeated efforts (think multiple shifts).

Again, there is much more discussion to be had on the methods and results of this study, but it provides reasonable evidence for the importance of developing aerobic systems even in sports that are seemingly anaerobic dominant, such as ice hockey. As I’ve alluded to in the past, there are appropriate times of year and methods to develop this system, but the idea that hockey players ONLY need to do high intensity intervals from 30-45s is just as misguided as the idea that they only need to go for long jogs or bike rides to develop their conditioning.

To your success,

Kevin Neeld

P.S. Special thanks to Joel Jamieson for directing me to this study.

P.S.2. If you want a structured off-ice hockey conditioning system, check this out: Ultimate Hockey Training!

Reference:
Parolin, M., Cheseley, A., Matsos, M., et al. (1999). Regulation of skeletal muscle glycogen phosphorylase and PDH during maximal intermittent exercise. American Journal of Physiology, 277: E890-900

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