By Jason Dierking, Assistant Director Of Sports Performance, University Of Louisville
There are basically two pathways by which you can maximize your cardiovascular fitness: central and peripheral. Central adaptations refer to what I like to call the “delivery” side of the fitness equation, or things that are responsible for blood and oxygen being delivered to the working muscles effectively. These include heart rate, stroke volume, cardiac output, myocardial contractility, etc. Peripheral adaptations are the “utilization” part of the equation, or the ability of your muscles to maximally utilize the oxygen being delivered to them. Things like muscle capillary density, aerobic enzyme activity, mitochondrial density, etc.
Here’s the key: Central adaptations respond best to high intensity work (intervals, etc., that create very high heart rates).
Peripheral adaptations respond best to low intensity work around the aerobic threshold.
This is where people often make big mistakes when doing fitness training. They think (as I once did) that no matter what distance they’re training at for a given session, just go as hard as you can all the time. If you’re doing 400-meter repeats, run them all out in the best times possible. If you’re running 5 miles, then run 5 miles as fast as you can. There is no thought to controlling intensity based on achieving specific adaptations; the goal is simply to empty the tank every workout.
Here’s the second point regarding the two sides of the cardiovascular fitness equation: Adaptation to high intensity work happens relatively quickly (4-6 weeks), whereas adaptation to low intensity work takes considerably more time (4-6 months) (See Fig. 1).
So if you’re looking to get fit in a hurry, you should hit high intensities often. But understand that you are getting fit by only attacking one side of the equation, and there’s a limit to how fit you can ultimately get this way (not to mention a greater risk of injury and overtraining). Complete aerobic fitness happens when you put in the work at low intensities over time and develop the “low end” aerobic adaptations to support the higher intensity work.
This concept has significant implications when considering how to handle “unfit” players in a preseason scenario, especially in the case of a Fall sport like college soccer or football. We know two things about players who are the least fit during pre-season: they incur the highest daily training loads from practice, and they are chronically under-recovered from session to session (See Fig. 2).
This essentially creates a negative feedback loop. So, how do we typically handle these players? With extra “punishment” conditioning! Not to mention those extra sessions are often held at 6:00 a.m., which results in even less sleep, which means even less recovery, and so on and so on. So again, how should we handle unfit players?
The following list provides some guidelines:
- Additional high-intensity conditioning is not appropriate for unfit players during a period of intensive training such as the preseason.
- Supplemental low intensity, non-impact conditioning such as swimming or biking around the aerobic threshold (65-70 percent max heart rate) can safely build aerobic capacity and improve recovery.
- Supplemental high-intensity interval training should be used only as a substitute for practice minutes. Extra running can be an effective alternative if fatigue begins to negatively affect sport-specific skill/technical development during training.
- Careful tracking of daily training loads through heart rate, GPS, or RPE-based methods should be utilized to ensure appropriate loading for all athletes.
- Limit players’ game minutes during preseason and early-season games based on fitness testing and/or heart-rate recovery data.
FIGURE 1: Theoretical rates of adaptation based on the average relative intensity of training.
FIGURE 2: Predicted recovery curves for an unfit soccer player (Endurance Level 1 Beep Test score = Level 8-4) during the first week of pre-season training, based on Polar Team2 System. The vertical black lines indicate training load per session, and the red shaded area indicates the predicted recovery times. Overlapping red curves show under-recovery between sessions.
Jason Dierking, MSCC, is Assistant Director of Olympic Sports Performance at the University of Louisville. In this role, he works directly with men’s and women’s swimming, men’s soccer, and men’s golf.