Friday, July 31, 2009
The Science of 'Steady'
On our Endurance Corner forum (www.endurancecorner.com) the following question was recently raised, regarding the emphasis Endurance Corner places on steady-state training:
“Help from the research literature gurus, please.
My involvement with Endurance Corner has generated plenty of great discussion at the cardiology practice I work in. Many of us in the practice pride ourselves on readily referencing the various studies that provide support for the diagnostic and therapeutic recommendations we make. If I can't reference a study, I am careful to qualify my position as being based on a theory or based on anecdotal experience.
Today I was making a case for endurance athletes spending a significant amount of the available training hours on 'steady" zone work. The very appropriate question came up, 'based on what research". My response "I'll get back to you'.
While there are a number of observational studies on elite swimmers, cyclists and runners that support a large percentage of training being spent in what we at EC would call the ‘steady’ training zone, i.e. at or slightly above the aerobic threshold, there are few controlled scientific studies on athletes that provide scientific validation. The reasons for this are multiple and more related to the difficulties in controlling the extraneous variables within an athlete’s life, coupled with the fact that most studies are, by their nature, short duration studies, and finally that it’s tough to convince an ethics board of the merits of ‘harvesting’ the athlete at the end of the study so that physiological adaptations can be investigated to their full extent :-)For this reason, we tend to turn to the rats to help to determine the training strategies that result in optimal physiological adaptation.
One of the studies that I referenced in reply to this athlete’s question was the landmark (rat) study of Dudley, Terjung and Abrahams (1982).
In the study, the researchers subjected rats to training protocols of varied durations and intensities over the course of 6 weeks ranging from 10mins/day at 116% of VO2max to 90mins/day at 50% of VO2max. They then looked at mitochondrial adapatation as a function of cytochrome c concentration in the 3 different fiber types – fast glycolytic, fast oxidative and slow oxidative.
While the optimal protocol for improving the aerobic capacity of FOG fibers was clearly maximized at 60-90 minutes per day of training just below the anaerobic threshold (~functional threshold pace/power), the slow twitch fibers exhibited a different pattern:
The aerobic capacity of the fiber is shown on the y axis (in the form of cytochrome c concentration) for the 3 different duration groups on the x axis (30, 60 and 90 minutes per day) for each respective intensity level.
In the first group – 10m/min or approximately 20% of the ‘athletes’ vVO2max, a very light level of intensity, only small improvement in aerobic capacity can be expected. Additionally, once the athlete is doing 60 minutes per day at this level, very little additional improvement can be expected with increased duration. In other words, there is little physiological benefit to ‘touring’ at very low intensities, whatever the duration.
This pattern continues for the second group (~40% of the ‘athletes’ vVO2max) albeit to a lesser extent. We may consider this ‘easy’ training, the type used for recovery or warm-up. This training is still quite limited in terms of the benefit to the aerobic capacity of the muscle fibers. However, 60-90 minute training sessions are still useful, though less so than 60 minutes of ‘steady’ which we’ll get to in a bit. But first…
The 40m/min protocol reflects a training level approaching the ‘athletes’ functional threshold. Clearly, this is not only a powerful stimulus for the fast oxidative fibers mentioned above, but also these slow twitch fibers. In fact, according to the data, 30 minutes of threshold training is more beneficial to the slow twitch fibers than 60 minutes of steady training.
The benefit of threshold training to the slow twitch fibers is ‘maxed out’ at ~60 minutes of training. Looking at the trend of the 30m/min curve (an intensity approximately equal to ‘steady’) it is clear to see that while 90 minutes of steady training only equals 60 minutes of threshold training, in terms of relative benefit, the ‘steady’ curve is still on the up and up.
In other words, we would expect continued benefit at 2hrs and potentially 3hrs and maybe even 4. In fact, this has been confirmed by a study by Harms and Hickson (1983) who found this near linear relationship existed through to 2hrs/day of steady training. However, despite the fact that we subject 10 year old swimmers to ‘2-a-days’ of 3-4hrs of training, we are yet to subject the rats to the same fate. So we can only guess on whether this trend will continue to 3 and 4 hours. Elite athletic practice would say yes!
In summary, the greatest aerobic benefit to your slowtwitch fibers will be had from the following sessions in order of importance:
- 2-4hrs of steady training
- 45-60 minutes of mod-hard to threshold training
- 30 minutes of threshold training
- 60 minutes of steady training
- 60-90 minutes of easy training
Of 4 intensity levels examined, only one offered continued benefit for the athlete willing/able to train for more than 90 minutes per day – steady. Not too easy. Not too hard. Steady is ‘just right’ :-)