As explained before, I retain full rights to the linked graphs. I foresee no problems with others linking to them for discussion purposes even on other fora, so long as they are not altered or amended in any way. My thanks, once again, to Weldon for hosting them and allowing the following discussion.
Okay, let me walk us through a well-known paper by Dudley, Abraham and Terjung. As much as possible I am going to be referring to direct quotes and graphs drawn used the given raw data from the paper itself. So any time you see "quote marks", you can be sure this is a direct quotation from the original paper. As much as possible we are going to be relying on the interpretations and conclusions of the original authors.
The paper is; Dudley, G.A., W.M. Abraham and R.L. Terjung (1982); Influence of exercise intensity and duration on biochemical adaptations in skeletal muscle. J. Appl. Physiol.; Respirat, Environ. Exercise Physiol. 53(4):844-850.
The scope of the paper (as explained in its title) is to see what effect training intensity and workout duration can have on muscle adaptations.
Before beginning, the researchers identified four variables that might contribute to the effectiveness of any training programme:
1: intensity of each workout
2: duration of each workout
3: duration of the whole exercise programme (ie: six weeks of a training programme should be better than two weeks of the same programme)
4: workout frequency (and they suggest near-daily is important)
To focus the research on the first two variables, they held the latter two variables constant, making sure that all trained subjects would train with the same frequency and for the same length of training programme (ie: all rats would be trained for a total of 8 weeks [including two weeks treadmill familiarisation], with the training of the last 6 weeks being unchanged. All rats would be trained 5 days/week so that different workout frequencies would not have an impact on results).
By doing this, and thereby canceling out the effects of the latter two variables, they could be confident that any adaptations they found would be due to one, or both, of the first two variables (ie: due either to exercise intensity and/or workout duration).
Understanding the precise relationship between the physiological adaptive response and the exercise parameters (intensity, workout duration, frequency) is the real key to optimal training. Dudley and co-workers focused on two major factors in this paper (the duration and intensity of each exercise bout) and then analysed the effects on each muscle fibre type.
They state that the cytochrome c concentration (a marker for mitochondrial mass) was assessed in three different muscle fibre types in rats (STR, FTR and FTW) which had been treadmill trained for 8 weeks (5 days/week) by any one of 19 different training protocols. They specifically note that the influence of training intensity was "very different between fibre types", in other words, not all fibre types responded in the same way (thereby making their findings very relevant to the scope behind this Cabral & Hadd thread).
As longtime runners, some things are obvious to most of us; a minimal training intensity is necessary, and the increase in oxidative capacity (the ability of each fibre to work "aerobically") will be specific only to the working muscle(s). In other words, this adaptation will not be found in the muscle groups that are not involved in the exercise effort. This should make sense, couch potatoes don't become "aerobic monsters" without some form of training ... and any adaptations that do occur will only do so in the muscles doing the exercising.
However, [the researchers note] even when a whole muscle is directly involved in the work effort, "the ordered pattern of motor-unit recruitment apparent with increasing intensity becomes important, and probably accounts for the non-homogenous muscle fibre response found within a trained muscle."
So, even though you think you are "working your quads, or hamstrings" with a particular type of training and exercise intensity; you are only working the particular muscle fibres that are getting recruited at that exercise intensity. If the intensity is low, not all fibres will be recruited. As we shall see, doing the exact same movement, but with greater, or lesser intensity, can recruit (and thus cause adaptation) in different fibre types within the same whole muscle.
In the researchers' own words, "this [made] it essential to assess the adaptive response in each of the individual skeletal muscle fibre types."
In other words, when we train at particular intensities, what muscle fibre type is getting trained, and how much adaptation is being caused in that fibre type by each intensity?
Okay, they used rats. I guess they found it tough to find humans willing to be decapitated and exsanguinated after the training programme was complete ...
The rats were segregated into six different training groups ranging in a progression of training intensities from the easiest, requiring "moderate submaximal oxygen requirement" (moderate-VO2), all the way up to the most intense, "a supramaximal exercise effort" surpassing the rat's maximal aerobic capacity.
At the same time, a number of workout durations were chosen for each exercise intensity "in an attempt to characterise the influence of exercise duration". For example, if 3 groups of rats were scheduled to always train at "intensity-1" (the easiest) then each of the 3 groups trained at that intensity would be given different workout durations (30, 60 and 90 mins per day).
So, one of the three groups might run at intensity-1 for 30 mins/day, 5 days/week for (the final) six weeks. A second group might run at intensity-1 for 60 mins/day, 5 days/week for (the final) six weeks, and so on. This way they expected to determine whether a longer duration of workout was advantageous, or not.
Of the six training intensities, the first four were run in a "continuous run" format, while the two most intense were run as "interval" type workouts.
So, at the lower four intensities (all submaximal), the runs were "continuous". Obviously at the highest two intensities (above VO2max pace) a continuous running format was not possible, so a format of interval training was used. At intensity-5, the format was 4:30 mins run with 2:30 mins rest. At intensity-6 (the fastest pace) the fomat was 2:30 mins run and 4:30 mins rest.
Let me make that more clear:
Groups 1 to 4; continuous running training format
Intensity-1 (easiest): 3 groups of rats training at same pace, but 3 different workout durations: 30, 60, 90 mins/day
Intensity-2: 3 groups, same pace: 30, 60, 90 mins/day
Intensity-3: 3 groups, same pace: 30, 60, 90 mins/day
Intensity-4: 4 groups, same pace: 15, 30, 60, 90 mins/day
Groups 5 and 6; interval training format
Intensity-5: 3 groups, same pace, different durations; 9, 18 and 27 mins/day (length of interval reps given above, 4:30 mins run and 2:30 mins rest)
Intensity-6 (hardest): 3 groups, same pace: 5, 10 and 15 mins/day (length of interval reps given above, 2:30 mins run and 4:30 mins rest)
Six intensities of training for a total 19 groups of rats. The exercise levels and durations were unchanged for the final six weeks of the training programme then the rats' muscles were analysed.
Now, as I will explain later, it does not matter what the intensities were in this study. I could have put them in, but I think they would have just been confusing. For a number of reasons: 1) the subjects were rats, so the training intensities used are not directly applicable to humans, 2) as I will argue, it depends on what percentage you have of each fibre type what the optimal training intensity will be for you.
After the training, samples of FTW (Fast Twitch White), FTR (Fast Twitch Red) and STR (Slow Twitch Red) muscle sections were obtained. Cytochrome c concentration was used as an index of training-induced changes in muscle oxidative capacity.
INFLUENCE OF EXERCISE INTENSITY ON TRAINING ADAPTATIONS
(I will discuss the influence of workout duration in a later post):
(and here we can look at the attached graph, redrawn from the raw data given in the original paper).
A quick explanation of the graph:
The horizontal axis shows the [increasing] exercise intensities from easiest (intensity-1) to the hardest (intensity-6). As already stated, intensities 1-4 are in continuous-running format, and intensities 5-6 are in interval-training format. The 0-zero value (the vertical axis) shows the "untrained" muscle fibre cytochrome c content. The Red dots show the cytochrome c content of those groups of rats trained at each intensity. There are between 5-19 rats per data point.
The researchers start off by saying, "... as treadmill speed is increased there is, in general, an increase in the peak adaptive response."
This makes sense; we would expect that a steady running pace is going to provoke a greater adaptive response than a jogging pace. However, they go on, "... even though exercise intensity increased the peak adaptive response in each fibre type, the pattern of influence was not identical."
For example, (and I quote) "the cytochrome c concentration in [STR fibres] increased, up to a limit, as the exercise intensity became greater; however, the adaptive response actually declined at the more intense exercise conditions." [no emphasis in original]
Let's look at the graph again. We can see that with the increase in training intensity from intensity-1 to intensity-3 there is a corresponding adaptive increase in mitochondrial mass (as measured by cytochrome c content). In other words, running steady is better than jogging. We can further see that training at intensity-4 offers little or no further increase in mitochondrial mass above that of intensity-3, and that intensities 5-6 result in an actual decline in adaptation, or poorer stimulus for adaptation for mitochondial mass when compared to intensities 3-4.
In fact, we could go further, and draw a horizontal line between the adaptation at intensity-6 and the adaptation at intensity-1 and see that training at intensity-6 (the greatest intensity) causes no further adaptation [in STR fibres] than training at intensity-1 (the least).
The conclusion seems quite clear; for STR fibres there appears to be a training intensity, or effort-level, beyond which no further increase in adaptation will occur in that fibre type. In short, for STR fibres, faster training (above a certain intensity) is definitely NOT better.
Why might that be? We'll be able to answer that question by looking at the next graph drawn from the same paper.