Although there is a bit of a drop during a typical ramp interval, a 10% range is minimal. To make O2 monitoring on a real time basis useful, a large dynamic range is needed since we will be making power adjustments on the fly without the luxury of careful study.
Looking at a given locomotor muscle itself is also problematic. Depending on the muscle, place on the muscle, depth of sensor measurement, time under load, readings are variable and confusing. For instance this is a tracing of the vastus lateralus on a 350 watt ramp to near exhaustion. Note the relative minimal drop, and even a rise toward the end. Clearly this is useless for dynamic real time decision making about ride intensity and pacing strategy.
During intense aerobic exercise, the pulmonary system needs to keep O2 supply high since the locomotor muscle activity is increased dramatically(need to feed the legs more oxygen). The old saying, robbing Peter to pay Paul, seems appropriate here. Looking at the costal O2 drop as a surrogate marker for locomotor muscle intensity status, overall body metabolic acid/base status as well as a danger point for respiratory muscle fatigue is the proposal.
A study was done looking at the change in respirarory muscle strength after ramp exercise in runners and cyclists. It was found that a significant drop in muscle strength occrred after an exhausting ramp:
So, the presumed respiratory muscular hypoxia/increased work of breathing is severe enough to manifest as reduced motor force after a ramping session.
For a given race situation it would be nice to have some idea on how long we can maintain a level of power without leading to decompensation/excess acidosis. At extreme examples, having a costal O2 near baseline would not be associated with any imminent decompensation, yet one that is rapidly and sharply dropping would be.
From multiple observations, I would classify potential zones as baseline/steady state, moderate efforts and HIT/SIT. The first two can be more easily determined by power/watts. But high and supra maximal interval determination may be better defined by how quickly and how low the costal O2 drops.
A couple of examples are in order.
First would be a tracing of 280 watts for 6 min:
In this example the costal O2 remained a steady 36% after the initial drop from about 70%
The exact watt figure is not as important as the observation (as well as the perceived effort) that this was a level that did not adversely lead to decompensation. So perhaps a "high intensity" zone.
The next example would be more of a HIT to SIT zone.
This was 3 min with the last half at 370 watts, O2 going from 66 to 14%. Clearly further duration at this power output would not be possible. There was significant respiratory and locomotor muscle fatigue by the end.
The final zone example would be a supra maximal effort, 530 watt average over 1 min.
Baseline O2 was about 70% with a nadir of 4%.
Note the slow gradual O2 rise after the max effort while still maintaining a power of about 140 watts. It still remained in the range well below normal until coasting. During that time, any further effort above a low level may not have been possible.
If the above observations are somewhat valid and we can use the costal O2 as a surrogate marker for locomotor effort/acidosis/decompensation it then follows that perhaps the same parameter can be used for real time road race pacing. Sure, one may know that they can do 5 minutes at xxx watts, or 30 seconds at yyy watts, but do they know what the most optimal way to handle undulating power output would be. Or how long can they afford to boost power in order to drop a rider following up a climb. Heart rate is going to be near max in many of these scenarios, watts variable and perceived effort possibly clouded by competitive psyche. Sensor on a leg muscle (at least from what I have seen and read in the literature) would not be helpful here-see some of the previous posts.
Here are a couple of examples of real time sensor use.
This tracing is up a climb, about 3 min of effort. The idea was to drop my "opponent" by going faster than usual for the first portion, getting a gap (they then lose drafting) and then back off when my costal O2 drops into an intermediate zone
Of course this is done all the time but it helps to know at what point do you back off a bit and perhaps how depleted one would be shortly after. As mentioned, depending on the degree of power output, duration and variability, the costal O2 tracing will vary. The hope is that it would give an indirect estimation of reserves, effort intensity and capacity to boost power later on.
The next tracing is of the same climb, similar average overall wattage, but different strategy.
Here a gradual ramping was done, leading to a good power effort, but costal O2 drop was lower (16%) and since no gap was achieved by distancing the rider behind me, he had no trouble keeping up. Therefore, at least in this example, pacing strategy and sensor data could be quite useful.
Conversely, the costal O2 could also be used as one of the clues on how to increase power to keep up with a rider/group. so if you are about to get dropped, passed or trying to catch up, a real time indicator of metabolic effort may be helpful.
Another example of costal O2 usage, also up a climb with a rider behind.
The plan was to do about 480 watts for 1 min, drop the rider behind, watch costal O2 (to avoid the "danger zone") and then back off power to something sustainable. The problem was, the following rider was still there at the 50 sec mark. I then boosted power somewhat and he quickly fell off the pace. Note the yellow O2 curve falling more sharply during this time.
That pace would not have been sustainable for long, but cutting back to a 290 watt average was fine for the next 3 min with a steady O2.
Finally, to validate that I was indeed capable of dropping costal O2 to an even lower level (perhaps 30% O2 sat was my limit that day) I did 2 min at near 400 watts:
- Costal O2 may provide guidance on more extreme intensity zones for training purposes.
- May help gauge real time watt output in a race situation to avoid excess acidosis, decompensation. Examples would include temporarily increasing power to break away, modulating power to catch up.
- Whether this would lead to better overall performance, better pacing strategy remains to be proven. But it is certainly intriguing.
Next: Cardiac output redistribution