So which is better at least in relation to muscle O2?
Before answering, one needs to know better at what? Outcomes such as muscle mass, peak strength or endurance may not be trained optimally by the same choice. Given that we are looking at low load training and in particular aiming for low muscle O2 saturation, lets examine that. Has this been looked at in this narrow perspective? Not really, but in my opinion it is pretty important to know. Going back to the premise of low load, ischemic training, we are not aiming for peak power/strength, but more for muscle mass and tendon/connective tissue improvement.
My personal experience with the O2 sensor and low loads with certain muscle groups(chest press) looks pretty much like this:
40% 1RM rest 45s same rest 45s same sensor on chest
This is about 40% 1RM, 60 sec then 45 sec x 2, 7-8 reps with 45 sec rest, chest press with the sensor on the chest. Notice the progressive blunting of the O2 drop with each set. This is in the face of increasing fatigue per set, with the last set pretty severe and shorter than the first. Given the restriction on load poundage, is it possible to get optimal O2 desaturation? Or can we make the loads even lighter and have it look the same (same bang for less bucks).
How about shorter rests? The following is the same exercise but 4 sets of 30 sec with 30 sec rest:
40% 1RM rest30s same rest 30s same rest 30s same sensor on chest
What about a drop set? I bit the bullet(or my rotator cuff did) and did a 10RM set, rested about 2 min then did 2 other sets as 45sec x 45 sec rest.
70% 1RM rest 120s low load 45s rest low load 45s sensor on chest
Next up, reverse drop set.
Proof of concept:
Can a lower weight on the first set give comparable hypoxia?
This is a trace looking at 3 reps (to avoid fatigue) of a low load baseline chest press (140 lbs), followed by over 60 seconds of 110 lbs (20 % less). I wanted to make sure that the lower load would do just as well as the baseline (on the first set). So the first set was just a test looking at that degree of oxygen drop given a low weight, then followed by an even lower load giving comparable results.
It seems that the first set is much more amenable to desaturation no matter what the load is.
15 sec test set rest extra low load, to compare to initial
Here I started with 12% less on the first set, then baseline, then 12% above baseline for the last, 45 sec rests, 70 sec for the first set then 45-40 sec each set x 2. My hunch was that this would work and I wanted to make it something that is practical in view of injury rehab.
40% 1RM minus 15% rest 45s 40% 1RM rest 45s 40% plus 15%
Just what I was looking for. After observing the O2 drop patterns for several months, it appears that the first set has the best chance to deoxygenate with low (or even lower than usual) loads. After the first set and as the routine progresses, more weight is needed to reach the same levels. If the load is past some critical threshold (easy to do on biceps), the deoxygenation is so profound, no real change occurs as the sets go by. We also see this in conventional training with 8-10 RM loads.
So in some exercises, the extra weight is not needed and the same low load is fine to do without any degradation of desaturation effect.
Here is a bicep curl, sensor on biceps, initially a 7RM (50 lbs) weight then followed by low load (25 lbs) 45 sec x 2 sets. As can be seen (pardon the artifacts) the low loads still do just fine with O2 drops even on the last set, as opposed to the chest press. The critical load to deoxygenate is still above even the low training weight.
7RM(heavy) rest 45s 40 % 1RM (very light) rest low load again
What does the literature show?
I did a medline search and did come up with a recent paper
Effects of the Drop-set and Reverse Drop-set Methods on the Muscle Activity and Intramuscular Oxygenation of the Triceps Brachii among Trained and Un-trained Individuals
They did O2 desat profiling with either drop set or reverse drop sets. From the paper:
So very much like my readings. But their conclusion was quite different:
Their reverse drop set group did not do as well in area under the curve of O2 sat.
Why? Lets look at their methods.
Notice the reverse drop set groups' initial set- only 3 reps of 55% 1RM(hardly challenging). I am willing to bet if they let the participants do a set to failure at that weight, the O2 drop area under the curve would have been quite good and totally changed the results. This is not meant as a criticism but we can't extrapolate this study to low load training because of how they did it.
I believe that the initial set can be done at a moderately lower weight and has the best chance for achieving the best deoxygenation you potentially can get. As the sets progress, the fatigue factor increases as well as the increased vascular flow making O2 drops even more difficult.
A word about fatigue. It is pretty easy to understand that after a set to failure of either heavy or light loads, there will be an interval where you are too "fatigued" to do any more muscular work. But can we assume that shortening the rest intervals, to take advantage of muscle fatigue chemistry (?low O2) is valid. As can be seen in many of the tracings above, the O2 recovery is quite rapid and certainly by 30 seconds is near baseline. To get a further drop of the O2 sat based on shortening the recovery (so you are already starting hypoxic) does not seem practical. Not only that, but it seems that the sensation of fatigue (at least at low loads) is not related to tissue hypoxia. Here is a study that looked at that. They used the mechanomyogram (MMG) which looks at muscle vibration (quivering when the muscle is tired) in subjects lifting a low load for 10 minutes. There was no O2 drop, but the MMG showed worsening fatigue.
Note the O2 sat was steady, or rising at the end.
But the mechanomyogram showed increased activity indicating fatigue:
The mechanisms for fatigue are many and can be reviewed here.
But it does not seem to be that related to muscle O2 as noted above. Here is another example from a study comparing time to task failure in subjects, with and without cuff occlusion:
You can see just minimal difference if the limb was occluded by a cuff (Kaatsu style) so the additional ischemia did not impact task failure by much.
In short, just because there is subjective weakness, pain and fatigue, high perceived exertion, you are not necessarily getting ischemia.
Summarizing the above:
- Utilizing an O2 sensor can help in maximizing the time and degree spent in hypoxia. Variables that can be manipulated (up to a point) are rest intervals, load, time under tension and interestingly the reverse drop set. The sensation of fatigue may or may not be helpful in guiding for optimal deoxygenation and can be present even without any tissue O2 drop.
- The best tissue deoxygenation will be on the first set, and it therefore is possible to lift an even lighter load than usual, for a longer time (even though it may not feel challenging) to get the same or better effect. On subsequent sets, to reach the same level of hypoxia, heavier loads are progressively needed. However, in the example above, only an extra 12% (from baseline) on the last set is required. If this is deemed too heavy a load, just staying at the previous baseline is still helpful.