The Issue
I recently read an article about how even though we may be training at low intensities or heart rate ranges that correlate to "aerobic" work, it does not necessarily mean our muscles are using oxygen to produce ATP. This is especially true if we typically spend most of our time training for power or strength qualities.
First, when training for strength and power, the primary systems at play are the glycolytic and alactic systems, not the oxidative system. Secondly, during strength and power, the nervous system adapts to the muscle repeatedly contracting maximally throughout the workout. Each of these contractions produces large amounts of tension in the muscle. After training for strength and power on a regular basis, our muscles tend to start contracting maximally every time movement is performed. This is even the case if the movement is performed at low intensity.
For example, the intensity of jogging is very low, so during the stance phase, the quad only needs to contract submaximally for the runner to continue to move efficiently. The benefit of the muscle contracting submaximally is there is little tension created in the muscle. Small amounts of tension do not cause vasoconstriction, so deoxygenated blood can leave the muscle, and oxygenated blood can enter the muscle without resistance. The opposite is true for a muscle that has adapted to always contracting maximally in training. Maximal contractions cause vasoconstriction, which produces a lot of resistance, reducing the ability of deoxygenated blood to leave the muscle and oxygenated blood to enter the muscle.
RECENT: A Coach's Guide to General Physical Preparedness
The sum of these events typically results in muscles with lower levels of oxygen saturation than is expected when performing submaximal activity. So when you think you may be training in the aerobic zone because your heart rate falls into the correct "training zone," you are training the glycolytic system because your muscle oxygen saturation is so low. I believe this is a common occurrence with most power/strength athletes when they attempt to perform long slow distance (LSD) style training sessions.
I witnessed first-hand the vasoconstriction issue with most of my hockey players during pre-season training a few years back. After a summer of exclusively training the lifting portion of their program I had prescribed (in addition to any other "bro lifting" they added themselves), no one could sustain low-intensity exercise while maintaining an aerobic zone. This was most notable during the giant aerobic circuit prescribed during our general physical preparedness (GPP) phase. Their ability to perform the low-intensity exercises for extended periods of time was not at the level I expected it to be. However, what was most interesting was that the limiting factor was their vascular system rather than their cardiovascular system. I knew this was the case because their cadence slowed during the workout because of the pump/burn they felt in their muscles rather than being out of breath. This demonstrated their inability to pump oxygenated blood into their muscles and deoxygenated blood out of their muscles.
A primary explanation for this occurrence was that my athletes had only been training for strength and power leading up to this circuit, so their bodies were conditioned to produce high levels of tension with every contraction. This muscle tension puts so much resistance on the vascular system that low-intensity exercise becomes glycolytic rather than oxidative because there is always a metabolite build-up in the tissue.
The Question
After coming to this conclusion, how do we train power athletes (such as hockey players) to continuously display high outputs like their sport demands, while also being able to fall back on their aerobic system for efficient recovery?
I had to address the athletes' vascular system to answer this question.
The ultimate goal is to decrease the "resistance" within the vascular system of my strength/power athletes. In doing so, they will be able to perform submaximal exercise aerobically when necessary without spending too much time developing the aerobic system itself.
From a time resource standpoint, too much low-intensity work will take away from the time the athletes could have otherwise spent improving their strength/power qualities. Therefore, addressing their vascular system problem helps improve their ability to recover without detracting from their ability to improve other qualities.
After speaking to Cal Dietz, I decided to start solving this problem by utilizing overcoming isometrics. He told me in the past, when his athletes had gone through supra-maximal isometric phases, he'd seen heart rates drop to 30-35 after two weeks. His theory was this happened because he would ask his athletes to hold their breath during the duration of the isometric movement.
The combination of the athlete holding their breath while producing maximal force to hold position leads to drastic increases in blood pressure. The high amounts of pressure created would make the circulatory system more elastic. A more elastic circulatory system would then pump blood more efficiently because it is more pliable. This is why the heart rates dropped so low—more blood would be pumped each beat.
Additionally, suppose the vascular system is more elastic. In that case, there will be fewer blockages within the system, and it will be less likely to pool blood in a muscle due to vasoconstriction. This is because a more elastic circulatory system has lower resistance for the blood flow to overcome. This allows oxygenated blood to flow in easier and deoxygenated blood to flow out easier.
The Answer Hopefully
With all of this in mind, I decided to run a test program on myself. After performing an eight-week strength cycle that focused primarily on sets that lasted roughly 18-30 seconds (glycolytic emphasis), I ran myself through a deload/aerobic reboot week phase.
I felt the timing of the program worked well because whenever I was performing conditioning, it felt like it was always lactic, even when I attempted to keep my intensity low. This effect was very similar to what I saw with my hockey players during the aerobic circuit in our GPP phase.
Additionally, I would feel very fatigued the day after an "active recovery" day, which consists of nasal breathing only training of 40s ON/20s OFF for 30-40 minutes rotating between a few different cardio machines. The fact that I would feel very fatigued after my active recovery days instead of fresh shows that I was glycolytic instead of aerobic. Lastly, my resting heart rate was abnormally high, which I usually notice as an indicator that I am not recovering as fast as I'd like to be and that I need to do some aerobic training.
During my deload/aerobic reboot week, I decided I would first perform three sets of Overcoming Isometrics (with a breath hold) for all major multi-joint movement patterns every day (Monday-Saturday). I chose movements like these because I figured it would lead to a more global effect on the whole body, developing the vascular system as a whole.
The purpose of using the overcoming isometric was to improve the elasticity of my circulatory system. My heart would then be capable of pumping more blood every beat and limiting the amount of pooling, preventing vasoconstriction.
Below is how I performed this portion of my training at the beginning of all my sessions:
1A. Right Split Squat Deadlift Overcoming Iso: 3x10 seconds
1B. Left Split Squat Deadlift Overcoming Iso: 3x10 seconds
1C. Bench Press Overcoming Iso: 3x10 seconds
1D. Bent Over Row Overcoming Iso: 3x10 seconds
*For more examples of overcoming isometric training, click this link and scroll to Strength: Section 1
Next, I performed either 10 minutes of extensive plyometrics or med ball throws for general athleticism purposes (and to prevent myself from moving like a complete meathead). I believe this portion of my training had nothing to do with my results, but I wanted to include it for the sake of thoroughness.
Finally, I finished with 30-50 minutes of an aerobic circuit that was performed via nasal breathing only. The template I based my aerobic circuit on was the GPP Giant Circuit I created. I find this circuit to work really well because you are constantly switching the working portions of the body. This forces your vascular system to constantly pump blood back and forth across different sides of the body. Shuttling the blood in this way naturally elevates the heart rate without the athlete having to exert additional effort. The constant shuttling of blood also reduces blood pooling in the muscles and prevents the system from entering a glycolytic state by staying aerobic.
The typical prescription of this workout involved working one side of the body for 30 seconds of work and 10 seconds of rest, then switching to the other side of the body and doing the same. Instead of this approach, I changed the prescription to two intervals per exercise alternating back and forth between sides of the body for 15 seconds of work and five seconds of rest. Both protocols have the same work-to-rest ratio, no matter what protocol you follow. I believe, however, that performing 15/5 and switching sides would lead to a more aerobic adaptation by limiting local fatigue and preventing vasoconstriction. Also, the more the blood is shuttled, the more the heart rate gets elevated with lower levels of exertion, making it the more efficient option for aerobic training.
The Results
For the 14 days prior to starting this week-long test program on myself, my resting heart rate was, on average, 52 bpm. Over the course of the seven-day cycle, my heart rate dropped to 39. This is the lowest resting heart rate I have ever recorded on myself, so to say the least, I was very happy with the result. As a competitive CrossFit athlete, conditioning has been a very important component of my training for the last five years. In the past, I have committed to week-long cycles to improve my aerobic fitness, but have never had a resting heart rate lower than 47 by the end of the week.
This leads me to believe the difference was including the overcoming isometrics with breath holds which was something I had never utilized before. In the future, once I am done with my current program, I am excited to commit two weeks to this same deload/aerobic reboot cycle. It will be interesting to see if I can get into the mid/low 30s after doing it for a longer period of time.
Future Considerations
As I begin the next three-week block of my strength cycle, I am excited to see how long the effect of this week-long phase lasts. The training residuals for aerobic training are said to last roughly 30 days, but I will be keeping a close eye on my RHR to see for myself.
The next time I start a phase similar to the deload/aerobic reboot, I will track my blood pressure every morning to see what effect the breath hold isometrics may have on that factor. I would assume my blood pressure would decrease if my circulatory system is more elastic. However, at the same time, if I have a lower RHR, it leads me to believe my heart would have to pump more blood every beat, which might then actually increase my blood pressure. I believe the answer to this conflict is probably simple; I need to spend more time addressing it. It most likely involves pulse wave velocity, which is the rate at which blood travels away from your heart within the circulatory system. This metric may be a factor that ties into the increase or decrease in blood pressure.
Lastly, I am excited to run a two-week phase of this program to see how low I can get my resting heart rate. If it does drop into the low 30s, I am curious to see if it will drastically affect my ability to recover and handle higher work volumes in future phases.
There will be a positive effect, but I would like to look at how my heart rate variability might be affected on a daily basis and see the difference in changes based on the volumes I am performing. I will have to perform two of the exact same phases following two different aerobic phases for this to be accurate. Another effect of having a lower resting heart rate is a reduced heart rate when training at higher intensities as compared to previous heart rates.
I am looking forward to updating this next time. I have the opportunity to run a phase similar to this one which should be in roughly three weeks.
Regan Quaal is the Assistant Sports Performance Coach at the University of Minnesota with Cal Dietz.
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