the 20-something’s guide to cardio (aka:: the truth behind cardio & why you should prioritize it for heart health & not weight loss)
let’s get real, does cardio confuse anyone else? with terms like “low intensity steady state”, “zone 2”, & “high intensity interval training” being thrown around, how are we supposed to make sense of it all & realize why we should or should not be doing it? well jump in, barbie, because we are about to take a deep dive on what it is, the reasons we should do cardio, & when cardio is not the best route for a certain goal (ahem, i’m looking at you, long term body composition changes)…
let’s define
when folks say “cardio”, they are commonly referring to a shortened version of “cardiovascular exercise”, which is simply a variation of exercise that targets our cardiovascular/circulatory system. this system includes our heart & vasculature & is closely related to our lymphatic system (hellooo detox system!) & our pulmonary system (breathing, uhmm yes!). on a macro level, oxygen comes into our bodies via inhalation & is transferred from our lungs to the bloodstream. the now oxygenated blood is pumped by the heart & distributed throughout the body to various organs & our muscles. the oxygen from the bloodstream is given to various cells throughout the body in a process called cellular respiration, which utilizes oxygen to help create energy for us to utilize. during the process of cellular respiration, waste products are produced (think carbon dioxide), & the circulatory system transfers that waste back to the heart, which pumps it to the lungs, allowing us to remove that carbon dioxide via exhalation & start the process all over again. further waste from the process of cellular respiration is removed via our lymphatic system.
why does it matter?
we want a strong cardiovascular system for the present moment, being able to play pickleball, run, ski, etc. & also for longevity, allowing us to play with future kiddos or be that super cool 70 year old still breaking it down on wedding dance floors. things like clotting, swelling, heart attacks, shortness of breath, etc. can all be indicative of a weakened cardiovascular system. as we age, our ability to positively affect this system diminishes, so it is extremely important to prioritize working on this system in our teens & 20s, since as we hit our 30s & beyond, our rate & ability to improve this system slowly declines. for example, our VO2 max, or an objective measure for the maximum amount of oxygen our muscles are able to consume during exercise, peaks in our mid 20s & starts to decline in our 30s if we don’t work to maintain it. a higher VO2 max is linked with factors like improved endurance, muscle function, recovery, increased fat utilization, & so many more benefits that we want to carry with us as we age. something that motivates me is wanting to be able to ski for as long as i can, so i want to keep this system functioning optimally so i can breathe better in the mountains, recover better after a day of skiing, & be able to keep up with my eventual kiddos, grandkiddos, & great-grandkiddos… right?! talk about a deeper why behind movement!
a few factors go into how strong our cardiovascular system is. for starters, we want to stress different parts of our cardiovascular system in different ways. for example, methods of cardiovascular exercise like hill sprints, tabata, & high intensity interval training utilize different energy systems compared to marathons, long walks on the beach, & swimming. we want to train a variety of these energy systems to allow for a well-rounded cardiovascular system.
in order to make sure we are challenging each of these systems & training them in an appropriate way, it is helpful to break up the different types of cardio into “zones”. typically it is broken up into 5 zones. 3 of these zones utilize oxygen for energy. the process of cellular respiration, where oxygen is utilized to create energy, takes awhile compared to the anaerobic systems, or systems that don’t require oxygen, so the zones that require oxygen for energy include lower intensity, longer duration episodes of exercise like running for longer distances, walking, swimming, etc. in contrast, zones 4 & 5 don’t require oxygen for energy. these activities include sprinting, jumping, tumbling, etc.,..basically activities that require a quicker energy production & are shorter duration. in the chart below, we differentiate between the zones of cardio based on the percentage of our max heart rate compared to the primary energy system utilized in that zone. (however, it is a fluid process between the utilization of these energy systems. for example, we could be running in zone 3 on level ground & then come to a hill, which might require a quicker burst of energy from an anaerobic energy system!)
* max heart rate can be calculated by taking 220-age. this is an estimation! for example, a 25 yo would have an estimated max HR of 195. so zone 2 training would include a HR between 117 & 136.
another factor that goes into the strength of our cardiovascular system involves our heart’s efficiency at delivery oxygen at rest & at various intensities. stay with me for a bit because things are about to get *physiological*…
our heart is a pump & a muscle, & one of its jobs is to deliver oxygen to meet our body’s demands. the amount of blood the heart can pump in 1 minute is termed cardiac output, & it is a measure of the heart’s ability to meet the oxygen needs of our body. cardiac output is calculated by multiplying heart rate (or the # of heartbeats per minute) by stroke volume (or the volume of blood ejected by the left ventricle each contraction of the heart). so in order to improve the efficiency of our heart to deliver oxygen, we can change heart rate or stroke volume.
cardiac output = heart rate x stroke volume
so at rest, like sitting & drinking a latte in a cute coffee shop, we aren’t needing as much oxygen, so a sign of a healthy heart is one that can pump less & still deliver the oxygen we need, so a low resting heart rate can be indicative of a strong cardiovascular system.
when we first start an exercise program, our heart is not as efficient at delivering oxygen at a certain intensity level, so our heart rate will elevate in order to deliver the appropriate cardiac output & meet the body’s oxygen demands. as we train, our heart muscle gets stronger & can pump out more blood each beat (stroke volume) which allows our heart rate to decrease in order to deliver the same cardiac output. this is why resting heart rate is a good measure of the strength of our cardiovascular system. typically, the lower our resting heart rate, the more efficient our hearts are at delivering oxygen! in the same way, seeing our heart rate lower at a certain intensity level is also indicative of a stronger cardiovascular system!
so let’s chat about the elephant in the room…cardio for weight loss
cardio can be utilized as a tool for weight loss, but there are a few reasons why it should not be the priority when trying to lose weight & maintain that weight loss. cardio training, when not combined with strength training, can lead to fat loss & muscle loss. muscle is more metabolically active than fat, so long term, it is more beneficial to have more muscle than it is to have less fat, as muscle requires more energy at rest. typically, people want weight loss combined with a look of being more “toned” or creating body composition changes. just because you are losing weight does not mean that comes with favorable body composition changes. strength training also creates longer-lasting caloric expenditure after exercise known as EPOC, or excess post-exercise oxygen consumption, which just means our muscles require energy & caloric expenditure even after we are done with the workout. combining strength training & cardio allows for these adaptations to occur without the loss or minimizing the loss of muscle mass, creating favorable body composition changes, while still training our cardiovascular system. for this reason, i like to look at “cardio” as more “longevity training”, or training for life, rather than training for weight loss.
the optimal way to incorporate “cardio” in our training
so what do we do about it so we have the right amount of cardio for the health & heart benefits & still have time for all the strength training, pilates, & pickleball? current recommendations for “cardio” revolve around implementing both zone 2 & zone 5 training every week. for zone 2, this is an intensity where we can chat with a friend but are still breathing heavily throughout… hellooo pickleball! zone 5 is absolute torture (but beneficial torture, amiright?), where we are exercising our little hearts out (no pun intended). for zone 2 training, it is recommended to get 120-180 minutes per week, with 45+ minute sessions for maximum benefit. it is also recommended to do one day of zone 5 training, which incorporates all out effort for a few seconds to a few minutes, followed by a rest break, & repeated multiple times. for me, this workout is my hill sprint workout each week, where i perform 20-30s hill sprints 10x through with a jog recovery in between. torturous, but so fun.
okay that wraps up this heart healthy post for american heart month! i hope you learned a lot from both a macro & micro level to take your cardio training to the next level & to understand a deeper why to cardio training. i know thinking of all of the lifelong benefits of cardio training helps to motivate me when i’m struggling to do a harder cardio workout… so i hope this motivates you guys in some way, too!
to all my cardio queens in health & happiness,
kelsy
