Cardio relates to the cardiovascular system aka our heart, blood vessels, and some 5 litres of blood our blood vessels transport each minute eveyr minute, all around our bodies. It's our cardiovascular system that moves oxygen, nutrients, hormones and the like hither and yon, pretty important stuff -- as well as removing waste products. Busy bugger. So "cardio" or cardiovascular exercise is exercise we engage in to stimulate and hopefully benefit, said system. Like anything, too much is counter-productive, as is too little. So we're looking for a balanced middle.
The term "cardio" has evolved into encapsulating a certain style of exercise that is aerobic-based as opposed to anaerobic-based. For the record, aerobic exercises are those where oxygen are the main driver: think running, swimming or the Jane Fonda aerobic craze of the 80s (why we don't have young women in leotards exercising on television today is a national disgrace). Anaerobic-exercises are those where more energy is needed, specifically muscular energy, because oxygen alone won't cut it: think strength-training, Olympic weight-lifting or just shifting heavy objects around at home.
Having a balance between strength-training and cardio is sensible. We need to strengthen the body, maintain and develop muscularity whilst at the same time ensuring our cardiovasuclar health is similarily maintained as best we can. Now when it comes to cardio there's essentially three types: slow, steady state cardio such as walking. Moderate to higher cardio such as running or aerobics, and HIT or "Hight Intensity Training" such as sprints -- shit for our age group -- or some similar exercise done at a high intensity over a (much) shorter period of time.
I recommend steady state cardio and HIT though if you find yourself preferring one over the other then it is what it is. It's important you engage in at least some form of cardio that you enjoy. That's the key right there: that you enjoy. If it's walking, then walk. If it's running, then run. If it's swimming, then swim. Use what's best for you. If you don't enjoy any of those things then you either need to suck it up and start, or do none of them. It really is up to you. You can strength-train without any cardio whatsoever if that's what you want to do.
You're a big boy now.
...but for the record: I recommend walking for steady-state cardio, running for moderate cardio, and short intense sessions for HIT.
For steady state cardio I would recommend walking, and walking anywhere from 20-40 minutes as often as possible or whenever you can. Personally, I'm more of a whenever-I-can sort of guy which could mean daily, every second day, or 2-3 days per week if you can afford the time. This shouldn't be a stroll but nor should it be a march rather, keep up a decent pace so your heart-rate is elevated but you could still talk about how low your testicles hang with a mate because you know your mate wants to talk about this.
Can you walk longer? Yes, yes you can walk longer.
As long as it doesn't interfere with your work outs, you can walk as long as you wish. Can you do something else rather than walk? Of course you can i.e. swimming, cycling, kayaking, paddle-boarding but the point is simply this: do your steady-state cardio (whatever you settle on) as often as possible or whenever you can. You might walk one day, swim the second and that's it, that's all the intended cardio you do for that week. Good-o. It is what it is. Something is better than nothing so start light, be kind to yourself, and see where it leads.
However. If you like running then yes, you can run on your off days instead of walking; obviously it will take your body awhile to adapt, what with strength-training and running but adapt it will. Whatever moderate cardio you opt for -- jump rope, boxing or just swimming faster -- you'll probably adapt to it. But. It is senseless over-stressing your body and accumulating fatigue just so you can claim you're doing something every day. No-one gives a shit what you're doing. So pay close attention to how you feel. Don't ruin yourself. Don't over-do it. Don't be a hero. Don't pretend you're 20yrs younger than you are.
Why?
...because no-one gives a shit.
There, I've said this twice now. They really don't.
Look, at least once every 3-4wks I find myself dropping cardio for a day -- or even for the week -- because I'm sore from strength-training, gardening or whatever it was I engaged in. The only person who gives a shit is me and I've been doing this for so long I'm totally unphased if I miss days, weeks or even months (that's right, months) doing no cardio. Your program doesn't dictate you rather you dictate your program. Yes, as newbie you need to follow whatever program you've chosen to start with but, life will throw curve-balls and you'll miss days. It's okay.
Every now and then I get back into running and run for, oh, roundabout 3-months then it falls out of favour with me. I don't know why but then and again, I don't really care either. I have no problem changing cardio preferences every few months or so which is yet another reminder not to get too hung up on what cardio you're doing let alone at what level -- steady state, moderate or HIT. No-one is keeping score out there in the cosmos. Relax, enjoy the moment and make a start. As you get used to it and, heaven forbid enjoy it, you'll start figuring out your next best steps.
For HIT or "High Intensity Training" I recommed some sort of machine -- think crosstrainer, cycle-machine, rowing-machine you get the idea -- simply because they're easier to use for HIT in my opinion. However, you can use practically any body movement from swimming to sprinting to jump-rope to a range of bodily exercises (jumping jacks, burpies, that sort of stuff) to achieve the desired affect which is simply this: warm-up for 1-2 minutes with your chosen movement then go all out for 30-60 seconds. A hundred percent. You don't need to do more than that.
Slow back down again, get your breath back give or take, then go all out for yet another 30-60 seconds. Repeat this cycle for 10min. Boom, you're done. That's your cardio for the day. Do this 2-3 times per week and look, if you want to do steady-state one day, HIT the next and moderate cardio after, knock yourself out. Nothing wrong with mixing and matching folks, but HIT is simply short, high-intensity bursts of energy whose affects are long-lasting.
Through my own research I've noticed a slow move towards increased time peforming HIT by netspurts (online "experts") but I don't buy into this myself. I don't personally believe increased HIT durations are all that necessary or add further benefit. A lot of people think to get bigger they need to work out more if they're not making the gains they expected. So they then double their sets which only leads to burn-out, plateaus and injury. Likewise, further HIT would be counter-productive in my (untrained) opinion. What say you?
However, at the end of the day you have to do what works best for you. So. If you want to do heaps, be my guest. Sort your strength-training program, select what type of cardio if any you wish to do (and you should be doing some), and give yourself a minimum 3months before changing your cardio round, if in fact it's even required. Why so long? Because it will probably -- and I do say this loosely as we're all different -- take roundabout 3months for you to accurately ascertain what's working for you. You have to be willling to experiment and give things a go.
Lastly, track everything you do. Get a little notebook and track every day, every work out, every weight and time duration so you can go back, reflect, compare and tweak. Yes, experienced lifters can train intuitively but are you an experienced lifter? If not, don't pretend you are. Keep a record of what you're doing so you can analyze where you increased in weight and why, where you went backward and why, what worked and what didn't. Because if six months from now you're still using the same weight for the same sets and reps, you're doing something wrong. Kia ora whanau.