Peter (not real name) asked me a long question concerning cardio workouts and strength training. He claims to be seriously interested in strength.
First of all, we need to know what you understand by “cardio workout”. Is it a walk on the park, jogging for 45 minutes in the treadmill, a “Fran” WOD ? The discussion about what is the most effective cardio training approach is and endless debate with no consensus in sight. Many, me included, tend to side with the argument that there is good scientific evidence for short interval, fast workouts with a high metabolic demand. No need to compete for the best Fran, but a session of multiple sets of kettlebell swings, for examples, qualifies as such.
Not only they seem to render the best cardio-vascular results, but they have a smaller competitive inhibitory effect, if at all, over your strength training proper.
Long-distance running or other endurance training program do have a competitive inhibitory effect over strength gains. So, if you are interested in strength, that this may not be the best approach for your “cardio training”.
A light jog or walk on the park are not cardio training. They have little effect on the cardio-vascular conditioning of a healthy person, but they have other very important roles. One which I consider relevant is being an endogenous anti-inflammatory. They decrease many pro-inflammatory indicators and help the body deal with the inflammatory burden of whatever is the burden: your strength training, for example.
So, when to do those: a walk on the park or light jog can be done anytime, preferably after your strength training workout.
A strong interval training with kettlebells or some circuit-like protocol involving useful movements is definitely not indicated do be done before your strength workout. It could be done after that, but the best is to do it in a different day.
“Not at all” is a dangerous option. To adopt higher than 80% loads powerlifting-only workouts with no cardio-vascular exercising at all may not only be extremely unhealthy, but in the end, might eat away your strength performance due to lack of recovery tools. Yes, oxidative ability is the name of the game during recovery.
Last but not least, cardio is NOT warmup. Running on the treadmill will offer you zero benefits when hitting the bar. Warmup involves volume sets with no weights and mobility exercises, but more of that later.