Conditioning is important, and what's also important is doing it right.
Now there are lots of ways to perform conditioning, but if gaining strength and muscle is a priority for you, then you need to ensure you do it correctly. Properly programmed cardio should enhance your lifting, not take away from it.
Here are 5 workouts you can do that will take your fitness to new levels.
1. Cardio Complex
Full disclosure, I did not create this workout. I found it on the 'Wodwell' site and have found it to be a great one, though quite long.
I'd strongly recommend taking this workout at a moderate pace. This gives you a lot of room to improve each time you do it, and also means you won't burn yourself out for the later rounds.
Also, for those of you who aren't up to scratch with your CrossFit terminology, a 'single-under' is what the rest of the planet calls a skip. Can't skip? Just hop on and off a plate instead (ideally to a 15/20kg bumper plate).
2. Ergs n' Abs
I'm not a huge fan of 'training' the abs. At least not through ab isolation exercises like sit-ups, planks, etc. However, ab exercises are very useful for conditioning workouts as they are low intensity and are great for getting your heart rate up.
This workout is very simple:
Step One: Pick one or more cardio machines (e.g. bike, ski erg, rowing machine, etc.)
Step Two: Pick a few ab exercises
Every time you do 20 calories on a machine, spend 1 minute on an ab exercise. Here's a sample workout:
Bike x 20 cals
Plank x 1 min
Bike x 20 cals
Hanging Knee Raise x 1 min
Rower x 20 cals
Hollow Hold x 1 min
3. Push the Prowler
The prowler is a great conditioning tool. It requires very little coaching, and all you need is a flat surface to push it on. Additionally, you can easily modify the intensity by adding or reducing weight.
Every now and then, it's fun to load the prowler up heavy and see what you can do. But for the most part, you should never have anything on there that makes you move any slower than a march. Remember, nobody cares what your '1 rep max prowler push' is. Just push the damn thing at a march/jog pace for 15 - 20 mins at a time.
4. Bodyweight Intervals
This workout only works if you're already somewhat strong. For example, 40 seconds of push-ups should not feel like strength work for you. If it does, you need to skip this workout for now.
40 seconds on, 20 seconds off (2 - 3 rounds)
5. Push, Pull, Bike
Now, I'm not a huge fan of doing this workout regularly. Reason being because I like to keep strength work and conditioning separate. However, there will be times when you're stuck for time, and on those days this workout can work really well.
Essentially you need to have two upper body accessory exercises; one push, and one pull.
I've only used this with dips and pull-ups, but I'm sure you could do dumbbell bench, dumbbell row, dumbbell press, push-ups etc.
You will perform the 2 exercises as a superset, and then hop on a bike for 2 mins. This will allow your arms to rest, but elevate your heart rate from the work rate on your legs.
The duration of the workout just depends on how many sets of accessories you're doing. Assuming you don't do more than 5 sets, the workout should be done in around 15 mins.
Notice there's no progression plan mentioned for these workouts. The reason for that is because trying to improve at conditioning and strength at the same time is hard, and almost entirely unfeasible when you get to higher levels of strength and fitness.
Keep these workouts in a rotation and try to do them at least twice per week. Note your progress if you like, and go ahead and improve your pace if it feels easy to.
But BEWARE: many a lifter (see: me) has burnt themselves out by trying to be a master of all trades. Use conditioning as a tool to improve your lifting, not as a way to boost your ego.