The quick answer is: it can be if you approach it correctly.
This may be a dumb question, but Medhi, the SL guy, basically says that SL is enough for cardio fitness. To me, that seems a little dubious and counter to common knowledge, so I thought I'd ask just to see. Not that common knowledge in fitness is often correct...
Medhi's basic program is good for building strength, but he markets it like an infomercial. He promises everything to everyone, so either he knows better and is purposefully writing click bait or he doesn't know better and doesn't want to learn. This is my biggest problem with the StrongLifts site. I got my start using StrongLifts, so I know that it works and what it's limitations are.
If you are going to use barbell exercises to train cardiovascularly, then you need to change your approach. StrongLifts won't be the right tool, particularly if you need long rest times to recover enough to do the next set.
- Use a heart rate monitor: you need to know how hard your heart is working, and keep it within a certain range most of the time. When I train with cardio in mind, I'm trying to keep my heart rate between 120 and 150 BPM most of the time. During a hard exercise it might go over, but I'll at least let it come back down to 150 BPM before I move on to the next exercise.
- User circuit training or barbell complexes: these two tools are very similar in nature, but vary a little in mindset. Both have 2 or more exercises in a full set. You'll do one set of each exercise before resting for the next super-set. The main difference between them is that a barbell complex has the concept that you pick the barbell up and don't set it down until you finish with the whole superset. That means you are using the same weight as you flow from one exercise to the next. Circuit training lets you change tools and weights, but you still need to keep it moving.
- Plan your overall training to balance cardio and strength: you can do primary movements normally and then use circuit training for your assistance work. Or you can have one or two days devoted to cardio training and one or two days devoted to strength work.
One of the things I'm not crazy about with both StrongLifts and Starting Strength is that the programs breed impatience in the people doing them. You get so used to increasing weight every time you do an exercise that when it's no longer possible you're in a quandary as to what to do about it. Even as a beginner, training to progress once a week will keep you going a lot longer.
My suggestion is to balance your approach a bit and train for weekly progression in the beginning. If you are training 3x a week, then a reasonable shell of a program would be something like this:
- Main lift, then use circuit training for the 2-4 assistance exercises and train 3x a week. Goal is to add 5lbs a week to each of the main lifts.
- Day 1:
- Squats 24-25 reps (any set/rep scheme will work, try for longer sets at first and shorten the length of each set as you need to)
- Circuit: Romanian Deadlifts (3x8), pushups (3x as many as possible [AMAP]), hip thrusts (3x12)
- Day 2:
- Bench Press 24-25 reps, same set/rep requirements as squats.
- Circuit: Front squats (3x5), Push Press (3x5), Pull Ups (3x AMAP)
- Day 3:
- Deadlifts: 5-6 reps, same set/rep requirements as squats.
- Circuit: Pause squats (3x5), close grip bench press (3x8), Farmer's walk 3x30 ft
The approach above is similar in spirit to SL and SS, but the work is spread out and incorporates circuit training after the main lift. With the circuit training, wait until your heart rate gets down to about 120 BPM before starting the next super-set. If you need a breather between each exercise (something I need at over 40 years old) then wait till the heart rate goes down to about 150 BPM before starting the next exercise.
The assistance exercises listed above are more guidelines. Feel free to change out parts or add an exercise or two to build up weaknesses. Just focus on higher reps and lighter weights with the assistance work and don't increase weight on them until what you are using just feels too light all the time.
The rough outline I gave you is more focused on building strength and cardio using barbells/dumbbells/machines, etc. If one of the exercises proves too difficult (like pull ups) feel free to substitute for something that hits the same muscle groups or do partials or use assistance. Your approach to training will evolve over time, particularly as you change the focus of your training. The outline I gave is also centered around the power lifting focus that SL/SS both employ. If you want to incorporate work that's inspired by a different strength sport, feel free. The only caveat is that the main exercises should be compound lifts that work the whole body if possible. If you want to substitute the military press instead of bench press, there is no harm or foul. If you are fatigued one day, cut down on the reps for the assistance work but try to keep the main work the same. If the fatigue is really bad, drop the assistance work altogether.